Manufacturing method of press-molded products

Abstract

To provide a method for manufacturing a press molding, which can sufficiently suppress wrinkles generated by shrunk flange deformation and can be applied to flexure molding.SOLUTION: The method for manufacturing a press molding is for manufacturing a press molding 1 targeting a shape of a press molding having a top plate 3 having a projected outer peripheral edge 3a and a longitudinal wall 5 connected to the top plate 3 via a punch shoulder R part 9,and comprises: a first molding step of forming a metal plate into an intermediate molding 15; and a second molding step of forming the intermediate molding 15 formed in the first molding step into the press molding 1 of the target shape. The intermediate molding 15 is configured such that the sectional curvature radius of the punch shoulder R part 29 is set larger than the targe shape and, in a part corresponding to at least the projected outer peripheral edge 3a of the top plate 3, the width of the top plate 27 is set wider than the target shape, and the R start position of the punch shoulder R part 29 on the top plate 27 side is separated more in the projecting direction of the projected outer peripheral edge 3a than the R opening position of the punch shoulder R part 9 of the target shape.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a press-formed product having a top plate portion and a vertical wall portion, and more particularly to a method for manufacturing a press-formed product that suppresses the occurrence of wrinkles associated with shrinkage flange deformation when forming the press-formed product. [Background technology]

[0002] As automobile crash safety standards become stricter, the crash safety of car bodies is being improved, but in response to carbon dioxide emission regulations, there is also a need to reduce the weight of car bodies in order to improve fuel efficiency and promote the shift to electric vehicles. In order to achieve both improved crash safety and reduced weight of car bodies, the use of high-strength steel sheets (also called high-tensile steel) of 590 MPa class or higher is becoming more common in car body structural parts. When press-forming high-tensile steel into car body structural parts, suppressing wrinkles caused by shrink flange deformation is an issue.

[0003] For example, some automobile parts have a top plate, a vertical wall, and a flange, such as an A-pillar upper, an A-pillar lower, or a bumper part. In such parts, when the outer periphery of the top plate or a part thereof is curved outwardly in a convex shape, the flange at that part may shrink and deform during press forming, causing wrinkles at the end of the flange. In particular, high-tensile steel is prone to buckling due to its high strength, and wrinkles are likely to occur. Similarly, parts that do not have a flange and are composed of a top plate and a vertical wall are prone to wrinkles at the end of the vertical wall due to shrink and flange deformation.

[0004] Therefore, Patent Document 1 discloses a method for manufacturing a press-formed product having a hat-shaped cross section in which the top plate and the flange are continuous in the width direction via the side wall, and the top plate and the flange have a curved portion that is curved convexly toward the top plate along the longitudinal direction. The method of Patent Document 1 has a step drawing process in which a wrinkle suppression region is set on the outer periphery of the flange position and forming is performed by step drawing, and further an additional region is set in part of the flange position where the wrinkles are pressed, thereby suppressing wrinkles that occur in the flange. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-034176 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, although the press molding method described in Patent Document 1 can suppress the occurrence of flange wrinkles, there is a problem in that it cannot be applied to press molding by bending (forming) because a wrinkle suppressor is used.

[0007] The present invention has been made to solve such problems, and aims to provide a manufacturing method for press-formed products that sufficiently suppresses wrinkles caused by shrinkage flange deformation and is also applicable to bending forming. [Means for solving the problem]

[0008] (1) A method for manufacturing a press-formed product according to the present invention is a method for manufacturing a press-formed product having a target shape including a top plate portion having a convex outer peripheral edge portion in which an outer peripheral edge or a part thereof is curved convexly outward, and a vertical wall portion continuing from the top plate portion via a punch shoulder R portion, The method comprises a first forming process in which a metal plate is formed into an intermediate formed product having a top plate portion having a convex outer peripheral edge portion and a vertical wall portion continuing from the top plate portion via a punch shoulder R portion, and a second forming process in which the intermediate formed product formed in the first forming process is formed into the press-formed product of a target shape, wherein the intermediate formed product has a radius of curvature of a cross-section of the punch shoulder R portion continuing from the convex outer peripheral edge portion that is larger than the radius of curvature of the cross-section of the punch shoulder R portion of the target shape, and the width of the top plate portion is wider than the target shape at least in a portion corresponding to the convex outer peripheral edge portion of the top plate portion, so that the R start position of the punch shoulder R portion on the top plate portion side is positioned away from the R start position of the punch shoulder R portion of the target shape in the convex direction of the convex outer peripheral edge portion.

[0009] (2) The manufacturing method of the press-formed product according to the present invention is a manufacturing method of a press-formed product for manufacturing a press-formed product having a target shape of an L-shaped cross-section part having a top plate portion having a convex outer peripheral edge portion in which an outer peripheral edge or a part thereof is curved convexly outward and a vertical wall portion continuing from the top plate portion via a punch shoulder R portion, or a Z-shaped cross-section part having a flange portion at a lower end of the vertical wall portion of the L-shaped cross-section part, This method is characterized by comprising: a first forming process in which a metal plate is press-formed into an intermediate formed product having a top plate portion with a convex outer peripheral edge portion and a vertical wall portion continuing from the top plate portion via a punch shoulder R portion, and in which the cross-sectional radius of curvature of the punch shoulder R portion continuing from the convex outer peripheral edge portion is larger than the cross-sectional radius of curvature of the punch shoulder R portion of a target shape; and a second forming process in which the intermediate formed product is placed on the punch with the R start position on the top plate portion side of the punch shoulder R portion of the intermediate formed product shifted in the convex direction of the convex outer peripheral edge portion from the R start position on the top plate forming portion side of the punch shoulder forming portion of the punch, and then press-formed into the target shape.

