JP7564448B2 - Manufacturing method and manufacturing equipment for press-molded products - Google Patents

Description

This disclosure relates to a manufacturing method and manufacturing equipment for press-molded products.

Press-formed products have traditionally been used as components for automobile bodies and the like. Press-formed products are manufactured by pressing metal sheets. More specifically, press-formed products are manufactured by drawing and bending metal sheets as raw materials using a metal mold that includes a die and a punch.

In press working of metal sheets, springback occurs when the press-formed product formed by the die is released from the die. That is, when the metal sheet is bent by the die during press working, tensile stress occurs on the outside of the bend and compressive stress occurs on the inside of the bend in the bent part, but when forming is completed and the press-formed product is removed from the die, the material undergoes elastic recovery. As a result, stress occurs in the bent part of the press-formed product in a direction opposite to the direction of the stress during press working. This reverse stress due to springback is added to the stress at the end of forming, so that compressive stress remains on the outside of the bend and tensile stress remains on the inside of the bend in the bent part of the press-formed product.

In press-formed products used as automotive parts, it is preferable for the tensile residual stress on the inside of the bend to be small. For example, in automotive undercarriage parts such as suspension members, relatively large stresses are repeatedly generated in the bent parts when the automobile starts, is running, or is braking, so the greater the tensile stress remaining on the inside of the bend, the lower the fatigue strength of the bent parts.

In order to resist fatigue failure caused by repeated loads, appropriate materials and plate thicknesses are used when manufacturing press-formed products for automotive parts. Also, to meet the need for lighter vehicles, metal plates, which are the raw material, are becoming stronger and thinner. However, thinner materials result in higher repeated loads on press-formed products manufactured from those materials. Therefore, to achieve both weight reduction (thinner materials) and fatigue strength, it is necessary to reduce the tensile stress remaining on the inside of the bend in the bent part of the press-formed product.

Heat treatment, shot peening, impact treatment with an ultrasonic vibrator, etc. are known as means for removing residual tensile stress from press-formed products. However, these treatments must be performed in a separate process from the press working process, which reduces the manufacturing efficiency of press-formed products and increases the number of steps and costs required for manufacturing press-formed products. In addition, with shot peening, it is difficult to treat only the bent parts of the press-formed product, and there is also the problem that it causes surface roughness on the press-formed product. Therefore, it is preferable that the tensile residual stress in the bent parts of the press-formed product be reduced in the press working process.

For example, Patent Document 1 discloses a technique for performing a so-called ironing process on a metal sheet material in order to reduce tensile residual stress. In Patent Document 1, the clearance between the die and the punch is set to be equal to or greater than the thickness of the metal sheet and equal to or less than 1.02 times the thickness. According to Patent Document 1, by setting the clearance in this manner, the residual stress in the portion of the metal sheet that is in contact with the shoulder of the die before bending begins is smaller than the residual stress in the portion that will finally come into contact with the shoulder, thereby improving the fatigue properties of the press-formed product.

Patent Document 2 discloses a press device that includes a die, a punch, and a pad that faces the top surface of the punch. In this press device, the die descends, and the die and punch shoulder press the metal sheet to form a bent portion in the metal sheet, after which the pad descends toward the top surface of the punch. A recess is formed in the top surface of the punch, and this recess forms a space below the metal sheet, so that when the descending pad presses the metal sheet, material from the metal sheet flows into the recess side of the top surface of the punch. According to Patent Document 2, this inflow of material applies a tensile force to the inside of the bend in the bent portion, reducing the compressive stress and reducing the amount of springback after demolding. This makes it possible to reduce the tensile residual stress on the inside of the bend.

Patent documents 3 to 5 disclose techniques for modifying the shape of the press-formed product itself in order to reduce the amount of springback after demolding. In patent documents 3 to 5, in a press-formed product having a roughly hat-shaped cross section, unevenness or steps are provided on the vertical wall portion.

JP 2002-316215 A International Publication No. 2017/131042 JP 2004-314123 A JP 2006-272378 A JP 2017-196646 A

As described above, when a press-formed product is manufactured by pressing a metal plate, compressive stress remains on the outside of the bend and tensile stress remains on the inside of the bend in the bent portion of the press-formed product. To obtain a press-formed product with better fatigue properties, it is particularly necessary to reduce the tensile residual stress on the inside of the bend. Furthermore, from the viewpoint of preventing an increase in the manufacturing steps and manufacturing costs of the press-formed product, it is preferable that the tensile residual stress on the inside of the bend be reduced in the press processing process.

The objective of this disclosure is to reduce the tensile residual stress that occurs on the inside of the bend in the bend of a press-molded product during the press working process.

The manufacturing method of the press-molded product according to the present disclosure includes a first step and a second step. In the first step, an intermediate molded product is obtained by pressing a metal plate. The intermediate molded product includes a top plate, a convex portion, a vertical wall, and a flange. The convex portion is connected to the top plate and protrudes upward from the top plate. The vertical wall extends downward from the convex portion. The flange extends from the lower end of the vertical wall to the opposite side of the top plate. In the second step, the intermediate molded product is press-molded using a die to obtain a press-molded product. The die includes a punch, a pad, and a die. The pad is disposed above the punch so as to face the punch. The die is disposed above the punch and to the side of the pad. The punch includes a punch top surface, a punch shoulder, and a punch side surface. The punch shoulder is continuous with the punch top surface. The punch side surface extends downward from the punch shoulder. The die includes an upper die shoulder, a die side surface, and a die lower surface. The upper die shoulder corresponds to the punch shoulder. The die side extends downward from the upper die shoulder in correspondence with the punch side. The die lower surface is connected to the lower end of the die side via the lower die shoulder. The second step includes the steps of placing the intermediate molded product on the punch so that the top plate is positioned on the punch top surface and the protrusion is positioned in a position corresponding to the punch shoulder, lowering the pad and pressing the top plate on the punch top surface with the pad, lowering the die and contacting the flange with the top plate pressed by the pad, and further lowering the die after it contacts the flange to crush the protrusion with the die.

According to this disclosure, the tensile residual stress that occurs on the inside of the bend in the bent portion of a press-molded product can be reduced during the press processing process.

FIG. 1 is a diagram that illustrates a manufacturing facility according to an embodiment and a process for manufacturing a press-formed product using the manufacturing facility. FIG. 2 is a cross-sectional view showing a schematic configuration of a press device for producing an intermediate molded product, which is included in the production facility according to the embodiment. FIG. 3 is a cross-sectional view showing a schematic configuration of a press device for producing a press-formed product, which is included in the production facility according to the embodiment. FIG. 4A is a schematic diagram for explaining a first step of the method for manufacturing a press-formed product according to the embodiment. FIG. 4B is a schematic diagram for explaining a first step of the method for manufacturing a press-formed product according to the embodiment. FIG. 4C is a schematic diagram for explaining a first step of the method for manufacturing a press-formed product according to the embodiment. FIG. 4D is a schematic diagram for explaining a first step of the method for manufacturing a press-formed product according to the embodiment. FIG. 4E is a schematic diagram for explaining a first step of the method for manufacturing a press-formed product according to the embodiment. FIG. 5A is a schematic diagram for explaining a second step of the method for manufacturing a press-formed product according to the embodiment. FIG. 5B is a schematic diagram for explaining a second step of the method for manufacturing a press-formed product according to the embodiment. FIG. 5C is a schematic diagram for explaining a second step of the manufacturing method of the press-formed product according to the embodiment. FIG. 5D is a schematic diagram for explaining a second step of the manufacturing method of the press-formed product according to the embodiment. FIG. 5E is a schematic diagram for explaining a second step of the manufacturing method of the press-formed product according to the embodiment. FIG. 5F is a schematic diagram for explaining a second step of the manufacturing method of the press-formed product according to the embodiment. FIG. 5G is a schematic diagram for explaining a second step of the method for manufacturing a press-formed product according to the embodiment. FIG. 5H is a schematic diagram for explaining a second step of the manufacturing method of the press-formed product according to the embodiment. FIG. 6 is a graph showing the relationship between the height/width of the convex portion of the intermediate product obtained in the first step and the tensile residual stress on the inner side of the bend in the bent portion of the press-molded product in the manufacturing method of the press-molded product according to the embodiment. FIG. 7 is a graph showing the relationship between the radius of curvature of the apex of a convex portion of an intermediate product and the tensile residual stress on the inner side of a bent portion of a press-formed product. FIG. 8 is a graph showing the relationship between the height of the intermediate product and the tensile residual stress on the inner side of the bend in the bent portion of the press-formed product. FIG. 9 is a graph showing the relationship between the flange angle of the intermediate product and the tensile residual stress on the inner side of the bend in the bent portion of the press-formed product. FIG. 10 is a graph showing the relationship between the length of the flange of the intermediate product and the tensile residual stress on the inner side of the bend in the bent portion of the press-formed product. FIG. 11 is a graph showing the relationship between the radius of curvature of the lower die shoulder of the die used in the second step in the manufacturing method of a press-molded product according to the embodiment and the tensile residual stress on the inner side of the bend in the bent portion of the press-molded product. FIG. 12 is a graph showing the relationship between the position of the convex portion of the intermediate product with respect to the pad profile of the die and the tensile residual stress on the inner side of the bend in the bent portion of the press-formed product in the second step. FIG. 13 is a graph showing the relationship between the work hardening exponent of a metal plate that is the material of a press-formed product and the tensile residual stress on the inner side of a bent portion of the press-formed product. FIG. 14 is a schematic diagram showing a manufacturing method of a press-formed product according to a modified example of the above embodiment. FIG. 15 is a graph showing the effects of the manufacturing method of the press-formed product according to the above-described modified example. FIG. 16 is a perspective view showing a schematic configuration of a press-formed product according to an embodiment. FIG. 17 is a graph showing the stress distribution in the plate thickness direction at the end of forming and the residual stress distribution in the plate thickness direction after springback, with respect to stress generated in the bending circumferential direction in the bent portion of a conventional press-formed product. FIG. 18 is a graph showing the stress distribution in the plate thickness direction at the end of forming and the residual stress distribution in the plate thickness direction after springback, based on the findings of the present inventors, for stress generated in the bending circumferential direction in the bent portion of a press-formed product.

In order to confirm the distribution of stress occurring in the bent portion of the press-formed product, the inventors carried out a CAE analysis of the press working using commercially available software (LS-DYNA ver971 rev7.12, manufactured by ANSYS). The analysis conditions are as follows:
-Material tensile strength: 980MPa
-Material thickness: 3.0 mm
Bend R (inner curvature radius): 4.0 mm
・Shape of press-molded product (after processing): Shape consisting of two vertical walls and a top plate connecting the vertical walls (no flanges)

Figure 17 shows the stress distribution in the plate thickness direction at the end of forming for the stress generated in the circumferential direction in the bent portion of a press-formed product, and the residual stress distribution in the plate thickness direction after springback. Figure 17 shows the stress (stress in the circumferential direction) generated on a line from the R apex (center of R) on the inside of the bend to the R apex on the outside of the bend in the bent portion of the press-formed product. As can be seen from Figure 17, at the end of forming, in the bent portion of the press-formed product, tensile stress occurs on the outside of the bend and compressive stress occurs on the inside of the bend. On the other hand, after springback, in the bent portion of the press-formed product, compressive residual stress occurs on the outside of the bend and tensile residual stress occurs on the inside of the bend.

The inventors noticed that compressive residual stress occurs in the bent portion of a press-formed product after springback not only in the region on the outside of the bend but also in the region on the inside of the bend near the neutral axis (center of plate thickness), and came up with the idea of applying tension to the bent portion during press working. The inventors believed that by performing press working while applying tension to the portion of the material that will become the bent portion, it would be possible to reduce the compressive stress in the region on the inside of the bend at the end of forming, and therefore the tensile residual stress after springback would also be reduced.

When a CAE analysis was performed under the same conditions as above, except that the material was bent while tension was applied, the stress distribution shown in Figure 18 was obtained. As can be seen from Figure 18, when the bent portion of the press-formed product was formed while tension was applied, the compressive stress on the inside of the bend at the end of forming was reduced, and the tensile residual stress on the inside of the bend after springback was reduced and further became compressive stress. Therefore, the inventors investigated a method for applying tension to the portion that will become the bent portion of the press-formed product during press working, and completed a manufacturing method for a press-formed product according to an embodiment.

The manufacturing method of the press-molded product according to the embodiment includes a first step and a second step. In the first step, an intermediate molded product is obtained by pressing a metal plate. The intermediate molded product includes a top plate, a convex portion, a vertical wall, and a flange. The convex portion is connected to the top plate and protrudes upward from the top plate. The vertical wall extends downward from the convex portion. The flange extends from the lower end of the vertical wall to the opposite side of the top plate. In the second step, the intermediate molded product is press-molded using a die to obtain a press-molded product. The die includes a punch, a pad, and a die. The pad is disposed above the punch so as to face the punch. The die is disposed above the punch and to the side of the pad. The punch includes a punch top surface, a punch shoulder, and a punch side surface. The punch shoulder is continuous with the punch top surface. The punch side surface extends downward from the punch shoulder. The die includes an upper die shoulder, a die side surface, and a die lower surface. The upper die shoulder corresponds to the punch shoulder. The die side extends downward from the upper die shoulder in correspondence with the punch side. The die lower surface is connected to the lower end of the die side via the lower die shoulder. The second step includes the steps of placing the intermediate molded product on the punch so that the top plate is positioned on the punch top surface and the convex portion is positioned in a position corresponding to the punch shoulder, lowering the pad and pressing the top plate on the punch top surface with the pad, lowering the die and contacting the flange with the top plate pressed by the pad, and further lowering the die after it contacts the flange to crush the convex portion with the die (first configuration).

