Manufacturing method for press-molded products

Abstract

To provide a press-molded product manufacturing method that suppresses spring back occurred by press molding of a vehicle body component of an automobile, and can obtain a press-molded product having good external appearance with good efficiency.SOLUTION: A press-molded product manufacturing method is a method for manufacturing a press-molded product having a top plate part 1 and a vertical wall part 5 continuous with the top plate part 1 via a ridge line part 3 and comprises: a first process of molding an intermediate molded product 17, which has an intermediate top plate part 21 and an intermediate vertical wall part 25 continuous with the intermediate top plate part 21 via an intermediate ridge line part 23 and the intermediate top plate part 21 is provided with a convex part 29 or a concave part; and a second process of crushing the convex part 29 or the concave part of the intermediate molded product 17 to mold the press-molded product. In the second process, by a material flow occurring due to the crushing of the convex part 29 or the concave part, a material of the intermediate ridge line part 23 is extruded to the vertical wall part 5 side to apply bend back to a part which has been the intermediate ridge line part 23.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing press-formed products having a good shape close to the target shape by suppressing springback, which is an increase in the angle between a top plate portion and a vertical wall portion after release from the mold, in press-forming of car body parts and the like. [Background technology]

[0002] As automobile crash safety standards become stricter, progress is being made in improving the crash safety of vehicle bodies, but recent carbon dioxide emission regulations also necessitate weight reduction of vehicle bodies. In order to achieve both crash safety performance and weight reduction of vehicle bodies, metal plates with even higher strength than before are being used in vehicle bodies. Recently, efforts are being made to use ultra-high tensile steel plates of 1.5 GPa class or higher.

[0003] These steel sheets have extremely high strength, so that large stresses are generated during press forming, and when released from the mold, large spring back occurs, making it easy for the steel sheets to deviate significantly from the target shape. Therefore, many measures have been taken to suppress springback. In particular, press forming methods such as those in Patent Documents 1 and 2 are disclosed to address springback in which the punch shoulder inner angle widens (the angle between the top plate portion and the vertical wall portion becomes larger).

[0004] Patent Document 1 describes a method of making the punch width in the second press forming wider than the punch width in the first press forming. By making the punch width in the second press forming wider, it is possible to impart reverse bending deformation to the wall of the formed product obtained in the first press forming, which is said to reduce the opening of the punch shoulder internal angle due to springback. Patent Document 2 describes a method for press-forming a workpiece while pressing a die-side pad against the workpiece with the punch-side pad protruding outward (toward the die). This method forms the workpiece while loosening it, and then crushes the looseness at the bottom dead center of the forming process. This method is said to balance the springback and spring-back of the workpiece and prevent the opening of the punch shoulder internal angle due to springback. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-111725 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-082660 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when these methods are used, not only are springback not sufficiently suppressed, but the resulting molded product has a poor appearance, which is a problem. In particular, in the case of Patent Document 1, the punch width for the second press molding is wider than the punch width for the first press molding, so that molding marks on the ridge lines of the top plate and vertical wall of the molded product obtained in the first press molding tend to remain on the top plate of the target molded product, resulting in a poor appearance of the target molded product. In Patent Document 2, if the cross-sectional line length of the workpiece is too long compared to the target shape, breakage is likely to occur at the punch shoulder, and if it is too short, the angle of the punch shoulder does not match the target shape, which is a problem.

[0007] The present invention has been made to solve the above-mentioned problems, and aims to provide a method for manufacturing press-formed products that can suppress springback that occurs during press forming of automobile body parts and efficiently obtain press-formed products with good appearance. [Means for solving the problem]

[0008] (1) A method for manufacturing a press-formed product according to the present invention is a method for manufacturing a press-formed product having a top plate portion and a vertical wall portion continuous with the top plate portion via a ridge line portion, a first step of molding an intermediate molded product having an intermediate top plate portion and an intermediate vertical wall portion connected to the intermediate top plate portion via an intermediate ridge portion, the intermediate top plate portion having a convex or concave portion extending in the same direction as the extending direction of the intermediate ridge portion and having a convex or concave shape in cross section perpendicular to the ridge portion; a second step of crushing the convex portion or the concave portion of the intermediate product to form the press-molded product, In the second step, the material flow generated by crushing the convex or concave portion is pushed out from the intermediate ridge portion toward the vertical wall portion, thereby bending back the portion that was previously the intermediate ridge portion.

