JP7617401B2 - Pressing device and method for manufacturing press-molded product - Google Patents

Description

The present invention relates to a press device and a method for manufacturing press-molded products using the press device.

Many of the parts that make up an automobile body are formed by press working using dies. This type of press-formed product is manufactured by drawing or bending a blank made of a metal plate. In recent years, there has been a demand for lightweight and strong press-formed products for automobiles. To meet this demand, blanks with high strength (tensile strength) are used when manufacturing press-formed products.

However, when using a high-strength blank, springback is likely to occur in the resulting press-formed product. For this reason, unless some measures are taken during press forming, it is difficult to ensure the target dimensional accuracy.

In particular, when a press-formed product is long, has a hat-shaped cross section, and includes a curved portion in plan view, the press-formed product is prone to twisting and warping of the vertical walls (hereinafter also referred to as "wall warping"). Examples of press-formed products for automobiles with such shapes include A-pillar uppers (front pillar uppers), roof rails, and front side members.

Generally, press-molded products are manufactured through multiple processes. For this reason, if the torsion and wall warping of the press-molded product is significant, it will not be possible to set the press-molded product in the mold in the next process. In this case, it will be difficult to even correct the problem in the next process. Therefore, there is a demand for technology to suppress torsion and wall warping of press-molded products.

Conventional techniques for suppressing twisting and wall warping are proposed, for example, in JP 2008-213028 A (Patent Document 1), JP 2008-000778 A (Patent Document 2), and JP 2016-002583 A (Patent Document 3).

Patent Document 1 discloses a technology for forming an embossment on the web surface of a channel material during press molding. Patent Document 1 states that by simply performing the relatively simple process of forming an embossment on the web surface during press molding, there is very little twisting of the molded product due to springback when the molded product is removed from the die after press processing, and this does not cause any inconvenience in assembling parts, etc.

Patent Document 2 discloses a technique for forming multiple holes with a width of 10 mm or less in at least a part of the vertical wall portion when manufacturing a hat-shaped metal part having a U-shaped or V-shaped cross-sectional shape by press molding, the holes relieving residual stress after press molding are formed in the part. Patent Document 2 states that a hat-shaped metal part with excellent shape freezing property without twisting or deformation can be obtained.

Patent Document 3 discloses a technique for manufacturing a molded product 11 having a groove-shaped portion 13 extending in the longitudinal direction and a pair of vertical wall portions 13b forming the groove-shaped portion 13, both of which have flange portions curved along the longitudinal direction. In the technique of Patent Document 3, press molding is performed using a punch 3 for forming the groove-shaped portion 13, a flange forming die 5 movably provided on both sides of the punch 3, and a die 7 having a groove-shaped forming portion 7a and a flange forming portion 7b. During press molding, if the distance from the bottom dead center of the die 7 during molding is H and the distance from the top dead center of the flange forming die 5 during molding is D, then H>0 and D>0 during molding, and H=D=0 at the time of molding into the product shape. Patent Document 3 describes that three-dimensional springback such as twisting and bending can be reduced.

JP 2008-213028 A JP 2008-000778 A JP 2016-002583 A

The techniques of Patent Document 1 and Patent Document 2 require the product to be embossed or holes to be drilled. In this case, the product is prone to deformation starting from the embossing or holes. This may result in a decrease in the product's rigidity, strength, and impact performance. In addition, with the technique of Patent Document 2, holes are drilled in the product, which raises concerns about a decrease in rust prevention performance. For this reason, the techniques of Patent Document 1 and Patent Document 2 are not practical.

The technology of Patent Document 3 requires a flange forming die 5 that can be moved during press forming. When using a general press machine, a predetermined load is simply applied to the mold equivalent to the flange forming die 5 from the die joint of the press machine via a cushion pin or via a gas cushion. For this reason, it is difficult to perform complex position control during forming, and the technology of Patent Document 3 is not practical.

Therefore, there is a strong demand for technology that can effectively suppress twisting and wall warping.

The objective of the present invention is to provide a press device and a method for manufacturing a press-molded product that can effectively suppress twisting and wall warping when manufacturing a press-molded product that is long, has a hat-shaped cross section, and includes a portion that is curved in plan view.

A press device according to one embodiment of the present invention includes a bed, a slide, a lower punch, a lower cushion, an inner lower jig, an upper pad, and an upper die. The slide can be raised and lowered relative to the bed. The lower punch has an elongated top surface, an inner side surface, an outer side surface, an inner bottom surface, and an outer bottom surface. The top surface has a curved portion that curves within the plane. The inner side surface is connected to the curved inner side edge of the curved portion of both side edges of the top surface. The outer side surface is connected to the curved outer side edge of the curved portion of both side edges of the top surface. The inner bottom surface is connected to the lower edge of the inner side surface. The outer bottom surface is connected to the lower edge of the outer side surface. The lower cushion supports the lower punch and is fixed to the bed.

The inner lower jig is positioned adjacent to the inner bottom surface of the lower punch and fixed to the bed. The inner lower jig has an inner lower blade on the edge of its upper surface adjacent to the inner bottom surface of the lower punch. The inner lower jig has an inner groove formed on its upper surface so as to follow the inner side edge of the curved portion. The upper pad is positioned opposite the top surface of the lower punch. The upper pad is supported by the slide via an elastic member.

The upper die is fixed to the slide. The upper die has an inner wall surface, an outer wall surface, an inner lower surface, an outer lower surface, and an inner recess. The inner wall surface corresponds to the inner side surface of the lower punch. The outer wall surface corresponds to the outer side surface of the lower punch. The inner lower surface faces the inner bottom surface of the lower punch. The outer lower surface faces the outer bottom surface of the lower punch. The inner recess is adjacent to the inner lower surface. The upper die has an inner upper blade on an edge of the inner lower surface adjacent to the inner recess. The upper die has an inner ridge that protrudes beyond the inner lower surface at a position on the bottom surface of the inner recess that faces the inner groove.

A method for manufacturing a press-molded product according to one embodiment of the present invention is a manufacturing method using the press device of the above-mentioned one embodiment. The press-molded product manufactured by this manufacturing method includes an elongated top plate, an inner vertical wall, an outer vertical wall, an inner flange, and an outer flange. The top plate has a curved portion that curves within a plane. The inner vertical wall is connected to the inner curved side edge of the curved portion of both side edges of the top plate. The outer vertical wall is connected to the outer curved side edge of the curved portion of both side edges of the top plate. The inner flange is connected to the lower edge of the inner vertical wall. The outer flange is connected to the lower edge of the outer vertical wall.

The manufacturing method includes steps (a) to (e). In step (a), a blank made of a metal plate is prepared. The blank has a size that exceeds the installation area of the inner ridge of the upper die. In step (b), the blank is placed on the top surface of the lower punch. In step (c), the slide is lowered to sandwich the blank between the upper pad and the top surface of the lower punch. In step (d), the slide is further lowered to press the blank with the upper die and lower punch, and also press the blank with the inner ridge and inner groove. In step (e), the slide is further lowered to cut the blank with the inner upper blade and inner lower blade.

A press device according to another embodiment of the present invention includes a bed, a slide, a lower punch, a lower cushion, an outer lower jig, an upper pad, and an upper die. The slide can be raised and lowered relative to the bed. The lower punch has an elongated top surface, an inner side surface, an outer side surface, an inner bottom surface, and an outer bottom surface. The top surface has a curved portion that curves within the plane. The inner side surface is connected to the curved inner side edge of the curved portion of both side edges of the top surface. The outer side surface is connected to the curved outer side edge of the curved portion of both side edges of the top surface. The inner bottom surface is connected to the lower edge of the inner side surface. The outer bottom surface is connected to the lower edge of the outer side surface. The lower cushion supports the lower punch and is fixed to the bed.

The outer lower jig is positioned adjacent to the outer bottom surface of the lower punch and is fixed to the bed. The outer lower jig has an outer lower blade on the edge of its upper surface adjacent to the outer bottom surface of the lower punch. The outer lower jig has an outer groove formed on its upper surface to follow the curved outer side edge of the curved portion. The upper pad is positioned opposite the top surface of the lower punch. The upper pad is supported by the slide via an elastic member.

The upper die is fixed to the slide. The upper die has an inner wall surface, an outer wall surface, an inner lower surface, an outer lower surface, and an outer recess. The inner wall surface corresponds to the inner side surface of the lower punch. The outer wall surface corresponds to the outer side surface of the lower punch. The inner lower surface faces the inner bottom surface of the lower punch. The outer lower surface faces the outer bottom surface of the lower punch. The outer recess is adjacent to the outer lower surface. The upper die has an outer upper blade on an edge of the outer lower surface adjacent to the outer recess. The upper die has an outer ridge that protrudes beyond the outer lower surface at a position on the bottom surface of the outer recess that faces the outer groove.

A method for manufacturing a press-molded product according to another embodiment of the present invention is a manufacturing method using the press device according to the other embodiment described above. The press-molded product manufactured by this manufacturing method includes an elongated top plate, an inner vertical wall, an outer vertical wall, an inner flange, and an outer flange. The top plate has a curved portion that curves within a plane. The inner vertical wall is connected to the inner curved side edge of the curved portion of both side edges of the top plate. The outer vertical wall is connected to the outer curved side edge of the curved portion of both side edges of the top plate. The inner flange is connected to the lower edge of the inner vertical wall. The outer flange is connected to the lower edge of the outer vertical wall.

The manufacturing method includes steps (a) to (e). In step (a), a blank made of a metal plate is prepared. The blank has a size that exceeds the installation area of the outer ridge of the upper die. In step (b), the blank is placed on the top surface of the lower punch. In step (c), the slide is lowered to sandwich the blank between the upper pad and the top surface of the lower punch. In step (d), the slide is further lowered to press the blank with the upper die and lower punch, and also to press the blank with the outer ridge and outer groove. In step (e), the slide is further lowered to cut the blank with the outer upper blade and the outer lower blade.

The press device and the method for manufacturing a press-molded product according to the embodiment of the present invention can effectively suppress twisting and wall warping when manufacturing a press-molded product that is long, has a hat-shaped cross section, and includes a portion that is curved in a plan view.

FIG. 1A is a perspective view showing the appearance of a press-formed product. FIG. 1B is a plan view showing the appearance of the press-formed product. FIG. 1C is a perspective view showing the appearance of another press-formed product. FIG. 2A is a plan view showing a variation of the press-formed product. FIG. 2B is a plan view showing a variation of the press-formed product. FIG. 2C is a plan view showing a variation of the press-formed product. FIG. 2D is a plan view showing a variation of the press-formed product. FIG. 2E is a plan view showing a variation of the press-formed product. FIG. 2F is a plan view showing a variation of the press-formed product. FIG. 2G is a plan view showing a variation of the press-formed product. FIG. 3A is a plan view showing stresses occurring in a plank during press forming by a typical press process. FIG. 3B is a perspective view showing stresses generated in a press-formed product upon completion of press forming by a general press working. FIG. 3C is a perspective view showing stress caused by springback in a molded product removed from a die after press molding by a general press process. FIG. 4A is a cross-sectional view showing stresses occurring in a blank during press forming by a typical press process. FIG. 4B is a cross-sectional view showing stresses occurring in a press-molded product removed from a die after press molding by a general press process. FIG. 4C is a cross-sectional view showing a press-formed product before and after the occurrence of springback when the press-formed product is formed by a general press working. FIG. 5 is a perspective view showing a press-formed product in which twisting and wall warping have occurred. FIG. 6 is a cross-sectional view illustrating an example of the press device according to the first embodiment. FIG. 7 is a perspective view of a die set provided in the press apparatus shown in FIG. FIG. 8A is a cross-sectional view showing one step in a method for manufacturing a press-formed product using the press apparatus of the first embodiment. FIG. 8B is a cross-sectional view showing a step subsequent to that shown in FIG. 8A. FIG. 8C is a cross-sectional view showing a step subsequent to that shown in FIG. 8B. FIG. 8D is a cross-sectional view showing a step following that of FIG. 8C. FIG. 8E is a cross-sectional view showing a step following that of FIG. 8D. FIG. 8F is a cross-sectional view showing a step following that of FIG. 8E. FIG. 9 is a plan view showing a blank applied to the method for manufacturing a press-formed product using the press apparatus of the first embodiment. FIG. 10 is a plan view for explaining a state when a press-formed product is formed by the manufacturing method using the press machine of the first embodiment. FIG. 11 is a cross-sectional view showing an example of a pressing device according to the second embodiment. FIG. 12 is a plan view showing a blank applied to a manufacturing method of a press-formed product using the press apparatus of the second embodiment. FIG. 13 is a plan view of the blank. FIG. 14 is a cross-sectional view showing a state during press molding. FIG. 15 is a plan view showing a preferred shape 1 of the blank. FIG. 16 is a plan view for explaining a state in which the blank shown in FIG. 15 is formed into a press-formed product. FIG. 17 is a diagram showing the relationship between θ2/θ1 and the twist angle of a press-formed product. FIG. 18 is a plan view showing a preferred shape 2 of the blank. FIG. 19 is a plan view showing a preferred shape 3 of the blank. FIG. 20 is a plan view for explaining a state in which the blank shown in FIG. 19 is formed into a press-formed product. FIG. 21 is a diagram showing the relationship between θ3/θ1 and the twist angle of a press-formed product. FIG. 22 is a plan view showing a preferred shape 4 of the blank. FIG. 23 is a cross-sectional view illustrating preferred dimensions of the inner ridge and the outer ridge. FIG. 24 is a cross-sectional view for explaining suitable dimensions of the inner lower jig and the outer lower jig. FIG. 25 is a cross-sectional view for explaining suitable initial height positions of the inner bottom surface and the outer bottom surface of the lower punch. FIG. 26 is a cross-sectional view for explaining a suitable amount of lowering of the lower punch and suitable depths of the inner and outer recesses of the upper die. FIG. 27A illustrates a preferred shape for the inside lowerknife. FIG. 27B illustrates a preferred shape for the outer lowerknife. FIG. 28A is a perspective view for explaining a method for evaluating torsion. FIG. 28B is a cross-sectional view for explaining a method for evaluating wall warpage.

The following describes an embodiment of the present invention. Note that in the following description, examples of the embodiment of the present invention are given, but the present invention is not limited to the examples described below. In the following description, specific numerical values and specific materials may be given as examples, but the present invention is not limited to these examples.

In order to solve the above problems, the inventors conducted a detailed study of the mechanism by which twisting and wall warping occurs when a press-molded product is manufactured. As a result, the following findings were obtained. Note that in this specification, a press-molded product is defined as a long product having a hat-shaped cross section and including a portion that is curved in a plan view.

[Press-molded products]
1A and 1B are diagrams showing the appearance of a press-molded product 101. Of these figures, FIG. 1A is a perspective view, and FIG. 1B is a plan view. Referring to FIG. 1A and FIG. 1B, the press-molded product 101 has a long, hat-shaped cross section. The press-molded product 101 includes a portion (hereinafter also referred to as a "curved portion") 111 that is curved in a plan view. Furthermore, the press-molded product 101 includes a straight portion 112 that extends linearly from an end of the longitudinal direction of the curved portion 111. In this specification, the cross section means a cross section perpendicular to the longitudinal direction of the press-molded product 101. The longitudinal direction means the direction in which the press-molded product 101 extends. The short direction means a direction perpendicular to the longitudinal direction. In addition, when a cross section and a direction are shown in a press device 1 described later for molding the press-molded product 101, the cross section and the direction are the same as those in the press-molded product 101. For example, in the press device 1, the direction in which the top surface 41 of the lower punch 4 extends is the longitudinal direction, and a cross section perpendicular to the direction in which the top surface 41 of the lower punch 4 extends is a transverse cross section.

The press-formed product 101 includes a top plate 102, an inner vertical wall 103i, an outer vertical wall 103o, an inner flange 104i, and an outer flange 104o. The top plate 102 is elongated and flat, and has a curved portion 121. The curved portion 121 of the top plate 102 is a portion that curves within the flat surface of the top plate 102. The curved portion 121 of the top plate 102 is included in the curved portion 111 of the press-formed product 101. In addition, the top plate 102 of the press-formed product 101 shown in Figures 1A and 1B has straight portions 122 that extend linearly in the longitudinal direction from each of both ends of the curved portion 121 of the top plate 102. The straight portions 122 of the top plate 102 are included in the straight portions 112 of the press-formed product 101.

The inner vertical wall 103i is connected to the side edge 121i of the curved portion 121 on the inner side of the curve of the top plate 102. The inner side of the curve means the center side of the radius of curvature of the curve with respect to one curved portion 121. The term inner side of the curve is also interpreted in the same sense when used in other elements. The inner vertical wall 103i has a curved portion 131i. The curved portion 131i of the inner vertical wall 103i is a portion that connects to the curved portion 121 of the top plate 102 and is curved concavely. In other words, the curved portion 131i of the inner vertical wall 103i is curved convexly toward the curved outward in the plate thickness direction. The curved portion 131i of the inner vertical wall 103i is included in the curved portion 111 of the press-molded product 101. The inner vertical wall 103i also has straight portions 132i that extend linearly in the longitudinal direction from both ends of the curved portion 131i of the inner vertical wall 103i. The straight portion 132i of the inner vertical wall 103i is connected to the straight portion 122 of the top plate 102. The straight portion 132i of the inner vertical wall 103i is included in the straight portion 112 of the press-formed product 101.

The outer vertical wall 103o is connected to the outer side edge 121o of the curved portion 121 of both side edges of the top plate 102. The outer side of the curved portion 121 means the side opposite to the center of the radius of curvature of the curve with respect to one curved portion 121. The term "outer side of the curved portion" is also interpreted in the same sense when used in other elements. The outer vertical wall 103o has a curved portion 131o. The curved portion 131o of the outer vertical wall 103o is a portion that is connected to the curved portion 121 of the top plate 102 and is curved convexly. In other words, the curved portion 131o of the outer vertical wall 103o is curved convexly toward the curved outer side in the plate thickness direction. The curved portion 131o of the outer vertical wall 103o is included in the curved portion 111 of the press-molded product 101. The outer vertical wall 103o also has straight portions 132o that extend linearly in the longitudinal direction from both ends of the curved portion 131o of the outer vertical wall 103o. The straight portion 132o of the outer vertical wall 103o is connected to the straight portion 122 of the top plate 102. The straight portion 132o of the outer vertical wall 103o is included in the straight portion 112 of the press-formed product 101.

The inner flange 104i is connected to the lower edge of the inner vertical wall 103i. The inner flange 104i has a curved portion 141i. The curved portion 141i of the inner flange 104i is connected to the curved portion 131i of the inner vertical wall 103i. The curved portion 141i of the inner flange 104i is included in the curved portion 111 of the press-formed product 101. The inner flange 104i also has straight portions 142i that extend linearly in the longitudinal direction from both ends of the curved portion 141i of the inner flange 104i. The straight portion 142i of the inner flange 104i is connected to the straight portion 132i of the inner vertical wall 103i. The straight portion 142i of the inner flange 104i is included in the straight portion 112 of the press-formed product 101.

The outer flange 104o is connected to the lower edge of the outer vertical wall 103o. The outer flange 104o has a curved portion 141o. The curved portion 141o of the outer flange 104o is connected to the curved portion 131o of the outer vertical wall 103o. The curved portion 141o of the outer flange 104o is included in the curved portion 111 of the press-formed product 101. The outer flange 104o also has straight portions 142o that extend linearly in the longitudinal direction from both ends of the curved portion 141o of the outer flange 104o. The straight portion 142o of the outer flange 104o is connected to the straight portion 132o of the outer vertical wall 103o. The straight portion 142o of the outer flange 104o is included in the straight portion 112 of the press-formed product 101.

As shown in FIG. 1C, a fillet R may be formed at the corner between the top plate 102 and the inner vertical wall 103i. This corner is a portion that connects the side edge 121i of the top plate 102 and the upper edge of the inner vertical wall 103i. The fillet R refers to the radius of curvature that appears in the cross section of the corner. The same can be said for the corner between the inner vertical wall 103i and the inner flange 104i, the corner between the top plate and the outer vertical wall 103o, and the corner between the outer vertical wall 103o and the outer flange 104o. For simplicity, FIG. 1A shows a shape without a fillet R, that is, a shape with a fillet R of 0 (zero). In the following figures, shapes without the fillet R at each corner are shown for simplicity.

1A and 1B, the press-formed product 101 is composed of a curved portion 111 and straight portions 112 extending linearly in the longitudinal direction from both ends of the curved portion 111. The curved portion 111 of the press-formed product 101 is composed of a curved portion 121 of the top plate 102, a curved portion 131i of the inner vertical wall 103i, a curved portion 131o of the outer vertical wall 103o, a curved portion 141i of the inner flange 104i, and a curved portion 141o of the outer flange 104o. The straight portion 112 of the press-formed product 101 is composed of a straight portion 122 of the top plate 102, a straight portion 132i of the inner vertical wall 103i, a straight portion 132o of the outer vertical wall 103o, a straight portion 142i of the inner flange 104i, and a straight portion 142o of the outer flange 104o. However, the press-formed product 101 may be composed of only the curved portion 111, or may be composed of the curved portion 111 and one straight portion 112.

