Method for manufacturing press-molded article

Abstract

This method for manufacturing a press-molded article (10) comprises: a preparation step for preparing a patchwork blank (20); and a molding step for obtaining the press-molded article (10) by cold-pressing the patchwork blank (20) using molds (30, 30A, 30B, 30C). A welded part (23) of the patchwork blank (20) is disposed on vertical walls (12, 13) of the press-molded article (10). In the molding step, dies (32, 32B) are pressed against the patchwork blank (20) by bending position adjustment means of the molds (30, 30A, 30B, 30C) so as to suppress bending of the patchwork blank (20) at the position of the welded part (23).

Description

Method for manufacturing a press-formed product

[0001] The present disclosure relates to a method for manufacturing a press-formed product.

[0002] For example, press-formed products are used in vehicle bodies such as automobiles. Press-formed products are manufactured by subjecting a blank to press working using a punch and a die. Conventionally, various techniques have been proposed regarding methods for manufacturing press-formed products.

[0003] For example, Patent Document 1 discloses a technique for manufacturing a press-formed product provided with a shape-changing portion at a ridge line portion between a top plate and a vertical wall. In Patent Document 1, the press-formed product is manufactured through a first press working step and a second press working step. In the first press working step, the top plate, the ridge line portion, and a part of the vertical wall are formed by subjecting the blank to press working using a first punch, a first die, and a first pad. In the second press working step, the remaining portion of the vertical wall and the flange are sequentially formed by a main and sub second punch, a second die, and a second pad. According to Patent Document 1, in the first press working step, the blank is not restrained by the first pad and the first punch until the bottom dead center of the pushing-in of the first punch with respect to the first die and the first pad, so that tensile bending deformation at the shape-changing portion is alleviated. Further, according to Patent Document 1, in the second press working step, since the flange is formed last, warping of the vertical wall caused by springback can be reduced.

[0004] Patent Document 2 discloses a technique for manufacturing a press-formed product from an intermediate material having a pair of bent portions by using a die and a punch provided with an inner pad. In Patent Document, with the inner pad protruding from the punch toward the die side, a portion between the pair of bent portions of the intermediate material is disposed on the inner pad. Then, after forming the vertical wall of the press-formed product by the punch and the die, the inner pad is pushed into the punch side to form the top plate of the press-formed product. According to Patent Document 2, by forming the press-formed product using a pre-processed intermediate material, generation of a moment in the top plate is suppressed, and springback of the press-formed product can be suppressed.

[0005] Patent Document 3 discloses a technique for manufacturing a press-formed product having a flange that curves along the longitudinal direction of the vertical wall, using an upper punch, a lower punch, and a die. The upper punch is provided so as to be able to move toward and away from the lower punch in the height direction. In Patent Document 3, the top plate and a part of the vertical wall of the press-formed product are formed by the upper punch and die with a predetermined punch gap between the upper punch and the lower punch (first bottom dead center), and then the die is moved toward the lower punch side, and the remaining part of the vertical wall and the flange are formed without a punch gap (second bottom dead center). According to Patent Document 3, residual stress is reduced as the strain of the flange is released during the process from the first bottom dead center to the second bottom dead center. Furthermore, according to Patent Document 3, the amount of strain release can be controlled by adjusting the punch gap between the upper punch and the lower punch, and springback can be prevented.

[0006] Patent Document 4 discloses a technology for manufacturing press-formed products by hot press working. In Patent Document 4, the blank is pressed against the top surface of the punch by a pad and against the side surface of the punch by a die that moves by a cam mechanism. According to Patent Document 4, errors in the thickness of the blank are absorbed by the movement of the pad and die, so even if there is variation in the thickness of the blank within the dimensional tolerance, the blank can be held tightly between the punch, pad and die without any gaps. As a result, molding defects and insufficient cooling do not occur, and the press-formed product can be hardened at a sufficient cooling rate.

[0007] International Publication No. 2016 / 051765, Japanese Patent Publication No. 2018-202440, Japanese Patent Publication No. 2019-72727, Japanese Patent Publication No. 2017-100183

[0008] Press-formed products are sometimes formed using patchwork blanks. A patchwork blank includes a blank body and reinforcing materials. In a patchwork blank, the reinforcing materials are superimposed on the blank body and joined to the blank body by welding. By performing molding using such a patchwork blank, the number of molds can be reduced compared to joining the blank body and reinforcing materials after each has been formed into a predetermined shape, thereby reducing the manufacturing cost of press-formed products.

[0009] Patchwork blanks have traditionally been used primarily for manufacturing press-formed products by hot stamping. However, cold stamping patchwork blanks is difficult. This is because when cold stamping patchwork blanks is used to manufacture press-formed products, cracks may occur at the welded joints.

[0010] The object of this disclosure is to provide a method for manufacturing press-formed products that can suppress cracking at the welded joints during cold pressing of patchwork blanks.

[0011] The method for manufacturing a press-formed product according to this disclosure comprises a preparation step of preparing a patchwork blank and a forming step of obtaining a press-formed product by cold pressing the patchwork blank using a die. The patchwork blank includes a blank body and reinforcing members. The reinforcing members are superimposed on the blank body and joined to the blank body by welding. The press-formed product includes a top plate, vertical walls, and flanges. The vertical walls are continuous with the top plate. The welded parts of the patchwork blank are located on the vertical walls. The flanges are continuous with the vertical walls on the opposite side of the top plate. The die includes a punch and a die. The punch includes a punch top surface, a punch side surface, and a punch flange surface. The punch top surface corresponds to the top plate of the press-formed product. The punch side surface is connected to the punch top surface via the punch shoulder. The punch side surface corresponds to the vertical walls of the press-formed product. The punch flange surface corresponds to the flanges of the press-formed product. The die includes a die side surface and a die flange surface. The die side surface corresponds to the punch side surface. The die flange surface is connected to the die side via the die shoulder. The die flange surface corresponds to the punch flange surface. In the forming process, the die is pressed against the patchwork blank using bending position adjustment means of the mold to suppress bending of the patchwork blank at the weld position.

[0012] According to the method for manufacturing press-formed products described herein, cracking at the welded joint can be suppressed during cold pressing of a patchwork blank.

[0013] Figure 1 is a perspective view of a press-formed product manufactured by the manufacturing method according to the first embodiment. Figure 2 is a cross-sectional view taken along line II-II of the press-formed product shown in Figure 1. Figure 3A is a schematic diagram illustrating the manufacturing method of a press-formed product according to the first embodiment. Figure 3B is a schematic diagram illustrating the manufacturing method of a press-formed product according to the first embodiment. Figure 3C is a schematic diagram illustrating the manufacturing method of a press-formed product according to the first embodiment. Figure 3D is a schematic diagram illustrating the manufacturing method of a press-formed product according to the first embodiment. Figure 3E is a schematic diagram illustrating the manufacturing method of a press-formed product according to the first embodiment. Figure 4 is a schematic diagram illustrating the mechanism by which the effects of the manufacturing method according to the first embodiment occur. Figure 5 is a schematic diagram illustrating the relationship between the mold and the patchwork blank in the manufacturing method according to the first embodiment. Figure 6A is a schematic diagram illustrating the manufacturing method of a press-formed product according to the second embodiment. Figure 6B is a schematic diagram illustrating the manufacturing method of a press-formed product according to the second embodiment. Figure 6C is a schematic diagram illustrating the manufacturing method of a press-formed product according to the second embodiment. Figure 6D is a schematic diagram illustrating the manufacturing method of a press-formed product according to the second embodiment. Figure 7 is a schematic diagram illustrating the relationship between the mold and the patchwork blank in the manufacturing method according to the second embodiment. Figure 8A is a schematic diagram illustrating the manufacturing method of a press-formed product according to the third embodiment. Figure 8B is a schematic diagram illustrating the manufacturing method of a press-formed product according to the third embodiment. Figure 8C is a schematic diagram illustrating the manufacturing method of a press-formed product according to the third embodiment. Figure 8D is a schematic diagram illustrating the manufacturing method of a press-formed product according to the third embodiment. Figure 9A is a schematic diagram illustrating the configuration of the mold used in the manufacturing method of a press-formed product according to the fourth embodiment. Figure 9B is a schematic diagram illustrating the configuration of the mold used in the manufacturing method of a press-formed product according to the fourth embodiment. Figure 10A is a schematic diagram illustrating the manufacturing method of a press-formed product according to the fourth embodiment. Figure 10B is a schematic diagram illustrating the manufacturing method of a press-formed product according to the fourth embodiment. Figure 10C is a schematic diagram illustrating the manufacturing method of a press-formed product according to the fourth embodiment.Figure 10D is a schematic diagram illustrating the manufacturing method of a press-formed product according to the fourth embodiment. Figure 10E is a schematic diagram illustrating the manufacturing method of a press-formed product according to the fourth embodiment. Figure 11 is a schematic diagram illustrating the configuration of a mold in a modified example of the first embodiment. Figure 12 is a schematic diagram illustrating the configuration of a mold in a modified example of the second embodiment. Figure 13 is a schematic diagram illustrating the configuration of a mold in a modified example of the second embodiment. Figure 14 is a schematic diagram illustrating the conditions of the patchwork blank, press-formed product, and mold in the first embodiment. Figure 15 is a schematic diagram illustrating the conditions of the patchwork blank and mold in the second embodiment.