In the manufacturing method of the press-formed product according to the first configuration, after the metal plate is pressed into an intermediate product in the first step, the intermediate product is pressed using a die including a punch, a pad, and a die in the second step to obtain a press-formed product. In the second step, the intermediate product is first placed on the punch, and the top plate of the intermediate product is pressed from above by the pad. In this state, the die is brought into contact with the flange of the intermediate product, and the die is lowered as it is. The flange of the intermediate product is not bent back immediately after the die comes into contact, but is bent back gradually as the die descends. Therefore, the flange is caught on the lower die shoulder as the forming proceeds, and tension acts on the convex portion and vertical wall between the top plate and the flange of the intermediate product. That is, tension is applied to the portion of the intermediate product that will become the bent portion in the final press-formed product. Therefore, the compressive stress on the inside of the bend at the end of forming can be reduced in the bent portion of the press-formed product. As a result, the tensile stress remaining on the inside of the bend after springback can be reduced.

Furthermore, in the second step, as the die descends, the protrusion of the intermediate formed product located at a position corresponding to the punch shoulder is crushed by the die and undergoes bending back deformation. As the protrusion is bent back by the die and pressed into the punch shoulder, compressive stress occurs in the area on the die side (outside of the bend) and tensile stress occurs in the area on the punch side (inside of the bend). These stresses can reduce the tensile stress that occurs on the outside of the bend and the compressive stress that occurs on the inside of the bend when the intermediate formed product fits (wraps) around the punch shoulder and a bent portion is formed, that is, when the second step is completed. As a result, the tensile residual stress that occurs on the inside of the bend in the bent portion of the press-formed product after springback can be reduced.

It is difficult to flatten a convex portion located at a position corresponding to the punch shoulder by simply applying tension from the periphery. However, in the manufacturing method of the press-formed product according to the first configuration, the convex portion is crushed by the die in the second step. This allows the convex portion to be firmly flattened. More specifically, the descending die hits the convex portion and crushes the convex portion from the top, generating a large stress from the base of the convex portion to the top. In other words, a large tensile stress is generated in the region on the inside of the bend. Therefore, the compressive stress generated on the inside of the bend at the end of the second step can be effectively reduced. As a result, the tensile residual stress generated on the inside of the bend can be reduced in the bent portion of the press-formed product after springback.

In this way, as the forming progresses while the flange is caught on the lower die shoulder, tension is applied to the convex portion and vertical wall between the top plate and the flange of the intermediate formed product, and by crushing this convex portion from the top, the compressive stress generated on the inside of the bend at the end of the second process can be significantly reduced. As a result, the tensile residual stress generated on the inside of the bend in the bent portion of the press-formed product after springback can be significantly reduced.

As described above, according to the manufacturing method of the press-molded product of the first configuration, the tensile residual stress that occurs on the inside of the bend in the bent portion of the press-molded product can be reduced during the press working process.

In the above manufacturing method, when the intermediate molded product is placed on the punch, it is preferable that the upper end of the convex portion is located inside the lower end of the die side in the width direction of the die, and the lower end of the vertical wall is located outside the upper end of the punch side in the width direction of the die (second configuration).

According to the second configuration, when the intermediate molded product is placed on the punch, that is, at the start of the second step, the upper end of the convex portion is located inside the lower end of the die side surface in the die width direction. This makes it possible to prevent the convex portion from being crushed by the lower die shoulder or the die underside at the beginning of the second step. In other words, it is possible to crush the convex portion by the die at the middle or end of the second step, and generate tensile stress in the area on the inside of the bend. This makes it possible to more effectively reduce the compressive stress generated on the inside of the bend at the end of the second step. Therefore, it is possible to more reliably reduce the tensile residual stress generated on the inside of the bend in the bent portion of the press-molded product.

In the intermediate molded product placed on the punch, if the lower end of the vertical wall is located inside the upper end of the punch side in the width direction of the die, the top plate of the intermediate molded product will be floating above the top surface of the punch. If press molding is performed in this state, the intermediate molded product cannot be stably held down by the pad, and the intermediate molded product may shift in the width direction (left and right direction) of the die during molding, and the dimensional accuracy of the final press molded product cannot be obtained. In contrast, in the second configuration, the intermediate molded product is configured so that, when placed on the punch, the lower end of its vertical wall is located outside the upper end of the punch side in the width direction of the die. Therefore, the top plate of the intermediate molded product does not float above the top surface of the punch, and the intermediate molded product can be stably placed on the punch. In addition, when the top plate of the intermediate molded product is held down by the pad, the pad can be prevented from floating. Therefore, the dimensional accuracy of the press molded product obtained in the second process can be stabilized.

In the intermediate molded product, when the vertical distance from the connection between the protrusion and the top plate to the top end of the protrusion is H1 [mm], and the widthwise distance of the intermediate molded product from the connection between the protrusion and the top plate to the top end of the protrusion is W1 [mm], it is preferable that H1/W1 is 0.5 or more and 2.0 or less (third configuration).

According to the third configuration, in the intermediate molded product, the ratio H1/W1 between the vertical distance (height of the convex) from the connection between the convex and the top plate to the top end of the convex and the widthwise distance (width of the convex) W1 from the connection between the convex and the top plate to the top end of the convex is 0.5 or more. This results in a shape in which the convex rises relatively steeply from the top plate, so that the amount of bending back deformation of the convex by the die can be ensured. Therefore, when the convex is bent back in the second step, tensile stress can be generated more effectively in the region on the inside of the bend. Therefore, the compressive stress generated on the inside of the bend at the end of the second step can be more reliably reduced, and the effect of reducing the tensile stress remaining on the inside of the bend can be improved in the bent part of the press molded product.

In the third configuration, the ratio of height H1 to width W1: H1/W1 in the convex portion of the intermediate molded product is 2.0 or less. This prevents the convex portion from becoming excessively steep in shape relative to the top plate, making it possible to prevent the convex portion from buckling when it is crushed by the die in the second process.

In the above manufacturing method, the convex portion may include an apex that is arc-shaped in cross-section of the intermediate molded product. The apex preferably has a radius of curvature of 4 mm or more and 16 mm or less (fourth configuration).

In the fourth configuration, the convex portion includes an arc-shaped apex in the cross-sectional view of the intermediate molded product. By making the radius of curvature of this apex 4 mm or more, it is possible to suppress buckling of the convex portion when it is crushed by the die. Furthermore, by making the radius of curvature of the apex 16 mm or less, the convex portion does not become excessively gentle in shape, so that in the second step, tensile stress can be more effectively generated on the inside of the bend due to bending back deformation of the convex portion. Therefore, the compressive stress generated on the inside of the bend at the end of the second step can be further reduced, and the tensile stress remaining on the inside of the bend in the bent portion of the press-molded product can be more reliably reduced.

In the die used in the second step of the above-mentioned manufacturing method, the punch shoulder has, for example, an arc shape in cross section of the punch. When the intermediate molded product is placed on the punch, a distance D2 [mm] in the width direction of the die from the end of the punch shoulder on the punch top side to the upper end of the convex portion is preferably positive when the upper end of the convex portion is located outside the end of the punch shoulder on the punch top side in the width direction and is negative when the upper end of the convex portion is located inside the end of the punch shoulder on the punch top side in the width direction, and satisfies the following formula (fifth configuration):
-1.0×Rp×(π-θ)≦D2≦2.5×Rp×(π-θ)
Here, Rp is the radius of curvature of the punch shoulder (mm), and θ is the angle (rad) between the top surface of the punch and the side surface of the punch.

According to the fifth configuration, the distance D2 in the width direction of the die from the end of the punch shoulder on the punch top side to the upper end of the convex portion is set to satisfy the above formula in relation to the radius of curvature Rp of the punch shoulder and the angle θ between the punch top and the punch side surface. By setting the distance D2 in this way, the convex portion is more likely to overlap the punch shoulder in the width direction of the die, so that tensile stress can be generated more widely on the inside of the bend during press forming due to the bending back deformation of the convex portion in the punch shoulder region. Therefore, the compressive stress generated on the inside of the bend when the intermediate formed product fits the punch shoulder to form the bent portion can be more effectively reduced. As a result, the tensile stress remaining on the inside of the bend after springback in the bent portion of the press formed product can be more reliably reduced.

In the intermediate molded product, it is preferable that the vertical distance from the end of the vertical wall of the flange to the top plate is 6 mm or more (sixth configuration).

If the height of the intermediate molded product, that is, the vertical distance from the end of the vertical wall of the flange to the top plate, is insufficient, when the die in contact with the flange descends in the second step, the vertical wall may bend overall, and the tension applied to the convex portion and the vertical wall may decrease. In contrast, in the sixth configuration, the height of the intermediate molded product is ensured to be 6 mm or more. This makes it possible to prevent the vertical wall of the intermediate molded product from bending in the second step, and to more effectively apply tension to the convex portion and the vertical wall. Therefore, in the bent portion of the press molded product, the compressive stress on the inside of the bend at the end of forming can be further reduced, and the effect of reducing the tensile stress remaining on the inside of the bend after springback can be improved.

In the above manufacturing method, when the intermediate molded product is placed on the punch, the angle that the flange makes with respect to the horizontal plane is preferably greater than -40° and less than 40°, with the angle being positive when the flange is rotated upward around the end of the vertical wall and negative when the flange is rotated downward (seventh configuration).

According to the seventh configuration, the angle that the flange of the intermediate product makes with respect to the horizontal plane is ensured to be -40° or more. As a result, in the second process, when the die comes into contact with the flange of the intermediate product and descends, the flange is more likely to catch on the lower die shoulder. Therefore, tension can be more reliably applied to the convex portion and vertical wall provided between the top plate and the flange in the intermediate product. Therefore, in the bent portion of the press-formed product, the compressive stress on the inside of the bend at the end of forming can be more effectively reduced, and the effect of reducing the tensile stress remaining on the inside of the bend after springback can be improved.

In the seventh configuration, the angle that the flange of the intermediate molded product makes with the horizontal plane is 40° or less. This makes it possible to prevent the flange from buckling or the die from being damaged by the tip of the flange when the die comes into contact with it.

In the above manufacturing method, it is preferable that the lower die shoulder has an arc shape with a radius of curvature of 1 mm or more and 12 mm or less when viewed in cross section of the die (8th configuration).

In the manufacturing method according to the embodiment, in the second step, the top plate of the intermediate molded product is pressed with a pad, and then the die is brought into contact with the flange of the intermediate molded product. When the die descends in this state, the flange is caught on the lower die shoulder, and tension is applied to the intermediate molded product between the pad and the lower die shoulder. In order to make it easier to catch the flange on the lower die shoulder, it is preferable to make the radius of curvature of the lower die shoulder smaller to a certain extent. In addition, a smaller radius of curvature of the lower die shoulder allows the flange to continue to be caught on the lower die shoulder until near the bottom dead center of the die. If the radius of curvature of the lower die shoulder is excessively large, the contact area between the intermediate molded product and the lower die shoulder will also be excessively large. In this case, when the die descends, the vertical wall and flange of the intermediate molded product are deflected as a whole, the catch of the flange on the lower die shoulder becomes weak, and the tension applied to the intermediate molded product between the pad and the lower die shoulder decreases. In consideration of this point, in the eighth configuration, the radius of curvature of the lower die shoulder is set to 12 mm or less. This limits the contact area between the intermediate product and the lower die shoulder in the second step, making it easier for the flange to catch on the lower die shoulder, and allows tension to be applied more effectively to the intermediate product between the pad and the lower die shoulder. This makes it possible to further reduce the compressive stress on the inside of the bend at the end of forming in the bent portion of the press-formed product, and improves the effect of reducing the tensile stress remaining on the inside of the bend after springback.

If the radius of curvature of the lower die shoulder is less than 1 mm, the lower die shoulder may leave a bite mark on the press-formed product or cause the press-formed product to have a large bending tendency. Therefore, as in the eighth configuration, it is preferable that the radius of curvature of the lower die shoulder is 1 mm or more.

In the above manufacturing method, it is preferable that the work hardening index of the metal plate is 0.04 or less (ninth configuration).

According to the ninth configuration, the work hardening index of the metal plate is sufficiently small, at 0.04 or less. Therefore, work hardening of the material is unlikely to occur in the first process of obtaining an intermediate formed product from this metal plate, and in the second process of obtaining a press-formed product from the intermediate formed product. In this case, the stress generated in the material is small in each process, and as a result, the stress due to springback is also small. Therefore, in each process, the residual stress, which is the sum of the stress at the end of forming and the reversal stress due to springback, can be reduced.

The manufacturing equipment according to the embodiment is a manufacturing equipment for manufacturing a press-molded product. The manufacturing equipment includes a first mold and a second mold. The first mold molds a metal plate into an intermediate molded product. The intermediate molded product includes a top plate, a convex portion, a vertical wall, and a flange. The convex portion is connected to the top plate and protrudes upward from the top plate. The vertical wall extends downward from the convex portion. The flange extends from the lower end of the vertical wall to the opposite side of the top plate. The second mold molds the intermediate molded product into a press-molded product. The second mold includes a punch, a pad, and a die. The punch includes a punch top surface, a punch shoulder continuous with the punch top surface, and a punch side surface extending downward from the punch shoulder. The punch is configured so that, when the intermediate molded product is molded into a press-molded product, the top plate is disposed on the punch top surface and the convex portion is disposed at a position corresponding to the punch shoulder. The pad is disposed above the punch and configured to be movable up and down. The pad is configured to face a top plate disposed on the top surface of the punch when the intermediate product is formed into a press-formed product. The die is disposed above the punch and to the side of the pad, and is configured to be movable up and down. The die includes an upper die shoulder corresponding to the punch shoulder, a die side surface extending downward from the upper die shoulder corresponding to the punch side surface, and a die lower surface connected to the lower end of the die side surface via the lower die shoulder. The die is configured so that the die lower surface faces the flange when the intermediate product is formed into a press-formed product.

Embodiments of the present disclosure will be described below with reference to the drawings. In each drawing, the same or equivalent components are given the same reference numerals, and the same description will not be repeated.

