METHOD FOR PRESS-FORMING METAL PLATE PARTS, AND METAL PLATE

Abstract

A press-forming method is provided that can further suppress cracks at the longitudinal end of a metal sheet part having a shape in which a convex ridge line portion on the top plate side and a concave ridge line portion on the outward flange side meet at the longitudinal end.The press-forming method is a press-forming method in which a target part shape (1) is formed by press-forming a convex ridge line portion (1D) on the top plate side (1A) and a concave ridge line portion (1E) on the outward flange side (1C) into a target part shape (1) in which the convex ridge line portion (1D) on the top plate side (1A) meets at the longitudinal end. The method includes a first press-forming step (11) of press-forming an intermediate part having an intermediate part shape (5) in which the vertical wall angle is larger than the vertical wall angle of the target part shape (1) and the convex ridge line portion (1D) and the concave ridge line portion (1E) meet at a longitudinal end portion where the meeting position is displaced toward the outward flange portion (1C) from the meeting position in the target part shape (1), and a second press-forming step (13) of press-forming the intermediate part into the target part shape (1).

Description

[Technical Field]

[0001] The present invention relates to a method for press-forming metal sheet parts such as automobile frame parts, and to a metal sheet that can be used in the press-forming. Here, the shape of the metal sheet part (target part shape) targeted by the present invention has a cross section including a top plate portion, a vertical wall portion, and an outward flange portion. The vertical wall portion is continuous in the width direction of the top plate portion via a first ridge portion. The outward flange portion is continuous with the longitudinal end of the vertical wall portion via a second ridge portion. Furthermore, the target part shape of the metal sheet part is a shape in which the first ridge portion and the second ridge portion each extend in the longitudinal direction and meet at least at one longitudinal end of the target part shape. The present invention also relates to a press-forming method that can effectively prevent cracks from occurring at the joining longitudinal end portions, even for metal sheet parts having such a target part shape. [Background technology]

[0002] To reduce the weight of the vehicle body and improve crash performance, there is a trend toward using ultra-high tensile steel (ultra-high tensile steel plate) for automotive frame parts. Ultra-high tensile steel is steel with a tensile strength of 780 MPa or more. While ultra-high tensile steel has high tensile strength, it also has the characteristic of reduced ductility. For this reason, when ultra-high tensile steel is used for press forming, there is an issue that cracks are likely to occur due to insufficient ductility. An example of a part shape that is difficult to press-form is a part that is used with its longitudinal direction aligned with the vehicle width direction. One such part is a floor cross member. The floor cross member is joined to other structural components, such as a center tunnel or side sills, via flanges. Such parts are used to suppress deformation of the vehicle body due to external forces, such as those caused by a side collision.

[0003] An example of the shape of a floor cross member is the shape of a press-formed body as described in Patent Document 1. The press-formed body has a generally groove-shaped cross section. The generally groove-shaped cross section includes a groove bottom, a ridge portion continuous with the groove bottom, and a vertical wall portion continuous with the ridge portion. The press-formed body also has an outward flange formed at its longitudinal end. The outward flange is formed over the ridge portion and at least a portion of the groove bottom and vertical wall portions on both sides of the ridge portion. Patent Document 1 also describes that the press-formed body is made of a high-tensile steel plate with a strength of 390 MPa or more. In such a press-formed body, deformation of the metal plate is concentrated between the outward flange portions continuous with the groove bottom and vertical wall portions during press forming. This poses a problem of the risk of stretch flange cracking due to insufficient ductility of the material.

[0004] Techniques for addressing such issues are described in Patent Documents 2 to 4. Patent Documents 2 to 4 propose press forming using a device that changes the position and timing at which a die comes into contact with a metal plate. The reason for changing the position and timing is to prevent deformation of the metal plate from concentrating at a specific location during press forming. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5569661 [Patent Document 2] Patent No. 5958644 [Patent Document 3] Patent No. 6648870 [Patent Document 4] Patent No. 7302747 Summary of the Invention [Problem to be solved by the invention]

[0006] The methods proposed in Patent Documents 1 to 4 are targeted at the following part shapes. That is, the part shape has a generally groove-shaped cross section having a groove bottom, a ridge line continuing from the groove bottom, and a vertical wall portion continuing from the ridge line. Furthermore, the part shape has an outward flange formed at the longitudinal end portion, over an area that extends to the ridge line and at least a portion of the groove bottom and the vertical wall portion on both sides.

[0007] However, as mentioned above, high-tensile steel sheets with a tensile strength exceeding 780 MPa tend to have insufficient ductility. Therefore, when such high-tensile steel sheets are used as materials, it is practically difficult to press-form parts having outward flanges with the above-mentioned shapes. In particular, it is difficult to avoid cracks near the ridges of the outward flanges. For this reason, the following part shape is often adopted instead of this part shape. This part shape has a top plate portion, a vertical wall portion that continues in the width direction of the top plate portion via a first ridge portion, and an outward flange portion that continues to the longitudinal end of the vertical wall portion via a second ridge portion. Furthermore, this part shape is such that the first ridge portion and the second ridge portion meet at the longitudinal end. Note that the first ridge portion has a convex cross-sectional shape. The second ridge portion has a concave cross-sectional shape.

