JP7803378B2 - Manufacturing method for press-molded products - Google Patents

Description

The present invention relates to a method for manufacturing a press-formed product having at least a top plate portion, a vertical wall portion, and a ridge portion that is the connection portion between the top plate portion and the vertical wall portion.

While stricter automobile crash safety standards are leading to improvements in vehicle crash safety, recent carbon dioxide emission restrictions have also made it necessary to reduce the weight of vehicle bodies. Therefore, to achieve both crash safety performance and vehicle weight reduction, metal plates with even higher strength than before are being used in vehicle bodies. Recently, efforts have been made to use ultra-high-tensile steel plates of 1.5 GPa class or higher. However, high-strength metal plates generally have poor ductility, so when press-formed products are manufactured for vehicle body parts, cracks are likely to occur from the edges during the press-forming process.

Conventionally, methods have been used to prevent cracks in press-formed products. For example, Patent Document 1 discloses a method for preventing cracks from occurring at the connection between a wall portion continuing from a connecting edge and a flange portion continuing from the wall portion when press-forming a T-shaped part having a T-shaped top plate portion in which vertical and horizontal edges are connected by a connecting edge. Furthermore, Patent Document 2 discloses a method for preventing cracks from occurring during stretch flange forming of a press-formed product having a flat plate portion with a concave outer peripheral edge portion in which part of the outer peripheral edge is recessed inward, and a flange portion bent along the concave outer peripheral edge portion.

JP 2019-13952 A JP 2016-104492 A

The method disclosed in Patent Document 1 begins with a first forming step in which an intermediate part is formed, which has a convex portion formed on the vertical side of the connecting edge of the top plate, and a curved R portion formed by raising the bottom R portion connecting the wall portion continuing from the connecting edge to the flange portion. Then, in a second forming step, the convex portion and curved R portion of the intermediate part are crushed to form a T-shaped part of the target shape. This allows material to flow into the wall portion continuing from the connecting edge, preventing cracks from occurring at the connection between the wall portion and the flange portion.

The method disclosed in Patent Document 2 involves applying plastic deformation to a portion of a blank material that corresponds to the flat portion, and as the material is drawn into the plastically deformed portion, it is pulled to a portion that corresponds to the bent portion of the flange, adding excess material to the bent portion. The blank material with the added excess material is then bent to form a press-formed product with a flange. This is said to effectively suppress the occurrence of stretch flange cracking without reducing the formability of the bent portion of the flange of the press-formed product.

As such, the methods disclosed in Patent Documents 1 and 2 prevent cracks in press-formed products at locations that are subject to stretch flange deformation. However, for example, in press-formed products with a top plate that is generally T-shaped or L-shaped in top view and has horizontal and vertical sides, cracks may occur at the end of the ridge connecting the vertical wall and horizontal side near the tip of the horizontal side, unlike cracks that occur due to stretch flange deformation. However, the methods disclosed in Patent Documents 1 and 2 above were unable to prevent cracks at the end of the ridge connecting the vertical wall and horizontal side of press-formed products with such generally T-shaped or L-shaped top plate.

Furthermore, even in press molding of a press-formed product that has a top plate portion, a vertical wall portion that continues to the top plate portion via a ridge portion, and a vertical flange portion that continues to the vertical wall portion, it has been difficult to prevent cracks from occurring at the end of the ridge portion.

Furthermore, even in press molding of a press-molded product that includes a top plate portion and a vertical wall portion that continues to the top plate portion via a ridge portion, where the top plate portion or a portion thereof is curved in top view and the vertical wall portion continues to the inside of the curve in the top plate portion, it has been difficult to prevent cracks from occurring at the end of the ridge portion.

The present invention was made in consideration of the above-mentioned problems, and its purpose is to provide a method for manufacturing a press-formed product that has a top plate portion and a vertical wall portion that is continuous with the top plate portion via a ridge portion, while suppressing the occurrence of cracks during press forming.

In order to solve the above problems and achieve the objectives,
(1) The manufacturing method of a press-formed product of the present invention is a manufacturing method of a press-formed product having at least a top plate portion, a vertical wall portion, and a ridge portion that is the connecting portion between the top plate portion and the vertical wall portion, and includes a first forming process of press-forming a metal plate blank into an intermediate formed product having an intermediate top plate portion, an intermediate vertical wall portion, and an intermediate ridge portion that connects the intermediate top plate portion and the intermediate vertical wall portion, and having a convex portion that is higher than the reference height of the top plate surface at one or more locations on the intermediate top plate portion including the intermediate ridge portion, and a second forming process of press-forming the intermediate formed product into the press-formed product.

(2) The manufacturing method of a press-molded product according to the present invention is the invention (1) above, wherein the shape of the press-molded product is such that the top plate portion has a horizontal side portion, a vertical side portion, and a connecting R portion where the horizontal side portion and the vertical side portion are connected, and is approximately T-shaped or approximately L-shaped in a top view, and is provided with a ridge portion connecting to the top plate portion from the horizontal side portion of the top plate portion across the connecting R portion and the vertical side portion, a vertical wall portion continuing via the ridge portion from the horizontal side portion of the top plate portion across the connecting R portion and the vertical side portion, and a bottom flange portion continuing from the vertical wall portion, and in the first molding process, The plate portion has an intermediate horizontal side portion, an intermediate vertical side portion, and an intermediate connecting R portion connecting the intermediate horizontal side portion and the intermediate vertical side portion, and is generally T-shaped or L-shaped when viewed from above, and the height of the intermediate vertical side portion of the intermediate top plate portion is lower than the height of the vertical side portion in the target product shape.Furthermore, in the first forming process, the intermediate molded product is press-formed to have a convex portion higher than the height of the vertical side portion at the end of the intermediate horizontal side portion of the intermediate top plate portion including the intermediate ridge line portion of the intermediate molded product and/or at the intermediate connecting R portion of the intermediate top plate portion including the intermediate ridge line portion of the intermediate molded product.

(3) The manufacturing method for a press-formed product according to the present invention is the invention (2) above, in which, in the first forming step, the intermediate top plate portion, including the intermediate ridge line portion, is press-formed into an intermediate formed product having a convex portion whose height gradually increases toward the tip end of the intermediate horizontal side portion.

(4) The manufacturing method of the press-formed product according to the present invention is the invention (2) above, in which, in the first forming step, the intermediate formed product is press-formed to have a convex portion whose height is constant up to the tip end of the intermediate horizontal side portion of the intermediate top plate portion, including the intermediate ridge line portion.

(5) The manufacturing method of the press-formed product according to the present invention is the invention (2) above, in which, in the first forming step, the convex portion is formed in the intermediate connection R portion including the intermediate ridge line portion, and further, press-formed into the intermediate formed product having the intermediate horizontal side portion of the intermediate top plate portion whose height matches the height of the convex portion of the intermediate connection R portion.

(6) In the method for manufacturing a press-formed product according to the present invention, in the invention (1) above, in the first forming step, press-forming is performed to produce an intermediate formed product having a convex portion higher than the reference height of the top plate surface at one or more locations on the intermediate top plate portion, including the end of the intermediate ridge line portion.

(7) The method for manufacturing a press-formed product according to the present invention is the invention (6) above, wherein the press-formed product has a vertical flange portion continuous with the vertical wall portion, and in the first forming step, the intermediate top plate portion including the intermediate ridge portion is press-formed into an intermediate formed product having the convex portion at the end of the press-formed product on the vertical flange portion side.

(8) The method for manufacturing a press-formed product according to the present invention is the invention (6) above, wherein the press-formed product has a top plate portion or a portion of the top plate portion that is curved when viewed from above, and the vertical wall portion is continuous with the inside of the curvature of the top plate portion, and in the first forming step, the press-formed product is press-formed into an intermediate formed product having the convex portion on the intermediate top plate portion including the end of the intermediate ridge portion.

The present invention can suppress cracking during press forming when manufacturing press-formed products that have a top plate portion and a vertical wall portion that continues to the top plate portion via a ridge portion. In particular, for press-formed products that have a top plate portion that is generally T-shaped or L-shaped in top view, which has horizontal and vertical sides, cracking at the ridge portion near the tip of the horizontal side can be suppressed. Furthermore, for press-formed products that have a top plate portion, a vertical wall portion that continues to the top plate portion via a ridge portion, and a vertical flange portion that continues to the vertical wall portion, cracking at the end of the ridge portion near the vertical flange can be suppressed. Furthermore, for press-formed products that have a top plate portion and a vertical wall portion that continues to the top plate portion via a ridge portion, where the top plate portion or a portion of the top plate portion is curved in top view and the vertical wall portion continues to the inside of the curve of the top plate portion, cracking at the end of the ridge portion can be suppressed.

