Press forming method for metal plate component, and metal plate

Abstract

Provided is a press forming method capable of better suppressing cracking in a longitudinal direction end portion of a metal plate component having a shape in which a convex ridge line portion on a top plate portion side and a concave ridge line portion on an outward-facing flange portion side merge in the longitudinal direction end portion. In the press forming method, a convex ridge line portion (1D) on a top plate portion (1A) side and a concave ridge line portion (1E) on an outward-facing flange portion (1C) side are press formed to a target component shape (1) in which the convex ridge line portion (1D) and the concave ridge line portion (1E) merge in the longitudinal direction end portion. The method includes: a first press forming step (11) for press forming an intermediate component having an intermediate component shape (5) in which a vertical wall angle is greater than the vertical wall angle of the target component shape (1), and in which, in the longitudinal direction end portion where the convex ridge line portion (1D) and the concave ridge line portion (1E) merge, the merging position is displaced to the outward-facing flange portion (1C) side relative to the merging position in the target component shape (1); and a second press forming step (13) for press forming the intermediate component to the target component shape (1).

Description

Press forming method for metal sheet parts, and metal sheet

[0001] This invention relates to a press forming method for metal sheet parts such as automotive frame parts, and to a metal sheet usable in this press forming. Here, the shape of the metal sheet part targeted by this invention (target part shape) has a cross section having a top plate portion, a vertical wall portion, and an outward-facing flange portion. The vertical wall portion is continuous with the top plate portion in the width direction via a first ridge portion. The outward-facing 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 has a shape in which the first ridge portion and the second ridge portion each extend in the longitudinal direction and merge at least at one end in the longitudinal direction of the target part shape. This invention relates to a press forming method that can effectively suppress cracking at the merging longitudinal end, even for a metal sheet part with such a target part shape.

[0002] To reduce vehicle weight and improve crash performance, ultra-high-strength steel is increasingly being used for automotive structural components. Ultra-high-strength steel is defined as steel with a tensile strength of 780 MPa or higher. While ultra-high-strength steel possesses high tensile strength, it also has the characteristic of reduced ductility. Therefore, when ultra-high-strength steel is used as the material for press forming, there is a problem 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 oriented along the vehicle width. Such a part is, for example, a floor cross member. A floor cross member is a part that is joined to other structural components such as the center tunnel and side sills via a flange. Such parts are used, for example, to suppress deformation of the vehicle body from external forces caused by side collisions.

[0003] As an example of the shape of the floor cross member, for example, there is the shape of a press-formed body as described in Patent Document 1. The press-formed body has a substantially groove-shaped cross section. The substantially groove-shaped cross section has a groove bottom portion, a ridge line portion continuous with the groove bottom portion, and a vertical wall portion continuous with the ridge line portion. Further, the press-formed body has an outward flange formed at the longitudinal end portion. The outward flange is formed in a range covering the above-mentioned ridge line portion and at least a part of each of the groove bottom portions and vertical wall portions on both sides thereof. Further, Patent Document 1 describes that the material of the press-formed body is made of a high-tensile steel sheet of 390 MPa or more. In such a press-formed body, during press forming, the deformation of the metal sheet concentrates between the outward flange portions continuous with the groove bottom portion and the vertical wall portion. Accordingly, there is a problem that there is a possibility of occurrence of elongation flange cracking due to insufficient ductility of the material.

[0004] Technologies for such problems 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 the die contacts the metal sheet. Changing the above-mentioned position and timing is for preventing the deformation of the metal sheet from concentrating at a specific location during press forming.

[0005] Japanese Patent No. 5569661 Japanese Patent No. 5958644 Japanese Patent No. 6648870 Japanese Patent No. 7302747

[0006] The methods proposed in Patent Documents 1 to 4 are targeted at the following part shapes. That is, the part shape has a substantially groove-shaped cross section having a groove bottom portion, a ridge line portion continuous with the groove bottom portion, and a vertical wall portion continuous with the ridge line portion. Further, the part shape is a shape in which an outward flange is formed in a range covering the ridge line portion and at least a part of each of the groove bottom portions and vertical wall portions on both sides thereof at the longitudinal end portion.