[0008] However, even with this part shape, there is a concern that cracks may occur at the longitudinal end where the first ridge line and the second ridge line join. In particular, with high-tensile steel plates with a tensile strength of 780 MPa or more, even a reduction in plate thickness of a few percent increases the risk of cracking. In contrast, the methods proposed in Patent Documents 1 to 4 are considered insufficient as measures against cracking for part shapes like this. One reason for this insufficiency is that the part shapes they target are different.

[0009] The present invention has been made in light of the above-mentioned problems. The present invention is directed to a metal sheet part having a shape in which a first ridge line between a top plate portion and a vertical wall portion and a second ridge line between the vertical wall portion and an outward flange portion join at a longitudinal end portion. The present invention aims to provide a press-forming method that can further suppress cracks that occur at the longitudinal end portion of such a metal sheet part when it is manufactured by press-forming. [Means for solving the problem]

[0010] In order to solve the problem, one aspect of the present invention is a metal sheet component that has a cross section having a top plate portion, a vertical wall portion that is continuous with the top plate portion via a first ridge portion, and an outward flange portion that is continuous with the vertical wall portion via a second ridge portion, and that extends along a longitudinal direction that is a direction intersecting the cross section, and at least one longitudinal end side, the distance between the first ridge portion and the second ridge portion becomes smaller toward the longitudinal end, and the first ridge portion and the second ridge portion join at the longitudinal end, by press-forming a metal sheet into a metal sheet component having a target part shape. and a second press-forming process of press-forming the intermediate part into the target part shape. The press-forming method for a metal sheet part includes a first press-forming process of press-forming a metal sheet into an intermediate part having an intermediate part shape in which a vertical wall angle, which is the angle between the vertical wall portion and the top plate portion, is larger than the vertical wall angle of the target part shape, and in which, at a longitudinal end portion where the first ridge line portion and the second ridge line portion join, the joining position is displaced toward the outward flange portion from the joining position in the target part shape.

[0011] The target metal sheet to be press-formed is, for example, a metal sheet having a tensile strength of 780 MPa or more. [Effects of the Invention]

[0012] This aspect of the present invention is directed to a metal sheet part having a shape in which a first ridge line between a top plate portion and a vertical wall portion and a second ridge line between the vertical wall portion and an outward flange portion meet at a longitudinal end. The first ridge line has a convex cross-sectional shape. The second ridge line has a concave cross-sectional shape. This aspect of the present invention makes it possible to further suppress cracks at the longitudinal end portion that occur when manufacturing such a metal sheet part by press forming. Furthermore, this aspect of the present invention does not require the use of a special press forming device. This aspect of the present invention is particularly effective for steel sheets having a tensile strength of 780 MPa or more. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 2 is a perspective view illustrating a target part shape of a metal sheet part according to an embodiment based on the present invention. [Figure 2] FIG. 10 is a perspective view showing an example of a part shape that is not the subject of the present invention. [Figure 3] FIG. 10 is a perspective view showing an example of a part shape that is not the subject of the present invention. [Figure 4] FIG. 10 is a perspective view showing an example of a part shape that is not the subject of the present invention. [Figure 5] 1A to 1C are diagrams illustrating steps of press molding according to an embodiment of the present invention. [Figure 6] 1 is a perspective view showing an intermediate part shape according to an embodiment of the present invention, in which the dashed-dotted line indicates the position of the target part shape. [Figure 7] 1 is a cross-sectional view showing an intermediate part shape according to an embodiment of the present invention, in which the dashed-dotted line indicates the position of the target part shape. [Figure 8] FIG. 1 is a side view showing an intermediate part shape according to an embodiment of the present invention. [Figure 9] FIG. 10 is a side view showing another example of the shape of the intermediate part. [Figure 10] 1A to 1C are diagrams showing a target part shape in an example, in which (a) is a perspective view, (b) is a cross-sectional view, and (c) is a side view. [Figure 11] FIG. 1 is a diagram showing a processing flow in an embodiment. [Figure 12] 1A to 1C are diagrams showing the shape of an intermediate part in an embodiment, in which (a) is a perspective view, (b) is a cross-sectional view, and (c) is a side view. DETAILED DESCRIPTION OF THE INVENTION

[0014] Next, an embodiment of the present invention will be described with reference to the drawings. (target part shape) FIG. 1 is a perspective view showing an example of a target part shape 1 of a metal sheet part. The metal plate part is a press-formed product manufactured by press-forming a metal plate into a target part shape 1. 1, the target part shape 1 of this embodiment has a cross section including a top plate portion 1A, a vertical wall portion 1B, and an outward flange portion 1C. The target part shape 1 is in the shape of a longitudinal member extending in a longitudinal direction that intersects with the cross section. In this embodiment, a shape in which vertical wall portions 1B are present on both sides of the top plate portion 1A will be described as an example. However, the target part shape 1 may have a shape in which the vertical wall portion 1B and the outward flange portion 1C are present on only one side of the top plate portion 1A.