Figure 1 shows an example of a method for manufacturing a press-formed product according to embodiment 1 of the present invention, in which the ridge line at the tip of the horizontal side and the entire horizontal side of the top plate are made higher as convex portions, and illustrates a first forming process in which the press-formed product is press-formed into an intermediate shape in which the vertical wall height at the vertical side of the top plate is lower than the target shape, a second forming process in which the press-formed product has the vertical wall height of the target shape, and the reason why cracks at the end of the ridge line on the horizontal side of the press-formed product of the target shape can be suppressed ((a) first forming process, (b) second forming process). Figure 2 is an example of a method for manufacturing a press-formed product according to embodiment 1 of the present invention, in which the convex portion is only the connecting R portion, and illustrates a first forming process in which the press-formed product is press-formed into an intermediate shape in which the vertical wall height at the vertical side portion of the top plate is lower than the target shape, a second forming process in which the press-formed product has the vertical wall height of the target shape, and the reason why cracks at the end of the horizontal side ridge portion of the press-formed product in the target shape can be suppressed ((a) first forming process, (b) second forming process). FIG. 3 is a diagram showing an example of a press-formed product having a top plate portion that is substantially T-shaped in top view, which is an object to be manufactured in the present invention, in which the roundness of the tip of the horizontal side portion of the top plate is small. FIG. 4 is a diagram showing an example of a press-formed product having a top plate portion that is substantially T-shaped in top view, which is an object to be manufactured in the present invention, in which the tips of the horizontal sides of the top plate are largely rounded. FIG. 5 is a diagram showing an example of a press-formed product to be manufactured in the present invention, which has a top plate portion that is substantially L-shaped when viewed from above. 6A and 6B are diagrams illustrating a conventional manufacturing method for press-forming a press-formed product having a substantially T-shape in top view in two steps ((a) first forming step, (b) second forming step). FIG. 7 is a contour diagram showing the results of determining the sheet thickness change rate at the bottom dead center of the intermediate shape and the target shape of a generally T-shaped press-formed product press-formed in two conventional steps ((a) intermediate shape, (b) target shape). FIG. 8 is a diagram illustrating the locations where cracks occur in a press-formed product having a generally T-shaped top plate portion press-formed by a conventional manufacturing method, and the reasons for this. Figure 9 is a diagram showing an example of a punch used to press-form an intermediate-shaped press-formed product in which a convex portion is formed on the top plate portion in the first molding process in the manufacturing method for a press-formed product according to embodiment 1 of the present invention. It is a diagram showing a specific example of a punch that forms a ``convex portion'' of uniform height on the ridge portion that continues from the position where the horizontal side portion of the top plate extends, and further forms an intermediate-shaped product having a top plate horizontal side portion that has a height that matches the height of the convex portion. Figure 10 is a diagram showing an example of a punch used to press-form an intermediate-shaped press-formed product in which a convex portion is formed on the top plate portion in the first molding process in the manufacturing method for a press-formed product according to embodiment 1 of the present invention. It is a diagram showing a specific example of a punch that forms a ``convex portion'' on the ridge portion that continues from the position where the lateral side portion of the top plate extends, so that the height gradually increases toward the tip of the ridge portion, and further forms an intermediate-shaped product having a top plate lateral side portion that has a height that matches the height of the convex portion. Figure 11 is a diagram showing an example of a punch used in press-forming an intermediate-shaped press-formed product in which a convex portion is formed on the top plate portion in the first forming process in a manufacturing method for a press-formed product according to embodiment 1 of the present invention, and is a diagram showing a specific example of a punch that forms a convex portion on the joint R portion of the top plate portion. FIG. 12 is a contour diagram showing the results of determining the sheet thickness change rate at the bottom dead center of the intermediate shape and the target shape of a substantially T-shaped press-formed product press-formed by the manufacturing method of the press-formed product using the punch shown in FIG. 10( a) according to the first embodiment of the present invention ((a) intermediate shape, (b) target shape). 13A and 13B are contour diagrams showing the results of determining the sheet thickness change rate at the bottom dead center of the intermediate shape and the target shape of a generally T-shaped press-formed product press-formed in two conventional steps when the product target shape is as shown in FIG. 4 ((a) intermediate shape, (b) target shape). FIG. 14 is a contour diagram showing the results of determining the sheet thickness change rate at the bottom dead center of forming for each of the intermediate shape and the target shape of a substantially T-shaped press-formed product press-formed by the manufacturing method of the press-formed product using the punch (convex portion) shown in FIG. 11( a) according to the first embodiment of the present invention ((a) intermediate shape, (b) target shape). FIG. 15 is a contour diagram showing the results of determining the sheet thickness change rate at the bottom dead center of the intermediate shape and the target shape of a substantially T-shaped press-formed product press-formed by the method for manufacturing a press-formed product using the punch (protrusion portion + horizontal side portion height Up) shown in FIG. 11(b) according to the first embodiment of the present invention ((a) intermediate shape, (b) target shape). FIG. 16 shows the results of the plate thickness change rate obtained for the intermediate shape and the target shape of a press-formed product having a generally L-shaped top plate portion press-formed by a conventional method ((a) intermediate shape, (b) target shape). FIG. 17 is a diagram showing the results of the plate thickness change rate obtained for the intermediate shape and the target shape of a press-formed product having a substantially L-shaped top plate portion press-formed by the method according to the first embodiment of the present invention ((a) intermediate shape, (b) target shape). FIG. 18 is an explanatory diagram of a method for manufacturing a press-formed product according to the second embodiment of the present invention. FIG. 19 is an explanatory diagram of an intermediate punch used in a method for manufacturing a press-formed product according to the second embodiment of the present invention. FIG. 20 is an explanatory diagram of an intermediate molded product according to the second embodiment of the present invention. FIG. 21 is a diagram illustrating the sheet thickness reduction rate of a press-formed product formed according to the second embodiment of the present invention. FIG. 22 is an explanatory diagram of another aspect of the intermediate punch according to the second embodiment of the present invention. FIG. 23 is an explanatory diagram of a press-formed product having a target shape according to the second embodiment of the present invention. FIG. 24 is an explanatory diagram of a conventional method for press-forming the press-formed product shown in FIG. 23 in one step. FIG. 25 is an explanatory diagram of the sheet thickness reduction rate when press-forming is performed using the conventional method shown in FIG. FIG. 26 is an explanatory diagram of a method for manufacturing a press-formed product according to the third embodiment of the present invention. FIG. 27 is an explanatory diagram of an intermediate punch used in a method for manufacturing a press-formed product according to a third embodiment of the present invention. FIG. 28 is an explanatory diagram of an intermediate molded product according to the third embodiment of the present invention. FIG. 29 is a diagram illustrating the sheet thickness reduction rate of a press-formed product formed according to the third embodiment of the present invention. FIG. 30 is an explanatory diagram of a press-formed product having a target shape according to the third embodiment of the present invention. FIG. 31 is an explanatory diagram of a conventional method for press-forming the press-formed product shown in FIG. 30 in one step. FIG. 32 is an explanatory diagram of the sheet thickness reduction rate when press-forming is performed using the conventional method shown in FIG. FIG. 33 is an explanatory diagram illustrating the mechanism by which cracks occur in a press-formed product press-formed by the conventional method shown in FIG. FIG. 34 is a diagram illustrating the inclination angle of the tip end of the horizontal side portion in the press-formed product of the intermediate shape in Example 1. FIG. 35 is a diagram illustrating a height increment for uniformly increasing the height of the portion on the tip side of the horizontal side portion of the press-formed product in the intermediate shape in Example 1.

(Embodiment 1)
Before describing the method for manufacturing a press-formed product according to the first embodiment of the present invention, a press-formed product to which the present invention is applied and the occurrence of cracks in the press-formed product will be described below. Note that identical or similar components are designated by the same reference numerals, and redundant descriptions will be omitted.

<Press-molded products targeted by the present invention>
FIG. 3 shows a press-formed product 1 having a top plate portion 3, a vertical wall portion 5, and a bottom flange portion 7 as an example of a press-formed product to be manufactured in the present invention.

As shown in Figure 3, the top panel 3 has a horizontal side 3a and a vertical side 3b, and is generally T-shaped when viewed from above. Furthermore, the top panel 3 has an arc-shaped connecting curve 3c extending from the horizontal side 3a to the vertical side 3b.

As shown in Figure 3, the vertical wall portion 5 continues from the horizontal side portion 3a to the vertical side portion 3b of the top panel portion 3 via the ridge portion 9. The vertical wall portion 5 has a horizontal side vertical wall portion 5a that continues from the horizontal side portion 3a via the horizontal side ridge portion 9a, and a vertical side vertical wall portion 5b that continues from the vertical side portion 3b via the vertical side ridge portion 9b. Furthermore, the vertical wall portion 5 has a connecting R side vertical wall portion 5c that continues from the connecting R portion 3c via the connecting R side ridge portion 9c and connects the horizontal side vertical wall portion 5a and the vertical side vertical wall portion 5b.

As shown in Figure 3, the bottom flange 7 is continuous with the vertical wall 5, and is formed continuously with the horizontal side vertical wall 5a, the vertical side vertical wall 5b, and the connecting R side vertical wall 5c.

Conventionally, such press-formed products 1 have been press-formed in two steps, a first forming step and a second forming step, as shown in Figure 6.

First, in the first forming step, as shown in Figure 6(a), a blank 11, which is a metal plate, is sandwiched between a punch 13 and a pad 15, and the die 17 is moved relatively toward the punch 13 to press-form an intermediate-shaped press-formed product 21 (see Figure 6(b)) whose vertical wall height is lower than the target shape. Here, the top plate portion 23 of the intermediate-shaped press-formed product 21 is press-formed into the same shape as the top plate portion 3 of the target-shaped press-formed product 1 (see Figure 3).

Then, in the subsequent second forming process, as shown in Figure 6(b), the top plate portion 23 of the intermediate-shaped press-formed product 21 is sandwiched between a punch 31 and a pad 33, and the die 35 is moved relatively toward the punch 31 to press-form a press-formed product 1 of the target shape, with a vertical wall height higher than that of the intermediate shape.

However, when the intermediate-shaped press-formed product 21 is press-formed into the target-shaped press-formed product 1 (Figure 3) in the second forming step, cracks may occur at the end of the horizontal edge ridge 9a connecting the horizontal edge 3a and the horizontal edge vertical wall 5a. The end of the horizontal edge ridge 9a refers to the portion of the horizontal edge ridge 9a toward the tip of the horizontal edge 3a in the direction in which the horizontal edge 3a extends.

In order to determine the cause of cracks occurring at the ends of the horizontal edge ridges 9a of the press-formed product 1 having such a roughly T-shaped top plate 3, a finite element method (FEM) analysis was performed on each of the two steps used to press-form the press-formed product 1 into the target shape, as shown in Figure 6.

Figure 7 shows the thickness change rate at the bottom dead center of the intermediate-shape press-formed product 21 and the target-shape press-formed product 1, determined by FEM analysis, for the first and second forming processes. The results shown in Figure 7 are for a case where a steel plate with a thickness of 1.2 mm and a tensile strength of 780 MPa was used as the blank 11, the vertical wall height of the intermediate-shape press-formed product 21 was 20 mm, and the vertical wall height of the target-shape press-formed product 1 was 30 mm. The thickness change rate shown in Figure 7 is the difference between the thickness of each portion of the intermediate-shape press-formed product 21 or press-formed product 1 and the thickness of the metal plate that is the blank 11, divided by the thickness of the blank 11. In this specification and drawings, a positive value for the thickness change rate is referred to as a thickness increase rate, and a negative value for the thickness change rate is referred to as a thickness decrease rate. The larger the absolute value of the thickness decrease rate, the more likely cracks will occur.