Figures 2A to 2G show examples of variations of the press-formed product 101. Figures 2A to 2G show plan views of the top plate 102 of the press-formed product 101.

The tabletop 102 shown in Figures 2A to 2D is composed of only one curved portion 121. In other words, the press-molded product 101 shown in Figures 2A to 2D is composed of only one curved portion 111. In the case of the tabletop 102 shown in Figure 2A, in a plan view, the side edge 121i (121o) of the curved portion 121 is composed of one circular arc. In the case of the tabletop 102 shown in Figure 2B, in a plan view, the side edge 121i (121o) of the curved portion 121 is composed of two circular arcs having mutually different radii of curvature. The two circular arcs are smoothly connected to each other. In the case of the tabletop 102 shown in Figure 2C, in a plan view, the side edge 121i (121o) of the curved portion 121 is composed of one elliptical arc. In the case of the tabletop 102 shown in FIG. 2D, in a plan view, the side edge 121i (121o) of the curved portion 121 is composed of two elliptical arcs of different sizes. The two elliptical arcs are smoothly connected to each other. In a plan view, the side edge 121i (121o) of the curved portion 121 may be another curve (e.g., a spline curve, a Bezier curve).

The top plate 102 shown in FIG. 2E is composed of one curved portion 121 and one straight portion 122. In other words, the press-molded product 101 shown in FIG. 2E is composed of one curved portion 111 and one straight portion 112. In the case of the top plate 102 shown in FIG. 2E, the straight portion 122 is provided at one end of the curved portion 121. The side edge 121i (121o) of the curved portion 121 smoothly connects to the side edge of the straight portion 122.

The top plate 102 shown in FIG. 2F is composed of one curved portion 121 and two straight portions 122. In other words, the press-molded product 101 shown in FIG. 2F is composed of one curved portion 111 and two straight portions 112. In the case of the top plate 102 shown in FIG. 2F, a straight portion 122 is provided at each end of the curved portion 121. The side edges 121i (121o) of the curved portion 121 are smoothly connected to the side edges of each straight portion 122.

The top plate 102 shown in FIG. 2G is composed of two curved portions 121 and one straight portion 122. In other words, the press-molded product 101 shown in FIG. 2G is composed of two curved portions 111 and one straight portion 112. In the case of the top plate 102 shown in FIG. 2G, a curved portion 121 is provided on each end of the straight portion 122. The side edges of the straight portion 122 smoothly connect to the side edges 121i (121o) of each curved portion 121.

Such a press-molded product 101 is formed by press working, such as by drawing or bending. Generally, a lower punch and an upper die are used as the metal mold for press working. A lower punch, an upper die, and an upper pad may also be used as the metal mold. The circumstances under which the press-molded product 101 is formed using such a metal mold are described below.

[Manufacturing of press-molded products by general press working]
3A to 3C are diagrams for explaining the situation when a press-formed product 101 is formed by a general press working. Of these diagrams, Fig. 3A is a plan view showing stresses occurring in a blank 1201 during press forming. Fig. 3B is a perspective view showing stresses occurring in the press-formed product 101 when press forming is completed. Fig. 3C is a perspective view showing stresses occurring in the press-formed product 101 removed from a die after press forming.

In Fig. 3A, the blank 1201 is shown by a solid line, and the press-formed product 101 formed from this blank 1201 is shown by a two-dot chain line. Also, in Fig. 3A, the longitudinal stresses occurring in the regions that become the inner vertical wall 103i, the inner flange 104i, the outer vertical wall 103o, and the outer flange 104o of the press-formed product 101 are shown by thick solid arrows. In Fig. 3B, the stresses occurring during forming in the inner vertical wall 103i and the outer vertical wall 103o of the press-formed product 101 are shown by thick solid arrows, and the stresses occurring during forming in the inner flange 104i and the outer flange 104o of the press-formed product 101 are shown by thin solid arrows. In FIG. 3C, the stress caused by springback in the inner vertical wall 103i and the outer vertical wall 103o of the press-formed product 101 after release from the die is indicated by thick solid arrows, and the stress caused by springback in the inner flange 104i and the outer flange 104o of the press-formed product 101 is indicated by thin solid arrows. The direction of each arrow indicates the direction in which the stress acts.

Referring to FIG. 3A, in the blank 1201 during press forming, the region corresponding to the inner curve of the curved portion 121 of the top plate 102 undergoes stretch flange deformation. That is, the region that is the inner curve of the curved portion 121 of the top plate 102 undergoes stretch flange deformation. This is because the perimeter (longitudinal length) of this region increases during press forming. On the other hand, in the blank 1201 during press forming, the region that is the outer curve of the curved portion 121 of the top plate 102 undergoes shrink flange deformation. That is, the region that is the outer curve of the curved portion 121 of the top plate 102 undergoes shrink flange deformation. This is because the perimeter (longitudinal length) of this region decreases during press forming.

In this case, in the blank 1201 being press-formed, tensile stress is generated in the longitudinal direction in the areas that will become the curved portion 131i of the inner vertical wall 103i and the curved portion 141i of the inner flange 104i. This is because these areas undergo stretch flange deformation. On the other hand, in the blank 1201 being press-formed, compressive stress is generated in the longitudinal direction in the areas that will become the curved portion 131o of the outer vertical wall 103o and the curved portion 141o of the outer flange 104o. This is because these areas undergo shrink flange deformation.

As a result, as shown in FIG. 3B, in the press-molded product 101 in the die when press molding is completed, tensile stress is generated in the curved portion 131i of the inner vertical wall 103i and the curved portion 141i of the inner flange 104i in the longitudinal direction. This is because these curved portions 131i and 141i are formed by stretch flange deformation and are restrained by the die in a state in which tensile stress is generated in the longitudinal direction. On the other hand, in the press-molded product 101 in the die when press molding is completed, compressive stress is generated in the curved portion 131o of the outer vertical wall 103o and the curved portion 141o of the outer flange 104o in the longitudinal direction. This is because these curved portions 131o and 141o are formed by shrink flange deformation and are restrained by the die in a state in which compressive stress is generated in the longitudinal direction.

When the press-formed product 101 is removed from the die after press forming, the constraint by the die is released. As a result, springback occurs in the press-formed product 101. In other words, as shown in FIG. 3C, the tensile stress at the time of completion of press forming is reversed in the curved portion 131i of the inner vertical wall 103i and the curved portion 141i of the inner flange 104i, and compressive stress occurs in the longitudinal direction. On the other hand, the compressive stress at the time of completion of press forming is reversed in the curved portion 131o of the outer vertical wall 103o and the curved portion 141o of the outer flange 104o, and tensile stress occurs in the longitudinal direction.

In short, in the press-formed product 101, springback generates longitudinal compressive stress in the curved portion 131i of the inner vertical wall 103i and the curved portion 141i of the inner flange 104i, and longitudinal tensile stress in the curved portion 131o of the outer vertical wall 103o and the curved portion 141o of the outer flange 104o. As a result, the entire press-formed product 101 twists. In other words, the press-formed product 101 twists due to the longitudinal compressive stress generated in the inner curved portion of the curved portion of the press-formed product 101. The press-formed product 101 also twists due to the longitudinal tensile stress generated in the outer curved portion of the curved portion of the press-formed product 101.

Figures 4A to 4C are diagrams for explaining the situation when the press-formed product 101 is formed by bending, which is a common press process, from a different perspective from the situation shown in Figures 3A to 3C. Of these figures, Figure 4A is a cross-sectional view showing the stress generated in the blank 1201 during press forming. Figure 4B is a cross-sectional view showing the stress generated in the press-formed product by springback when it is removed from the die after press forming. Figure 4C is a cross-sectional view showing the press-formed product 101 before and after springback occurs.

Figures 4A to 4C show cross sections of the curved portion of the press-formed product 101. In addition, in Figure 4A, the stress generated in the regions that become the inner vertical wall 103i and the outer vertical wall 103o of the press-formed product 101 is shown with solid arrows. In Figure 4B, the stress generated in the inner vertical wall 103i and the outer vertical wall 103o of the press-formed product 101 is shown with solid arrows. In Figure 4C, the press-formed product 101 before the occurrence of springback is shown with a two-dot chain line, and the press-formed product 101 after the occurrence of springback is shown with a solid line. The direction of each arrow indicates the direction in which the stress acts.

Referring to FIG. 4A, a lower punch 1004, an upper die 1008, and an upper pad 1007 are used as a die for press processing. In this case, first, the blank 1201 is sandwiched between the upper pad 1007 and the lower punch 1004 by the downward movement of the slide (not shown). Then, the inner vertical wall 103i and the outer vertical wall 103o are gradually formed by the further downward movement of the slide. At that time, the inner vertical wall 103i and the outer vertical wall 103o are bent and bent back by the die shoulder 1086 of the upper die 1008. As a result, tensile stress is generated in the short side direction (height direction) on the outer surface of the region that becomes the inner vertical wall 103i. On the other hand, compressive stress is generated in the short side direction (height direction) on the inner surface of the region that becomes the inner vertical wall 103i. The same phenomenon as that of the inner vertical wall 103i occurs in the region that becomes the outer vertical wall 103o. In other words, tensile stress is generated in the short-side direction (height direction) on the outer surface of the region that will become the outer vertical wall 103o. On the other hand, compressive stress is generated in the short-side direction (height direction) on the inner surface of the region that will become the outer vertical wall 103o. In these regions, the outer surface refers to the surface that contacts the upper die 1008 (particularly the die shoulder 1086), and the inner surface refers to the surface that contacts the lower punch 1004.

As a result, in the press-molded product 101 in the die when press molding is completed, tensile stress occurs in the short-side direction on the outer surfaces of the inner vertical wall 103i and the outer vertical wall 103o. This is because the inner vertical wall 103i and the outer vertical wall 103o are restrained by the die when tensile stress in the short-side direction occurs on each outer surface. On the other hand, in the press-molded product 101 in the die when press molding is completed, compressive stress occurs in the short-side direction on the inner surfaces of the inner vertical wall 103i and the outer vertical wall 103o. This is because the inner vertical wall 103i and the outer vertical wall 103o are restrained by the die when compressive stress in the short-side direction occurs on each inner surface.

When the press-formed product 101 is removed from the die after press forming, the constraint imposed by the die is released. As a result, springback occurs in the press-formed product 101. In other words, as shown in FIG. 4B, the tensile stress at the time of completion of press forming is reversed on the outer surfaces of the inner vertical wall 103i and the outer vertical wall 103o, and compressive stress occurs in the short direction. On the other hand, the compressive stress at the time of completion of press forming is reversed on the inner surfaces of the inner vertical wall 103i and the outer vertical wall 103o, and tensile stress occurs in the short direction.

In short, in the press-formed product 101, due to springback, a compressive stress in the short-side direction is generated on the outer surface of each of the inner vertical wall 103i and the outer vertical wall 103o, and a tensile stress in the short-side direction is generated on the inner surface of each of the inner vertical wall 103i and the outer vertical wall 103o. In this way, stresses in different directions are generated on the outer surface and the inner surface. Due to this stress difference, as shown in FIG. 4C, the inner vertical wall 103i and the outer vertical wall 103o are warped outward. In other words, the wall warping occurs in the inner vertical wall 103i of the press-formed product 101 due to the difference between the compressive stress in the short-side direction generated on the outer surface of the inner vertical wall 103i and the tensile stress in the short-side direction generated on the inner surface of the inner vertical wall 103i. In addition, the wall warping occurs in the outer vertical wall 103o of the press-formed product 101 due to the difference between the compressive stress in the short-side direction generated on the outer surface of the outer vertical wall 103o and the tensile stress in the short-side direction generated on the inner surface of the outer vertical wall 103o.

Figure 5 is a perspective view showing a press-formed product 101 in which twisting and wall warping have occurred. In Figure 5, a press-formed product 101 in which twisting and wall warping have not occurred is shown by a two-dot chain line. With reference to Figure 5, as described above, in general press working, twisting and wall warping occur in the press-formed product 101 due to springback.

[Study on suppression of twisting and wall warping]
As described above, when the press-molded product 101 is removed from the die after press molding and the constraint by the die is released, the press-molded product 101 is twisted by the longitudinal compressive stress generated in the curved inner part of the curved part of the press-molded product 101. That is, the press-molded product 101 is twisted by the longitudinal compressive stress generated in the curved part 131i of the inner vertical wall 103i and the curved part 141i of the inner flange 104i. Also, when the press-molded product 101 is removed from the die after press molding and the constraint by the die is released, the press-molded product 101 is twisted by the longitudinal tensile stress generated in the curved outer part of the curved part of the press-molded product 101. That is, the press-molded product 101 is twisted by the longitudinal tensile stress generated in the curved part 131o of the outer vertical wall 103o and the curved part 141o of the outer flange 104o.

In addition, when the press-molded product 101 is removed from the die after press molding and the constraint by the die is released, wall warping of the press-molded product 101 occurs due to the difference between the compressive stress in the short-side direction that occurs on the outer surface of the inner vertical wall 103i and the tensile stress in the short-side direction that occurs on the inner surface of the inner vertical wall 103i. In addition, wall warping of the press-molded product 101 occurs due to the difference between the compressive stress in the short-side direction that occurs on the outer surface of the outer vertical wall 103o and the tensile stress in the short-side direction that occurs on the inner surface of the outer vertical wall 103o.

Therefore, to suppress the twisting of the press-formed product 101, it is necessary to reduce the longitudinal tensile stress that occurs in the inner curved part of the curved part of the press-formed product 101 when the press-formed product 101 is completed. The inner curved part of the curved part of the press-formed product 101 is the curved part 131i of the inner vertical wall 103i and the curved part 141i of the inner flange 104i. Also, to suppress the twisting of the press-formed product 101, it is necessary to reduce the longitudinal compressive stress that occurs in the outer curved part of the curved part of the press-formed product 101 when the press-formed product 101 is completed. The outer curved part of the curved part of the press-formed product 101 is the curved part 131o of the outer vertical wall 103o and the curved part 141o of the outer flange 104o. To further suppress the twisting of the press-formed product 101, it is necessary to reduce both these tensile stresses and compressive stresses.

To suppress wall warping in the inner vertical wall 103i of the press-molded product 101, it is necessary to reduce the difference between the tensile stress in the short-side direction that occurs on the outer surface of the inner vertical wall 103i and the compressive stress in the short-side direction that occurs on the inner surface of the inner vertical wall 103i when the molding of the press-molded product 101 is completed. Also, to suppress wall warping in the outer vertical wall 103o of the press-molded product 101, it is necessary to reduce the difference between the tensile stress in the short-side direction that occurs on the outer surface of the outer vertical wall 103o and the compressive stress in the short-side direction that occurs on the inner surface of the outer vertical wall 103o when the molding of the press-molded product 101 is completed.

In this way, the inventors have investigated the mechanism by which twisting and wall warping occurs when manufacturing the press-molded product 101, and have found a direction for suppressing twisting and wall warping of the press-molded product 101. The inventors have then investigated a press device and a manufacturing method for the press-molded product 101 that are compatible with this direction. As a result of their diligent investigation, the following findings have been obtained.

In a typical press forming process of the blank 1201, the area that will become the inner vertical wall 103i and the inner flange 104i is simply drawn toward the area that will become the top plate 102. Similarly, the area that will become the outer vertical wall 103o and the outer flange 104o is simply drawn toward the area that will become the top plate 102.

For the part that is deformed by stretch flange, that is, the part on the inner side of the curve of the curved part of the press-formed product 101 (the curved part 131i of the inner vertical wall 103i and the curved part 141i of the inner flange 104i), tension is applied to the area that will become that part during press molding against the pulling force toward the area that will become the top plate 102, and if the molding of the press-formed product 101 is completed while applying this tension, the tensile stress in the longitudinal direction can be reduced, and the difference between the tensile stress and the compressive stress in the transverse direction can be reduced. This is because, during press molding, compressive stress is applied in the longitudinal direction as a component force in the longitudinal direction by applying tension, and as a result, the tensile stress in the longitudinal direction associated with the stretch flange deformation is alleviated. In order to realize the application of tension, an excess inner valley part that does not become the final product is formed further inward of the curve of the curved part 141i of the inner flange 104i during press molding. This inner valley portion is formed to follow the curved inner side edge 121i of the curved portion 121 of the top plate 102.

However, if the inner valley portion still exists after the press forming is completed, twisting will occur in the inner valley portion. This is because the inner valley portion corresponds to the small-sized press-formed product 101. In this case, twisting of the inner valley portion may cause twisting of the press-formed product 101 that will become the final product. Therefore, the area including the inner valley portion is removed from the press-formed product 101 at least before the press-formed product 101 is removed from the die.

In this way, the tensile stress in the longitudinal direction can be reduced in the inner curved portion of the curved portion of the press-molded product 101 when it is placed in the die (the curved portion 131i of the inner vertical wall 103i and the curved portion 141i of the inner flange 104i), and the difference between the tensile stress on the outer surface and the compressive stress on the inner surface can be reduced in the lateral direction. As a result, the compressive stress in the longitudinal direction can be reduced in the inner curved portion of the curved portion of the press-molded product 101 removed from the die, and the difference between the compressive stress on the outer surface and the tensile stress on the inner surface can be reduced in the lateral direction. As a result, twisting and wall warping of the press-molded product 101 can be effectively suppressed.

In addition, for the part where the shrink flange deforms, that is, the part on the outer side of the curved part of the press-formed product 101 (the curved part 131o of the outer vertical wall 103o and the curved part 141o of the outer flange 104o), tension is applied to the area that will become that part during press forming against the pulling force toward the area that will become the top plate 102, and if the molding of the press-formed product 101 is completed while applying this tension, the compressive stress in the longitudinal direction can be reduced, and the difference between the tensile stress and the compressive stress in the transverse direction can be reduced. This is because, during press forming, the application of tension applies a tensile stress in the longitudinal direction as a component force in the longitudinal direction, and as a result, the compressive stress in the longitudinal direction associated with the shrink flange deformation is alleviated. In order to achieve the application of tension, an excess outer valley portion that does not become part of the final product is formed further outward of the curved part 141o of the outer flange 104o during press forming. This outer valley portion is formed to follow the curved outer side edge 121o of the curved portion 121 of the top plate 102.

However, if the outer valley portion still exists after the press forming is completed, twisting will occur in the outer valley portion. This is because the outer valley portion corresponds to the small-sized press-formed product 101. In this case, twisting of the outer valley portion may cause twisting of the press-formed product 101 that will become the final product. Therefore, the area including the outer valley portion is removed from the press-formed product 101 at least before the press-formed product 101 is removed from the die.

In this way, the compressive stress in the longitudinal direction can be reduced in the outer curved portion of the curved portion of the press-molded product 101 when it is placed in the die (the curved portion 131o of the outer vertical wall 103o and the curved portion 141o of the outer flange 104o), and the difference between the tensile stress on the outer surface and the compressive stress on the inner surface in the lateral direction can be reduced. As a result, the tensile stress in the longitudinal direction can be reduced in the outer curved portion of the curved portion of the press-molded product 101 removed from the die, and the difference between the compressive stress on the outer surface and the tensile stress on the inner surface in the lateral direction can be reduced. As a result, twisting and wall warping of the press-molded product 101 can be effectively suppressed.

However, if both the inner valley portion and the outer valley portion are formed during press molding, and both the inner recess portion and the outer recess portion are removed from the press-molded product 101 at least before the press-molded product 101 is removed from the die, twisting and wall warping of the press-molded product 101 can be further suppressed.

The present invention was completed based on the above findings.

A press device according to one embodiment of the present invention includes a bed, a slide, a lower punch, a lower cushion, an inner lower jig, an upper pad, and an upper die. The slide can be raised and lowered relative to the bed. The lower punch has an elongated top surface, an inner side surface, an outer side surface, an inner bottom surface, and an outer bottom surface. The top surface has a curved portion that curves within the plane. The inner side surface is connected to the curved inner side edge of the curved portion of both side edges of the top surface. The outer side surface is connected to the curved outer side edge of the curved portion of both side edges of the top surface. The inner bottom surface is connected to the lower edge of the inner side surface. The outer bottom surface is connected to the lower edge of the outer side surface. The lower cushion supports the lower punch and is fixed to the bed.

The inner lower jig is positioned adjacent to the inner bottom surface of the lower punch and fixed to the bed. The inner lower jig has an inner lower blade on the edge of its upper surface adjacent to the inner bottom surface of the lower punch. The inner lower jig has an inner groove formed on its upper surface so as to follow the inner side edge of the curved portion. The upper pad is positioned opposite the top surface of the lower punch. The upper pad is supported by the slide via an elastic member.