[0015] Here, the upper end of the vertical wall portion 1B is continuous with the widthwise end of the top plate portion 1A via a first ridge portion 1D. The first ridge portion 1D has an arc-shaped cross section that bulges outward. For this reason, in this specification, the first ridge portion 1D is also referred to as a convex ridge portion 1D. Furthermore, the lower end of the vertical wall portion 1B is continuous with an outward flange portion 1C via a second ridge portion 1E. The second ridge portion 1E has an arc-shaped cross section that is concave outward. For this reason, in this specification, the second ridge portion 1E is also referred to as a concave ridge portion 1E. The first ridgeline 1D and the second ridgeline 1E are bent portions, and the angle between the two portions that are continuous with each other via a bent portion is usually the angle on the concave side of the bent portion.

[0016] In the target part shape 1 of this embodiment, at one longitudinal end (the left side in FIG. 1), a convex ridge line portion 1D and a concave ridge line portion 1E each extend in the longitudinal direction. The distance between the convex ridge line portion 1D and the concave ridge line portion 1E decreases along the longitudinal direction toward the longitudinal end. The convex ridge line portion 1D and the concave ridge line portion 1E meet at the longitudinal end. In FIG. 1, the reference numeral 2 indicates the meeting point. The distance between the convex ridge line portion 1D and the concave ridge line portion 1E corresponds to the height of the vertical wall portion 1B. Furthermore, the outward flange portion 1C is connected to the recessed ridge portion 1E, so that if the recessed ridge portion 1E is inclined in side view, the outward flange portion 1C is also inclined in the same manner.

[0017] In this embodiment, a shape in which the convex ridge line portion 1D and the concave ridge line portion 1E join only at one end in the longitudinal direction is illustrated as an example. However, this is not limiting. The target part shape 1 may have a shape in which the convex ridge line portion 1D and the concave ridge line portion 1E join at both ends in the longitudinal direction. The concave ridge portion 1E rises toward the top plate portion 1A in side view toward the joining longitudinal end. In FIG. 1, the starting position 3 where the rise begins is located at the joining longitudinal end. However, the starting position 3 does not have to be at the longitudinal end. The starting position 3 may be located at the longitudinal center. The starting position 3 may also be located at the other longitudinal end. The gradient of the rise does not have to be constant along the rising direction.

[0018] The start position 3 is the position along the longitudinal direction where the change in the vertical extension direction begins. Of the recessed ridge portion 1E, the portion designated by the symbol 1Ea indicates the portion that slopes from the start position 3 toward the top plate portion 1A in side view. The start position 3 is also the starting point where the distance between the convex ridge portion 1D and the recessed ridge portion 1E decreases along the longitudinal direction toward the longitudinal end. Between the start position 3 and the joining position 2, the outward flange portion 1C is continuous with the longitudinal end of the vertical wall portion 1B via the recessed ridge portion 1E.

[0019] The target part shape 1 may have a shape that satisfies the following two conditions at the joining longitudinal end (left side in FIG. 1 ). The first condition is that the shape is such that the convex ridge line portion 1D and the concave ridge line portion 1E approach each other in the height direction of the vertical wall portion 1B as they approach the joining longitudinal end. The second condition is that the convex ridge line portion 1D and the concave ridge line portion 1E meet at the joining longitudinal end. In this embodiment, the location of the start position 3 is not particularly limited as long as the convex ridge line portion 1D and the concave ridge line portion 1E meet at the joining longitudinal end in a side view.

[0020] In this embodiment, the convex ridgeline portion 1D and the concave ridgeline portion 1E joining together refers to a state in which at least a portion of the convex ridgeline portion 1D and the concave ridgeline portion 1E overlap. In this embodiment, the mere contact between the convex ridgeline portion 1D and the concave ridgeline portion 1E does not constitute joining together. Here, in this specification, "arc-shaped" does not necessarily mean a cross-sectional shape that is a perfect circle, but may also be an elliptical arc. Furthermore, the junction of the end of the convex ridgeline portion 1D and the end of the concave ridgeline portion 1E does not have to be arc-shaped in cross section. This is because the shape of the junction is a shape where a concave ridgeline portion and a convex ridgeline portion join together. However, it is preferable that the junction and its vicinity have a cross section that does not have a steep curvature.

[0021] Furthermore, the target part shape 1 does not have to extend linearly along the longitudinal direction. It may have portions that curve in the vertical or horizontal directions (width direction of the top plate portion 1A) along the extension direction (longitudinal direction). FIG. 1 illustrates an example in which the top plate portion 1A and the convex ridge portion 1D in the target part shape 1 extend linearly in a side view. However, the top plate portion 1A and the convex ridge portion 1D do not have to extend linearly.

[0022] (Example of target part shape 1) The part shape shown in FIGS. 2 and 3 is an example of a part shape 1' that is not the subject of the present invention. In the part shape 1' in Fig. 2, the convex ridge 1D, the concave ridge 1E, and the outward flange 1C approach each other at the left longitudinal end. However, in the part shape 1' in Fig. 2, the left and right outward flanges 1C are connected to each other at the longitudinal end via the flange 1F at the longitudinal end. The flange 1F at the end extends in the width direction of the top plate 1A.

