Manufacturing method of press-molded product and press-molded product

Abstract

This method for manufacturing press-molded articles (10, 50) comprises: a preparing step for preparing materials (40, 80); a first molding step for molding the materials (40, 80) by using first molds (21, 61) and second molds (22, 62); and a second molding step for molding the materials (40, 80) by using third molds (31, 71) and fourth molds (32, 72) after the first molding step. When the curvature radius of shoulder parts (212, 612) of the first molds (21, 61) is defined as R1, an angle formed by the side surfaces (213, 613) and the top surfaces (211, 611) is defined as θ1, a line length of the top surfaces (211, 611) from a reference point (P) to the shoulder parts (212, 612) is defined as L1, the curvature radius of the shoulder parts (312, 712) of the third molds (31, 71) is defined as R2, the angle formed by the side surfaces (313, 713) and the top surfaces (311, 711) is defined as θ2, and a line length of the top surfaces (311, 711) from the reference point (P) to the shoulder parts (312, 712) is defined as L2, R2 / R1 < 1.0, θ2 / θ1 > 1.0, and 0.0 < L2-L1 ≦ 4.0 are satisfied.

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a press-molded product and the press-molded product. [Background technology]

[0002] Press-formed products are used in, for example, moving bodies such as automobiles and ships. Press-formed products are manufactured by pressing a material made of a metal plate using a mold. When the material is bent in the manufacture of press-formed products, cracks may occur on the outer surface of the bent portion formed in the material.

[0003] Patent Document 1 discloses a method for manufacturing a press-formed product that can suppress cracks on the outer surface of a bent portion. The manufacturing method in Patent Document 1 includes a first forming step and a second forming step. In the first forming step, a metal plate is press-formed using a die to form an intermediate formed product from the material, the intermediate formed product including a bent portion with a bend radius R1 (mm) and a bend angle θ1 (°). In the second forming step, the intermediate formed product is press-formed using a die to form a bent portion with a bend radius R2 (mm) and a bend angle θ2 (°) at the position of the bent portion of the intermediate formed product. The bend radius R1 in the first forming step is larger than the bend radius R2 in the second forming step. The bend angle θ1 in the first forming step is smaller than the bend angle θ2 in the second forming step. The bend radii R1 and R2 and the bend angles θ1 and θ2 are set to satisfy a predetermined relationship. According to Patent Document 1, by setting the bending radii R1, R2 and bending angles θ1, θ2 in this manner, the surface strain of the bent portion is reduced, so that even when a high-strength steel plate with a tensile strength of 590 MPa or more is used as the raw material, the occurrence of cracks is suppressed and press-formed products having bent portions with smaller bending radii can be manufactured. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2016 / 121358 Summary of the Invention [Problem to be solved by the invention]

[0005] For example, in the automotive industry, in order to achieve both weight reduction and crashworthiness, the materials used for press-formed parts have become increasingly strong and thin in recent years. However, the stronger the material, the more likely it is that cracks will occur on the outer surface of the bent part when the material is bent to manufacture the press-formed part. For example, when steel plate with a tensile strength of 980 MPa or more is used as the material, cracks are particularly likely to occur at the bent part. Therefore, there is a need for technology that can further suppress the occurrence of cracks at the bent part.

[0006] An object of the present disclosure is to provide a method for manufacturing a press-formed product that can further suppress the occurrence of cracks in bent portions. [Means for solving the problem]

[0007] The manufacturing method of the press-formed product according to the present disclosure includes a preparation step of preparing a material made of a metal plate, a first forming step of forming the material using a first mold and a second mold, and a second forming step of forming the material using a third mold and a fourth mold after the first forming step. The first mold includes a first top surface and a first side surface. The first side surface is connected to the first top surface via a first shoulder. The second mold includes a second top surface and a second side surface. The second side surface is connected to the second top surface via a second shoulder. The third mold includes a third top surface and a third side surface. The third side surface is connected to the third top surface via a third shoulder. The fourth mold includes a fourth top surface and a fourth side surface. The fourth side surface is connected to the fourth top surface via a fourth shoulder. In the first forming step, the material is disposed between the first mold and the second mold such that the material faces the first top surface and the second top surface. In the first forming step, the portion of the material facing the second top surface is pushed toward the portion facing the first top surface on the first mold side and clamped by the first side surface and the second side surface by the second mold moving relatively to the first mold, thereby forming the material by the first top surface, the first shoulder, and the first side surface. In the second forming step, the material is disposed between the third mold and the fourth mold such that the portion of the material formed by the first top surface faces the third top surface and the portion of the material formed by the first side surface is disposed on the third side surface side. In the second forming step, the material is formed along the third top surface, the third shoulder, and the third side surface by the fourth mold moving relatively to the third mold. The first top surface includes a main body portion and a raised portion. The raised portion connects the main body portion and the first shoulder. The raised portion protrudes with respect to the main body portion such that the first shoulder side is farther from the main body portion in the relative movement direction of the second mold with respect to the first mold than the main body portion side. In the first forming step, when viewing the first mold in a cross section including a reference point set in the portion of the material formed by the first top surface, the radius of curvature of the first shoulder is R1 [mm], the angle formed by the first side surface and the raised portion is θ1 [°], and the linear length of the first top surface from the reference point to the first shoulder is L1 [mm]. In the second forming step, when viewing the third mold in a cross section including the reference point, the radius of curvature of the third shoulder is R2 [mm], the angle formed by the third side surface and the third top surface is θ2 [°], and the linear length of the third top surface from the reference point to the third shoulder is L2 [mm], then R2 / R1 < 1.0, θ2 / θ1 > 1.0, and 0.0 < L2 - L1 ≦ 4.0 are satisfied. [Effects of the Invention]

[0008] According to the method for manufacturing a press-formed product according to the present disclosure, the occurrence of cracks in bent portions can be further suppressed. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view schematically showing a press-formed product according to the first embodiment. [Figure 2] FIG. 2 is a perspective view schematically showing another press-formed product according to the first embodiment. [Figure 3] FIG. 3 is a cross-sectional view of a die unit used in the method for manufacturing a press-formed product according to the first embodiment. [Figure 4] FIG. 4 is a cross-sectional view of another die unit used in the method for manufacturing a press-formed product according to the first embodiment. [Figure 5A] FIG. 5A is a schematic view for explaining the method for manufacturing a press-formed product according to the first embodiment. [Figure 5B] FIG. 5B is a schematic view for explaining the method for manufacturing a press-formed product according to the first embodiment. [Figure 5C] FIG. 5C is a schematic view for explaining the method for manufacturing a press-formed product according to the first embodiment. [Figure 5D] FIG. 5D is a schematic view for explaining the method for manufacturing a press-formed product according to the first embodiment. [Figure 5E] FIG. 5E is a schematic view for explaining the method for manufacturing a press-formed product according to the first embodiment. [Figure 5F] FIG. 5F is a schematic view for explaining the method for manufacturing a press-formed product according to the first embodiment. [Figure 5G] FIG. 5G is a schematic view for explaining the method for manufacturing a press-formed product according to the first embodiment. [Figure 6] FIG. 6 is a cross-sectional view of the press-formed product according to the first embodiment. [Figure 7]FIG. 7 is a perspective view schematically showing a press-formed product according to the second embodiment. [Figure 8] FIG. 8 is a cross-sectional view of a die unit used in the method for manufacturing a press-formed product according to the second embodiment. [Figure 9] FIG. 9 is a cross-sectional view of another die unit used in the method for manufacturing a press-formed product according to the second embodiment. [Figure 10A] FIG. 10A is a schematic view for explaining the method for manufacturing a press-formed product according to the second embodiment. [Figure 10B] FIG. 10B is a schematic view for explaining the method for manufacturing a press-formed product according to the second embodiment. [Figure 10C] FIG. 10C is a schematic view for explaining the method for manufacturing a press-formed product according to the second embodiment. [Figure 10D] FIG. 10D is a schematic view for explaining the method for manufacturing a press-formed product according to the second embodiment. [Figure 10E] FIG. 10E is a schematic view for explaining the method for manufacturing a press-formed product according to the second embodiment. [Figure 10F] FIG. 10F is a schematic view for explaining the method for manufacturing a press-formed product according to the second embodiment. [Figure 11] FIG. 11 is a cross-sectional view of a press-formed product according to the second embodiment. [Figure 12] FIG. 12 is a graph showing the results of the analysis carried out as the first example. [Figure 13] FIG. 13 is another graph showing the results of the analysis carried out as the first example. [Figure 14] FIG. 14 is a graph showing the results of the analysis carried out as the second example. [Figure 15] FIG. 15 is a graph showing the results of the analysis carried out as the third example. DETAILED DESCRIPTION OF THE INVENTION

[0010] The manufacturing method of the press-formed product according to the embodiment includes a preparation step of preparing a material made of a metal plate, a first forming step of forming the material using a first mold and a second mold, and a second forming step of forming the material using a third mold and a fourth mold after the first forming step. The first mold includes a first top surface and a first side surface. The first side surface is connected to the first top surface via a first shoulder portion. The second mold includes a second top surface and a second side surface. The second side surface is connected to the second top surface via a second shoulder portion. The third mold includes a third top surface and a third side surface. The third side surface is connected to the third top surface via a third shoulder portion. The fourth mold includes a fourth top surface and a fourth side surface. The fourth side surface is connected to the fourth top surface via a fourth shoulder portion. In the first forming step, the material is disposed between the first mold and the second mold such that the material faces the first top surface and the second top surface. In the first forming step, the portion of the material facing the second top surface is pushed toward the portion facing the first top surface on the side of the first mold and clamped by the first side surface and the second side surface by the second mold that moves relatively to the first mold, thereby forming the material by the first top surface, the first shoulder portion, and the first side surface. In the second forming step, the material is disposed between the third mold and the fourth mold such that the portion of the material formed by the first top surface faces the third top surface and the portion of the material formed by the first side surface is disposed on the side of the third side surface. In the second forming step, the material is formed along the third top surface, the third shoulder portion, and the third side surface by the fourth mold that moves relatively to the third mold. The first top surface includes a main body portion and a raised portion. The raised portion connects the main body portion and the first shoulder portion. The raised portion bulges with respect to the main body portion such that the side of the first shoulder portion is farther from the main body portion in the relative movement direction of the second mold with respect to the first mold than the side of the main body portion. In the first forming step, when viewing the first mold in a cross section including a reference point set in the portion of the material formed by the first top surface, the radius of curvature of the first shoulder portion is R1 [mm], the angle formed by the first side surface and the raised portion is θ1 [°], and the linear length of the first top surface from the reference point to the first shoulder portion is L1 [mm]. In the second forming step, when viewing the third mold in a cross section including the reference point, the radius of curvature of the third shoulder portion is R2 [mm], the angle formed by the third side surface and the third top surface is θ2 [°], and the linear length of the third top surface from the reference point to the third shoulder portion is L2 [mm], R2 / R1 < 1.0, θ2 / θ1 > 1.0, and 0.0 < L2 - L1 ≦ 4.0 are satisfied (the first configuration).