[0009] (2) Furthermore, in the above (1), the press-molded product is characterized in that it is a hat-shaped cross-section part or a U-shaped cross-section part having a pair of vertical wall portions on both sides of the top plate portion.

[0010] (3) Furthermore, the method described in (2) above is characterized in that it further comprises a dividing step of cutting and dividing the top plate portion of the hat cross-section shaped part or the U cross-section shaped part formed in the second step in the extension direction of the ridge line portion to obtain two Z cross-section shaped parts or two L cross-section shaped parts.

[0011] (4) In the device described in (3) above, one or both sides of the portion of the top plate where the convex or concave portion is provided are cut out in the ridge line direction, The dividing step is characterized in that the top plate portion is divided by cutting off the cut-out portion of the top plate portion.

[0012] (5) In the above (1), the press-formed product is a Z-shaped cross-sectional part or an L-shaped cross-sectional part having a vertical wall portion on only one side of the top plate portion, The second step is characterized in that molding is performed while restraining an end portion of the intermediate top plate portion of the intermediate molded product that does not have the intermediate vertical wall portion. [Effects of the Invention]

[0013] According to the present invention, it is possible to manufacture press-formed products made of high-strength metal sheets that have good dimensional accuracy and suppress springback without impairing the appearance of the press-formed products. Furthermore, by manufacturing a vehicle body using the press-molded product, it becomes possible to achieve both collision safety performance and a lighter vehicle body weight. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is an explanatory diagram of a method for manufacturing a press-formed product according to a first embodiment. [Figure 2] 1 is a diagram showing an example of a press-formed product to which the present invention is applied; [Figure 3] Figure 3(a) is a cross-sectional view of the ridgeline near the intermediate ridgeline at the bottom dead center of forming in the first step, which explains the stress generated in the area shown in gray in the figure. Figure 3(b) is a cross-sectional view of the ridgeline near the bottom dead center of forming in the second step, which explains the material flow in the second step and the stress generated in the area shown in gray in the figure. [Figure 4] 10 is a diagram showing the stress distribution on the outside of the target molded product at the bottom dead center of molding in the second step, obtained by FEM analysis of the manufacturing method of the first embodiment, and the cross-sectional shape of the ridge line orthogonal to the target molded product after demolding. FIG. [Figure 5] FIG. 10 is an explanatory diagram of a method for manufacturing a press-formed product according to a second embodiment, and is a perspective view of an intermediate formed product and a target formed product when an L-shaped cross-sectional part is set as the target shape. [Figure 6] 6A and 6B are diagrams illustrating a molding method for molding the intermediate molded product of FIG. 5A into the L-shaped cross-sectional part of FIG. 5B in the second step of the second embodiment. [Figure 7] 10 is a perspective view of an intermediate molded product and a target molded product when a Z-section shaped part is set as the target shape in the second embodiment. FIG. [Figure 8]10 is a diagram showing the stress distribution on the outside of the target molded product at the bottom dead center of molding in the second step, obtained by FEM analysis of the manufacturing method of embodiment 2, and the cross-sectional shape of the target molded product taken along the line perpendicular to the ridge line after demolding. [Figure 9] FIG. 10 is a diagram showing the stress distribution on the outside of a target molded product at the bottom dead center of molding, obtained by FEM analysis of a conventional manufacturing method, and the cross-sectional shape of the ridge line orthogonal to the target molded product after demolding. DETAILED DESCRIPTION OF THE INVENTION

[0015] [Embodiment 1] The method for manufacturing a press-formed product according to the first embodiment of the present invention is a method for manufacturing a press-formed product having a top plate portion and a vertical wall portion continuous with the top plate portion via a ridge portion. An example of a press-formed product to which the present invention is applied is shown in FIG.

[0016] Figures 2(a) and 2(b) show examples of a hat-shaped cross-sectional part 9 having a top plate portion 1 and a pair of vertical wall portions 5 connected to both sides of the top plate portion 1 via ridge portions 3, and having a flange portion 7 at the lower end of the vertical wall portion 5, and an U-shaped cross-sectional part 11 not having a flange portion 7 at the lower end of the vertical wall portion 5.

[0017] Figures 2(c) and 2(d) are examples of a Z-shaped cross-sectional part 13 and an L-shaped cross-sectional part 15, respectively, which are press-formed products having a top plate portion 1 and one vertical wall portion 5 that is continuous with one side of the top plate portion 1 via a ridge portion 3. The method for producing a press-formed product of the present invention can be applied to the production of any of the press-formed products shown in Figs. 2(a) to 2(d).