[0023] 3 has a flange portion 1F at the longitudinal end, similar to the part shape 1' shown in Fig. 2. However, in the part shape 1' in Fig. 3, the flange portion 1F at the end is bent so as to be closer to the surface of the top plate portion 1A. Here, the part shape 1' shown in Figures 2 and 3 has a large flange area that can be joined to a mating part. This is because it has end flange portions 1F that connect the left and right outward flange portions 1C. Therefore, this part shape 1' is a shape that improves vehicle performance in terms of crashworthiness and rigidity. However, if a metal plate with a tensile strength exceeding 780 MPa is used for this part shape 1', it is practically difficult to press-form it into a shape that fully satisfies vehicle performance due to the lack of ductility of the material.

[0024] FIG. 4 is also an example of a part shape 1' that is not the subject of the present invention. In the part shape 1' in Fig. 4, the convex ridge 1D, the concave ridge 1E, and the outward flange 1C approach each other toward the left longitudinal end. However, in the part shape 1' in Fig. 4, the convex ridge 1D and the concave ridge 1E do not merge and are separated toward the left longitudinal end. In this respect, the part shape 1' in Fig. 4 differs from the target part shape 1. The part shape 1' shown in Fig. 4 is simply a shape in which the convex ridge line portion 1D is bent during press forming. For this reason, the part shape 1' shown in Fig. 4 has a low risk of cracking at the longitudinal end portion.

[0025] (Press molding method) Next, a method for press-forming a metal sheet part having the target part shape 1 in this embodiment will be described. In this embodiment, as shown in Fig. 5, a metal plate is press-formed through at least two steps to manufacture a metal plate part 14 having a target part shape 1. The two steps are a first press-forming step 11 and a second press-forming step 13. Note that the forming method in each of the steps 11 and 13 may be bending or drawing, as long as the characteristics of the target part shape 1 formed in the first and second press-forming steps 11 and 13 are satisfied.

[0026] <First press forming process 11> The first press-forming step 11 is a step of press-forming a blank 10 into an intermediate part 12 having an intermediate part shape 5 . As shown by the solid lines in FIG. 6 , the basic shape of the intermediate part shape 5 is modeled after the target part shape 1. Specifically, like the target part shape 1, the intermediate part shape 5 has a cross section with a top plate portion, a vertical wall portion, and an outward flange portion. The intermediate part shape 5 is shaped like a longitudinal member extending in the longitudinal direction, which is a direction intersecting the cross section. The intermediate part shape 5 of this embodiment has a shape in which a convex ridgeline and a concave ridgeline join at the left longitudinal end. The basic dimensions of each part of the intermediate part shape 5 of this embodiment are the same as those of the target part shape 1. The basic dimensions of each part include the width of the top plate portion, the height of the vertical wall portion, and the width of the outward flange portion. For this reason, in this specification, the names and symbols of the parts of the intermediate part shape 5 will be described using the same names and symbols as those of the target part shape 1. However, the intermediate part shape 5 differs from the target part shape 1 in the following points.

[0027] 6 to 8, the dashed dotted lines indicate the target part shape 1. That is, the dashed dotted lines are lines for indicating the difference between the intermediate part shape 5 and the target part shape 1. As shown in FIG. 7, the vertical wall angle θ1 of intermediate part shape 5 is larger than the vertical wall angle θ0 of target part shape 1. The vertical wall angle is the angle between top plate portion 1A and vertical wall portion 1B. In other words, the angle between top plate portion 1A and vertical wall portion 1B of intermediate part shape 5, centered on the ridge line continuing from the widthwise end of top plate portion 1A, is set larger in the opening direction than that of target part shape 1, which is the final part shape. Note that the vertical wall angle is the angle taken on the inner surface side. The inner surface side is the concave side of convex ridge portion 1D. "θ1-θ0" is set to be in the range of 10 degrees to 60 degrees, for example, with the vertical wall angle θ1 being less than 180 degrees.

[0028] 6 and 8, the intermediate part shape 5 has the following shape at the longitudinal end where the convex ridge line portion 1D and the concave ridge line portion 1E join: That is, the joining position 2 is displaced toward the flange portion 1C from the joining position in the target part shape 1. The flange portion 1C side is the lower side in FIG. 8. In the intermediate part shape 5 of this embodiment, the convex ridge line portion 1D is bent midway along the longitudinal direction in a direction opposite to the protruding direction of the top plate portion 1A in a side view. The opposite direction is toward the flange portion 1C (the lower side in FIG. 1). As a result, the joining position 2 is shifted toward the flange portion 1C from the joining position 2 in the target part shape 1. In other words, the joining position 2 in the intermediate part shape 5 is shifted downward.

[0029] 8, reference numeral 6 indicates the starting point of the bending of the convex ridgeline portion 1D. At the left end of the starting point 6, the convex ridgeline portion 1D and the top plate portion 1A in the intermediate part shape 5 are located lower than the positions of the convex ridgeline portion 1D and the top plate portion 1A in the target part shape 1 in a side view. 6 to 8 show a state in which the intermediate part shape 5 and the target part shape 1 are aligned on the surface of the top plate portion on the right side of the starting point position 6, and the two shapes 1 and 5 are overlapped.