[0010] (3) Furthermore, in the above-mentioned (1) or (2), the first forming step is characterized in that drawing or bending is applied, and the second forming step is characterized in that bending is applied.

[0011] (4) Moreover, in the device according to any one of (1) to (3) above, the metal plate is a steel plate having a tensile strength of 590 MPa or more. Effect of the Invention

[0012] In the present invention, an intermediate molded product having a smaller amount of shrink flange deformation than the target shape is molded in the first molding process, and the intermediate molded product is molded into the target shape in the second molding process, so that material movement due to shrink flange deformation is less likely to occur in the second molding process, and wrinkles are less likely to occur. Therefore, the present invention can suppress an increase in plate thickness of a molded product having a target shape, and can obtain press-molded products having a good shape without wrinkles, which leads to improved yields in press molding. Furthermore, since the present invention does not require a blank holder, it is also applicable to bending. [Brief description of the drawings]

[0013] [Figure 1] 1 is an explanatory diagram of a method for manufacturing a press-molded product according to an embodiment of the present invention. FIG. [Diagram 2] 2A and 2B are explanatory diagrams of a part (target shape) targeted in the embodiment, where FIG. 2A is a perspective view and FIG. 2B is a plan view. [Diagram 3] FIG. 11 is a diagram showing a molding process in a second molding step in the embodiment (part 1). [Figure 4] FIG. 11 is a diagram showing a molding process in a second molding step in the embodiment (part 2). [Diagram 5] FIG. 4 is an explanatory diagram of the amount of material flowing in the first molding step and the second molding step. [Figure 6] FIG. 13 is a diagram showing a comparison of cross-sectional shapes of intermediate formed products in which the R start position (separation distance a) of the punch shoulder R portion is changed. [Figure 7] 1 is a graph showing the relationship between the distance a of the R start position of the punch shoulder R portion of the intermediate formed product and the amount of material flowing in each process. [Figure 8] FIG. 1 is a diagram showing a plate thickness increase rate distribution and a maximum plate thickness increase rate of a press-molded product manufactured by a conventional manufacturing method. [Figure 9] FIG. 1 is a diagram showing a molding process in a conventional manufacturing method (part 1). [Figure 10] FIG. 2 is a diagram showing the molding process in a conventional manufacturing method (part 2). [Figure 11] 11A and 11B are diagrams showing another example of a part (target shape) to which the present invention can be applied, where FIG. 11A is a perspective view and FIG. 11B is a plan view. [Figure 12] 12 is a diagram showing wrinkles that occur when the component in FIG. 11 is manufactured by a conventional manufacturing method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] A press-formed product, which is a target shape of the manufacturing method for a press-formed product according to this embodiment, will be described with reference to the example of FIG. In this specification, the target shape is not necessarily the final shape. In other words, after press molding into the target shape, the final shape may be obtained by adding necessary processing such as providing a bead shape to the top plate portion or trimming as necessary. Furthermore, after molding a hat cross-section part into the target shape, the part may be divided to produce two Z cross-section parts. 2 shows the whole or a characteristic part of the press-molded product. The press-molded product 1 shown in FIG. 2 has a top plate portion 3, a vertical wall portion 5, and a flange portion 7, and has a portion of the outer periphery of the top plate portion 3 that is curved outwardly in a convex shape (hereinafter referred to as "convex outer periphery portion 3a"). The boundary between the convex outer periphery portion 3a and other portions is, for example, limited to the R of the convex outer periphery portion 3a when the top plate portion 3 is viewed in plan. In addition, the angle between the top plate portion 3 and the vertical wall portion 5 of the press-molded product 1 of this example, and the angle between the vertical wall portion 5 and the flange portion 7 were both set to 90°.

[0015] The boundary between the top plate portion 3 and the vertical wall portion 5 in the press-formed product 1 has an R shape corresponding to the shape of the punch shoulder forming portion of the punch used in press forming, and therefore this portion is referred to as the "punch shoulder R portion 9." In addition, the boundary between the vertical wall portion 5 and the flange portion 7 has an R shape corresponding to the shape of the die shoulder forming portion of the die, and therefore this portion is referred to as the "die shoulder R portion 11." Hereinafter, when the terms "punch shoulder R portion 9" and "die shoulder R portion 11" are used simply in this specification, they refer to the above-mentioned portions on the press-formed product 1 side, not the die side.