[0007] However, high-tensile steel sheets with a tensile strength exceeding 780 MPa tend to lack ductility, as described above. Therefore, when such high-tensile steel sheets are used as the material, it is practically difficult to press-form a part shape with an outward-facing flange as described above. In particular, it is difficult to avoid cracking near the ridge of the outward-facing flange. For this reason, the following part shape is often adopted instead. This part shape has a top plate portion, a vertical wall portion that is continuous with the top plate portion in the width direction via a first ridge, and an outward-facing flange portion that is continuous with the longitudinal end of the vertical wall portion via a second ridge. Furthermore, in this part shape, the first ridge and the second ridge merge at the longitudinal end. The first ridge has a convex cross-section. The second ridge has a concave cross-section.

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

[0009] This invention was made in view of the above-mentioned problems. This invention relates to a metal plate part having a shape in which a first ridge between the top plate portion and the vertical wall portion and a second ridge between the vertical wall portion and the outward-facing flange portion merge at the longitudinal end. The object of this invention is to provide a press forming method that can more effectively suppress cracking at the longitudinal end of such a metal plate part that occurs when the metal plate part is manufactured by press forming.

[0010] To solve the problem, one aspect of the present invention provides a metal plate part having a cross-section comprising a top plate portion, a vertical wall portion continuous with the top plate portion via a first ridge portion, and an outward-facing flange portion continuous with the vertical wall portion via a second ridge portion, and extending along the longitudinal direction which intersects the cross-section, wherein at least one longitudinal end, the distance between the first ridge portion and the second ridge portion decreases towards the longitudinal end, and the first ridge portion and the second ridge portion merge at the longitudinal end to form a metal plate part with a target part shape, which is then press-formed from a metal plate. A press forming method for manufacturing metal sheet parts, comprising: a first press forming step of press forming a metal sheet into an intermediate part having an intermediate part shape in which the vertical wall angle, which is the angle formed by the vertical wall portion with respect to the top plate portion, is greater than the vertical wall angle of the target part shape, and at the longitudinal end side where the first ridge portion and the second ridge portion merge, the position where the merge occurs is displaced toward the outward flange portion than the position where the merge occurs in the target part shape; and a second press forming step of press forming the intermediate part into the target part shape.

[0011] The metal sheet to be press-formed is, for example, a metal sheet with a tensile strength of 780 MPa or higher.

[0012] One aspect of the present invention relates to a metal plate component having a shape in which a first ridge between the top plate portion and the vertical wall portion and a second ridge between the vertical wall portion and the outward-facing flange portion converge at the longitudinal end. The first ridge portion has a convex cross-section, and the second ridge portion has a concave cross-section. According to this aspect of the present invention, it is possible to further suppress cracking at the longitudinal end that occurs when such a metal plate component is manufactured by press forming. Moreover, according to this aspect of the present invention, it is not necessary to use a special press forming apparatus. This aspect of the present invention is particularly effective for steel plates with a tensile strength of 780 MPa or more.

[0013] This is a perspective view illustrating the target part shape of a metal plate part according to an embodiment of the present invention. This is a perspective view showing an example of a part shape that is not covered by diagram showing the press forming process according to an embodiment of the present invention. This is a perspective view showing the intermediate part shape according to an embodiment of the present invention. The dashed line indicates the position of the target part shape. This is a cross-sectional view showing the intermediate part shape according to an embodiment of the present invention. The dashed line indicates the position of the target part shape. This is a side view showing the intermediate part shape according to an embodiment of the present invention. This is a side view showing another example of the intermediate part shape. This is a diagram showing the target part shape in an embodiment. (a) is a perspective view, (b) is a cross-sectional view, and (c) is a side view. This is a diagram showing the processing flow in an embodiment. This is a diagram showing the intermediate part shape in an embodiment. (a) is a perspective view, (b) is a cross-sectional view, and (c) is a side view.

[0014] Next, embodiments of the present invention will be described with reference to the drawings. (Target part shape) Figure 1 is a perspective view showing an example of a target part shape 1 of a metal plate part. The metal plate part is a press-formed product manufactured by press-forming a metal plate into the target part shape 1. As shown in Figure 1, the target part shape 1 of this embodiment has a cross section having a top plate portion 1A, a vertical wall portion 1B, and an outward-facing flange portion 1C. Furthermore, the target part shape 1 is the shape of a longitudinal member that extends in the longitudinal direction, which is the direction intersecting its cross section. In this embodiment, a shape in which vertical wall portions 1B exist on both sides of the top plate portion 1A will be described as an example. However, the target part shape 1 may also have a vertical wall portion 1B and an outward-facing flange portion 1C 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 toward the outer surface. 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-facing flange portion 1C via a second ridge portion 1E. The second ridge portion 1E has an arc-shaped cross-section that is concave toward the outer surface. For this reason, in this specification, the second ridge portion 1E is also referred to as a concave ridge portion 1E. Note that the first ridge portion 1D and the second ridge portion 1E consist of bent portions. The angle between the two portions continuous via the bent portion is usually the angle on the concave side of the bent portion.