The upper die is fixed to the slide. The upper die has an inner wall surface, an outer wall surface, an inner lower surface, an outer lower surface, and an inner recess. The inner wall surface corresponds to the inner side surface of the lower punch. The outer wall surface corresponds to the outer side surface of the lower punch. The inner lower surface faces the inner bottom surface of the lower punch. The outer lower surface faces the outer bottom surface of the lower punch. The inner recess is adjacent to the inner lower surface. The upper die has an inner upper blade on an edge of the inner lower surface adjacent to the inner recess. The upper die has an inner ridge that protrudes beyond the inner lower surface at a position on the bottom surface of the inner recess that faces the inner groove (first configuration).

According to the press device of the first configuration, press forming is performed by lowering the slide. During press forming, the press-formed product 101 is formed by the lower punch, upper die, and upper pad, and an excess inner valley portion that does not become part of the final product is formed further inward of the curved portion of the press-formed product 101 by the inner convex ridge of the upper die and the inner groove of the inner lower jig. Then, the boundary between the press-formed product 101 and the area including the inner valley portion is cut by the inner upper blade of the upper die and the inner lower blade of the inner lower jig. This removes the area including the inner valley portion from the press-formed product 101.

During press molding, in the process of forming the inner valley portion, tension is applied to the area that will become the inner curved portion of the curved portion of the press-molded product 101 (the curved portion 131i of the inner vertical wall 103i and the curved portion 141i of the inner flange 104i) against the pulling force toward the area that will become the top plate 102. In this case, the application of tension applies a compressive stress in the longitudinal direction as a longitudinal component force, and as a result, the longitudinal tensile stress associated with the stretch flange deformation is alleviated. This allows the longitudinal tensile stress to be reduced, and in the lateral direction, the difference between the tensile stress on the outer surface and the compressive stress on the inner surface can be reduced. Furthermore, the inner valley portion is removed during the press molding process. By applying such tension and removing the inner valley, the compressive stress in the longitudinal direction caused by springback can be reduced in the inner curved portion of the curved portion of the press-formed product 101 removed from the die (the curved portion 131i of the inner vertical wall 103i and the curved portion 141i of the inner flange 104i), and the difference between the compressive stress on the outer surface and the tensile stress on the inner surface in the transverse direction can be reduced. As a result, the torsion and wall warping of the press-formed product 101 can be effectively suppressed.

A press device according to another embodiment of the present invention includes a bed, a slide, a lower punch, a lower cushion, an outer lower jig, an upper pad, and an upper die. The slide can be raised and lowered relative to the bed. The lower punch has an elongated top surface, an inner side surface, an outer side surface, an inner bottom surface, and an outer bottom surface. The top surface has a curved portion that curves within the plane. The inner side surface is connected to the curved inner side edge of the curved portion of both side edges of the top surface. The outer side surface is connected to the curved outer side edge of the curved portion of both side edges of the top surface. The inner bottom surface is connected to the lower edge of the inner side surface. The outer bottom surface is connected to the lower edge of the outer side surface. The lower cushion supports the lower punch and is fixed to the bed.

The outer lower jig is positioned adjacent to the outer bottom surface of the lower punch and is fixed to the bed. The outer lower jig has an outer lower blade on the edge of its upper surface adjacent to the outer bottom surface of the lower punch. The outer lower jig has an outer groove formed on its upper surface to follow the curved outer side edge of the curved portion. The upper pad is positioned opposite the top surface of the lower punch. The upper pad is supported by the slide via an elastic member.

The upper die is fixed to the slide. The upper die has an inner wall surface, an outer wall surface, an inner lower surface, an outer lower surface, and an outer recess. The inner wall surface corresponds to the inner side surface of the lower punch. The outer wall surface corresponds to the outer side surface of the lower punch. The inner lower surface faces the inner bottom surface of the lower punch. The outer lower surface faces the outer bottom surface of the lower punch. The outer recess is adjacent to the outer lower surface. The upper die has an outer upper blade on an edge of the outer lower surface adjacent to the outer recess. The upper die has an outer protrusion that protrudes beyond the outer lower surface at a position on the bottom surface of the outer recess that faces the outer groove (second configuration).

According to the press device of the second configuration, press forming is performed by lowering the slide. During press forming, the press-formed product 101 is formed by the lower punch, upper die, and upper pad, and an excess outer valley portion that does not become part of the final product is formed further outward of the curved portion of the press-formed product 101 by the outer convex ridge of the upper die and the outer groove of the outer lower jig. Then, the boundary between the press-formed product 101 and the area including the outer valley portion is cut by the outer upper blade of the upper die and the outer lower blade of the outer lower jig. This removes the area including the outer valley portion from the press-formed product 101.

During press molding, in the process of forming the outer valley portion, tension is applied to the area that will become the outer curved portion of the curved portion of the press-molded product 101 (curved portion 131o of the outer vertical wall 103o and curved portion 141o of the outer flange 104o) against the pulling force toward the area that will become the top plate 102. In this case, the application of tension applies a tensile stress in the longitudinal direction as a longitudinal component force, and as a result, the longitudinal compressive stress associated with the shrink flange deformation is alleviated. This allows the longitudinal compressive stress to be reduced, and in the lateral direction, the difference between the tensile stress on the outer surface and the compressive stress on the inner surface can be reduced. Furthermore, the outer valley portion is removed during the press molding process. By applying such tension and removing the inner valley, the longitudinal tensile stress caused by springback can be reduced in the outer curved portion of the curved portion of the press-formed product 101 removed from the die (the curved portion 131o of the outer vertical wall 103o and the curved portion 141o of the outer flange 104o), and the difference between the compressive stress on the outer surface and the tensile stress on the inner surface in the short direction can be reduced. As a result, the twisting and wall warping of the press-formed product 101 can be effectively suppressed.

The press device of the first configuration may be combined with a press device of the second configuration. In this case, the press device of the first configuration further includes an outer lower jig. The outer lower jig is arranged adjacent to the outer bottom surface of the lower punch and is fixed to the bed. The outer lower jig has an outer lower blade on the edge of the upper surface of the outer lower jig that is adjacent to the outer bottom surface of the lower punch. The outer lower jig has an outer groove formed on the upper surface so as to follow the curved outer side edge of the curved portion. The upper die further has an outer recess. The outer recess is adjacent to the outer lower surface. The upper die has an outer upper blade on the edge of the outer lower surface that is adjacent to the outer recess. The upper die has an outer protrusion that protrudes beyond the outer lower surface at a position on the bottom surface of the outer recess that faces the outer groove (third configuration).

The press device of the third configuration is a press device that combines the first and second configurations. Therefore, with the press device of the third configuration, both the inner valley portion and the outer valley portion are formed during press molding, and further, both the inner valley portion and the outer valley portion are removed during the press molding process. Therefore, the effects of the press device of the first configuration and the effects of the press device of the second configuration are expressed synergistically, and twisting and wall warping of the press-molded product 101 can be more effectively suppressed.

In the lower punch, the inner side surface may be connected directly to the top surface or may be connected to the top surface via a corner portion. The outer side surface may be connected directly to the top surface or may be connected to the top surface via a corner portion. The inner bottom surface may be connected directly to the inner side surface or may be connected to the inner side surface via a corner portion. The outer bottom surface may be connected directly to the outer side surface or may be connected to the outer side surface via a corner portion.

In the press device of the first or third configuration, it is preferable that the inner ridge protrudes from the inner underside by 5 mm or more (fourth configuration).

If the protruding amount of the inner ridge is 5 mm or more, tension is more effectively applied to the area that becomes the inner curved portion of the curved portion of the press-formed product 101 (the curved portion 131i of the inner vertical wall 103i and the curved portion 141i of the inner flange 104i) during the process of forming the inner valley portion by the inner ridge of the upper die and the inner groove of the inner lower jig. The protruding amount of the inner ridge is more preferably 9 mm or more. There is no particular limit to the upper limit of the protruding amount of the inner ridge. However, if the protruding amount of the inner ridge is 20 mm or more, the effect of suppressing twisting and wall warping becomes saturated. For this reason, the preferred upper limit of the protruding amount of the inner ridge is 20 mm.

In any one of the press devices of the first, third, and fourth configurations, it is preferable that the width of the inner ridge is 0.8 times or more the height of the inner ridge (fifth configuration).

If the width of the inner ridge is 0.8 times or more the height of the inner ridge, the strength of the inner ridge itself can be ensured more sufficiently. In this case, deformation and chipping of the inner ridge can be suppressed. The width of the inner ridge is more preferably 1.2 times or more the height of the inner ridge. There is no particular upper limit to the width of the inner ridge. However, if the width of the inner ridge exceeds 2.0 times the height of the inner ridge, there will be no change in the strength of the inner ridge, and the material yield will actually deteriorate. For this reason, it is preferable that the width of the inner ridge is 2.0 times or less the height of the inner ridge.

In any one of the press devices of the first, third, fourth, and fifth configurations, it is preferable that the inner lower blade is inclined in a longitudinal range corresponding to the curved inner side edge of the curved portion so that the center of the range is lower than both ends of the range (sixth configuration).

The inclination of the inner lower blade is the so-called shear angle. In this case, when the region including the inner valley portion is removed from the press-formed product 101 by the inner upper blade of the upper die and the inner lower blade of the inner lower jig, the curved inner side edge of the curved portion of the press-formed product 101 (the side edge of the curved portion 141i of the inner flange 104i) is not cut simultaneously, but is gradually cut from both ends of the side edge toward the center of the side edge. Therefore, the press load required for cutting can be small. In addition, compressive stress is applied in the longitudinal direction during cutting. Therefore, the longitudinal tensile stress during press forming and at the completion of forming is further alleviated. As a result, the longitudinal tensile stress during press forming and at the completion of forming can be further reduced, and the difference between the tensile stress on the outer surface and the compressive stress on the inner surface in the short direction can be further reduced.

In the press device of the second or third configuration, it is preferable that the outer convex rib protrudes from the outer underside by 5 mm or more (seventh configuration).

If the protruding amount of the outer convex rib is 5 mm or more, tension is more effectively applied to the area that will become the curved outer part of the curved part of the press-formed product 101 (the curved part 131o of the outer vertical wall 103o and the curved part 141o of the outer flange 104o) during the process of forming the outer valley part by the outer convex rib of the upper die and the outer groove of the outer lower jig. The protruding amount of the outer convex rib is more preferably 9 mm or more. There is no particular limit to the upper limit of the protruding amount of the outer convex rib. However, if the protruding amount of the outer convex rib is 20 mm or more, the effect of suppressing twisting and wall warping becomes saturated. For this reason, the preferred upper limit of the protruding amount of the outer convex rib is 20 mm.

In any one of the press devices of the second, third, and seventh configurations, it is preferable that the width of the outer ridge is 0.8 times or more the height of the outer ridge (eighth configuration).

If the width of the outer convex rib is 0.8 times or more the height of the outer convex rib, the strength of the outer convex rib itself can be ensured more sufficiently. In this case, deformation, chipping, etc. of the outer convex rib can be suppressed. The width of the outer convex rib is more preferably 1.2 times or more the height of the outer convex rib. There is no particular upper limit to the width of the outer convex rib. However, if the width of the outer convex rib exceeds 2.0 times the height of the outer convex rib, there will be no change in the strength of the outer convex rib, and instead the material yield will deteriorate. For this reason, it is preferable that the width of the outer convex rib is 2.0 times or less the height of the outer convex rib.

In any one of the press devices of the second, third, seventh, and eighth configurations, it is preferable that the outer lower blade is inclined in a longitudinal range corresponding to the curved outer side edge of the curved portion so that the center of the range is higher than both ends of the range (ninth configuration).

The inclination of the outer lower blade is the so-called shear angle. In this case, when the area including the outer valley portion is removed from the press-formed product 101 by the outer upper blade of the upper die and the outer lower blade of the outer lower jig, the curved outer side edge of the curved portion of the press-formed product 101 (the side edge of the curved portion 141o of the outer flange 104o) is not cut at the same time, but is gradually cut from the center of the side edge toward both ends of the side edge. Therefore, the press load required for cutting can be small. In addition, tensile stress is applied in the longitudinal direction during cutting. Therefore, the longitudinal compressive stress during press forming and at the completion of forming is further alleviated. As a result, the longitudinal compressive stress during press forming and at the completion of forming can be further reduced, and the difference between the tensile stress on the outer surface and the compressive stress on the inner surface in the short direction can be further reduced.

A method for manufacturing a press-molded product according to one embodiment of the present invention is a manufacturing method using a press machine of any one of the first, third, fourth, fifth and sixth configurations. The press-molded product manufactured by this manufacturing method has an elongated top plate, an inner vertical wall, an outer vertical wall, an inner flange and an outer flange. The top plate has a curved portion that curves within a plane. The inner vertical wall is connected to the inner curved side edge of the curved portion of both side edges of the top plate. The outer vertical wall is connected to the outer curved side edge of the curved portion of both side edges of the top plate. The inner flange is connected to the lower edge of the inner vertical wall. The outer flange is connected to the lower edge of the outer vertical wall.

The manufacturing method includes steps (a) to (e). In step (a), a blank made of a metal plate is prepared. The blank has a size that exceeds the installation area of the inner ridge of the upper die. In step (b), the blank is placed on the top surface of the lower punch. In step (c), the slide is lowered to sandwich the blank between the upper pad and the top surface of the lower punch. In step (d), the slide is further lowered to press the blank with the upper die and lower punch, and also press the blank with the inner ridge and inner groove. In step (e), the slide is further lowered to cut the blank with the inner upper blade and inner lower blade (tenth configuration).

In the tenth manufacturing method, the press-formed product 101 is manufactured using the press device of the first configuration. Therefore, according to the tenth manufacturing method, in step (d), the press-formed product 101 is formed by the lower punch, the upper die, and the upper pad, and an excess inner valley portion that does not become the final product is formed further inward of the curved portion of the press-formed product 101 by the inner convex strip of the upper die and the inner groove of the inner lower jig. In the process of forming the inner valley portion, tension is applied to the area that will become the inner part of the curved portion of the press-formed product 101 (the curved portion 131i of the inner vertical wall 103i and the curved portion 141i of the inner flange 104i) against the pulling force toward the area that will become the top plate 102. Furthermore, in step (e), the boundary between the press-formed product 101 and the area including the inner valley portion is cut by the inner upper blade of the upper die and the inner lower blade of the inner lower jig. As a result, the area including the inner valley portion is removed from the press-formed product 101.

Therefore, according to the tenth configuration of the manufacturing method, the compressive stress in the longitudinal direction caused by springback can be reduced in the inner curved portion of the curved portion of the press-formed product 101 removed from the die (the curved portion 131i of the inner vertical wall 103i and the curved portion 141i of the inner flange 104i), and the difference between the compressive stress on the outer surface and the tensile stress on the inner surface in the transverse direction can be reduced. As a result, the torsion and wall warping of the press-formed product 101 can be effectively suppressed.

A manufacturing method for a press-molded product according to another embodiment of the present invention is a manufacturing method using any one of the press devices of the second, third, seventh, eighth, and ninth configurations. The press-molded product manufactured by this manufacturing method has an elongated top plate, an inner vertical wall, an outer vertical wall, an inner flange, and an outer flange. The top plate has a curved portion that curves in-plane. The inner vertical wall is connected to the inner curved side edge of the curved portion of both side edges of the top plate. The outer vertical wall is connected to the outer curved side edge of the curved portion of both side edges of the top plate. The inner flange is connected to the lower edge of the inner vertical wall. The outer flange is connected to the lower edge of the outer vertical wall.

The manufacturing method includes steps (a) to (e). In step (a), a blank made of a metal plate is prepared. The blank has a size that exceeds the installation area of the outer ridge of the upper die. In step (b), the blank is placed on the top surface of the lower punch. In step (c), the slide is lowered to sandwich the blank between the upper pad and the top surface of the lower punch. In step (d), the slide is further lowered to press the blank with the upper die and lower punch, and also to press the blank with the outer ridge and outer groove. In step (e), the slide is further lowered to cut the blank with the outer upper blade and the outer lower blade (eleventh configuration).

In the manufacturing method of the eleventh configuration, the press-formed product 101 is manufactured using the press device of the first configuration. Therefore, according to the manufacturing method of the eleventh configuration, in step (d), the press-formed product 101 is formed by the lower punch, the upper die, and the upper pad, and an excess outer valley portion that does not become the final product is formed further outward of the curved portion of the press-formed product 101 by the outer convex strip of the upper die and the outer groove of the outer lower jig. In the process of forming the outer valley portion, a tension that resists the pulling force toward the region that will become the top plate 102 is applied to the region that will become the curved outer portion of the curved portion of the press-formed product 101 (the curved portion 131o of the outer vertical wall 103o and the curved portion 141o of the outer flange 104o). Furthermore, in step (e), the boundary between the press-formed product 101 and the region including the outer valley portion is cut by the outer upper blade of the upper die and the outer lower blade of the outer lower jig. As a result, the region including the outer valley portion is removed from the press-formed product 101.

Therefore, according to the manufacturing method of the eleventh configuration, the longitudinal tensile stress caused by springback can be reduced in the outer curved portion of the curved portion of the press-formed product 101 removed from the die (the curved portion 131o of the outer vertical wall 103o and the curved portion 141o of the outer flange 104o), and the difference between the compressive stress on the outer surface and the tensile stress on the inner surface in the short direction can be reduced. As a result, the torsion and wall warping of the press-formed product 101 can be effectively suppressed.

The manufacturing method of the tenth configuration may be combined with the manufacturing method of the eleventh configuration. In this case, the manufacturing method is a manufacturing method using a press machine of the third configuration, or any one of the fourth to ninth configurations including the third configuration. The press-molded product manufactured by this manufacturing method has a long and slender top plate, an inner vertical wall, an outer vertical wall, an inner flange, and an outer flange. The top plate has a curved portion that curves within a plane. The inner vertical wall is connected to the inner curved side edge of the curved portion of both side edges of the top plate. The outer vertical wall is connected to the outer curved side edge of the curved portion of both side edges of the top plate. The inner flange is connected to the lower edge of the inner vertical wall. The outer flange is connected to the lower edge of the outer vertical wall.

The manufacturing method includes steps (a) to (e). In step (a), a blank made of a metal plate is prepared. The blank has a size that exceeds the installation area of the inner convex rib of the upper die and exceeds the installation area of the outer convex rib of the upper die. In step (b), the blank is placed on the top surface of the lower punch. In step (c), the slide is lowered to sandwich the blank between the upper pad and the top surface of the lower punch. In step (d), the slide is further lowered to press the blank with the upper die and the lower punch, press the blank with the inner convex rib and the inner groove, and press the blank with the outer convex rib and the outer groove. In step (e), the slide is further lowered to cut the blank with the inner upper blade and the inner lower blade, and cut the blank with the outer upper blade and the outer lower blade (12th configuration).

In the manufacturing method of the 12th configuration, the press-molded product 101 is manufactured using the press device of the third configuration. In other words, the manufacturing method of the 12th configuration is a manufacturing method that combines the 10th and 11th configurations. Therefore, according to the manufacturing method of the 12th configuration, the effects of the manufacturing method of the 10th configuration and the manufacturing method of the 11th configuration are expressed synergistically, and twisting and wall warping of the press-molded product 101 can be more effectively suppressed.

In the manufacturing method of the tenth or twelfth configuration, it is preferable that in the blank prepared in step (a), a first region corresponding to at least the longitudinal center of the installation area of the inner ridge of the upper die extends beyond the installation area of the inner ridge, and the regions on the outside from both ends of the first region are cut out (thirteenth configuration).

In this case, no inner valley is formed in the notch region adjacent to the first region in the blank. In other words, the notch region does not provide tension. As a result, the direction of the tension applied during the forming process of the inner valley is tilted from the short direction. The longitudinal component of the tension tilted from the short direction becomes larger and is applied as a longitudinal compressive stress. As a result, the longitudinal tensile stress during press forming associated with stretch flange deformation is further alleviated.

In the manufacturing method of the 11th or 12th configuration, it is preferable that in the blank prepared in step (a), the second regions corresponding to at least both longitudinal ends of the installation area of the outer ridge of the upper die extend beyond the installation area of the outer ridge, and the regions on the inside between the second regions are cut out (14th configuration).

In this case, no outer valley is formed in the notch region adjacent to the second region in the blank. In other words, the notch region does not provide tension. As a result, the direction of tension applied during the forming process of the outer valley is tilted from the short direction. The longitudinal component of the tension tilted from the short direction becomes larger and is applied as longitudinal tensile stress. As a result, the longitudinal compressive stress during press forming associated with shrink flange deformation is further alleviated.

The manufacturing method of the 14th configuration may be combined with the manufacturing method of the 13th configuration. In this case, the manufacturing method is similar to the manufacturing method of the 12th configuration. Specifically, in the blank prepared in step (a), a first region corresponding to at least the longitudinal center of the installation area of the inner ridge of the upper die extends beyond the installation area of the inner ridge, and the regions on the outside from both ends of the first region are cut out. Furthermore, in the blank prepared in step (a), a second region corresponding to at least both longitudinal ends of the installation area of the outer ridge of the upper die extends beyond the installation area of the outer ridge, and the regions on the inside between the second regions are cut out (15th configuration).