[0011] In the first configuration, the radius of curvature R1 of the first shoulder portion of the first mold used in the first molding step is larger than the radius of curvature R2 of the third shoulder portion of the third mold used in the second molding step. Also, the angle θ1 formed by the first top surface and the first side surface in the first mold is smaller than the angle θ2 formed by the third top surface and the third side surface in the third mold. Therefore, first, in the first molding step, a bent portion having a relatively large bending radius (radius of curvature on the inner side of the bend) and a relatively small bending angle is formed on the material by the first shoulder portion of the first mold. Subsequently, in the second molding step, the bent portion formed in the first molding step is formed into a bent portion having a smaller bending radius (radius of curvature on the inner side of the bend) and a larger bending angle by the third shoulder portion of the third mold. Thus, by performing the bending forming on the material in two steps, compared with the case of forming the bent portion by a single bending forming, the strain on the outer surface of the bent portion can be dispersed and reduced. Therefore, cracking at the bent portion is less likely to occur.

[0012] In the first configuration, the first top surface of the first mold includes a raised portion on the first shoulder side. In the first mold of the first molding step, the line length L2 measured along the third top surface from the same reference point to the third shoulder in the third mold of the second molding step is larger than the line length L1 measured along the first top surface from the reference point set on the material to the first shoulder. L2 - L1 is greater than 0.0 mm and not more than 4.0 mm. By configuring the shape of the first top surface, the line length L1 of the first top surface, and the line length L2 of the third top surface in this way, the strain on the outer surface of the bent portion becomes more easily dispersed, and the strain can be further reduced. More specifically, by setting 0.0 < L2 - L1 ≤ 4.0 and changing the distance from the reference point of the material to the shoulder of the mold between the first molding step and the second molding step, in the material, the position where a large tensile strain occurs due to the bending by the shoulder of the mold can be shifted between the first molding step and the second molding step. Therefore, not only the bent portion but also the adjacent portion of the bent portion is widely dispersed with strain, and the maximum value (peak) of the final tensile strain can be reduced. Therefore, in the manufacture of the press-formed product, the occurrence of cracking at the bent portion can be more effectively suppressed.

[0013] In the first configuration, a first top surface of the first die has a raised portion that is raised relative to the main body portion. In the first molding step, the material is bent outward from the first die at the boundary between the main body portion and the raised portion, thereby causing work hardening in the material at that position. The formation of such a work-hardened portion can increase the initial reaction force against an input load in the press-formed product produced. Therefore, the yield strength of the press-formed product can be improved.

[0014] In the manufacturing method according to the first configuration, a fifth mold may be used in the first molding step in addition to the first and second molds. In the first molding step, the fifth mold can sandwich the material together with the first top surface (second configuration).

[0015] In the second configuration, in the first forming step, the material is bent by the first top surface, first shoulder, and first side surface of the first die while the fifth die holds down the material on the first top surface of the first die. In this case, deflection of the material at the position of the first top surface is less likely to occur, and work hardening of the material at the boundary between the main body portion and the protrusion can be more reliably generated. Therefore, the yield strength of the press-formed product can be further improved. In addition, by using the fifth die, the first forming step can be performed while suppressing misalignment of the material.

[0016] In the manufacturing method according to the first or second configuration, a sixth mold may be used in addition to the third and fourth molds in the second molding step. In the second molding step, the sixth mold can sandwich the material together with the third top surface (third configuration).

[0017] According to the third configuration, in the second molding step, the material is sandwiched between the third mold and the sixth mold, which makes it possible to perform the second molding step while suppressing displacement of the material.

[0018] In the manufacturing method according to any one of the first to third configurations, the metal plate may be a steel plate having a tensile strength of 980 MPa or more (fourth configuration).

[0019] According to the method for manufacturing a press-formed product of the embodiment, strain on the outer surface of the bent portion is easily dispersed, and the maximum value of strain on the outer surface of the bent portion can be reduced more than in the past. As a result, even when the press-formed product is manufactured from a material made of a high-strength steel plate of 980 MPa or more, as in the fourth configuration, cracks in the bent portion can be suppressed.

[0020] A press-formed product according to an embodiment includes a first plate portion, a bent portion, and a second plate portion. The bent portion is continuous with the first plate portion. The second plate portion is connected to the first plate portion via the bent portion. When the plate thickness of the first plate portion at a position 10.0 mm away from the boundary between the first plate portion and the bent portion is defined as a reference plate thickness, the ratio H2 / H1 of the average Vickers hardness H1 measured at 0.5 mm intervals in the first plate portion from a position 3.0 times the reference plate thickness from the boundary to a position 4.0 times the reference plate thickness to the average Vickers hardness H2 measured at 0.5 mm intervals from a position 1.0 times the reference plate thickness from the boundary to a position 3.0 times the reference plate thickness from the boundary is greater than 1.1 (fifth configuration).

[0021] In the press-formed product according to the fifth configuration, in the first plate portion continuous with the bent portion, the average Vickers hardness H2 near the bent portion is greater than the average Vickers hardness H1 at a position relatively distant from the bent portion. That is, in the press-formed product according to the fifth configuration, work hardening during press forming extends not only to the bent portion but also to the outside of the bent portion. The widespread presence of such work-hardened portions increases the initial reaction force when a load is input to the press-formed product, allowing the press-formed product to exhibit excellent yield strength.

[0022] In the press-molded product according to the fifth configuration, when the Vickers hardness is measured at 1.0 mm intervals in the first plate portion beyond a position 4.0 times the standard plate thickness from the boundary, and the average value of the Vickers hardness of three adjacent measurement points is taken as H3, there may be an H3 that satisfies H3 / H1>1.1 (sixth configuration).

[0023] In the press-formed product according to the sixth configuration, in the first plate portion continuous with the bent portion, the average Vickers hardness H3 at a position further away from the bent portion is greater than the average Vickers hardness H1 at a position relatively far from the bent portion. That is, the press-formed product according to the sixth configuration has work-hardened portions not only at and near the bent portion but also at positions far from the bent portion. This makes it easier to increase the initial reaction force when a load is input to the press-formed product, and makes it easier for the press-formed product to exhibit excellent yield strength.

[0024] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, the same or equivalent components are designated by the same reference numerals, and the same description will not be repeated.

[0025] [First embodiment] (press-molded products) 1 and 2 are perspective views schematically showing a press-formed product 10 according to this embodiment. The press-formed product 10 is used, for example, in mobile objects such as automobiles and ships. The press-formed product 10 is preferably used as an automobile part. However, the use of the press-formed product 10 is not limited to this.

[0026] 1, a press-formed product 10 according to this embodiment has, for example, an elongated shape. The press-formed product 10 may have a straight shape or may be curved entirely or partially. The press-formed product 10 includes a first plate portion 11, second plate portions 12L, 12R, and bent portions 13L, 13R.

[0027] In this embodiment, the first plate portion 11 is a top plate of the press-formed product 10. The first plate portion 11 extends in the longitudinal direction of the press-formed product 10. The bent portions 13L and 13R are each continuous with the first plate portion 11. The bent portions 13L and 13R extend along both side edges of the first plate portion 11. Each of the bent portions 13L and 13R can have a substantially arc-shaped cross section perpendicular to the longitudinal direction of the press-formed product 10. At least the outer surfaces of the bent portions 13L and 13R have a substantially arc-shaped cross section. One second plate portion 12L is connected to the first plate portion 11 via the bent portion 13L. The other second plate portion 12R is connected to the first plate portion 11 via the bent portion 13R. The second plate portion 12R is disposed on the opposite side of the second plate portion 12L with respect to the first plate portion 11. The second plate portions 12L, 12R extend along the bent portions 13L, 13R, respectively. The second plate portions 12L, 12R are vertical walls of the press-formed product 10. Hereinafter, unless there is a particular need to distinguish between them, the second plate portions 12L, 12R will be collectively referred to as the second plate portion 12, and the bent portions 13L, 13R will be collectively referred to as the bent portion 13.

[0028] 2, the press-formed product 10 may further include flanges 14L, 14R. The flanges 14L, 14R are connected to the second plate portions 12L, 12R, respectively, on the opposite side of the first plate portion 11. The flanges 14L, 14R protrude, for example, from the second plate portions 12L, 12R to the outside of the press-formed product 10.

[0029] (Method of manufacturing press-molded products) The following describes a method for manufacturing the press-formed product 10. First, the configurations of the die units 20 and 30 used in manufacturing the press-formed product 10 will be described with reference to FIGS.

[0030] The die unit 20 extends in a direction intersecting the plane of the drawing in FIG. 3. FIG. 3 is a cross-sectional view of the die unit 20 taken along a plane perpendicular to the extension direction of the die unit 20. As shown in FIG. 3, the die unit 20 includes dies 21, 22L, 22R, and 23. The dies 21, 22L, 22R, and 23 are attached to, for example, a known press machine. The die 21 is capable of moving relatively close to and away from the dies 22L, 22R, and 23. For example, the die 21 may be attached to a slide of the press machine and configured to move together with the slide, or the dies 22L, 22R, and 23 may be attached to a slide of the press machine and configured to move together with the slide. Hereinafter, the relative approach direction (movement direction) between the die 21 and the dies 22L, 22R, and 23 is referred to as the press direction D1. The direction perpendicular to the press direction D1 and the extension direction of the die unit 20 is referred to as the width direction of the die unit 20.

[0031] The mold 21 includes a top surface 211, shoulders 212L and 212R, and side surfaces 213L and 213R.

[0032] The top surface 211 includes a main body portion 211a and raised portions 211Lb and 211Rb. The main body portion 211a intersects with the pressing direction D1. For example, the main body portion 211a is substantially perpendicular to the pressing direction D1. The main body portion 211a may have a generally flat shape, or may partially have an uneven shape such as a bead.