[0018] Prior to describing this embodiment, problems that may arise when manufacturing the press-formed products shown in FIG. 2 will be described with reference to FIG. 9A to 9C show only one half of the top plate 1 of the hat-shaped cross-section part 9 or the U-shaped cross-section part 11, which is divided in half along the direction in which the ridge line 3 extends. Figure 9(a-1) shows the outer stress distribution at the bottom dead center of forming, based on an FEM analysis of the press forming of the hat cross-section part 9 shown in Figure 2(a). Figure 9(a-2) shows the cross-sectional shape perpendicular to the ridge line of the hat cross-section part 9 in Figure 9(a-1) after release from the mold, using a solid line, and the cross-sectional shape perpendicular to the ridge line at the bottom dead center of forming, using a dashed line.

[0019] Similarly, Fig. 9(b-1) shows the outer stress distribution at the bottom dead center of the press forming of the U-shaped cross-section part 11 shown in Fig. 2(b) through an FEM analysis. Fig. 9(b-2) shows the cross-sectional shape of the U-shaped cross-section part 11 at the orthogonal cross section of the ridge line after release from the mold with a solid line, and the cross-sectional shape of the ridge line at the bottom dead center of the press with a dashed line.

[0020] In Figures 9(a-1) and 9(b-1), tensile stress occurs in the light-colored areas, and compressive stress occurs in the dark-colored areas. As shown in Figures 9(a-1) and 9(b-1), when a hat-shaped cross-section part 9 or a U-shaped cross-section part 11 is press-formed, tensile stress occurs on the outside and compressive stress occurs on the inside of the ridge line portion 3 due to bending deformation.

[0021] Therefore, when the part is released from the mold after press molding, the tensile stress generated on the outside of the ridge portion 3 and the compressive stress generated on the inside act to cause springback, and as shown in Figures 9(a-2) and 9(b-2), the interior angle θ2 of the ridge portion 3 after release from the mold becomes larger than the target angle θ1.

[0022] Therefore, in order to bring the interior angle θ2 of the ridge portion 3 after demolding closer to the target angle θ1, the inventor considered applying a stress near the ridge portion 3 that is equivalent to and offsets the stress generated by the bending deformation of the ridge portion 3. The inventors then considered that if compressive stress could be applied to the outside near the ridge line portion 3 and tensile stress to the inside, the external tensile stress and internal compressive stress caused by bending could be offset, thereby suppressing springback. To this end, the inventors came up with the idea that if the material of the bent ridge line portion 3 could be extruded toward the vertical wall portion 5, it would be possible to generate the above-mentioned stress in the extruded portion.

[0023] That is, by extruding the material of the ridge line portion 3 after bending onto the flat vertical wall portion 5, the bent portion is bent back. This bent back portion generates compressive stress on the outside and tensile stress on the inside. Therefore, it is possible to generate stresses in the vicinity of the ridge line portion 3 (top of the vertical wall portion 5) that are opposite to the stresses generated in the ridge line portion 3 (tensile stress on the outside and compressive stress on the inside), so the two stresses cancel each other out and springback is less likely to occur.

[0024] Therefore, a method for manufacturing a hat-shaped cross section part or a U-shaped cross section part by press molding will be described. Figures 1(a) and 1(b) show an example of the manufacturing process when press-forming a hat-shaped cross-section part.

[0025] The manufacturing method of the press-molded product of this embodiment 1 includes a first step of molding an intermediate molded product 17 and a second step of molding the intermediate molded product 17 into a hat cross-section shaped part 19, as shown in Figures 1(a) and 1(b).

[0026] <1st process> The first step is a step of molding an intermediate molded product 17 having an intermediate top plate portion 21, an intermediate vertical wall portion 25 continuing from the intermediate top plate portion 21 via an intermediate ridge portion 23, and an intermediate flange portion 27 continuing from the intermediate vertical wall portion 25, as shown in Figure 1(a).

[0027] The intermediate top plate portion 21 of the intermediate molded product 17 is formed with a convex portion 29 that is curved so that the cross section perpendicular to the ridge portion is convex upward and extends in the same direction as the intermediate ridge portion 23. The overall shape of the intermediate molded product 17 is the same as the hat-shaped cross-section part 19, which is the target shape of the second step, except that the intermediate top plate portion 21 has a convex portion 29.