[Manufacturing Equipment]
1 is a diagram showing a manufacturing facility 100 according to the present embodiment and a process for manufacturing a press-molded product by the manufacturing facility 100. The press-molded product is, for example, an automobile suspension part or a frame part such as a ladder frame. Examples of the automobile suspension part include arm parts such as an upper arm, a lower arm, or a trail link, as well as suspension members and torsion beams.

As shown in FIG. 1, the manufacturing facility 100 includes press devices 10 and 20. The press device 10 forms an intermediate product 40 from a metal plate 30 as a material. The press device 20 forms a press-formed product 50 as a final product from the intermediate product 40. The configuration of each of the press devices 10 and 20 will be described below with reference to FIG. 2 and FIG. 3.

[Pressing device for intermediate molded products]
FIG. 2 is a cross-sectional view showing a schematic configuration of the press device 10 for obtaining the intermediate molded product 40 shown in FIG. 1. As shown in FIG. 2, the press device 10 includes a die 11, a bed 12, a slide 13, and die holders 14 and 15. The die 11 includes a punch 16 and a die 17. The punch 16 and the die 17 extend in a direction intersecting the plane of FIG. 2. Hereinafter, for the convenience of explanation, with respect to the press device 10 and its components, the direction in which the die 11, i.e., the punch 16 and the die 17 extend is referred to as the longitudinal direction, and the direction in which the punch 16 and the die 17 approach and move away from each other (the vertical direction in the plane of FIG. 2) is referred to as the vertical direction (vertical direction). The direction perpendicular to the plane consisting of the longitudinal direction and the vertical direction, i.e., the direction crossing the punch 16 and the die 17, is referred to as the left-right direction or width direction. Also, with respect to the press device 10 and its components, a cross section cut by a plane perpendicular to the longitudinal direction is referred to as a transverse section.

The punch 16 is supported by the bed 12, which is part of the main body of the press device 10, via the die holder 14. That is, the die holder 14 is fixed to the upper surface of the bed 12, and the punch 16 is placed on the die holder 14. A plate-shaped spacer may be inserted between the bed 12 and the die holder 14 to adjust the position of the punch 16 in the vertical direction.

The punch 16 includes a punch top surface 161, left and right convex surfaces 162L, 162R, left and right punch side surfaces 163L, 163R, and left and right punch flange surfaces 164L, 164R.

In this embodiment, the punch top surface 161 has a groove portion 161a extending in the longitudinal direction. The groove portion 161a may extend over the entire longitudinal direction of the punch top surface 161, or may be provided on a portion of the longitudinal direction of the punch top surface 161. In this embodiment, the punch top surface 161 has an asymmetric shape with respect to a vertical plane parallel to the longitudinal direction, that is, an asymmetric shape. However, the punch top surface 161 may also have a symmetric shape.

Convex surfaces 162L and 162R are provided on both sides of punch top surface 161. Convex surfaces 162L and 162R are provided continuously with punch top surface 161. Convex surfaces 162L and 162R are typically provided continuously with punch top surface 161 over the entire punch top surface 161.

The convex surface 162L is connected to the left edge of the punch top surface 161. The convex surface 162L protrudes upward from the punch top surface 161. More specifically, the convex surface 162L protrudes upward compared to the portion of the punch top surface 161 that is on the outer side (left side) of the groove portion 161a in the width direction. The convex surface 162L has a convex shape that rises once from the punch top surface 161 toward the outer side in the width direction and then descends. The top of the convex surface 162L is, for example, substantially arc-shaped in the cross section of the punch 16. Hereinafter, the term "substantially arc-shaped" includes not only a curve that constitutes a part of a perfect circle, but also smooth curves such as elliptical curves and spline curves. In addition, the radius of curvature in the case of a smooth curve other than a curve that constitutes a part of a perfect circle is defined as the radius of a circle that passes through three points, the both ends of the curve and the midpoint of the curve, when cut in cross section.

The convex surface 162R is provided continuously with the right edge of the punch top surface 161. The convex surface 162R protrudes upward from the punch top surface 161. More specifically, the convex surface 162R protrudes upward compared to the portion of the punch top surface 161 that is on the outer side (right side) in the width direction from the groove portion 161a. The convex surface 162R has a convex shape that rises once from the punch top surface 161 toward the outer side in the width direction and then descends. For example, the top of the convex surface 162R is substantially arc-shaped in the cross section of the punch 16. The convex surface 162R may have a shape symmetrical to the convex surface 162L with respect to a vertical plane parallel to the longitudinal direction, or may have an asymmetric shape.

In the cross-sectional view of the punch 16, the punch side surfaces 163L and 163R extend downward from the convex surfaces 162L and 162R, respectively. The punch side surface 163L is provided continuously with the left convex surface 162L. The punch side surface 163R is provided continuously with the right convex surface 162R. In the example of this embodiment, each of the punch side surfaces 163L and 163R is inclined with respect to a vertical plane parallel to the longitudinal direction so that its lower end is located outward in the width direction from its upper end. The punch side surfaces 163L and 163R may have a symmetrical shape with respect to a vertical plane parallel to the longitudinal direction, or may have an asymmetrical shape. The punch side surfaces 163L and 163R may also be smooth curves provided continuously with the convex surfaces 162L and 162R. The punch side surfaces 163L, 163R or the convex surfaces 162L, 162R may be curved (inflected) inward or outward in the width direction on the way from the upper end of the convex surfaces 162L, 162R toward the punch flange surfaces 164L, 164R.

In a cross-sectional view of the punch 16, the punch flange surfaces 164L and 164R extend outward in the width direction from the punch side surfaces 163L and 163R, respectively. The punch flange surfaces 164L and 164R may extend substantially horizontally from the punch side surfaces 163L and 163R, but at least one of them may extend at an angle relative to the horizontal plane. For example, the angle that each of the punch flange surfaces 164L and 164R makes with respect to the horizontal plane can be set in the range of -40° or more and 40° or less, with the case where the punch flange surfaces 164L and 164R rotate upward around the inner end in the width direction being positive, and the case where they rotate downward being negative. The angle between the punch flange surfaces 164L and 164R and the horizontal plane is preferably -10° or more and 10° or less. Here, the horizontal plane refers to a plane perpendicular to the direction (up-down direction) in which the punch 16 and the die 17 approach and separate from each other. The angle that the punch flange surfaces 164L, 164R make with respect to the horizontal plane means the angle (acute angle side) that the punch flange surfaces 164L, 164R make with the width direction in a cross section cut along a plane consisting of the vertical and width directions.

The punch flange surface 164L is provided contiguous to the lower end of the left punch side surface 163L. The punch flange surface 164R is provided contiguous to the lower end of the right punch side surface 163R. The boundary between the punch flange surface 164L and the punch side surface 163L is preferably subjected to R-chamfering. Similarly, the boundary between the punch flange surface 164R and the punch side surface 163R is preferably subjected to R-chamfering. In other words, the boundary between the punch flange surface 164L and the punch side surface 163L, and the boundary between the punch flange surface 164R and the punch side surface 163R are preferably each substantially arc-shaped in a cross-sectional view of the punch 16.

The die 17 is disposed above the punch 16. The die 17 is attached to the slide 13 via the die holder 15. That is, the die holder 15 is fixed to the lower surface of the slide 13, and the die 17 is fixed to the lower surface of the die holder 15. A plate-shaped spacer may be inserted between the slide 13 and the die holder 15 to adjust the position of the die 17 in the vertical direction. The slide 13 is configured to be able to rise and fall relative to the punch 16, for example, by a mechanical or hydraulic mechanism (not shown) provided in the press device 10. As the slide 13 rises and falls, the die 17 also rises and falls relative to the punch 16.

The die 17 has a forming surface that corresponds to the forming surface of the punch 16. The forming surface of the die 17 has a shape that is offset from the forming surface of the punch 16 by approximately the same amount as the thickness of the metal sheet 30 to be processed by the mold 11. The forming surface of the die 17 has a shape that is offset from the forming surface of the punch 16 by, for example, 0.9 to 1.2 times the thickness of the metal sheet 30. The die 17 includes a die bottom surface 171, left and right concave surfaces 172L, 172R, left and right die side surfaces 173L, 173R, and left and right die flange surfaces 174L, 174R.

The die bottom surface 171 faces the punch top surface 161. The die bottom surface 171 is formed in a shape that corresponds to the shape of the punch top surface 161. In this embodiment, the die bottom surface 171 has a protruding ridge portion 171a that corresponds to the groove portion 161a of the punch top surface 161.

On both sides of the die bottom surface 171, concave surfaces 172L, 172R are provided corresponding to the convex surfaces 162L, 162R of the punch 16, respectively. The concave surfaces 172L, 172R are provided continuously with the die bottom surface 171. Like the convex surfaces 162L, 162R of the punch 16, the concave surfaces 172L, 172R are typically provided continuously with the die bottom surface 171 over the entire longitudinal direction of the die bottom surface 171.

The concave surface 172L is connected to the left edge of the die bottom surface 171. The concave surface 172L is recessed upward relative to the die bottom surface 171. More specifically, the concave surface 172L is recessed upward compared to a portion of the die bottom surface 171 that is on the outer side (left side) in the width direction than the protruding rib portion 171a. The concave surface 172L has a concave shape that rises once from the die bottom surface 171 toward the outer side in the width direction and then descends. The concave shape of the concave surface 172L corresponds to the convex shape of the convex surface 162L of the punch 16. For example, the bottom of the concave surface 172L is substantially arc-shaped when viewed in a cross section of the die 17.

The concave surface 172R is provided continuously with the right edge of the die bottom surface 171. The concave surface 172R is recessed upward with respect to the die bottom surface 171. More specifically, the concave surface 172R is recessed upward compared to the portion of the die bottom surface 171 that is on the outer side (right side) in the width direction than the protruding rib portion 171a. The concave surface 172R has a concave shape that rises once from the die bottom surface 171 toward the outer side in the width direction and then descends. The concave shape of the concave surface 172R corresponds to the convex shape of the convex surface 162R of the punch 16. For example, the bottom of the concave surface 172R is substantially arc-shaped when viewed in cross section of the punch 16.

The die side surfaces 173L and 173R extend downward from the concave surfaces 172L and 172R, respectively, in a cross-sectional view of the die 17. The die side surfaces 173L and 173R correspond to the punch side surfaces 163L and 163R, respectively. The die side surface 173L is provided continuous with the left concave surface 172L. The die side surface 173R is provided continuous with the right concave surface 172R. In this embodiment, each of the die side surfaces 173L and 173R corresponds to the punch side surfaces 163L and 163R, and is inclined with respect to a vertical plane parallel to the longitudinal direction.

In a cross-sectional view of the die 17, the die flange surfaces 174L and 174R extend outward in the width direction from the lower ends of the die side surfaces 173L and 173R, respectively. The die flange surfaces 174L and 174R correspond to the punch flange surfaces 164L and 164R, respectively. The angles that the die flange surfaces 174L and 174R make with respect to the horizontal plane are substantially equal to the angles that the punch flange surfaces 164L and 164R make with respect to the horizontal plane.

The die flange surface 174L is provided continuously with the left die side surface 173L. The die flange surface 174R is provided continuously with the right die side surface 173R. It is preferable that the corners between the die flange surface 174L and the die side surface 173L are R-chamfered. Similarly, it is preferable that the corners between the die flange surface 174R and the die side surface 173R are R-chamfered. In other words, it is preferable that the corners between the die flange surface 174L and the die side surface 173L, and the corners between the die flange surface 174R and the die side surface 173R, are each substantially arc-shaped when viewed in cross section of the die 17.

[Pressing device for final molded products]
FIG. 3 is a cross-sectional view showing a schematic configuration of the press device 20 for obtaining the press-molded product 50 (FIG. 1) as the final product.

As shown in FIG. 3, the press device 20 includes a die 21, a bed 22, a slide 23, and die holders 24 and 25. The die 21 includes a punch 26, left and right dies 27L and 27R, and a pad 28. The punch 26 and the dies 27L and 27R extend in a direction intersecting the plane of FIG. 3. With respect to the press device 20 and its components, the direction in which the die 21, particularly the punch 26 and the dies 27L and 27R, extend is referred to as the longitudinal direction, and the direction in which the punch 26 and the dies 27L and 27R approach and move away from each other (the vertical direction in FIG. 3) is referred to as the vertical direction (the up-down direction in FIG. 3). The direction perpendicular to the plane consisting of the longitudinal direction and the up-down direction, i.e., the direction crossing the punch 26 and the dies 27L and 27R, is referred to as the left-right direction or width direction. With respect to the press device 20 and its components, a cross section cut by a plane perpendicular to the longitudinal direction is referred to as a transverse section.

The punch 26 is supported by the bed 22, which is part of the main body of the press device 20, via the die holder 24. That is, the die holder 24 is fixed to the upper surface of the bed 22, and the punch 26 is placed on the die holder 24. A plate-shaped spacer may be inserted between the bed 22 and the die holder 24 to adjust the position of the punch 26 in the vertical direction.

The punch 26 includes a punch top surface 261, left and right punch shoulders 262L, 262R, and left and right punch side surfaces 263L, 263R.

In this embodiment, the punch top surface 261 has a groove 261a extending in the longitudinal direction. The groove 261a is formed, for example, in a shape and dimensions corresponding to the groove 161a (FIG. 2) of the punch top surface 161 in the press device 10 shown in FIG. 2. In the example shown in FIG. 3, the punch top surface 261, like the punch top surface 161 (FIG. 2), has an asymmetric shape with respect to a vertical plane parallel to the longitudinal direction, that is, an asymmetric shape. However, the punch top surface 261 may also have a symmetric shape.

The punch shoulders 262L, 262R are provided contiguous with the punch top surface 261. More specifically, the punch shoulder 262L is continuous with the left edge of the punch top surface 261, and the punch shoulder 262R is continuous with the right edge of the punch top surface 261. Each of the punch shoulders 262L, 262R is substantially arc-shaped in a cross-sectional view of the punch 26. The punch shoulders 262L, 262R are ridges (corners) between the punch top surface 261 and the punch side surfaces 263L, 263R, respectively.