[0016] First, before describing the method for producing a press-formed product according to the present embodiment, a problem that occurs when a press-formed product 1 as shown in FIG. 2 is press-formed by a conventional method will be described. FIG. 8 shows the results of an FEM analysis of a case where a press-formed product 1 is press-formed by a conventional method, and the distribution of the plate thickness increase rate is shown by color shading. The plate thickness increase rate is calculated by calculating the difference (plate thickness increment) between the plate thickness of the press-formed product 1 after press forming and the plate thickness of the blank before press forming, and expressed as a ratio (proportion) to the plate thickness of the blank, with a larger value indicating a greater increase in plate thickness. Furthermore, the more the plate thickness increases, the more likely wrinkles are to occur in that portion of the press-formed product 1. Furthermore, the more localized the plate thickness increase is, the more likely wrinkles are to occur.

[0017] When a press-formed product 1 as shown in FIG. 2 is formed by a conventional method, for example, a punch and a die having a shape corresponding to the target shape are used to form a flat blank into the target shape in one process. In this case, the vertical wall portion 5 connected to the convex outer peripheral edge portion 3a of the top plate portion 3 and the flange portion 7 connected to this vertical wall portion 5 are likely to shrink and deform, causing material to concentrate and increasing the plate thickness. In the case of the press-formed product 1 shown in FIG. 2, the plate thickness increased the most at the end of the flange portion 7 indicated by the arrow in FIG. 8, and the maximum plate thickness increase rate was +12.5%. In this way, the local increase in plate thickness causes wrinkles in the relevant portion, which is a problem. The reason why the plate thickness of the flange portion 7 increases locally as shown in FIG. 8 will be explained using FIG. 9 and FIG. 10.

[0018] 9 and 10 show the forming process when the press-formed product 1 is formed by the above-mentioned conventional manufacturing method. Figure 9 shows the deformation process of blank 13 in a front view (the upper view of Figure 9, seen from the direction of the arrow in Figure 2(b)) and a cross-sectional view (the lower view of Figure 9, corresponding to the AA' cross section in Figure 2(b)). 10 shows a top view, a front view (same as the front view in FIG. 9), and a side view of the deformation process of the blank 13. In FIG. 10, the die 23 is omitted in order to make the shape of the blank 13 easier to understand. In addition, numerical values ​​such as "10mmup" in the figure indicate the distance in the pressing direction between the punch 21 and the die 23, taking into account the sheet thickness of the blank 13. Therefore, "10mmup" indicates that the gap between the flange forming portion of the punch 21 and the flange forming portion of the die 23 is the sheet thickness of the blank 13 plus +10mm. Also, "0mmup" indicates the bottom dead center state of forming.

[0019] When the vertical wall portion 5 (see FIG. 2(a)) continuing from the convex outer peripheral edge portion 3a of the top plate portion 3 starts to be formed, for example, two large mountain-shaped wrinkles are generated at the end portion of the blank 13 due to shrink flange deformation, as shown in the front views of "10 mm up" in FIG. 9 and FIG. 10. As the shrink flange deformation progresses, these two large mountain-shaped wrinkles become concentrated in the center and take on a distinct shape (see the front views of "5 mm up" and "3 mm up" in FIG. 10).

[0020] As the forming process progresses, the die 23 descends and when the bottom surface of the die 23 reaches the top of the wrinkle, the forming process proceeds as if the die 23 were squashing the wrinkle. However, when the forming process reaches "1 mm up", the blank 13 is restrained with the wrinkles remaining, and the blank 13 reaches the bottom dead point of the forming process (see "0 mm up").

[0021] As described above, in the conventional forming process, large wrinkles occur in the gap between the punch 21 and the die 23, and the flange portion 7 is formed without completely squeezing these wrinkles, so wrinkles remain in the press-formed product 1 and the plate thickness of the wrinkled portion increases locally.

[0022] As a means for preventing wrinkles from occurring during the forming process, it is advisable to use a wrinkle suppressor at the portion corresponding to the flange portion 7, but this cannot be applied to bending that does not use a wrinkle suppressor.

[0023] The above-mentioned wrinkles due to the shrink flange deformation also occur in the case of a press-molded product 14 as shown in Fig. 11. The press-molded product 14 in Fig. 11 does not have a flange portion, and is composed of a top plate portion 3 and a vertical wall portion 5, and has a portion (convex outer peripheral edge portion 3a) where part of the outer peripheral edge of the top plate portion 3 is curved outwardly in a convex shape, similar to the press-molded product 1 in Fig. 2.

[0024] When a press-formed product 14 as shown in Figure 11 is produced by the conventional method, i.e., by using a punch and die shaped corresponding to the target shape to form a flat blank into the target shape in one process, wrinkles will occur at the end of the vertical wall portion 5 corresponding to the convex outer peripheral edge portion 3a of the top plate portion 3 (the portion surrounded by a dashed circle in the figure), as shown in Figure 12.