[0030] Here, there are optimal amounts for the starting point position 6 and the bending amount of the convex ridgeline portion 1D depending on the material, strength, and thickness of the metal plate used, as well as the target part shape. The bending amount is indicated, for example, by the amount of downward displacement of the joining position 2. For this reason, a preferred range for the starting point position 6 and the bending amount is determined by forming analysis using a computer such as CAE or by experiment. Then, the starting point position 6 and the bending amount can be appropriately selected from the preferred range.

[0031] 6 and 8 show an example of intermediate part shape 5 in which convex ridgeline portion 1D is bent so as to be inclined linearly from bending start point 6 to the left end, but is not limited to this. For example, as shown in FIG. 9, there are no particular limitations as long as the convex ridge portion 1D is displaced toward the outward flange portion 1C between the starting point 6 of the bend and the joining position 2 at the left end in a side view. For example, as shown in Figures 9(a) and 9(b), the convex ridgeline portion 1D may be bent in a manner that has multiple steps along the longitudinal direction between the starting point position 6 and the left end portion (joining position 2). Also, as shown in Figures 9(c) and 9(d), the convex ridgeline portion 1D may be bent in a curved shape between the starting point position 6 and the left end portion to form an intermediate part shape 5. The curve is formed by multiple bends.

[0032] Here, it is acceptable if the convex ridgeline portion 1D of the target product is not linear in the longitudinal direction of the part, but is curved along the way. Even in this case, the convex ridgeline portion 1D in the above range in the intermediate part shape 5 is set to be displaced toward the outward flange portion 1C compared to the final target part shape 1. This achieves the same effect. Here, a larger difference in area between the convex ridgeline portion 1D of the target part shape 1 and the convex ridgeline portion 1D of the intermediate part shape 5 at the end to the left of the starting point 6 in side view is effective when returning the intermediate part shape 5 to the target part shape 1 in the second press-forming process 13. Therefore, among the examples in Fig. 9, the shapes shown in Fig. 9(b) and Fig. 9(d) have a greater effect due to bending.

[0033] Furthermore, it is preferable that the radius of curvature of at least one of the convex ridgeline 1D and the concave ridgeline 1E in the intermediate part shape 5 is set to be smaller than the radius of curvature of the corresponding ridgeline in the target part shape 1. By making the radius of curvature of the ridgeline in the intermediate part shape 5 smaller than that in the final part shape, the line length of the end of the intermediate part 12 can be made longer than that in the target part shape 1. As a result, a greater crack suppression effect can be achieved. Here, the inclination angle of the upper surface of the outward flange portion 1C relative to the upper surface of the top plate portion 1A in the part shape is referred to as the flange inclination angle. The flange inclination angle is the angle on the concave side of the concave ridge portion 1E.

[0034] In this embodiment, the flange inclination angle in intermediate part shape 5 is set to be equal to the flange inclination angle in target part shape 1. For example, if the surface of top plate portion 1A and the surface of outward flange portion 1C are horizontal in target part shape 1, the surface of top plate portion 1A and the surface of outward flange portion 1C are also set to be horizontal in intermediate part shape 5. In this case, the flange inclination angle is 0 degrees. The flange angle difference is preferably set smaller than the vertical wall angle difference. Here, the difference in angle between the flange inclination angle in the intermediate part shape and the flange inclination angle in the target part shape is referred to as the flange angle difference. Furthermore, the difference in angle between the vertical wall angle θ1 in the intermediate part shape 5 and the vertical wall angle θ0 in the target part shape is referred to as the vertical wall angle difference.

[0035] In this way, it is preferable to increase the angle of the outward flange portion 1C of the intermediate part shape 5 by an amount that makes the vertical wall angle θ1 of the intermediate part shape 5 larger than the vertical wall angle θ0 of the target part shape 1. The angle of the flange portion 1C is the angle of the outer surface of the outward flange portion 1C relative to the vertical wall portion 1B. In this case, it is possible to more effectively suppress the occurrence of wrinkles in the outward flange portion 1C. Note that when the amount by which the vertical wall angle θ1 is increased is small, it is preferable to increase the angle of the flange portion 1C of the intermediate part shape 5 by an amount greater than the vertical wall angle difference. A small increase in the vertical wall angle θ1 occurs when the vertical wall angle difference is small.

[0036] <Second press forming process 13> The second press-forming process 13 is a process of press-forming the intermediate part 12 into a metal sheet part 14 having the target part shape 1. In the second press-forming process 13, for example, press-forming is performed using a mold that takes into account dimensional fluctuations due to elastic recovery after press-forming so that the target part shape 1 can be obtained. Here, in the second press-forming process 13, the elastic recovery of the metal sheet when it is released from the die may cause a deterioration in the dimensional accuracy of the part. For this reason, it is advisable to set the shape of the forming surface of the die, taking into account the change in shape due to the elastic recovery. The shape of the forming surface corresponds to the part shape at the bottom dead center of the forming. In this case, the expected shape is usually determined by prediction using computer simulation. Another method is to determine the expected shape by making corrections through trial and error based on the results of actual press forming.