The punch side surface 263L extends downward from the left punch shoulder 262L in the cross-sectional view of the punch 26. The punch side surface 263R extends downward from the right punch shoulder 262R in the cross-sectional view of the punch 26. Each of the punch sides 263L, 263R is inclined with respect to a vertical plane parallel to the longitudinal direction so that the lower end is located outward in the width direction from the upper end. The angles (acute angle side) that the punch sides 263L, 263R make with the vertical plane may be the same or different. The angles between the punch sides 263L, 263R and the vertical plane are preferably 20° or less. The angle (acute angle side) that the punch sides 263L, 263R make with the vertical plane parallel to the longitudinal direction means the angle (acute angle side) that the punch sides 263L, 263R make with the vertical direction in a cross section cut by a plane consisting of the up-down direction and the width direction.

The dies 27L and 27R are disposed above the punch 26 and to the side of the pad 28. The dies 27L and 27R are attached to the slide 23 via the die holder 25. That is, the die holder 25 is fixed to the lower surface of the slide 23, and the dies 27L and 27R are fixed to the lower surface of the die holder 25. A plate-shaped spacer may be inserted between the slide 23 and the die holder 25 to adjust the positions of the dies 27L and 27R in the vertical direction. The slide 23 is configured to be able to rise and fall relative to the punch 26, for example, by a mechanical or hydraulic mechanism (not shown) provided in the press device 20. As the slide 23 rises and falls, the dies 27L and 27R also rise and fall relative to the punch 26.

The left die 27L includes an upper die shoulder 271L, a die side surface 272L, a lower die shoulder 273L, a die lower surface 274L, and a die upper surface 275L. The right die 27R includes an upper die shoulder 271R, a die side surface 272R, a lower die shoulder 273R, a die lower surface 274R, and a die upper surface 275R. The left and right dies 27L and 27R may have a symmetrical shape with respect to a vertical plane parallel to the longitudinal direction, or may have an asymmetrical shape.

The upper die shoulders 271L, 271R are provided corresponding to the left and right punch shoulders 262L, 262R, respectively. The upper die shoulders 271L, 271R correspond to the punch shoulders 262L, 262R, respectively, and are substantially arc-shaped in the cross-sectional view of the dies 27L, 27R. The upper die shoulders 271L, 271R are ridges (corners) between the die side surfaces 272L, 272R and the die top surfaces 275L, 275R.

The die top surfaces 275L, 275R are disposed on the inside of the upper die shoulders 271L, 271R in the width direction. The die top surface 275L is provided continuous with the right end of the upper die shoulder 271L and faces the punch top surface 261. The die top surface 275R is provided continuous with the left end of the upper die shoulder 271R and faces the punch top surface 261. The die side surfaces 272L, 272R are disposed on the outside of the upper die shoulders 271L, 271R in the width direction. The die side surface 272L is provided continuous with the left end of the upper die shoulder 271L. The die side surface 272R is provided continuous with the right end of the upper die shoulder 271R.

The die side 272L extends downward from the upper die shoulder 271L in a cross-sectional view of the die 27L. The die side 272R extends downward from the upper die shoulder 271R in a cross-sectional view of the die 27R. The die side 272L, 272R are provided corresponding to the left and right punch side 263L, 263R, respectively. The die side 272L, 272R is inclined with respect to a vertical plane parallel to the longitudinal direction so that the lower end is positioned outward in the width direction from the upper end, corresponding to the punch side 263L, 263R, respectively. The angle (acute angle side) that the die side 272L, 272R makes with respect to the vertical plane is substantially equal to the angle (acute angle side) that the punch side 263L, 263R makes with respect to a vertical plane parallel to the longitudinal direction.

In the left die 27L, the lower die shoulder 273L is provided continuous with the lower end of the die side surface 272L. In the right die 27R, the lower die shoulder 273R is provided continuous with the lower end of the die side surface 272R. The lower die shoulders 273L, 273R are substantially arc-shaped in the cross-sectional view of the dies 27L, 27R, respectively. The lower die shoulders 273L, 273R are ridges (corners) between the die side surfaces 272L, 272R and the die lower surfaces 274L, 274R. The radii of curvature _RdL , _RdR of the lower die shoulders 273L, 273R are preferably 1 mm or more and 12 mm or less, respectively.

In the left die 27L, the die lower surface 274L is connected to the lower end of the die side surface 272L via the lower die shoulder 273L. In the right die 27R, the die lower surface 274R is connected to the lower end of the die side surface 272R via the lower die shoulder 273R. The die lower surfaces 274L, 274R extend outward in the width direction from the lower die shoulders 273L, 273R in a cross-sectional view of the dies 27L, 27R, respectively. In this embodiment, the die lower surfaces 274L, 274R extend horizontally from the lower die shoulders 273L, 273R. However, at least one of the die lower surfaces 274L, 274R may be inclined with respect to the horizontal plane. The horizontal plane refers to a plane perpendicular to the direction in which the dies 27L, 27R rise and fall (up and down direction).

The pad 28 is disposed above the punch 26 so as to face the punch top surface 261. The pad 28 is disposed between the left and right dies 27L, 27R. The pad 28 is attached to the slide 23 via the die holder 25, so that it can be raised and lowered relative to the punch 26.

The pad 28 has a pad body 281 and a support member 282. The lower surface of the pad body 281 faces the punch top surface 261. The lower surface of the pad body 281 is formed in a shape corresponding to the punch top surface 261. In this embodiment, a convex rib portion 281a extending in the longitudinal direction is provided on the lower surface of the pad body 281 in correspondence with the groove portion 261a of the punch top surface 261. The support member 282 elastically supports the pad body 281 against the die holder 25. The support member 282 is an expandable member constituted of, for example, a spring or a fluid pressure cylinder.

[Method of manufacturing press-molded products]
Hereinafter, a method for manufacturing a press-formed product using the manufacturing equipment 100 will be described. The manufacturing method for a press-formed product according to this embodiment includes a first step of obtaining an intermediate product 40 by pressing a metal plate 30, and a second step of obtaining a press-formed product 50 by pressing the intermediate product 40. In the first step, a press device 10 is used, and in the second step, a press device 20 is used.

(First step)
4A to 4E are schematic diagrams for explaining the first step. First, referring to FIG. 4A, when the first step is performed, a metal plate 30, which is a material, is prepared. The metal plate 30 is typically a steel plate. The plate thickness t of the metal plate 30 is, for example, 2.0 mm or more and 8.0 mm or less. The metal plate 30 has a tensile strength of, for example, 270 MPa or more and 1180 MPa or less. When the press-molded product 50 to be manufactured is an arm part among the suspension parts of an automobile, the tensile strength of the metal plate 30 is usually 590 MPa or more. Also, when the press-molded product 50 to be manufactured is a frame part such as a ladder frame of an automobile, the tensile strength of the metal plate 30 is usually 590 MPa or more.

The work hardening index of the metal plate 30 is preferably 0.04 or less. In addition, the metal plate 30 is preferably one in which the ratio of the yield stress YS to the tensile strength TS (yield ratio) YR=YS/TS is 0.95 or more. The work hardening index is an index showing the ease of work hardening of the metal plate 30, and the larger the value, the easier the material is to work harden. The work hardening index (n value) is defined in JIS G 0202:2013, and is measured, for example, by the method specified in JIS Z 2253:2011. The yield ratio YR is a value that is inversely correlated with the n value, so it decreases as the n value increases.

Next, the prepared metal plate 30 is pressed using the die 11 included in the press device 10. When the press process is started, as shown in FIG. 4B, the metal plate 30 is placed on the punch 16 with the die 17 positioned at the top dead center. The metal plate 30 is supported, for example, by at least one of the convex surfaces 162L, 162R. Next, the slide 13 is lowered to lower the die 17 toward the metal plate 30 on the punch 16.

As shown in FIG. 4C, when the die 17 comes into contact with the metal sheet 30, the metal sheet 30 begins to deform along the forming surfaces of the punch 16 and the die 17. As shown in FIG. 4D, when the die 17 reaches the bottom dead center, the metal sheet 30 is pressed between the punch 16 and the die 17, and the intermediate formed product 40 is completed.

Figure 4E is a cross-sectional view (transverse cross-sectional view) of the intermediate molded product 40 obtained in the first step, cut along a plane perpendicular to its longitudinal direction. The longitudinal and width directions of the intermediate molded product 40 coincide with the longitudinal and width directions of the mold 11 (Figure 2). As shown in Figure 4E, the intermediate molded product 40 includes a top plate 41, left and right protrusions 42L, 42R, left and right vertical walls 43L, 43R, and left and right flanges 44L, 44R.

The top plate 41 is a portion of the intermediate molded product 40 that is formed by the punch top surface 161 and the die bottom surface 171 (Figure 2). The top plate 41 has a groove 41a formed therein that corresponds to the groove 161a of the punch top surface 161 and the protruding ridge 171a of the die bottom surface 171.

The left and right convex portions 42L, 42R are connected to the top plate 41. The convex portion 42L is a portion of the intermediate molded product 40 formed by the convex surface 162L of the punch 16 and the concave surface 172L of the die 17 (FIG. 2). The convex portion 42R is a portion of the intermediate molded product 40 formed by the convex surface 162R of the punch 16 and the concave surface 172R of the die 17 (FIG. 2). Each of the convex portions 42L, 42R protrudes upward from the top plate 41. More specifically, the convex portion 42L protrudes upward from the portion of the top plate 41 that is on the outer side (left side) of the groove portion 41a in the width direction. The convex portion 42R protrudes upward from the portion of the top plate 41 that is on the outer side (right side) of the groove portion 41a in the width direction.

The convex portions 42L, 42R include apexes 421L, 421R, respectively. Each of the apexes 421L, 421R is substantially arc-shaped in a cross-sectional view of the intermediate molded product 40. Each of the apexes 421L, 421R preferably has a radius of curvature of 4 mm or more and 16 mm or less. The radius of curvature here is the radius of curvature on the inner side of the bend of the apexes 421L, 421R.

The portion of the left convex portion 42L on the top plate 41 side, that is, the base portion 422L of the convex portion 42L, is, for example, substantially arc-shaped in the cross-sectional view of the intermediate molded product 40. The end (R end) of the base portion 422L on the top plate 41 side is the connection portion between the convex portion 42L and the top plate 41. In the example of this embodiment, the distance in the width direction of the intermediate molded product 40 from this connection portion to the upper end of the convex portion 42L is the width _W1L [mm] of the convex portion 42L. Also, the distance in the vertical direction from the connection portion between the convex portion 42L and the top plate 41 to the upper end of the convex portion 42L is the height _H1L [mm] of the convex portion 42L. However, the height _H1L is the vertical distance between the plate thickness center of the connection portion and the plate thickness center of the upper end of the convex portion 42L.

The height _H1L of the protrusion 42L is preferably 5 mm or more and 25 mm or less. In the protrusion 42L, the ratio of the height _H1L to the width _W1L : _H1L / _W1L is preferably 0.5 or more and 2.0 or less.

Similarly, the portion of the right convex portion 42R on the top plate 41 side, that is, the base portion 422R of the convex portion 42R, is, for example, substantially arc-shaped in the cross-sectional view of the intermediate molded product 40. The end (R end) of the base portion 422R on the top plate 41 side is the connection portion between the convex portion 42R and the top plate 41. In the example of this embodiment, the distance in the width direction of the intermediate molded product 40 from this connection portion to the upper end of the convex portion 42R is the width _W1R [mm] of the convex portion 42R. Also, the distance in the vertical direction from the connection portion between the convex portion 42R and the top plate 41 to the upper end of the convex portion 42R is the height _H1R [mm] of the convex portion 42R. However, the height _H1R is the vertical distance between the plate thickness center of the connection portion and the plate thickness center of the upper end of the convex portion 42R.

The height _H1R of the protrusion 42R is preferably 5 mm or more and 25 mm or less. In the protrusion 42R, the ratio of the height _H1R to the width _W1R : _H1R / _W1R is preferably 0.5 or more and 2.0 or less.

The left and right vertical walls 43L, 43R extend downward from the convex portions 42L, 42R, respectively, in a cross-sectional view of the intermediate molded product 40. The vertical wall 43L is disposed to the left of the convex portion 42L and connects the convex portion 42L and the flange 44L. The vertical wall 43R is disposed to the right of the convex portion 42R and connects the convex portion 42R and the flange 44R. The connection portion between the vertical wall 43L and the convex portion 42L and the connection portion between the vertical wall 43R and the convex portion 42R may each have a smooth shape that is continuously provided from the convex portions 42L, 42R to the vertical walls 43L, 43R. The vertical walls 43L, 43R or the convex portions 42L, 42R may be curved (inflected) inward or outward in the width direction on the way from the upper ends of the convex portions 42L, 42R to the left and right flanges 44L, 44R.

The left and right flanges 44L, 44R extend from the lower ends of the vertical walls 43L, 43R, respectively, to the opposite side of the top plate 41, in a cross-sectional view of the intermediate molded product 40. The left flange 44L extends from the vertical wall 43L to the outside in the width direction (left side), in a cross-sectional view of the intermediate molded product 40. The right flange 44R extends from the vertical wall 43R to the outside in the width direction (right side), in a cross-sectional view of the intermediate molded product 40. The flanges 44L, 44R are connected to the vertical walls 43L, 43R via arc-shaped corners 45L, 45R, respectively, in a cross-sectional view of the intermediate molded product 40.