Figure 7(a) shows the thickness change rate at the bottom dead center of the intermediate-shaped press-formed product 21 press-formed in the first forming process shown in Figure 6(a). The thickness reduction rate at the end of the horizontal edge ridge 29a was -4.7%. Figure 7(b) shows the thickness change rate at the bottom dead center of the press-formed product 1 of the target shape press-formed in the second forming process shown in Figure 6(b). The thickness reduction rate at the end of the horizontal edge ridge 9a was -16.9%. As such, the absolute value of the thickness reduction rate at the end of the horizontal edge ridge 9a of the target shape is large. As a result, the thickness at the end of the horizontal edge ridge 9a is significantly reduced in the second forming process, making it more susceptible to cracking.

The reason for the large thickness reduction rate at the end of the horizontal edge ridge 9a of the press-formed product 1 of the target shape is explained with reference to Figure 8. Conventionally, as described above, in the first forming process, an intermediate-shaped press-formed product 21 with a vertical wall height lower than the target shape is press-formed, and then in the second forming process, the intermediate-shaped press-formed product 21 is press-formed into a press-formed product 1 with the vertical wall height of the target shape. In this case, in the second forming process, as shown in Figure 8, the horizontal edge ridge 29a is stretched, and a large tensile force is applied to the horizontal edge ridge 9a. As a result, this large tensile force increases the absolute value of the thickness reduction rate at the end of the horizontal edge ridge 9a of the target shape, as shown in Figure 7(b) described above, leading to the occurrence of cracks.

Therefore, the inventors conducted extensive research into methods for reducing the tensile force acting on the horizontal edge ridge 9a during the two-step press-forming of a target-shaped press-formed product 1. As a result, as shown in Figures 1 and 2, the inventors came up with the idea of forming the vertical wall height of the tip of the horizontal edge 23a of the top plate 23 of the intermediate-shaped press-formed product 21 (Figure 1) higher than the vertical wall height of the vertical edge 23b, and forming an upwardly raised convex portion 23d in the region extending from the horizontal edge 23a to the vertical edge 23b, including the connecting curve 23c, of the top plate 23 of the intermediate-shaped press-formed product 21 (Figure 2). As shown in Figure 2, when the upwardly raised convex portion 23d is crushed in the subsequent second forming step to form the connecting curve 3c that will become the target-shaped top plate, material flows from the upwardly raised convex portion 23d toward the tip of the horizontal edge ridge 9a. It was discovered that this reduces the tensile force acting on the horizontal edge ridge portion 9a and prevents cracks from forming at the end of the horizontal edge ridge portion 9a. The present invention was made based on the results of the above study, and its specific configuration is as follows.

<Method of manufacturing press-molded products>
The manufacturing method of the press-formed product according to the first embodiment involves press-forming the press-formed product 1 shown in FIG. 2 described above into an intermediate shape in which the vertical wall height of the vertical side portion of the top plate is lower than the target shape in a first forming process, and then press-forming it to the vertical wall height of the target shape in a subsequent second forming process.

In the manufacturing method of the press-formed product according to the first embodiment, in the first forming step, as shown in FIG. 1(a), the vertical wall height of the horizontal side portion 23a of the top plate portion 23 of the intermediate-shaped press-formed product 21 is formed to include a "protrusion" that is higher than the vertical wall height of the vertical side portion. Note that in the first forming step, the intermediate-shaped press-formed product 21 may be press-formed using a punch 71 that includes a region that is higher in the portion forming the horizontal side portion 23a of the top plate portion 23 than the portion forming the vertical side portion 23b, as illustrated in FIGS. 9 and 10. Alternatively, in the manufacturing method of the press-formed product according to the first embodiment, in the first forming step, as shown in FIG. 2(a), a protrusion 23d that is higher than the surrounding height (the reference height of the top plate surface) is formed in the region from the horizontal side portion 23a to the vertical side portion 23b, including the connecting R portion 23c. Here, the protrusion 23d is formed to be higher than the vertical side portion 23b of the intermediate-shaped top plate portion 23. In the first forming step, an intermediate-shaped press-formed product 21 can be formed by press-forming using a punch 71 having a convex portion forming portion 73d formed in the region from the horizontal side forming portion 73a, including the connecting R forming portion 73c of the top plate forming portion 73, to the vertical side forming portion 73b, as shown in Figure 11(a). In the first forming step, an intermediate-shaped press-formed product 21 can also be formed by press-forming using a punch 61 having a convex portion forming portion formed in the region from the convex portion forming portion 63d of the top plate forming portion to the horizontal side tip forming portion 63a1, as shown in Figure 11(b).

Furthermore, in the manufacturing method of the press-formed product according to embodiment 1, in the subsequent second forming step, the intermediate formed product formed in the first forming step is press-formed into the top plate portion 3 having the target shape.

<Reason for preventing cracks>
The reason why the method for manufacturing a press-formed product according to the first embodiment can suppress the occurrence of cracks at the end of the horizontal edge ridge portion 9a of the press-formed product 1 having a target shape will be described with reference to FIGS. 1 and 2. FIG.

In embodiment 1, as described above, in the first forming step, press-molding is performed to form an intermediate-shaped press-formed product 21 including a "protrusion" in which the horizontal side 23a of the intermediate-shaped top plate portion 23 is higher than the vertical side 23b ( FIG. 1(a) ). Alternatively, in the first forming step, press-molding is performed to form an intermediate-shaped press-formed product 21 in which a protrusion 23d is formed on the top plate portion 23 that is higher than the vertical side 23b of the intermediate-shaped top plate portion 23 ( FIG. 2(a) ).

When this intermediate-shape press-formed product 21 is press-formed into the target-shape press-formed product 1 in the second forming process, material flows from the higher parts of the intermediate shape to the horizontal edge ridges 9a, as shown in Figures 1(b) and 2(b). This reduces the tensile force acting on the horizontal edge ridges 9a in the target-shape press-formed product 1. As a result, the reduction in plate thickness at the ends of the horizontal edge ridges 9a is reduced, preventing cracks.

<Mode of Horizontal Side Portion>
In the above description, the first forming step, as shown in FIG. 1( a), involves uniformly raising the tip end portion of the horizontal edge portion 23a of the intermediate press-formed product 21 in the direction of extension. Examples of this process are shown in FIGS. 9( a) and 9(b). FIG. 9( a) is a schematic diagram of a punch (die) that uniformly raises the tip end portion of the horizontal edge portion 73a relative to the boundary line between the region where the vertical edge portion 73b of the top plate forming portion 73 extends toward the horizontal edge portion 73a and the horizontal edge portion 73a. FIG. 9( b) is a schematic diagram of a punch (die) that uniformly raises the region from the boundary line between the region where the vertical edge portion 73b of the top plate forming portion 73 extends toward the horizontal edge portion 73a and the horizontal edge portion 73a to the tip. Thus, the range in which the tip end portion of the horizontal edge portion 73a is uniformly raised is not particularly limited. However, from the viewpoint of suppressing wrinkles in the vicinity of the connecting R portion 3c in the second forming step, it is preferable to make the tip end portion of the intermediate horizontal edge forming portion 73a higher than the boundary line with the region where the vertical edge forming portion 73b is extended. Therefore, only the tip end portion of the horizontal edge forming portion 73a may be made uniformly higher than that shown in Figure 9(a) (not shown).

Furthermore, when the tip end portion of the horizontal edge portion 23a is uniformly elevated in the first forming step, the increment in height of the tip end portion is preferably 0.05 or more and 0.5 or less in ratio to the vertical wall height of the horizontal edge side vertical wall portion 25a of the intermediate shape press-formed product 21. If the increment in height of the tip end portion of the horizontal edge portion 23a is less than 0.05, the height of the horizontal edge portion 23a (see Figure 8) will be insufficient, resulting in only a slight decrease in the absolute value of the thickness reduction rate at the end of the horizontal edge side ridge portion 9a of the target shape, and it may be difficult to prevent cracks. Furthermore, if the increment in height of the tip end portion of the horizontal edge portion 23a is greater than 0.5, the vertical wall height at the tip end of the horizontal edge portion 23a will be too high in the first forming step, causing the horizontal edge side ridge portion 29a to be elongated, increasing the absolute value of the thickness reduction rate and potentially increasing the risk of cracks occurring in the first forming step.

Furthermore, in the first forming step, the present invention may also be configured such that the intermediate-shaped horizontal edge forming portion 73a is gradually inclined in the extension direction so as to become higher toward the tip end, as illustrated in Figure 10.

Figure 12 shows the results of calculating the plate thickness change rate for the intermediate-shaped press-formed product 21 and the target-shaped press-formed product 1, which were produced in the first forming process with horizontal side portions 23a that are gradually inclined toward the tip. The results shown in Figure 12 were obtained when a steel plate with a plate thickness of 1.2 mm and a tensile strength of 780 MPa was used as the blank 11. Furthermore, the vertical wall height of the intermediate shape was 20 mm, the vertical wall height of the target shape was 30 mm, the inclination angle of the tip side of the horizontal side portions 23a in the intermediate-shaped press-formed product 21 was 15.4°, and the height increment at the tip was 5.5 mm.

As shown in Figure 12(a), in the intermediate-shape press-formed product 21, the thickness reduction rate at the tip of the horizontal edge ridge portion 29a was -9.1%, an absolute value that was greater than the -4.7% achieved with the conventional method shown in Figure 7(a) described above. However, as shown in Figure 12(b), in the target-shape press-formed product 1, the thickness reduction rate at the tip of the horizontal edge ridge portion 9a was -11.9%, an absolute value that was less than the -16.9% achieved with the conventional method shown in Figure 7(b) described above. These results demonstrate that even when the tip of the horizontal edge portion 23a is inclined in the intermediate-shape press-formed product 21, cracks can be suppressed at the end of the horizontal edge ridge portion 9a of the target-shape press-formed product 1.

Specific examples of inclining the tip end of the horizontal side portion 23a of the intermediate shape are shown in Figures 10(a) and 10(b). In Figure 10(a), the vertical side molding portion 73b of the top plate molding portion 73 is inclined from the boundary line between the region where the vertical side molding portion 73b extends toward the horizontal side molding portion 73a and the horizontal side molding portion 73a as the starting point, and gradually becomes higher toward the tip in the direction in which the horizontal side molding portion 73a extends. In Figure 10(b), the vertical side molding portion 73b is inclined from the boundary line between the region where the vertical side molding portion 73b extends toward the horizontal side molding portion 73a and the extended region of the vertical side molding portion 73b as the starting point, and gradually becomes higher toward the tip in the direction in which the horizontal side molding portion 73a extends.