[0037] <Other processes> The present invention is characterized by having at least the above-mentioned first and second press-forming steps 11 and 13. However, other steps may also be included depending on the final target part shape 1 to be achieved. Other processes include, for example, a cutting process (trim process) to shape the outer shape of the product, a punching process to open holes, etc. The holes formed are used to join other parts to the metal plate or to reduce weight. Such other steps are performed, for example, before the first press-molding step 11. Alternatively, the other steps are performed between the first press-molding step 11 and the second press-molding step 13. Alternatively, the other steps are performed after the second press-molding step 13, etc.

[0038] (Metal plate for pressing) The metal plate of the intermediate part shape 5 may be a metal plate for press-forming into the target part shape 1. By using the metal plate of the intermediate part shape 5 as a metal plate for press-forming, it is possible to more effectively suppress cracks at the longitudinal end portions. (Operation etc.) According to this embodiment, it is possible to further suppress cracks at the longitudinal ends. Cracks at the longitudinal ends occur when the metal sheet part 14 having the target part shape 1 is manufactured by press forming. Moreover, according to this embodiment, it is possible to manufacture the metal sheet part 14 having the target part shape 1 without using a special press forming device. This embodiment is particularly effective for steel sheets with low ductility and a tensile strength of 780 MPa or more.

[0039] (others) The present disclosure may also be configured as follows. (1) Disclosure 1 is a method for press-forming a metal sheet part, the method comprising: press-forming a metal sheet into a metal sheet part having a cross section with a top plate portion, a vertical wall portion continuing to the top plate portion via a first ridge portion, and an outward flange portion continuing to the vertical wall portion via a second ridge portion; the metal sheet part has a shape extending along a longitudinal direction that is a direction intersecting the cross section; and at least one longitudinal end side, the distance between the first ridge portion and the second ridge portion becomes smaller toward the longitudinal end, and the first ridge portion and the second ridge portion join at the longitudinal end, a first press-forming step of press-forming a metal plate into an intermediate part having an intermediate part shape in which a vertical wall angle, which is an angle formed by a vertical wall portion with respect to a top plate portion, is larger than the vertical wall angle of the target part shape, and a position where the first ridge line portion and the second ridge line portion join at a longitudinal end portion is displaced toward the outward flange portion relative to the position where the ridge line portions join in the target part shape; a second press-forming step of press-forming the intermediate part into the target part shape; A press forming method for a metal plate part, comprising: (2) In Disclosure 2, the first ridge portion of the intermediate part shape is bent toward the outward flange portion midway along the longitudinal direction in a side view, and the portion of the first ridge portion on the confluence side of the bent position is displaced toward the outward flange portion relative to the position of the first ridge portion in the target part shape. (3) In Disclosure 3, the intermediate part shape is set such that the radius of curvature of one or more ridge portions selected from the first ridge portion and the second ridge portion is smaller than the radius of curvature of the corresponding ridge portion in the target part shape. (4) In Disclosure 4, the difference in angle between the inclination angle of the outward flange portion relative to the surface of the top plate portion in the intermediate part shape and the inclination angle of the outward flange portion relative to the surface of the top plate portion in the target part shape is set to be smaller than the difference in angle between the vertical wall angle in the intermediate part shape and the vertical wall angle in the target part shape. (5) In Disclosure 5, the tensile strength of the metal plate is 780 MPa or more. (6) Disclosure 6 is a metal plate for producing, by press molding, a metal plate part having a target part shape, the metal plate part having a cross section with a top plate part, a vertical wall part continuing to the top plate part via a first ridge part, and an outward flange part continuing to the vertical wall part via a second ridge part, and a shape extending along a longitudinal direction that is a direction intersecting the cross section, and at least one longitudinal end side, the distance between the first ridge part and the second ridge part becomes smaller toward the longitudinal end, and the first ridge part and the second ridge part join at the longitudinal end, a vertical wall angle, which is the angle formed by the vertical wall portion with respect to the top plate portion, is larger than the vertical wall angle of the target part shape, and at a longitudinal end side where the first ridge line portion and the second ridge line portion join, the joining position is displaced toward the outward flange portion from the joining position in the target part shape, forming a plate shape. metal plate. (7) In Disclosure 7, the first ridge line portion is such that, in a side view, the top plate portion is bent toward the outward flange portion midway in the longitudinal direction, and the joining position is displaced toward the outward flange portion from the joining position in the target part shape. The metal plate according to Disclosure 6. [Example]

[0040] Next, an example based on this embodiment will be described. 10 is a diagram showing an example of the shape of a metal sheet part 14 that imitates a floor cross member as an automobile frame part. The part shape shown in this Fig. 10 was set as target part shape 1 in this example. Then, a press forming analysis based on the present embodiment was carried out using FEM, thereby verifying the effects of the present embodiment. The metal plate material used in the analysis was a hot-dip galvanized steel plate with a tensile strength of 1180 MPa. The thickness of the steel plate was 1.0 mm. The coefficient of friction between the die and the material was set to 0.15. The dimensions of each part are as shown in Figure 10.