[0016] In this embodiment, the target part shape 1 has a convex ridge portion 1D and a concave ridge portion 1E extending in the longitudinal direction at one longitudinal end (left side in Figure 1). The distance between the convex ridge portion 1D and the concave ridge portion 1E decreases along the longitudinal direction towards the longitudinal end. The convex ridge portion 1D and the concave ridge portion 1E merge at the longitudinal end. In Figure 1, reference numeral 2 indicates the position of the merger. The distance between the convex ridge portion 1D and the concave ridge portion 1E corresponds to the height of the vertical wall portion 1B. The outward-facing flange portion 1C is connected to the concave ridge portion 1E. Therefore, in a side view, if the concave ridge portion 1E is inclined, the outward-facing flange portion 1C is also inclined in the same way.

[0017] In this embodiment, a shape is illustrated in which the convex ridge portion 1D and the concave ridge portion 1E merge only at one end in the longitudinal direction. However, it is not limited to this. The target part shape 1 may have a shape in which the convex ridge portion 1D and the concave ridge portion 1E merge at both ends in the longitudinal direction. The concave ridge portion 1E rises toward the top plate portion 1A side view toward the longitudinal end where it merges. In Figure 1, the starting position 3 where this rise begins is located toward the longitudinal end where it merges. However, the starting position 3 does not have to be on the longitudinal end side. The starting position 3 may be located toward the longitudinal center. Also, the starting position 3 may be located toward the other longitudinal end. Furthermore, the gradient of the rise does not have to be constant along the direction of rise.

[0018] The starting position 3 is the position where the change in the vertical extension direction begins along the longitudinal direction. Of the concave ridge portion 1E, the portion indicated by reference numeral 1Ea is the part that, in a side view, is inclined toward the top plate portion 1A from the starting position 3. The starting position 3 is also the starting point where the distance between the convex ridge portion 1D and the concave ridge portion 1E decreases along the longitudinal direction toward the longitudinal end. Furthermore, between the starting position 3 and the merging position 2, the outward-facing flange portion 1C has a shape that is continuous with the longitudinal end of the vertical wall portion 1B via the concave ridge portion 1E.

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

[0020] In this embodiment, the convex ridge portion 1D and the concave ridge portion 1E are said to merge, meaning that at least a portion of the convex ridge portion 1D and the concave ridge portion 1E overlap. In this embodiment, merely touching the convex ridge portion 1D and the concave ridge portion 1E does not constitute a merge. Here, in this specification, "arc-shaped" is not limited to a circular arc in cross-sectional shape, but may also be an elliptical arc, etc. Furthermore, the merging portion between the end of the convex ridge portion 1D and the end of the concave ridge portion 1E does not have to be an arc-shaped cross-section. This is because the shape of the merging portion is the shape of the merged concave ridge portion and the convex ridge portion. However, it is preferable that the merging portion and its vicinity have a cross-section without steep sections where the curvature becomes sharp.

[0021] Furthermore, the target part shape 1 does not necessarily have to extend in a straight line along its longitudinal direction. There may be curved portions along the extension direction (longitudinal direction) in the vertical or horizontal directions (width direction of the top plate portion 1A). Figure 1 illustrates a case where the top plate portion 1A and the convex ridge portion 1D of the target part shape 1 extend in a straight line when viewed from the side. However, the top plate portion 1A and the convex ridge portion 1D do not need to extend in a straight line.

[0022] (Examples other than target part shape 1) The part shapes shown in Figures 2 and 3 are examples of part shapes 1' that are not targeted by the present invention. In part shape 1' of Figure 2, at the left longitudinal end, the convex ridge portion 1D, the concave ridge portion 1E, and the outward-facing flange portion 1C move closer to each other as they approach the longitudinal end. However, in part shape 1' of Figure 2, at the longitudinal end, the left and right outward-facing flange portions 1C are continuous via the flange portion 1F on the longitudinal end side. The flange portion 1F on the end side extends in the width direction of the top plate portion 1A.