The manufacturing method of the 15th configuration is a combination of the 13th and 14th configurations. Therefore, according to the manufacturing method of the 15th configuration, the effects of the manufacturing method of the 13th configuration and the manufacturing method of the 14th configuration are synergistically realized, and twisting and wall warping of the press-molded product 101 can be more effectively suppressed.

Below, specific examples of the press device and the method for manufacturing press-molded products according to this embodiment will be described with reference to the drawings. The same or corresponding parts in the drawings will be given the same reference numerals and their description will not be repeated.

[First embodiment]
[Configuration of the Pressing Device]
Fig. 6 is a cross-sectional view showing an example of the press apparatus 1 of the first embodiment. Fig. 7 is a perspective view of a die set provided in the press apparatus shown in Fig. 6. The press apparatus 1 shown in Figs. 6 and 7 is used to manufacture the press-formed product 101 shown in Figs. 1A and 1B. Fig. 6 shows a cross-section at a position where a curved portion of the press-formed product 101 is formed. The right side of Fig. 6 corresponds to the curved inner side of the curved portion of the press-formed product 101, and the left side of Fig. 6 corresponds to the curved outer side of the curved portion of the press-formed product 101.

Referring to Figures 6, 7, 1A and 1B, the press device 1 of the first embodiment includes a bed 2, a slide 3, a lower punch 4, a lower cushion 5, an inner lower jig 6i, an outer lower jig 6o, an upper pad 7 and an upper die 8. The slide 3 is disposed above the fixed bed 2. The slide 3 is capable of ascending and descending relative to the bed 2. The lower punch 4, the inner lower jig 6i and the outer lower jig 6o constitute a lower die set for press molding, and the upper pad 7 and the upper die 8 constitute an upper die set for press molding.

In the press device 1 shown in Figures 6 and 7, a lower die holder 10 is fixed to the upper surface of the bed 2, and an upper die holder 11 is fixed to the lower surface of the slide 3. The lower die set is held by the lower die holder 10. The upper die set is held by the upper die holder 11.

[Lower die set]
The lower punch 4 has a top surface 41, an inner side surface 42i, an outer side surface 42o, an inner bottom surface 43i, and an outer bottom surface 43o. The top surface 41 is elongated and flat, and has a curved portion. The curved portion of the top surface 41 is a portion that curves within the flat surface of the top surface 41. The top surface 41 does not have to be a strictly flat surface. In other words, the top surface 41 may have some unevenness. The shape of the top surface 41 reflects the shape of the top plate 102 of the press-molded product 101. For example, when the top plate 102 of the press-molded product 101 is composed of a curved portion 121 and straight portions 122 connected to both ends of the curved portion 121, the top surface 41 includes the curved portion and straight portions connected to both ends of the curved portion.

The inner side surface 42i is connected to the curved inner side edge of the curved portion of both side edges of the top surface 41. The shape of the inner side surface 42i reflects the shape of the inner vertical wall 103i of the press-formed product 101. The outer side surface 42o is connected to the curved outer side edge of the curved portion of both side edges of the top surface 41. The shape of the outer side surface 42o reflects the shape of the outer vertical wall 103o of the press-formed product 101. For example, when the inner vertical wall 103i of the press-formed product 101 is composed of a curved portion 131i and straight portions 132i connected to both ends of the curved portion 131i, the inner side surface 42i includes a curved portion and straight portions connected to both ends of the curved portion. When the outer vertical wall 103o of the press-formed product 101 is composed of a curved portion 131o and straight portions 132o connected to both ends of the curved portion 131o, the outer side surface 42o includes a curved portion and straight portions connected to both ends of the curved portion.

The inner bottom surface 43i is connected to the lower edge of the inner side surface 42i. The shape of the inner bottom surface 43i reflects the shape of the inner flange 104i of the press-formed product 101. The outer bottom surface 43o is connected to the lower edge of the outer side surface 42o. The shape of the outer bottom surface 43o reflects the shape of the outer flange 104o of the press-formed product 101. For example, when the inner flange 104i of the press-formed product 101 is composed of a curved portion 141i and straight portions 142i connected to both ends of the curved portion 141i, the inner bottom surface 43i includes the curved portion and straight portions connected to both ends of the curved portion. When the outer flange 104o of the press-formed product 101 is composed of a curved portion 141o and straight portions 142o connected to both ends of the curved portion 141o, the outer bottom surface 43o includes the curved portion and straight portions connected to both ends of the curved portion.

The lower cushion 5 supports the lower punch 4 via the cushion pin 51. The lower cushion 5 is fixed to the bed 2. The lower cushion 5 is, for example, a hydraulic cylinder. The lower cushion 5 supports the lower punch 4 in a floating state under a high load. If a load greater than that applied to the lower punch 4 by the lower cushion 5 is applied from above to the lower punch 4, the lower punch 4 can move downward.

The inner lower jig 6i is arranged adjacent to the inner bottom surface 43i of the lower punch 4. The inner lower jig 6i is fixed to the bed 2. In the press device 1 shown in Figures 6 and 7, the inner lower jig 6i is fixed to the lower die holder 10. The inner lower jig 6i has an inner lower blade 61i on its edge adjacent to the inner bottom surface 43i of the lower punch 4.

The inner lower jig 6i has an inner groove 62i on its upper surface. The inner groove 62i is formed so as to follow the inner side edge of the curved portion of the top surface 41. From another perspective, the inner groove 62i is formed parallel to the inner side edge of the curved portion of the top surface 41. Parallel here does not only mean completely parallel, but also allows a slight deviation from completely parallel. In other words, the inner groove 62i is curved in a plan view like the curved portion of the top surface 41. When the top surface 41 includes a curved portion and straight portions connected to both ends of this curved portion, the inner groove 62i extends to a region corresponding to the straight portions of the top surface 41. The cross-sectional shape of the inner groove 62i is a trapezoid. The trapezoid here means a trapezoid that does not form a negative angle when the inner groove 62i is press-molded. In other words, when the inner groove 62i is viewed in cross section, the width of the upper side is wider than the width of the bottom side. However, the cross-sectional shape of the inner groove 62i is not limited to a trapezoid, and may be a rectangle, a semicircle, or the like. In addition, to prevent cracking, appropriate fillet R may be provided at each corner of the trapezoid, rectangle, and semicircle. Furthermore, the depth of the inner groove 62i must be such that it does not interfere with the inner ridge 85i at the bottom dead center of the press. In a typical example, the depth of the inner groove 62i is greater than the height of the inner ridge 85i.

The height position of the upper surface of the inner lower jig 6i coincides with the initial height position of the inner bottom surface 43i of the lower punch 4. However, the height position of the upper surface of the inner lower jig 6i may be slightly lower than the initial height position of the inner bottom surface 43i of the lower punch 4.

The outer lower jig 6o is positioned adjacent to the outer bottom surface 43o of the lower punch 4. The outer lower jig 6o is fixed to the bed 2. In the press device 1 shown in Figures 6 and 7, the outer lower jig 6o is fixed to the lower die holder 10. The outer lower jig 6o has an outer lower blade 61o on its edge adjacent to the outer bottom surface 43o of the lower punch 4.

The outer lower jig 6o has an outer groove 62o on its upper surface. The outer groove 62o is formed so as to follow the curved outer side edge of the curved portion of the top surface 41. From another perspective, the outer groove 62o is formed parallel to the curved outer side edge of the curved portion of the top surface 41. Parallel here does not only mean completely parallel, but also allows for a slight deviation from completely parallel. In other words, the outer groove 62o is curved in a plan view like the curved portion of the top surface 41. When the top surface 41 includes a curved portion and straight portions connected to both ends of this curved portion, the outer groove 62o extends to a region corresponding to the straight portions of the top surface 41. The cross-sectional shape of the outer groove 62o is a trapezoid. The trapezoid here means a trapezoid that does not form a negative angle when the outer groove 62o is press-molded. In other words, when the outer groove 62o is viewed in cross section, the width of the upper side is wider than the width of the bottom side. However, the cross-sectional shape of the outer groove 62o is not limited to a trapezoid, and may be rectangular, semicircular, or the like. In addition, appropriate fillet R may be provided at each corner of the trapezoid, rectangle, and semicircle to prevent cracking. Furthermore, the depth of the outer groove 62o must be such that it does not interfere with the outer protrusion 85o at the bottom dead center of the press. In a typical example, the depth of the outer groove 62o is greater than the height of the outer protrusion 85o.

The height position of the upper surface of the outer lower jig 6o coincides with the initial height position of the outer bottom surface 43o of the lower punch 4. However, the height position of the upper surface of the outer lower jig 6o may be slightly lower than the initial height position of the outer bottom surface 43o of the lower punch 4.

In the press device 1 shown in Figures 6 and 7, a bottoming member is provided between the lower punch 4 and the lower die holder 10. The bottoming member is composed of a bottomed upper plate 12 attached to the underside of the lower punch 4 and a bottomed lower plate 13 attached to the upper surface of the lower die holder 10. The bottomed upper plate 12 faces the bottomed lower plate 13. The lower surface of the bottomed upper plate 12 comes into contact with the upper surface of the bottomed lower plate 13, thereby restricting the descent of the lower punch 4.

[Upper set]
The upper pad 7 is disposed so as to face the top surface 41 of the lower punch 4. The shape of the lower surface of the upper pad 7 reflects the shape of the top plate 102 of the press-molded product 101. The upper pad 7 is supported by the slide 3 via an elastic member 71. In the press device 1 shown in Fig. 6 and Fig. 7, the elastic member 71 is fixed to the upper die holder 11.

The elastic member 71 is, for example, a spring and a gas cylinder. When a load is applied to the upper pad 7 from below, the elastic member 71 contracts, allowing the upper pad 7 to move upward relative to the upper die 8. In order for the blank 201 to be cut by the inner upper blade 84i and the inner lower blade 61i, or the outer upper blade 84o and the outer lower blade 61o after the blank 201 is clamped between the lower punch 4 and the upper die 8 and the inner vertical wall 103i, the outer vertical wall 103o, the inner bottom surface 43i, and the outer bottom surface 43o are formed, the lower punch 4 must not move downward due to the load of only the upper pad 7 via the elastic member 71. To achieve this, the upper pad 7 needs to be supported by the elastic member 71 with a load smaller than that of the lower cushion 5.

The upper die 8 is fixed to the slide 3. In the press device 1 shown in Figures 6 and 7, the upper die 8 is fixed to the upper die holder 11. The upper die 8 has an inner wall surface 81i, an outer wall surface 81o, an inner lower surface 82i, an outer lower surface 82o, an inner recess 83i, and an outer recess 83o.

The inner wall surface 81i corresponds to the inner side surface 42i of the lower punch 4. The shape of the inner wall surface 81i reflects the shape of the inner vertical wall 103i of the press-formed product 101. The outer wall surface 81o corresponds to the outer side surface 42o of the lower punch 4. The shape of the outer bottom surface 43o reflects the shape of the outer vertical wall 103o of the press-formed product 101.

The inner lower surface 82i faces the inner bottom surface 43i of the lower punch 4. The shape of the inner lower surface 82i reflects the shape of the inner flange 104i of the press-formed product 101. The outer lower surface 82o faces the outer bottom surface 43o of the lower punch 4. The shape of the outer lower surface 82o reflects the shape of the outer flange 104o of the press-formed product 101.

The inner recess 83i is adjacent to the inner lower surface 82i. The inner recess 83i is disposed above the inner lower jig 6i. The outer recess 83o is adjacent to the outer lower surface 82o. The outer recess 83o is disposed above the outer lower jig 6o.

The boundary between the inner wall surface 81i and the inner lower surface 82i is the inner die shoulder 86i. The boundary between the outer wall surface 81o and the outer lower surface 82o is the outer die shoulder 86o.

The upper die 8 also has an inner upper blade 84i on the edge of the inner lower surface 82i adjacent to the inner recess 83i. The inner upper blade 84i pairs with the inner lower blade 61i of the inner lower jig 6i.

Furthermore, the upper die 8 has an inner convex streak 85i at a position of the inner recess 83i facing the inner groove 62i. The inner convex streak 85i protrudes from the inner lower surface 82i. In other words, the inner convex streak 85i protrudes downward. The inner convex streak 85i pairs with the inner groove 62i of the inner lower jig 6i. For this reason, the inner convex streak 85i is curved in a plan view, similar to the inner groove 62i. When the top surface 41 includes a curved portion and straight portions connected to both ends of the curved portion, the inner convex streak 85i extends to a region corresponding to the straight portion of the top surface 41. The cross-sectional shape of the inner convex streak 85i is a trapezoid corresponding to the cross-sectional shape of the inner groove 62i. However, the cross-sectional shape of the inner convex streak 85i may be a rectangle, a semicircle, or the like, as long as it corresponds to the cross-sectional shape of the inner groove 62i. In addition, in order to prevent cracking, appropriate fillets R may be taken at each corner of the trapezoid, rectangle, and semicircle.

It is preferable that the initial height position of the lower surface of the inner convex 85i is the same as the initial height position of the lower surface of the upper pad 7 or higher than the initial height position of the lower surface of the upper pad 7. This is to prevent the inner convex 85i from contacting the blank 201 before the top surface 41 is pressed by the upper pad 7. If the inner convex 85i contacts the blank 201 before the top surface 41 is pressed by the upper pad 7, the blank 201 moves in the product width direction, making it difficult to obtain a product of the specified dimensions. In addition, if the initial height position of the lower surface of the inner convex 85i is too high compared to the initial height position of the lower surface of the upper pad 7, the elastic member 71 connected to the upper pad 7 must be made longer, which increases the cost of the mold. For this reason, it is preferable that the initial height position of the lower surface of the inner convex 85i is a position that is up to 20 mm higher than the initial height position of the lower surface of the upper pad 7. However, the initial height position of the lower surface of the upper pad 7 is lower than the initial height position of the inner lower surface 82i of the upper die 8.

In addition, the upper die 8 has an outer upper blade 84o on the edge of the outer lower surface 82o adjacent to the outer recess 83o. The outer upper blade 84o pairs with the outer lower blade 61o of the outer lower jig 6o.

Furthermore, the upper die 8 has an outer convex streak 85o at a position of the outer recess 83o facing the outer groove 62o. The outer convex streak 85o protrudes from the outer lower surface 82o. In other words, the outer convex streak 85o protrudes downward. The outer convex streak 85o pairs with the outer groove 62o of the outer lower jig 6o. For this reason, the outer convex streak 85o is curved in a plan view, similar to the outer groove 62o. When the top surface 41 includes a curved portion and straight portions connected to both ends of the curved portion, the outer convex streak 85o extends to a region corresponding to the straight portion of the top surface 41. The cross-sectional shape of the outer convex streak 85o is a trapezoid corresponding to the cross-sectional shape of the outer groove 62o. However, the cross-sectional shape of the outer convex streak 85o may be a rectangle, a semicircle, or the like, as long as it corresponds to the cross-sectional shape of the outer groove 62o. In addition, in order to prevent cracking, appropriate fillets R may be taken at each corner of the trapezoid, rectangle, and semicircle.

It is preferable that the initial height position of the lower surface of the outer convex streak 85o is the same as the initial height position of the lower surface of the upper pad 7 or higher than the initial height position of the lower surface of the upper pad 7. This is to prevent the outer convex streak 85o from contacting the blank 201 before the top surface 41 is pressed by the upper pad 7. If the outer convex streak 85o contacts the blank 201 before the top surface 41 is pressed by the upper pad 7, the blank 201 moves in the product width direction, making it difficult to obtain a product of the specified dimensions. In addition, if the initial height position of the lower surface of the outer convex streak 85o is too high compared to the initial height position of the lower surface of the upper pad 7, the elastic member 71 connected to the upper pad 7 must be made longer, which increases the cost of the mold. For this reason, it is preferable that the initial height position of the lower surface of the outer convex streak 85o is a position that is up to 20 mm higher than the initial height position of the lower surface of the upper pad 7. However, the initial height position of the lower surface of the upper pad 7 is lower than the initial height position of the outer lower surface 82o of the upper die 8.

[Method of manufacturing press-molded product 101]
The method for manufacturing the press-formed product 101 according to this embodiment is a method for manufacturing the press-formed product 101 shown in Figures 1A and 1B using the press apparatus 1 shown in Figures 6 and 7. The method for manufacturing the press-formed product 101 according to this embodiment includes steps (a) to (e). Each step will be described below with reference to Figures 8A to 8F, 9, and 10.

Figures 8A to 8F are diagrams for explaining a method for manufacturing a press-formed product 101 using the press apparatus 1 of the first embodiment. The manufacturing steps proceed in the order shown in Figures 8A to 8F. Figures 8A to 8F show a cross section of the press-formed product 101 at the position where the curved portion is formed.

Figure 9 is a plan view showing a blank 201 applied to a manufacturing method of a press-molded product 101 using the press device 1 of the first embodiment. In Figure 9, the blank 201 is shown by a solid line, and the press-molded product 101 molded from this blank 201 is shown by a two-dot chain line. In Figure 9, both side edges (side edge 106i of the inner flange 104i and side edge 106o of the outer flange 104o) when the press-molded product 101 to be molded is developed on the same plane are shown by imaginary lines (thin two-dot chain lines in Figure 9 that are not numbered). In Figure 9, the installation areas of the inner groove 62i and inner ridge 85i of the press device 1, and the installation areas of the outer groove 62o and outer ridge 85o are shown by dotted lines.

Figure 10 is a plan view for explaining the situation when the press-formed product 101 is formed by the manufacturing method using the press device 1 of the first embodiment. In Figure 10, the blank 201 is shown by a solid line, and the press-formed product 101 formed from this blank 201 is shown by a two-dot chain line. Also, in Figure 10, the tension applied to the areas that will become the inner vertical wall 103i, the inner flange 104i, the outer vertical wall 103o, and the outer flange 104o of the press-formed product 101 is shown by dotted arrows, and the longitudinal stress (component force) applied to each area by the application of this tension is shown by solid arrows.

[Step (a)]
8A and 9, first, in step (a), a blank 201 made of a metal plate is prepared. The blank 201 has a high strength (tensile strength) of, for example, 590 MPa or more. The plate thickness of the blank 201 is about 0.8 to 2.3 mm. The metal plate used for the blank 201 is, for example, a steel plate. The blank 201 having a predetermined shape is obtained by subjecting the metal plate to punching, cutting, machining, laser trimming, electric discharge machining, and the like.

As described above, in the press device 1 of this embodiment, the inner groove 62i and the inner ridge 85i are provided in the region further inward of the curved portion of the press-formed product 101. Furthermore, the inner groove 62i and the inner ridge 85i are also provided in the region further inward of the curved straight portions that connect to both ends of the curved portion of the press-formed product 101. In other words, the inner groove 62i and the inner ridge 85i are provided throughout the entire longitudinal area of the press-formed product 101.

In addition, in the press device 1 of this embodiment, as described above, the outer groove 62o and the outer ridge 85o are provided in a region further outward of the curved portion of the press-formed product 101. Furthermore, the outer groove 62o and the outer ridge 85o are also provided in a region further outward of the curved straight portions that connect to both ends of the curved portion of the press-formed product 101. In other words, the outer groove 62o and the outer ridge 85o are provided throughout the entire longitudinal area of the press-formed product 101.

The blank 201 has a size that exceeds the area where the inner ridge 85i (inner groove 62i) is arranged (the installation area of the inner ridge 85i), and also exceeds the area where the outer ridge 85o (outer groove 62o) is arranged (the installation area of the outer ridge 85o). In other words, the inner edge 203i of the blank 201 exceeds the installation area of the inner ridge 85i (inner groove 62i). The outer edge 203o of the blank 201 exceeds the installation area of the outer ridge 85o (outer groove 62o).

From another perspective, the width of the blank 201 is greater than the width of the press-formed product 101 when it is developed on the same plane. That is, an inner margin 202i is provided on the inside of the curve of the blank 201. An outer margin 202o is provided on the outside of the curve of the blank 201. In the blank 201, the inner edge 203i of the inner margin 202i exceeds the position of the side edge 106i of the inner flange 104i when the press-formed product 101 is developed on the same plane, and further exceeds the installation area of the inner ridge 85i (inner groove 62i). Also, in the blank 201, the outer edge 203o of the outer margin 202o exceeds the position of the side edge 106o of the outer flange 104o when the press-formed product 101 is developed on the same plane, and further exceeds the installation area of the outer ridge 85o (outer groove 62o).

The installation area of the inner convex rib 85i referred to here means the installation area of the inner convex rib 85i when each forming surface of the upper die 8 is developed into a plane. In other words, the installation area of the inner groove 62i means the installation area of the inner groove 62i when each forming surface of the lower punch 4 and the inner lower jig 6i is developed into a plane. Also, the installation area of the outer convex rib 85o referred to here means the installation area of the outer convex rib 85o when each forming surface of the upper die 8 is developed into a plane. In other words, the installation area of the outer groove 62o means the installation area of the outer groove 62o when each forming surface of the lower punch 4 and the outer lower jig 6o is developed into a plane.