[0041] In this example, the forming process based on the embodiment was carried out according to the process flow shown in Fig. 11. That is, in the material input 20, a rectangular material made of the metal plate was input into a press machine. Then, in the trimming process 21, the outer periphery of the rectangular metal plate was cut to obtain a plate having the target part shape 1. That is, the metal plate was shaped by this cutting, and a blank for pressing was produced. Next, in a first press-forming step 22, the blank for pressing was subjected to the first press-forming step 11 of this embodiment to produce an intermediate part 12. Subsequently, in a second press-forming step 23, the intermediate part 12 was subjected to the second press-forming step 13 of this embodiment to produce a final metal sheet part 14 having a shape as shown in FIG.

[0042] An intermediate part shape 5 in this embodiment is shown in FIG. In the first press-forming process 22 of the example, the vertical wall portion 1B was bent around the position of the first ridge portion 1D that is continuous with the width direction end portion of the top plate portion 1A, to produce an intermediate part 12 having the intermediate part shape 5. At this time, the vertical wall angle θ1 formed by the top plate portion 1A and the vertical wall portion 1B was set to an angle that was 30 degrees wider than the vertical wall angle θ0 of the target part shape 1. The vertical wall angle θ1 was 125 degrees. In this example, the flange portion 1C continuing from the vertical wall portion 1B in the intermediate part shape 5 was set to be parallel to the top plate portion 1A. In other words, the angle of the flange portion 1C relative to the vertical wall portion 1B was also set to be 30 degrees wider than the angle of the flange portion 1C in the target part shape 1.

[0043] In the first press-molding process 11, an intermediate part 12 having an intermediate part shape 5 is formed. In the intermediate part shape 5, the top plate portion 1A and the convex ridge portion 1D are bent toward the outward flange portion (downward) at the end of the part in the longitudinal direction. This shape is shown in Figure 12 (a) and (b). The symbol 6 indicates the bending position. In this example, nine conditions, Condition 2 to Condition 10, as shown in Table 1, were set as the bending conditions. Evaluation was performed for each condition. The variables of the bending conditions are distance L and bending amount h (see FIG. 12(b)). Distance L is the length from confluence position 2 to bending start position 6. Bend amount h is the downward displacement h (mm) of confluence position 2.

[0044] That is, in this example, the bending condition is expressed as a combination of the distance L (mm) and the downward displacement h (mm) of the joining position 2, as shown in Table 1. Condition 1 is a comparative example in which the amount of bending is set to zero (L=0, h=0). Analysis was also performed under this condition 1. The evaluation under condition 1 serves as the evaluation standard. As described above, condition 1 was set with no countermeasures. Furthermore, the distance L was set to three levels: 20, 70, and 120 mm. Furthermore, the amount of bending h was set to three levels: 1, 2, and 3 mm. Nine conditions were set with the distance L and amount h as variables. A total of 10 conditions were evaluated. The results are shown in Table 1.

[0045] [Table 1]

[0046] In the example, the part shape (target part shape 1) formed in the second press-forming process 23 was the same as the target part shape shown in FIG. Press forming analysis was performed under each of the above conditions. Evaluation was based on the thickness reduction rate of the part at the bottom dead center of the second press forming process 23. At this time, the maximum thickness reduction rate was determined at the longitudinal end of the part where the convex ridge line and the concave ridge line meet. The maximum thickness reduction rate was determined separately for both the left and right sides of the top plate portion. Next, the average value of the maximum thickness reduction rates at the left and right longitudinal end portions was determined. The determined average value was then used as the thickness reduction rate for evaluation.

[0047] Table 2 shows the evaluation results of each thickness reduction rate under Condition 1 where no countermeasure was taken, and Conditions 1 to 9 where the shape was changed to the level shown in Table 1. The thickness reduction rate is shown in %.

[0048] [Table 2]

[0049] As can be seen from Table 2, when no measures were taken (Condition 1), the sheet thickness reduction rate was 6.35%. This sheet thickness reduction rate is the sheet thickness reduction rate at the bottom dead center of forming in the second press forming process 23. In contrast, as can be seen from Table 2, an improvement in the plate thickness reduction rate was observed in eight of the nine conditions for the countermeasure method. Although not shown in Table 2, when the test was also carried out under the condition of L = 150 mm, the evaluation was similar to that for L = 120 mm.

[0050] On the other hand, under conditions such as Conditions 4 and 7 in Table 1, little improvement in the thickness reduction rate was observed, or even worse. These conditions involve a short distance L from the longitudinal end of the part, and a large bending amount h. In other words, under conditions where the convex ridgeline is bent sharply near the longitudinal end of the part, little improvement in the thickness reduction rate was observed, or even worse. This suggests that there is an appropriate bending amount h as a condition for crack suppression depending on the part shape and material.