[0028] In the example of FIG. 1, the convex portion 29 is formed at the middle position of the intermediate top panel portion 21. By forming the convex portion 29 at the middle position of the intermediate top plate portion 21, when the convex portion 29 is crushed in the second step described below, the material tends to flow evenly on both sides.

[0029] Furthermore, the intermediate top plate portion 21 of the intermediate molded product 17 in Figure 1 has both sides cut out in the extension direction of the intermediate ridge portion 23 at the location where the convex portion 29 is to be added in accordance with the target shape, but it may be cut out on only one side, or may not be cut out at all.

[0030] <Second process> As shown in FIG. 1(b), the second step is a step of crushing the convex portion 29 of the intermediate molded product 17 molded in the first step to form a hat-shaped cross-section part 19.

[0031] As described above, the overall shape of the intermediate molded product 17 is the same as the hat cross-sectional shaped part 19, which is the target shape for the second step, except for the convex portion 29 to be crushed. Therefore, in the second step, it is advisable to use a mold in which the top plate portion of the mold used in the first step is flattened.

[0032] When the intermediate molded product 17 is press-molded using the above-described mold, the convex portions 29 are crushed while maintaining their outer shape, and as shown by the dashed arrows in FIG. 1(b), material flows from the convex portions 29 toward the intermediate vertical wall portions 25 on both sides. When this material flow occurs, the material of the intermediate ridge portions 23 is pushed toward the vertical wall portions 5. As a result, the area or a part of the area that was the intermediate ridge portion 23 is bent back from its bent shape to a flat shape. The movement of the material of the intermediate ridge portions 23 at this time and the stress generated in this area will be explained with reference to FIG. 3.

[0033] Figure 3(a) is a cross-sectional view of the intermediate ridge line portion 23 and its surrounding ridge line portion at the bottom dead center of forming in the first step, and Figure 3(b) is a cross-sectional view of the ridge line portion 3 and its surrounding ridge line portion at the bottom dead center of forming in the second step. When the intermediate molded product 17 is press-molded in the first step, as shown in Figure 3(a), tensile stress occurs on the outside and compressive stress occurs on the inside of the bent intermediate ridge portion 23 (the part shown in gray in the figure).

[0034] Then, when the convex portion 29 of the intermediate molded product 17 is crushed in the second step, a material flow occurs as shown by the white arrow in Figure 3(b), and some or all of the material of the intermediate ridge portion 23 is pushed out toward the vertical wall portion 5 (the portion shown in gray in the figure). As described above, the portion that was the intermediate ridge portion 23 is pushed toward the vertical wall portion 5, and the bent portion or a part of it is bent back flat, resulting in compressive stress on the outside of the portion and tensile stress on the inside. Since the above stress is opposite to the stress generated at the ridge line 3 of the hat cross-section shaped part 19, the two stresses cancel each other out, reducing the stress acting at the time of demolding. This point will be explained using FIG. 4.

[0035] Figure 4(a-1) shows the stress distribution on the outside of the hat cross-section shaped part 19 at the bottom dead center of forming in the second step. Note that Figure 4(a-1) shows only one half of the top plate portion 1 of the hat cross-section shaped part 19, which is divided in half along the extension direction of the ridge portion 3. FIG. 4(a-2) shows the cross-sectional shape perpendicular to the ridge line of the hat-shaped cross-section part 19 in FIG. 4(a-1) after release from the mold, indicated by a solid line, and the cross-sectional shape perpendicular to the ridge line at the bottom dead center of molding, indicated by a dashed line.

[0036] As described above, in the second step, the material flow caused by crushing the convex portion 29 causes the material of the portion that was the intermediate top plate portion 21 to flow into the ridge portion 3, and the material that has flowed into the ridge portion 3 pushes the material of the portion that was the intermediate ridge portion 23 out into the vertical wall portion 5. Therefore, a part of the intermediate top plate portion 21 that was flat is bent into the ridge portion 3, and tensile stress is generated on the outside of the ridge portion 3 as shown in Fig. 4(a-1). In addition, although not shown, compressive stress is generated on the inside of the ridge portion 3 due to the bending. On the other hand, the portion that was the intermediate ridge line 23 flows into the upper end of the vertical wall portion 5, and the bent portion is bent back, so that compressive stress is generated on the outer side of the upper end of the vertical wall portion 5 as shown in Fig. 4(a-1). Furthermore, although not shown, tensile stress is generated on the inner side of the upper end of the vertical wall portion 5 due to the bending back.