[0033] The raised portions 211Lb and 211Rb are arranged on both sides of the main body portion 211a. The raised portions 211Lb and 211Rb are provided continuously with the main body portion 211a. The raised portion 211Lb is arranged between the main body portion 211a and the shoulder portion 212L and connects the main body portion 211a and the shoulder portion 212L. The raised portion 211Lb rises relative to the main body portion 211a so that the shoulder portion 212L side is farther away from the main body portion 211a in the pressing direction D1 than the main body portion 211a side. The raised portion 211Rb is arranged between the main body portion 211a and the shoulder portion 212R and connects the main body portion 211a and the shoulder portion 212R. The raised portion 211Rb is raised relative to the main body portion 211a so that the shoulder portion 212R side is farther away from the main body portion 211a in the pressing direction D1 than the main body portion 211a side.

[0034] The raised portions 211Lb, 211Rb are, for example, inclined surfaces that are inclined relative to the main body portion 211a. In this case, fillet processing may be applied to the connection portion between the raised portion 211Lb and the main body portion 211a. Similarly, fillet processing may be applied to the connection portion between the raised portion 211Rb and the main body portion 211a. The raised portions 211Lb, 211Rb may have an overall linear shape in a cross-sectional view of the mold 21 as shown in FIG. 3, or may have a curved shape in a cross-sectional view of the mold 21. The raised portions 211Lb, 211Rb may be configured such that the ends on the shoulder portions 212L, 212R side are positioned closer to the outside of the mold 21 in the pressing direction D1 than the ends on the main body portion 211a side. The shape of the raised portions 211Lb, 211Rb is not limited to the example shown in FIG. 3. Hereinafter, when there is no need to particularly distinguish between the raised portions 211Lb and 211Rb, they will be collectively referred to as raised portion 211b.

[0035] The shoulders 212L, 212R are continuous with the top surface 211. One shoulder 212L is located on the opposite side of the top surface 211 from the other shoulder 212R. The shoulder 212L is adjacent to one raised portion 211Lb of the top surface 211. The shoulder 212R is adjacent to the other raised portion 211Rb of the top surface 211. Each of the shoulders 212L, 212R can have a substantially arc-shaped cross section. Hereinafter, when there is no need to particularly distinguish between the shoulders 212L, 212R, they will be collectively referred to as shoulders 212.

[0036] The side surfaces 213L and 213R are continuous with the shoulder portions 212L and 212R, respectively. One side surface 213L is connected to the top surface 211 via the shoulder portion 212L. The other side surface 213R is connected to the top surface 211 via the shoulder portion 212R. The side surfaces 213L and 213R may have a substantially flat shape. That is, the side surfaces 213L and 213R may have a linear shape in a cross-sectional view of the mold 21. Hereinafter, when there is no need to particularly distinguish between the side surfaces 213L and 213R, they will be collectively referred to as the side surfaces 213.

[0037] Each of the molds 22L and 22R includes a top surface 221, a shoulder 222, and a side surface 223.

[0038] The top surface 221 is positioned offset outward in the width direction from the top surface 211 of the mold 21. That is, the top surfaces 221 of the molds 22L and 22R do not face the top surface 211 of the mold 21 in the pressing direction D1. The shoulder portion 222 is continuous with the top surface 221. The shoulder portion 222 can have a substantially arc-shaped cross section. The side surface 223 is continuous with the shoulder portion 222. The side surface 223 is connected to the top surface 221 via the shoulder portion 222. The side surface 223 can have a substantially flat shape. That is, the side surface 223 can have a linear shape in a cross-sectional view of the mold 22. The side surface 223 of the mold 22L has a shape corresponding to the side surface 213L of the mold 21. The side surface 223 of the mold 22R has a shape corresponding to the side surface 213R of the mold 21. The molds 22L and 22R may be separate bodies or may be integrally formed. Hereinafter, when there is no need to particularly distinguish between the molds 22L and 22R, they will be collectively referred to as the mold 22.

[0039] The die 23 is disposed so as to face the die 21 in the pressing direction D1. The die 23 is disposed between the dies 22L and 22R. The die 23 includes a pressing surface 231.

[0040] The pressing surface 231 faces the top surface 211 of the die 21 in the pressing direction D1. The pressing surface 231 has a shape corresponding to the main body portion 211a and the raised portion 211b of the top surface 211 of the die 21. For example, the pressing surface 231 is configured to form a substantially constant clearance between itself and the top surface 211 of the die 21.

[0041] The die unit 30 extends in a direction intersecting the plane of the drawing in FIG. 4. As shown in FIG. 4, the die unit 30 includes dies 31, 32L, 32R, and 33. The dies 31, 32L, 32R, and 33 are attached to, for example, a known press machine. The die 31 is capable of moving relatively close to and away from the dies 32L, 32R, and 33. For example, the die 31 may be attached to a slide of the press machine and configured to move together with the slide, or the dies 32L, 32R, and 33 may be attached to a slide of the press machine and configured to move together with the slide. Hereinafter, the relative approach direction (movement direction) between the die 31 and the dies 32L, 32R, and 33 is referred to as the press direction D2. The direction perpendicular to the press direction D2 and the extension direction of the die unit 30 is referred to as the width direction of the die unit 30.

[0042] The mold 31 includes a top surface 311, shoulders 312L and 312R, and side surfaces 313L and 313R.

[0043] The top surface 311 intersects with the pressing direction D2. For example, the top surface 311 is substantially perpendicular to the pressing direction D2. The top surface 311 has a substantially flat shape overall. That is, the top surface 311 does not have any raised portions like the top surface 211 of the mold 21 shown in FIG. 3. However, the top surface 311 may partially have an uneven shape such as a bead.

[0044] The shoulders 312L, 312R are continuous with the top surface 311. One shoulder 312L is located on the opposite side of the top surface 311 from the other shoulder 312R. Each of the shoulders 312L, 312R may have a substantially arc-shaped cross section. The shoulders 312L, 312R may form a non-rounded corner (pin angle) when viewed in cross section of the mold 31. Hereinafter, when there is no need to particularly distinguish between the shoulders 312L, 312R, they will be collectively referred to as shoulders 312.

[0045] The side surfaces 313L and 313R are continuous with the shoulder portions 312L and 312R, respectively. One side surface 313L is connected to the top surface 311 via the shoulder portion 312L. The other side surface 313R is connected to the top surface 311 via the shoulder portion 312R. The side surfaces 313L and 313R may have a substantially flat shape. That is, the side surfaces 313L and 313R may have a linear shape in a cross-sectional view of the mold 31. Hereinafter, when there is no need to particularly distinguish between the side surfaces 313L and 313, they will be collectively referred to as the side surface 313.

[0046] Each of the molds 32L and 32R includes a top surface 321, a shoulder 322, and a side surface 323.

[0047] The top surface 321 is positioned outward in the width direction from the top surface 311 of the mold 31. That is, the top surfaces 321 of the molds 32L and 32R do not face the top surface 311 of the mold 31 in the pressing direction D2. The shoulder portion 322 is continuous with the top surface 321. The shoulder portion 322 may have a substantially arc-shaped cross section. The side surface 323 is continuous with the shoulder portion 322. The side surface 323 is connected to the top surface 321 via the shoulder portion 322. The side surface 323 may have a substantially flat shape. That is, the side surface 323 may have a linear shape in a cross-sectional view of the mold 32. The side surface 323 of the mold 32L has a shape corresponding to the side surface 313L of the mold 31. The side surface 323 of the mold 32R has a shape corresponding to the side surface 313R of the mold 31. The molds 32L and 32R may be separate bodies or may be integrally formed. Hereinafter, when there is no need to particularly distinguish between the molds 32L and 32R, they will be collectively referred to as the mold 32.

[0048] The die 33 is disposed so as to face the die 31 in the pressing direction D2. The die 33 is disposed between the dies 32L and 32R. The die 33 includes a pressing surface 331.

[0049] The pressing surface 331 faces the top surface 311 of the die 31 in the pressing direction D2. The pressing surface 331 has a shape corresponding to the top surface 311 of the die 31.

[0050] Fig. 3 shows an example in which the cross section of the mold unit 20 including molds 21, 22, and 23 has a shape and dimensions that are symmetrical with respect to a center line CL1 in the width direction. Fig. 4 shows an example in which the cross section of the mold unit 30 including molds 31, 32, and 33 has a shape and dimensions that are symmetrical with respect to a center line CL2 in the width direction. However, the mold unit 20 may have a shape and / or dimensions that are asymmetrical with respect to the width center line CL1. Similarly, the mold unit 30 may have a shape and / or dimensions that are asymmetrical with respect to the width center line CL2.

[0051] Next, a method for manufacturing the press-formed product 10 using the die units 20, 30 will be described with reference to Figures 5A to 5G. Figures 5B to 5G show only one side of the width center lines CL1, CL2 of the die units 20, 30.

[0052] The method for manufacturing the press-formed product 10 includes a preparation step, a first forming step, and a second forming step.

[0053] Referring to FIG. 5A, in the preparation step, a raw material 40 made of a metal plate is prepared. The raw material 40 is, for example, a blank having a shape obtained by unfolding the press-formed product 10 (FIG. 1). The metal plate constituting the raw material 40 may be a steel plate. This steel plate has a tensile strength of, for example, 590 MPa or more, preferably 980 MPa or more, and more preferably 1180 MPa or more. The plate thickness t of the raw material 40 is, for example, 1.0 mm or more. The plate thickness t of the raw material 40 may be 6.0 mm or less.

[0054] 5B , in the first molding step, a mold unit 20 including molds 21, 22, and 23 is used. In the first molding step, first, the material 40 is placed between the molds 21 and 22 so that the material 40 faces the top surface 211 of the mold 21 and the top surface 221 of the mold 22. The material 40 is placed, for example, on the top surface 211 of the mold 21. At this time, a portion of the material 40 is placed between the top surface 211 of the mold 21 and the pressing surface 231 of the mold 23. The other portion of the material 40 faces the top surface 221 of the mold 22 outside the molds 21 and 23.