[0025] When formed in a single process, wrinkles occur in the flange portion 7 of the press-formed product 1 in Figure 2 and in the vertical wall portion 5 of the press-formed product 14 in Figure 11 because the material moves toward the convex curved portion in a concentrated manner due to shrinkage flange deformation. In order to prevent the concentration of the metal sheet in the convexly curved area due to the shrink flange deformation, it is advisable to change the deformation state of the metal sheet in the convexly curved area and disperse the strain during press forming without concentrating it locally. In addition, by forming an intermediate product to increase its rigidity and restrain free deformation, wrinkles are less likely to occur. Therefore, the inventors have studied a method for reducing the amount of shrink flange deformation in each step by using a two-step press forming method in which a target shape is formed via an intermediate product, and have devised a shape of the intermediate product that can form the product while suppressing the amount of shrink flange deformation, and can reduce the material movement in the shrink direction by generating an elongation material flow during the target forming. The method for manufacturing a press-molded product according to this embodiment is based on the above idea. Hereinafter, a specific description will be given of the case where the press-molded product 1 shown in Fig. 2 is molded as an example.

[0026] The manufacturing method of a press-formed product in this embodiment is a method of forming a press-formed product 1 as shown in Figure 2, and includes a first forming process of forming a blank 13 into an intermediate formed product 15, and a second forming process of forming the intermediate formed product 15 into the press-formed product 1, as shown in Figure 1.

[0027] FIG. 1(a) is a perspective view of a punch 17, a die 19 and a blank 13 before forming in the first forming step, and FIG. 1(b) is a cross-sectional view taken along line B of FIG. 1(a). FIG. 1(c) is a perspective view of a punch 21, a die 23 and an intermediate formed product 15 before forming in the second forming step, and FIG. 1(d) is a cross-sectional view taken along line C of FIG. 1(c). In addition, in each of the dies in Figs. 1(a) to 1(d), only the shape of the molding surface portion is shown as a plate, ignoring the thick portions. Each step will be described in detail below.

[0028] <First molding process> The first forming process is a process in which a blank 13, which is a metal plate, as shown in Figures 1(a) and 1(b) is press-formed into an intermediate formed product 15 (Figure 1(c)) which has a top plate portion 27 with a convex outer peripheral edge portion and a vertical wall portion 31 which continues from the top plate portion 27 via a punch shoulder R portion 29. The punch 17 used in the first forming step has a cross-sectional radius of curvature R 1 The cross-sectional radius of curvature R of the shoulder of the punch 21 having a shape corresponding to the target shape used in the second forming step 2 (R 1 >R 2 ).

[0029] 1(b), in the first forming step, the die 19 is moved relatively while part of the blank 13 is clamped between the upper surface of the top plate forming surface of the punch 17 and the pad 25 to form the intermediate formed product 15. This forms the intermediate formed product 15 in which the cross-sectional radius of curvature of the punch shoulder R portion 29 is larger than the cross-sectional radius of curvature of the punch shoulder R portion 9 of the target shape. In addition, the width of the top plate portion 27 of the intermediate product 15 is made wider than the width of the top plate portion 3 of the target shape. Therefore, the R start position on the top plate portion 27 side of the punch shoulder R portion 29 of the intermediate product 15 is located away from the R start position of the punch shoulder R portion 9 of the target shape (hereinafter referred to as the "target R start position") in the convex direction of the convex outer circumferential edge portion 3a.

[0030] Since the top plate portion 27 of the intermediate formed product 15 is wider than the target shape and the cross-sectional radius of curvature of the punch shoulder R portion 29 is larger than the target shape, it can be formed with a smaller amount of shrink flange deformation compared to when a flat blank 13 is formed into the target shape. Therefore, in the first forming step, the plate thickness of the end portion of the vertical wall portion 31 of the intermediate formed product 15 is unlikely to increase, and wrinkles are unlikely to occur.

[0031] <Second molding process> The second forming process is a process for forming the intermediate product 15 formed in the first forming process into a press-formed product 1 having a target shape. The punch 21 and die 23 in the second forming process have shapes corresponding to the target shape and are similar to the conventional mold shown in Fig. 9, so they are denoted by the same reference numerals.

[0032] 1(d), in the second forming step, a portion of the top plate portion 27 of the intermediate product 15 that corresponds to the top plate portion 3 of the target shape is set to match the upper surface of the punch 21. Specifically, a portion of the top plate portion 27 of the intermediate product 15 that corresponds to the R start position (target R start position) of the punch shoulder R portion 9 of the target shape is set to match the R start position of the punch shoulder forming portion of the punch 21. When the intermediate molded product 15 is set on the top plate molding surface of the punch 21, the portion of the intermediate molded product 15 from the punch shoulder R portion 29 to the vertical wall portion 31 is curved in the circumferential direction and separated from the vertical wall molding surface of the punch 21, resembling an open umbrella. In this state, the top plate 27 of the intermediate product 15 is clamped between the top plate forming surface of the punch 21 and the pad 25, and the die 23 is moved relatively to form the intermediate product 15 into a target shape. The molding process in the second molding step is shown in Figures 3 and 4.

[0033] In Fig. 3, the deformation process of the intermediate molded product 15 is shown in a front view and a cross-sectional view, similar to Fig. 9. In Fig. 4, the deformation process of the intermediate molded product 15 is shown in a top view, a front view, and a side view, similar to Fig. 10. The meaning of numerical values ​​such as "10mm up" and the omission of the die 23 from the top view, front view, and side view are also the same as in Fig. 10.