[0014] A method for manufacturing a press-formed product according to an embodiment comprises a preparation step of preparing a patchwork blank and a forming step of obtaining a press-formed product by cold pressing the patchwork blank using a die. The patchwork blank includes a blank body and reinforcing members. The reinforcing members are superimposed on the blank body and joined to the blank body by welding. The press-formed product includes a top plate, vertical walls, and flanges. The vertical walls are continuous with the top plate. The welded parts of the patchwork blank are located on the vertical walls. The flanges are continuous with the vertical walls on the opposite side of the top plate. The die includes a punch and a die. The punch includes a punch top surface, a punch side surface, and a punch flange surface. The punch top surface corresponds to the top plate of the press-formed product. The punch side surface is connected to the punch top surface via the punch shoulder. The punch side surface corresponds to the vertical walls of the press-formed product. The punch flange surface corresponds to the flanges of the press-formed product. The die includes a die side surface and a die flange surface. The die side surface corresponds to the punch side surface. The die flange surface is connected to the die side surface via the die shoulder. The die flange surface corresponds to the punch flange surface. In the forming process, the die is pressed against the patchwork blank using bending position adjustment means of the mold to suppress bending of the patchwork blank at the weld position (first configuration).

[0015] When manufacturing press-formed products from patchwork blanks by cold pressing, the punch and die are brought relatively close together, and the patchwork blank is sandwiched between the punch and die to form the top plate, vertical walls, and flanges. At this time, in the vertical walls, bending deformation occurs during forming, for example, when the die shoulder presses against them, and then, as forming progresses, back-bending deformation occurs as the vertical walls are sandwiched between the punch side and the die side. If a weld is located in the portion of the patchwork blank that is formed into vertical walls, bending and back-bending deformation will also occur at the location of the weld during the forming process of the vertical walls by the punch and die, and cracks may occur at the weld. Bending and back-bending deformation of the vertical walls, including the weld, also occurs when the end of the patchwork blank comes into contact with the punch flange surface. That is, if the end of the patchwork blank comes into contact with the punch flange surface early, bending occurs relatively quickly in the portion of the patchwork blank that is formed into vertical walls as the punch and die come closer together, and the amount of bending at or near the weld becomes large. Then, as forming progresses, the vertical walls are sandwiched between the punch side and the die side, and back-bending deformation occurs.

[0016] For example, when the blank body and reinforcing material are welded together, heat-affected zone (HAZ softening) may occur. In this case, the patchwork blank, which has a HAZ softened area at the weld, is subjected to cold pressing. If bending and unbending deformation occurs at the weld during the vertical wall forming process, strain will concentrate in the HAZ softened area, making it easier for cracks to occur at the weld. Alternatively, even if HAZ softening does not occur during welding, if bending and unbending deformation occurs at the weld, strain will concentrate, for example, at the edge of the weld metal, making it easier for cracks to occur at the weld.

[0017] In contrast, in the manufacturing method relating to the first configuration, a die having a bending position adjustment means is used for cold pressing of the patchwork blank. More specifically, in the forming process in which the patchwork blank is cold pressed, the die is pressed against the patchwork blank by the bending position adjustment means of the die in such a way as to suppress bending at the welded area. In other words, the die contacts the patchwork blank at a position where bending at the welded area is less likely to occur, and forms the vertical wall. As a result, in the patchwork blank formed into a press-formed product, strain concentration due to bending deformation is less likely to occur at the welded area, and cracking at the welded area can be suppressed.

[0018] In the manufacturing method relating to the first configuration, during the molding process, the die shoulder may be pressed against the flange-side portion of the patchwork blank relative to the weld portion by a bending position adjustment means (second configuration).

[0019] In the second configuration, the die's bending position adjustment means presses the die shoulder against the flange-side portion of the patchwork blank where the vertical wall is formed, rather than the weld. In this case, bending caused by the die shoulder occurs mainly at the flange-side portion of the weld, suppressing bending at the weld. As a result, in the patchwork blank formed into a press-formed product, strain concentration due to bending deformation is less likely to occur at the weld, and cracking at the weld is more easily suppressed.

[0020] In the manufacturing method relating to the first or second configuration, the die may have a punch flange surface configured such that X < Y - W, where X is the length of the punch flange surface in the width direction of the punch, Y is the distance in the width direction from the boundary between the punch top surface and the punch shoulder to the end of the patchwork blank when the portion of the patchwork blank that is formed into the vertical wall and flange is extended linearly from the punch shoulder to the position of the punch flange surface, and W is the distance in the width direction from the boundary between the punch top surface and the punch shoulder to the end of the punch flange surface on the punch side side (third configuration).

[0021] In the third configuration, the die has a narrow punch as a bending position adjustment means. More specifically, the punch flange surface is configured such that X < Y - W. In this case, the timing at which the end of the patchwork blank, which is pushed towards the punch by the die, contacts the punch flange surface can be delayed. Therefore, the timing at which the die presses against the patchwork blank and the patchwork blank is bent is also delayed, and the amount of bending and unbending deformation in and near the weld is easily reduced. Consequently, in the patchwork blank formed into a press-formed product, strain associated with bending deformation is less likely to concentrate in the weld, and cracking in the weld is easily suppressed.

[0022] In the manufacturing method relating to the third configuration, it is preferable that X, Y, and W satisfy X < Y - W - A (fourth configuration).

[0023] However, A = L1・sin(θ'-θ) / sinθ. L1 is the cross-sectional line length from the boundary between the punch top surface and the punch shoulder to the weld area of ​​the patchwork blank placed between the punch and the die in the forming process, θ is the angle that the portion of the patchwork blank that is formed into a vertical wall and flange makes with the punch flange surface when that portion is extended linearly from the punch shoulder to the punch flange surface, and θ' is the angle that the punch side surface makes with a plane parallel to the punch flange surface.

[0024] When X, Y, and W satisfy the above relationship, it becomes easier to delay the timing at which the end of the patchwork blank contacts the punch flange surface. As a result, the amount of bending and unbending deformation in and near the weld can be further reduced. Consequently, strain concentration in the weld is less likely to occur, and cracking in the weld is more easily suppressed.

[0025] In a manufacturing method relating to any of the first to fourth configurations, the mold may have a punch including a punch body and an inner pad as a bending position adjustment means. In this case, the punch body includes at least a portion of the punch flange surface, and the inner pad includes at least a portion of the punch top surface. The inner pad is configured to be movable relative to the punch body in the height direction of the punch. In the forming process, cold pressing of the patchwork blank may begin with the inner pad protruding from the punch body toward the die side, and end with the inner pad pushed toward the punch body side (fifth configuration).

[0026] In the fifth configuration, the mold has a punch including a punch body and an inner pad as a bending position adjustment means. In this case, the forming process can be started with the inner pad protruding from the punch body toward the die side. At the end of the forming process, the inner pad is pushed toward the punch body side by the die. By making the inner pad protrude from the punch body toward the die side, the height dimension of the punch is temporarily increased, and the timing at which the end of the patchwork blank, which is pushed toward the punch side by the die, contacts the punch flange surface can be delayed. Therefore, the timing at which the die is pressed against the patchwork blank and the patchwork blank is bent is also delayed, and the amount of bending and unbending deformation in and near the weld is easily reduced. As a result, in the patchwork blank formed into a press-formed product, strain due to bending deformation is less likely to concentrate in the weld, and cracking in the weld is easily suppressed.

[0027] In the manufacturing method relating to the fifth configuration, the stroke S is the relative movement distance of the inner pad with respect to the punch body in the height direction, L1 is the cross-sectional line length from the boundary between the punch top surface and the punch shoulder of the patchwork blank placed between the punch and the die in the forming process, L2 is the cross-sectional line length from the weld to the end of the patchwork blank, H is the height direction length of the punch side surface at the completion of the forming process, and θ' is the angle that the punch side surface makes with a plane parallel to the punch flange surface, then S > C × {(L1 + L2)・sinθ' - H} (where C > 0) (sixth configuration).