[Steps (b) and (c)]
In step (b), referring to Fig. 8A, the blank 201 is placed on the top surface 41 of the lower punch 4. Then, in step (c), the press device 1 is operated. That is, the slide 3 is lowered. The upper pad 7 and the upper die 8 are lowered by the lowering of the slide 3. As a result, the blank 201 is first sandwiched between the lower surface of the upper pad 7 and the top surface 41 of the lower punch 4. That is, the upper pad 7 presses the region of the blank 201 that will become the top plate 102 (the curved portion 121 and the straight portion 122).

[Step (d)]
In step (d), the slide 3 is further lowered. As a result, the blank 201 is pressed by the upper die 8 and the lower punch 4, and the blank 201 is pressed by the inner convex rib 85i and the inner groove 62i, and the blank 201 is pressed by the outer convex rib 85o and the outer groove 62o. During step (d), the lower punch 4 hardly moves downward and is supported by the lower cushion 5 via the cushion pin 51. The area sandwiched between the lower punch 4 and the upper die 8 is formed with a force equal to or less than the load set by the lower cushion 5.

Specifically, referring to FIG. 8B, the upper die 8 is lowered by the descent of the slide 3. At that time, the upper pad 7 continues to press the blank 201, while the elastic member 71 supporting the upper pad 7 is contracted. As the upper die 8 is lowered, the inner die shoulder 86i of the upper die 8 comes into contact with the region that will become the inner vertical wall 103i (curved portion 131i and straight portion 132i) of the blank 201, and the inner vertical wall 103i of the press-formed product 101 is gradually formed by this inner die shoulder 86i and the inner side surface 42i of the lower punch 4. At the same time, the outer die shoulder 86o of the upper die 8 comes into contact with the region that will become the outer vertical wall 103o (curved portion 131o and straight portion 132o) of the blank 201, and the outer vertical wall 103o of the press-formed product 101 is gradually formed by this outer die shoulder 86o and the outer side surface 42o of the lower punch 4.

At this time, as shown in FIG. 8C, as the forming of the inner vertical wall 103i and the outer vertical wall 103o begins, the inner ridge 85i of the upper die 8 comes into contact with the blank 201, and the inner valley portion 105i is gradually formed by this inner ridge 85i and the inner groove 62i of the inner lower jig 6i. At the same time, the outer ridge 85o of the upper die 8 comes into contact with the blank 201, and the outer valley portion 105o is gradually formed by this outer ridge 85o and the outer groove 62o of the outer lower jig 6o.

When the forming of the inner valley portion 105i and the outer valley portion 105o starts, tension is generated in the region of the blank 201 between the inner die shoulder 86i and the inner ridge 85i (see the dotted arrows in Figs. 8C and 10). That is, tension against the pulling force toward the region that will become the top plate 102 is applied to the region of the blank 201 that will become the inner vertical wall 103i (curved portion 131i and straight portion 132i) and the inner flange 104i (curved portion 141i and straight portion 142i). At the same time, tension in the short direction is generated in the region of the blank 201 between the outer die shoulder 86o and the outer ridge 85o (see the dotted arrows in Figs. 8C and 10). In other words, in the blank 201, tension is applied to the areas that will become the outer vertical wall 103o (curved portion 131o and straight portion 132o) and the outer flange 104o (curved portion 141o and straight portion 142o) against the pulling force toward the area that will become the top plate 102.

In this case, referring to FIG. 10, in the area that undergoes stretch flange deformation, i.e., the inner curved portion of the curved portion of the press-formed product 101 (the curved portion 131i of the inner vertical wall 103i and the curved portion 141i of the inner flange 104i), compressive stress is applied in the longitudinal direction as a component force in the longitudinal direction due to the application of tension (see the solid arrow in FIG. 10).

In this case, referring to FIG. 10, in the area where the shrink flange deforms, i.e., the outer curved portion of the curved portion of the press-formed product 101 (the curved portion 131o of the outer vertical wall 103o and the curved portion 141o of the outer flange 104o), a tensile stress is applied in the longitudinal direction as a component force in the longitudinal direction by applying tension (see the solid arrow in FIG. 10).

Then, as shown in FIG. 8D, the press-formed product 101 is formed by the respective surfaces of the lower punch 4 (inner side surface 42i, outer side surface 42o, inner bottom surface 43i, and outer bottom surface 43o) and the respective surfaces of the upper die 8 (inner wall surface 81i, outer wall surface 81o, inner bottom surface 82i, and outer bottom surface 82o).

In this case, as described above, the inner curved portion of the curved portion of the press-formed product 101 formed by stretch flange deformation (the curved portion 131i of the inner vertical wall 103i and the curved portion 141i of the inner flange 104i) is subjected to compressive stress in the longitudinal direction due to the application of tension during the forming process, and the tensile stress in the longitudinal direction during press forming due to stretch flange deformation is alleviated. This allows the tensile stress in the longitudinal direction to be reduced, and in the transverse direction, the difference between the tensile stress on the outer surface and the compressive stress on the inner surface can be reduced.

In this case, as described above, the outer curved portion of the curved portion of the press-formed product 101 formed by shrink flange deformation (the curved portion 131o of the outer vertical wall 103o and the curved portion 141o of the outer flange 104o) is subjected to longitudinal tensile stress due to the application of tension during the forming process, and the longitudinal compressive stress during press forming due to shrink flange deformation is alleviated. This makes it possible to reduce the longitudinal compressive stress, and in the short direction, the difference between the tensile stress on the outer surface and the compressive stress on the inner surface can be reduced.

[Step (e)]
In step (e), the slide 3 is further lowered. As a result, the blank 201 is cut by the inner upper blade 84i and the inner lower blade 61i, and the blank 201 is cut by the outer upper blade 84o and the outer lower blade 61o.

Specifically, referring to FIG. 8E, the upper die 8 descends as the slide 3 descends. Accordingly, the lower punch 4 supported by the lower cushion 5 descends. At that time, the press-formed product 101 descends together with the upper die 8 and the lower punch 4 while remaining contained between them.

Then, as shown in FIG. 8F, the boundary between the press-formed product 101 and the area including the inner valley portion 105i is cut by the inner upper blade 84i of the upper die 8 and the inner lower blade 61i of the inner lower jig 6i. This boundary is the curved inner side edge of the press-formed product 101, i.e., the side edge 106i of the inner flange 104i. As a result, the area including the inner valley portion 105i is removed from the press-formed product 101. At the same time, the boundary between the press-formed product 101 and the area including the outer valley portion 105o is cut by the outer upper blade 84o of the upper die 8 and the outer lower blade 61o of the outer lower jig 6o. This boundary is the curved outer side edge of the press-formed product 101, i.e., the side edge 106o of the outer flange 104o. As a result, the area including the outer valley portion 105o is removed from the press-formed product 101.

As shown in FIG. 8F, the bottomed upper plate 12 contacts the bottomed lower plate 13, limiting the descent of the lower punch 4. In other words, the bottom dead point of the lower punch 4 occurs when the bottomed upper plate 12 contacts the bottomed lower plate 13. Until the bottomed upper plate 12 contacts the bottomed lower plate 13, the press-formed product 101 in the area sandwiched between the lower punch 4 and the upper die 8 is formed at or below the cushion load set by the lower cushion 5. When the bottomed upper plate 12 contacts the bottomed lower plate 13, the press-formed product 101 can be pressed at the press load set by the press machine. In general, the cushion load is lower than the press load, and the upper die 8 can be slightly lowered after the lower punch 4 reaches the bottom dead point due to the difference between the cushion load and the press load. In other words, the bottom dead point of the upper die 8 is slightly delayed from the bottom dead point of the lower punch 4. The slight descent of the upper die 8 presses the press-formed product 101 powerfully, and the shape of the press-formed product 101 becomes a precise product shape.

According to the manufacturing method of the press-formed product 101 of this embodiment, as described above, the longitudinal tensile stress during press forming can be reduced in the inner curved portion of the curved portion of the press-formed product 101 formed by stretch flange deformation (the curved portion 131i of the inner vertical wall 103i and the curved portion 141i of the inner flange 104i), and the difference between the tensile stress of the outer surface and the compressive stress of the inner surface can be reduced in the lateral direction. Therefore, in the inner curved portion of the curved portion of the press-formed product 101 removed from the mold, the longitudinal compressive stress due to springback can be reduced, and the difference between the compressive stress of the outer surface and the tensile stress of the inner surface can be reduced in the lateral direction. As a result, the torsion and wall warping of the press-formed product 101 can be effectively suppressed.

In addition, according to the manufacturing method of the press-formed product 101 of this embodiment, as described above, the compressive stress in the longitudinal direction during press forming can be reduced for the curved outer portion of the curved portion of the press-formed product 101 formed by shrink flange deformation (the curved portion 131o of the outer vertical wall 103o and the curved portion 141o of the outer flange 104o), and the difference between the tensile stress of the outer surface and the compressive stress of the inner surface in the lateral direction can be reduced. Therefore, in the curved outer portion of the curved portion of the press-formed product 101 removed from the mold, the tensile stress in the longitudinal direction due to springback can be reduced, and the difference between the compressive stress of the outer surface and the tensile stress of the inner surface in the lateral direction can be reduced. As a result, the torsion and wall warping of the press-formed product 101 can be effectively suppressed.

In particular, according to the manufacturing method of the press-formed product 101 of this embodiment, the longitudinal stress can be reduced in both the inner curved portion and the outer curved portion of the curved portion of the press-formed product 101. Therefore, twisting and wall warping of the press-formed product 101 can be more effectively suppressed.

In addition, when the boundary between the press-formed product 101 and the region including the inner valley portion 105i is cut by the inner upper blade 84i and the inner lower blade 61i in step (e), the formation of the inner valley portion 105i by the inner convex ridge 85i of the upper die 8 and the inner groove 62i of the inner lower jig 6i continues. This is because the upper die 8 is lowered relative to the inner lower jig 6i. For this reason, the application of tension also continues. In a state in which tension is applied, the press-formed product 101 easily breaks when the inner upper blade 84i and the inner lower blade 61i slightly bite into it. This makes cutting easy. In general, the amount of work hardening on the cut end surface is smaller and the end surface properties are better when the lower blade or upper blade easily breaks after biting into the press-formed product, rather than when it does not break easily. Therefore, when the curved inner side edge (side edge 106i of the inner flange 104i) of the press-formed product 101 is cut, the quality of the side edge is good. Also, because it breaks easily, there is little damage to the inner upper blade 84i and the inner lower blade 61i.

From a similar viewpoint, when the boundary between the press-formed product 101 and the region including the outer valley portion 105o is cut by the outer upper blade 84o and the outer lower blade 61o in step (e), the outer valley portion 105o continues to be formed by the outer convex ridge 85o of the upper die 8 and the outer groove 62o of the outer lower jig 6o. This is because the upper die 8 is lowered relative to the outer lower jig 6o. For this reason, the application of tension also continues. In a state in which tension is applied, if the outer upper blade 84o and the outer lower blade 61o slightly bite into the press-formed product 101, it easily breaks. Then, cutting can be easily performed. Therefore, when the curved outer side edge (side edge 106o of the outer flange 104o) of the press-formed product 101 is cut, the quality of the side edge becomes good. In addition, since it breaks easily, there is little damage to each of the outer upper blade 84o and the outer lower blade 61o.

[Second embodiment]
11 and 12, a press apparatus 1 and a method for manufacturing a press-formed product 101 according to the second embodiment will be described below. The second embodiment is a modification of the first embodiment described above.

Figure 11 is a cross-sectional view showing an example of the press device 1 of the second embodiment. The press device 1 shown in Figure 11 is used to manufacture the press-formed product 101 shown in Figures 1A and 1B. Figure 11 shows a cross-section at a position where the curved portion of the press-formed product 101 is formed. The right side of Figure 11 corresponds to the inner curve of the curved portion of the press-formed product 101, and the left side of Figure 6 corresponds to the outer curve of the curved portion of the press-formed product 101.

Figure 12 is a plan view showing a blank 201 applied to a manufacturing method of a press-formed product 101 using the press device 1 of the second embodiment. In Figure 12, the blank 201 is shown in a solid line, and the press-formed product 101 formed from this blank 201 is shown in a two-dot chain line. In Figure 12, both side edges (side edge 106i of inner flange 104i and side edge 106o of outer flange 104o) when the press-formed product 101 to be formed is developed on the same plane are shown in imaginary lines (thin two-dot chain lines without symbols in Figure 12). Also, in Figure 12, the installation areas of the inner groove 62i and inner ridge 85i of the press device 1 are shown in dotted lines.

Referring to FIG. 11, the press device 1 of this embodiment includes a bed 2, a slide 3, a lower punch 4, a lower cushion 5, an inner lower jig 6i, an upper pad 7, and an upper die 8. In other words, the press device 1 of this embodiment does not include an outer lower jig 6o. Therefore, there is no outer lower blade 61o and outer groove 62o as in the first embodiment. Furthermore, there is no outer recess 83o, outer recess 83o, or outer protrusion 85o as in the first embodiment in the upper die 8 of this embodiment. The other configurations are the same as those of the press device 1 of the first embodiment.

The method for manufacturing the press-formed product 101 according to this embodiment is a method for manufacturing the press-formed product 101 shown in FIGS. 1A and 1B using the press device 1 shown in FIG. 11. The method for manufacturing the press-formed product 101 according to this embodiment includes steps (a) to (e) similar to the first embodiment.

Referring to FIG. 12, the blank 201 prepared in step (a) has a size that exceeds the installation area of the inner ridge 85i (inner groove 62i) as in the first embodiment. From another perspective, an inner margin 202i is provided on the inside of the curve of the blank 201. That is, as in the first embodiment, the inner edge 203i of the blank 201 exceeds the position of the side edge 106i of the inner flange 104i when the press-molded product 101 is developed on the same plane, and further exceeds the installation area of the inner ridge 85i (inner groove 62i). In contrast, an outer margin 202o is not provided on the outside of the curve of the blank 201. That is, the outer edge 203o of the blank 201 corresponds to the side edge 106o of the outer flange 104o when the press-molded product 101 is developed on the same plane.

In this case, in step (d), the blank 201 is press-formed by the upper die 8 and the lower punch 4, as in the first embodiment, and the blank 201 is press-formed by the inner convex rib 85i and the inner groove 62i. Then, in step (e), the blank 201 is cut by the inner upper blade 84i and the inner lower blade 61i, as in the first embodiment. Therefore, the part that is stretch-flanged, i.e., the part inside the curve of the curved part of the press-formed product 101 (the curved part 131i of the inner vertical wall 103i and the curved part 141i of the inner flange 104i), is given a compressive stress in the longitudinal direction due to the application of tension during the forming process, and the tensile stress in the longitudinal direction during press forming due to the stretch-flange deformation is alleviated. This reduces the tensile stress in the longitudinal direction, and reduces the difference between the tensile stress on the outer surface and the compressive stress on the inner surface in the short direction.

On the other hand, no tension is applied to the portion that shrinks and deforms the flange, i.e., the outer curved portion of the curved portion of the press-formed product 101 (the curved portion 131o of the outer vertical wall 103o and the curved portion 141o of the outer flange 104o), due to the absence of the outer convex rib 85o and outer groove 62o as in the first embodiment.

In the case of the second embodiment, a reduction in longitudinal and lateral stresses cannot be expected in the outer curved portion of the curved portion of the press-formed product 101 removed from the die. However, as in the first embodiment, the longitudinal compressive stress due to springback can be reduced in the inner curved portion of the curved portion of the press-formed product 101 removed from the die, and the difference between the compressive stress on the outer surface and the tensile stress on the inner surface in the lateral direction can be reduced. As a result, twisting and wall warping of the press-formed product 101 can be effectively suppressed.

In addition, according to the manufacturing method using the press device 1 of the second embodiment, it is also possible to manufacture a press-molded product 101 that does not have an outer flange 104o. In this case, the outer edge 203o of the prepared blank 201 only needs to correspond to the curved outer side edge (the lower edge of the outer vertical wall 103o) when the press-molded product 101 to be molded is developed on the same plane.

[Modification of the second embodiment]
The press apparatus 1 and the method for manufacturing the press-formed product 101 according to the second embodiment shown in FIGS. 11 and 12 can be modified as follows.

The press device 1 of the modified second embodiment includes a bed 2, a slide 3, a lower punch 4, a lower cushion 5, an outer lower jig 6o, an upper pad 7, and an upper die 8. In other words, the press device 1 of the modified second embodiment does not include an inner lower jig 6i. Therefore, the inner lower blade 61i and the inner groove 62i as in the first embodiment do not exist. Furthermore, the upper die 8 of the modified second embodiment does not include the inner recess 83i, the inner recess 83i, and the inner ridge 85i as in the first embodiment. The other configurations are the same as those of the press device 1 of the first embodiment.

In the manufacturing method of the press-formed product 101 according to the modified second embodiment, the blank 201 prepared in step (a) has a size exceeding the installation area of the outer convex rib 85o (outer groove 62o) as in the first embodiment. From another perspective, an outer margin 202o is provided on the outer side of the curve of the blank 201. That is, as in the first embodiment, the outer edge 203o of the blank 201 exceeds the position of the side edge 106o of the outer flange 104o when the press-formed product 101 is developed on the same plane, and further exceeds the installation area of the outer convex rib 85o (outer groove 62o). In contrast, an inner margin 202i is not provided on the inner side of the curve of the blank 201. That is, the inner edge 203i of the blank 201 corresponds to the side edge 106i of the inner flange 104i when the press-formed product 101 is developed on the same plane.

In this case, in step (d), the blank 201 is press-formed by the upper die 8 and the lower punch 4, as in the first embodiment, and the blank 201 is press-formed by the outer convex rib 85o and the outer groove 62o. Then, in step (e), the blank 201 is cut by the outer upper blade 84o and the outer lower blade 61o, as in the first embodiment. Therefore, for the part that is deformed by shrinking flange, that is, the part on the outer side of the curved part of the press-formed product 101 (the curved part 131o of the outer vertical wall 103o and the curved part 141o of the outer flange 104o), a tensile stress in the longitudinal direction is applied with the application of tension during the forming process, and the compressive stress in the longitudinal direction during press forming associated with the shrinking flange deformation is alleviated. This reduces the compressive stress in the longitudinal direction, and reduces the difference between the tensile stress on the outer surface and the compressive stress on the inner surface in the short direction.

On the other hand, no tension is applied to the part that undergoes stretch flange deformation, i.e., the part on the inner side of the curved part of the press-formed product 101 (the curved part 131i of the inner vertical wall 103i and the curved part 141i of the inner flange 104i), due to the absence of the inner ridge 85i and inner groove 62i as in the first embodiment.

In the case of the modified example of the second embodiment, a reduction in longitudinal and lateral stresses cannot be expected in the inner curved portion of the curved portion of the press-formed product 101 removed from the die. However, as in the first embodiment, the longitudinal tensile stress due to springback can be reduced in the outer curved portion of the curved portion of the press-formed product 101 removed from the die, and the difference between the compressive stress on the outer surface and the tensile stress on the inner surface in the lateral direction can be reduced. As a result, twisting and wall warping of the press-formed product 101 can be effectively suppressed.

In addition, according to the manufacturing method using the press device 1 of the modified example of the second embodiment, it is also possible to manufacture a press-molded product 101 that does not have an inner flange 104i. In this case, the inner edge 203i of the prepared blank 201 only needs to correspond to the curved inner side edge (the lower edge of the inner vertical wall 103i) of the press-molded product 101 to be molded when it is unfolded.

Other variations and preferred aspects are described below.

[Inner margin 202i and outer margin 202o of blank 201]
As described above, in this embodiment, when the inner valley portion 105i is formed together with the formation of the press-formed product 101, the inner marginal portion 202i is provided on the inner side of the curve of the blank 201. When the outer valley portion 105o is formed together with the formation of the press-formed product 101, the outer marginal portion 202o is provided on the outer side of the curve of the blank 201. Hereinafter, with reference to Figs. 13 and 14, preferred ranges for the total width Wi of the inner marginal portion 202i and the total width Wo of the outer marginal portion 202o will be described.

Figure 13 is a plan view of the blank 201. In Figure 13, the blank 201 is shown in solid lines, and the press-molded product 101 formed from this blank 201 is shown in two-dot chain lines. In Figure 13, both side edges (side edge 106i of inner flange 104i and side edge 106o of outer flange 104o) when the press-molded product 101 to be molded is developed on the same plane are shown in imaginary lines (thin two-dot chain lines without symbols in Figure 13). Also, in Figure 13, the installation areas of the inner groove 62i and inner ridge 85i of the press device 1, and the installation areas of the outer groove 62o and outer ridge 85o are shown in dotted lines.

Figure 14 is a cross-sectional view showing the state during press molding. Figure 14 shows a cross-section at the position where the curved portion of the press-molded product 101 is molded. Note that Figure 14 corresponds to Figure 8F above.