The height H2 of the intermediate molded product 40 is preferably 6 mm or more. The height H2 of the intermediate molded product 40 refers to the vertical distance from the end of the vertical wall 43L, 43R of the flanges 44L, 44R, that is, the R end of the flanges 44L, 44R of the corners 45L, 45R on the flanges 44L, 44R side, to the top plate 41. However, the height H2 is the vertical distance between the center of the plate thickness of the end of the vertical wall 43L, 43R of the flanges 44L, 44R and the center of the plate thickness of the top plate 41 at the connection with the convex portions 42L, 42R. If the vertical distance from the center of thickness of the end of flange 44L on the vertical wall 43L side to the center of thickness of top plate 41 at the connection with convex portion 42L is different from the vertical distance from the center of thickness of the end of flange 44R on the vertical wall 43R side to the center of thickness of top plate 41 at the connection with convex portion 42R, the smaller of the two distances is taken as the height H2 of intermediate molded product 40.

(Second step)
After the first step is completed, the second step is carried out. Figures 5A to 5H are schematic diagrams for explaining the second step. In the second step, the intermediate molded product 40 obtained in the first step is subjected to press working by a die 21 included in a press device 20. The second step includes steps (a) to (d) described below.

Step (a)
5A, first, in step (a), the intermediate molded product 40 is placed on the punch 26 of the die 21. More specifically, the intermediate molded product 40 is placed on the punch 26 so that the top plate 41 is placed on the punch top surface 261. The intermediate molded product 40 is also placed on the punch 26 so that the protrusions 42L, 42R are placed at positions corresponding to the punch shoulders 262L, 262R, respectively. The top plate 41 is placed, for example, so that the position of the groove 41a coincides with the position of the groove 261a of the punch top surface 261. The protrusions 42L, 42R continuing from the top plate 41 are preferably positioned outside the pad profile P in the width direction of the die 21. The pad profile P is a boundary portion between the pad main body 281 and the dies 27L, 27R.

The protrusions 42L, 42R are positioned in positions corresponding to the punch shoulders 262L, 262R, respectively, meaning that the protrusions 42L, 42R are positioned so that at least a portion of the protrusions 42L, 42R is pressed by the punch shoulders 262L, 262R and the upper die shoulders 271L, 271R. For example, the protrusions 42L, 42R are positioned so that at least a portion of the protrusions 42L, 42R overlaps with the punch shoulders 262L, 262R in the width direction of the die 21.

5B, when the intermediate molded product 40 is placed on the punch 26, the upper end of the convex portion 42L is preferably located inside the lower end of the die side surface 272L (the end of the R on the die side surface 272L side of the lower die shoulder 273L) in the width direction of the mold 21. That is, if the distance in the width direction between the upper end of the convex portion 42L and the lower end of the die side surface 272L is _D1L [mm], it is preferable that _D1L > 0. Regarding the distance _D1L , a case where the upper end of the convex portion 42L is located inside the lower end of the die side surface 272L in the width direction is positive, and a case where the upper end of the convex portion 42L is located outside the lower end of the die side surface 272L in the width direction is negative.

Similarly, when the intermediate molded product 40 is placed on the punch 26, the upper end of the convex portion 42R is preferably located more inward than the lower end of the die side surface 272R (the R end of the lower die shoulder 273R on the die side surface 272R side) in the width direction of the mold 21. That is, if the distance in the width direction between the upper end of the convex portion 42R and the lower end of the die side surface 272R is _D1R [mm], it is preferable that _D1R > 0. Regarding the distance _D1R , a case in which the upper end of the convex portion 42R is more inward in the width direction than the lower end of the die side surface 272R is positive, and a case in which the upper end of the convex portion 42R is more outward in the width direction than the lower end of the die side surface 272R is negative.

More preferably, when the intermediate molded product 40 is placed on the punch 26, the distances D2L, D2R [mm] in the width direction of the die 21 from the ends (R end) of the punch shoulders 262L, 262R on the punch top surface 261 side to the upper ends of the protrusions _42L , 42R are set to satisfy the following formula (1). In formula (1), the distances _D2L , _D2R are collectively represented as D2. In formula (1), the radii of curvature _RpL , _RpR "mm _" of the punch shoulders 262L, 262R and the angles _θL , _θR [rad] between the punch top surface 261 and the punch side surface 263L in a cross-sectional view are collectively represented as Rp and θ. That is, in the following formula (1), when the distance D2 is the distance _D2L , Rp and θ are _RpL and _θL , respectively, and when the distance D2 is the distance _D2R , Rp and θ are _RpR and _θR , respectively. The distance D2 is positive when the upper ends of the convex portions 42L, 42R are located on the outer side in the width direction than the ends of the corresponding punch shoulders 262L, 262R on the punch top surface 261 side, and is negative when the upper ends are located on the inner side in the width direction.
-1.0×Rp×(π-θ)≦D2≦2.5×Rp×(π-θ)...(1)

When the intermediate molded product 40 is placed on the punch 26, the lower end of the vertical wall 43L is preferably located outside the upper end of the punch side surface 263L (the R end of the punch side surface 263L of the punch shoulder 262L) in the width direction of the die 21. That is, if the distance in the width direction between the lower end of the vertical wall 43L and the upper end of the punch side surface 263L is _D3L [mm], it is preferable that _D3L >0. Regarding the distance _D3L , it is positive when the lower end of the vertical wall 43L is located outside the upper end of the punch side surface 263L in the width direction, and it is negative when the lower end of the vertical wall 43L is located inside the upper end of the punch side surface 263L in the width direction. In addition, regarding the distance _D3L , the lower end of the vertical wall 43L refers to the R end on the vertical wall 43L side of the bend outside of the corner portion 45L, that is, of the two R ends on the inside (punch 26 side) of the intermediate molded product 40.

Similarly, when the intermediate molded product 40 is placed on the punch 26, the lower end of the vertical wall 43R is preferably located outside the upper end of the punch side surface 263R (the R end of the punch side surface 263R of the punch shoulder 262R) in the width direction of the die 21. That is, if the distance in the width direction between the lower end of the vertical wall 43R and the upper end of the punch side surface 263R is _D3R [mm], it is preferable that _D3R >0. Regarding the distance _D3R , it is positive when the lower end of the vertical wall 43R is located outside the upper end of the punch side surface 263R in the width direction, and it is negative when the lower end of the vertical wall 43R is located inside the upper end of the punch side surface 263R in the width direction. In addition, regarding the distance _D3R , the lower end of the vertical wall 43R refers to the R end on the vertical wall 43R side of the bend outside of the corner portion 45R, that is, of the two R ends on the inside (punch 26 side) of the intermediate molded product 40.

5C, when the intermediate molded product 40 is placed on the punch 26, the angles φ _L and φ _R that the flanges 44L and 44R make with the horizontal plane are preferably not less than -40° and not more than 40°. More preferably, the angles φ _L and φ _R are not less than -10° and not more than 10°. Even more preferably, the angles φ _L and φ _R are substantially 0°. The angles φ _L and φ _R that the flanges 44L and 44R make with the horizontal plane refer to the angles (acute angle side) that the flanges 44L and 44R make with the width direction in a cross section cut along a plane consisting of the up-down direction and the width direction. Regarding the angles _φL and _φR , when the flanges 44L and 44R rotate upward about the end of the vertical walls 43L and 43R (the R end (inside of the bend) of the corners 45L and 45R on the flanges 44L and 44R), it is considered positive, and when the flanges 44L and 44R rotate downward, it is considered negative. The angles _φL and _φR of the flanges 44L and 44R may be equal to each other or may be different from each other.

The lengths L _L and L _R of the flanges 44L and 44R are preferably 10 mm or more, respectively. The lengths L _L and L _R are lengths along the flanges 44L and 44R from the ends of the flanges 44L and 44R on the vertical walls 43L and 43R sides (the ends of the R on the flanges 44L and 44R sides of the corners 45L and 45R (inside the bend)) to the tips (free ends) of the flanges 44L and 44R.

Step (b)
Referring again to Fig. 5A, in step (a), when the intermediate molded product 40 is placed on the punch 26, the die lower surfaces 274L and 274R face the flanges 44L and 44R, and the pad 28 faces the top plate 41 on the punch top surface 261. Referring to Fig. 5D, in step (b), the pad 28 is lowered to press the top plate 41 of the intermediate molded product 40 on the punch top surface 261 with the pad 28. Specifically, by lowering the slide 23, the dies 27L and 27R attached to the slide 23 and the pad 28 are lowered toward the intermediate molded product 40. The pad 28 contacts the intermediate molded product 40 on the punch 26 prior to the dies 27L and 27R. The pad 28 presses the top plate 41 of the intermediate molded product 40 from above with the pad body 281.

Step (c)
5E, after the top plate 41 of the intermediate molded product 40 is pressed by the pad body 281, the slide 23 further descends. At this time, the support member 282 supporting the pad body 281 contracts, causing the dies 27L, 27R to descend relatively to the pad body 281 pressing the top plate 41. In step (c), the dies 27L, 27R are thus lowered, and the dies 27L, 27R are brought into contact with the flanges 44L, 44R with the top plate 41 pressed by the pad 28.

Step (d)
After the dies 27L and 27R come into contact with the flanges 44L and 44R of the intermediate molded product 40, the dies 27L and 27R are further lowered while the flanges 44L and 44R and their vicinity are hooked on the lower die shoulders 273L and 273R. That is, after the dies 27L and 27R come into contact with the flanges 44L and 44R of the intermediate molded product 40, the dies 27L and 27R are further lowered while still in contact with the flanges 44L and 44R. Referring to FIG. 5F, as the dies 27L and 27R descend, the upper die shoulders 271L and 271R or their vicinity come into contact with the convex portions 42L and 42R and start to crush the convex portions 42L and 42R. The convex portions 42L and 42R are gradually crushed, for example, by the upper die shoulders 271L and 271R as well as the die upper surfaces 275L and 275R. When crushed, the convex portions 42L, 42R do not buckle locally, but rather the entire convex portions 42L, 42R conform to the punch 26. Thus, in step (d), after the dies 27L, 27R come into contact with the flanges 44L, 44R of the intermediate molded product 40, the dies 27L, 27R are further lowered to crush the convex portions 42L, 42R by the dies 27L, 27R. Meanwhile, the flanges 44L, 44R are gradually drawn toward the punch 26 as the dies 27L, 27R descend.

Referring to FIG. 5G, the dies 27L, 27R are finally brought to bottom dead center, and the intermediate molded product 40 is pressed between the upper die shoulders 271L, 271R and the punch shoulders 262L, 262R, and between the die sides 272L, 272R and the punch sides 263L, 263R. The intermediate molded product 40 is also pressed between the pad body 281 and the punch top surface 261. This produces the press-molded product 50.

When the dies 27L, 27R reach the bottom dead point, the flanges 44L, 44R of the intermediate product 40 are completely drawn toward the punch 26 and positioned between the die side surfaces 272L, 272R and the punch side surfaces 263L, 263R. However, it is preferable that the flanges 44L, 44R are in contact with the dies 27L, 27R until just before the dies 27L, 27R reach the bottom dead point. On the other hand, the protruding portions 42L, 42R of the intermediate product 40 are completely crushed by the dies 27L, 27R when the dies 27L, 27R reach the bottom dead point. At least a part of the protruding portions 42L, 42R is pressed between the upper die shoulders 271L, 271R and the punch shoulders 262L, 262R.

Figure 5H is a perspective view partially showing the manufactured press-molded product 50. The press-molded product 50 has a top plate 51, left and right vertical walls 52L, 52R, and left and right bent portions 53L, 53R. A groove portion 51a extending in the longitudinal direction is formed in the top plate 51. The upper end of the left vertical wall 52L is connected to the left edge of the top plate 51 via the left bent portion 53L. The upper end of the right vertical wall 52R is connected to the right edge of the top plate 51 via the right bent portion 53R. The lower ends of the vertical walls 52L, 52R are each free ends. Each of the bent portions 53L, 53R is substantially arc-shaped in a cross-sectional view of the press-molded product 50.

[effect]
In the manufacturing method according to the present embodiment, the metal plate 30 is pressed into the intermediate product 40 in the first step, and then the intermediate product 40 is pressed in the second step to obtain the press-formed product 50. In the second step, the dies 27L and 27R are brought into contact with the flanges 44L and 44R of the intermediate product 40 while the top plate 41 of the intermediate product 40 is pressed from above by the pad 28. The dies 27L and 27R are lowered while the flanges 44L and 44R are hooked on the lower die shoulders 273L and 273R. This allows tension to be applied to the intermediate product 40, which is a portion that is on the outer side in the width direction from the region pressed by the pad 28 and reaches the region that is in contact with the lower die shoulders 273L and 273R, that is, the portion that will become the bent portion 53L and 53R of the press-formed product 50. Therefore, the compressive stress on the inner side of the bend at the end of forming can be reduced in the bent portion 53L and 53R of the press-formed product 50. As a result, the tensile stress caused by springback is reduced, and the tensile stress remaining on the inner side of the bend in the bent portions 53L, 53R of the press-formed product 50 can be reduced.

In the manufacturing method according to this embodiment, the convex portions 42L, 42R of the intermediate molded product 40 are crushed by the dies 27L, 27R in the second step and undergo bending back deformation. In the process in which the convex portions 42L, 42R are bent back by the dies 27L, 27R and pressed into the punch shoulders 262L, 262R, compressive stress occurs in the region of the convex portions 42L, 42R on the die 27L, 27R side (outside of the bend), and tensile stress occurs in the region of the punch 26 side (inside of the bend). These stresses can reduce the tensile stress occurring on the outside of the bend and the compressive stress occurring on the inside of the bend when the intermediate molded product 40 fits into the punch shoulders 262L, 262R to form the bent portions 53L, 53R. Therefore, the tensile stress remaining on the inside of the bend can be reduced in the bent portions 53L, 53R of the press molded product 50 after springback.