[0055] 5C and 5D , in the first molding step, the dies 22 and 23 are moved relatively with respect to the die 21 to bring the die 21 and the dies 22 and 23 closer to each other. The die 22 presses the portion of the material 40 facing the top surface 221 of the die 22 toward the die 21 with respect to the portion facing the top surface 211 of the die 21, and sandwiches the material 40 between the side surface 213 of the die 21 and the side surface 223 of the die 22, thereby molding the material 40 with the top surface 211 of the die 21, the shoulder portion 212, and the side surface 213 of the die 21. The die 23 sandwiches the material 40 together with the top surface 211 of the die 21. More specifically, the portion of the material 40 facing the top surface 211 of the die 21 is pressed by the pressing surface 231 of the die 23. The pressing surface 231 of the die 23 may come into contact with the material 40 before the die 22 does.

[0056] After the die 23 presses the material 40 on the die 21, the die 22 moves toward the die 21 relative to the die 23, thereby bending the material 40 at the position of the shoulder 212 of the die 21. The material 40 is finally held between the side surface 213 of the die 21 and the side surface 223 of the die 22, and is formed into a shape that follows the top surface 211, shoulder 212, and side surface 213 of the die 21.

[0057] In the first molding step, when a reference point P is set on a portion of the raw material 40 that will be molded by the top surface 211 of the mold 21, in a cross-sectional view of the mold 21 including the reference point P, the shoulder 212 has a radius of curvature R1 [mm], and the protrusion 211b of the top surface 211 and the side surface 213 form an angle θ1 [°]. The angle θ1 is the angle formed by a tangent to the end of the shoulder 212 on the top surface 211 side (where the radius ends) and a tangent to the end of the shoulder 212 on the side surface 213 side (where the radius ends). Furthermore, in a cross-sectional view of the mold 21 including the reference point P set on the raw material 40, the top surface 211 has a line length L1 [mm]. The line length L1 is the line length of the top surface 211 from the reference point P of the raw material 40 to the shoulder 212. That is, the line length L1 is the line length of the top surface 211 from the reference point P of the raw material 40 to the boundary between the raised portion 211b and the shoulder portion 212 (the R of the shoulder portion 212 on the top surface 211 side ends). More specifically, the line length L1 is the length along the top surface 211 from the point where a straight line drawn from the reference point P of the raw material 40 along the press direction D1 intersects with the top surface 211 to the boundary between the raised portion 211b and the shoulder portion 212.

[0058] The reference point P is not particularly limited as long as it is a point (position) that can serve as a reference in the material 40. For example, if a hole is formed in the material 40 in a portion that faces the top surface 211 of the mold 21, the reference point P can be set at the edge of this hole. For example, the portion of the material 40 that faces the top surface 211 of the mold 21 can be marked with a writing implement or the like, and the given mark can be used as the reference point P.

[0059] 5E, the material 40 after the first forming step includes a first plate portion 41, a second plate portion 42, and a bent portion 43. The first plate portion 41 is a portion formed by the top surface 211 of the mold 21 in the first forming step. The bent portion 43 is a portion formed by the shoulder portion 212 of the mold 21 in the first forming step. The second plate portion 42 is a portion formed by the side surface 213 of the mold 21 in the first forming step. The second plate portion 42 is connected to the first plate portion 41 via the bent portion 43.

[0060] After the first molding step, the blank 40 is subjected to the second molding step. Referring to FIG. 5F , in the second molding step, a mold unit 30 including molds 31, 32, and 33 is used. In the second molding step, the blank 40 is placed between the molds 31 and 32 so that the first plate portion 41 faces the top surface 311 of the mold 31 and the second plate portion 42 is located on the side surface 313 of the mold 31. The blank 40 is placed, for example, on the top surface 311 of the mold 31. At this time, the first plate portion 41 of the blank 40 is located between the top surface 211 of the mold 21 and the pressing surface 331 of the mold 33. The bent portion 43 of the blank 40 is located near the shoulder portion 312 of the mold 31. The second plate portion 42 of the blank 40 is located so that at least a portion of it corresponds to the side surface 313 of the mold 31.

[0061] 5F and 5G, in the second forming step, the dies 32 and 33 are moved relatively to the die 31 to bring the die 31 and the dies 32 and 33 closer to each other. The die 32 forms the material 40 along the top surface 311, shoulder portion 312, and side surface 313 of the die 31, and the material 40 is sandwiched between the side surface 313 of the die 31 and the side surface 323 of the die 32. In the second forming step, the die 33 sandwiches the material 40 together with the top surface 311 of the die 31. More specifically, the first plate portion 41 of the material 40 is pressed by the pressing surface 331 of the die 33. As a result, the first plate portion 41 of the material 40 is formed into a shape that follows the top surface 311 of the die 31. The pressing surface 331 of the die 33 may come into contact with the material 40 before the die 32 does.

[0062] After the die 33 presses the material 40 on the die 31, the die 32 moves toward the die 31 relative to the die 33, whereby the bent portion 43 of the material 40 is deformed into a shape that follows the shoulder portion 312 of the die 31. The material 40 is finally held between the side surface 313 of the die 31 and the side surface 323 of the die 32, and formed into a shape that follows the top surface 311, shoulder portion 312, and side surface 313 of the die 31. In this way, the press-formed product 10 is produced from the material 40.

[0063] In the second molding process, in a cross-sectional view of the mold 31 including the same reference point P as in the first molding process, the shoulder 312 has a radius of curvature R2 [mm], and the top surface 311 and the side surface 313 form an angle θ2 [°]. Furthermore, in a cross-sectional view of the mold 31 including the reference point P of the material 40, the top surface 311 has a line length L2 [mm]. Line length L2 is the line length of the top surface 311 from the reference point P of the material 40 to the shoulder 312. If the shoulder 312 has a substantially arc shape in cross-sectional view, line length L2 is the line length of the top surface 311 from the reference point P of the material 40 to the boundary between the top surface 311 and the shoulder 312 (the radius of the shoulder 312 on the top surface 311 side ends). If the shoulder 312 forms an unrounded corner in cross-sectional view, line length L2 is the line length of the top surface 311 from the reference point P of the material 40 to the apex of the shoulder 312. More specifically, the line length L2 is the length along the top surface 311 from the point where a straight line drawn from the reference point P of the material 40 along the press direction D2 intersects with the top surface 311 in the cross section of the mold 31 to the boundary between the top surface 311 and the shoulder portion 312 or to the apex of the shoulder portion 312.

[0064] The radius of curvature R2 of shoulder portion 312 of mold 31 is smaller than the radius of curvature R1 (FIG. 5D) of shoulder portion 212 of mold 21. The angle θ2 between top surface 311 and side surface 313 of mold 31 is larger than the angle θ1 (FIG. 5D) between top surface 211 and side surface 213 of mold 21. The line length L2 of top surface 311 of mold 31 is larger than the line length L1 (FIG. 5D) of top surface 211 of mold 21. The radii of curvature R1, R2, angles θ1, θ2, and line lengths L1, L2 satisfy the following formulas (1) to (3). R2 / R1<1.0 (1) θ2 / θ1>1.0 (2) 0.0 <L2-L1≦4.0 (3)

[0065] The radius of curvature R1 is, for example, 1.0 mm or more and 10.0 mm or less. The radius of curvature R2 is, for example, 0.0 mm or more and 6.0 mm or less, preferably greater than 0.0 mm and less than 6.0 mm. When the shoulder portion 312 forms an unrounded corner (pin angle) between the top surface 311 and the side surface 313, the radius of curvature R2 is 0.0 mm. On the other hand, when the shoulder portion 312 has a substantially arc-shaped cross section, the radius of curvature R2 is greater than 0.0 mm. The radii of curvature R1 and R2 may satisfy formula (1), but more preferably, R2 / R1<0.5. The angle θ1 is, for example, 45° or more and 90° or less. The angle θ2 is, for example, 90° or more and 120° or less. The angles θ1 and θ2 may satisfy formula (2), but more preferably, θ2 / θ1>1.5. The line lengths L1 and L2 may be any lengths as long as they satisfy the formula (3), but more preferably, they satisfy 1.0≦L2−L1≦4.0.

[0066] For example, when the tensile strength of the blank 40 is 1180 MPa or more, the thickness t of the blank 40 and the radius of curvature R2 of the shoulder portion 312 of the mold 31 preferably satisfy R2 / t≦1.5, and more preferably satisfy R2 / t≦1.0. When the tensile strength of the blank 40 is 1180 MPa or more, the thickness t and the radius of curvature R2 preferably satisfy R2 / t>0.3, and more preferably satisfy R2 / t≧0.7. The tensile strength of the blank 40 may be 1470 MPa or less. Furthermore, when the tensile strength of the blank 40 is 980 MPa or more but less than 1180 MPa, the thickness t and the radius of curvature R2 preferably satisfy R2 / t<1.0, and more preferably satisfy R2 / t≦0.7. When the tensile strength of the blank 40 is 980 MPa or more but less than 1180 MPa, the thickness t and the radius of curvature R2 may be, for example, R2 / t>0.1.

[0067] Fig. 6 is a cross-sectional view of a press-formed product 10 obtained by the manufacturing method according to this embodiment. Fig. 6 partially shows a cross section of the press-formed product 10 along the plate thickness direction. A bent portion 13 is formed in the press-formed product 10 by two-stage bending using a shoulder portion 212 of the die 21 in the first forming step and a shoulder portion 312 of the die 31 in the second forming step. On both sides of the bent portion 13, a first plate portion 11 formed mainly by the top surfaces 211, 311 of the dies 21, 31, and a second plate portion 12 formed mainly by the side surfaces 213, 313 of the dies 21, 31 are arranged.

[0068] In the first plate portion 11, the ratio H2 / H1 of the average Vickers hardness H1 [HV] measured at 0.5 mm intervals from position A1 to position A2 to the average Vickers hardness H2 [HV] measured at 0.5 mm intervals from position A0 to position A1 is greater than 1.1. Position A1 is a position 3.0 times the reference plate thickness t0 along the outer surface of the first plate portion 11 from the boundary 15 between the first plate portion 11 and the bent portion 13 on the outside of the bend, i.e., from the end of the R on the first plate portion 11 side of the outer surface of the bent portion 13. Position A2 is a position 4.0 times the reference plate thickness t0 along the outer surface of the first plate portion 11 from the boundary 15. Position A0 is a position 1.0 times the reference plate thickness t0 along the outer surface of the first plate portion 11 from the boundary 15 between the first plate portion 11 and the bent portion 13. The reference thickness t0 refers to the thickness of the first plate portion 11 at a position 10.0 mm away from the boundary 15 between the first plate portion 11 and the bent portion 13. The reference thickness t0 corresponds to the thickness t of the blank 40 (FIG. 5A).