[0037] In this way, at the bottom dead center of the forming process in the second step, stress is generated in the ridge portion 3 of the hat cross-sectional shaped part 19, which tends to increase the interior angle of the ridge portion 3 when the part is released from the mold, but a stress opposite to the above stress is generated in the vicinity of the ridge portion 3 (the upper end of the vertical wall portion 5). Therefore, the two stresses are offset during demolding, reducing the stress acting during demolding, and as shown in Figure 4(a-2), the interior angle θ2 of the ridge portion 3 after demolding can be made closer to the target angle θ1 than in the conventional case of Figure 9.

[0038] Although the above is an example in which a hat-shaped cross-section part 19 is molded, the same effect can be obtained with a U-shaped cross-section part that does not have a flange part 7 at the lower end of the vertical wall part 5. FIG. 4(b-1) shows only one half of the top plate portion 1 of the U-shaped cross section part 31, which is divided in half along the direction in which the ridge line portion 3 extends. Figure 4(b-1) shows the stress distribution on the outer side of the plate at the bottom dead center of forming when the target formed product in the second step is a U-shaped cross-section part 31. Figure 4(b-2) shows the cross-sectional shape orthogonal to the ridge line of the U-shaped cross-section part 31 after demolding with a solid line, and the cross-sectional shape orthogonal to the ridge line at the bottom dead center of forming with a dashed line.

[0039] Even when the target molded product in the second step is a U-shaped cross-section part 31, the action described above in Figure 3 causes tensile stress on the outside of the ridge portion 3 and compressive stress on the inside, as shown in Figure 4(b-1), and compressive stress on the outside of the upper end of the vertical wall portion 5 and tensile stress on the inside. Therefore, the stress generated in the ridge portion 3 and the stress generated in the upper end of the vertical wall portion 5 cancel each other out, reducing the stress acting during demolding. As shown in Figure 4(b-2), springback during demolding is suppressed, and the interior angle θ2 of the ridge portion 3 after demolding becomes closer to the target angle θ1.

[0040] <Dividing process> To improve the manufacturing efficiency of parts, the hat cross-section shaped part 9 of Fig. 2(a) may be press-formed, and the top plate 1 of the hat cross-section shaped part 9 may be cut in the ridge line extending direction and divided to produce two Z cross-section shaped parts 13. Also, the U cross-section shaped part 11 of Fig. 2(b) may be press-formed, and the top plate 1 of the U cross-section shaped part 11 may be cut in the ridge line extending direction and divided to produce two L cross-section shaped parts 15. The dividing step is a step of cutting and dividing the top plate portion 1 of the hat cross-section shaped part 19 formed in the second step to obtain two Z cross-section shaped parts 13, as shown in FIG. 1(c). For example, it is possible to cut the top plate 1 at the two locations indicated by the broken lines in FIG. 1(c) and remove the cut-out portions to form two Z-shaped cross-section shaped parts 13 as shown in FIG. 1(d).

[0041] However, the dividing method in the dividing step is not limited to this. For example, a hat cross-sectional shaped part 9 with no cutout in the top plate portion 1 as shown in Figure 2(a) may be formed, and the center of the top plate portion 1 may be cut at one point along the extension direction of the ridge portion 3 to divide the hat cross-sectional shaped part 9 into two, thereby obtaining two Z cross-sectional shaped parts 13.

[0042] As described above, the hat-shaped cross-section part 19 formed through the first and second steps has reduced springback and has a good shape in which the interior angle θ2 of the ridge line part 3 (the angle between the top plate part 1 and the vertical wall part 5) is close to the target angle θ1. Therefore, by dividing this, two good-shaped Z-shaped cross-section parts 13 can be obtained.

[0043] In addition, by press-forming a U-shaped cross-section shaped part 11 in the first and second steps in the same manner as the hat-shaped cross-section shaped part 19 described in Figure 1, and then dividing the U-shaped cross-section shaped part 11, two L-shaped cross-section shaped parts 15 (Figure 2(d)) can be manufactured.