In this way, there is no particular limitation on the starting position for tilting the tip end portion of the horizontal edge molding portion 73a, and the tilt may be started from the tip end side of the boundary line between the extended region of the vertical edge molding portion 73b and the horizontal edge molding portion 73a (not shown).

Furthermore, as shown in Figures 10(a) and 10(b), when tilting the tip side of the horizontal edge forming portion 73a in the intermediate shape press-formed product 21, the tilt angle based on the horizontal edge portion 3a of the target shape is preferably 3 degrees or more and 25 degrees or less.

If the inclination angle is less than 3 degrees, the absolute value of the thickness reduction rate of the horizontal edge ridge portion 9a in the press-formed product 1 of the target shape will only decrease slightly, and it may be difficult to prevent cracks. Furthermore, if the inclination angle is greater than 25 degrees, the horizontal edge ridge portion 29a between the horizontal edge portion 23a and the horizontal edge vertical wall portion 25a will be stretched in the first forming step (see Figure 12(a)), increasing the absolute value of the thickness reduction rate and potentially increasing the risk of cracks occurring in the first forming step.

Note that Figures 9(a) and 9(b) and Figures 10(a) and 10(b) illustrate specific shapes of the punch (die) that forms the horizontal side portion 23a of the intermediate-shaped press-formed product 21, but the present invention is not limited to these shapes. Any shape other than the horizontal side forming portion 73a shown in Figures 9 and 10 may be used as long as the punch (die) forms the height of the tip end of the horizontal side portion of the top plate portion of the intermediate shape so that it is higher than the vertical side portion of the top plate portion of the intermediate shape.

For example, in the first molding process, the height of the region of the horizontal side of the intermediate shape that is an extension of the vertical side may be made higher than the height of the vertical side of the intermediate shape.

The above description has been directed to a press-formed product 1 having a top plate portion 3 that is approximately T-shaped when viewed from above. However, the present invention may also be directed to a press-formed product 41 that includes a top plate portion 43 that is approximately L-shaped when viewed from above and has a horizontal side portion 43a and a vertical side portion 43b, a vertical wall portion 45, and a bottom flange portion 47, as shown in Figure 5.

Press-formed products 41 having a generally L-shaped top plate portion 43 have also been conventionally manufactured by press-forming them into an intermediate shape with a low vertical wall height in the first forming process, as shown in FIG. 16, and then press-forming them to the target vertical wall height in the second forming process. Therefore, similar to the press-formed product 1 having a generally T-shaped top plate portion 3, the horizontal side vertical wall portion 55a of the intermediate-shaped press-formed product 51 in FIG. 16(a) is stretched in the vertical wall height direction in the second forming process in FIG. 16(b). This causes a large tensile force to act on the horizontal side vertical wall portion 45a and horizontal side ridge portion 49a of the target shape. As a result, this large tensile force increases the absolute value of the thickness reduction rate at the end of the horizontal side ridge portion 49a (17.7%), leading to cracking.

As shown in Figure 17(a), in the first forming process, the tip end portion of the horizontal side portion 53a of the top plate is raised so that it is higher than the vertical side portion. In the subsequent second forming process, the tip end portion of the horizontal side portion 53a of the intermediate shape is adjusted to the height of the target shape.

As a result, just as in the case of manufacturing the press-formed product 1 having the aforementioned approximately T-shaped top plate portion 3, the absolute value of the plate thickness reduction rate at the end of the horizontal edge ridge portion 49a of the target shape can be reduced (-12.6%), thereby suppressing cracking.

In the intermediate-shaped press-formed product 51 shown in Figure 17(a), the height of the tip end portion of the horizontal side portion 53a of the top plate portion is uniformly higher than the tip end portion of the vertical side portion 53b of the top plate portion. However, even when manufacturing a generally L-shaped press-formed product 41, the tip end portion of the horizontal side portion 53a of the intermediate shape may be inclined so that the height gradually increases toward the tip in the direction in which the horizontal side portion 53a connects to the vertical wall portion and extends.

Next, we conducted FEM analysis of each process of press-forming the press-formed product 1 into the target shape through the first and second forming processes to verify that intermediate forming using the punch shape shown in Figure 11 reduces the reduction in plate thickness at the end of the horizontal edge ridge portion 9a.

Figure 14 shows the results of FEM analysis of the first and second forming processes of embodiment 1 to determine the sheet thickness change rate at the bottom dead center of forming for the intermediate-shape press-formed product 21 and the target-shape press-formed product 1. Note that the results shown in Figure 14 are for a case where a 780 MPa-class steel plate is used as the blank 11, the vertical wall height of the intermediate-shape press-formed product 21 is 20 mm, and the vertical wall height of the target-shape press-formed product 1 is 30 mm. The sheet thickness change rate is the difference between the sheet thickness at each location of the press-formed product 1 or intermediate-shape press-formed product 21 and the sheet thickness of the metal sheet that is the blank 11, divided by the sheet thickness of the blank 11.

As shown in Figure 14(a), the thickness reduction rate at the end of the horizontal edge ridge 29a of the intermediate-shaped press-formed product 21 was -1.8%. This thickness reduction rate is slightly higher in absolute value than the thickness reduction rate of the intermediate-shaped press-formed product 21 press-formed using the conventional method (-1.2%, see Figure 13(a)).

On the other hand, the thickness reduction rate for the press-formed product 1 of the target shape press-formed in the second forming process shown in Figure 14(b) was -8.1%. This value is a smaller absolute value than the thickness reduction rate at the end of the horizontal edge ridge portion 9a of the press-formed product 1 press-formed using the conventional method (= -11.0%, see Figure 13(b)). As a result, it can be seen that cracks at the end of the horizontal edge ridge portion 9a of the press-formed product 1 of the target shape can be suppressed.

As described above, in the manufacturing method for a press-formed product according to embodiment 1, in the second forming step, the convex portion 23d is crushed to form the top plate portion 3 in the target shape. This reduces the tensile force acting on the horizontal edge ridge portion 9a that continues from the horizontal edge portion 3a of the top plate portion 3 in the target shape, thereby suppressing cracks at the end of the horizontal edge ridge portion 9a.

The height increment of the convex portion 23d formed on the intermediate-shaped top plate portion 23 in the first molding process (the height to the apex of the convex portion 23d when the vertical side portion 23b of the intermediate-shaped top plate portion 23 is used as the reference) should be 5% to 50% of the width of the horizontal-side vertical wall portion 25a.

If the height increase of the convex portion 23d is less than 5%, there will be insufficient material flow to the horizontal edge ridge portion 9a when the convex portion 23d is crushed in the second molding process, and cracks may not be sufficiently suppressed. Furthermore, if the height increase of the convex portion 23d exceeds 50%, there will be excessive material flow to the horizontal edge ridge portion 9a when the convex portion 23d is crushed in the second molding process, and while cracks may be suppressed, excess material may cause wrinkles, which may be a problem.

The present invention may be applied to protrusions of other shapes than the protrusion 23d shown in Figure 2(a), as long as the protrusions are formed at the connecting curves that connect the horizontal and vertical sides of the intermediate-shaped top panel.

In another aspect of embodiment 1, the first forming step may press-form an intermediate-shaped press-formed product 21 as illustrated in FIG. 15(a). Here, the intermediate-shaped press-formed product 21 has a convex portion 23d formed on the top plate portion 23, and the tip portion 23a1 of the horizontal side portion 23a is higher than the vertical side portion 23b of the intermediate-shaped top plate portion 23. In this case, the first forming step may use, for example, a punch 61 having a convex portion forming portion 63d and a horizontal side tip forming portion 63a1 that forms the intermediate-shaped portion 23a1 uniformly higher than the vertical side portion 23b, as shown in FIG. 11(b). Then, in the subsequent second forming step, the convex portion 23d is crushed, and the intermediate-shaped portion 23a1 is adjusted to the height of the target shape.

Figure 15(a) is a diagram showing the results of FEM analysis of the sheet thickness change rate at the bottom dead center of forming of an intermediate-shaped press-formed product 51 according to another aspect of embodiment 1. Figure 15(b) is a diagram showing the results of FEM analysis of the sheet thickness change rate at the bottom dead center of forming of a target-shaped press-formed product 1 according to another aspect of embodiment 1. Note that the results shown in Figure 15 are for a case where a 780 MPa-class steel plate is used as the blank 11, the vertical wall height of the intermediate-shaped press-formed product 51 is 20 mm, and the vertical wall height of the target-shaped press-formed product 1 is 30 mm. Furthermore, the sheet thickness change rate shown in Figure 15 is the value obtained by dividing the difference between the sheet thickness at each portion of the intermediate-shaped press-formed product 51 or press-formed product 1 and the sheet thickness of the metal sheet that is the blank 11 by the sheet thickness of the blank 11.

As shown in Figure 15(a), the thickness reduction rate at the end of the horizontal edge ridge portion 29a of the intermediate-shaped press-formed product 51 was -2.5%. The absolute value of this thickness reduction rate is greater than the thickness reduction rate (-1.2%) of the intermediate-shaped press-formed product 51 press-formed using the conventional method (see Figure 13(a)).

On the other hand, when the intermediate-shaped press-formed product 51 shown in Figure 15(a) was press-formed into the target-shaped press-formed product 1 in the second forming process, the thickness reduction rate at the end of the horizontal edge ridge 9a was -4.7%, as shown in Figure 15(b). This value is significantly smaller in absolute value than the thickness reduction rate obtained using conventional methods (-11.0%, see Figure 13(b)). Furthermore, the absolute value is smaller than the thickness reduction rate obtained when only the convex portion 23d was formed (-8.1%, Figure 14(b)). Therefore, by forming the convex portion 23d on the intermediate-shaped press-formed product 51 in the first forming process and raising the tip portion 23a1 of the horizontal edge 23a, the thickness reduction at the end of the horizontal edge ridge 9a can be further suppressed, which is preferable.