[0069] The Vickers hardness is measured at 1.0 mm intervals beyond position A2, which is 4.0 times the reference plate thickness t0 from the boundary 15 with the bent portion 13 in the first plate portion 11, and the average value of the Vickers hardnesses of three adjacent measurement points is defined as H3. The first plate portion 11 has H3 such that H3 / H1>1.1.

[0070] H1, H2, and H3 can be obtained as follows. For H1, a test piece including a cross section along the thickness direction of the first plate portion 11 is taken from the press-formed product 10. A Vickers hardness test (test force of 1 kgw (9.8 N)) conforming to JIS Z 2244:2020 is performed on this cross section (test surface) at a position ¼ of the reference plate thickness t0 from the bent outer surface of the press-formed product 10, starting from position A1 at 0.5 mm intervals until position A2 is reached, thereby measuring the Vickers hardness. The average of the measured Vickers hardness values ​​is calculated, and this value is designated as H1. For H2, a Vickers hardness test (test force of 1 kgw (9.8 N)) conforming to JIS Z 2244:2020 is performed on the test surface at a position ¼ of the reference plate thickness t0 from the bent outer surface of the press-formed product 10, starting from position A0 at 0.5 mm intervals until position A1 is reached, thereby measuring the Vickers hardness. The average value of the measured Vickers hardnesses is then calculated and designated as H2. Regarding H3, a Vickers hardness test (test force 1 kgw (9.8 N)) conforming to JIS Z 2244:2020 is performed on the test surface at a position 1 / 4 of the reference plate thickness t0 from the bent outer surface of the press-formed product 10, starting from position A2 and measuring at 1.0 mm intervals until reaching the center of the width of the first plate portion 11, for example. While shifting the measurement points one by one from position A2, the average value of the Vickers hardness of each measurement point, including the measurement point and the measurement points on both sides of it, is calculated, and each calculated value is designated as H3.

[0071] H1 is substantially equal to the Vickers hardness of the blank 40 (FIG. 5A). When H1≧370, it can be determined that a steel plate having a tensile strength of 1180 MPa or more was used as the blank 40. When H1≧370, the reference plate thickness t0 and the curvature radius R, where R is the radius of curvature on the inner side of the bent portion 13, preferably satisfy R / t0≦1.5, and more preferably satisfy R / t0≦1.0. When H1≧370, it is preferable that the reference plate thickness t0 and the curvature radius R satisfy R / t0>0.3, and more preferably satisfy R / t0≧0.7. H1 may be 466 or less (H1≦466). When 370≦H1≦466, it can be determined that a steel plate having a tensile strength of 1180 MPa or more and 1470 MPa or less was used as the blank 40. If 308≦H1<370, it can be determined that a steel plate having a tensile strength of 980 MPa or more and less than 1180 MPa was used as the raw material 40. If 308≦H1<370, the reference plate thickness t0 and the radius of curvature R preferably satisfy R / t0<1.0, and more preferably R / t0≦0.7. If 308≦H1<370, the reference plate thickness t0 and the radius of curvature R may, for example, satisfy R / t0>0.1.

[0072] (effect) In this embodiment, the radius of curvature R1 of the shoulder portion 212 of the mold 21 used in the first forming step and the radius of curvature R2 of the shoulder portion 312 of the mold 31 used in the second forming step satisfy the formula (1): R2 / R1<1.0. Furthermore, the angle θ1 between the top surface 211 and the side surface 213 of the mold 21 used in the first forming step and the angle θ2 between the top surface 311 and the side surface 313 of the mold 31 used in the second forming step satisfy the formula (2): θ2 / θ1>1.0. In this embodiment, first, in the first forming step, the shoulder portion 212 of the mold 21 forms a bent portion 43 with a relatively large bend radius and a relatively small bend angle in the blank 40. In the second forming step, the shoulder portion 312 of the mold 31 forms the bent portion 43 into a bent portion 13 with a smaller bend radius and a larger bend angle. The bend radii of the bent portions 43 and 13 are both the radii of curvature of the inner surfaces of the bends. The bending radius and bending angle (inside the bend) of the bent portion 13 are substantially equal to the radius of curvature R2 and angle θ2 in the second forming step. By bending the blank 40 in two steps in this way, strain on the outer surface of the bent portion 13 can be dispersed and reduced compared to when the bent portion 13 is formed in a single bending step. As a result, cracks are less likely to occur in the bent portion 13.

[0073] In this embodiment, a raised portion 211b is provided on the top surface 211 of the mold 21 used in the first molding step. The linear length L1 of the top surface 211 of the mold 21 in the first molding step and the linear length L2 of the top surface 311 of the mold 31 in the second molding step satisfy the formula (3): 0.0 < L2 - L1 ≤ 4.0. Thereby, the strain on the outer surface of the bent portion 13 is more likely to be dispersed, and the strain can be further reduced. More specifically, by setting it as 0.0 < L2 - L1 ≤ 4.0 and making the distance from the reference point P of the material 40 to the shoulder portion 212 of the mold 21 in the first molding step different from the distance from the reference point P of the material 40 to the shoulder portion 312 of the mold 31 in the second molding step, in the material 40, the position where a large tensile strain occurs along with bending can be shifted between the first molding step and the second molding step. Therefore, in the press-formed product 10, in addition to the bent portion 13, the strain is also widely dispersed in the first plate portion 11, and the maximum value (peak) of the final tensile strain can be reduced. Therefore, when manufacturing the press-formed product 10 by performing bend forming on the material 40, the occurrence of cracks in the bent portion 13 can be more suppressed.

[0074] In this embodiment, in the first molding step, the material 40 is bent outward of the mold 21 at the boundary position between the main body portion 211a and the raised portion 211b of the top surface 211 of the mold 21. Thereby, work hardening can be caused in the portion of the material 40 that becomes the first plate portion 11 of the press-formed product 10. In this case, the initial reaction force when a load is input to the press-formed product 10 can be increased, and the yield strength of the press-formed product 10 can be improved.

[0075] In this embodiment, in the first molding step, a mold 23 is used in addition to the molds 21 and 22. The mold 23 can clamp the material 40 together with the mold 21. Since the mold 23 presses the material 40 on the top surface 211 of the mold 21, deflection of the material 40 at the position of the top surface 211 is less likely to occur in the first molding step, and work hardening of the material 40 can be more reliably caused at the boundary between the main body portion 211a and the protrusion portion 211b. Therefore, the yield strength of the press-molded product 10 can be further improved. In addition, molding can be performed using the molds 21 and 22 while the mold 23 suppresses positional deviation of the material 40.

[0076] In this embodiment, in the second molding step, a mold 33 is used in addition to the molds 31 and 32. The mold 33 can clamp the material 40 together with the mold 31. Therefore, molding can be performed using the molds 31 and 32 while suppressing misalignment of the material 40.

[0077] According to the manufacturing method of this embodiment, strain is easily dispersed on the outer surface of the bent portion 13, and therefore the maximum strain on the outer surface of the bent portion 13 can be significantly reduced compared to conventional manufacturing methods. Therefore, even if the raw material 40 is made of a high-strength steel plate of 980 MPa or more, cracking in the bent portion 13 can be suppressed when the raw material 40 is bent to form the bent portion 13.

[0078] In this embodiment, in the first plate portion 11 of the press-formed product 10, the average Vickers hardness H2 near the bent portion 13 is more than 1.1 times the average Vickers hardness H1 at a position relatively distant from the bent portion 13. That is, when the press-formed product 10 is manufactured using the manufacturing method according to this embodiment, work hardening occurs not only in the bent portion 13 but also on the outside of the bent portion 13 (the first plate portion 11 side). With such a wide work-hardened portion in the first plate portion 11, for example, in the event of a collision with the first plate portion 11, a colliding object is more likely to come into contact with the work-hardened portion, thereby increasing the initial reaction force against the collision load. Therefore, the press-formed product 10 can exhibit excellent yield strength.

[0079] In the press-formed product 10 according to this embodiment, the first plate portion 11 has a Vickers hardness average value H3 at a position further away from the bent portion 13 that is larger than the Vickers hardness average value H1 at a position relatively far from the bent portion 13. The first plate portion 11 has work-hardened portions not only near the bent portion 13 but also at positions far from the bent portion 13. This makes it easier to increase the initial reaction force when a load is input to the press-formed product 10, thereby further improving the yield strength of the press-formed product 10.

[0080] In this embodiment, when producing the press-formed product 10 with the flanges 14L, 14R shown in Fig. 2, each of the die units 20, 30 may further include a blank holder. In this case, in the first forming step, press forming using the dies 21, 22, 23 proceeds with the die 22 and the blank holder gripping the end of the material 40, and the press forming ends with the die 22 and the blank holder gripping the end of the material 40. In the second forming step, press forming using the dies 31, 32, 33 proceeds with the die 32 and the blank holder gripping the end of the material 40, and the press forming ends with the die 32 and the blank holder gripping the end of the material 40.

[0081] [Second embodiment] (press-molded products) FIG. 7 is a perspective view schematically showing a portion of a press-formed product 50 according to this embodiment. Like the press-formed product 10 according to the first embodiment, the press-formed product 50 can be used in mobile objects such as automobiles and ships. The press-formed product 50 may be used as an automobile part. However, the use of the press-formed product 50 is not limited to this.

[0082] Referring to FIG. 7 , the press-formed product 50 includes a first plate portion 51, a second plate portion 52, and a bent portion 53. The first plate portion 51 has a substantially or roughly flat plate shape. The second plate portion 52 has a cylindrical shape. In this embodiment, the second plate portion 52 has a cylindrical shape. The second plate portion 52 stands upright on one side in the plate thickness direction from the first plate portion 51. The second plate portion 52 is, for example, a burring portion provided on the press-formed product 50. The second plate portion 52 is connected to the first plate portion 51 via a bent portion 53. The bent portion 53 can have a substantially arc-shaped cross section, similar to the bent portion 13 of the first embodiment. At least the surface of the bent portion 53 on the outer side of the bend has a substantially arc-shaped cross section in a cross-sectional view of the press-formed product 50.