[0034] As shown in Fig. 3, when the shoulder of the die 23 comes into contact with the top plate 27 of the intermediate formed product 15 at "10 mm up," the intermediate formed product 15 starts to be formed into the vertical wall 5 of the target shape. In the conventional example, shrinkage flange deformation occurs during the formation of the vertical wall 5, resulting in large mountain-shaped wrinkles in the gap between the punch 21 and the die 23 (see "10 mm up" to "3 mm up" in Fig. 9). In contrast, in the second forming step of this embodiment, the lower part (the part corresponding to the flange part 7) of the vertical wall part 31 of the intermediate formed product 15 is located near the flange forming surface part of the punch 21, and no wrinkles are formed, regardless of the size of the gap between the punch 21 and the die 23. This is because the intermediate formed product 15 has a higher rigidity than the flat blank 13 due to work hardening, so the material of the vertical wall part 31 is less likely to move.

[0035] When the die 23 descends to "1 mm up," it begins to form the lower part of the vertical wall portion 31 into the die shoulder R portion 11 and flange portion 7 of the target shape. At this time, shrinkage flange deformation progresses in the area corresponding to the flange portion 7, making it easier for material to move. However, since the gap between the flange forming surface of the punch 21 and the flange forming surface of the die 23 at this point is small, at the plate thickness + 1 mm, the flange portion 7 reaches the bottom dead point of forming with almost no shrinkage flange deformation. Therefore, wrinkles are less likely to occur in the flange portion 7 of the press-formed product 1 after forming is completed.

[0036] In addition, the second forming process has the effect of dispersing the strain generated during the forming process without concentrating it locally, which further reduces the shrink flange deformation. This point will be explained with reference to FIG.

[0037] As shown in FIG. 4, in the “15 mm up” state, the die 23 has not yet come into contact with the intermediate molded product 15, and the portion of the intermediate molded product 15 from the punch shoulder R portion 29 to the vertical wall portion 31 has a shape resembling an open umbrella. When the die 23 is lowered from the "15 mm up" state, the die 23 comes into contact with the top plate portion 27 of the intermediate molded product 15 at "10 mm up," and as shown in the side view of "10 mm up," a bend occurs and the vertical wall portion 5 of the target shape begins to be formed.

[0038] In forming the vertical wall portion 5, the die 23 presses the curved punch shoulder R portion 29 and the vertical wall portion 31, and the forming proceeds while dispersing the strain occurring during forming in the circumferential direction. This causes a force that stretches the material in the circumferential direction to act against the shrink flange deformation and alleviates the material flow in the shrink direction, thereby further alleviating the shrink flange deformation.

[0039] In this way, due to the high rigidity of the intermediate molded product 15, material movement is less likely to occur during the molding process in the second molding step, and further, a material flow occurs that alleviates shrinkage flange deformation, so that the plate thickness of the flange portion 7 of the press-molded product 1 after molding is completed is less likely to increase.

[0040] As described above, in this embodiment, an intermediate formed product 15 with a small amount of shrinkage flange deformation is formed in the first forming process, and the intermediate formed product 15 is formed into the target shape in the second forming process, thereby eliminating the problem of localized increase in plate thickness and suppressing wrinkles that occur in the flange portion 7 of the press-formed product 1.

[0041] Furthermore, the manufacturing method of the press-formed product of this embodiment can suppress wrinkles in the flange portion 7 without using a blank holder, and is therefore applicable to press forming by bending (forming). That is, this is particularly effective when drawing or bending is applied in the first forming step for forming the intermediate product 15, and bending is applied in the second forming step for forming the target shape.

[0042] Furthermore, the method for manufacturing a press-formed product according to the present embodiment is particularly effective when using a high-strength steel sheet that is prone to wrinkles due to shrink flange deformation. For example, the blank, which is a metal sheet, may be a steel sheet having a tensile strength of 590 MPa or more, and in that case too, a sufficient wrinkle reduction effect can be achieved.

[0043] The above has been explained using the example of molding a press-molded product 1 having a flange portion 7 as shown in Figure 2, but wrinkles can also be reduced by a similar effect when molding a press-molded product 14 that does not have a flange portion as shown in Figures 11 and 12.

[0044] As described above, the manufacturing method of the press-formed product of this embodiment is designed to reduce wrinkles occurring in the press-formed product 1 by using the intermediate product 15 having a smaller amount of shrink flange deformation than the target shape. The amount of shrink flange deformation of this intermediate product 15 becomes smaller as the distance from the R start position of the punch shoulder R portion 29 to the target R start position (hereinafter, this will be referred to as "separation distance a") increases. This point will be further explained.

[0045] In Fig. 5(a), the cross-sectional shape of the blank 13 before forming in the first forming step is shown by a dashed line, and the cross-sectional shape of the intermediate formed product 15 at the bottom dead center after forming is shown by a solid line. Here, the distance from the end of the blank 13 to the end of the vertical wall portion 31 of the intermediate formed product 15 in Fig. 5(a) is defined as the amount of material flow in the first forming step. The amount of material flowing in this first forming step decreases as the distance a between the R start positions of the punch shoulder R portion 29 increases. A specific example is shown in FIG.