[0023] Furthermore, the part shape 1' in Figure 3 has a flange portion 1F on the longitudinal end side, similar to the part shape 1' shown in Figure 2. However, in the part shape 1' of Figure 3, the flange portion 1F on the end side is bent so that it is in a direction close to the surface of the top plate portion 1A. Here, the part shape 1' shown in Figures 2 and 3 has a large area of ​​flange portion that can be joined with the mating part. This is because it has an end-side flange portion 1F that connects the left and right outward-facing flange portions 1C. For this reason, this part shape 1' is a shape that improves vehicle performance in terms of impact resistance and rigidity. On the other hand, 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 insufficient ductility of the material.

[0024] Furthermore, Figure 4 is also an example of a part shape 1' that is not targeted by the present invention. In the part shape 1' of Figure 4, at the left longitudinal end, the convex ridge portion 1D, the concave ridge portion 1E, and the outward-facing flange portion 1C come closer together as you move towards the longitudinal end. However, in the part shape 1' of Figure 4, at the left longitudinal end, the convex ridge portion 1D and the concave ridge portion 1E are separated rather than merging. In this respect, the part shape 1' of Figure 4 is different from the target part shape 1. In the part shape 1' of Figure 4, the convex ridge portion 1D is simply a shape that undergoes bending during press forming. For this reason, the part shape 1' of Figure 4 inherently has a low risk of cracking at the longitudinal end.

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

[0026] <First Press Forming Process 11> The first press forming process 11 is a process of press forming the blank 10 into an intermediate part 12 of the intermediate part shape 5. As shown by the solid lines in Figure 6, the basic shape of the intermediate part shape 5 is the same as that of the target part shape 1. Specifically, the intermediate part shape 5 has a cross section having a top plate portion, a vertical wall portion, and an outward-facing flange portion, similar to the target part shape 1. The intermediate part shape 5 also has the shape of a longitudinal member that extends in the longitudinal direction, which is the direction intersecting its cross section. Furthermore, the intermediate part shape 5 of this embodiment has a shape in which a convex ridge portion and a concave ridge portion merge at the left longitudinal end. In addition, the dimensions of each basic part of the intermediate part shape 5 of this embodiment are the same as those of the target part shape 1. The dimensions of each basic part are the width of the top plate portion, the height of the vertical wall portion, and the width of the outward-facing flange portion. For this reason, in this specification, the names and reference numerals of each part of the intermediate part shape 5 are the same as those of the target part shape 1. However, the intermediate part shape 5 differs from the target part shape 1 in the following respects.

[0027] In Figures 6 to 8, the dashed-dotted lines represent the target part shape 1. That is, the dashed-dotted lines are used to show the difference between the intermediate part shape 5 and the target part shape 1. As shown in Figure 7, the vertical wall angle θ1 of the intermediate part shape 5 is greater than the vertical wall angle θ0 of the target part shape 1. The vertical wall angle is the angle formed by the vertical wall portion 1B with respect to the top plate portion 1A. In other words, the intermediate part shape 5 has a larger angle formed by the top plate portion 1A and the vertical wall portion 1B in the opening direction than the final part shape, the target part shape 1, with respect to the ridge line that is continuous with the widthwise end of the top plate portion 1A as the axis. The vertical wall angle is the angle taken on the inner side. The inner side is the concave side of the convex ridge line portion 1D. "θ1-θ0" is, for example, in the range of 10 degrees to 60 degrees. However, the vertical wall angle θ1 is less than 180 degrees.

[0028] Furthermore, as shown in Figures 6 and 8, the intermediate part shape 5 has the following shape at the longitudinal end where the convex ridge portion 1D and the concave ridge portion 1E merge. That is, the merging position 2 is displaced toward the flange portion 1C side compared to the merging position in the target part shape 1. In Figure 8, the flange portion 1C side is the lower side. In this embodiment, the intermediate part shape 5 has a convex ridge portion 1D that, in a side view, bends in the opposite direction to the direction in which the top plate portion 1A protrudes, midway along the longitudinal direction. The opposite direction is toward the flange portion 1C side (the lower side in Figure 1). As a result, the merging position 2 is displaced toward the flange portion 1C side compared to the merging position 2 in the target part shape 1. In other words, the merging position 2 in the intermediate part shape 5 is displaced toward the lower side.