[0051] For example, an optimal range of combinations of (L, h) can be determined by analysis, and the values ​​of L and h to be adopted can be set from within that range based on other conditions. In the case of Table 2, for example, L is in the range of 20 to 120 [mm] and h is in the range of 1 to 2 [mm]. Also, for example, when L is set to 70 mm or less, h is set to a small value of 1 to 2 mm, and when L is set to 120 to 150 mm, h is set to 2 to 3 mm. In this way, an appropriate range for h may be set individually depending on the range of L.

[0052] Also, for example, the settings are made to satisfy the following conditions. 0.2×H ≦ L ≦ 1.5×H 1 [mm] ≦ h ≦ 0.1 × H Here, H is the height of the vertical wall portion 1B (see FIG. 10(c)). In this embodiment, H is set to 100 mm. H may be a value at a position other than the longitudinal end side.

[0053] The above examples have revealed the following: Regarding cracks at the longitudinal end of the ridge of a metal sheet part 14 having a shape in which a convex ridge 1D and a concave ridge 1E join at the longitudinal end, appropriate bending conditions are set for the intermediate part shape. It has been found that this effectively suppresses cracks at the longitudinal end. Here, the range of the appropriate bending conditions (L, h) can be determined appropriately by computer-based forming analysis or experiments.

[0054] The entire contents of Japanese Patent Application No. 2024-174549 (filed October 3, 2024), from which this application claims priority, are incorporated herein by reference. While the present application has described a limited number of embodiments, the scope of the invention is not limited thereto, and modifications of each embodiment based on the above disclosure would be obvious to those skilled in the art. [Explanation of symbols]

[0055] 1. Target part shape 1A Top plate 1B Vertical wall section 1C Outward flange 1D First ridge (convex ridge) 1E Second ridge (concave ridge) 1F flange on end 3 Starting position 5. Intermediate part shape 6. Starting point of bending 11, 22 First press forming process 12 Intermediate parts 13, 23 Second press forming process 14 Metal plate parts L distance h Displacement θ0 Vertical wall angle in the target part shape θ1 Vertical wall angle in intermediate part shape

Claims

1. a metal plate part having a cross section including a top plate portion, a vertical wall portion continuing to the top plate portion via a first ridge portion, and an outward flange portion continuing to the vertical wall portion via a second ridge portion, the cross section extending along a longitudinal direction that is a direction intersecting the cross section, wherein at least one longitudinal end side, a distance between the first ridge portion and the second ridge portion becomes smaller toward the longitudinal end, and the first ridge portion and the second ridge portion join at the longitudinal end, the metal plate part being manufactured by press-forming a metal plate into a target part shape; a first press-forming step of press-forming a metal plate into an intermediate part having an intermediate part shape in which a vertical wall angle, which is an angle formed by a vertical wall portion with respect to a top plate portion, is larger than the vertical wall angle of the target part shape, and a position where the first ridge line portion and the second ridge line portion join at a longitudinal end portion is displaced toward the outward flange portion relative to the position where the ridge line portions join in the target part shape; a second press forming step of press-forming the intermediate part into the target part shape; A press forming method for a metal plate part, comprising:

2. the first ridge line portion of the intermediate part shape is bent toward the outward flange portion midway in the longitudinal direction in a side view, and a portion of the first ridge line portion on the merging position side of the bent position is displaced toward the outward flange portion side with respect to a position of the first ridge line portion in the target part shape; 2. A method for press-forming a metal sheet part according to claim 1.

3. the intermediate part shape has one or more ridge portions selected from the first ridge portion and the second ridge portion, the radii of curvature of which are set to be smaller than the radii of curvature of the corresponding ridge portions in the target part shape; 3. A method for press-forming a metal sheet part according to claim 1 or 2.

4. a difference in angle between the inclination angle of the outward flange portion relative to the surface of the top plate portion in the intermediate part shape and the inclination angle of the outward flange portion relative to the surface of the top plate portion in the target part shape is set to be smaller than a difference in angle between the vertical wall angle in the intermediate part shape and the vertical wall angle in the target part shape; 3. A method for press-forming a metal sheet part according to claim 1 or 2.

5. The tensile strength of the metal plate is 780 MPa or more.

3. A method for press-forming a metal sheet part according to claim 1 or 2.

6. A metal plate for producing, by press forming, a metal plate part having a target part shape, the metal plate part having a cross section including a top plate portion, a vertical wall portion continuing to the top plate portion via a first ridge portion, and an outward flange portion continuing to the vertical wall portion via a second ridge portion, the metal plate having a shape extending along a longitudinal direction that is a direction intersecting the cross section, wherein at least one longitudinal end side, the distance between the first ridge portion and the second ridge portion becomes smaller toward the longitudinal end, and the first ridge portion and the second ridge portion join at the longitudinal end, a vertical wall angle, which is the angle formed by the vertical wall portion with respect to the top plate portion, is larger than the vertical wall angle of the target part shape, and at a longitudinal end side where the first ridge line portion and the second ridge line portion join, the joining position is displaced toward the outward flange portion from the joining position in the target part shape, forming a plate shape. metal plate.

7. the top plate portion of the first ridge portion is bent toward the outward flange portion midway in the longitudinal direction in a side view, so that the joining position is displaced toward the outward flange portion with respect to the joining position in the target part shape. The metal plate according to claim 6.

Images