[0083] (Method of manufacturing press-molded products) 8 and 9 are diagrams schematically showing die units 60, 70 used in manufacturing the press-formed product 50. In Fig. 8 and Fig. 9, only one side of the central axis of a cross section including the central axis of the die units 60, 70 is shown. When the second plate portion 52 of the press-formed product 50 is cylindrical as in this embodiment (Fig. 7), the die units 60, 70 have a shape that is symmetrical (axially symmetrical) with respect to the central axis.

[0084] As shown in Fig. 8, the die unit 60 includes dies 61, 62, and 63. The dies 61, 62, and 63 are attached to, for example, a known press device. The die 61 is capable of moving toward and away from the dies 62 and 63 relatively. For example, the die 61 may be attached to a slide of the press device and configured to move together with the slide, or the dies 62 and 63 may be attached to a slide of the press device and configured to move together with the slide. The direction of relative approach (movement) between the die 61 and the dies 62 and 63 is the pressing direction D1.

[0085] The mold 61 includes a top surface 611, a shoulder portion 612, and a side surface 613. The top surface 611 includes a main body portion 611a and a raised portion 611b. The mold 62 includes a top surface 621, a shoulder portion 622, and a side surface 623. The mold 63 includes a pressing surface 631. The configurations of the molds 61, 62, and 63 in a cross-sectional view of the mold unit 60 are similar to the configurations of the molds 21, 22, and 23 of the mold unit 20 in the first embodiment ( FIG. 3 ). Therefore, in this embodiment, detailed description of the molds 61, 62, and 63 will be omitted.

[0086] As shown in Fig. 9, the die unit 70 includes dies 71, 72, and 73. The dies 71, 72, and 73 are attached to, for example, a known press device. The die 71 is capable of moving relatively close to and away from the dies 72 and 73. For example, the die 71 may be attached to a slide of the press device and configured to move together with the slide, or the dies 72 and 73 may be attached to a slide of the press device and configured to move together with the slide. The direction of relative approach (movement) between the die 71 and the dies 72 and 73 is the pressing direction D2.

[0087] The mold 71 includes a top surface 711, a shoulder portion 712, and a side surface 713. The mold 72 includes a top surface 721, a shoulder portion 722, and a side surface 723. The mold 73 includes a pressing surface 731. The configurations of the molds 71, 72, and 73 in a cross-sectional view of the mold unit 70 are similar to the configurations of the molds 31, 32, and 33 of the mold unit 30 in the first embodiment ( FIG. 4 ). Therefore, in this embodiment, detailed description of the molds 71, 72, and 73 will be omitted.

[0088] A method for manufacturing a press-formed product 50 using die units 60, 70 will be described with reference to Figures 10A to 10F. The method for manufacturing the press-formed product 50 is the same as the method for manufacturing the press-formed product 10 according to the first embodiment. As with the first embodiment, the method for manufacturing the press-formed product 50 includes a step of preparing a raw material 80, a first forming step of press-forming the raw material 80 using die unit 60, and a second forming step of press-forming the raw material 80 using die unit 70 after the first forming step.

[0089] Referring to FIG. 10A, in the preparation step, a raw material 80 made of a metal plate is prepared. In this embodiment, the raw material 80 is prepared having a through hole 81 formed therein. The through hole 81 has a shape corresponding to the second plate portion 52 (FIG. 7) of the press-molded product 50 to be manufactured. In this embodiment, the through hole 81 has a circular shape in a plan view. The metal plate constituting the raw material 80 may be a steel plate. The preferred tensile strength and plate thickness of the raw material 80 are the same as those of the raw material 40 described in the first embodiment.

[0090] 10B , in the first molding step, first, the material 80 is placed between the molds 61 and 62 so that the material 80 faces the top surface 611 of the mold 61 and the top surface 621 of the mold 62. The material 80 is placed on the top surface 611 of the mold 61 so that the outer periphery of the through hole 81 in the material 80 faces the top surface 621 of the mold 62.

[0091] 10C , in the first molding step, the dies 62 and 63 are brought relatively close to the die 61. The die 62 presses a portion of the material 80 facing the top surface 621 of the die 62 toward the die 61 relative to a portion facing the top surface 611 of the die 61, and sandwiches the material 80 between the side surface 613 of the die 61 and the side surface 623 of the die 62, thereby molding the material 80 with the top surface 611, shoulder portion 612, and side surface 613 of the die 61. The die 63 sandwiches the material 80 together with the top surface 611 of the die 61. More specifically, the portion of the material 80 facing the top surface 611 of the die 61 is pressed by the pressing surface 631 of the die 63. The pressing surface 631 of the die 63 may come into contact with the material 80 before the die 62 does.

[0092] 10D, the material 80 after the first forming step includes a first plate portion 82, a second plate portion 83, and a bent portion 84. The first plate portion 82 is a portion formed by the top surface 611 of the mold 61 in the first forming step. The bent portion 84 is a portion formed by the shoulder portion 612 of the mold 61 in the first forming step. The second plate portion 83 is a portion formed by the side surface 613 of the mold 61 in the first forming step, with the outer periphery of the through hole 81 (FIGS. 10A and 10B) being raised. The second plate portion 83 is connected to the first plate portion 82 via the bent portion 84.

[0093] After the first molding step, the blank 80 is subjected to the second molding step. Referring to FIG. 10E , in the second molding step, a mold unit 70 including molds 71, 72, and 73 is used. In the second molding step, the blank 80 is placed between the molds 71 ​​and 72 so that the first plate portion 82 faces the top surface 711 of the mold 71 and the second plate portion 83 is located on the side surface 713 of the mold 71. The blank 80 is placed, for example, on the top surface 711 of the mold 71. At this time, the first plate portion 82 of the blank 80 is located between the top surface 711 of the mold 71 and the pressing surface 731 of the mold 73. The bent portion 84 of the blank 80 is located near the shoulder portion 712 of the mold 71. The second plate portion 83 of the blank 80 is located so that at least a portion of it corresponds to the side surface 713 of the mold 71.

[0094] 10E and 10F , in the second forming step, the dies 72 and 73 are brought relatively close to the die 71. The die 72 forms the material 80 along the top surface 711, shoulder portion 712, and side surface 713 of the die 71, and the material 80 is sandwiched between the side surface 713 of the die 71 and the side surface 723 of the die 72. In the second forming step, the die 73 sandwiches the material 80 together with the top surface 711 of the die 71. More specifically, the first plate portion 82 of the material 80 is pressed by the pressing surface 731 of the die 73. As a result, the first plate portion 82 of the material 80 is formed into a shape that follows the top surface 711 of the die 71. The pressing surface 731 of the die 73 may come into contact with the material 80 before the die 72 does.

[0095] After the die 73 presses the material 80 on the die 71, the die 72 moves toward the die 71 relative to the die 73, whereby the bent portion 84 of the material 80 is deformed into a shape that follows the shoulder portion 212 of the die 71. The material 80 is finally held between the side surface 713 of the die 71 and the side surface 723 of the die 72, and is formed into a shape that follows the top surface 711, shoulder portion 712, and side surface 713 of the die 71. In this way, the press-formed product 50 is produced from the material 80.

[0096] As in the first embodiment, when a reference point P is set on a portion of the raw material 80 that is to be molded by the top surface 611 of the mold 61, in a cross section of the mold 61 that includes the reference point P, the shoulder 612 has a radius of curvature R1 [mm], and the protrusion 611b of the top surface 611 and the side surface 613 form an angle θ1 [°] ( FIG. 10C ). Also, in this cross section, the top surface 611 has a line length L1 ( FIG. 10C ). In a cross section of the mold 71 that includes the reference point P, the shoulder 712 has a radius of curvature R2 [mm], and the top surface 711 and the side surface 713 form an angle θ2 [°] ( FIG. 10F ). Also, in this cross section, the top surface 711 has a line length L2 ( FIG. 10F ). The definitions of the radii of curvature R1 and R2, the angles θ1 and θ2, and the line lengths L1 and L2 are the same as those described in the first embodiment. The radii of curvature R1, R2, angles θ1, θ2, and line lengths L1, L2 satisfy the following formulas (1) to (3), similarly to the first embodiment. Therefore, the method for manufacturing the press-formed product 50 according to this embodiment can also achieve the same effects as the first embodiment. R2 / R1<1.0 (1) θ2 / θ1>1.0 (2) 0.0 <L2-L1≦4.0 (3)

[0097] In this embodiment, the thickness t of the blank 80 and the radius of curvature R2 of the shoulder portion 712 of the die 71 can have the same relationship as the thickness t of the blank 40 and the radius of curvature R2 of the shoulder portion 312 of the die 31 in the first embodiment. That is, when the tensile strength of the blank 80 is 1180 MPa or more, the thickness t and the radius of curvature R2 preferably satisfy R2 / t≦1.5, and more preferably satisfy R2 / t≦1.0. When the tensile strength of the blank 80 is 1180 MPa or more, the thickness t and the radius of curvature R2 preferably satisfy R2 / t>0.3, and more preferably satisfy R2 / t≧0.7. The tensile strength of the blank 80 may be 1470 MPa or less. When the tensile strength of the blank 80 is 980 MPa or more but less than 1180 MPa, the thickness t and the radius of curvature R2 preferably satisfy R2 / t<1.0, and more preferably satisfy R2 / t≦0.7. When the tensile strength of the raw material 80 is equal to or greater than 980 MPa and less than 1180 MPa, the thickness t and the radius of curvature R2 may be, for example, R2 / t>0.1.

[0098] Fig. 11 is a cross-sectional view of a press-formed product 50 obtained by the manufacturing method according to this embodiment. Fig. 11 partially shows a cross section of the press-formed product 50 along the plate thickness direction. A bent portion 53 is formed in the press-formed product 50 by two-stage bending using a shoulder portion 612 of a die 61 in a first forming step and a shoulder portion 712 of a die 71 in a second forming step. On both sides of the bent portion 53, a first plate portion 51 formed mainly by the top surfaces 611, 711 of the dies 61, 71, and a second plate portion 52 formed mainly by the side surfaces 613, 713 of the dies 61, 71 are arranged.

[0099] In this embodiment, the ratio H2 / H1 of the average Vickers hardness H1 [HV] measured at 0.5 mm intervals from position A1 to position A2 to the average Vickers hardness H2 [HV] measured at 0.5 mm intervals from position A0 to position A1 is greater than 1.1. Furthermore, when the Vickers hardness is measured at 1.0 mm intervals beyond position A2 and the average Vickers hardness of three adjacent measurement points is taken as H3, there is preferably an H3 such that H3 / H1 > 1.1. Therefore, the press-formed product 50 according to this embodiment can achieve the same effects as the first embodiment. The definitions of positions A0, A1, and A2 and the reference plate thickness t0, as well as the method for obtaining (measuring) H1, H2, and H3, are the same as those described in the first embodiment.