[0029] As shown in Figure 8, reference numeral 6 indicates the starting point of the bend in the convex ridge portion 1D. At the left end of the starting point 6, the convex ridge portion 1D and the top plate portion 1A of the intermediate part shape 5 are located lower in a side view than the positions of the convex ridge portion 1D and the top plate portion 1A of the target part shape 1. Figures 6 to 8 show the intermediate part shape 5 and the target part shape 1 aligned on the top plate portion to the right of the starting point 6, with both shapes 1 and 5 superimposed.

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

[0031] Furthermore, Figures 6 and 8 illustrate an intermediate part shape 5 in which the convex ridge portion 1D is bent linearly from the starting point 6 of the bend to the left end. However, it is not limited to this. For example, as shown in Figure 9, there is no particular limitation 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 confluence point 2 at the left end in a side view. For example, as shown in Figures 9(a) and (b), the convex ridge portion 1D may be bent in a manner that has multiple steps along the longitudinal direction between the starting point 6 and the left end (confluence point 2). Alternatively, as shown in Figures 9(c) and (d), the convex ridge portion 1D may be bent in a curved manner between the starting point 6 and the left end, forming an intermediate part shape 5. Note that the curve is formed by multiple bends.

[0032] Here, it is also acceptable if the convex ridge portion 1D of the target product is not straight in the longitudinal direction of the part, but has a curved shape. Even in that case, the convex ridge portion 1D in the above range of the intermediate part shape 5 is set to be displaced toward the outward flange portion 1C side compared to the final target part shape 1. This will produce a similar effect. Here, in a side view, the wider the difference in area between the convex ridge portion 1D of the target part shape 1 and the convex ridge portion 1D of the intermediate part shape 5 at the left end of the starting position 6, the more effective it is 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 Figure 9, the shapes shown in Figure 9(b) and Figure 9(d) show a greater effect due to bending.

[0033] Furthermore, it is preferable that the radius of curvature of at least one of the convex ridge portion 1D and concave ridge portion 1E of the intermediate part shape 5 is set to be smaller than the radius of curvature of the corresponding ridge portion in the target part shape 1. By making the radius of curvature of the ridge portion in the intermediate part shape 5 smaller than that of the final part shape, the wire length of the end of the intermediate part 12 can be made longer than that of the target part shape 1. As a result, a greater crack suppression effect can be obtained. Here, the angle of inclination of the upper surface of the outward-facing flange portion 1C with respect 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 of the intermediate part shape 5 is set to the same angle as the flange inclination angle of the target part shape 1. For example, if the surface of the top plate portion 1A and the surface of the outward flange portion 1C are horizontal planes in the target part shape 1, then the surface of the top plate portion 1A and the surface of the outward flange portion 1C are also set to be horizontal planes in the intermediate part shape 5. In this case, the flange inclination angle is 0 degrees. Furthermore, it is preferable to set the flange angle difference to be smaller than the vertical wall angle difference. Here, the difference in angle between the flange inclination angle of the intermediate part shape and the flange inclination angle of the target part shape is referred to as the flange angle difference. Also, the difference in angle between the vertical wall angle θ1 of the intermediate part shape 5 and the vertical wall angle θ0 of the target part shape is referred to as the vertical wall angle difference.

[0035] Thus, it is preferable that the angle of the outward-facing flange portion 1C of the intermediate part shape 5 is increased in proportion to the amount by which the vertical wall angle θ1 of the intermediate part shape 5 is increased compared to 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-facing flange portion 1C relative to the vertical wall portion 1B. In this case, wrinkle formation in the outward-facing flange portion 1C can be suppressed more effectively. Note that if 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 more than the difference in vertical wall angles. If the amount by which the vertical wall angle θ1 is increased is small, then the difference in vertical wall angles 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 with the target part shape 1. In the second press forming process 13, for example, press forming is performed using a die that takes into account the dimensional change 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, it is conceivable that the dimensional accuracy of the part may deteriorate due to the elastic recovery of the metal sheet when the die is released. For this reason, it is advisable to set the molding surface shape of the die taking into account the shape change due to the elastic recovery. The molding surface shape corresponds to the part shape at the bottom dead center of forming. At this time, the expected shape is usually predicted and determined by computer simulation. Alternatively, there is a method of determining 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 first and second press forming processes 11 and 13 described above. However, other processes may be included depending on the final target part shape 1. Other processes include, for example, a cutting process (trim process) to shape the outer shape of the product and a hole punching process to make holes. The formed holes are used for joining other parts to the metal plate or for weight reduction. Such other processes may be performed, for example, before the first press forming process 11. Alternatively, the other processes may be performed between the first press forming process 11 and the second press forming process 13. Alternatively, the other processes may be performed after the second press forming process 13, etc.