It is difficult to flatten the convex portions 42L, 42R by simply applying tension from the periphery to the convex portions 42L, 42R arranged at positions corresponding to the punch shoulders 262L, 262R. However, in the manufacturing method according to the present embodiment, in the second step, the convex portions 42L, 42R are crushed from above by the dies 27L, 27R, so that the convex portions 42L, 42R can be flattened firmly. More specifically, the descending dies 27L, 27R hit the convex portions 42L, 42R and crush the convex portions 42L, 42R from the tops 421L, 421R. This generates a large stress from the bases 422L, 422R of the convex portions 42L, 42R toward the tops 421L, 421R. That is, a large tensile stress is generated in the region of the convex portions 42L, 42R on the punch 26 side (inside the bend). This effectively reduces the compressive stress that occurs on the inside of the bend at the end of the second step, and reduces the tensile residual stress that occurs on the inside of the bend in the bent parts 53L and 53R of the press-formed product 50 after springback.

In this way, the dies 27L, 27R descend with the flanges 44L, 44R hooked on the lower die shoulders 273L, 273R, and while applying tension to the portions that will become the bent portions 53L, 53R of the press-formed product 50, they hit the convex portions 42L, 42R and crush the convex portions 42L, 42R from the apexes 421L, 421R. This significantly reduces the compressive stress that occurs on the inside of the bend at the end of the second process, and significantly reduces the tensile residual stress that occurs on the inside of the bend in the bent portions 53L, 53R of the press-formed product 50 after springback.

As described above, according to the manufacturing method of the press-molded product 50 according to this embodiment, the tensile residual stress that occurs on the inner side of the bends 53L and 53R of the press-molded product 50 can be reduced during the press processing process.

The press working process is preferably carried out using a simple press mechanism and a simple forming motion. A press working process using a simple press mechanism and a simple forming motion refers to a press working process that can be realized, for example, by using a single-action press device and essentially only by the movement of the upper die downward toward the lower die. In the manufacturing method according to this embodiment, a single-action press device 20 is used in the second step. The press device 20 essentially forms the press-formed product 50 from the intermediate product 40 simply by simultaneously lowering the dies 27L, 27R and the pad 28 toward the punch 26. That is, in this embodiment, the press working process using a simple press mechanism and a simple forming motion can reduce the tensile residual stress that occurs on the inside of the bend in the bent portions 53L, 53R of the press-formed product 50.

In the manufacturing method according to this embodiment, when the intermediate molded product 40 is placed on the punch 26, that is, at the start of the second step, it is preferable that the upper ends of the convex portions 42L, 42R are located inside the lower ends of the die sides 272L, 272R in the width direction of the die 21. This makes it possible to prevent the convex portions 42L, 42R from being crushed by the lower die shoulders 273L, 273R or the die lower surfaces 274L, 274R at the beginning of the second step. In other words, after tension is applied to the convex portions 42L, 42R by contact between the dies 27L, 27R and the flanges 44L, 44R, the convex portions 42L, 42R can be crushed by the dies 27L, 27R, and tensile stress can be generated more effectively in the region inside the bend. As a result, the compressive stress that occurs on the inside of the bend at the end of the second process in the bent portions 53L and 53R of the press-formed product 50 can be more reliably reduced, and the effect of reducing the tensile stress remaining on the inside of the bend after springback can be improved.

In the manufacturing method according to this embodiment, when the intermediate molded product 40 is placed on the punch 26, the lower ends of the vertical walls 43L, 43R are positioned outward in the width direction of the die 21 from the upper ends of the punch side surfaces 263L, 263R. That is, at the start of the second step, the intermediate molded product 40 is fitted into the punch 26 without the top plate 41 floating up from the punch 26. Therefore, in the second step, when the top plate 41 of the intermediate molded product 40 is pressed by the pad 28, the pad 28 can be prevented from floating up, and molding can be performed stably. Therefore, the dimensional accuracy of the press-molded product 50 obtained in the second step can be stabilized.

In the convex portion 42L of the intermediate molded product 40, the ratio of the height _H1L to the width _W1L : _H1L / _W1L is preferably 0.5 or more and 2.0 or less. Similarly, in the convex portion 42R of the intermediate molded product 40, the ratio of the height _H1R to the width _W1R : _H1R / _W1R is preferably 0.5 or more and 2.0 or less. Fig. 6 is a graph showing the relationship between the height H1/width W1 and the tensile residual stress on the inner side of the bend in the bent portions 53L, 53R of the press-molded product 50. In Fig. 6, the widths _W1L , _W1R and the heights _H1L , _H1R of the convex portions 42L, 42R are collectively referred to as the width W1 and the height H1. FIG. 6 and FIGS. 7 to 13 described later show the results obtained when a CAE analysis was performed using commercially available software (LS-DYNA ver971 rev7.12, manufactured by ANSYS) on the press working for forming a press-formed product 50 having a bending R (inner curvature radius of bending) of bending portions 53L, 53R of 4.0 mm and a vertical wall height of 25 mm from a metal plate 30 having a tensile strength of 980 MPa and a plate thickness of 3.0 mm.

As shown in FIG. 6, when H1/W1 is 0.5 or more, the tensile residual stress on the inside of the bend is reduced by 100 MPa or more compared to when conventional press processing is performed without using the intermediate molded product 40. Therefore, H1/W1 is preferably 0.5 or more. The tensile residual stress on the inside of the bend is reduced as H1/W1 increases. However, as H1/W1 increases, the convex portions 42L, 42R rise more steeply from the top plate 41, and therefore there is a possibility that the convex portions 42L, 42R will buckle when the convex portions 42L, 42R are crushed by the dies 27L, 27R in the second step. In order to make it difficult for the convex portions 42L, 42R to buckle, it is preferable that H1/W1 is 2.0 or less.

In this embodiment, the convex portions 42L, 42R of the intermediate molded product 40 each include a top portion 421L, 421R that is substantially arc-shaped in cross section. The radius of curvature of each of the top portions 421L, 421R is preferably 4 mm or more and 16 mm or less. The radius of curvature here refers to the value on the inside (punch 16 side) of the convex portions 42L, 42R. Figure 7 is a graph showing the relationship between the radius of curvature of the top portions 421L, 421R and the tensile residual stress on the inside of the bend in the bent portions 53L, 53R of the press-molded product 50.

As can be seen from FIG. 7, if the radius of curvature of the apexes 421L, 421R is 16 mm or less, the tensile residual stress on the inside of the bend is reduced by 100 MPa or more compared to when conventional press processing is performed without using the intermediate molded product 40. Therefore, the radius of curvature of the apexes 421L, 421R is preferably 16 mm or less. The tensile residual stress on the inside of the bend is reduced as the radius of curvature of the apexes 421L, 421R becomes smaller. However, it is preferable that the radius of curvature of the apexes 421L, 421R is 4 mm or more. This is to make it difficult for buckling of the convex portions 42L, 42R to occur when the convex portions 42L, 42R are crushed by the dies 27L, 27R in the second step.

In this embodiment, when the intermediate molded product 40 is placed on the punch 26, that is, at the start of the second process, it is preferable that each distance D2 [mm] in the width direction of the mold 21 from the end of the punch shoulders 262L, 262R on the punch top surface 261 side to the upper ends of the convex portions 42L, 42R is set so as to satisfy the following formula (1).
-1.0×Rp×(π-θ)≦D2≦2.5×Rp×(π-θ)...(1)

By setting the distance D2 in this manner, the convex portions 42L, 42R tend to overlap in the range of the punch shoulders 262L, 262R in the width direction of the die 21. Therefore, stress due to bending back deformation of the convex portions 42L, 42R can be generated widely in the area of the punch shoulders 262L, 262R. Therefore, the compressive stress generated on the inside of the bend when the intermediate molded product 40 fits into the punch shoulders 262L, 262R and the bent portions 53L, 53R are formed can be more effectively reduced. As a result, the tensile residual stress generated on the inside of the bend in the bent portions 53L, 53R of the press-molded product 50 can be more reliably reduced.

In this embodiment, the height H2 of the intermediate molded product 40 is preferably 6 mm or more. Figure 8 is a graph showing the relationship between the height H2 of the intermediate molded product 40 and the tensile residual stress on the inner side of the bend in the bent portions 53L and 53R of the press-molded product 50.

As shown in FIG. 8, the tensile residual stress on the inner side of the bend is reduced as the height H2 of the intermediate molded product 40 increases, compared to when conventional press processing is performed without using the intermediate molded product 40. In particular, if the height H2 of the intermediate molded product 40 is 6 mm or more, the tensile residual stress on the inner side of the bend is reduced by 200 MPa or more, and a significant residual stress reduction effect is achieved. This is because the height H2 of the intermediate molded product 40 is sufficiently secured, so that in the second step, when the dies 27L, 27R in contact with the flanges 44L, 44R descend, the vertical walls 43L, 43R are prevented from bending, and the flanges 44L, 44R are firmly hooked onto the lower die shoulders 273L, 273R during molding, so that tension can be applied to the intermediate molded product 40 more effectively.

In this embodiment, the height H2 of the intermediate molded product 40 is defined as the vertical distance from the ends of the vertical walls 43L, 43R of the flanges 44L, 44R to the top plate 41. If the vertical distance from the center of thickness of the end of the vertical wall 43L of the flange 44L to the center of thickness of the top plate 41 at the connection with the convex portion 42L is different from the vertical distance from the center of thickness of the end of the vertical wall 43R of the flange 44R to the center of thickness of the top plate 41 at the connection with the convex portion 42R, the smaller of the two distances becomes the height H2. However, it is preferable that the two distances are substantially equal.

For example, if the intermediate molded product 40 has a long vertical distance on the flange 44L side, that is, if the left punch side 163L is higher than the right punch side 163R in the die 11 in the first step, the die flange surface 174L will contact the metal sheet 30 before the die flange surface 174R when pressing the metal sheet 30. This may cause the metal sheet 30 to move into the space between the punch flange surface 164L and the die flange surface 174L, making it difficult to perform the press processing stably. On the other hand, if the height of the left punch side 163L is substantially equal to the height of the right punch side 163R, the metal sheet 30 is less likely to move, and stable press processing can be achieved in the first step.

In this embodiment, when the intermediate product 40 is placed on the punch 26, that is, at the start of the second step, the angles φ _L and φ _R of the flanges 44L, 44R with respect to the horizontal plane are preferably not less than -40° and not more than 40°. Fig. 9 is a graph showing the relationship between the angle φ and the tensile residual stress on the inner side of the bend in the bent portions 53L, 53R of the press-formed product 50. In Fig. 9, the angles φ _L and φ _R of the flanges 44L, 44R are collectively referred to as angle φ.

As shown in FIG. 9, when the angle φ of the flanges 44L, 44R is -40° or more, the tensile residual stress on the inside of the bend is reduced by 100 MPa or more compared to when a conventional press process is performed without using the intermediate molded product 40. Therefore, the angle φ is preferably -40° or more. The tensile residual stress on the inside of the bend is reduced as the angle φ increases. However, if the angle φ is too large, in the second step, the free ends of the flanges 44L, 44R, rather than the surfaces of the flanges 44L, 44R, may come into contact with the dies 27L, 27R, causing the flanges 44L, 44R to buckle. In addition, the flanges 44L, 44R may come into contact with the dies 27L, 27R at their tips, increasing the contact surface pressure of the flanges 44L, 44R against the dies 27L, 27R, which may damage the dies 27L, 27R. Therefore, the angle φ of the flanges 44L, 44R is preferably 40° or less. More preferably, the angle φ of the flanges 44L and 44R is greater than or equal to -10° and less than or equal to 10°.

In this embodiment, the lengths L _L , L _R of the flanges 44L, 44R of the intermediate product 40 are preferably 10 mm or more. Fig. 10 is a graph showing the relationship between the length L and the tensile residual stress on the inner side of the bent portions 53L, 53R of the press-formed product 50. In Fig. 10, the lengths L _L , L _R of the flanges 44L, 44R are collectively referred to as length L.

As shown in FIG. 10, if the length L of the flanges 44L, 44R is 10 mm or more, the tensile residual stress on the inside of the bend is reduced by 100 MPa or more compared to when conventional press working is performed without using the intermediate molded product 40. This is because the length L of the flanges 44L, 44R is sufficiently secured, so that the flanges 44L, 44R are more likely to be caught by the lower die shoulders 273L, 273R in the second step until the later stages of molding, and tension is more effectively applied to the convex portions 42L, 42R and the vertical walls 43L, 43R. The tensile residual stress on the inside of the bend is reduced as the length L of the flanges 44L, 44R is larger. Therefore, it is preferable that the length L of the flanges 44L, 44R is 10 mm or more.

Regarding the die 21 used in the second step of the manufacturing method according to this embodiment, it is preferable that the lower die shoulders 273L, 273R are substantially arc-shaped with radii of curvature _RdL , _RdR of 1 mm or more and 12 mm or less in a cross-sectional view of the dies 27L, 27R. Fig. 11 is a graph showing the relationship between the radius of curvature Rd and the tensile residual stress on the inner side of the bent portion 53L, 53R of the press-formed product 50. In Fig. 11, the radii of curvature _RdL , _RdR of the lower die shoulders 273L, 273R are collectively referred to as the radius of curvature Rd.

As shown in FIG. 11, if the radius of curvature Rd of the lower die shoulders 273L, 273R is 12 mm or less, the tensile residual stress on the inside of the bend is significantly reduced compared to when conventional press processing is performed without using the intermediate molded product 40. Therefore, the radius of curvature Rd is preferably 12 mm or less. The tensile residual stress on the inside of the bend is reduced as the radius of curvature Rd becomes smaller. However, if the radius of curvature Rd is less than 1 mm, the lower die shoulders 273L, 273R may leave bite marks on the press-molded product 50 or cause a large bending tendency in the press-molded product 50. Therefore, it is preferable that the radius of curvature Rd of the lower die shoulders 273L, 273R is 1 mm or more.

In this embodiment, when the intermediate molded product 40 is placed on the punch 26, that is, at the start of the second step, it is preferable that each of the convex portions 42L, 42R is located outside the pad profile P in the width direction of the die 21. Figure 12 is a graph showing the relationship between the positions of the convex portions 42L, 42R relative to the pad profile P and the tensile residual stress on the inner side of the bend in the bent portions 53L, 53R of the press-molded product 50.