[0100] In this embodiment, the reference plate thickness t0 of the press-formed product 50 and the curvature radius R of the bent portion 53 on the inner side of the bend can have the same relationship as the reference plate thickness t0 and the curvature radius R of the bent portion 13 on the inner side of the bend in the first embodiment. That is, when H1≧370, it can be determined that a steel plate having a tensile strength of 1180 MPa or more was used as the raw material 80. When 308≦H1<370, it can be determined that a steel plate having a tensile strength of 980 MPa or more but less than 1180 MPa was used as the raw material 80. When H1≧370, the reference plate thickness t0 and the curvature radius R preferably satisfy R / t0≦1.5, and more preferably R / t0≦1.0. When H1≧370, the reference plate thickness t0 and the curvature radius R preferably satisfy R / t0>0.3, and more preferably R / t0≧0.7. H1 may be 466 or less (H1≦466). If 370≦H1≦466, it can be determined that a steel plate having a tensile strength of 1180 MPa or more and 1470 MPa or less was used as the raw material 80. If 308≦H1<370, the reference plate thickness t0 and the radius of curvature R preferably satisfy R / t0<1.0, and more preferably R / t0≦0.7. If 308≦H1<370, the reference plate thickness t0 and the radius of curvature R may, for example, satisfy R / t0>0.1.

[0101] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

[0102] In the first embodiment, when the first molding step is completed, the raw material 40 is sandwiched between the side surface 213 of the mold 21 and the side surface 223 of the mold 22. However, the side surface 223 of the mold 22 may be configured to sandwich the raw material 40 together with the shoulder portion 212 and the side surface 213 of the mold 21. Similarly, in the second embodiment, the side surface 623 of the mold 62 may be configured to sandwich the raw material 80 together with the shoulder portion 612 and the side surface 613 of the mold 61 when the first molding step is completed. In this case, the widths of the molds 23 and 63 can be reduced so that the molds 22 and 62 do not interfere with the molds 23 and 63, respectively.

[0103] In the first embodiment described above, when the second molding step is completed, the raw material 40 is sandwiched between the side surface 313 of the mold 31 and the side surface 323 of the mold 32. However, the side surface 323 of the mold 32 may be configured to sandwich the raw material 40 together with the shoulder portion 312 and the side surface 313 of the mold 31. Similarly, in the second embodiment described above, the side surface 723 of the mold 72 may be configured to sandwich the raw material 80 together with the shoulder portion 712 and the side surface 713 of the mold 71 when the second molding step is completed. In this case, the widths of the molds 33 and 73 can be reduced so that the molds 32 and 72 do not interfere with the molds 33 and 73, respectively.

[0104] In the above-described embodiments, in the first molding step, the mold 23 or the mold 63 is used in addition to the molds 21 and 22 or the molds 61 and 62. However, the mold 23 or the mold 63 does not necessarily have to be used in the first molding step. For example, in the above-described embodiments, the mold 22 or the mold 62 may be extended, and the material 40 or the material 80 may be held by the mold 22 or the mold 62 instead of the mold 23 or the mold 63.

[0105] In the above-described embodiments, in the second molding step, in addition to the molds 31 and 32 or the molds 71 ​​and 72, the mold 33 or the mold 73 is used. However, the mold 33 or the mold 73 does not necessarily have to be used in the second molding step. For example, in the above-described embodiments, the mold 32 or the mold 72 may be extended, and the material 40 or the material 80 may be held by the mold 32 or the mold 72 instead of the mold 33 or the mold 73. [Example]

[0106] The present disclosure will be described in more detail below with reference to examples, although the present disclosure is not limited to the following examples.

[0107] [First Example] In order to confirm the effects of the manufacturing method according to the present disclosure, a press-forming analysis was performed using commercially available analysis software (Abaqus / Standard, manufactured by Dassault Systèmes) to form a bent portion 13 between the first plate portion 11 and the second plate portion 12 as in the first embodiment. In this analysis, strain along the circumferential direction on the outer surface of the bent portion 13 was evaluated for a case in which press-forming was performed in the same manner as in the first embodiment with R2 / R1<1.0, θ2 / θ1>1.0, and L2-L1=3.0 (Example 1), and a case in which press-forming was performed with R2 / R1<1.0, θ2 / θ1=1.0, and L2-L1=0.0 (Comparative Example 1-1). In Example 1, the bending radius (radius of curvature R1 of shoulder portion 212 of mold 21) in the first molding step was 3.0 mm, and the bending angle (angle θ1 between top surface 211 and side surface 213) was 60°. In the second molding step, the bending radius (radius of curvature R2 of shoulder portion 312 of mold 31) was 1.0 mm, and the bending angle (angle θ2 between top surface 311 and side surface 313) was 90°. In Comparative Example 1-1, the bending radius in the first molding step was 3.0 mm, the bending radius in the second molding step was 1.0 mm, and the bending angles in both the first and second molding steps were 90°. In Example 1, a raised portion 211b was present on top surface 211 of mold 21 in the first molding step, whereas in Comparative Example 1-1, no raised portion 211b was provided on top surface 211 of mold 21 in the first molding step. In addition, press forming analysis was also performed for the case where a bent portion 13 with a bend radius of 1.0 mm and a bend angle of 90° was formed in a single bending process (Comparative Example 1-2). In all of Example 1, Comparative Example 1-1, and Comparative Example 1-2, the material for press forming was a steel plate with a plate thickness of 2.9 mm and a tensile strength of 980 MPa.

[0108] FIG. 12 is a graph showing the distribution of circumferential strain on the outer surface of the bent portion 13 of Example 1, Comparative Example 1-1, and Comparative Example 1-2. The horizontal axis of FIG. 12 represents the distance along the outer surface of the bent portion 13 from the end of the R on the first plate portion 11 side of the bent portion 13. FIG. 12 shows that the maximum value of circumferential strain in Comparative Example 1-1 is reduced compared to Comparative Example 1-2. In Example 1, the circumferential strain is more dispersed than in Comparative Example 1-1, resulting in a further reduction in the maximum value of circumferential strain.

[0109] Therefore, according to the manufacturing method of the present disclosure, it is possible to reduce distortion on the outer surface of the bent portion 13, and to suppress cracking of the bent portion 13.

[0110] FIG. 13 is a graph showing the distribution of Vickers hardness of the first plate portion 11 and the bent portion 13 for the press-formed products formed in Example 1 and Comparative Examples 1-2. The horizontal axis of FIG. 13 is the distance along the outer surface of the bent portion from the boundary 15 between the first plate portion 11 and the bent portion 13 / reference plate thickness t0. The distance from the boundary 15 (the end of the bent portion 13) is set to 0 at the position of the boundary 15, negative on the first plate portion 11 side, and positive on the bent portion 13 side. The vertical axis of FIG. 13 is Vickers hardness, which is the ratio to the average value H1 [HV] of Vickers hardness measured at 0.5 mm intervals from position A1 (FIG. 6) to position A2 (FIG. 6) on the first plate portion 11. H1 is substantially equal to the Vickers hardness (base material hardness) of the steel plate used as the blank 40 for press forming.

[0111] 13, in Example 1, the Vickers hardness of the first plate portion 11 from position A0, which is 1.0 times the standard plate thickness t0, away from the boundary 15 between the first plate portion 11 and the bent portion 13, to position A1, which is 3.0 times the standard plate thickness t0, greatly exceeded 1.1 times H1. Therefore, in Example 1, the average value H2 of the Vickers hardness measured at 0.5 mm intervals from position A0 to position A1 satisfied H2 / H1 > 1.1. On the other hand, in Comparative Example 1-2, the Vickers hardness was equivalent to H1 over most of the range from position A0 to position A1 in the first plate portion 11, and H2 / H1 did not exceed 1.1.

[0112] In Example 1, there was a region in the first plate portion 11 where the Vickers hardness exceeded 1.1 times H1 even beyond position A2, which was 4.0 times the reference plate thickness t0 from the boundary 15. That is, in Example 1, when the Vickers hardness was measured at 1.0 mm intervals beyond position A2, there was an H3, which was the average value of the Vickers hardness at three consecutive points and satisfied H3 / H1>1.1. On the other hand, in Comparative Example 1-2, the Vickers hardness of the first plate portion 11 beyond position A2 was equivalent to H1, and there was no H3 that satisfied H3 / H1>1.1.

[0113] Therefore, when a press-formed product is manufactured using the manufacturing method according to the present disclosure, work hardening can be widely induced in the first plate portion 11. This makes it possible to reduce the likelihood of fracture of the press-formed product, even when the press-formed product is used in an automobile or the like and is subjected to an impact due to an automobile collision or the like. Specifically, as shown in FIGS. 12 and 13 , even when the curvature radius of the inner side of the bend of the bent portion 13 is the same, in Comparative Example 1-2, strain (work hardening) is concentrated in the bent portion 13 and the strain peak is large, whereas in Example 1, strain (work hardening) is widely dispersed around the bent portion 13 and the strain peak is reduced. As the strain is widely dispersed, the strain of the press-formed product is reduced relative to the critical strain at which fracture occurs. Therefore, even when a larger strain occurs during a collision, fracture of the press-formed product is less likely to occur. As a result, the press-formed product is more likely to absorb a large amount of energy when subjected to an impact.

[0114] [Second Example] To verify the influence of the line length L1 of the top surface 211 of the die 21 in the first molding step and the line length L2 of the top surface 311 of the die 31 in the second molding step, a press molding analysis similar to that in Example 1 was performed while changing L2-L1. The analysis conditions other than L2-L1 were the same as in Example 1. Figure 14 shows the results of this analysis.