Referring to FIG. 14, the line length in the cross section from the side edge 106i of the inner flange 104i of the press-formed product 101 to the curved inner side edge 151i of the inner valley portion 105i is Wi1. Hereinafter, this line length Wi1 is also referred to as the inner first line length Wi1. In addition, the line length in the cross section from the curved inner side edge 151i of the inner valley portion 105i to the inner edge 203i of the blank 201 is Wi2. Hereinafter, this line length Wi2 is also referred to as the inner second line length Wi2. The sum (Wi1+Wi2) of the line lengths of the inner first line length Wi1 and the inner second line length Wi2 expanded on the same plane corresponds to the total width Wi of the inner excess portion 202i shown in FIG. 13.

The larger the inner second line length Wi2, the greater the tension applied with the formation of the inner valley portion 105i. If the inner second line length Wi2 is 20 mm or more, this tension can be sufficiently secured. For this reason, the lower limit of the inner second line length Wi2 is preferably 20 mm. On the other hand, the upper limit of the inner second line length Wi2 is not particularly limited. However, if the inner second line length Wi2 is 200 mm or more, the increase in tension saturates. For this reason, the preferred upper limit of the inner second line length Wi2 is 200 mm.

Similarly, referring to FIG. 14, the line length in the cross section from the side edge 106o of the outer flange 104o of the press-formed product 101 to the curved outer side edge 151o of the outer valley portion 105o is Wo1. Hereinafter, this line length Wo1 is also referred to as the outer first line length Wo1. In addition, the line length in the cross section from the curved outer side edge 151o of the outer valley portion 105o to the outer edge 203o of the blank 201 is Wo2. Hereinafter, this line length Wo2 is also referred to as the outer second line length Wo2. The sum (Wo1+Wo2) of the line lengths of the outer first line length Wo1 and the outer second line length Wo2 expanded on the same plane corresponds to the total width Wo of the outer excess portion 202o shown in FIG. 13.

The larger the outer second line length Wo2, the greater the tension applied with the formation of the outer valley portion 105o. If the outer second line length Wo2 is 20 mm or more, this tension can be sufficiently secured. For this reason, the lower limit of the outer second line length Wo2 is preferably 20 mm. On the other hand, the upper limit of the outer second line length Wo2 is not particularly limited. However, if the outer second line length Wo2 is 200 mm or more, the increase in tension will saturate. For this reason, the preferred upper limit of the outer second line length Wo2 is 200 mm.

[Preferable shape 1 of blank 201]
As described above, in this embodiment, by forming the inner valley portion 105i together with forming the press-formed product 101, tension is applied to the area that will be the portion that undergoes stretch flange deformation, i.e., the inner curved portion of the curved portion of the press-formed product 101 (the curved portion 131i of the inner vertical wall 103i and the curved portion 141i of the inner flange 104i), and a longitudinal compressive stress is applied to this area. If the longitudinal compressive stress applied with the application of tension can be increased, it is possible to further alleviate the longitudinal tensile stress during press forming associated with stretch flange deformation. To achieve this, it is sufficient to change the shape of the inner curve of the blank 201.

Typically, in the blank 201, a first region corresponding to at least the longitudinal center of the curved portion of the installation region of the inner ridge 85i (inner groove 62i) exceeds the installation region of the inner ridge 85i (inner groove 62i), and the region on the outside from both ends of the first region is cut out. In this case, in the blank 201, the inner valley portion 105i is not formed in the notch region adjacent to the first region. Therefore, the direction of the tension applied during the forming process of the inner valley portion 105i is tilted from the short side direction. The longitudinal component of the tension tilted from the short side direction becomes large and is applied as a longitudinal compressive stress. As a result, the longitudinal tensile stress during press forming associated with stretch flange deformation is further alleviated.

Below, an example of a suitable shape 1 of the blank 201 is described with reference to Figures 15 and 16.

Figure 15 is a plan view showing a preferred shape 1 of the blank 201. In Figure 15, the blank 201 is shown in solid lines, and the press-molded product 101 molded from this blank 201 is shown in two-dot chain lines. In Figure 15, both side edges (side edge 106i of inner flange 104i and side edge 106o of outer flange 104o) when the press-molded product 101 to be molded is developed on the same plane are shown in imaginary lines (thin two-dot chain lines without symbols in Figure 15). Also, in Figure 15, the installation areas of the inner groove 62i and inner ridge 85i of the press device 1, and the installation areas of the outer groove 62o and outer ridge 85o are shown in dotted lines.

Figure 16 is a plan view for explaining the situation when the blank 201 shown in Figure 15 is formed into the press-formed product 101 by the manufacturing method of this embodiment. In Figure 16, the blank 201 is shown in a solid line, and the press-formed product 101 formed from this blank 201 is shown in a two-dot chain line. Also in Figure 16, the tension applied to the areas that will become the inner vertical wall 103i and the inner flange 104i of the press-formed product 101 is shown by dotted arrows, and the longitudinal stress (component force) applied to each area by the application of this tension is shown by solid arrows.

Figures 15 and 16 also show an example of manufacturing a press-molded product 101 corresponding to Figure 2F, in which straight sections 112 are provided at both ends of the curved section 111. The same effect is obtained when manufacturing a press-molded product that does not have straight sections on either side of the curved section 111 or when manufacturing a press-molded product that has a straight section only on one side.

15, the inner excess portion 202i of the blank 201 is provided in a part of the region corresponding to the curved portion 111 of the press-formed product 101. In other words, the inner excess portion 202i of the blank 201 is not provided in the region corresponding to the straight portion 112 of the press-formed product 101. The curved portion 111 of the press-formed product 101 is composed of the curved portion 121 of the top plate 102, the curved portion 131i of the inner vertical wall 103i, the curved portion 131o of the outer vertical wall 103o, the curved portion 141i of the inner flange 104i, and the curved portion 141o of the outer flange 104o (see FIG. 1B). The straight portion 112 of the press-formed product 101 is composed of the straight portion 122 of the top plate 102, the straight portion 132i of the inner vertical wall 103i, the straight portion 132o of the outer vertical wall 103o, the straight portion 142i of the inner flange 104i, and the straight portion 142o of the outer flange 104o (see FIG. 1B).

From another perspective, the inner ridge 85i (inner groove 62i) of the press device 1 is installed inside the curve of the curved portion 111 of the press-molded product 101, and the inner margin 202i is provided in the blank 201 in an area corresponding to at least the center of the installation area of the inner ridge 85i (inner groove 62i). The area outside the both ends 202ip of the inner margin 202i is cut out. In other words, the blank 201 has a notch 204i area outside both end edges 202ie of the inner margin 202i (first area). The notch 204i is formed so that the contour shape of the inner margin 202i is gentle. At both ends 202ip of the inner margin 202i, the edge 202ie appears due to the notch 204i. In a typical example, the edge 202ie of the inner margin 202i is a straight line in a plan view. The edge 202ie is inclined relative to the short side direction.

In this case, as shown in FIG. 16, during press forming, the inner valley portion 105i is not formed in the region of the notch 204i on the inner side of the curve in the blank 201. In other words, the region of the notch 204i on the inner side of the curve does not provide tension. Therefore, the direction of the tension applied during the forming process of the inner valley portion 105i is further tilted from the short side direction. This is because the tension is concentrated near both end edges 202ie of the inner excess portion 202i. The longitudinal component of the tension tilted from the short side direction becomes larger and is applied as a longitudinal compressive stress. As a result, the tensile stress during longitudinal forming associated with stretch flange deformation is further alleviated.

To effectively exert such an effect, when the blank 201 is viewed in a plane, it is preferable that the angle γi between the tangent Lfi at both ends 202ip of the inner edge 203i and the edge 202ie is 10° or more and 70° or less. If the angle γi is greater than 70°, deformation will concentrate on the edge 202ie of the inner excess portion 202i and the end 202ip of each inner excess portion 202i, causing cracks. If the angle γi is less than 10°, the notch 204i cannot be positioned in the inner valley portion 105i, and the notch 204i may not be formed.

The curved portion 111 of the press-formed product 101 shown in FIG. 15 is composed of one arc. In this case, it is preferable that the angle θ2 [°] between the arc center line Lc and the excess length end connecting line Lei and the angle θ1 [°] between the arc center line Lc and the curved portion end connecting line Ld satisfy the relationship of the following formula (1). In this specification, the arc center line Lc means a line connecting the center of the arc constituting the curved portion 111 and the center of curvature of the arc. The curved portion end connecting line Ld means a line connecting the end of the curved portion 111 and the center of curvature of the arc constituting the curved portion 111. The excess length end connecting line Lei means a line connecting the end 202ip of the inner edge 203i and the center of curvature of the arc constituting the curved portion 111.
0.2≦θ2/θ1≦0.9 (1)

If θ2/θ1 satisfies the relationship of formula (1), the longitudinal compressive stress applied with the application of tension can be effectively increased in the area that undergoes stretch flange deformation, i.e., the area that is the inner part of the curved portion 111 of the press-molded product 101, and the longitudinal tensile stress during press molding that accompanies stretch flange deformation can be further alleviated. As a result, the longitudinal tensile stress can be further reduced, and the difference between the tensile stress on the outer surface and the compressive stress on the inner surface can be further reduced in the short direction. In this case, the longitudinal compressive stress can be further reduced in the inner part of the curved portion 111 of the press-molded product 101 removed from the mold, and the difference between the compressive stress on the outer surface and the tensile stress on the inner surface can be further reduced in the short direction. As a result, the torsion and wall warping of the press-molded product 101 can be effectively suppressed.

Figure 17 is a diagram showing the relationship between θ2/θ1 and the twist angle of the press-formed product 101. The twist angle shown in Figure 17 means the angle [°] by which the press-formed product 101 is twisted from the design dimensions. For comparison, Figure 17 also shows the twist angle of the press-formed product 101 manufactured by a general press process that does not form the inner valley portion 105i and the outer valley portion 105o. As is clear from Figure 17, if θ2/θ1 is in the range of 0.2 or more and 0.9 or less, that is, in the range shown in formula (1), the twist angle of the press-formed product 101 is significantly small.

[Preferable shape 2 of blank 201]
An example of a suitable shape 2 of the blank 201 will now be described with reference to FIG.

Figure 18 is a plan view showing a preferred shape 2 of the blank 201. In Figure 18, the blank 201 is shown in a solid line, and the press-molded product 101 molded from this blank 201 is shown in a two-dot chain line. In Figure 18, both side edges (side edge 106i of the inner flange 104i and side edge 106o of the outer flange 104o) when the press-molded product 101 to be molded is developed on the same plane are shown in imaginary lines (thin two-dot chain lines without symbols in Figure 18). Also, in Figure 18, the installation areas of the inner groove 62i and inner ridge 85i of the press device 1, and the installation areas of the outer groove 62o and outer ridge 85o are shown in dotted lines.

The curved portion 111 of the press-formed product 101 shown in FIG. 18 is composed of two arcs and has a shape similar to that of FIG. 2B. One arc with a smaller radius of curvature Ra is also called the first arc, and the other arc with a larger radius of curvature Rb is also called the second arc. The first arc is connected to the second arc.

In this case, it is preferable that the angle θa2 [°] between the first arc center line Lc1 and the first excess length end connecting line Lei1 and the angle θa1 [°] between the first arc center line Lc1 and the first curved portion end connecting line Ld1 satisfies the relationship of the following formula (2). In this specification, the first arc center line Lc1 means a line connecting the center of the first arc constituting the curved portion 111 and the center of curvature of the first arc. The first curved portion end connecting line Ld1 means a line connecting the end of the curved portion 111 on the first arc side and the center of curvature of the first arc. The first excess length end connecting line Lei1 means a line connecting one end 202ip of the inner excess length portion 202i and the center of curvature of the first arc.
0.2≦θa2/θa1≦0.9 (2)

In addition, it is preferable that the angle θb2 [°] between the second arc center line Lc2 and the second curved portion end connecting line Ld2 and the angle θb2 [°] between the second arc center line Lc2 and the second excess length end connecting line Lei2 satisfies the relationship of the following formula (3). In this specification, the second arc center line Lc2 means a line connecting the center of the second arc constituting the curved portion 111 and the center of curvature of the second arc. The second curved portion end connecting line Ld2 means a line connecting the end of the curved portion 111 on the second arc side and the center of curvature of the second arc. The second excess length end connecting line Lei2 means a line connecting the other end 202ip of the inner excess length portion 202i and the center of curvature of the second arc.
0.2≦θb2/θb1≦0.9 (3)

When the curved portion 111 of the press-formed product 101 is composed of two arcs (a first arc and a second arc), if θa2/θa1 satisfies the relationship in formula (2) and θb2/θb1 satisfies the relationship in formula (3), the above-mentioned effect is the same as when θ2/θ1 satisfies the relationship in formula (1). However, other arcs may be arranged between the first arc and the second arc. In other words, the curved portion 111 of the press-formed product 101 may be composed of three or more arcs.

[Preferable shape 3 of blank 201]
As described above, in this embodiment, by forming the outer valley portion 105o together with forming the press-formed product 101, tension is applied to the area that will be the portion that undergoes shrink flange deformation, i.e., the curved outer portion of the curved portion of the press-formed product 101 (the curved portion 131o of the outer vertical wall 103o and the curved portion 141o of the outer flange 104o), and a longitudinal tensile stress is applied to this area. If the longitudinal tensile stress applied with the application of tension can be increased, it is possible to further alleviate the longitudinal compressive stress during press forming that accompanies shrink flange deformation. To achieve this, the shape of the curved outer side of the blank 201 can be changed.

Typically, in the blank 201, the second regions corresponding to at least both ends of the installation region of the outer ridge 85o (outer groove 62o) extend beyond the installation region of the outer ridge 85o (outer groove 62o), and a portion of the region on the inside of the second regions is cut out. In this case, in the blank 201, the outer valley portion 105o is not formed in the notch region adjacent to the second region. Therefore, the direction of the tension applied during the molding process of the outer valley portion 105o is tilted from the short side direction. The longitudinal component of the tension tilted from the short side direction becomes larger and is applied as a longitudinal tensile stress. As a result, the longitudinal compressive stress during press molding associated with the shrink flange deformation is further alleviated.

Below, an example of a suitable shape 3 of the blank 201 is described with reference to Figures 19 and 20.

Figure 19 is a plan view showing a preferred shape 3 of the blank 201. In Figure 19, the blank 201 is shown in solid lines, and the press-molded product 101 molded from this blank 201 is shown in two-dot chain lines. In Figure 19, both side edges (side edge 106i of inner flange 104i and side edge 106o of outer flange 104o) when the press-molded product 101 to be molded is developed on the same plane are shown in imaginary lines (thin two-dot chain lines without symbols in Figure 19). Also, in Figure 19, the installation areas of the inner groove 62i and inner ridge 85i of the press device 1, and the installation areas of the outer groove 62o and outer ridge 85o are shown in dotted lines.

Figure 20 is a plan view for explaining the situation when the blank 201 shown in Figure 19 is formed into the press-formed product 101 by the manufacturing method of this embodiment. In Figure 20, the blank 201 is shown in a solid line, and the press-formed product 101 formed from this blank 201 is shown in a two-dot chain line. Also in Figure 20, the tension applied to the areas that will become the outer vertical wall 103o and outer flange 104o of the press-formed product 101 is shown by dotted arrows, and the longitudinal stress (component force) applied to each area by the application of this tension is shown by solid arrows.

Figures 19 and 20 show an example of manufacturing a press-molded product 101 corresponding to Figure 2F, in which straight sections 112 are provided at both ends of the curved section 111. The same effect is obtained when manufacturing a press-molded product that does not have straight sections on either side of the curved section 111 or when manufacturing a press-molded product that has a straight section only on one side.

19, the outer excess portion 202o of the blank 201 is provided in an area corresponding to each straight portion 112 of the press-formed product 101. The outer excess portion 202o of the blank 201 is continuous with an area corresponding to each of both ends of the curved portion 111 of the press-formed product 101. The curved portion 111 of the press-formed product 101 is composed of the curved portion 121 of the top plate 102, the curved portion 131i of the inner vertical wall 103i, the curved portion 131o of the outer vertical wall 103o, the curved portion 141i of the inner flange 104i, and the curved portion 141o of the outer flange 104o (see FIG. 1B). The straight portion 112 of the press-formed product 101 is composed of the straight portion 122 of the top plate 102, the straight portion 132i of the inner vertical wall 103i, the straight portion 132o of the outer vertical wall 103o, the straight portion 142i of the inner flange 104i, and the straight portion 142o of the outer flange 104o (see FIG. 1B).

From another perspective, the outer convex 85o (outer groove 62o) of the press device 1 is installed outside the curve of the curved portion 111 of the press-molded product 101, and the outer excess portion 202o is provided in each area of the blank 201 corresponding to at least both ends of the installation area of the outer convex 85o (outer groove 62o). The area inside the ends 202op of each outer excess portion 202o is cut out. In other words, the blank 201 has a notch 204o area inside the edges 202oe of each outer excess portion 202o (second area). The notch 204o is formed so that the contour shape of each outer excess portion 202o becomes gentle. At the end 202op of each outer excess portion 202o, the edge 202oe appears due to the notch 204o. In a typical example, the edge 202oe of the outer excess portion 202o is a straight line in a plan view. The edge 202oe is inclined relative to the short side direction.

In this case, as shown in FIG. 20, during press forming, part of the outer valley portion 105o is not formed in the region of the curved outer notch 204o in the blank 201. In other words, the region of the curved outer notch 204o does not provide tension. As a result, the direction of the tension applied during the forming process of the outer valley portion 105o is tilted further away from the short side direction. This is because the tension is concentrated near the edge 202oe of the outer excess portion 202o. The longitudinal component of the tension tilted away from the short side direction becomes larger and is applied as a longitudinal tensile stress. As a result, the compressive stress during forming in the longitudinal direction due to the shrink flange deformation is further alleviated.

To effectively exert such an effect, when the blank 201 is viewed in a plane, it is preferable that the angle γo between the tangent Lfo at the end 202op of the outer edge 203o and the end edge 202oe is 10° or more and 70° or less. If the angle γo is greater than 70°, deformation will concentrate on the end edge 202oe of the outer excess portion 202o and the end 202op of each outer excess portion 202o, causing cracks. If the angle γo is less than 10°, the notch 204o cannot be positioned in the outer valley portion 105o, and the notch 204o may not be formed.

The curved portion 111 of the press-formed product 101 shown in Fig. 19 is composed of one arc. In this case, it is preferable that the angle θ3 [°] between the arc center line Lc and the excess length end connecting line Leo and the angle θ1 [°] between the arc center line Lc and the curved portion end connecting line Ld satisfy the relationship of the following formula (4). In this specification, the excess length end connecting line Leo means a line connecting the end 202op of the edge 202oe and the center of curvature of the arc constituting the curved portion 111. The meanings of the arc center line Lc and the curved portion end connecting line Ld are as described above.
0.15≦θ3/θ1≦0.7 (4)

If θ3/θ1 satisfies the relationship of formula (4), the longitudinal tensile stress applied with the application of tension can be effectively increased in the area where the shrink flange deformation occurs, i.e., the area that is the outer curved portion of the curved portion 111 of the press-molded product 101, and the longitudinal compressive stress during press molding associated with the shrink flange deformation can be further alleviated. As a result, the longitudinal compressive stress can be further reduced, and the difference between the tensile stress on the outer surface and the compressive stress on the inner surface in the short direction can be further reduced. In this case, the longitudinal tensile stress can be further reduced in the outer curved portion of the curved portion 111 of the press-molded product 101 removed from the mold, and the difference between the compressive stress on the outer surface and the tensile stress on the inner surface in the short direction can be further reduced. As a result, the torsion and wall warping of the press-molded product 101 can be effectively suppressed.

Figure 21 is a diagram showing the relationship between θ3/θ1 and the twist angle of the press-formed product 101. The twist angle shown in Figure 21 means the angle [°] by which the press-formed product 101 is twisted from the design dimensions. For comparison, Figure 21 also shows the twist angle of the press-formed product 101 manufactured by a general press process that does not form the inner valley portion 105i and the outer valley portion 105o. As is clear from Figure 21, if θ3/θ1 is in the range of 0.15 or more and 0.7 or less, that is, in the range shown in formula (4), the twist angle of the press-formed product 101 is significantly small.

[Preferable shape 4 of blank 201]
It is also possible to combine the preferred shapes 1 and 2 of the blank 201 described above. Fig. 22 shows a plan view of a preferred shape 4 of the blank 201. In the blank 201 shown in Fig. 22, the situation on the inside of the curve is the same as that of shape 1 shown in Fig. 15, and the situation on the outside of the curve is the same as that of shape 3 shown in Fig. 19. Therefore, the longitudinal stress can be reduced in both the inner curved portion and the outer curved portion of the curved portion of the press-formed product 101. Therefore, a press-formed product 101 with better dimensional accuracy can be obtained compared to the case where the longitudinal stress is reduced only on the inner curved portion or the case where the longitudinal stress is reduced only on the outer curved portion.