[0046] 6 shows the cross-sectional shapes of the intermediate formed product 15 when the cross-sectional radius of curvature of the punch shoulder R portion 29 is fixed at 8 mm and the separation distance a is set to 2 mm, 4 mm, 6 mm, and 8 mm, respectively, with respect to the target shape where the cross-sectional radius of curvature of the punch shoulder R portion 9 is 4 mm. The cross-sectional shapes of the above four examples are overlapped with the part that will be the R start position of the punch shoulder R portion 9 when formed into the target shape (target R start position). Also shown as a comparative example is a cross-sectional shape in which the cross-sectional radius of curvature of the punch shoulder R portion 29 is 8 mm, the same as the above four examples, but the R start position of the punch shoulder R portion 29 is the same position as the target R start position (separation distance a = 0 mm).

[0047] As shown in Fig. 6, when the cross-sectional radius of curvature of the punch shoulder R portion 29 is the same, the intermediate product 15 with a larger distance a from the R start position of the punch shoulder R portion 29 has an end portion of the vertical wall portion 31 located on the right side of the paper. In other words, it can be said that the intermediate product 15 with a larger distance a has a smaller amount of material inflow shown in Fig. 5(a). When the amount of material flow is small, the amount of shrinkage flange deformation in the first forming process is small, so by increasing the separation distance a of the punch shoulder R portion 29 of the intermediate formed product 15, the increase in plate thickness in the first forming process (the increase in plate thickness from the blank 13) can be reduced.

[0048] 5(b) shows the cross-sectional shape of the intermediate product 15 at the bottom dead center in the first forming step by a dashed line, and the cross-sectional shape of the press-formed product 1 at the bottom dead center in the second forming step by a solid line. Here, the distance from the end of the vertical wall portion 31 of the intermediate product 15 to the end of the flange portion 7 of the press-formed product 1 in FIG. 5(b) is defined as the amount of material flow in the second forming step. The amount of material flowing in the second forming step is greater for the intermediate formed product 15 having a larger distance a from the R start position of the punch shoulder R portion 29. If the amount of material flowing in is large, the amount of shrink flange deformation in the second forming step is large, so by increasing the distance a, the increase in plate thickness in the second forming step (the increase in plate thickness from the intermediate formed product 15) is increased.

[0049] As described above, the larger the distance a of the R start position of the punch shoulder R portion 29, the smaller the amount of material inflow in the first forming process and the larger the amount of material inflow in the second forming process. The relationship between the distance a and the amount of material inflow in each process for the five examples shown in Fig. 6 is shown in Fig. 7.

[0050] As shown in FIG. 7, as the distance a of the R start position of the punch shoulder R portion 29 is increased, the amount of material flowing in the first forming process is reduced and the increase in plate thickness is reduced, but the amount of material flowing in the second forming process is increased, resulting in an increase in plate thickness. Therefore, the present invention becomes more effective by setting the separation distance a so as to minimize the increase in plate thickness after the second forming process, while taking into consideration improving the rigidity of the intermediate formed product 15 and mitigating shrink flange deformation in the first forming process described above.

[0051] Note that the above describes the relationship between the separation distance a and the amount of material flowing in each process when the cross-sectional radius of curvature of the punch shoulder R portion 29 is constant, but the same applies when the cross-sectional radius of curvature of the punch shoulder R portion 29 of the intermediate molded product 15 is increased. The cross-sectional radius of curvature of the punch shoulder R portion 29 of the intermediate formed product 15 is preferably about 1.5 to 4 times the cross-sectional radius of curvature of the punch shoulder R portion 9 of the target shape.

[0052] The above embodiment is not limited to Z-shaped cross-section parts as shown in FIG. 2 or L-shaped cross-section parts as shown in FIG. 11, but can also be applied to U-shaped cross-section parts having a pair of vertical wall portions on both sides of the top plate portion, and hat-shaped cross-section parts further having a pair of flange portions. In addition, while the above describes a case in which the present invention is characterized by the shape of the intermediate molded product, when the target part is an L-shaped cross-section part or a Z-shaped cross-section part, the present invention can also be characterized as follows by the molding method, i.e., the molding manner in the first and second molding steps.

[0053] That is, the method includes a first forming process for forming an intermediate formed product 15, and a second forming process for placing the intermediate formed product 15 on a punch with the R start position of the punch shoulder R portion of the intermediate formed product 15 shifted in the convex direction of the convex outer peripheral edge portion from the R start position of the punch shoulder forming portion of the punch, and forming the intermediate formed product 1 into a press-formed product 1 of the target shape. The invention characterized in this way has many points in common with the invention described above, so each step will be described in detail with reference to the above-mentioned FIGS.

[0054] <1st molding process> The first forming step is a step of press-forming a blank 13, which is a metal plate, into an intermediate formed product 15. The punch 17 used in the first forming step has a cross-sectional radius of curvature R 1 The cross-sectional curvature radius R of the shoulder of the punch 21 having a shape corresponding to the target shape used in the second forming process 2 is greater than (R 1 >R 2 As a result, in the first forming step, an intermediate formed product 15 is formed which has a top plate portion 27 having a convex outer peripheral edge portion and a vertical wall portion 31 continuing from the top plate portion 27 via a punch shoulder R portion 29, and the cross-sectional radius of curvature of the punch shoulder R portion 29 is larger than the cross-sectional radius of curvature of the punch shoulder R portion 9 of the target shape.