[0028] By setting the inner pad stroke S to satisfy the above relationship, it becomes easier to delay the timing at which the end of the patchwork blank contacts the punch flange surface. As a result, the amount of bending and unbending deformation in and near the weld can be further reduced. Consequently, strain concentration in the weld is less likely to occur, and cracking in the weld is more easily suppressed.

[0029] In a manufacturing method relating to any of the first to sixth configurations, the mold may have a die configured to be accessible to the side of the punch from the outside in the width direction of the punch as a bending position adjustment means (seventh configuration).

[0030] In the seventh configuration, the mold has a die configured to be able to approach the punch side from the outside in the width direction of the punch, as a bending position adjustment means. By using such a die, the contact position of the die with respect to the patchwork blank can be controlled. For example, the die can be brought closer to the punch side so that the die shoulder is pressed against the part of the patchwork blank on the flange side rather than the weld during the forming process. In this case, direct bending by the die shoulder does not occur at the weld, and the amount of bending at the weld can be reduced. Therefore, in the patchwork blank formed into a press-formed product, strain due to bending deformation is less likely to concentrate at the weld, and cracking at the weld is more easily suppressed.

[0031] In a manufacturing method relating to any of the first to seventh configurations, the mold may include a first mold and a second mold as bending position adjustment means. The second mold may include the punch and die described above. In this case, the forming process may include a first step of bending the patchwork blank using the first mold to form the flange of the press-formed product, and a step of cold pressing the patchwork blank using the second mold after the first step to form the vertical wall of the press-formed product (eighth configuration).

[0032] In the eighth configuration, the die includes a first die and a second die as bending position adjustment means. In the first forming step, the flange of the press-formed product is formed by the first die, and then in the second forming step, the vertical wall of the press-formed product is formed by the second die. In the second step, the patchwork blank, which already has the flange formed, is subjected to cold pressing. In this case, when the patchwork blank is pushed towards the punch side by the die in the second step, the end of the patchwork blank does not come into contact with the punch flange surface. Therefore, bending and unbending deformation caused by contact between the end of the patchwork blank and the punch flange surface does not occur in the vertical wall. As a result, in the patchwork blank formed into a press-formed product, strain associated with bending deformation is less likely to concentrate at the weld, and cracking at the weld is easily suppressed.

[0033] Embodiments of this disclosure will be described below with reference to the drawings. In these drawings, the same or equivalent components are denoted by the same reference numerals, and the same description will not be repeated.

[0034] <First Embodiment> [Structure of Press-Formed Product] Figure 1 is a perspective view of a press-formed product 10 manufactured by the manufacturing method according to this embodiment. Figure 2 is a cross-sectional view (II-II cross-section) of the press-formed product 10 shown in Figure 1.

[0035] Referring to Figure 1, the press-formed product 10 includes a top plate 11, vertical walls 12 and 13, and flanges 14 and 15.

[0036] The top plate 11 extends in the longitudinal direction of, for example, the press-formed product 10. The vertical wall 12 is continuous with the top plate 11. The vertical wall 13 is continuous with the top plate 11 on the opposite side of the vertical wall 12. The vertical walls 12 and 13 each extend along the top plate 11. The flange 14 is continuous with one of the vertical walls 12 on the opposite side of the top plate 11. The flange 15 is continuous with the other vertical wall 13 on the opposite side of the top plate 11. The flanges 14 and 15 each extend along the vertical walls 12 and 13.

[0037] Referring to Figure 2, in this embodiment, the press-formed product 10 has a substantially hat shape in cross-sectional view. In the press-formed product 10, the vertical walls 12 and 13 face each other with the top plate 11 in between. The vertical wall 12 includes a vertical wall body 121 and ridge portions 122 and 123. Similarly, the vertical wall 13 includes a vertical wall body 131 and ridge portions 132 and 133.

[0038] In a cross-sectional view of the press-formed product 10, the vertical wall body 121 extends from the top plate 11 side to the flange 14 side. The vertical wall body 121 is connected to the top plate 11 via the ridge portion 122. The vertical wall body 121 is connected to the flange 14 via the ridge portion 123. The flange 14 protrudes outward from the vertical wall 12 towards the outside of the press-formed product 10.

[0039] In a cross-sectional view of the press-formed product 10, the vertical wall body 131 extends from the top plate 11 side to the flange 15 side. The vertical wall body 131 is connected to the top plate 11 via the ridge portion 132. The vertical wall body 131 is connected to the flange 15 via the ridge portion 133. The flange 15 protrudes from the vertical wall 13 toward the outside of the press-formed product 10.

[0040] In a cross-sectional view of the press-formed product 10, the vertical wall bodies 121 and 131 may be arranged parallel to each other or non-parallel to each other. For example, in a cross-sectional view of the press-formed product 10, the vertical wall bodies 121 and 131 may be spaced further apart from each other as they move from the top plate 11 side toward the flange 14 and 15 side.

[0041] As shown in Figure 2, the press-formed product 10 is formed from a plurality of metal plates 21 and 22. In the example in Figure 2, the metal plate 22 is smaller than the metal plate 21. The metal plate 22 is superimposed on the metal plate 21, partially reinforcing the metal plate 21. In this embodiment, the metal plate 22 is superimposed on the metal plate 21 from the inside of the press-formed product 10.

[0042] The metal plate 22 reinforces the metal plate 21 in at least a portion of the vertical wall 12 and / or vertical wall 13. More specifically, the metal plates 21 and 22 are superimposed in at least a portion of the vertical wall 12 and / or vertical wall 13 on the top plate 11 side. In this embodiment, the metal plates 21 and 22 are superimposed in a portion of the vertical walls 12 and 13 and on the top plate 11. More specifically, the metal plates 21 and 22 are superimposed over a portion of the vertical wall body 121, the ridge portion 122, the top plate 11, the ridge portion 132, and a portion of the vertical wall body 131. On the other hand, the metal plate 22 is not superimposed on the metal plate 21 in the flanges 14 and 15. More specifically, the metal plate 22 is not superimposed on the metal plate 21 in the remaining portion of the vertical wall bodies 121 and 131, the ridge portions 123 and 133, and the flanges 14 and 15.

[0043] The metal plates 21 and 22 are joined by welding. In the example in Figure 2, the welded portions 23 of the metal plates 21 and 22 are located on the vertical walls 12 and 13. More specifically, the welded portions 23 are located on the vertical wall bodies 121 and 131. The welded portions 23 may also be located on parts other than the vertical walls 12 and 13. For example, in addition to the vertical walls 12 and 13, the welded portions 23 of the metal plates 21 and 22 may be provided on the top plate 11, or on the ridge portions 122 and 132.

[0044] The thickness of the metal plates 21 and 22 may be the same or different. The material of the metal plates 21 and 22 may be the same or different. The metal plates 21 and 22 are, for example, steel plates. The metal plates 21 and 22 may have the same tensile strength or different tensile strengths. The tensile strength of the metal plates 21 and 22 is, for example, 780 MPa or more, preferably 980 MPa or more, and more preferably 1180 MPa or more.

[0045] [Method for manufacturing a press-formed product] The method for manufacturing the press-formed product 10 according to this embodiment includes a preparation step and a forming step. Hereinafter, the method for manufacturing the press-formed product 10 will be described while referring to FIGS. 3A to 3E.

[0046] (Preparation step) Referring to FIG. 3A, in the preparation step, a patchwork blank 20 is prepared. The patchwork blank 20 includes a blank body 21 which is a metal plate and a reinforcing material 22 which is a metal plate. The blank body 21 has, for example, the shape obtained by unfolding the press-formed product 10 shown in FIGS. 1 and 2. In the example of this embodiment, the entire reinforcing material 22 is overlapped with the blank body 21. However, a part of the reinforcing material 22 may be overlapped with the blank body 21; that is, the reinforcing material 22 may be overlapped with the blank body 21 in a state where the reinforcing material 22 is shifted from the blank body 21.

[0047] The reinforcing material 22 is joined to the blank body 21 by welding. Therefore, a welded portion 23 is formed in the patchwork blank 20. The blank body 21 and the reinforcing material are joined by, for example, spot welding. However, the blank body 21 and the reinforcing material 22 may be joined by, for example, laser welding

[0048] (Forming step) As shown in FIGS. 3B to 3E, in the forming step, cold press working is performed on the patchwork blank 20 using a die 30 to obtain the press-formed product 10. In FIGS. 3B to 3E, a cross section (transverse cross section) perpendicular to the longitudinal direction of the die 30 is shown. First, the configuration of the die 30 used in the forming step will be described.

[0049] Referring to FIG. 3B, the die 30 includes a punch 3 and a die plate 32. The die 30 is attached to, for example, a known press device so that the punch 31 and the die plate 32 can approach and separate relatively. Hereinafter, the relative approach direction of the punch 31 and the die plate 32 is referred to as a press direction P. The die 30 can further include a pad 33.