[Dimensions of the inner convex strip 85i and the outer convex strip 85o]
Fig. 23 is a cross-sectional view for explaining suitable dimensions of the inner convex rib 85i and the outer convex rib 85o. Fig. 23 shows a cross section at a position where a curved portion of the press-formed product 101 is formed.

Referring to FIG. 23, in the upper die 8 of the press device 1 of this embodiment, the amount of protrusion hi1 of the inner ridge 85i from the inner lower surface 82i is preferably 5 mm or more. Similarly, the amount of protrusion ho1 of the outer ridge 85o from the outer lower surface 82o is preferably 5 mm or more.

As described above, in order to apply tension to the portion that undergoes stretch flange deformation, i.e., the area that will become the inner curved portion of the curved portion of the press-formed product 101, the inner valley portion 105i is formed by the inner convex rib 85i of the upper die 8 and the inner groove 62i of the inner lower jig 6i. If the protruding amount hi1 of the inner convex rib 85i is 5 mm or more, tension is effectively applied to the area that will become the inner curved portion of the curved portion of the press-formed product 101 during the process of forming the inner valley portion 105i. The protruding amount hi1 of the inner convex rib 85i is more preferably 9 mm or more. There is no particular limit to the upper limit of the protruding amount hi1 of the inner convex rib 85i. However, if the protruding amount hi1 of the inner convex rib 85i is 20 mm or more, the effect of suppressing twisting and wall warping is saturated. For this reason, the preferable upper limit of the protruding amount hi1 of the inner convex rib 85i is 20 mm.

As described above, in order to apply tension to the area that will be the part of the shrink flange deformation, i.e., the part on the outer side of the curved part of the press-molded product 101, the outer valley portion 105o is formed by the outer convex rib 85o of the upper die 8 and the outer groove 62o of the outer lower jig 6o. If the protruding amount ho1 of the outer convex rib 85o is 5 mm or more, tension is effectively applied to the area that will be the part on the outer side of the curved part of the press-molded product 101 during the process of forming the outer valley portion 105o. The protruding amount ho1 of the outer convex rib 85o is more preferably 9 mm or more. The upper limit of the protruding amount ho1 of the outer convex rib 85o is not particularly limited. However, if the protruding amount ho1 of the outer convex rib 85o is 20 mm or more, the effect of suppressing twisting and wall warping is saturated. For this reason, the preferable upper limit of the protruding amount ho1 of the outer convex rib 85o is 20 mm.

Also, referring to FIG. 23, in the upper die 8 of the press device 1 of this embodiment, the width wi1 of the inner convex streak 85i is preferably 0.8 times or more the height hi2 of the inner convex streak 85i. Similarly, the width wo1 of the outer convex streak 85o is preferably 0.8 times or more the height ho2 of the outer convex streak 85o. In this specification, the width wi1 of the inner convex streak 85i means the widthwise length of the inner convex streak 85i at the bottom surface of the inner recess 83i. The width wo1 of the outer convex streak 85o means the widthwise length of the outer convex streak 85o at the bottom surface of the outer recess 83o. The height hi2 of the inner convex streak 85i means the heightwise length from the bottom surface of the inner recess 83i to the lower end of the inner convex streak 85i. The height ho2 of the outer convex streak 85o means the heightwise length from the bottom surface of the outer recess 83o to the lower end of the outer convex streak 85o.

If the width wi1 of the inner ridge 85i is 0.8 times or more the height hi2 of the inner ridge 85i, the strength of the inner ridge 85i itself can be sufficiently ensured. In this case, deformation and chipping of the inner ridge 85i can be suppressed. There is no particular upper limit to the width wi1 of the inner ridge 85i. However, if the width wi1 of the inner ridge 85i exceeds 2.0 times the height hi2 of the inner ridge 85i, there will be no change in the strength of the inner ridge 85i, and the material yield will actually deteriorate. For this reason, it is preferable that the width wi1 of the inner ridge 85i be 2.0 times or less the height hi2 of the inner ridge 85i.

In addition, if the width wo1 of the outer convex rib 85o is 0.8 times or more the height ho2 of the outer convex rib 85o, the strength of the outer convex rib 85o itself can be sufficiently ensured. In this case, deformation, chipping, etc. of the outer convex rib 85o can be suppressed. There is no particular upper limit to the width wo1 of the outer convex rib 85o. However, if the width wo1 of the outer convex rib 85o exceeds 2.0 times the height ho2 of the outer convex rib 85o, there will be no change in the strength of the outer convex rib 85o, and the material yield will actually deteriorate. For this reason, it is preferable that the width wo1 of the outer convex rib 85o is 2.0 times or less the height ho2 of the outer convex rib 85o.

[Dimensions of the inner lower jig 6i and the outer lower jig 6o]
Fig. 24 is a cross-sectional view for explaining suitable dimensions of the inner lower jig 6i and the outer lower jig 6o. Fig. 24 shows a cross section at a position where a curved portion of the press-formed product 101 is formed.

Referring to FIG. 24, in the inner lower jig 6i of the press device 1 of this embodiment, the edge adjacent to the inner bottom surface 43i of the lower punch 4 functions as the inner lower blade 61i. The smaller the distance wi2 on the upper surface of the inner lower jig 6i from the edge adjacent to the inner bottom surface 43i of the lower punch 4 to the edge of the inner groove 62i on the lower punch 4 side, the higher the material yield of the blank 201. However, if the distance wi2 is too small, it becomes difficult to ensure the strength of the inner lower blade 61i. For this reason, it is preferable that the distance wi2 be 20 mm or more and 100 mm or less.

Also, referring to FIG. 24, in the outer lower jig 6o of the press device 1 of this embodiment, the edge adjacent to the outer bottom surface 43o of the lower punch 4 functions as the outer lower blade 61o. The smaller the distance wo2 on the upper surface of the outer lower jig 6o from the edge adjacent to the outer bottom surface 43o of the lower punch 4 to the edge of the outer groove 62o on the lower punch 4 side, the more the material yield of the blank 201 improves. However, if the distance wo2 is too small, it becomes difficult to ensure the strength of the outer lower blade 61o. For this reason, it is preferable that the distance wo2 be 20 mm or more and 100 mm or less.

[Initial Height Positions of the Inner Bottom Surface 43i and the Outer Bottom Surface 43o of the Lower Punch 4]
Fig. 25 is a cross-sectional view for explaining suitable initial height positions of the inner bottom surface 43i and the outer bottom surface 43o of the lower punch 4. Fig. 25 shows a cross section at a position where a curved portion of a press-formed product 101 is formed.

25, the initial height position of the inner bottom surface 43i of the lower punch 4 may be slightly higher than the height position of the upper surface of the inner lower jig 6i. In other words, the relative height hi3 between the initial height position of the inner bottom surface 43i of the lower punch 4 and the initial height position of the inner bottom surface 43i of the lower punch 4 may be positive. If the relative height hi3 is negative, the blank 201 may be bitten into the lower blade and the upper blade and cutting may begin while the area sandwiched between the upper die 8 and the lower punch 4 is being formed, that is, during the above-mentioned step (d). However, if the relative height hi3 is positive, after the press-formed product 101 is formed by each surface of the lower punch 4 and each surface of the upper die 8, the press-formed product 101 descends together with the upper die 8 and the lower punch 4. Then, cutting is performed by the inner upper blade 84i and the inner lower blade 61i, and cutting is performed by the outer upper blade 84o and the outer lower blade 61o. In other words, cutting is not performed immediately after the press-formed product 101 is formed by the surfaces of the lower punch 4 and the surfaces of the upper die 8.

Even in such a case, the inner valley portion 105i continues to be formed by the inner convex ridge 85i of the upper die 8 and the inner groove 62i of the inner lower jig 6i until the cutting is performed. This is because the upper die 8 is lowered relative to the inner lower jig 6i. For this reason, the application of tension also continues. Therefore, in the part that undergoes stretch flange deformation, that is, the area that is the inner part of the curved part of the press-formed product 101, a compressive stress in the longitudinal direction can be applied with the application of tension. For this reason, the tensile stress in the longitudinal direction during press forming associated with stretch flange deformation can be reduced, and the difference between the tensile stress on the outer surface and the compressive stress on the inner surface in the lateral direction can be reduced. In this case, the compressive stress in the longitudinal direction can be reduced in the inner part of the curved part of the press-formed product 101 removed from the die, and the difference between the compressive stress on the outer surface and the tensile stress on the inner surface in the lateral direction can be reduced. As a result, the twisting and wall warping of the press-formed product 101 can be suppressed.

However, the larger the relative height hi3, the smaller the tension. Therefore, it is preferable that the relative height hi3 is 3 mm or less. The most preferable relative height hi3 is 0 (zero) mm. In this case, the initial height position of the inner bottom surface 43i of the lower punch 4 coincides with the height position of the upper surface of the inner lower jig 6i.

Also, referring to FIG. 25, the initial height position of the outer bottom surface 43o of the lower punch 4 may be slightly higher than the height position of the upper surface of the outer lower jig 6o. In other words, the relative height ho3 between the initial height position of the outer bottom surface 43o of the lower punch 4 and the initial height position of the outer bottom surface 43o of the lower punch 4 may be positive. In this case, after the press-molded product 101 is molded by each surface of the lower punch 4 and each surface of the upper die 8, the press-molded product 101 descends together with the upper die 8 and the lower punch 4. Then, cutting is performed by the outer upper blade 84o and the outer lower blade 61o, and cutting is performed by the outer upper blade 84o and the outer lower blade 61o. In other words, cutting is not performed immediately after the press-molded product 101 is molded by each surface of the lower punch 4 and each surface of the upper die 8.

Even in such a case, the outer valley portion 105o continues to be formed by the outer convex ridge 85o of the upper die 8 and the outer groove 62o of the outer lower jig 6o until cutting is performed. This is because the upper die 8 is lowered relative to the outer lower jig 6o. For this reason, the application of tension also continues. Therefore, in the part where the shrink flange deformation occurs, that is, the area that is the outer curved part of the curved part of the press-formed product 101, a tensile stress in the longitudinal direction can be applied with the application of tension. Therefore, the compressive stress in the longitudinal direction during press forming due to the shrink flange deformation can be reduced, and the difference between the tensile stress of the outer surface and the compressive stress of the inner surface in the short direction can be reduced. In this case, the tensile stress in the longitudinal direction can be reduced in the outer curved part of the curved part of the press-formed product 101 removed from the mold, and the difference between the compressive stress of the outer surface and the tensile stress of the inner surface in the short direction can be reduced. As a result, the twisting and wall warping of the press-formed product 101 can be suppressed.

However, the larger the relative height ho3, the smaller the tension. Therefore, it is preferable that the relative height ho3 is 3 mm or less. The most preferable relative height ho3 is 0 (zero) mm. In this case, the initial height position of the outer bottom surface 43o of the lower punch 4 coincides with the height position of the upper surface of the outer lower jig 6o.

[Load Applied to the Lower Punch 4 from the Lower Cushion 5]
An upward load is applied to the lower punch 4 by the lower cushion 5. This load is called a cushion load F. After the region sandwiched between the upper die 8 and the lower punch 4 has been formed, i.e., after the above-mentioned step (d) is completed, in order to perform the cutting in the above-mentioned step (e), it is necessary that the lower punch 4 does not descend until the press-formed product 101 is formed by each surface of the lower punch 4 and each surface of the upper die 8.

Therefore, it is desirable that the cushion load F satisfies the following formula (5).
F≧L×TS×t×0.2 (5)
The meanings of each symbol in formula (5) are as follows:
L: Length of the press-molded product 101 in the longitudinal direction [mm],
TS: tensile strength of blank 201 [MPa], and t: thickness of blank 201 [mm].

[Descent amount of the lower punch 4, and depths of the inner recess 83i and the outer recess 83o of the upper die 8]
Fig. 26 is a cross-sectional view for explaining a suitable amount of descent of the lower punch 4 and a suitable depth of each of the inner recess 83i and the outer recess 83o of the upper die 8. Fig. 26 shows a cross-section at a position where a curved portion of the press-formed product 101 is formed.

With reference to FIG. 26, it is preferable that the lowering amount h4 of the lower punch 4 satisfies the following formula (6).
1.1×t≦h4≦9.0×t (6)
The symbols in formula (6) have the following meanings:
t: thickness of blank 201 [mm].

In the press device 1 shown in FIG. 26, the lowering amount h4 of the lower punch 4 is the heightwise gap between the bottomed upper plate 12 and the bottomed lower plate 13. The bottomed upper plate 12 comes into contact with the bottomed lower plate 13, thereby limiting the lowering of the lower punch 4.

As the lower punch 4 descends, the blank 201 is cut by the outer upper blade 84o and the outer lower blade 61o. If the amount of descent h4 of the lower punch 4 is too small, cutting cannot be performed. Therefore, it is preferable that the amount of descent h4 of the lower punch 4 is 1.1 times or more the thickness t of the blank 201. On the other hand, if the amount of descent h4 of the lower punch 4 is too large, the height of the die will be larger than necessary, and the material cost of the die will also increase. Therefore, it is preferable that the amount of descent h4 of the lower punch 4 is 9.0 times or less the thickness t of the blank 201.

Also, referring to FIG. 26, it is preferable that the depth hi5 of the inner recess 83i of the upper die 8 is greater than the amount of descent h4 of the lower punch 4. In this specification, the depth hi5 of the inner recess 83i means the length in the height direction from the inner lower surface 82i of the upper die 8 to the bottom surface of the inner recess 83i. If the depth hi5 of the inner recess 83i is greater than the amount of descent h4 of the lower punch 4, the lower punch 4 can reliably reach the bottom dead center.

Also, referring to FIG. 26, it is preferable that the depth ho5 of the outer recess 83o of the upper die 8 is greater than the amount of descent h4 of the lower punch 4. In this specification, the depth ho5 of the outer recess 83o means the length in the height direction from the outer lower surface 82o of the upper die 8 to the bottom surface of the outer recess 83o. If the depth ho5 of the outer recess 83o is greater than the amount of descent h4 of the lower punch 4, the lower punch 4 can reliably reach the bottom dead center.

[Shapes of the inner lower blade 61i and the outer lower blade 61o]
A preferred shape of each of the inner lower blade 61i and the outer lower blade 61o will be described with reference to Figures 27A and 27B.

Figure 27A is a diagram showing a suitable shape of the inner lower blade 61i. Figure 27A shows a side view of part of the inner lower jig 6i when viewed horizontally from the lower punch 4 side, including the inner lower blade 61i that cuts the area corresponding to the curved portion of the press-formed product 101. Figure 27A also shows the inner upper blade 84i that pairs with the inner lower blade 61i in imaginary lines (thin two-dot chain lines in Figure 27A). Figure 27A shows the blank 201 in hatching.

Referring to FIG. 27A, the inner lower blade 61i is inclined in the range corresponding to the inner side edge of the curved portion so that the center Ric of the range is lower than both ends Rie of the range. On the other hand, the inner upper blade 84i is linear and has a constant height. The inner upper blade 84i of the upper die 8 descends, and the blank 201 is cut by the inner upper blade 84i and the inner lower blade 61i.

When the inner upper blade 84i and the inner lower blade 61i remove the region including the inner valley portion 105i from the press-formed product 101, the inner side edges of the curved other curves of the press-formed product 101 are not cut simultaneously, but are gradually cut from both ends of the side edges toward the center of the side edges. This is because the inner lower blade 61i has the shear angle βi of the above form. Therefore, the press load required for cutting is small. In addition, compressive stress is applied in the longitudinal direction during cutting. Therefore, the longitudinal tensile stress during press forming is further alleviated. As a result, the longitudinal tensile stress can be further reduced.

The shear angle βi is preferably 0.5° or more and 4.5° or less. If the shear angle βi is less than 0.5°, it is almost the same as when there is no shear angle, and the effect of suppressing torsion and reducing load is low. If the shear angle βi is more than 4.5°, the forming stroke hzi until punching increases, which increases the size of the die and increases the die cost.

Figure 27B is a diagram showing a suitable shape of the outer lower blade 61o. Figure 27B shows a side view of part of the outer lower jig 6o when viewed horizontally from the lower punch 4 side, including the outer lower blade 61o that cuts the area corresponding to the curved portion of the press-formed product 101. Figure 27B also shows the outer upper blade 84o that pairs with the outer lower blade 61o in imaginary lines (thin two-dot chain lines in Figure 27B). Figure 27B shows the blank 201 in hatching.

Referring to FIG. 27B, the outer lower blade 61o is inclined in the range corresponding to the curved outer side edge of the curved portion so that the center Roc of the range is higher than both ends Roe of the range. On the other hand, the outer upper blade 84o is linear and has a constant height. The outer upper blade 84o of the upper die 8 descends, and the blank 201 is cut by the outer upper blade 84o and the outer lower blade 61o.

When the outer upper blade 84o and the outer lower blade 61o remove the area including the outer valley portion 105o from the press-formed product 101, the curved outer side edge of the curved portion of the press-formed product 101 is not cut simultaneously, but is gradually cut from the center of the side edge toward each end of the side edge. This is because the outer lower blade 61o has the shear angle βo of the above form. Therefore, the press load required for cutting is small. In addition, tensile stress is applied in the longitudinal direction during cutting. Therefore, the longitudinal compressive stress during press forming is further alleviated. As a result, the longitudinal compressive stress can be further reduced.

The shear angle βo is preferably 0.5° or more and 4.5° or less. If the shear angle βo is less than 0.5°, it will be almost the same as if there was no shear angle, and the effects of suppressing torsion and reducing load will be low. If the shear angle βo is greater than 4.5°, the forming stroke hzo until punching will increase, which will increase the size of the die and the cost of the die.

To confirm the effect of this embodiment, a CAE analysis was performed. For the CAE analysis, LS-DYNA ver. 971, a commercially available general-purpose solver, was used. In the CAE analysis, a model of the press-molded product 101 shown in Figures 1A and 1B was created under various conditions.

The main dimensions of the press-molded product 101 were as follows. These dimensions were reflected in various dies.
Radius of curvature of the inner side edge of the curved portion 121 of the tabletop 102 in plan view: 1200 mm
・Width of top plate 102: 32 mm
Radius of curvature in the cross section of the inner surface of the corner portion between the top plate 102 and the inner vertical wall 103i: 4.5 mm
Radius of curvature in the cross section of the inner surface of the corner portion between the top plate 102 and the outer vertical wall 103o: 4.5 mm
Height of the inner vertical wall 103i: 40 mm
Height of outer vertical wall 103o: 40 mm
Radius of curvature in the cross section of the inner surface of the corner portion between the inner vertical wall 103i and the inner flange 104i: 4.5 mm
Radius of curvature in the cross section of the inner surface of the corner portion between the outer vertical wall 103o and the outer flange 104o: 4.5 mm
Width of inner flange 104i: 18 mm
Width of outer flange 104o: 18 mm

A molding analysis and a springback analysis were performed on the press-formed product 101 using various dies. The results of the springback analysis were used to evaluate the torsion and wall warpage of the press-formed product 101. The evaluation method is shown in Figures 28A and 28B.

Figure 28A is a perspective view for explaining a method for evaluating torsion. In Figure 28A, the press-formed product 101 after springback is shown in a solid line. Also, in Figure 28A, the press-formed product 101 before springback is shown in a two-dot chain line.

The torsion was evaluated by the torsion angle [°]. Specifically, referring to FIG. 28A, one edge of the top plate 102 of the press-formed product 101 after springback was aligned with one edge of the top plate 102 of the press-formed product 101 before springback. Then, the angle α [°] at which the other edge of the top plate 102 of the press-formed product 101 after springback was twisted relative to the other edge of the top plate 102 of the press-formed product 101 before springback was calculated, and this was taken as the torsion angle. The smaller the torsion angle, the smaller the torsion of the press-formed product 101.

Figure 28B is a cross-sectional view for explaining a method for evaluating wall warpage. In Figure 28B, the press-formed product 101 after springback is shown by a solid line. Also, in Figure 28B, the press-formed product 101 before springback is shown by a two-dot chain line.

The wall warping was evaluated in terms of the wall warping curvature [/mm]. Specifically, referring to FIG. 28B, in a cross section at the center of the longitudinal direction of the press-formed product 101, the top plate 102 of the press-formed product 101 after springback was aligned with the top plate 102 of the press-formed product 101 before springback. Then, in the press-formed product 101 after springback, the average value of the curvature C of the lower end side of the inner vertical wall 103i and the curvature C of the lower end side of the outer vertical wall 103o was calculated, and this was taken as the wall warping curvature. The smaller the wall warping curvature, the smaller the wall warping.

The results are summarized in Table 1 below.

In the comparative example, the press-formed product 101 was formed by a general press process. In other words, in the comparative example, neither the inner valley portion 105i nor the outer valley portion 105o was formed.