[0055] Since the cross-sectional radius of curvature of the punch shoulder R portion 29 of the intermediate formed product 15 is larger than the target shape, it can be formed with a smaller amount of shrink flange deformation compared to when a conventional flat blank 13 is formed into a target shape. Therefore, in the first forming step, the plate thickness of the end portion of the intermediate formed product 15 is unlikely to increase, and wrinkles are unlikely to occur.

[0056] <Second molding process> The second forming process is a process for forming the intermediate product 15 formed in the first forming process into a press-formed product 1 having a target shape. The punch 21 and die 23 in the second forming process have shapes corresponding to the target shape, and are similar to the conventional mold shown in FIG.

[0057] In the second forming step, the intermediate product 15 is placed at a position where the R start position on the top plate portion 27 side of the punch shoulder R portion 29 is spaced apart in the convex direction of the convex outer peripheral edge portion 3a from the R start position on the top plate forming portion side of the punch shoulder forming portion of the punch 21. Therefore, when the intermediate product 15 is set on the upper surface of the punch 21, the portion of the intermediate product 15 from the punch shoulder R portion 29 to the vertical wall portion 31 is in an open umbrella-like state. In this state, the top plate portion 27 of the intermediate product 15 is clamped between the upper surface of the punch 21 and the pad 25, and the die 23 is moved relatively in the press forming direction to form the intermediate product 15 into the target shape. The state of the forming process in the second forming step is as shown in Figures 3 and 4, similar to the above.

[0058] As shown in Fig. 3, in the process of forming the intermediate product into a target shape, the lower part of the vertical wall part 31 of the intermediate product 15 (the part corresponding to the flange part 7) is located near the flange forming surface part of the punch 21, regardless of the size of the gap between the punch 21 and the die 23. Also, large mountain-shaped wrinkles that were generated in the forming process of the conventional example (Figs. 9 and 10) are not generated. This is because the intermediate product 15 has a higher rigidity than the flat blank 13 due to work hardening, so the material of the vertical wall part 31 is less likely to move.

[0059] When the die 23 descends to "1 mm up," the gap between the flange forming surface of the punch 21 and the flange forming surface of the die 23 is small, at the plate thickness + 1 mm, so the flange portion 7 shrinks almost to the point where it reaches the bottom dead point without deformation. Therefore, wrinkles are unlikely to occur in the flange portion 7 of the press-formed product 1 after forming is completed.

[0060] As shown in Fig. 4, the second forming step disperses the strain generated during the forming process without concentrating it locally, which further reduces the shrink flange deformation. That is, the intermediate formed product 15 has a shape resembling an open umbrella from the punch shoulder R portion 29 to the vertical wall portion 31, and the die 23 presses the curved punch shoulder R portion 29 and the vertical wall portion 31, so that forming proceeds while dispersing the strain generated during forming in the circumferential direction. This causes a force that stretches the material in the circumferential direction to act against the shrink flange deformation and reduces the material flow in the shrink direction, which further reduces the shrink flange deformation.

[0061] In this way, the intermediate product 15 has high rigidity and a material flow occurs that alleviates the shrinkage and deformation of the flange, so that the plate thickness of the flange portion 7 of the press-formed product 1 after forming is difficult to increase. EXAMPLES

[0062] A specific study was conducted using FEM analysis to examine the effect of suppressing wrinkles caused by shrink flange deformation in the manufacturing method for press-molded products of the present invention, and the results are described below. In this example, a steel plate having a thickness of 1.0 mm and a tensile strength of 980 MPa was used as a blank, and the press-formed product 1 in FIG. 2 was press-formed to a target shape. FEM analysis was performed on a conventional example in which the steel plate is formed into the target shape in one process and an example of the present invention in which the steel plate is formed into the target shape in two processes, and the maximum plate thickness increase rate of the shrink flange deformation area was obtained. Note that the analysis results of the conventional example are as explained in Figure 8, so the analysis results of the example of the present invention will be explained below.

[0063] In the present invention, for a target shape in which the cross-sectional radius of curvature of the punch shoulder R portion 9 is 4 mm, the cross-sectional radius of curvature of the punch shoulder R portion 29 of the intermediate formed product 15 is constant at 8 mm, and the distance a of the R start position of the punch shoulder R portion 29 is set to 2 mm, 4 mm, 6 mm, and 8 mm. FEM analysis was performed on four examples (see FIG. 6). The results are shown in Table 1. Note that both the maximum thickness increase rate of the intermediate formed product and the maximum thickness increase rate of the target formed product shown in Table 1 indicate the increase rate based on the thickness of the blank.

[0064] [Table 1]

[0065] As shown in Table 1, in the conventional example (No. 1), the maximum thickness increase rate of the target formed product (press-formed product 1) was 12.5%, whereas in the present invention examples (Nos. 2 to 5), the maximum thickness increase rate of the target formed product was all lower than in the conventional example. As a result, as described above, in this example, it was shown that the present invention can suppress flange wrinkles due to shrink flange deformation more than in the conventional example. As described above, wrinkles can be more effectively suppressed by setting the cross-sectional radius of curvature of the punch shoulder R portion 29 of the intermediate product 15 and the distance between the R start positions so as to minimize the increase in plate thickness of the target product after the second forming step. This point will be described in detail below.