[0050] The punch 31 includes a punch top surface 311, punch side surfaces 312 and 3 and punch flange surfaces 314 and 315.

[0051] The punch top surface 311 corresponds to the top plate 11 (Figure 1) of the press-formed product 10. The punch top surface 311 is positioned to intersect with the pressing direction P. In a cross-sectional view of the die 30, the punch top surface 311 extends substantially in the width direction of the punch 31. The width direction of the punch 31 is perpendicular to the pressing direction P in a cross-sectional view of the die 30. The height direction of the punch 31 coincides with the pressing direction P.

[0052] The punch sides 312 and 313 correspond to the vertical walls 12 and 13 (Figure 1) of the press-formed product 10, respectively. Punch side 312 is connected to the punch top surface 311 via the punch shoulder 316. Punch side 313 is connected to the punch top surface 311 via the punch shoulder 317 on the opposite side of punch side 312.

[0053] The punch sides 312 and 313 extend from the top plate 11 side to the punch flange sides 314 and 315 side, respectively, in a cross-sectional view of the die 30. The punch sides 312 and 313 may extend in the press direction P, or they may be inclined with respect to the press direction P, in a cross-sectional view of the die 30. The angle that each of the punch sides 312 and 313 makes with the punch top surface 311 is, for example, 90° or more, and preferably greater than 90°.

[0054] The punch flange surfaces 314 and 315 correspond to the flanges 14 and 15 (Figure 1) of the press-formed product 10, respectively. The punch flange surface 314 is connected to the punch side surface 312 via a corner portion 318. The punch flange surface 315 is connected to the punch side surface 312 via a corner portion 319 on the opposite side of the punch flange surface 314. In a cross-sectional view of the die 30, the punch flange surfaces 314 and 315 extend outward in the width direction of the punch 31 from the punch side surfaces 312 and 313, respectively. In the punch 31, the end faces in the width direction adjacent to the punch flange surfaces 314 and 315 may be parallel to the press direction P, or they may be inclined with respect to the press direction P, as shown by the dashed line in Figure 3B.

[0055] The die 32 includes die side surfaces 321, 322 and die flange surfaces 323, 324.

[0056] The die sides 321 and 322 correspond to the punch sides 312 and 313, respectively. That is, die side 321 is configured to form the vertical wall 12 (Figure 1) of the press-formed product 10 together with the punch side 312. Die side 322 is configured to form the vertical wall 13 (Figure 1) of the press-formed product 10 together with the punch side 313.

[0057] In this embodiment, a series of corner portions 325 are provided on the die side surface 321. A series of corner portions 326 are provided on the die side surface 322. The corner portions 325 and 326 correspond to the punch shoulders 316 and 317.

[0058] The die flange surfaces 323 and 324 are connected to the die sides 321 and 322, respectively, on the opposite side of the corner portions 325 and 326. The die flange surface 323 is connected to the die side 321 via the die shoulder 327. The die flange surface 324 is connected to the die side 322 via the die shoulder 328.

[0059] The die flange surfaces 323 and 324 correspond to the punch flange surfaces 314 and 315, respectively. One die flange surface 323 faces the punch flange surface 314 in the pressing direction P. The die flange surface 323 is configured to form the flange 14 (Figure 1) of the press-formed product 10 together with the punch flange surface 314. The other die flange surface 324 faces the punch flange surface 315 in the pressing direction P. The die flange surface 324 is configured to form the flange 15 (Figure 1) of the press-formed product 10 together with the punch flange surface 315.

[0060] In this embodiment, the die 32 is divided into a first portion 32L including a die side surface 321, a die shoulder 327, and a die flange surface 323, and a second portion 32R including a die side surface 322, a die shoulder 328, and a die flange surface 324. The pad 33 is positioned between the first portion 32L and the second portion 32R of the die 32. The pad 33 faces the punch top surface 311 in the press direction P.

[0061] The mold 30 has a bending position adjustment means. The bending position adjustment means is a means for adjusting the position in which the die 32 bends the patchwork blank 20 during the process of forming the vertical walls 12 and 13. In this embodiment, the mold 30 has punch flange surfaces 314 and 315 that are relatively short in length in the width direction of the punch 31 as the bending position adjustment means.

[0062] In the molding process, a press-formed product 10 (Figure 1) is formed from the patchwork blank 20 using the mold 30 configured in this way. Continuing with reference to Figure 3B, at the start of the molding process, the patchwork blank 20 is placed between the punch 31 and the die 32. If the punch 31 is positioned below the die 32, the patchwork blank 20 is placed on the punch 31. In this embodiment, the patchwork blank 20 is placed between the punch 31 and the die 32 with the reinforcing material 22 facing the punch 31. In this case, the molding surface of the punch 31 may be provided with a recess 310 to absorb the step difference between the blank body 21 and the reinforcing material 22.

[0063] With the patchwork blank 20 positioned between the punch 31 and the die 32, the die 32 and the pad 33 are brought relatively closer to the punch 31 in the pressing direction P. The patchwork blank 20 is first held between the pad 33 and the top surface 311 of the punch. With the patchwork blank 20 held between the pad 33 and the top surface 311, the die 32 is brought relatively closer to the punch 31 in the pressing direction P. As a result, as shown in Figure 3C, the portion of the patchwork blank 20 not held down by the pad 33 is pushed towards the punch 31 by the die 32, and the bending of the patchwork blank 20 along the punch shoulders 316, 317 begins.

[0064] As will be explained in more detail later, in this embodiment, the length of the punch flange surfaces 314 and 315 is shortened in the width direction of the punch 31. Therefore, when the patchwork blank 20 is pushed towards the punch 31 by the die 32, the ends of the patchwork blank 20 are less likely to come into contact with the punch flange surfaces 314 and 315. The ends of the patchwork blank 20 are positioned outside the punch flange surfaces 314 and 315 in the width direction of the punch 31 until partway through the molding process.

[0065] In this state, if the relative approach of the punch 31 and die 32 in the pressing direction P continues, the formation of the vertical wall 12 (Figure 1) by the punch side surface 312 and the die side surface 321 will proceed, and the formation of the vertical wall 13 (Figure 1) by the punch side surface 312 and the die side surface 321 will proceed.

[0066] The die 32 is pressed against the patchwork blank 20 during the forming of the vertical walls 12 and 13, causing bending deformation in the patchwork blank 20. For example, bending deformation occurs in the patchwork blank 20 when the die shoulders 327 and 328 are pressed against the patchwork blank 20. However, the die 32 is pressed against the patchwork blank 20 in such a way as to suppress bending at the location of the weld 23 by the bending position adjustment means of the mold 30. For example, as shown in Figure 3D, the die shoulder 327 may be pressed against the part of the patchwork blank 20 on the flange 14 side (Figures 1 and 2) relative to the weld 23 by the bending position adjustment means. Similarly, the die shoulder 328 may be pressed against the part of the patchwork blank 20 on the flange 15 side (Figures 1 and 2) relative to the weld 23 by the bending position adjustment means. Here, when the die 32 is pressed against the patchwork blank 20, it means that the die 32 does not simply slide over the patchwork blank 20 as the punch 31 and die 32 approach each other, but rather that the die 32 makes contact with the patchwork blank 20 in such a way that it substantially generates a bend in the patchwork blank 20. Similarly, when the die shoulders 327 and 328 are pressed against the patchwork blank 20, it means that the die shoulders 327 and 328 do not simply slide over the patchwork blank 20 as the punch 31 and die 32 approach each other, but rather that the die shoulders 327 and 328 make contact with the patchwork blank 20 in such a way that it substantially generates a bend originating from the die shoulders 327 and 328. For example, when the end of the patchwork blank 20 is in contact with the punch flange surfaces 314 and 315, and the die shoulders 327 and 328 or other parts of the die 32 make contact with the patchwork blank 20, a bend caused by the die 32 occurs in the patchwork blank 20. In this embodiment, the short length of the punch flange surfaces 314 and 315 in the width direction of the punch 31 delays the timing at which the die 32 is pressed against the patchwork blank 20. As a result, the patchwork blank 20 is bent by the die 32 closer to the ends. For example, the patchwork blank 20 is bent by the die shoulders 327 and 328 closer to the ends than the welded portion 23.

[0067] Referring to Figure 3E, the patchwork blank 20 is ultimately clamped together by the punch 31 and die 32 to form a press-formed product 10. The top plate 11 of the press-formed product 10 is formed mainly by the punch top surface 311 and the pad 33. The vertical walls 12 and 13 are formed mainly by the punch sides 312 and 313 and the die sides 321 and 322. The flanges 14 and 15 are formed mainly by the punch flange surfaces 314 and 315 and the die flange surfaces 323 and 324.