[0044] As described above, according to this embodiment, a stress opposite to the stress generated at the ridge line 3 of the press-formed product is generated near the ridge line 3, and the two stresses are offset to reduce springback during demolding. This makes it possible to manufacture a hat cross-sectional shaped part 9 or 19 or a U-shaped cross-sectional shaped part 11 with a good shape close to the target shape. Furthermore, by dividing a well-shaped hat cross section shaped part 9 or 19 or a well-shaped U cross section shaped part 11, a well-shaped Z cross section shaped part 13 (FIG. 2(c)) or an L cross section shaped part 15 can be manufactured.

[0045] In the above-described embodiment, an example was given in which the intermediate top plate portion 21 of the intermediate molded product 17 is provided with a curved convex portion 29 whose cross section perpendicular to the ridge line is convex upward, but the present invention is not limited to this. For example, a concave portion curved downward may be provided instead of the convex portion 29. In this case, by crushing the concave portion in the second step, the same effect as in the first embodiment is achieved, and springback can be reduced.

[0046] [Embodiment 2] In the second embodiment, a method for manufacturing a Z-shaped cross-section part or an L-shaped cross-section part individually in the first and second steps will be described. The manufacturing method of this embodiment will be described below by taking an example in which an L-shaped cross-section part is manufactured as a single unit.

[0047] The method for manufacturing a press-molded product according to the second embodiment includes a first step of molding an intermediate product as shown in Fig. 5(a) and a second step of molding the intermediate product into an L-shaped cross-sectional part as shown in Fig. 5(b). In Fig. 5(a) and Fig. 5(b), parts corresponding to those in Fig. 1(a) and Fig. 1(b) are denoted by the same reference numerals. Each step will be described in detail below.

[0048] <1st process> The first step is a step of molding an intermediate molded product 33 having an intermediate top plate portion 21 and one intermediate vertical wall portion 25 connected to one side of the intermediate top plate portion 21 via an intermediate ridge portion 23, as shown in Figure 5(a). The intermediate top plate portion 21 of the intermediate molded product 33 is formed with a curved convex portion 29 extending in the direction in which the intermediate ridge portion 23 extends, the convex portion 29 having an upwardly convex cross section perpendicular to the ridge portion. The overall shape of the intermediate molded product 33 is the same as the L-shaped cross-sectional part 35, which is the target shape of the second step, except that the intermediate top plate portion 21 has a convex portion 29 added thereto.

[0049] <Second process> As shown in FIG. 5(b), the second step is a step of crushing the convex portion 29 of the intermediate molded product 33 molded in the first step to form an L-shaped cross-sectional part 35. The molding method in the second step of the second embodiment will be described with reference to FIG.

[0050] FIG. 6 is a cross-sectional view showing a state during molding in the second step. As shown in FIG. 6, in the second step, the intermediate formed product 33 is formed into an L-shaped cross-sectional part 35 using a punch 37, a die 39, and a pad 41.

[0051] As explained in embodiment 1, the present invention works by crushing the convex portion, causing the material of the intermediate ridge portion to be pushed out into the vertical wall portion through the material flow, and then bending back the pushed-out portion, thereby reducing the stress that causes springback. Therefore, when the target shape has a vertical wall portion 5 on only one side, such as the L-shaped cross-sectional part 35 of this embodiment, it is preferable to perform the second process so that the material flow is directed toward the side having the intermediate vertical wall portion 25.

[0052] Therefore, in the second step of this embodiment, as shown in FIG. 6, a restraining portion 37a is provided on the punch 37, and forming is performed in a state where the end portion of the intermediate top plate portion 21 is restrained. By carrying out the second step as described above, it becomes easier to push out a part of the intermediate ridge portion 23 toward the vertical wall portion 5 side. The method of restraining one end of the intermediate top panel portion 21 is not limited to the example shown in FIG. 6, and the end may be fixed with a pin or the like.

[0053] Furthermore, the above explanation has been given for the case where the L-shaped cross-section part 35 is manufactured as a single unit, but the same applies to the case where a Z-shaped cross-section part is manufactured as a single unit. In this case, in the first step, an intermediate molded product 43 having a convex portion 29 as shown in Figure 7(a) is molded, and in the second step, the convex portion 29 is crushed to form a Z-shaped cross-section part 45 as shown in Figure 7(b).