[0115] FIG. 14 is a graph showing the relationship between L2 - L1 and the circumferential strain on the outer side of the bent portion 13 in bending. In FIG. 14, the vertical axis represents the strain ratio (the ratio to the maximum value of the circumferential strain when L2 - L1 = 0.0). Also, in FIG. 14, the conditions when cracks actually occurred in the bent portion 13 in the actually performed press forming (bending forming) experiment were reproduced by analysis, and the maximum value of the obtained circumferential strain (however, the ratio to the maximum value of the circumferential strain when L2 - L1 = 0.0) is shown by a broken line. If the strain ratio is above the threshold value shown by the broken line, there is a high possibility that cracks will occur in the bent portion 13. As shown in FIG. 14, when L2 - L1 = 0.0, since the strain ratio exceeds the threshold value, it can be said that there is a high possibility that cracks will occur in the bent portion 13. Also, when L2 - L1 > 4.0, since the strain ratio exceeds the threshold value, there is a high possibility that cracks will occur in the bent portion 13. On the other hand, if 0.0 < L2 - L1 ≤ 4.0, the strain ratio becomes smaller than the threshold value, and cracks are unlikely to occur in the bent portion 13. When 1.0 ≤ L2 - L1 ≤ 4.0, the occurrence of cracks in the bent portion 13 is more reliably suppressed.

[0116] [Third Embodiment] Regarding the press forming (flange up forming) in which the second plate portion 52 is raised with respect to the first plate portion 51 as in the second embodiment to form a bent portion 53 between the first plate portion 51 and the second plate portion 52, press forming analysis was carried out in the same manner as in the first embodiment. In this analysis, the radius of curvature R1 of the shoulder portion 612 of the mold 61 in the first forming step was 4.0 mm, the angle θ1 between the top surface 611 and the side surface 613 was 80°, the radius of curvature R2 of the shoulder portion 712 of the mold 71 in the second forming step was 1.0 mm, and the angle θ2 between the top surface 711 and the side surface 713 was 90° (Example 3). Other conditions of the analysis were the same as those in the first embodiment. For comparison, press forming analysis was also carried out for the case of forming a bent portion 53 with a bending radius of 1.0 mm and a bending angle of 90° in a single bending forming step (Comparative Example 3). FIG. 15 shows the results of this analysis.

[0117] Fig. 15 is a graph showing the distribution of circumferential strain on the outer surface of the bent portion 53 in Example 3 and Comparative Example 3. The horizontal axis in Fig. 15 represents the distance along the outer surface of the bent portion 53 from the end of the R on the first plate portion 51 side of the bent portion 53. As can be seen from Fig. 15, in Example 3, the circumferential strain was clearly more dispersed and the maximum value of the circumferential strain was significantly reduced compared to Comparative Example 3, in which bending was performed in a single stage. Therefore, it was confirmed that the manufacturing method according to the present disclosure reduces strain on the outer surface of the bent portion 53 even in flange-up forming.

[0118] [Fourth Example] To confirm the effect of R / t on cracking during forming, a test was conducted in which a bent portion 13 was formed between the first plate portion 11 and the second plate portion 12 as in the first embodiment. In this test, as an example, a bent portion 13 was formed between the first plate portion 11 and the second plate portion 12 using the same method as in the first embodiment, and then the outer surface of the bent portion 13 was observed with a microscope (magnification: 25x) to determine whether or not cracking occurred. For the example, the bending radius (curvature radius R1 of the shoulder portion 212 of the mold 21) in the first forming step was 5.0 mm, the bending angle (angle θ1 between the top surface 211 and the side surface 213) was 70°, and the bending angle (angle θ2 between the top surface 311 and the side surface 313) in the second forming step was 90°. Furthermore, L2-L1 = 3.8 mm. As a comparative example, after forming the bent portion 13 in a single bending process, the outer surface of the bent portion 13 was similarly observed with a microscope (magnification: 25x) to determine whether or not cracks were present. In both the example and the comparative example, the material for press forming was a steel plate with a plate thickness t = 2.9 mm.

[0119] Other conditions and results of this test are shown in Table 1. In Table 1, R is the radius of curvature on the inside of the bent portion 13 after forming, and is substantially the same as the radius of curvature R2 of the shoulder portion 212 of the mold 21 in the second forming step.

[0120] [Table 1]

[0121] As shown in Table 1, when the tensile strength of the raw material was 980 MPa, cracks occurred in the bent portion 13 in the comparative example when R / t was less than 1.0. On the other hand, when the tensile strength of the raw material was 980 MPa, cracks did not occur in the bent portion 13 in the examples even when R / t was less than 1.0. In the examples, cracks did not occur in the bent portion 13 even when R / t was 0.7 and 0.3. Therefore, with the manufacturing method of a press-formed product according to the present disclosure, it is possible to form the bent portion 13 without cracks even when the raw material is a high-strength steel plate with a tensile strength of 980 MPa or more and R / t is a relatively small value of less than 1.0.

[0122] As shown in Table 1, when the tensile strength of the raw material was 1180 MPa, cracks occurred in the bent portion 13 in the comparative example when R / t was 1.5 or less. On the other hand, when the tensile strength of the raw material was 1180 MPa, cracks did not occur in the bent portion 13 in the examples even when R / t was 1.5 or less. In the examples, cracks did not occur in the bent portion 13 even when R / t was 1.0 or less. Therefore, with the manufacturing method of a press-formed product according to the present disclosure, it is possible to form the bent portion 13 without cracks even when the raw material is a high-strength steel plate with a tensile strength of 1180 MPa or more and has a relatively small R / t of 1.5 or less.

[0123] As described above, in the example, it is possible to form a bent portion 13 with a smaller bending radius (radius of curvature on the inside of the bend) without cracking compared to the comparative example. When the bending radius of the bent portion 13 is small, the distance between the R end on the first plate portion 11 side of the bent portion and the second plate portion 12 is shortened, so that when the press-formed product receives an impact, the load is more easily transmitted to the second plate portion 12, improving the load transmission efficiency of the press-formed product. Therefore, the load (reaction force) of the press-formed product tends to be higher, and the amount of energy absorption can also be increased. [Explanation of symbols]

[0124] 10,50: Press-molded products 11,51: 1st plate part 12, 12L, 12R, 52: Second plate section 13, 13L, 13R, 53: Bent section 15: Boundary 21,61: Gold type (1st gold type) 211,611: Top surface (first top surface) 211a, 611a: Ontology 211b, 211Lb, 211Rb, 611b: Elevated portion 212, 212L, 212R, 612: Shoulder (First Shoulder) 213, 213L, 213R, 613: Side view (first side view) 22, 22L, 22R, 62: Gold type (2nd gold type) 221,621: Top surface (second top surface) 222,622: Shoulder (Second Shoulder) 223,623: Side view (second side view) 23,63: Gold type (5th gold type) 31,71: Gold type (3rd gold type) 311,711: Top surface (3rd top surface) 312, 312L, 312R, 712: Shoulder (3rd shoulder) 313, 313L, 313R, 713: Side view (3rd side view) 32, 32L, 32R, 72: Gold type (4th gold type) 321,721: Top surface (4th top surface) 322, 722: Shoulder (4th shoulder) 323,723: Side view (4th side view) 33,73: Gold type (6th gold type) 40,80: Material

Claims

1. A method for manufacturing a press-molded product, a preparation step of preparing a material made of a metal plate; a first molding step of molding the material using a first mold including a first top surface and a first side surface connected to the first top surface via a first shoulder portion, and a second mold including a second top surface and a second side surface connected to the second top surface via a second shoulder portion; a second molding step of molding the material using a third mold including a third top surface and a third side surface connected to the third top surface via a third shoulder portion, and a fourth mold including a fourth top surface and a fourth side surface connected to the fourth top surface via a fourth shoulder portion, after the first molding step; Equipped with The metal plate is a steel plate having a tensile strength of 980 MPa or more, In the first molding step, the material is placed between the first mold and the second mold so that the material faces the first top surface and the second top surface, and the second mold moves relatively to the first mold to press the portion of the material facing the second top surface toward the first mold with respect to the portion facing the first top surface, and to sandwich the material between the first side surface and the second side surface, thereby molding the material with the first top surface, the first shoulder portion, and the first side surface; In the second molding step, the material is placed between the third mold and the fourth mold so that a portion of the material formed by the first top surface faces the third top surface and a portion of the material formed by the first side surface faces the third side surface, and the material is molded along the third top surface, the third shoulder portion, and the third side surface by the fourth mold that moves relatively to the third mold; the first top surface includes a main body portion and a protruding portion that connects the main body portion and the first shoulder portion and protrudes from the main body portion such that a side of the first shoulder portion is spaced apart from the main body portion in a relative movement direction of the second mold with respect to the first mold, a manufacturing method in which, in the first molding step, when the first mold is viewed at a cross section including a reference point set on a portion of the material to be molded by the first top surface, the radius of curvature of the first shoulder is R1 [mm], the angle between the first side surface and the protruding portion is θ1 [°], and the line length of the first top surface from the reference point to the first shoulder is L1 [mm]; and in the second molding step, when the third mold is viewed at a cross section including the reference point, the radius of curvature of the third shoulder is R2 [mm], the angle between the third side surface and the third top surface is θ2 [°], and the line length of the third top surface from the reference point to the third shoulder is L2 [mm], the following relationships are satisfied: R2 / R1<1.0, θ2 / θ1>1.0, and 0.0<L2-L1≦4.

0.

2. The method of claim 1, A manufacturing method in which a fifth mold is used in addition to the first mold and the second mold in the first molding step, and the fifth mold clamps the material together with the first top surface.

3. The method of claim 1, A manufacturing method in which a sixth mold is used in addition to the third mold and the fourth mold in the second molding step, and the sixth mold clamps the material together with the third top surface.

4. A press-molded product, A first plate portion; a bent portion continuous with the first plate portion; a second plate portion connected to the first plate portion via the bent portion; Equipped with When the plate thickness of the first plate portion at a position 10.0 mm away from the boundary between the first plate portion and the bent portion is taken as the reference plate thickness, the ratio H2 / H1 of the average Vickers hardness H1 measured at 0.5 mm intervals in the first plate portion from a position 3.0 times the reference plate thickness from the boundary to a position 4.0 times the reference plate thickness from the boundary to the average Vickers hardness H2 measured at 0.5 mm intervals from a position 1.0 times the reference plate thickness from the boundary to a position 3.0 times the reference plate thickness from the boundary is greater than 1.

1. A press-molded product.

5. The press-molded product according to claim 4, When the Vickers hardness is measured at 1.0 mm intervals at a position in the first plate portion that is 4.0 times the reference plate thickness from the boundary, and the average value of the Vickers hardnesses of three adjacent measurement points is defined as H3, there exists H3 that satisfies H3 / H1>1.

1. A press-molded product.

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