[0068] [Effects] In this embodiment, a press-formed product 10 is manufactured by cold-pressing a patchwork blank 20 using a mold 30 having a bending position adjustment means. During the forming process, the die 32 is pressed against the patchwork blank 20 by the bending position adjustment means of the mold 30 in such a way as to suppress bending of the patchwork blank 20 at the location of the weld 23. Preferably, the die shoulders 327 and 328 are pressed against the part of the patchwork blank 20 on the flange 14 and 15 side (end side) relative to the weld 23. In this case, bending caused by the die 32 is less likely to occur at the location of the weld 23 in the patchwork blank 20. Therefore, the amount of bending at the weld 23 can be reduced in the part of the patchwork blank 20 that is formed into the vertical walls 12 and 13. Consequently, in the manufacture of the press-formed product 10, strain concentration due to bending deformation is less likely to occur at the weld 23, and cracking at the weld 23 can be suppressed.

[0069] For example, as shown in Figure 4, when using a general mold in which the length of the punch flange surfaces 314 and 315 in the width direction of the punch 31 is relatively long, when bending of the patchwork blank 20 along the punch shoulders 316 and 317 is started in the forming process, and the patchwork blank 20 is pushed toward the punch 31 by the die 32, the ends of the patchwork blank 20 come into contact with the punch flange surfaces 314 and 315 at an early stage. In this case, the die 32 is pressed against the patchwork blank 20 at an early timing, causing bending in the parts of the patchwork blank 20 that become the vertical walls 12 and 13 (Figures 1 and 2). As a result, the parts of the patchwork blank 20 that become the vertical walls 12 and 13 are bent by the die 32 before the part where the welded portion 23 is located is formed by the punch sides 312 and 313. Consequently, the amount of bending and unbending deformation at the welded portion 23 becomes large, and cracks are likely to occur in the patchwork blank 20 at the welded portion 23.

[0070] On the other hand, in this embodiment, the mold 30 has a narrow punch 31 as a bending position adjustment means. More specifically, the mold 30 has a punch flange surface 314 configured to satisfy X < Y - W as a bending position adjustment means.

[0071] Referring to Figure 5, X is the length of the punch flange surface 314 in the width direction of the punch 31 (punch flange width). Y is the distance in the width direction of the punch 31 from the boundary between the punch top surface 311 and the punch shoulder 316 to the end of the patchwork blank 20 when the portion of the patchwork blank 20 that will be formed into the vertical wall 12 and flange 14 is extended linearly from the punch shoulder 316 to the position of the punch flange surface 314. W is the distance in the width direction of the punch 31 from the boundary between the punch top surface 311 and the punch shoulder 316 to the end of the punch flange surface 314 on the punch side surface 312 side. The boundary between the punch top surface 311 and the punch shoulder 316 is typically the radius end of the punch shoulder 316 on the punch top surface 311 side. The end of the punch flange surface 314 on the punch side surface 312 side is, for example, the radius end of the corner portion 318 on the punch flange surface 314 side.

[0072] For example, if W + X ≥ Y, then in the forming process, bending of the patchwork blank 20 along the punch shoulder 316 begins, and when the patchwork blank 20 is pushed toward the punch 31 by the die 32, the end of the patchwork blank 20 contacts the punch flange surface 314 early, causing bending at the vertical wall 12 to occur at an early timing. On the other hand, if the punch flange surface 314 is configured to satisfy X < Y - W, i.e., W + X < Y, then the timing at which the end of the patchwork blank 20 contacts the punch flange surface 314 in the forming process can be delayed. This delays the timing at which the die 32 presses against the patchwork blank 20 and deforms it, allowing bending by the die 32 to occur in the patchwork blank 20 after forming by the punch side surface 312 has begun at the location of the weld 23. For example, the die shoulder 327 is pressed against the portion of the vertical wall 12 on the flange 14 side (end side) relative to the weld 23 so as not to substantially cause bending at the weld 23 (Figure 3D). Therefore, strain concentration associated with bending deformation is less likely to occur in the welded joint 23, and cracking in the welded joint 23 is more easily suppressed.

[0073] In this embodiment, it is preferable that the punch flange width X, together with Y and W, satisfies the following equation (1): X < Y - W - A ... (1)

[0074] In equation (1), A is calculated as A = L1・sin(θ'-θ) / sinθ. L1 is the cross-sectional line length of the patchwork blank 20 placed between the punch 31 and the die 32 (Figure 3B) in the forming process, and is the cross-sectional line length from the boundary between the punch top surface 311 and the punch shoulder 316 to the welded portion 23. More specifically, in a cross-sectional view of the mold 30, L1 is the length along the blank body 21 (Figure 3B) from the R-end on the punch top surface 311 side of the punch shoulder 316 to the end of the welded portion 23 on the end side of the patchwork blank 20. For example, in a cross-section of the press-formed product 10 after forming, L1 may be obtained by measuring the distance along the inner surface from the R-end on the top plate 11 side of the ridge portion 122 of the vertical wall 12 to the flange 14 side end of the welded portion 23. θ is the angle that the portion of the patchwork blank 20 that is formed into the vertical wall 12 and flange 14 makes with the punch flange surface 314 when that portion extends linearly from the punch shoulder 316 to the position of the punch flange surface 314. θ' is the angle that the punch side surface 312 makes with a plane parallel to the punch flange surface 314.

[0075] When the punch flange width X satisfies equation (1), the timing of contact between the end of the patchwork blank 20 and the punch 31 is more likely to be delayed, and the timing of bending during the forming of the vertical wall 12 is also delayed. As a result, strain concentration at the welded joint 23 is less likely to occur, and cracking at the welded joint 23 is further suppressed.

[0076] In this embodiment, the punch flange surface 315 is also configured to satisfy X < Y - W. It is preferable that the punch flange width X of the punch flange surface 315 also satisfies the above formula (1). Since the punch side surface 313 and the punch flange surface 315, as well as the vertical wall 13 and flange 15 of the press-formed product 10, have basically the same configuration as the punch side surface 312 and the punch flange surface 314, and the vertical wall 12 and flange 14 of the press-formed product 10 shown in Figure 5, a detailed explanation of the configuration of the punch flange surface 315 will be omitted.

[0077] <Second Embodiment> Figures 6A to 6D are schematic diagrams illustrating the manufacturing method of the press-formed product 10 (Figures 1 and 2) according to this embodiment. In the manufacturing method according to this embodiment, the mold 30A has a bending position adjustment means different from the mold 30 in the first embodiment.

[0078] Referring to Figure 6A, the mold 30A has a punch 31A including a punch body 31a and an inner pad 31b as a bending position adjustment means.

[0079] The punch body 31a includes at least a portion of the punch flange surfaces 314 and 315. In this embodiment, the punch body 31a includes the entirety of the punch flange surfaces 314 and 315. The punch body 31a may further include portions of each of the punch sides 312 and 313.

[0080] The inner pad 31b includes at least a portion of the punch top surface 311. In this embodiment, the inner pad 31b includes the entire punch top surface 311. The inner pad 31b may further include the punch shoulders 316, 317 and the remaining portions of the punch sides 312, 313, respectively.

[0081] The inner pad 31b is configured to be movable relative to the punch body 31a in the height direction of the punch 31A. The inner pad 31b may be supported by, for example, an elastic member 31c disposed within the punch body 31a. The elastic member 31c is a member that can expand and contract in the height direction of the punch 31A, and is, for example, a fluid pressure actuator or a spring. The inner pad 31b can move in the height direction of the punch 31A by expanding and contracting the elastic member 31c.

[0082] In the molding process of the manufacturing method according to this embodiment, the cold pressing of the patchwork blank 20 is started with the inner pad 31b protruding from the punch body 31a toward the die 32. At the start of the molding process, the inner pad 31b protrudes from the punch body 31a toward the die 32 by a predetermined stroke S, and the patchwork blank 20 is placed between the punch 31A and the die 32, similar to the first embodiment. Then, the die 32 and the pad 33 are brought relatively closer to the punch 31A in the press direction P.

[0083] The patchwork blank 20 is first held between the pad 33 and the top surface 311 of the punch, and then bent along the punch shoulders 316, 317 due to the relative approach of the punch 31A and the die 32 in the pressing direction P. Referring to Figure 6B, in this embodiment, because the inner pad 31b protrudes from the punch body 31a, the height dimension of the punch 31A is greater than the height of the vertical walls 12, 13 (Figures 1 and 2) of the press-formed product 10 until partway through the forming process. Therefore, when the patchwork blank 20 is pushed towards the punch 31A by the die 32, the ends of the patchwork blank 20 are less likely to come into contact with the punch flange surfaces 314, 315. This makes it possible to delay the timing of the die 32 pressing against the patchwork blank 20.