[0054] Figures 8(a-1) and 8(b-1) show the stress distribution at the bottom dead center of the forming process in the second step of the Z-shaped cross-section part 45 or the L-shaped cross-section part 35 produced by the manufacturing method of embodiment 2. Figures 8(a-2) and 8(b-2) show the cross-sectional shapes of the Z-shaped cross-section part 45 and the L-shaped cross-section part 35 perpendicular to the ridge line after release from the mold with solid lines, and the cross-sectional shapes of the L-shaped cross-section part 35 perpendicular to the ridge line at the bottom dead center of the forming process with dashed lines.

[0055] As shown in Figures 8(a-1) and 8(b-1), in the Z-shaped cross-section shaped part 45 and the L-shaped cross-section shaped part 35 manufactured by the manufacturing method of this embodiment, tensile stress occurs on the outside of the ridge portion 3 at the bottom dead center of the forming in the second step, and compressive stress occurs on the outside of the upper end portion of the vertical wall portion 5, as in embodiment 1. Although not shown, compressive stress occurs on the inside of the ridge line portions 3 of the Z-shaped cross-section shaped part 45 and the L-shaped cross-section shaped part 35, and tensile stress occurs on the inside of the upper end portions of the vertical wall portions 5.

[0056] As described above, in the manufacturing method of this embodiment, as in Embodiment 1, a stress opposite to the stress at ridge line 3 is generated near ridge line 3, and the two stresses cancel each other out, reducing the stress acting during demolding. As a result, as shown in Figures 8(a-2) and 8(b-2), springback during demolding is suppressed, and the interior angle θ2 of ridge line 3 after demolding becomes closer to the target angle θ1. [Example]

[0057] The effect of reducing springback by the method for producing a press-formed product of the present invention will be described based on specific examples. In this example, a 1470 MPa grade steel plate with a thickness of 1.0 mm was used as a blank, and a hat cross section shaped part or a U cross section shaped part was press-formed. The top plate portion of the press-formed part was then cut to produce two Z cross section shaped parts or two L cross section shaped parts. The target angle θ1 of the interior angle of the ridge line portion of the Z-shaped cross section part or the L-shaped cross section part was set to 100°.

[0058] In a conventional example, when the above-mentioned blank was press-formed into a hat-shaped cross section part or a U-shaped cross section part, press-forming was performed in one step using a punch and a die with a flat top plate forming surface.

[0059] As an example of the invention, when the above-mentioned blank is press-formed into a hat cross section shaped part or a U-shaped cross section shaped part, it is press-formed in two steps as in the first embodiment described with reference to FIG. 1, and then divided into two parts. Specifically, in the first step, an intermediate formed product is formed by adding a convex or concave portion to the intermediate top plate, and in the second step, the convex or concave portion is crushed to form the hat cross section shaped part or the U-shaped cross section shaped part. The convex or concave portion added to the intermediate top plate is located at the center of the ridge line direction of the intermediate formed product, and has a length of 1 / 5 of the total length of the intermediate top plate. The two parts are then divided.

[0060] The interior angle θ2 of the ridge line portion of the Z-shaped cross section shaped parts or L-shaped cross section shaped parts manufactured in the above conventional example and invention example after release was measured and compared. The results are shown in Table 1.

[0061] [Table 1]

[0062] In Table 1, "Part cross-sectional shape" indicates whether the manufactured part is a Z-shaped cross-sectional part or an L-shaped cross-sectional part. Furthermore, "shape given to the top plate portion in the first step" indicates whether a convex portion or a concave portion is given to the intermediate top plate portion of the intermediate molded product in the invention examples. The "height of unevenness" indicates the height of the top of the convex portion or the depth of the bottom of the concave portion from the outer surface of the intermediate top plate portion. The "inner angle between the top plate portion and the vertical wall portion after the second process" refers to the inner angle θ2 of the ridge portion of the Z-shaped cross-section shaped part or the L-shaped cross-section shaped part obtained by dividing the hat-shaped cross-section shaped part or the U-shaped cross-section shaped part after demolding.

[0063] In the conventional example No. 1, a hat-shaped cross-section part was formed in one process, and then divided to produce a Z-shaped cross-section part. The interior angle θ2 of the ridge line of the produced Z-shaped cross-section part was 115°. When Z-shaped cross-section parts were produced using the conventional manufacturing method, the difference in the interior angle of the ridge line was large compared to the target angle θ1 of 100°, and there was significant springback.