12, when a part of the convex parts 42L, 42R is located on the inner side of the pad profile P in the width direction and interferes with the pad body 281, the effect of reducing the tensile residual stress on the inner side of the bend is smaller than when the convex parts 42L, 42R are located on the outer side of the pad profile P in the width direction and do not interfere with the pad body 281. Furthermore, when a part of the convex parts 42L, 42R is located on the inner side of the pad profile P in the width direction and interferes with the pad body 281, the outer periphery of the pad body 281 may be pierced by the convex parts 42L, 42R, causing scratches on the press-molded product 50. Therefore, at the start of the second process, it is preferable that the entire convex parts 42L, 42R are located on the outer side of the pad profile P in the width direction so that the convex parts 42L, 42R do not interfere with the pad body 281. However, as can be seen from FIG. 12, when the intermediate molded product 40 is used to obtain the press-molded product 50, even if the convex portions 42L and 42R interfere with a part of the pad body 281, the tensile residual stress on the inside of the bend can be significantly reduced compared to conventional press processing that does not use the intermediate molded product 40.

The residual stress of the press-formed product 50 is the sum of the stress at the end of forming the press-formed product 50 and the reversal stress due to springback when the press-formed product 50 is released from the mold. If the stress generated in the material during forming is small, the stress due to springback will also be small, and the residual stress of the press-formed product 50 will be reduced. Therefore, in the manufacturing method according to this embodiment, a metal plate 30 with a work hardening index of 0.04 or less is preferably used as the material for the press-formed product 50. If the work hardening index of the material is 0.04 or less, work hardening is unlikely to occur in the first and second steps, and the stress generated in the press-formed product 50 at the end of forming will also be small. Therefore, the residual stress of the press-formed product 50 can be reduced.

Figure 13 is a graph showing the relationship between the work hardening index (n value) of the metal plate 30 and the tensile residual stress on the inner side of the bend at the bent portions 53L and 53R of the press-formed product 50. As shown in Figure 13, when the press-formed product 50 is obtained using the intermediate formed product 40, the tensile residual stress on the inner side of the bend can be reduced compared to conventional press processing that does not use the intermediate formed product 40. However, when the n value of the metal plate 30 is 0.04, the tensile residual stress on the inner side of the bend can be reduced more significantly than when the n value of the metal plate 30 is 0.08. Therefore, it is preferable that the n value of the metal plate 30 is 0.04 or less.

For example, when a press-formed product is manufactured from a metal plate material by drawing, the widthwise end of the material is clamped between a die having a horizontal lower surface and a holder having a horizontal upper surface from the beginning of the forming process. In this case, tension is applied to the material from the beginning of the forming process. However, in drawing, the end of the material is still clamped between the die and the holder even at the end of the forming process. Therefore, the press-formed product manufactured has a shape having a top plate, vertical walls connected to the left and right side edges of the top plate, and flanges protruding outward in the width direction from the lower ends of each vertical wall, that is, an approximately hat shape in cross section. In order to manufacture a press-formed product without flanges using drawing, it is necessary to first form the material into an approximately hat shape using a punch, a die, and a holder, and then trim the formed material with the left and right vertical walls. However, since the trimming of the material is generally performed parallel to the plate thickness direction, for example, when trimming left and right vertical walls that are inclined relative to a vertical plane, a trimming blade of a pull-out type equipped with a complex cam mechanism or the like is required. In this case, problems arise such as an increase in the number of steps required to design the trim blade and an increase in the manufacturing costs of the trim blade. There is also the problem that trimming the vertical wall reduces the material yield.

On the other hand, in this embodiment, although the flanges 44L, 44R of the intermediate molded product 40 come into contact with the dies 27L, 27R during the second step, when the dies 27L, 27R reach the bottom dead center, they are completely drawn toward the punch 26 and pressed between the die sides 272L, 272R and the punch sides 263L, 263R. Therefore, it is possible to directly mold the press-molded product 50 without a flange, without performing trimming. This eliminates the need for design labor and manufacturing costs for trimming blades, as is the case when drawing is used, and also prevents a decrease in material yield.

In general press working, misalignment of the material can be a problem. For example, if the heights of the left and right punch sides are different, the die with the larger punch side height will come into contact with the material first, which is likely to cause misalignment of the material. When positioning the material using a pilot pin or the like, if the material is misaligned, the periphery of the hole for the pilot pin in the material will be deformed. On the other hand, in this embodiment, in the second step, the pad 28 (the lower surface of the pad body 281) presses the top plate 41 of the intermediate molded product 40, and then the dies 27L and 27R are brought into contact with the intermediate molded product 40. This makes it possible to prevent misalignment of the intermediate molded product 40 during press working. This makes it possible to manufacture the press molded product 50 with high precision.

Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

In the above embodiment, the metal plate 30 is formed into the intermediate product 40 in the first step, and then in the second step, this intermediate product 40 is used as is and formed into the press-formed product 50. However, one or more intermediate steps can be provided between the first and second steps. That is, the intermediate product 40 can be processed after the first step, and the processed intermediate product 40 can be provided to the second step.

For example, between the first and second steps, one or more through holes can be formed in the top plate 41 of the intermediate molded product 40. The through holes may be simply round holes, or may be holes with protruding edges formed by burring (burring holes).

Also, for example, as shown diagrammatically in FIG. 14, the intermediate molded product 40 obtained in the first step can be processed to change the shapes of the vertical walls 43L, 43R and the flanges 44L, 44R while maintaining the shapes of the top plate 41 and the protrusions 42L, 42R. The intermediate molded product 40 processed in the intermediate step between the first and second steps is molded into a press-molded product 50 in the second step, as in the above embodiment.

Figure 15 is a graph showing the relationship between the presence or absence of an intermediate process and the tensile residual stress on the inner side of the bend in the bent parts 53L, 53R of the press-formed product 50. Figure 15 shows the results obtained when a CAE analysis was performed using the above-mentioned commercially available software on a press process for forming a press-formed product 50 with a bend R (inner curvature radius of the bend) of the bent parts 53L, 53R of 4.0 mm and a vertical wall height of 25 mm from a metal plate 30 with a tensile strength of 980 MPa and a plate thickness of 3.0 mm. In the intermediate process, the vertical walls 43L, 43R and flanges 44L, 44R were processed as shown in Figure 14 while maintaining the shapes of the top plate 41 and the convex parts 42L, 42R, and were formed into a shape between the intermediate product 40 obtained in the first process and the press-formed product 50 obtained in the second process.

As can be seen from FIG. 15, regardless of whether or not there is an intermediate step between the first and second steps, by subjecting the intermediate molded product 40 including the protrusions 42L, 42R and the flanges 44L, 44R to the second step, the tensile residual stress on the inside of the bend can be reduced compared to conventional press working.

In the above embodiment, an example has been described in which the intermediate product 40 is press-formed by the die 11 composed of the punch 16 and the die 17. That is, in the above embodiment, in the first step, the intermediate product 40 is formed from the metal plate 30 by so-called stamping. However, the method of obtaining the intermediate product 40 is not limited to this. The intermediate product 40 can be obtained, for example, by pad bending forming in which the top plate 41 is pressed with a pad while being formed, or by drawing forming in which the flanges 44L, 44R are pressed with a holder while being formed. The configuration of the die 11 for forming the intermediate product 40 can be selected as appropriate.

In the above embodiment, an example was described in which a press device 10 including a die 11 is used in the first step, and a press device 20 including a die 21 and separate from the press device 10 is used in the second step. However, the die 11 for the first step and the die 21 for the second step may be installed in a single press device. For example, the first step and the second step can be performed by a transfer type press device provided with both the dies 11 and 21.

In the above embodiment, the intermediate molded product 40 includes left and right convex portions 42L, 42R. However, the intermediate molded product 40 may include only one of the left and right convex portions 42L, 42R. That is, one of the left and right bent portions 53L, 53R of the press-molded product 50 can be formed while applying tension due to bending back deformation of the convex portion, and the other can be formed without applying tension due to bending back deformation of the convex portion. For example, if it is necessary to reduce the tensile residual stress on the inside of the bend and obtain excellent fatigue characteristics in one of the left and right bent portions 53L, 53R of the press-molded product 50, while excellent fatigue characteristics are not necessary in the other, tension due to bending back deformation of the convex portion can be applied only to the side requiring excellent fatigue characteristics.

Similarly, the intermediate molded product 40 may include only one of the left and right flanges 44L, 44R. That is, in the second step, one of the left and right bent portions 53L, 53R of the press-molded product 50 can be formed while applying tension by hooking the flange onto the lower die shoulder, and the other can be formed without applying such tension. For example, if one of the left and right bent portions 53L, 53R of the press-molded product 50 needs to reduce the tensile residual stress on the inside of the bend to obtain excellent fatigue properties, while the other does not need excellent fatigue properties, tension from the flange can be applied only to the side that needs excellent fatigue properties.

In the above embodiment, the convex portions 42L, 42R of the intermediate molded product 40 each have a top portion 421L, 421R that is entirely arc-shaped. However, the top portions 421L, 421R do not necessarily have to be entirely arc-shaped. For example, the top portions 421L, 421R may have a flat portion that extends outward in the width direction when viewed in cross section of the intermediate molded product 40 so that the convex portions 42L, 42R have a wide shape.

In the above embodiment, the punches 16, 26 used in each step have grooves 161a, 261a formed on the punch top surfaces 161, 261. However, the punch top surfaces 161, 261 may have steps (steps) instead of the grooves 161a, 261a. This step may extend over the entire punch top surface 161, 261 in the longitudinal direction, or may be provided on a part of the punch top surface 161, 261. When the punch top surfaces 161, 261 have steps, the bottom surface 171 of the die 17 used in the first step and the lower surface of the pad 28 used in the second step also have corresponding steps. When the punch top surface 161 has steps, the top plate 41 of the intermediate molded product 40 has steps corresponding to the steps on the punch top surface 161. If a step is provided on the punch top surface 261, a step corresponding to the step on the punch top surface 261 is formed on the top plate 51 of the press-formed product 50.

However, the punch top surfaces 161, 261, the top plate 41 of the intermediate molded product 40, and the top plate 51 of the press-molded product 50 do not have to have grooves or steps. In other words, the punch top surfaces 161, 261, the top plate 41 of the intermediate molded product 40, and the top plate 51 of the press-molded product 50 may be flat overall.

The overall shape of the press-molded product 50 can be appropriately selected according to the purpose of use, etc. For example, the press-molded product 50 may be straight when viewed from the top plate 51 side (in a plan view), may be curved to the left or right, or may be curved up or down (curved when viewed from the width direction). The press-molded product 50 may have a shape that combines two or more types of straight parts and curved parts when viewed from the width direction. Furthermore, the press-molded product 50 may have a shape in which a part having a roughly U-shaped cross section branches into multiple parts, such as a three-pronged shape or a four-pronged shape. The shapes of the first-step mold 11 and the second-step mold 21 can be selected according to the final shape of the press-molded product 50.

The press-molded product 50 does not need to have a uniform cross-sectional shape throughout. As long as the press-molded product has at least a portion that is roughly U-shaped, the press device and manufacturing method according to each of the above embodiments can be applied.

The present disclosure will be described in more detail below with reference to examples. However, the present disclosure is not limited to the following examples.

In order to confirm the effect of the present disclosure, a CAE analysis was performed on the press processing in which a metal plate (steel plate) with a tensile strength TS = 980 MPa and a plate thickness t = 3.0 mm is formed into a press-formed product 60 shown in FIG. 16 by the manufacturing method according to the above embodiment. The press-formed product 60 has a top plate 61, left and right vertical walls 62, and left and right bending portions 63. A groove portion 61a is formed in the top plate 61. The lower end of each vertical wall 62 is a free end. In other words, no flange is provided at the lower end of each vertical wall 62. The width of the top plate 61 is 80.0 mm, and the height of the vertical wall 62 is 25.0 mm. In addition, the bending R (curvature radius on the inner side of the bending) of the bending portion 63 is 4.0 mm. The press-formed product 60 is curved in a plan view. The curvature R on the inner side of the curve of the press-formed product 60 is 250.0 mm. The curvature R of the outer curve is 36.0 mm, calculated by adding the curvature R of the inner curve to the width of the top plate 61. Note that these dimensions are the dimensions on the inside of the press-formed product 60 (the inner surface of the bend of the bent portion 63).

In the CAE analysis, commercially available software (LS-DYNA ver971 rev7.12, manufactured by ANSYS) was used to perform forming analysis and springback analysis to evaluate the maximum value of the residual stress (maximum principal stress) on the inner surface of the bent portion 63 as the residual stress on the inner side of the bend. If the residual stress value is positive, it is tensile, and if it is negative, it is compressive. In the CAE analysis, of the elements divided in the plate thickness direction, the value of the element on the inner surface of the bend was used as the value of the inner surface of the bend. The analysis results are shown in Table 1.

No. 1 in Table 1 is the result (comparative example) when a press-formed product 60 was formed by general pad bending. That is, in No. 1, the press-formed product 60 was formed from a metal plate as a material using a die consisting of a punch, a die, and a pad, without forming an intermediate formed product 40 as described in the above embodiment. In No. 1, after the press forming was completed and springback occurred, a residual stress of 580 MPa occurred on the inner surface of the bent portion 63 of the press-formed product 60.

No. 2 to No. 27 in Table 1 are the results when the press-formed product 60 was formed by the method according to the present disclosure. That is, in No. 2 to No. 27, first, an intermediate product similar to the intermediate product 40 described in the above embodiment is formed (first step), and then this intermediate product is pad-bent to form the press-formed product 60 (second step). In the second step, at the start of forming, the upper ends of the convex portions of the intermediate product are positioned widthwise inward from the lower ends of the die side surfaces, and the lower ends of the vertical walls of the intermediate product are positioned widthwise outward from the upper ends of the punch side surfaces.