[0084] As shown in Figure 6C, as the relative approach of the punch 31A and the die 32 in the pressing direction P progresses, the inner pad 31b is pushed toward the punch body 31a by the die 32. Consequently, for example, the die shoulders 327 and 328 come into contact with the patchwork blank 20, causing bending to occur in the patchwork blank 20. The die shoulder 327 is preferably pressed against the part of the patchwork blank 20 on the flange 14 side (Figures 1 and 2) relative to the weld 23. Similarly, the die shoulder 328 is preferably pressed against the part of the patchwork blank 20 on the flange 15 side (Figures 1 and 2) relative to the weld 23. In other words, it is preferable that the patchwork blank 20 is bent by the die shoulders 327 and 328 on the end side of the weld 23.

[0085] The inner pad 31b moves toward the punch body 31a by a stroke S. As shown in Figure 6D, the cold pressing of the patchwork blank 20 is completed with the inner pad 31b pushed toward the punch body 31a. Similar to the first embodiment, the patchwork blank 20 is ultimately clamped together by the punch 31A and the die 32 to become the press-formed product 10.

[0086] In this embodiment, the mold 30A has a punch 31A including a punch body 31a and an inner pad 31b as a bending position adjustment means. In this case, the inner pad 31b can be made to protrude from the punch body 31a toward the die 32 until partway through the molding process. This temporarily increases the height dimension of the punch 31A, delaying the timing at which the end of the patchwork blank 20, which is pushed toward the punch 31A by the die 32, contacts the punch 31A. As a result, the timing at which the die 32 is pressed against the patchwork blank 20 and the patchwork blank 20 is bent is also delayed, making it less likely for bending and unbending deformation to occur in and near the welded portion 23. Therefore, in the manufacturing of the press-formed product 10, strain concentration due to bending deformation is less likely to occur in the welded portion 23, and cracking in the welded portion 23 is easily suppressed.

[0087] Referring to Figure 7, in this embodiment, the stroke S of the inner pad 31b preferably satisfies the following equation (2). The stroke S is the relative movement distance of the inner pad 31b with respect to the punch body 31a, and is the movement distance of the punch 31A in the height direction. S > C × {(L1 + L2)・sinθ' - H} ... (2)

[0088] In equation (2), L1 is the cross-sectional line length of the patchwork blank 20 from the boundary between the punch top surface 311 and the punch shoulder 316 to the welded portion 23, as in the first embodiment. L2 is the cross-sectional line length of the patchwork blank 20 from the welded portion 23 to the end of the patchwork blank 20. More specifically, L2 is the length along the blank body 21 (Figure 6A) from the end of the patchwork blank 20 on the end side of the welded portion 23 to the end of the patchwork blank 20. H is the length in the height direction of the punch side surface 312 at the completion of the forming process. That is, H is the distance in the height direction of the punch 31A from the punch top surface 311 to the punch flange surface 314 when the inner pad 31b is completely pushed towards the punch body 31a side. θ' is the angle that the punch side surface 312 makes with a plane parallel to the punch flange surface 314, as in the first embodiment. C is a constant satisfying C > 0, preferably C ≥ 0.25. The upper limit of C is not particularly limited, but for example, C ≤ 1.35 may be used.

[0089] If S + H > (L1 + L2)・sinθ', the flange 14 is formed after the vertical wall 12 is formed, thus reducing the strain generated in the vertical wall 12. However, even if the flange 14 is formed before the vertical wall 12 is formed, it is believed that the effect of reducing strain in the welded portion 23 and its vicinity of the vertical wall 12 can be obtained by delaying the timing at which the end of the patchwork blank 20 contacts the punch 31A. Specifically, if the stroke S of the inner pad 31b is set to satisfy the above equation (2), the timing at which the end of the patchwork blank 20 contacts the punch 31A can be effectively delayed, and the timing at which bending occurs during the formation of the vertical wall 12 is also delayed. As a result, strain concentration in the welded portion 23 is less likely to occur, and cracking in the welded portion 23 is further suppressed.

[0090] <Third Embodiment> Figures 8A to 8D are schematic diagrams illustrating the manufacturing method of the press-formed product 10 (Figures 1 and 2) according to this embodiment. In the manufacturing method according to this embodiment, the mold 30B has a bending position adjustment means that differs from the molds 30 and 30A in the other embodiments.

[0091] Referring to Figure 8A, the mold 30B has a die 32B as a bending position adjustment means. The die 32B is configured to be accessible from the outside in the width direction of the punch 31 to the punch sides 312 and 313. More specifically, the first portion 32L of the die 32B is configured to be movable from the outside in the width direction of the punch 31 toward the punch side 312 and the punch flange surface 314, along a direction inclined with respect to the press direction P. The second portion 32R of the die 32B is configured to be movable from the outside in the width direction of the punch 31 toward the punch side 313 and the punch flange surface 315, along a direction inclined with respect to the press direction P. The die 32B may be configured to be movable by, for example, a known cam mechanism.

[0092] In the molding process of the manufacturing method according to this embodiment, the die 32B is separated from the punch 31 in the pressing direction P, and the cold pressing of the patchwork blank 20 is started with the die 32B separated from the punch 31 in the width direction. In this state, as in other embodiments, the patchwork blank 20 is placed between the punch 31 and the die 32B. Then, as shown in Figure 8B, the die 32B and the pad 33 are brought relatively closer to the punch 31 in the pressing direction P. The patchwork blank 20 is first held between the pad 33 and the top surface 311 of the punch, and is bent along the punch shoulders 316, 317 due to the relative approach of the punch 31 and the die 32B in the pressing direction P.

[0093] As shown in Figure 8C, after bending along the punch shoulders 316 and 317 in the patchwork blank 20 begins, the die 32B approaches the punch 31 in the pressing direction P and in the width direction of the punch 31. The movement of the die 32B is controlled so that it is pressed against a position in the patchwork blank 20 where bending at the weld 23 is less likely to occur. For example, the movement of the die 32B is controlled so that the die shoulders 327 and 328 are pressed against the part of the patchwork blank 20 on the flange 14 and 15 side (Figures 1 and 2) relative to the weld 23. In this case, the patchwork blank 20 is bent by the die shoulders 327 and 328 on the end side of the weld 23.

[0094] As shown in Figure 8D, the patchwork blank 20 is ultimately clamped together by the punch 31 and die 32B, as in other embodiments, to form a press-formed product 10.

[0095] In this embodiment, the mold 30B has a die 32B as a bending position adjustment means. The die 32B is configured to move along a direction inclined with respect to the pressing direction P so that it can approach the punch sides 312, 313 from the outside in the width direction. In this case, by controlling the movement of the die 32B, the die shoulders 327, 328 can be pressed against the patchwork blank 20 during the forming process, for example, on the flange 14, 15 side (end side) rather than the welded portion 23. Therefore, bending at the welded portion 23 is less likely to occur in the patchwork blank 20 during the forming process. Consequently, strain concentration due to bending deformation is less likely to occur at the welded portion 23, and cracking at the welded portion 23 is more easily suppressed.

[0096] <Fourth Embodiment> In the manufacturing method according to this embodiment, the mold 30C has a bending position adjustment means that differs from the molds 30, 30A, and 30B in the other embodiments. Figures 9A and 9B are schematic diagrams illustrating the configuration of the mold 30C.

[0097] As shown in Figures 9A and 9B, the mold 30C has a first mold 30a and a second mold 30b as bending position adjustment means.

[0098] Referring to Figure 9A, the first mold 30a may include, for example, punches 33L and 33R, a die 34, and a blank holder 35. The punches 33L and 33R are positioned on both sides of the blank holder 35. The die 34 faces the blank holder 35.

[0099] Referring to Figure 9B, the second mold 30b includes a punch 31, a die 32, and a pad 33 similar to those in the first embodiment.

[0100] Figures 10A to 10E are schematic diagrams illustrating the manufacturing method of the press-formed product 10 (Figures 1 and 2) according to this embodiment. In the manufacturing method according to this embodiment, the molding process includes a first step and a second step.

[0101] As shown in Figures 10A and 10B, in the first step, the patchwork blank 20 is bent using the first mold 30a to form the flanges 14 and 15.

[0102] Referring to Figure 10A, in this embodiment, first, the patchwork blank 20 is placed between the die 34, the punches 33L, 33R and the blank holder 35. The patchwork blank 20 may also be placed between the die 34, the punches 33L, 33R and the blank holder 35 with the reinforcing material 22 facing the blank holder 35. In this case, a recess 351 may be formed on the die 34 side surface of the blank holder 35 to absorb the step difference between the blank body 21 and the reinforcing material 22.