[0038] (Metal sheet for pressing) The metal sheet with the intermediate part shape 5 described above may also be used as a metal sheet for press forming into the target part shape 1 described above. By using the metal sheet with the intermediate part shape 5 as a metal sheet for press forming, it becomes possible to more effectively suppress cracking at the longitudinal ends. (Operation and other aspects) According to this embodiment, it becomes possible to further suppress cracking at the longitudinal ends. Cracking at the longitudinal ends is a crack that occurs when manufacturing the metal sheet part 14 of the target part shape 1 by press forming. Moreover, according to this embodiment, it becomes possible to manufacture the metal sheet part 14 of the target part shape 1 without using a special press forming apparatus. This embodiment is particularly effective for steel sheets with low ductility and a tensile strength of 780 MPa or more.

[0039] (Other) This disclosure may also be configured as follows: (1) Disclosure 1 is a press forming method for a metal sheet part, wherein the metal sheet part has a cross section having a top plate portion, a vertical wall portion continuous with the top plate portion via a first ridge portion, and an outward-facing flange portion continuous with the vertical wall portion via a second ridge portion, and has a shape that extends along the longitudinal direction which intersects the cross section, and at least one longitudinal end side, the distance between the first ridge portion and the second ridge portion decreases as it approaches the longitudinal end, and the first ridge portion and the second ridge portion merge at the longitudinal end to form a target part shape, and is manufactured by press forming a metal sheet part, A method for press forming a metal plate part, comprising: a first press forming step of press forming a metal plate into an intermediate part having an intermediate part shape in which the vertical wall angle, which is the angle formed by the vertical wall portion with respect to the top plate portion, is greater than the vertical wall angle of the target part shape, and at the longitudinal end side where the first ridge portion and the second ridge portion merge, the position where they merge is displaced toward the outward flange portion than the position where they merge in the target part shape; and a second press forming step of press forming the intermediate part into the target part shape. (2) Disclosure 2 is that, in a side view, the first ridge portion of the intermediate part shape bends toward the outward flange portion in the middle of the longitudinal direction, and the portion on the side of the bend that is toward the merging position is displaced toward the outward flange portion than the position of the first ridge portion in the target part shape. (3) Disclosure 3 states that the intermediate part shape is configured such that the radius of curvature of one or more ridges selected from the first ridge and the second ridge is set to be smaller than the radius of curvature of the corresponding ridge in the target part shape. (4) Disclosure 4 states that the difference in angle between the inclination angle of the outward-facing flange portion with respect to the surface of the top plate portion in the intermediate part shape and the inclination angle of the outward-facing flange portion with respect 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) Disclosure 5 states that the tensile strength of the metal plate is 780 MPa or more.(6) Disclosure 6 is a metal sheet for press forming to manufacture a metal sheet part having a shape that extends along the longitudinal direction which intersects the cross-section, wherein at least one longitudinal end side, the distance between the first ridge and the second ridge decreases as it approaches the longitudinal end, and the first ridge and the second ridge merge at the longitudinal end, wherein the vertical wall angle, which is the angle made by the vertical wall with respect to the top plate, is greater than the vertical wall angle of the target part shape, and the position where the first ridge and the second ridge merge at the longitudinal end side is displaced toward the outward flange side than the position where the merge occurs in the target part shape. (7) Disclosure 7 is a metal plate as described in Disclosure 6, wherein, in a side view, the first ridge portion is bent toward the outward flange portion in the middle of the longitudinal direction, so that the confluence point is displaced toward the outward flange portion than the confluence point in the target part shape.

[0040] Next, an embodiment based on this embodiment will be described. Figure 10 shows an example of the shape of a metal plate part 14 that mimics a floor cross member as an automotive frame component. The part shape shown in Figure 10 was designated as the target part shape 1 in this embodiment. Then, a press forming analysis using FEM was performed on the press forming based on this embodiment. This verified the effectiveness of this embodiment. The metal plate material used in the analysis was a hot-dip galvanized steel sheet with a tensile strength of 1180 MPa. The thickness of the steel sheet was 1.0 mm. The coefficient of friction between the mold and the material was set to 0.15. The dimensions of each part are as shown in Figure 10.