[0064] In contrast, in Examples No. 2 and No. 3, an intermediate molded product was formed by adding a convex or concave portion to the intermediate top plate, and the convex or concave portion was crushed to form a hat-shaped cross-section part, which was then divided to produce a Z-shaped cross-section part. In Examples No. 2 and No. 3, the interior angle θ2 of the ridge line of the manufactured Z-shaped cross-section part was both 105°, and springback was reduced compared to Conventional Example No. 1.

[0065] In the conventional example No. 4, a U-shaped cross-section part was formed in one process, and then divided to produce an L-shaped cross-section part, and the inner angle θ2 of the ridge line of the produced L-shaped cross-section part was 111°. When an L-shaped cross-section part was produced using the conventional manufacturing method, the difference in the inner angle of the ridge line was large compared to the target angle θ1 of 100°, and springback was large, just like in the case of a Z-shaped cross-section part.

[0066] In contrast, in Examples No. 5 and No. 6, an intermediate molded product was formed by adding a convex or concave portion to an intermediate top plate portion, and the convex or concave portion was crushed to form a U-shaped cross-section part, which was then divided to produce an L-shaped cross-section part. In Examples No. 5 and No. 6, the interior angle θ2 of the ridge line of the manufactured L-shaped cross-section part was 101° and 102°, respectively, and springback was reduced compared to Conventional Example No. 4.

[0067] As described above, in this embodiment, it was confirmed that by using the manufacturing method of the press-molded product of the present invention, springback that opens the interior angle of the ridge line (the interior angle formed by the top plate portion and the vertical wall portion) can be reduced. [Explanation of symbols]

[0068] 1 Top plate 3 Ridgeline 5 Vertical wall section 7 Flange 9 Hat-shaped cross-section parts 11. U-shaped cross-section parts 13 Z-shaped cross-section parts 15 L-shaped cross-section parts 17 Intermediate molded product (embodiment 1) 19 Hat-shaped cross-section part (first embodiment) 21 Intermediate top plate 23 Middle ridge 25 Intermediate vertical wall 27 Intermediate flange 29 Convex shape part 31 U-shaped cross-section part (embodiment 1) 33 Intermediate molded product (embodiment 2) 35 L-shaped cross-section part (embodiment 2) 37 Punch 37a Restraint part 39 Die 41 Pad 43 Intermediate molded product (embodiment 2) 45 Z-shaped cross-section part (embodiment 2)

Claims

1. A method for manufacturing a press-molded product, which manufactures a press-molded product having a top plate portion and a vertical wall portion continuous with the top plate portion via a ridge line portion, a first step of molding an intermediate molded product having an intermediate top plate portion and an intermediate vertical wall portion connected to the intermediate top plate portion via an intermediate ridge portion, the intermediate top plate portion having a convex or concave portion extending in the same direction as the extending direction of the intermediate ridge portion and having a convex or concave shape in cross section perpendicular to the ridge portion; a second step of crushing the convex or concave portion of the intermediate product to form a press-formed product in which the shapes of the top plate portion, the ridge portion, and the vertical wall portion other than the convex or concave portion are the same as those of the intermediate top plate portion, the intermediate ridge portion, and the intermediate vertical wall portion, A method for manufacturing a press-molded product, characterized in that in the second step, the material flow generated by crushing the convex or concave portion pushes the material of the intermediate ridge portion toward the vertical wall portion, thereby bending back the area that was previously the intermediate ridge portion.

2. 2. The method for manufacturing a press-formed product according to claim 1, wherein the press-formed product is a hat-shaped or U-shaped cross-sectional part having a pair of vertical wall portions on both sides of the top plate portion.

3. 3. The method for manufacturing a press-molded product according to claim 2, further comprising a dividing step of cutting and dividing the top plate portion of the hat cross-section shaped part or the U-shaped cross-section shaped part formed in the second step in the extension direction of the ridge line portion to obtain two Z-shaped cross-section shaped parts or two L-shaped cross-section shaped parts.

4. One or both sides of a ridge line direction of a portion of the top plate portion where the convex portion or the concave portion is provided are cut out, 4. The method for manufacturing a press-formed product according to claim 3, wherein the dividing step divides the top plate portion by cutting off the notched portion of the top plate portion.

5. The press-formed product is a Z-shaped cross-sectional part or an L-shaped cross-sectional part having a vertical wall portion on only one side of the top plate portion, 2. The method for manufacturing a press-formed product according to claim 1, wherein the second step comprises constraining an end of the intermediate top plate portion of the intermediate formed product that does not have the intermediate vertical wall portion while forming the intermediate formed product.

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