[0066] As can be seen by comparing the maximum thickness increase rates of the intermediate products 15 Nos. 2 to 5, when the cross-sectional radius of curvature of the punch shoulder R portion 29 of the intermediate product 15 is constant, the maximum thickness increase rate of the intermediate product 15 in the first forming step decreases as the separation distance a of the R start position increases. This is because, as shown in Fig. 6, the intermediate product 15 with a larger separation distance a of the R start position has an end of the vertical wall portion 31 protruding to the right side of the paper, and the amount of material flowing in the first forming step (see Fig. 5(a)) decreases.

[0067] Also, as can be seen by comparing the maximum sheet thickness increase rates of the target molded products of No. 2 to No. 5, when the cross-sectional curvature radius of the punch shoulder R portion 29 of the intermediate molded product 15 is constant, the larger the separation distance a of the R start position, the smaller the maximum sheet thickness increase rate of the target molded product in the second molding process. Here, the maximum sheet thickness increase rate was the smallest for No. 5 with the largest separation distance a.

[0068] In this embodiment where the cross-sectional curvature radius of the punch shoulder R portion 29 is constant, the example with the largest separation distance a of the R start position had the lowest sheet thickness increase rate. Note that even when the cross-sectional curvature radius of the punch shoulder R portion 29 is increased, the material inflow amount in the first molding process can be reduced in the same manner as when the separation distance a is increased. Therefore, the separation distance a of the R start position of the punch shoulder R portion 29 of the intermediate molded product 15 or the cross-sectional curvature radius of the punch shoulder R portion 29 may be set so that the sheet thickness increase of the target molded product after the second molding process becomes as small as possible. As a result, the wrinkle suppression effect can be maximized, which is effective.

Explanation of Reference Numerals

[0069] 1 Press Molded Product (Target Shape) 3 Top Plate Portion 3a Convex Outer Peripheral Edge Portion 5 Vertical Wall Portion 7 Flange Portion 9 Punch Shoulder R Portion 11 Die Shoulder R Portion 13 Blank (Metal Sheet) 14 Press Molded Product (Another Example of Target Shape) 15 Intermediate Molded Product 17 Punch (First Molding Process) 19 Die (First Molding Process) 21 Punch (Second Molding Process or Conventional Example) 23 Die (Second Molding Process or Conventional Example) 25 Pad 27 Top Plate Portion (Intermediate Molded Product) 29 Punch Shoulder R Portion (Intermediate Molded Product) 31 Vertical Wall Portion (Intermediate Molded Product)

Claims

1. A method for manufacturing a press-formed product having a target shape including a top plate portion having a convex outer peripheral edge portion in which an outer peripheral edge or a part thereof is curved outwardly in a convex shape, and a vertical wall portion continuing from the top plate portion via a punch shoulder R portion, a first forming step of forming the metal plate into an intermediate formed product having a top plate portion having a convex outer peripheral edge portion and a vertical wall portion continuing from the top plate portion via a punch shoulder R portion; a second forming step of forming the intermediate product formed in the first forming step into the press-formed product having a target shape, a punch shoulder R portion of the punch cut portion having a width greater than that of the punch shoulder R portion of the target shape; and a punch shoulder R portion of the punch cut portion having a width greater than that of the target shape, at least in a portion of the top plate portion corresponding to the convex outer peripheral edge of the top plate portion.

2. A method for manufacturing a press-formed product, the method comprising the steps of: manufacturing a press-formed product having a target shape of an L-shaped cross-section part having a top plate part with a convex outer periphery part in which an outer periphery or a part thereof is curved outwardly in a convex shape; and a vertical wall part continuing from the top plate part via a punch shoulder R part; or a Z-shaped cross-section part having a flange part at a lower end of the vertical wall part of the L-shaped cross-section part, a first forming step in which a metal plate is press-formed into an intermediate formed product having a top plate portion having a convex outer peripheral edge portion and a vertical wall portion continuing from the top plate portion via a punch shoulder R portion, the cross-sectional radius of curvature of the punch shoulder R portion continuing to the convex outer peripheral edge portion being larger than the cross-sectional radius of curvature of the punch shoulder R portion of a target shape; a second forming process in which the intermediate formed product is placed on the punch with the R start position on the top plate portion side of the punch shoulder R portion of the intermediate formed product shifted in the convex direction of the convex outer peripheral edge portion from the R start position on the top plate forming portion side of the punch shoulder forming portion of the punch, and press-formed into a target shape.

3. The first forming step applies drawing or bending, The method for manufacturing a press-formed product according to claim 1 or 2, characterized in that the second forming step applies bending forming.

4. 3. The method for manufacturing a press-formed product according to claim 1, wherein the metal plate is a steel plate having a tensile strength of 590 MPa or more.

5. The method for manufacturing a press-formed product according to claim 3, characterized in that the metal plate is a steel plate having a tensile strength of 590 MPa or more.

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