When press-forming the intermediate-shaped press-formed product 21, if the portion 23a1 at the tip of the horizontal edge portion 23a is made taller, it is preferable that the height increase be equal to or less than the height increase of the convex portion 23d. By making the convex portion 23d taller than the portion 23a1, the convex portion 23d can be crushed during the press-forming process into the target shape, causing material to flow toward the horizontal edge portion 9a.

In addition, the intermediate-shaped press-formed product 21 shown in Figure 15 has the vertical side 23b higher from the extended area side of the vertical side 23b than the boundary line between the area extended toward the horizontal side 23a and the horizontal side 23a, and the portion 23a1 from the boundary line to the tip of the horizontal side 23a is uniformly higher.

However, in the present invention, other than making the convex portion 23d higher than the portion 23a1, there are no particular limitations on the form or extent to which the portion at the tip of the horizontal edge portion of the intermediate-shaped press-formed product press-formed in the first forming step is raised.

Furthermore, the present invention may also be a press-formed product 41 that includes a top plate portion 43 that is generally L-shaped in top view and has a horizontal side portion 43a and a vertical side portion 43b, a vertical wall portion 45, and a bottom flange portion 47, as shown as an example in Figures 5 and 16(b).

In the case of a press-formed product 41 having a generally L-shaped top plate portion 43, cracks were likely to occur at the end of the horizontal edge ridge portion 49a when the product was press-formed into an intermediate shape with a low vertical wall height in the first forming process and then press-formed to the target vertical wall height in the subsequent second forming process.

In this invention, as with the aforementioned approximately T-shaped press-formed product 1, in the first forming process, a convex portion is formed at the connecting R portion connecting the horizontal and vertical sides of the top plate portion, the convex portion being higher than the height of the vertical side portion 53b of the intermediate-shaped top plate portion 53 (the reference height of the top plate surface). Then, in the subsequent second forming process, the convex portion is crushed to form the top plate portion in the target shape.

As a result, even when manufacturing a press-formed product 41 having a generally L-shaped top plate portion 43, it is possible to minimize the reduction in plate thickness at the end of the horizontal edge ridge portion 49a of the target shape and suppress cracking. Furthermore, in the first forming process, a convex portion may be formed on the top plate portion of the intermediate shape, and the portion on the tip side of the horizontal edge portion may be made higher than the vertical edge portion of the top plate portion of the intermediate shape.

The manufacturing method for a press-formed product according to this embodiment 1 can suppress cracking at the end of the horizontal edge ridge portion 9a of the press-formed product 1 having the target shape, even when high-strength steel plate is used. Therefore, the press-formed product 1 manufactured using high-tensile steel plate according to the manufacturing method for a press-formed product according to embodiment 1 can be manufactured as a vehicle body part.

(Embodiment 2)
The target shape of the press-formed product targeted in embodiment 2 will be described with reference to Fig. 23. The press-formed product 101 includes a top plate portion 103, a top plate flange portion 105 extending from one longitudinal end of the top plate portion 103, and a vertical wall portion 109 continuing from the top plate portion 103 via a ridge portion 107. The press-formed product also includes a vertical flange portion 111 bent outward on one longitudinal end side of the vertical wall portion 109, and a horizontal flange portion 113 bent outward at the lower end of the vertical wall portion 109.

Using the press-formed product 101 as an example, we will explain how we arrived at the invention of embodiment 2. Figure 24 is an explanatory diagram of a conventional manufacturing method in which the press-formed product 101 shown in Figure 23 is press-formed in a single step.

The blank 115 used to form the press-formed product 101 shown in Figure 23 is made of a metal plate, and as shown in Figure 24, its overall shape is approximately rectangular, with a top plate flange equivalent portion 117 formed on one end and vertical flange equivalent portions 119 formed on both sides of the top plate flange equivalent portion 117.

The mold 121 used in the conventional method for manufacturing the press-formed product 101 includes a punch 123, a pad 125 that presses the blank 115, and a die 127 that cooperates with the punch 123 to form the top plate portion 103, vertical wall portion 109, horizontal flange portion 113, and vertical flange portion 111. The punch 123 includes a top plate forming surface portion 129 that primarily forms the top plate portion 103. It also includes a top plate horizontal edge forming surface portion 168 that forms the horizontal edges of the top plate forming surface portion 129, a punch-side vertical wall forming surface portion 131 that forms the vertical wall portion 109 continuous with the vertical edge, and a punch-side horizontal flange forming surface portion 133 that forms the flange portion continuous with the punch-side vertical wall forming surface portion 131. It also includes a punch-side vertical flange forming surface portion 135 that forms the vertical flange portion 111 continuous with the horizontal edge of the top plate forming surface portion 129.

The pad 125 has a shape corresponding to the top plate forming surface 129 of the punch 123. The die 127 consists of a pair of left and right die parts, and is equipped with a die-side vertical wall forming surface 137, a die-side horizontal flange forming surface 139, and a die-side vertical flange forming surface 141.

The conventional method for manufacturing the press-formed product 101 involves clamping the blank 115 between the pad 125 and punch 123, moving the die 127 relative to the punch 123, press-forming the top plate portion 103, vertical wall portion 109, and horizontal flange portion 113, and bending the vertical flange portion 111 laterally to form the target shape. Regarding this conventional method for manufacturing the press-formed product 101, press-forming analysis was performed using the finite element method (FEM) when using a metal plate with a tensile strength of 1.5 GPa, and the plate thickness reduction rate of the press-formed product 101 after forming was determined.

Figure 25 shows the thickness reduction rate at the bottom dead center of forming as a contour, with lighter colored areas indicating greater thickness reduction rates. In the following explanation, the thickness reduction rate is expressed as a value (ratio) obtained by dividing the difference between the thickness of the metal plate (blank 115) and the thickness of each portion after press forming by the thickness of the metal plate (blank 115). As the thickness reduction rate increases, cracks become more likely to occur. As shown in the enlarged partial view of Figure 25, the end of the ridge line portion 107 on the side where the vertical flange portion 111 is formed (hereinafter simply referred to as "end portion 142 of ridge line portion 107") has a thickness reduction rate of 8.9%, indicating that it has the largest thickness reduction rate and is most susceptible to cracks.

The reason for the large thickness reduction rate at the end 142 of the ridge line portion 107 will be explained with reference to Figure 25. The arrows in Figure 25 indicate the tensile forces generated during the forming process. When the vertical wall portion 109 is formed via the ridge line portion 107, a tensile force is applied to the plate surface of the ridge line portion 107 as indicated by arrow (i) in Figure 25. Furthermore, when the vertical flange portion 111 is bent laterally, an additional tensile force is applied to the end 142 of the ridge line portion 107 as indicated by arrow (ii). In this way, both the tensile force during the forming of the vertical wall portion 109 and the tensile force during the laterally bending of the vertical flange portion 111 act on the end 142 of the ridge line portion 107, resulting in a large thickness reduction rate and making it more susceptible to cracking.

Therefore, the inventors investigated methods for reducing the tensile force acting on the end 142 of the ridgeline portion 107. As a result, when press-forming the press-formed product 101 of the target shape shown in Figure 23, the press forming is performed in two steps, a first forming step and a second forming step. A convex portion higher than the surrounding height (the reference height of the top plate surface) is formed on the end of the ridgeline portion of the intermediate formed product formed in the first forming step, closer to the intermediate vertical flange portion. In the second forming step, the convex portion is crushed to the height of the target formed product. This method reduces the tensile force acting on the end 142 of the ridgeline portion 107, while preventing wrinkles from forming in the top plate portion 103 or vertical wall portion 109. The present invention is based on this finding. A method for manufacturing a press-formed product 101 according to embodiment 2 will be described with reference to Figure 18.

The manufacturing method of the press-formed product 101 according to the second embodiment includes a first forming step ( FIG. 18( a) ) and a second forming step ( FIG. 18( b) ). The first forming step is a step of press-forming an intermediate formed product 149 (see FIG. 20( a) ). The intermediate formed product 149 has an intermediate top plate portion 143, an intermediate vertical wall portion 145 connected to the intermediate top plate portion 143 via an intermediate ridge portion 144, and a convex portion 147 formed on the end portion 142 of the intermediate ridge portion 144 closer to the intermediate vertical flange portion 153, the convex portion 147 being higher than the surrounding height (the reference height of the top plate surface). The intermediate formed product 149 also has an intermediate horizontal flange portion 151 and an intermediate vertical flange portion 153. The second forming step is a step of press-forming the intermediate formed product 149 into the target shape of the press-formed product 101. Each step is described in detail below.

<First molding process>
18( a), the first forming step is a step of press-forming the blank 115 using an intermediate punch 155, an intermediate pad 157, and an intermediate die 159 to produce the intermediate formed product 149 shown in FIG. 20. The blank 115 is similar to that shown in FIG. 24. As shown in FIGS. 18 and 19, the intermediate punch 155 includes a T-shaped intermediate top plate forming surface 161 having vertical and horizontal sides in a plan view, a punch-side intermediate vertical wall forming surface 163 that forms the intermediate vertical wall portion 145, a punch-side intermediate horizontal flange forming surface 165 that forms the intermediate horizontal flange portion 151, and a punch-side intermediate vertical flange forming surface 167 that forms the intermediate vertical flange portion 153.

Convex portion forming portions 169 for forming the convex portions 147 are formed on both widthwise sides of the end of the intermediate top plate forming surface portion 161. In the intermediate punch 155 shown in Figure 19, the convex portion forming portions 169 extend toward the top plate flange portion 105 (see Figure 20), increasing the overall height of the intermediate top plate forming surface portion 161. The punch-side intermediate vertical wall forming surface portion 163 has a gentler inclination angle than the conventional punch-side vertical wall forming surface portion 131 shown in Figure 24. In addition, the angle between the punch-side intermediate horizontal flange forming surface portion 165 and the punch-side intermediate vertical wall forming surface portion 163 is set to the same angle as the angle between the vertical wall portion 109 of the target shape and the horizontal flange portion 113 of the target shape.