[0041] In this embodiment, the molding process based on the embodiment was carried out using the processing flow shown in Figure 11. Specifically, as material input 20, a rectangular material made of the above-mentioned metal plate was fed into the press equipment. Then, in the trimming process 21, the outer periphery of the rectangular metal plate was cut to form a plate with the target part shape 1. In other words, the metal plate was shaped by this cutting to produce a blank for pressing. Next, in the first press forming process 22, the first press forming process 11 of this embodiment was performed on the blank for pressing to manufacture an intermediate part 12. Subsequently, in the second press forming process 23, the second press forming process 13 of this embodiment was performed on the intermediate part 12 to manufacture a final metal plate part 14 with the shape shown in Figure 10.

[0042] Figure 12 shows the intermediate part shape 5 in the embodiment. In the first press forming step 22 of the embodiment, the vertical wall portion 1B was bent and formed around the position of the first ridge portion 1D, which is continuous with the widthwise end of the top plate portion 1A, to manufacture the intermediate part 12 of 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 30 degrees wider than the vertical wall angle θ0 in the target part shape 1. The vertical wall angle θ1 is 125 degrees. In this embodiment, the flange portion 1C continuous with the vertical wall portion 1B in the intermediate part shape 5 was set to be parallel to the top plate portion 1A. That is, the angle of the flange portion 1C with respect to the vertical wall portion 1B was similarly set to an angle 30 degrees wider than the angle of the flange portion 1C in the target part shape 1.

[0043] In the first press forming process 11, the intermediate part 12 of the 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 outward toward the outward flange portion side (downward side) at the longitudinal end of the part. This shape is shown in Figures 12(a) and 12(b). Reference numeral 6 indicates the bending position. In this embodiment, nine different bending conditions, conditions 2 to 10, as shown in Table 1, were set. An evaluation was then performed for each condition. The variables for the bending conditions are distance L and bending amount h (see Figure 12(b)). Distance L is the length from the confluence position 2 to the bending starting point position 6. Bending amount h is the downward displacement h (mm) of the confluence position 2.

[0044] That is, in this embodiment, as shown in Table 1, the bending conditions were expressed as a combination of the distance L (mm) and the displacement amount h (mm) downward at the confluence position 2. Note that Condition 1 is a comparative example in which the bending amount was set to zero (L = 0, h = 0). Analysis was also performed for this Condition 1. The evaluation of Condition 1 serves as the evaluation criterion. As described above, Condition 1 without countermeasures was set. Also, the distance L was set at three levels of 20, 70, and 120 mm. Further, the bending amount h was set at three levels of 1, 2, and 3 mm. Then, nine conditions were set with the distance L and the amount h as variables. A total of 10 conditions described above were evaluated. The results are shown in Table 1.

[0045]

[0046] Note that the part shape (target part shape 1) formed in the second press forming step 23 in the embodiment was the same shape as the target part shape shown in FIG. 10. Press forming analysis was performed for each of the above conditions. The evaluation was made based on the sheet thickness reduction rate of the part at the bottom dead center of the second press forming step 23. At this time, the maximum sheet thickness reduction rate at the end of the part in the longitudinal direction where the convex ridge line part and the concave ridge line part merge was obtained. The maximum sheet thickness reduction rate was obtained individually on both the left and right sides sandwiching the top plate part. Next, the average value of the maximum sheet thickness reduction rate values at the left and right longitudinal ends was obtained. Then, the obtained average value was used as the sheet thickness reduction rate for evaluation.

[0047] Table 2 shows the evaluation results of the sheet thickness reduction rates in Condition 1 without countermeasures and Conditions 1 to 9 in which the shape was changed at the levels shown in Table 1. Note that the sheet thickness reduction rate is shown in %.

[0048]

[0049] As can be seen from Table 2, in the case without countermeasures (Condition 1), the plate thickness reduction rate was 6.35%. This plate thickness reduction rate is the rate of plate thickness reduction at the bottom dead center of 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 8 out of the 9 countermeasures. Although not shown in Table 2, when the condition L = 150 mm was also implemented, the evaluation was similar to that of L = 120 mm.

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

[0051] For example, analysis can be used to determine a suitable range of (L, h) combinations. Then, within that range, the values ​​of L and h to be adopted can be set based on other conditions. In the case of Table 2, for example, L is set to the range of 20 to 120 [mm] and h is set to the range of 1 to 2 [mm]. Also, for example, if L is 70 mm or less, h is reduced to 1 to 2 mm, and if L is 120 to 150 mm, h is set to 2 to 3 mm. In this way, an appropriate range for h can be set individually according to the range of L.