[0103] Referring to Figure 10B, the patchwork blank 20 is held between the die 34 and the blank holder 35. In this state, the punches 33L and 33R are moved relative to the die 34 and the blank holder 35 in the thickness direction of the patchwork blank 20. This bends the patchwork blank 20, forming the flanges 14 and 15.

[0104] After the first step, the second step is carried out. Referring to Figures 10C to 10E, in the second step, the second mold 30b is used to cold press the patchwork blank 20 after the first step to form the vertical walls 12 and 13.

[0105] Referring to Figure 10C, in the second step, first, the patchwork blank 20 with the flanges 14 and 15 formed is placed between the punch 31 and the die 32. Then, as in other embodiments, the patchwork blank 20 is held between the pad 33 and the top surface 311 of the punch, and the die 32 pushes the patchwork blank 20 towards the punch 31.

[0106] Referring to Figure 10D, in this embodiment, flanges 14 and 15 are already formed on the patchwork blank 20. Therefore, when the patchwork blank 20 is pushed towards the punch 31 by the die 32, the end of the patchwork blank 20 faces towards the die 32 and does not come into contact with the punch flange surfaces 314 and 315. As a result, the die shoulders 327 and 328 come into contact with the portion of the patchwork blank 20 that is on the flange 14 and 15 side relative to the welded portion 23.

[0107] As shown in Figure 10E, the patchwork blank 20 is ultimately clamped together by the punch 31 and die 32, as in other embodiments, to form a press-formed product 10.

[0108] In this embodiment, the die 30C has a first die 30a and a second die 30b as bending position adjustment means, and the forming process includes a first step and a second step. In the first step, the flanges 14 and 15 of the press-formed product 10 are formed by the first die 30a, and in the subsequent second step, the vertical walls 12 and 13 of the press-formed product 10 are formed by the second die 30b. In the second step, the patchwork blank 20, which already has the flanges 14 and 15 formed, is subjected to cold pressing. In this case, when the patchwork blank 20 is pushed towards the punch 31 by the die 32, the ends of the patchwork blank 20 do not come into contact with the punch flange surfaces 314 and 315. Therefore, during the forming process, no bending occurs in the patchwork blank 20 due to contact between the ends of the patchwork blank 20 and the punch flange surfaces 314 and 315, and bending at the welded portion 23 is substantially eliminated. Therefore, strain concentration associated with bending deformation is less likely to occur in the welded joint 23, and cracking in the welded joint 23 is more easily suppressed.

[0109] While embodiments relating to this disclosure have been described above, this disclosure is not limited to the embodiments described above, and various modifications are possible as long as they do not deviate from its spirit.

[0110] In the first embodiment described above, the die 30 has punch flange surfaces 314 and 315 configured to satisfy X < Y - W as a bending position adjustment means. In the second embodiment described above, the die 30A has a punch 31A including a punch body 31a and an inner pad 31b as a bending position adjustment means. In the third embodiment described above, the die 30B has a die 32B configured to be accessible from the outside in the width direction of the punch 31 to the punch side surfaces 312 and 313 and the punch flange surfaces 314 and 315 as a bending position adjustment means. These bending position adjustment means can be combined as appropriate. That is, each die 30, 30A, and 30B may have a plurality of bending position adjustment means.

[0111] For example, as shown in Figure 11, the die 30 may have, as a first bending position adjustment means, punch flange surfaces 314, 315 configured to satisfy X < Y - W, and as a second bending position adjustment means, a punch 31 including the punch body 31a and inner pad 31b, as described in the second embodiment. Furthermore, the die 30 in the example shown in Figure 11 may further have, as a third bending position adjustment means, a die 32 configured to be accessible from the outside in the width direction of the punch 31 to the punch sides 312, 313, as described in the third embodiment. Alternatively, the die 30 in the example shown in Figure 11 may have, as a second bending position adjustment means, the bending position adjustment means described in the third embodiment instead of the bending position adjustment means described in the second embodiment.

[0112] Similarly, the mold 30A in the second embodiment may have a punch 31A including a punch body 31a and an inner pad 31b as a first bending position adjustment means, and a die 32 configured to be accessible from the outside in the width direction of the punch 31, i.e., the bending position adjustment means described in the third embodiment, i.e., the die 32 configured to be accessible from the outside in the width direction of the punch 31. Furthermore, in the mold 30C of the fourth embodiment, the second mold 30b may have one or more of the bending position adjustment means described in the first to third embodiments.

[0113] In the mold 30A of the second embodiment described above, the punch 31A is divided into a punch body 31a and an inner pad 31b at the positions of the punch sides 312 and 313. However, as shown in Figure 12, the punch 31A may be divided into a punch body 31a and an inner pad 31b at the positions of the punch flange surfaces 314 and 315. Alternatively, as shown in Figure 13, the punch 31A may be divided into a punch body 31a and an inner pad 31b at the position of the punch top surface 311. However, the division position between the punch body 31a and the inner pad 31b is preferably at the punch sides 312 and 313 or the punch flange surfaces 314 and 315, as in the example of the second embodiment and Figure 12. More specifically, the division position between the punch body 31a and the inner pad 31b is preferably located outside the width direction of the punch 31 from the overlapping portion of the metal plates 21 and 22 in the press-formed product 10 formed by the punch 31A and the die 32.

[0114] In the above embodiment, each of the molds 30, 30A, 30B, and 30C includes a pad 33. However, the molds 30, 30A, 30B, and 30C do not necessarily have to include a pad 33. The top plate 11 of the press-formed product 10 may be formed by the punch top surface 311 and a die 32 or 32B. In this case, the first portion 32L and the second portion 32R of the die 32 and 32B may be formed integrally. Even if the molds 30, 30A, 30B, and 30C include a pad 33, the first portion 32L and the second portion 32R of the die 32 and 32B may be formed integrally.

[0115] In the above embodiment, recesses 310 are provided in the punches 31 and 31A to absorb the step difference between the blank body 21 and the reinforcing material 22. However, recesses to absorb the step difference between the blank body 21 and the reinforcing material 22 may also be provided in the dies 32 and 32B. In this case, during the molding process, the patchwork blank 20 is positioned with the reinforcing material 22 facing the dies 32 and 32B.

[0116] In the above embodiment, the press-formed product 10 includes two vertical walls 12, 13 and two flanges 14, 15. However, the press-formed product 10 may not include either one of the flanges 14, 15, nor may it include either one of the vertical walls 12, 13. If the press-formed product 10 has only one of the flanges 14, 15, then the molds 30, 30A, 30B, 30C only need to have bending position adjustment means on the side corresponding to one of the flanges 14, 15. The molds 30, 30A, 30B, 30C do not necessarily need to be configured symmetrically.

[0117] In the press-formed product 10 manufactured according to the above embodiment, a portion of the top plate 11 and the vertical walls 12 and 13 are reinforced by a single reinforcing member 22. However, the reinforcing member 22 may be divided, for example, into a vertical wall 12 side and a vertical wall 13 side. Alternatively, the reinforcing member 22 may be joined to the blank body 21 on one of the vertical walls 12 and 13, and the other vertical wall 12 and 13 may not have a reinforcing member 22. In this case, the molds 30, 30A, 30B, and 30C may have bending position adjustment means only on the side where the reinforcing member 22 and the welded portion 23 are present.

[0118] In the above embodiment, the molds 30, 30A, 30B, and 30C may further include a blank holder. In this case, the blank holder is positioned to face the die flange surface 323 or 324 in the pressing direction. The blank holder is configured to form the flange 14 or 15 together with the die flange surface 323 or 324.

[0119] The present disclosure will be further described below with reference to examples. However, the present disclosure is not limited to the following examples.

[0120] [First Embodiment] Using general-purpose analysis software (LS-DYNA, manufactured by Ansys), a CAE analysis was performed to form a press-formed product 10 from a patchwork blank 20 using a mold having the same configuration as the mold 30 according to the first embodiment.

[0121] As shown in Figure 14, the patchwork blank 20 includes a blank body 21 and two reinforcing members 22. In this analysis, the blank body 21 was made of steel plate with a tensile strength of 1180 MPa and a thickness of 1.4 mm, and each reinforcing member 22 was made of steel plate with a tensile strength of 1180 MPa and a thickness of 1.6 mm. The length of the blank body 21 in the width direction of the mold was 180.5 mm, and the length of each reinforcing member 22 was 40.0 mm. Multiple welds (spot welds) 23 were arranged at intervals of 25.0 mm in the width direction of the mold and 15.0 mm in the depth direction as joints between the blank body 21 and each reinforcing member 22. In the heat-affected zone of each weld 23, the inner tensile strength was equivalent to 980 MPa, and the outer tensile strength was equivalent to 1180 MPa.