The intermediate pad 157 in Figure 18 has a shape corresponding to the intermediate top plate forming surface portion 161 of the intermediate punch 155. The intermediate die 159 has a die-side intermediate vertical wall forming surface portion 171 shaped to correspond to the punch-side intermediate vertical wall forming surface portion 163, and a die-side intermediate horizontal flange forming surface portion 173 shaped to correspond to the punch-side intermediate horizontal flange forming surface portion 165. It also has a die-side intermediate vertical flange forming surface portion 175 shaped to correspond to the punch-side intermediate vertical flange forming surface portion 167.

The intermediate formed product 149 shown in Figure 20(a) is manufactured using an intermediate punch 155, intermediate pad 157, and intermediate die 159. As described above, the intermediate formed product 149 has an intermediate top plate portion 143, an intermediate vertical wall portion 145, a top plate flange portion 105, an intermediate horizontal flange portion 151, and an intermediate vertical flange portion 153. In addition, a convex portion 147 is formed on the end portion 146 of the intermediate ridge portion 144 of the intermediate formed product 149.

Figure 20(b) shows the A-A cross section of the intermediate formed product 149 in Figure 20(a) in comparison with the press-formed product 1 (Figure 21) (two-dot chain line) of the target shape. As shown in Figure 20(b), a convex portion 147 is formed at the end of the ridge portion of the intermediate formed product 149, causing the end 146 of the intermediate ridge portion 144 to bulge. This makes the bending radius of the top plate portion 103 and the vertical wall portion 109 larger than the target shape, thereby reducing the tensile force when bending the top plate portion 103 and the vertical wall portion 109 in the first forming process. As shown in Figure 20(a), the thickness reduction rate at the end 146 of the intermediate ridge portion 144 is 2.8%, which is smaller than the 8.9% of the conventional press-formed product 101 shown in Figure 25.

<Second molding process>
The second forming step is a step of press-forming the intermediate formed product 149 into a target shape, that is, the press-formed product 101. The punch 123, pad 125, and die 127 used in the second forming step have the same shapes as the conventional punch 123, pad 125, and die 127 shown in FIG.

In the second forming process, the convex portion 147 at the end 146 of the intermediate ridge portion 144 shown in Figure 20 is crushed to form the target shape, causing material to flow toward the end 146 of the intermediate ridge portion 144, reducing tensile force and preventing cracking of the end 142 of the ridge portion 107 of the press-formed product 101, which has the target shape shown in Figure 23. Furthermore, because the convex portion 147 is added only to the end 146 of the intermediate ridge portion 144, not the entire area, no excess material flow occurs in the second forming process, and wrinkles do not form in the top plate portion 103 or vertical wall portion 109 of the press-formed product 101, which has the target shape.

Figure 21 shows a press-formed product 101 formed by the second forming process. As shown in Figure 21, the thickness reduction rate at the end 142 of the ridge line portion 107 in the press-formed product 101 formed by the second forming process after passing through the first forming process was 4.1%. As such, compared to the conventional thickness reduction rate at the end 142 of the ridge line portion 107 of 8.9% (see Figure 25) shown in Figure 25, it can be seen that the thickness reduction rate is smaller in the present invention, making it possible to prevent cracks.

The shape of the intermediate punch 155 in the first forming step is not limited to that shown in Figure 19, and may be, for example, that shown in Figures 22(a) and 22(b). In the one shown in Figure 22(a), the convex portion forming portions 169 are formed only on both widthwise sides of the end of the intermediate top plate forming surface portion 161, while in the one shown in Figure 22(b), the convex portion forming portions 169 extend onto the top plate side edge forming surface portion 168, but other areas of the side of the top plate side edge forming surface portion 168 are not elevated.

Furthermore, the press-formed product 101, which is the target shape of embodiment 2, has a vertical flange portion 111, but the press-formed product of the target shape of the present invention also includes those that do not have a vertical flange.

(Embodiment 3)
The target shape of the press-formed product targeted in embodiment 3 will be described with reference to Fig. 30. The press-formed product 177 has a top plate portion 179 having a curved portion in top view, and a vertical wall portion 183 that continues from a part of the inside of the curve of the top plate portion 179 via a ridge portion 181, and an end portion 185 of the ridge portion 181 has an R-shape.

Using press-molded product 177 as an example, we will explain how we arrived at the invention of embodiment 3. Figure 31 is an explanatory diagram of a conventional method for manufacturing press-molded product 177, in which press-molded product 177 shown in Figure 30 is press-molded in a single process.

The blank 187 used to form the press-formed product 177 is made of a metal plate, and as shown in Figure 31, the top plate equivalent portion 189 formed into the top plate portion 179 is curved in an arc. Furthermore, inside the curve of the top plate equivalent portion 189, vertical wall equivalent portions 191 are formed inward in the longitudinal direction from both ends of the top plate equivalent portion 189. Furthermore, the end portions 193 of the vertical wall equivalent portions 191 are formed in an R-shape.

The conventional method for manufacturing the press-formed product 177 involves clamping the blank 187 between the pad 199 and punch 197 of the mold 195, moving the die 201 relative to the punch 197, and press-forming the top plate portion 179 and vertical wall portion 183 into the target shape. Regarding this conventional method for manufacturing the press-formed product 177, a press-forming analysis was performed using the finite element method (FEM) when a metal plate with a tensile strength of 980 MPa was used for the blank 187, and the plate thickness reduction rate of the press-formed product 177 after forming was determined.

Figure 32 shows the thickness reduction rate at the bottom dead center of forming as a contour plot, with lighter colored areas indicating a larger thickness reduction rate. As shown in Figure 32, the end 185 of the ridge line 181 has a thickness reduction rate of 10.8%, which is the largest thickness reduction rate and indicates that cracks are most likely to occur.

The reason for the large thickness reduction rate at the end 185 of the ridge line portion 181 will be explained with reference to Figure 33. The arrows in Figure 33 indicate the tensile force generated during the forming process. When the vertical wall portion 183 is formed via the ridge line portion 181, a tensile force is applied to the plate surface of the ridge line portion 181 as indicated by arrow (iii) in Figure 33. Furthermore, as indicated by arrow (iv), a tensile force is generated at the end 185 of the ridge line portion as the vertical wall portion 183 is pulled inward. Furthermore, because the end 185 of the ridge line portion has a notch shape, as indicated by arrow (v), tensile force is concentrated and a large tensile force is applied, resulting in a large thickness reduction rate and making the plate more susceptible to cracking.

The inventors therefore investigated ways to reduce the tensile force acting on the edge 185 of the ridge line portion. As a result, they decided to perform press molding in two steps: a first molding step and a second molding step. In the first molding step, they impart a convex portion higher than the surrounding height (the reference height of the top plate surface) to the edge of the ridge line portion of the intermediate molded product, and in the second molding step, they crush the convex portion to the height of the target molded product. They found that this reduces the tensile force on the edge 185 of the ridge line portion 181 while preventing wrinkles from forming in the top plate portion 179 or vertical wall portion 183. The present invention is based on this finding, and a manufacturing method for a press-molded product 177 according to embodiment 3 will be described with reference to Figure 26.

The manufacturing method for the press-formed product 177 according to embodiment 3 includes a first forming step (FIG. 26(a)) and a second forming step (FIG. 26(b)). The first forming step is a step of press-forming an intermediate formed product 211 (see FIG. 28) having an intermediate top plate portion 203, an intermediate vertical wall portion 207 that is continuous with the intermediate top plate portion 203 via an intermediate ridge portion 205, and a convex portion 209 formed at the end portion 206 of the intermediate ridge portion 205 and that is higher than the surrounding height (the reference height of the top plate surface). The second forming step is a step of press-forming the intermediate formed product 211 into the press-formed product 177 (FIG. 29). Each step is described in detail below.

<First molding process>
In the first forming step, as shown in Fig. 26(a), a blank 187 is press-formed using an intermediate punch 213, an intermediate pad 215, and an intermediate die 217 to produce an intermediate formed product 211 shown in Fig. 28. The blank 187 is similar to that shown in Fig. 31. As shown in Fig. 26(a) and Fig. 27 which schematically shows the intermediate punch 213 of Fig. 26(a), the intermediate punch 213 has an intermediate top plate forming surface portion 219 and a punch-side intermediate vertical wall forming surface portion 221 which forms the intermediate ridge portion 205.

Punch-side convexity forming portions 223 for forming the convexity 209 are formed on both widthwise sides of the end of the intermediate top plate forming surface portion 219. The punches shown in Figures 26(a) and 27 are positioned so that the center of the punch-side convexity forming portion 223 overlaps with the end 206 of the intermediate ridge portion 205.

The intermediate pad 215 has a shape corresponding to the intermediate top plate forming surface 219 of the intermediate punch 213. The intermediate die 217 has a die-side intermediate vertical wall forming surface 225 shaped to correspond to the punch-side intermediate vertical wall forming surface 221, and a die-side convex portion forming portion 226 shaped to correspond to the punch-side convex portion forming portion 223.

Figure 28(b) shows the B-B cross section of Figure 28(a) in comparison with the cross section of the target press-formed product shape (two-dot chain line). As shown in Figure 28(b), a convex portion 209 is formed at the end of the ridge portion of the intermediate formed product 211, causing the end 206 of the intermediate ridge portion 205 to bulge. This makes the bending radius of the intermediate top plate portion 203 and the intermediate vertical wall portion 207 larger than the target shape, thereby reducing the tensile force required when bending the intermediate top plate portion 203 and the intermediate vertical wall portion 207 in the first forming process. As shown in Figure 28(a), the thickness reduction rate at the end 206 of the intermediate ridge portion 205 is 5.5%, which is smaller than the 10.8% reduction achieved for the conventional press-formed product 177 shown in Figure 32.

<Second molding process>
The second forming step is a step of press-forming the intermediate formed product 211 into a target shape, that is, a press-formed product 177. The punch 197, pad 199, and die 201 used in the second forming step have the same shapes as the conventional punch 197, pad 199, and die 201 shown in FIG.

In the second forming process, the convex portion 209 at the end 206 of the intermediate ridge portion 205 in Figure 28 is crushed to form the target shape, causing material to flow toward the end 206 of the intermediate ridge portion 205, reducing tensile force and preventing cracking of the end 185 of the ridge portion 181 of the press-formed product 177, which has the target shape. Furthermore, because the convex portion 209 is added only to the end 206 of the intermediate ridge portion 205, not the entire area, no excess material flow occurs, and wrinkles do not form in the top plate portion 179 or vertical wall portion 183 of the press-formed product 177, which has the target shape.