[0052] Furthermore, for example, the following conditions are set to be satisfied: 0.2 × H ≤ L ≤ 1.5 × H 1 [mm] ≤ h ≤ 0.1 × H Here, H is the height of the vertical wall section 1B (see Figure 10(c)). In this embodiment, H was set to 100 mm. H can be a value used at any position other than the longitudinal end.

[0053] From the above examples, the following was found: For metal plate parts 14 having a shape in which a convex ridge portion 1D and a concave ridge portion 1E meet at the longitudinal end, appropriate bending conditions are set for the intermediate part shape to prevent cracking at the longitudinal end of the ridge portion. It was found that this effectively suppresses cracking at the longitudinal end. Here, the range of the appropriate bending conditions (L, h) can be appropriately determined by forming analysis using a computer or by experimentation.

[0054] Herein, the entire contents of Japanese Patent Application No. 2024-174549 (filed October 3, 2024), on which this application claims priority, constitute part of this disclosure by reference. While a limited number of embodiments have been described here with reference, the scope of the rights is not limited thereto, and modifications of each embodiment based on the above disclosure will be obvious to those skilled in the art.

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

Claims

1. A method for press forming a metal sheet part, wherein the metal sheet is press-formed to produce a metal sheet part having a cross-section comprising a top plate portion, a vertical wall portion continuous with the top plate portion via a first ridge portion, and an outward-facing flange portion continuous with the vertical wall portion via a second ridge portion, and the shape extends along the longitudinal direction which intersects the cross-section, and at least one longitudinal end, the distance between the first ridge portion and the second ridge portion decreases towards the longitudinal end, and the first ridge portion and the second ridge portion merge at the longitudinal end to form a target part shape, A press forming method for a metal plate part, comprising: a first press forming step of press forming a metal plate into an intermediate part having an intermediate part shape in which the vertical wall angle formed by the vertical wall portion with respect to the top plate portion is greater than the vertical wall angle of the target part shape, and at the longitudinal end side where the first ridge portion and the second ridge portion merge, the position where the merge occurs is displaced toward the outward flange portion than the position where the merge occurs in the target part shape; and a second press forming step of press forming the intermediate part into the target part shape.

2. The press forming method for a metal plate part according to claim 1, wherein, in a side view, the first ridge of the intermediate part shape bends toward the outward-facing flange part in the middle of the longitudinal direction, and the portion on the side of the confluence point beyond the bending point is displaced toward the outward-facing flange part than the position of the first ridge in the target part shape.

3. The intermediate part shape is characterized in that the radius of curvature of one or more ridges selected from the first ridge and the second ridge is set to be smaller than the radius of curvature of the corresponding ridge in the target part shape, according to the press forming method for a metal sheet part as described in claim 1 or claim 2.

4. A press forming method for a metal plate part according to any one of claims 1 to 3, wherein the difference in angle between the inclination angle of the outward-facing flange portion with respect to the surface of the top plate portion in the intermediate part shape and the inclination angle of the outward-facing flange portion with respect 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. A press forming method for a metal sheet part according to any one of claims 1 to 4, wherein the tensile strength of the metal sheet is 780 MPa or more.

6. A metal sheet for press forming to manufacture a metal sheet part having a cross-section comprising a top plate portion, a vertical wall portion continuous with the top plate portion via a first ridge portion, and an outward-facing flange portion continuous with the vertical wall portion via a second ridge portion, and having a shape that extends along the longitudinal direction which intersects the cross-section, wherein at least one longitudinal end side, the distance between the first ridge portion and the second ridge portion decreases as it approaches the longitudinal end, and the first ridge portion and the second ridge portion merge at the longitudinal end, wherein the vertical wall angle, which is the angle formed by the vertical wall portion with respect to the top plate portion, is greater than the vertical wall angle of the target part shape, and the position where the first ridge portion and the second ridge portion merge at the longitudinal end side is displaced toward the outward-facing flange portion than the position where they merge in the target part shape.

7. The metal plate according to claim 6, wherein, in a side view, the first ridge portion is displaced towards the outward flange portion because the top plate portion bends toward the outward flange portion portion midway along the longitudinal direction, so that the confluence point is displaced toward the outward flange portion portion than the confluence point in the target part shape.

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