As shown in Table 1, most of No. 2 to No. 27 had reduced residual stress on the inner surface of the bent portion 63 of the press-molded product 60 compared to the comparative example No. 1. In particular, No. 2 to No. 15 had reduced residual stress by 100 MPa or more compared to the comparative example No. 1. Therefore, according to the method disclosed herein, it is possible to reduce the tensile stress remaining on the inner surface of the bent portion 63 of the press-molded product 60.

[Work hardening index (n value)]
In No. 15, in which the work hardening index (n value) of the raw metal plate is as low as 0.04, the residual stress on the inner surface of the bent portion 63 of the press-formed product 60 was significantly smaller than that in No. 2, in which the raw material n value is 0.09. Therefore, it can be said that the effect of reducing the tensile residual stress is improved by using a metal plate having an n value of 0.04 or less.

[Dimensions of protruding parts]
(Height H1/Width W1)
In No. 16, the ratio of height H1 to width W1 in the convex portion of the intermediate molded product molded in the first step: H1/W1 is 0.4. In this No. 16, the residual stress on the inner surface of the bent portion 63 of the press-molded product 60 was 531 MPa, and the effect of reducing the tensile residual stress was relatively small compared to the comparative example No. 1. On the other hand, in No. 4, in which H1/W1 was 0.5, the residual stress was 463 MPa, and a high effect of reducing the tensile residual stress was obtained. Therefore, in order to further improve the effect of reducing the tensile residual stress, it is preferable that H1/W1 is 0.5 or more. In addition, from the results of No. 16 and No. 4, it is preferable that the height H1 of the convex portion is 5 mm or more.

In No. 17, where H1/W1 was 2.1, buckling of the convex portion of the intermediate molded product occurred when the convex portion was crushed by the die in the second step. On the other hand, in No. 3, where H1/W1 was 2.0, buckling of the convex portion did not occur. Therefore, in order to suppress buckling of the convex portion, it is preferable that H1/W1 is 2.0 or less. Also, based on the results of No. 17 and No. 3, it is preferable that the height H1 of the convex portion is 25 mm or less.

(Apex curvature radius)
In No. 18, the bend R (radius of curvature on the inside of the bend) of the top of the convex part of the intermediate molded product molded in the first step is 2 mm. In this No. 18, buckling of the convex part occurred when the convex part was crushed by the die in the second step. On the other hand, in No. 5, in which the bend R of the top of the convex part is 4 mm, buckling of the convex part did not occur, and the residual stress was also significantly reduced compared to No. 1, which is a comparative example. Therefore, in order to obtain a high reduction effect of the tensile residual stress without causing buckling of the convex part, it is preferable that the bend R of the top of the convex part is 4 mm or more.

In No. 19, in which the bending radius of the top of the convex portion was 20 mm, the residual stress on the inner surface of the bent portion 63 of the press-formed product 60 was 509 MPa, and the effect of reducing the tensile residual stress was relatively small compared to the comparative example No. 1. On the other hand, in No. 6, in which the bending radius of the top of the convex portion was 16 mm, the residual stress was 396 MPa, which was reduced by nearly 200 MPa compared to No. 1. From these results, in order to further improve the effect of reducing the tensile residual stress, it is preferable that the bending radius of the top of the convex portion is 16 mm or less.

(flange length)
In No. 20, the flange length L of the intermediate product formed in the first step is 8 mm. In this No. 20, the residual stress on the inner surface of the bent portion 63 of the press-formed product 60 was 537 MPa, and the effect of reducing the tensile residual stress was relatively small compared to the comparative example No. 1. On the other hand, in No. 7, in which the flange length L was 10 mm, the residual stress was 415 MPa, which was reduced by 100 MPa or more compared to No. 1. Therefore, in order to further improve the effect of reducing the tensile residual stress, it is preferable that the flange length L is 10 mm or more.

[Molding height of intermediate molded product]
In No. 21, the height H2 of the intermediate molded product molded in the first step is 4 mm. In this No. 21, the residual stress on the inner surface of the bent portion 63 of the press-molded product 60 was 529 MPa, and the effect of reducing the tensile residual stress was relatively small compared to the comparative example No. 1. On the other hand, in No. 8, in which the height H2 of the intermediate molded product was 6 mm, the residual stress was 391 MPa, which was significantly reduced compared to No. 1. Therefore, in order to further improve the effect of reducing the tensile residual stress, it is preferable that the height H2 of the intermediate molded product is 6 mm or more.

[Relationship between intermediate molded product and mold for second process]
(Relative position of protrusion with respect to die)
At the start of the second step, when the intermediate molded product is placed in the mold, the distance D2 [mm] in the width direction of the mold from the R end of the punch top side of the punch shoulder to the upper end of the convex portion can be set in relation to the radius of curvature Rp [mm] of the punch shoulder and the angle θ [rad] of the punch side relative to the punch top. In No. 22, in which D2/(Rp×(π-θ)) was set to -1.2, the residual stress on the inner surface of the bent portion 63 of the press-molded product 60 was 503 MPa, and the effect of reducing the tensile residual stress was relatively small compared to No. 1, which is a comparative example. In No. 23, in which D2/(Rp×(π-θ)) was set to 2.7, the residual stress was 543 MPa, and the effect of reducing the tensile residual stress was relatively low. On the other hand, in No. 22, in which D2/(Rp×(π-θ)) was set to -1.0, the residual stress on the inner surface of the bent portion 63 of the press-molded product 60 was 503 MPa, and the effect of reducing the tensile residual stress was relatively small compared to No. 1, which is a comparative example. In No. 9, where D2/(Rp×(π-θ)) was set to 2.5, the residual stresses were 341 MPa and 451 MPa, respectively, which was reduced by 100 MPa or more compared to No. 1. From this result, in order to further improve the effect of reducing the tensile residual stress, it is preferable to set the distance D2 to be -1.0×Rp×(π-θ) or more and 2.5×Rp×(π-θ) or less.

(Flange angle)
In No. 24, the angle φ of the flange of the intermediate product with respect to the horizontal plane is −45° at the start of the second step. That is, the flange of the intermediate product is rotated 45° downward around the end of the vertical wall side. In this No. 24, the residual stress on the inner surface of the bent portion 63 of the press-molded product 60 is 524 MPa, and the effect of reducing the tensile residual stress compared to the comparative example No. 1 is relatively small. On the other hand, in No. 11, in which the flange angle φ is −40°, the residual stress is 463 MPa, which is reduced by 100 MPa or more compared to No. 1. Therefore, in order to further improve the effect of reducing the tensile residual stress, it is preferable that the angle φ of the flange of the intermediate product at the start of the second step is −40° or more.

In No. 25, the angle φ that the flange of the intermediate molded product makes with the horizontal plane at the start of the second process is 45°. That is, the flange of the intermediate molded product rotates 45° upward around the end on the vertical wall side. In this No. 25, the tip (free end) of the flange of the intermediate molded product comes into contact with the die and buckles in the second process. In addition, in the case of No. 25, the tip of the flange is likely to rub against the die, which may cause damage to the die. On the other hand, in No. 12, in which the flange angle φ is 40°, no buckling of the flange occurs, and the residual stress is also significantly reduced compared to No. 1, which is a comparative example. Therefore, in order to obtain a high reduction effect of tensile residual stress without causing flange buckling, it is preferable that the flange angle φ is 40° or less.

(Radius of curvature of lower die shoulder)
In No. 26, the radius of curvature (die shoulder Rd) of the lower die shoulder in the die used in the second step was set to 0.5 mm. The lower die shoulder is the part on which the flange of the intermediate molded product is caught when the die is lowered in the second step. In No. 26, the lower die shoulder caused a large bending tendency in the press-formed product 60 in the second step. On the other hand, in No. 13, in which the die shoulder Rd was set to 1 mm, the bending tendency of the press-formed product 60 was substantially not generated, and the residual stress on the inner surface of the bent portion 63 of the press-formed product 60 was also significantly reduced compared to the comparative example No. 1. Therefore, in order to obtain a high reduction effect of the tensile residual stress without generating a bending tendency, it is preferable that the die shoulder Rd is 1 mm or more.

In No. 27, where the die shoulder Rd was 15 mm, the residual stress was 513 MPa, and the effect of reducing the tensile residual stress was relatively small compared to the comparative example No. 1. On the other hand, in No. 14, where the die shoulder Rd was 12 mm, the residual stress was 438 MPa, which was reduced by more than 100 MPa compared to No. 1. Therefore, in order to improve the effect of reducing the tensile residual stress, it is preferable that the die shoulder Rd in the second process be 12 mm or less.

100: Manufacturing equipment 11: Mold (first mold)
21: Mold (second mold)
26: Punch 261: Punch top surface 262L, 262R: Punch shoulder 263L, 263R: Punch side surface 27L, 27R: Die 271L, 271R: Upper die shoulder 272L, 272R: Die side surface 273L, 273R: Lower die shoulder 274L, 274R: Die bottom surface 28: Pad 30: Metal plate 40: Intermediate formed product 41: Top plate 42L, 42R: Convex portion 421L, 421R: Top portion 43L, 43R: Vertical wall 44L, 44R: Flange 50: Press-formed product

Claims (10)

A method for manufacturing a press-molded product, comprising the steps of:
a first step of obtaining an intermediate molded product by pressing a metal plate, the intermediate molded product including a top plate, a protrusion connected to the top plate and protruding upward from the top plate, a vertical wall extending downward from the protrusion, and a flange extending from a lower end of the vertical wall to an opposite side of the top plate;
a second step of pressing the intermediate product using a die including a punch, a pad disposed above the punch so as to face the punch, and a die disposed above the punch and to the side of the pad to obtain the press-molded product;
Equipped with
The punch includes a punch top surface, a punch shoulder continuous with the punch top surface, and a punch side surface extending downward from the punch shoulder,
The die includes an upper die shoulder corresponding to the punch shoulder, a die side surface extending downward from the upper die shoulder corresponding to the punch side surface, and a die lower surface connected to a lower end of the die side surface via a lower die shoulder,
The second step comprises:
placing the intermediate product on the punch such that the top plate is disposed on the top surface of the punch and the protrusion is disposed at a position corresponding to the punch shoulder;
a step of lowering the pad and pressing the top plate on the top surface of the punch with the pad;
a step of lowering the die and bringing the die into contact with the flange while the top plate is pressed by the pad;
a step of further lowering the die after the die has come into contact with the flange, and crushing the protrusion with the die;
A manufacturing method comprising: The method according to claim 1,
a manufacturing method in which, when the intermediate molded product is placed on the punch, an upper end of the convex portion is positioned more inward than a lower end of the die side surface in the width direction of the mold, and a lower end of the vertical wall is positioned more outward than an upper end of the punch side surface in the width direction of the mold. The method according to claim 1 or 2,
A manufacturing method in which, when the vertical distance from the connection between the convex portion and the top plate to the upper end of the convex portion is H1 [mm], and the widthwise distance of the intermediate molded product from the connection to the upper end is W1 [mm], H1/W1 is 0.5 or more and 2.0 or less. The method according to any one of claims 1 to 3,
The convex portion has an arc shape in a cross-sectional view of the intermediate molded product and includes an apex having a radius of curvature of 4 mm or more and 16 mm or less. The method according to any one of claims 1 to 4,
The punch shoulder has an arc shape in a cross-sectional view of the punch,
a manufacturing method in which, when the intermediate molded product is placed on the punch, a distance D2 [mm] in the width direction of the die from the end of the punch shoulder on the punch top surface side to the upper end of the convex portion satisfies the following formula, where the distance D2 [mm] is positive when the upper end is located outside the end of the punch shoulder in the width direction and is negative when the upper end is located inside in the width direction.
-1.0×Rp×(π-θ)≦D2≦2.5×Rp×(π-θ)
Here, Rp is the radius of curvature of the punch shoulder (mm), and θ is the angle (rad) between the punch top surface and the punch side surface. The method according to any one of claims 1 to 5,
A manufacturing method in which, in the intermediate molded product, the vertical distance from the end of the flange on the vertical wall side to the top plate is 6 mm or more. The method according to any one of claims 1 to 6,
when the intermediate molded product is placed on the punch, the angle that the flange forms with respect to the horizontal plane is positive when the flange is rotated upward around the end of the vertical wall, and negative when the flange is rotated downward, and is greater than -40° and less than 40°. The method according to any one of claims 1 to 7,
The method of claim 1, wherein the lower die shoulder is arcuate in shape having a radius of curvature of 1 mm or more and 12 mm or less when viewed in cross section of the die. The method according to any one of claims 1 to 8,
The manufacturing method, wherein the metal plate has a work hardening coefficient of 0.04 or less. A manufacturing facility for manufacturing a press-molded product,
a first mold for molding a metal plate into an intermediate molded product including a top plate, a protrusion connected to the top plate and protruding upward from the top plate, a vertical wall extending downward from the protrusion, and a flange extending from a lower end of the vertical wall to an opposite side of the top plate;
A second mold for molding the intermediate molded product into the press-molded product;
Equipped with
The second mold is
a punch including a punch top surface, a punch shoulder continuous with the punch top surface, and a punch side surface extending downward from the punch shoulder, wherein when the intermediate formed product is formed into the press-formed product, the top plate is disposed on the punch top surface and the protrusion is disposed at a position corresponding to the punch shoulder;
a pad that is movable up and down and is disposed above the punch, the pad facing the top plate that is disposed on a top surface of the punch when the intermediate molded product is molded into the press-molded product;
a die that can be raised and lowered and is disposed above the punch and to the side of the pad, the die including an upper die shoulder corresponding to the punch shoulder, a die side surface that corresponds to the punch side surface and extends downward from the upper die shoulder, and a die lower surface that is connected to a lower end of the die side surface via a lower die shoulder, the die lower surface facing the flange when the intermediate molded product is molded into the press-molded product;
Including, manufacturing facilities.

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