Figure 29 shows a press-formed product 177 formed by the second forming process. As shown in Figure 29, the thickness reduction rate at the end 185 of the ridge line portion 181 in the press-formed product 177 formed by the second forming process after passing through the first forming process was 7.0%. This is a significant reduction compared to the thickness reduction rate of 10.8% at the end 185 of the ridge line portion 181 when press-forming is performed in a conventional single process (see Figure 32), demonstrating that cracking can be prevented.

The shape of the intermediate punch 213 in the first forming step is not limited to that shown in Figure 27(a) and may be, for example, that shown in Figure 27(b). In the example shown in Figure 27(a), the apex of the punch-side convex portion forming portion 223 is positioned so that it extends to the outside of the end portion 206 of the intermediate ridge portion 205, while in the example shown in Figure 27(b), the punch-side convex portion forming portion 223 extends along the ridge portion to the edge of the intermediate top plate forming surface portion 219.

In addition, the curvature of the ridgeline 181 of the top plate portion 179 and the vertical wall portion 183 in Figure 29 does not necessarily have to be constant, and some parts may be straight. Furthermore, the intermediate vertical wall portion 207 of the intermediate molded product 211 does not have to have the same angle as the target shape, and may have a gentler slope than the target shape, or may not have any slope at all.

An analysis was carried out to verify the effects of the present invention, which will be described below.
Example 1
In Example 1, the targets were a press-formed product 1 having a generally T-shaped top plate portion 3 shown in Fig. 3 and a press-formed product 41 having a generally L-shaped top plate portion 43 shown in Fig. 5. Each of the press-formed product 1 and the press-formed product 41 was manufactured by the first forming step and the second forming step of the manufacturing method for a press-formed product according to the first embodiment described above.

In the analysis, a steel sheet with a thickness of 1.2 mm and a tensile strength of 780 MPa was used as the metal sheet blank. FEM analysis was then performed for each of the first and second forming processes to examine the effectiveness of suppressing cracking at the ends of the horizontal edge ridge 9a (generally T-shaped press-formed product 1) and horizontal edge ridge 49a (generally L-shaped press-formed product 41) in the target shape. The effectiveness of suppressing cracking was evaluated using the thickness reduction rate. As mentioned above, the thickness reduction rate is a negative value of the thickness change rate, calculated by dividing the difference between the thickness of each part of the press-formed product in the intermediate or target shape and the thickness of the metal sheet blank by the thickness of the blank.

In Example 1, the height of the tip end of the horizontal side 23a of the intermediate-shaped top plate portion in the first forming process was made higher than the height of the vertical side end of the intermediate-shaped top plate portion, which was an example of the invention. In this example, the horizontal side forming portion of the top plate forming portion formed into the intermediate shape in the first forming process was shaped as shown in Figures 34 and 35. In Figure 34, the tip end of the horizontal side of the intermediate-shaped top plate portion is inclined so that it gradually becomes higher toward the tip in the direction in which the horizontal side extends. Here, the inclination angle was changed to various angles for the intermediate-shaped press-formed product in which the tip end of the horizontal side is inclined.

On the other hand, Figure 35 shows an intermediate-shaped top plate in which the horizontal side of the top plate is uniformly higher at the tip end in the direction in which the horizontal side extends. Furthermore, in intermediate shapes in which the tip end of the horizontal side is uniformly higher, a convex portion 23d is formed that is raised upward from the horizontal side to the vertical side, spanning the connecting curve of the approximately T-shaped or approximately L-shaped portion. Here, for intermediate shapes in which the tip end of the horizontal side is uniformly higher, the height increment of the tip end of the horizontal side is varied in various ways, and the height of the convex portion 23d is made the same height as the tip end of the horizontal side.

In Example 1, for comparison, a conventional example was used in which the height of the tip end of the horizontal edge portion 23a, 53a of the top plate portion 23, 53 of the intermediate-shape press-formed product 21, 51 was set to the height of the top plate portion 3, 43 of the target shape, as shown in Figure 7(a) or Figure 16(a) described above. As with the inventive example, FEM analysis was also performed on the conventional example for each of the first and second forming steps, and the sheet thickness reduction rate was determined for each of the intermediate-shape and target-shape press-formed products at the bottom dead center of forming.

Table 1 shows the results of the inclination angle of the tip end of the horizontal edge portion 23a or the tip end of the horizontal edge portion 53a of the top plate portion of the intermediate shape, and the plate thickness reduction rate at the end of the horizontal edge side ridge portion 9a of the press-formed product of the target shape or the horizontal edge side ridge portion 49a of the press-formed product 41. Note that the greater the absolute value of the plate thickness reduction rate, the greater the plate thickness reduction.

In the conventional example No. 1, the inclination of the tip of the horizontal side portion 23a (generally T-shaped) or the tip of the horizontal side portion 53a (generally L-shaped) of the intermediate-shaped top plate was set to 0°. The thickness reduction rate at the end of the horizontal side ridge portion 9a (generally T-shaped) of the target shape in No. 1 was -16.9%, and the thickness reduction rate at the end of the horizontal side ridge portion 49a (generally L-shaped) was -17.7%. These absolute values are large, and it is thought that cracks will occur.

In contrast, in No. 2 to No. 9, the inclination angle of the tip of the horizontal edge portion 23a or the tip of the horizontal edge portion 53a in the top plate portion of the intermediate shape was set to 3.8° to 23.7°. It can be seen that the absolute value of the thickness reduction rate at the end of the horizontal edge side ridge portion 9a or the horizontal edge side ridge portion 49a of the target shape in No. 2 to No. 9 is reduced compared to the conventional example (-17.7%). In particular, in No. 7, where the inclination angle was 18.3°, the thickness reduction rate was -10.6%, a significant absolute reduction and favorable result.

Table 2 shows the height of the tip of the horizontal edge portion 23a or the tip of the horizontal edge portion 53a in the top plate portion of the intermediate shape, and the plate thickness reduction rate at the end of the horizontal edge side ridge portion 9a or the horizontal edge side ridge portion 49a in the press-formed product of the target shape.

In the conventional example No. 1, the height increase at the tip of the horizontal side portion 23a (generally T-shaped) or the tip of the horizontal side portion 53a (generally L-shaped) of the intermediate-shaped top plate portion was set to 0 mm. The thickness reduction rate at the end of the horizontal side ridge portion 9a (generally T-shaped) of the target shape in No. 1 was -16.9%, and the thickness reduction rate at the end of the horizontal side ridge portion 49a (generally L-shaped) was -17.7%. These absolute values are large, and it is believed that cracks will occur.

In contrast, in Nos. 11 to 17, the height increment at the tip of the horizontal edge 23a (generally T-shaped) or the tip of the horizontal edge 53a (generally L-shaped) of the intermediate-shaped top plate portion was set to 3 mm to 25 mm. It can be seen that the thickness reduction rate at the end of the horizontal edge 9a (generally T-shaped) or horizontal edge 49a (generally L-shaped) of the target shape in Nos. 11 to 17 is reduced compared to the conventional example. In particular, in No. 17, where the height increment was set to 25 mm, the thickness reduction rate was -8.0%, a significant decrease in absolute value and favorable.

As described above, the method of the present invention has been shown to be effective in suppressing cracks at the ends of the horizontal edge ridges when manufacturing press-formed products with a roughly T-shaped or L-shaped top plate portion by press-forming them in two steps.

Example 2
In Example 2, a press-formed product 1 having an approximately T-shaped top plate portion 3 with the dimensions shown in Figure 4 was targeted, and was press-formed using the first and second forming steps of the manufacturing method for press-formed products according to the above-mentioned embodiment 1.

A steel plate with a thickness of 1.2 mm and a tensile strength of 780 MPa was used as the blank. FEM analysis of the first and second forming processes was then performed to examine the effectiveness of suppressing cracking at the ends of the horizontal edge ridges 9a of the target shape. The effectiveness of suppressing cracking was evaluated using the thickness reduction rate of the press-formed product of the target shape obtained by FEM analysis. As mentioned above, the thickness reduction rate is a negative value of the thickness change rate, calculated by dividing the difference between the thickness of each part of the press-formed product of the intermediate or target shape and the thickness of the metal plate that is the blank by the thickness of the blank.

In the example of the invention, in the first forming step, the punch 71 shown in Figure 11(a) or the punch 61 shown in Figure 11(b) was used to press-form an intermediate-shaped press-formed product 21 (Figure 2(a)) or an intermediate-shaped press-formed product 51 (Figure 15(a)).

By changing the height of the convex portion forming portion 73d of the punch 71 shown in Figure 11(a), the height increment of the convex portion 23d was varied.

Furthermore, by making the heights of the convex portion forming portion 63d and the horizontal edge tip forming portion 63a1 of the punch 61 shown in Figure 11(b) equal and varying their heights, the height increment of the convex portion 23d was varied.

For comparison, a conventional example was prepared in which no protrusion was formed on the connecting R portion 23c of the top plate portion 23 of the intermediate-shape press-formed product 21, as shown in Figure 13 above. As with the inventive example, FEM analysis was then performed on the conventional example for the first and second forming steps to determine the thickness reduction rate for the press-formed product 1 of the target shape at the bottom dead center of forming. In this example, it was previously determined through actual press forming and press forming analysis that cracks would occur if the absolute value of the thickness reduction rate exceeded 10%.

Table 3 shows the height increase at the convex portion 23d of the press-formed product 21 in the intermediate shape shown in Figure 2(a) or Figure 13(a) and the plate thickness reduction rate at the end of the horizontal edge ridge portion 9a of the press-formed product 1 in the target shape. Note that the greater the absolute value of the plate thickness reduction rate, the greater the plate thickness reduction.

In the conventional example of No. 21, no protrusions were formed on the intermediate-shape press-formed product 21, and the height increase at the protrusions was set to 0 mm. The thickness reduction rate at the end of the horizontal edge ridge 9a of the target shape in No. 21 was -11.0%, a large absolute value that resulted in cracks.