[0122] In the patchwork blank 20 before forming, the cross-sectional line length L1 from each of the punch shoulders 316 and 317 to the welded parts 23 located on the vertical walls 12 and 13 was set to 20.0 mm. The height H of the punch sides 312 and 313 was set to 50.0 mm, and the angle θ' was set to 80°. During forming, the angle θ that the patchwork blank 20 made with each of the punch flange surfaces 314 and 315 was 45°, and the length Y in the width direction of the mold from each of the punch shoulders 316 and 317 to the end of the patchwork blank 20 was 48.0 mm (Figure 5). W and A (Figure 5) were calculated from these parameter values, and W was 8.8 mm and A was 11.4 mm.

[0123] In the press-formed product 10 after molding, the radius of curvature of the ridge on the top plate 11 side was 5.0 mm, and the radius of curvature of the ridge on the flange 14 and 15 side was 8.0 mm. The length of the flanges 14 and 15 in the width direction of the mold was 12.0 mm.

[0124] In this analysis, the strain generated in the welded joint 23 was investigated while varying the value of the punch flange width X. The conditions for the punch flange width X and the measured strain values ​​in this analysis are shown in Table 1. In Table 1, "strain" refers to the strain measured in the heat-affected zone (surface) of a specific welded joint 23 located on one of the vertical walls 13 immediately after forming (bottom dead center) of the press-formed product 10.

[0125]

[0126] In Table 1, Comparative Examples 1-1 and 1-2 are examples in which press-formed products 10 were formed from a patchwork blank 20 using a general mold where X ≥ Y - W. On the other hand, Examples 1-1 to 1-5 are examples in which press-formed products 10 were formed from a patchwork blank 20 using a mold where X < Y - W, similar to the first embodiment. Table 1 also shows the relationship between the punch flange width X and W, Y, and A for each comparative example and each example.

[0127] As shown in Table 1, in Examples 1-1 to 1-5, satisfying X < Y - W resulted in smaller strain in the heat-affected zone of the welded joint 23 located on the vertical wall 13 compared to each comparative example. In particular, in Examples 1-3 to 1-5, which satisfy the above-mentioned formula (1): X < Y - W - A, the amount of strain reduction was greater compared to each comparative example, compared to Examples 1-1 and 1-2, which do not satisfy formula (1).

[0128] The results of this analysis confirmed that the strain at the welded portion 23 of the vertical wall 13 is reduced when the punch flange surface is configured such that X < Y - W. Furthermore, it was confirmed that the strain at the welded portion 23 of the vertical wall 13 is further reduced when X < Y - W - A is satisfied.

[0129] [Second Embodiment] Using the same analysis software as in the first embodiment, a CAE analysis was performed to form a press-formed product 10 from a patchwork blank 20 using a mold having the same configuration as the mold 30A according to the second embodiment.

[0130] Referring to Figure 15, the basic conditions for the patchwork blank 20 and the press-formed product 10 were the same as in the first embodiment. However, in the patchwork blank 20 before forming, the cross-sectional line length L2 from the welded parts 23 located on the vertical walls 12 and 13 to the end of the patchwork blank 20 was set to 50.0 mm, so L1 + L2 = 70.0 mm.

[0131] In this analysis, the appropriate range of the constant C for equation (2) described in the second embodiment was investigated while varying the stroke S of the inner pad of the punch. The conditions for stroke S and constant C in this analysis are shown in Table 2. In Table 2, "strain" is the strain measured at the heat-affected zone (surface) of a specific weld 23 located on one of the vertical walls 13 immediately after forming (bottom dead center) of the press-formed product 10, as in the first embodiment.

[0132]

[0133] As shown in Table 2, in Comparative Example 2, the stroke S of the inner pad is zero. On the other hand, in Examples 2-1 to 2-4, the stroke S of the inner pad is positive. That is, in each of Examples 2-1 to 2-4, the forming of the press-formed product 10 starts with the inner pad protruding from the punch body in the height direction of the punch, and the forming of the press-formed product 10 is completed when the inner pad moves toward the punch body by a stroke S. In Examples 2-1 to 2-4, the strain in the heat-affected zone of the welded part 23 was reduced compared to Comparative Example 2.

[0134] Table 2 shows the value of the constant C calculated from the stroke S of the inner pad based on equation (2) described in the second embodiment. In all of Examples 2-1 to 2-4, the stroke S is 4.8 mm or more, and the constant C is 0.25 or more. As described above, it has been confirmed that these embodiments have a strain reduction effect. According to the results of this analysis, it is preferable that C ≥ 0.25 in equation (2).

[0135] 10: Press-formed product 11: Top plate 12, 13: Vertical wall 14, 15: Flange 20: Patchwork blank 21: Blank body 22: Reinforcement material 23: Welded part 30, 30A, 30B, 30C: Mold 30a: First mold 30b: Second mold 31, 31A: Punch 311: Punch top surface 312, 313: Punch side surface 314, 315: Punch flange surface 316, 317: Punch shoulder 31a: Punch body 31b: Inner pad 32, 32B: Die 321, 322: Die side surface 323, 324: Die flange surface 327, 328: Die shoulder

Claims

1. A method for manufacturing a press-formed product, comprising: a preparation step of preparing a patchwork blank including a blank body and a reinforcing material superimposed on the blank body and joined to the blank body by welding; and a forming step of using a mold including a punch and a die to cold press the patchwork blank to obtain the press-formed product including a top plate, a vertical wall continuous with the top plate and on which the welded portion of the patchwork blank is located, and a flange continuous with the vertical wall on the opposite side of the top plate, wherein the punch includes a punch top surface corresponding to the top plate, a punch side connected to the punch top surface via a punch shoulder and corresponding to the vertical wall, and a punch flange surface corresponding to the flange; the die includes a die side corresponding to the punch side, and a die flange surface connected to the die side via a die shoulder and corresponding to the punch flange surface, and in the forming step, the die is pressed against the patchwork blank so as to suppress bending of the patchwork blank at the location of the welded portion using bending position adjustment means of the mold.

2. A manufacturing method according to claim 1, wherein in the molding step, the die shoulder is pressed against the portion of the patchwork blank on the flange side relative to the welded portion by the bending position adjustment means.

3. A manufacturing method according to claim 1, wherein the mold has a punch flange surface configured such that X < Y - W, where X is the length of the punch flange surface in the width direction of the punch, Y is the distance in the width direction from the boundary between the punch top surface and the punch shoulder to the end of the patchwork blank when the portion of the patchwork blank that is formed into the vertical wall and the flange is extended linearly from the punch shoulder to the position of the punch flange surface, and W is the distance in the width direction from the boundary between the punch top surface and the punch shoulder to the end of the punch flange surface on the punch side side.

4. A manufacturing method according to claim 3, wherein X, Y, and W satisfy X < Y - W - A, where A = L1・sin(θ'-θ) / sinθ, where L1 is the cross-sectional line length from the boundary between the punch top surface and the punch shoulder to the weld portion of the patchwork blank, which is positioned between the punch and the die in the forming step, θ is the angle that the portion of the patchwork blank that is formed into the vertical wall and the flange makes with the punch flange surface when the portion is extended linearly from the punch shoulder to the position of the punch flange surface, and θ' is the angle that the punch side surface makes with a plane parallel to the punch flange surface.

5. A manufacturing method according to claim 1, wherein the mold has a punch, the bending position adjustment means comprising a punch body including at least a portion of the punch flange surface, and an inner pad including at least a portion of the punch top surface, configured to be movable relative to the punch body in the height direction of the punch, and in the forming step, cold pressing of the patchwork blank is started with the inner pad protruding from the punch body toward the die, and cold pressing of the patchwork blank is finished with the inner pad pushed toward the punch body.

6. A manufacturing method according to claim 5, wherein the stroke S is the relative distance of the inner pad to the punch body in the height direction, L1 is the length of the cross section of the patchwork blank, which is placed between the punch and the die in the forming process, from the boundary between the punch top surface and the punch shoulder to the welded portion, L2 is the length of the cross section from the welded portion to the end of the patchwork blank, H is the length of the punch side surface in the height direction at the completion of the forming process, and θ' is the angle that the punch side surface makes with a plane parallel to the punch flange surface, such that S > C × {(L1 + L2)・sinθ' - H} (where C > 0).

7. A manufacturing method according to claim 1, wherein the mold has a die configured to be accessible to the side surface of the punch from the outside in the width direction of the punch as the bending position adjustment means.

8. A manufacturing method according to claim 1, wherein the mold comprises a first mold and a second mold including the punch and the die as the bending position adjustment means, and the forming step comprises: a first step of bending the patchwork blank using the first mold to form the flange, and a step of cold pressing the patchwork blank using the second mold after the first step to form the vertical wall.

Images