In Example 1, both the inner valley portion 105i and the outer valley portion 105o were formed during the forming process of the press-formed product 101, and finally the area including the inner valley portion 105i and the outer valley portion 105o was cut off. During forming, in the blank 201, the total width Wi of the inner excess portion 202i was set to 80 mm, and the total width Wo of the outer excess portion 202o was set to 80 mm. In the inner valley portion 105i, the height was set to 10 mm, and the width was set to 20 mm. In the outer valley portion 105o, the height was set to 10 mm, and the width was set to 20 mm.

In Example 2, only the inner valley portion 105i was formed during the process of forming the press-formed product 101, and the area including the inner valley portion 105i was finally cut off. During forming, the total width Wi of the inner excess portion 202i of the blank 201 was set to 80 mm. The height of the inner valley portion 105i was set to 10 mm, and the width was set to 20 mm.

In Example 3, only the outer valley portion 105o was formed during the process of forming the press-formed product 101, and the area including the outer valley portion 105o was finally cut off. During forming, the total width Wo of the outer excess portion 202o of the blank 201 was set to 80 mm. The height of the outer valley portion 105o was set to 10 mm, and the width was set to 20 mm.

In Example 4, both the inner valley portion 105i and the outer valley portion 105o were formed in the process of forming the press-formed product 101, and finally, the area including the inner valley portion 105i and the outer valley portion 105o was cut. During forming, in the blank 201, the total width Wi of the inner excess portion 202i was set to 80 mm, and the total width Wo of the outer excess portion 202o was set to 80 mm. In the inner valley portion 105i, the height was set to 2 mm and the width was set to 5 mm. In other words, the cross-sectional size of the inner valley portion 105i in Example 4 was smaller than that of the inner valley portion 105i in Example 1. In the outer valley portion 105o, the height was set to 2 mm and the width was set to 5 mm. In other words, the cross-sectional size of the outer valley portion 105o in Example 4 was smaller than that of the outer valley portion 105o in Example 1.

In Example 5, both the inner valley portion 105i and the outer valley portion 105o were formed in the process of forming the press-formed product 101, and finally, the area including the inner valley portion 105i and the outer valley portion 105o was cut. During forming, in the blank 201, the total width Wi of the inner excess portion 202i was set to 80 mm, and the total width Wo of the outer excess portion 202o was set to 80 mm. In the inner valley portion 105i, the height was 10 mm and the width was 8 mm. In other words, the width of the inner valley portion 105i in Example 5 was smaller than that of the inner valley portion 105i in Example 1. In the outer valley portion 105o, the height was 10 mm and the width was 8 mm. In other words, the width of the outer valley portion 105o in Example 5 was smaller than that of the outer valley portion 105o in Example 1.

In Example 6, only the inner valley portion 105i was formed during the process of forming the press-formed product 101, and the area including the inner valley portion 105i was finally cut off. During forming, the total width Wi of the inner excess portion 202i of the blank 201 was set to 80 mm. The height of the inner valley portion 105i was set to 10 mm, and the width was set to 8 mm. In other words, the width of the inner valley portion 105i in Example 6 was smaller than that of the inner valley portion 105i in Example 2.

In Example 7, only the outer valley portion 105o was formed during the process of forming the press-formed product 101, and the area including the outer valley portion 105o was finally cut off. During forming, the total width Wo of the outer excess portion 202o of the blank 201 was set to 80 mm. The height of the outer valley portion 105o was set to 10 mm, and the width was set to 8 mm. In other words, the width of the outer valley portion 105o in Example 7 was smaller than that of the outer valley portion 105o in Example 3.

In Example 8, both the inner valley portion 105i and the outer valley portion 105o were formed in the process of forming the press-formed product 101, and finally, the area including the inner valley portion 105i and the outer valley portion 105o was cut. During forming, in the blank 201, the total width Wi of the inner excess portion 202i was set to 80 mm, and the total width Wo of the outer excess portion 202o was set to 80 mm. In the inner valley portion 105i, the height was set to 20 mm and the width was set to 30 mm. In other words, the height of the inner valley portion 105i in Example 8 was greater than that of the inner valley portion 105i in Example 1. In the outer valley portion 105o, the height was set to 20 mm and the width was set to 30 mm. In other words, the height of the outer valley portion 105o in Example 8 was greater than that of the outer valley portion 105o in Example 1.

In Example 9, only the inner valley portion 105i was formed during the process of forming the press-formed product 101, and the area including the inner valley portion 105i was finally cut off. During forming, the total width Wi of the inner excess portion 202i of the blank 201 was set to 80 mm. The height of the inner valley portion 105i was set to 20 mm, and the width was set to 30 mm. In other words, the height of the inner valley portion 105i in Example 9 was greater than the inner valley portion 105i in Example 2.

In Example 10, only the outer valley portion 105o was formed during the process of forming the press-formed product 101, and the area including the outer valley portion 105o was finally cut off. During forming, the total width Wo of the outer excess portion 202o of the blank 201 was set to 80 mm. The height of the outer valley portion 105o was set to 20 mm, and the width was set to 30 mm. In other words, the height of the outer valley portion 105o in Example 10 was greater than the outer valley portion 105o in Example 3.

In Example 11, both the inner valley portion 105i and the outer valley portion 105o were formed in the process of forming the press-formed product 101, and finally the area including the inner valley portion 105i and the outer valley portion 105o was cut. During forming, in the blank 201, the total width Wi of the inner excess portion 202i was set to 80 mm, and the total width Wo of the outer excess portion 202o was set to 80 mm. In the inner valley portion 105i, the height was set to 5 mm and the width was set to 7.5 mm. In other words, the height of the inner valley portion 105i in Example 11 was smaller than the inner valley portion 105i in Example 1. In the outer valley portion 105o, the height was set to 5 mm and the width was set to 7.5 mm. In other words, the height of the outer valley portion 105o in Example 11 was smaller than the outer valley portion 105o in Example 1.

In Example 12, only the inner valley portion 105i was formed during the process of forming the press-formed product 101, and the area including the inner valley portion 105i was finally cut off. During forming, the total width Wi of the inner excess portion 202i of the blank 201 was set to 80 mm. The height of the inner valley portion 105i was set to 5 mm, and the width was set to 7.5 mm. In other words, the height of the inner valley portion 105i in Example 12 was smaller than the inner valley portion 105i in Example 2.

In Example 13, only the outer valley portion 105o was formed during the process of forming the press-formed product 101, and finally the area including the outer valley portion 105o was cut off. During forming, the total width Wo of the outer excess portion 202o of the blank 201 was 80 mm. The height of the outer valley portion 105o was 5 mm, and the width was 7.5 mm. In other words, the height of the outer valley portion 105o in Example 13 was smaller than the outer valley portion 105o in Example 3.

In the reference example, both the inner valley portion 105i and the outer valley portion 105o were formed in the process of forming the press-formed product 101. During forming, in the blank 201, the total width Wi of the inner excess portion 202i was 80 mm, and the total width Wo of the outer excess portion 202o was 80 mm. In the inner valley portion 105i, the height was 10 mm and the width was 20 mm. In the outer valley portion 105o, the height was 10 mm and the width was 20 mm. Unlike Example 1, the area including the inner valley portion 105i and the outer valley portion 105o was not ultimately cut.

The results in Table 1 show the following:

In Example 1, the twist angle was significantly smaller than in the comparative example, and the wall warp curvature was significantly smaller than in the comparative example. This shows that when both the inner valley portion 105i and the outer valley portion 105o are molded, twist and wall warp can be most effectively suppressed.

In Example 2, although not as much as in Example 1, the twist angle was smaller than in the comparative example, and the wall warp curvature was smaller than in the comparative example. This shows that when the inner valley portion 105i is formed, twisting and wall warping can be effectively suppressed.

In Example 3, the twist angle was smaller than in the comparative example, although not as large as in Example 1. The wall warp curvature in Example 3 was smaller than in the comparative example. This shows that when the outer valley portion 105o is formed, twist and wall warp can be effectively suppressed.

In Example 4, the twist angle was slightly smaller than in the comparative example. The wall warp curvature in Example 4 was slightly smaller than in the comparative example. This shows that when the inner valley portion 105i and the outer valley portion 105o to be molded are small in size, twisting and wall warping can be suppressed to a certain extent.

In Example 5, as in Example 1, the twist angle was significantly smaller than in the comparative example, and the wall warp curvature was significantly smaller than in the comparative example. This shows that if both the inner valley portion 105i and the outer valley portion 105o are formed and the width of each valley portion is 0.8 times or more its height, twisting and wall warping can be effectively suppressed.

In Example 6, the twist angle was smaller than in the comparative example, and the wall warp curvature was smaller than in the comparative example, although not as large as in Example 5. This shows that by forming the inner valley portion 105i and making the width of the valley portion 0.8 times or more its height, twisting and wall warping can be effectively suppressed.

In Example 7, the twist angle was smaller than in the comparative example, and the wall warp curvature was smaller than in the comparative example, although not as large as in Example 5. This shows that by forming the outer valley portion 105o and making the width of the valley portion 0.8 times or more its height, twisting and wall warping can be effectively suppressed.

In Example 8, the twist angle was significantly smaller than in the comparative example, and the wall warp curvature was significantly smaller than in the comparative example. In addition, since the twist angle and wall warp curvature were smaller than in Example 1, in which the valley height was lower than in Example 8, it was found that the higher the valley height, the more effective it was. This shows that when both the inner valley portion 105i and the outer valley portion 105o, each of which has a height of 20 mm, are molded, twist and wall warp can be most effectively suppressed.

In Example 9, the twist angle was smaller than in the comparative example, and the wall warp curvature was smaller than in the comparative example, although not as large as in Example 8. In addition, since the twist angle and wall warp curvature were smaller than in Example 2, in which the valley height was lower than in Example 9, it was found that the higher the valley height, the more effective it was. This shows that when an inner valley portion 105i with a height of 20 mm is formed, twisting and wall warping can be effectively suppressed.

In Example 10, the twist angle was smaller than in the comparative example, and the wall warp curvature was smaller than in the comparative example, although not as large as in Example 8. In addition, since the twist angle and wall warp curvature were smaller than in Example 3, which has a lower valley height compared to Example 10, it was found that the higher the valley height, the more effective it is. This shows that when an outer valley portion 105o with a height of 20 mm is formed, twisting and wall warping can be effectively suppressed.

In Example 11, the twist angle was smaller than in the comparative example, and the wall warp curvature was smaller than in the comparative example. In addition, the twist angle and wall warp curvature were larger than in Example 1, in which the valley height was higher than in Example 11. This shows that the higher the valley height, the more effective it is, but if the valley height is 5 mm or more, twisting and wall warping can be effectively suppressed.

In Example 12, the twist angle was smaller than in the comparative example, and the wall warp curvature was smaller than in the comparative example. In addition, the twist angle and wall warp curvature were larger than in Example 2, which has a higher valley height than Example 12. This shows that the higher the valley height, the more effective it is, but if the valley height is 5 mm or more, twisting and wall warping can be effectively suppressed.

In Example 13, the twist angle was smaller than in the comparative example, and the wall warp curvature was smaller than in the comparative example. In addition, the twist angle and wall warp curvature were larger than in Example 3, which has a higher valley height than Example 13. This shows that the higher the valley height, the more effective it is, but if the valley height is 5 mm or more, twisting and wall warping can be effectively suppressed.

In the reference example, the twist angle was equivalent to that of the comparative example. The wall warp curvature in the reference example was equivalent to that of the comparative example. In other words, unless the area including the inner valley portion 105i and the outer valley portion 105o was ultimately cut, twisting and wall warping could not be suppressed.

The above describes an embodiment of the present invention. However, the above-described embodiment is merely an example for implementing the present invention. Therefore, the present invention is not limited to the above-described embodiment, and the above-described embodiment can be modified as appropriate within the scope of the spirit of the present invention.

1 Press device 2: Bed 3: Slide 4: Lower punch 41: Top surface 42i: Inner side surface 42o: Outer side surface 43i: Inner bottom surface 43o: Outer bottom surface 5: Lower cushion 6i: Inner lower jig 61i: Inner lower blade 62i: Inner groove 6o: Outer lower jig 61o: Outer lower blade 62o: Outer groove 7: Upper pad 8: Upper die 84i: Inner upper blade 84o: Outer upper blade 85i: Inner convex ridge 85o: Outer convex ridge 101: Press-molded product 111: Curved portion 102: Top plate 103i: Inner vertical wall 103o: Outer vertical wall 104i: Inner flange 104o: Outer flange 105i: Inner valley portion 105o: Outer valley portion 201: Blank 202i: Inner excess portion 202o: Outer excess portion 203i: inner edge 203o: outer edge

Claims (15)

A bed and
A slide that can be raised and lowered relative to the bed;
a lower punch having an elongated top surface having a curved portion that curves within a plane, an inner side surface connected to the inner side edge of the curved portion among both side edges of the top surface, an outer side surface connected to the outer side edge of the curved portion among both side edges of the top surface, an inner bottom surface connected to a lower edge of the inner side surface, and an outer bottom surface connected to a lower edge of the outer side surface;
a lower cushion that supports the lower punch and is fixed to the bed;
an inner lower jig disposed adjacent to the inner bottom surface of the lower punch and fixed to the bed, the inner lower jig having an inner lower blade on an edge of an upper surface of the inner lower jig that is adjacent to the inner bottom surface of the lower punch, and an inner groove formed on the upper surface to follow the side edge on the inner side of the curve of the curved portion;
an upper pad disposed so as to face the top surface of the lower punch and supported by the slide via an elastic member;
a press device comprising: an upper die fixed to the slide, the upper die having an inner wall surface corresponding to the inner side surface of the lower punch, an outer wall surface corresponding to the outer side surface of the lower punch, an inner lower surface facing the inner bottom surface of the lower punch, an outer lower surface facing the outer bottom surface of the lower punch, and an inner recess adjacent to the inner lower surface, the upper die having an inner upper blade on an edge of the inner lower surface adjacent to the inner recess, and an inner convex rib protruding beyond the inner lower surface at a position on the bottom surface of the inner recess facing the inner groove. A bed and
A slide that can be raised and lowered relative to the bed;
a lower punch having an elongated top surface having a curved portion that curves within a plane, an inner side surface connected to the inner side edge of the curved portion among both side edges of the top surface, an outer side surface connected to the outer side edge of the curved portion among both side edges of the top surface, an inner bottom surface connected to a lower edge of the inner side surface, and an outer bottom surface connected to a lower edge of the outer side surface;
a lower cushion that supports the lower punch and is fixed to the bed;
an outer lower jig disposed adjacent to the outer bottom surface of the lower punch and fixed to the bed, the outer lower jig having an outer lower blade on an edge of an upper surface of the outer lower jig adjacent to the outer bottom surface of the lower punch, and an outer groove formed on the upper surface to follow the side edge on the outer side of the curved portion;
an upper pad disposed so as to face the top surface of the lower punch and supported by the slide via an elastic member;
a press device comprising: an upper die fixed to the slide, the upper die having an inner wall surface corresponding to the inner side surface of the lower punch, an outer wall surface corresponding to the outer side surface of the lower punch, an inner lower surface facing the inner bottom surface of the lower punch, an outer lower surface facing the outer bottom surface of the lower punch, and an outer recess adjacent to the outer lower surface, the upper die having an outer upper blade on an edge of the outer lower surface adjacent to the outer recess, and an outer convex ridge protruding beyond the outer lower surface at a position on the bottom surface of the outer recess facing the outer groove. The press device according to claim 1,
The press apparatus further includes an outer lower jig that is disposed adjacent to the outer bottom surface of the lower punch and is fixed to the bed, the outer lower jig having an outer lower blade on an edge of an upper surface of the outer lower jig that is adjacent to the outer bottom surface of the lower punch, and an outer groove formed on the upper surface to follow the side edge on the outer side of the curved portion,
The upper die further has an outer recess adjacent to the outer lower surface, an outer upper blade on an edge of the outer lower surface adjacent to the outer recess, and an outer convex ridge protruding beyond the outer lower surface at a position on a bottom surface of the outer recess facing the outer groove. The press device according to claim 1 or 3,
A press apparatus, wherein the inner convex rib protrudes from the inner lower surface by 5 mm or more. A press apparatus according to any one of claims 1, 3 and 4,
A press device, wherein the width of the inner ridge is 0.8 times or more the height of the inner ridge. A press apparatus according to any one of claims 1, 3, 4 and 5,
a pressing device, wherein the inner lower blade is inclined such that a center of a longitudinal range corresponding to the side edge on the inner side of the curved portion is lower than both ends of the range. The press device according to claim 2 or 3,
A press apparatus, wherein the outer convex rib protrudes from the outer lower surface by 5 mm or more. A press apparatus according to any one of claims 2, 3 and 7,
A press device, wherein the width of the outer ridge is 0.8 times or more the height of the outer ridge. A press apparatus according to any one of claims 2, 3, 7 and 8,
A press device, wherein the outer lower blade is inclined such that the center of a longitudinal range corresponding to the curved outer side edge of the curved portion is higher than both ends of the range. A method for manufacturing a press-formed product including an elongated top plate having a curved portion that curves in a plane, an inner vertical wall connected to one of both side edges of the top plate on the inner side of the curved portion, an outer vertical wall connected to one of both side edges of the top plate on the outer side of the curved portion, an inner flange connected to a lower edge of the inner vertical wall, and an outer flange connected to a lower edge of the outer vertical wall, using the press device according to any one of claims 1, 3, 4, 5, and 6,
The manufacturing method includes:
(a) preparing a blank made of a metal plate having a size exceeding an installation area of the inner protrusion of the upper die;
(b) placing the blank on the top surface of the lower punch;
(c) lowering the slide to clamp the blank between the upper pad and the top surface of the lower punch;
(d) further lowering the slide to press the blank with the upper die and the lower punch, and pressing the blank with the inner ridge and the inner groove;
(e) further lowering the slide and cutting the blank with the inner upper blade and the inner lower blade. A method for manufacturing a press-formed product including an elongated top plate having a curved portion that curves in a plane, an inner vertical wall connected to one of both side edges of the top plate on the inner side of the curved portion, an outer vertical wall connected to one of both side edges of the top plate on the outer side of the curved portion, an inner flange connected to a lower edge of the inner vertical wall, and an outer flange connected to a lower edge of the outer vertical wall, using the press device according to any one of claims 2, 3, 7, 8, and 9,
The manufacturing method includes:
(a) preparing a blank made of a metal plate having a size exceeding an installation area of the outer protrusion of the upper die;
(b) placing the blank on the top surface of the lower punch;
(c) lowering the slide to clamp the blank between the upper pad and the top surface of the lower punch;
(d) further lowering the slide to press the blank with the upper die and the lower punch, and pressing the blank with the outer ridge and the outer groove;
(e) further lowering the slide and cutting the blank with the outer upper blade and the outer lower blade. A method for manufacturing a press-formed product using a press apparatus according to claim 3 and any one of claims 4 to 9 that cite claim 3, the press apparatus comprising: an elongated top plate having a curved portion that curves in a plane; an inner vertical wall connected to the curved inner side edge of the curved portion among both side edges of the top plate; an outer vertical wall connected to the curved outer side edge of the curved portion among both side edges of the top plate; an inner flange connected to a lower edge of the inner vertical wall; and an outer flange connected to a lower edge of the outer vertical wall,
The manufacturing method includes:
(a) preparing a blank made of a metal plate having a size that exceeds an installation area of the inner convex strip of the upper die and exceeds an installation area of the outer convex strip of the upper die;
(b) placing the blank on the top surface of the lower punch;
(c) lowering the slide to clamp the blank between the upper pad and the top surface of the lower punch;
(d) further lowering the slide to press the blank with the upper die and the lower punch, while pressing the blank with the inner ridge and the inner groove, and pressing the blank with the outer ridge and the outer groove;
(e) further lowering the slide to cut the blank with the inner upper blade and the inner lower blade, and cutting the blank with the outer upper blade and the outer lower blade. A method for producing a press-molded product according to claim 10 or 12,
A manufacturing method for a press-molded product, wherein in the blank prepared in step (a), a first region corresponding to at least the longitudinal center of the installation area of the inner convex rib of the upper die extends beyond the installation area of the inner convex rib in the width direction , and regions located outside both longitudinal ends of the first region are cut out. A method for producing a press-molded product according to claim 11 or 12,
A manufacturing method for a press-molded product, wherein in the blank prepared in step (a), second regions corresponding to at least both longitudinal ends of the installation area of the outer convex rib of the upper die extend beyond the installation area of the outer convex rib in the width direction , and an area sandwiched between the second regions in the longitudinal direction is cut out. A method for producing a press-molded product according to claim 12,
A manufacturing method for a press-molded product, wherein in the blank prepared in step (a), a first region corresponding to at least the longitudinal center of the installation area of the inner convex rib of the upper die extends beyond the installation area of the inner convex rib in the width direction , and regions located outside from both longitudinal ends of the first region are cut out, and second regions corresponding to at least both longitudinal ends of the installation area of the outer convex rib of the upper die extend beyond the installation area of the outer convex rib in the width direction, and regions sandwiched between the second regions in the longitudinal direction are cut out.

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