In contrast, in Examples No. 22 to No. 25, a convex portion 23d is formed on the intermediate-shaped top plate portion 23, with a height increase of 3 mm to 10 mm. It can be seen that the absolute value of the thickness reduction rate at the end of the horizontal edge ridge portion 9a of the target shape in Examples No. 22 to No. 25 is reduced compared to the conventional example (-11.0%). In particular, in Example No. 25, where the height increase was 10 mm, the thickness reduction rate was -8.1%, a significant decrease in absolute value.

Table 4 shows the height increments at the protrusions 23d and tip end portions 23a1 of the horizontal edge portions 23a of the intermediate-shape press-formed product 21 shown in Figure 15 or Figure 13, and the plate thickness reduction rate at the end of the horizontal edge ridge portion 9a of the target-shape press-formed product 1. Note that, as with Table 3, the greater the absolute value of the plate thickness reduction rate, the greater the plate thickness reduction.

In the conventional example No. 21, similar to Table 3 above, the thickness reduction rate at the end of the horizontal edge ridge portion 9a of the target shape was -11.0%, which was a large absolute value and caused cracks.

In contrast, in the invention examples No. 31 to No. 34, the height increments at the intermediate shape's convex portion 23d and the tip end portion 23a1 of the horizontal side portion 23a were set to 3 mm to 10 mm. It can be seen that the absolute value of the thickness reduction rate at the end of the horizontal side ridge portion 9a of the target shape in No. 31 to No. 34 is reduced compared to the conventional example. In particular, in No. 34, where the height increment was 10 mm, the thickness reduction rate was -4.7%, which was favorable.

As described above, the method of the present invention has been shown to be able to suppress cracks at the ends of the ridges on the horizontal sides when manufacturing a press-formed product with a roughly T-shaped top plate portion by press-forming in two steps.

Example 3
In Example 3, a 1.5 GPa-class material having a thickness of 1.2 mm was used as the metal plate of the blank 115, and press-forming was performed by the method of the present invention, the comparative method, and the conventional method for the press-formed product 101 having the target dimensions shown in FIG.

In the method of the present invention, the intermediate punch 155 shown in Figure 19 was used in the first forming step to change the height h of the convex portion forming portion 169 of the intermediate punch 155, thereby press-forming into an intermediate formed product 149 shown in Figure 20, in which the height increment Δh of the end 146 of the intermediate ridge portion 144 was changed. Then, in the second forming step, press-forming was performed into the target press-formed product 101 shown in Figure 23. The comparative method was press-formed in two steps, but is a manufacturing method for a press-formed product in which the convex portion 147 is not formed in the first step. The conventional method was press-formed in one step, as shown in Figure 24.

The thickness reduction rate of the end 142 of the ridgeline portion 107 (see Figure 23) was determined by FEM analysis. The thickness reduction rate is the difference between the thickness of the metal plate that is the blank and the thickness of each portion of the formed product divided by the thickness of the metal plate that is the blank 115. Table 5 shows the ridgeline portion end height increment Δh and the maximum thickness reduction rate of the target press-formed product 101. Note that, based on actual press forming and press forming analysis, it was previously determined that cracks would occur in the target press-formed product 101 of Example 3 if the maximum thickness reduction rate was 7.0% or more.

No. 41, a conventional example press-formed in one process, had a height increment Δh at the ridge end of 0 and a large maximum thickness reduction rate of 8.9%, resulting in cracking. No. 42, a comparative example press-formed in two processes, had a height increment Δh at the ridge end of 0 and a large maximum thickness reduction rate of 7.2%, resulting in cracking. In contrast, Nos. 43 to 50 had reduced maximum thickness reduction rates, demonstrating that cracking was suppressed. No. 44, in particular, had a maximum thickness reduction rate of 3.9%, less than half the original rate, demonstrating remarkable success.

Example 4
In Example 4, a 1.4 mm thick 980 MPa-grade blank metal plate was used as a blank metal plate. A press-formed product 177 with target dimensions shown in FIG. 30 was press-formed by the present invention method, the comparative method, and the conventional method. In the present invention method, the intermediate punch 213 shown in FIG. 27(a) was used in the first forming step to change the height H of the punch-side convex portion forming portion 223 of the intermediate punch 213, thereby press-forming an intermediate formed product 211 with a changed height increment ΔH of the end 206 of the intermediate ridge portion 205 shown in FIG. 28(a). Subsequently, in the second forming step, the target press-formed product 177 shown in FIG. 30 was press-formed. The comparative method was press-formed in two steps, but is a manufacturing method for the press-formed product 101 in which the convex portion 209 was not formed in the first step. The conventional method was press-formed in one step, as shown in FIG. 31.

The thickness reduction rate of the end 185 of the ridgeline portion 181 (see Figure 30) was determined by FEM analysis. Table 6 shows the ridgeline end height increment ΔH and the maximum thickness reduction rate of the target press-formed product 177. Note that, prior to actual press forming and press forming analysis, it was determined that cracks would occur in the target press-formed product 229 of Example 4 at a maximum thickness reduction rate of 10.5% or more.

No. 51, a conventional example press-formed in one process, had a height increase ΔH at the ridge end of 0 and a large maximum thickness reduction of 10.8%, resulting in cracking. No. 52, a comparative example press-formed in two processes, had a height increase ΔH at the ridge end of 0 and a large maximum thickness reduction of 10.5%, resulting in cracking. In contrast, Nos. 53 to 59 had reduced maximum thickness reductions, demonstrating that cracking was suppressed. No. 58, in particular, had a maximum thickness reduction of 4.6%, less than half the original amount, demonstrating remarkable success.

The present invention provides a method for manufacturing a press-molded product that can suppress the occurrence of cracks when manufacturing a press-molded product having a generally T-shaped or L-shaped top plate portion by press molding.

1 Press-formed product 3 Top plate portion 3a Horizontal side portion 3b Vertical side portion 3c Connecting R portion 5 Vertical wall portion 5a Horizontal side vertical wall portion 5b Vertical side vertical wall portion 5c Connecting R side vertical wall portion 7 Bottom flange portion 9 Ridge portion 9a Horizontal side ridge portion 9b Vertical side ridge portion 9c Connecting R side ridge portion 11 Blank 13 Punch 15 Pad 17 Die 21 Intermediate-shaped press-formed product 23 Top plate portion 23a Horizontal side portion 23a1 Tip side portion 23b Vertical side portion 23c Connecting R portion 23d Convex portion 25a Horizontal side vertical wall portion 29a Horizontal side ridge portion 31 Punch 33 Pad 35 Die 41 Press-formed product (approximately L-shaped)
43 Top plate portion 43a Horizontal side portion 43b Vertical side portion 45 Vertical wall portion 45a Horizontal side vertical wall portion 47 Bottom flange portion 49a Horizontal side ridge portion 51 Intermediate shape press-molded product (approximately L-shaped)
53 Top plate portion 53a Horizontal side portion 53b Vertical side portion 55a Horizontal side vertical wall portion 61 Punch 63a1 Horizontal side tip side forming portion 63b Vertical side forming portion 63d Convex portion forming portion 71 Punch 73 Top plate forming portion 73a Horizontal side forming portion 73b Vertical side forming portion 73c Connection R forming portion 73d Convex portion forming portion 101 Press-formed product 103 Top plate portion 105 Top plate flange portion 107 Ridge line portion 109 Vertical wall portion 111 Vertical flange portion 113 Horizontal flange portion 115 Blank 117 Top plate flange equivalent portion 119 Vertical flange equivalent portion 121 Die 123 Punch 125 Pad 127 Die 129 Top plate forming surface portion 131 Punch side vertical wall forming surface portion 133 Punch side horizontal flange forming surface portion 135 Punch side vertical flange forming surface portion 137 Die side vertical wall forming surface portion 139, die side horizontal flange forming surface portion 141, die side vertical flange forming surface portion 142, edge portion 143, intermediate top plate portion 144, intermediate ridge portion 145, intermediate vertical wall portion 146, edge portion 147, convex portion 149, intermediate formed product 151, intermediate horizontal flange portion 153, intermediate vertical flange portion 155, intermediate punch 157, intermediate pad 159, intermediate die 161, intermediate top plate forming surface portion 163, punch side intermediate vertical wall forming surface portion 165, punch side intermediate horizontal flange forming surface portion 167, punch side intermediate vertical flange forming surface portion 168, top plate horizontal side forming surface portion 169, convex portion forming portion 171, die side intermediate vertical wall forming surface portion 173, die side intermediate horizontal flange forming surface portion 175, die side intermediate vertical flange forming surface portion 177, press-formed product 179, top plate portion 181, ridge portion 183 Vertical wall portion 185, end portion 187 of ridge portion, blank 189, portion equivalent to top plate 191, portion equivalent to vertical wall 193, end portion 195 of portion equivalent to vertical wall, mold 197, punch 199, pad 201, die 203, intermediate top plate portion 205, intermediate ridge portion 206, end portion 207 of intermediate ridge portion, intermediate vertical wall portion 209, convex portion 211, intermediate formed product 213, intermediate punch 215, intermediate pad 217, intermediate die 219, intermediate top plate forming surface portion 221, punch side intermediate vertical wall forming surface portion 223, punch side convex portion forming portion 225, die side intermediate vertical wall forming surface portion 226, die side convex portion forming portion 229, press-formed product

Claims (1)

A method for manufacturing a press-formed product having a top plate portion having a curved portion in top view and a vertical wall portion continuing from a part of the inner side of the curve of the top plate portion via a ridge portion,
a first forming step of press-forming the metal plate blank into an intermediate formed product having an intermediate top plate portion, an intermediate vertical wall portion, and an intermediate ridge portion connecting the intermediate top plate portion and the intermediate vertical wall portion, and having a convex portion at an end of the intermediate ridge portion that is higher than a reference height of the top plate surface;
a second forming step of press-forming the intermediate formed product into the press-formed product;
It is equipped with
The intermediate punch used in the first forming step is
The punch includes an intermediate top plate forming surface portion and a punch-side intermediate vertical wall forming surface portion that forms the intermediate ridge line portion,
a punch-side convex portion forming portion for forming the convex portion is formed on both sides of the end of the intermediate top plate forming surface portion in the width direction,
the punch-side convex-portion-forming portion is disposed so that a central portion thereof overlaps an end portion of the intermediate ridge portion;
Manufacturing method for press-molded products .