EP4616971A1

EP4616971A1 - Method for manufacturing press-molded article

Info

Publication number: EP4616971A1
Application number: EP23906384.5A
Authority: EP
Inventors: Hiroyuki Tanaka
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2022-12-23
Filing date: 2023-09-07
Publication date: 2025-09-17
Also published as: EP4616971A4; WO2024135007A1; JP7794118B2; JP2024090336A; MX2025007347A; CN120322298A; KR20250111186A

Abstract

A press-formed product manufacturing method according to the present invention is a method of manufacturing a press-formed product having a top plate 1 and a vertical wall 5 continuous with the top plate 1 via a ridge 3. The method includes a first step of forming a metal sheet blank into an intermediate press-formed product 17 having an intermediate top plate 21 provided with a convex/concave portion 29 and an intermediate vertical wall 25 continuous with the intermediate top plate 21 via an intermediate ridge 23, and a second step of crushing the convex/concave portion 29 of the intermediate press-formed product 17 to form the press-formed product. In the second step, a material flow generated by crushing the convex/concave portion 29 pushes out a material corresponding to the intermediate ridge 23 toward the vertical wall 5 to cause reverse bending of a portion that has been the intermediate ridge 23.

Description

Field

The present invention relates to a method of manufacturing a press-formed product having a preferable shape close to a target shape by suppressing a spring-back in which an angle between a top plate and a vertical wall increases after releasing from a die in press-forming a vehicle body component or the like.

Background

Collision safety of a vehicle body is improving in line with the tightening of vehicle collision safety standards and it is also necessary to reduce the weight of the vehicle body under recent carbon dioxide emission regulations. In order to achieve both collision safety performance and weight reduction of the vehicle body, a metal sheet having higher strength than a conventional metal sheet is being adopted in the vehicle body. Most recently, ultrahigh tensile steel sheets of 1.5 GPa or more have been adopted.
Since these steel sheets have significantly high strength, a stress generated at the time of press-forming is large, and a large spring-back occurs at a die release. As a result, a steel sheet is likely to significantly deviate from a target shape. Therefore, many measures for suppressing the spring-back have been adopted. In particular, with respect to a spring-back with respect to an increase of a punch shoulder inner angle (larger angle between a top plate and a vertical wall), press-forming methods in Patent Literatures 1 and 2 are disclosed.
Patent Literature 1 discloses a method of widening a punch width in a second press-forming than a punch width in the first press-forming. By increasing the punch width in the second press-forming, reverse bending deformation can be applied to a wall of the press-formed product obtained by the first press-forming. Thus, an increase of the punch shoulder inner angle due to the spring-back can be reduced. Patent Literature 2 discloses a method of press-forming a workpiece while pushing a die-side pad against the workpiece in a state a punch-side pad projects outward (die side). In this method, the workpiece is formed while being loosened, and a loosened portion is crushed at a forming bottom dead center, so that a spring-back and a spring-go of the workpiece can be balanced. Thus, an increase of the punch shoulder inner angle due to the spring-back can be prevented.

Citation List

Patent Literature

Patent Literature 1: JP 2007-111725 A
Patent Literature 2: 2010-082660 A

Summary

Technical Problem

However, when these methods are used, there is a problem that a press-formed product has a poor appearance in addition to insufficient suppression of a spring-back. In particular, in Patent Literature 1, since the punch width in the second press-forming is wider than the punch width in the first press-forming, a forming mark on a ridge between a top plate and a vertical wall in a press-formed product obtained by the first press-forming is likely to remain on the top plate of a target press-formed product. Thus, the target press-formed product has a poor appearance. Also in Patent Literature 2, when a cross-sectional line length of a workpiece is longer than a target shape, the punch shoulder easily breaks. When the cross-sectional line length is short, the punch shoulder angle does not become the target shape.
The present invention has been made in view of the above problems, and an object of the present invention is to provide a press-formed product manufacturing method capable of efficiently obtaining a press-formed product having a good appearance while suppressing a spring-back caused by press-forming of a vehicle body component. Solution to Problem
To solve the above-described problem and achieve the object, (1) a press-formed product manufacturing method according to the present invention manufactures a press-formed product including a top plate and a vertical wall continuous with the top plate via a ridge, and includes: a first step of forming a metal sheet blank into an intermediate press-formed product including an intermediate top plate, and an intermediate vertical wall continuous with the intermediate top plate via an intermediate ridge, the intermediate top plate being provided with a convex/concave portion extending in a direction same as an extending direction of the intermediate ridge, the convex/concave portion having at least a convex or concave ridge-orthogonal cross-sectional shape; and a second step of crushing the convex/concave portion of the intermediate press-formed product to form the press-formed product, wherein the crushing of the convex/concave portion in the second step generates a material flow, and the material flow pushes out a material corresponding to the intermediate ridge toward the vertical wall to cause reverse bending of a portion that has been the intermediate ridge.
(2) In the above-described press-formed product manufacturing method according to the invention (1), the press-formed product is a hat-shaped cross-section component or a U-shaped cross-section component having a pair of vertical walls on both sides of the top plate.
(3) The above-described press-formed product manufacturing method according to the invention (2) further includes a dividing step of cutting and dividing the top plate of the hat-shaped cross-section component or the U-shaped cross-section component formed in the second step in an extending direction of the ridge to acquire two Z-shaped cross-section components or two L-shaped cross-section components.
(4) In the above-described press-formed product manufacturing method according to the invention (3), the top plate is cut out at one side or both sides, in a ridge direction, of a portion where the convex/concave portion is provided, and the dividing step includes dividing the top plate by cutting and removing a cut-out portion of the top plate.
(5) In the above-described press-formed product manufacturing method according to the invention (1), the press-formed product is a Z-shaped cross-section component or an L-shaped cross-section component having the vertical wall only on one side of the top plate, and the second step includes restraining, during forming, an end of the intermediate top plate of the intermediate press-formed product on a side without the intermediate vertical wall. Advantageous Effects of Invention
A press-formed product manufacturing method according to the present invention is capable of manufacturing a press-formed product with good dimensional accuracy in which a spring-back is suppressed without impairing an appearance of the press-formed product made of a high-strength metal sheet. Further, by manufacturing a vehicle body using the above press-formed product, it is possible to achieve both collision safety performance and weight reduction of the vehicle body.

Brief Description of Drawings

[FIG. 1] FIG. 1 is an explanatory diagram illustrating a press-formed product manufacturing method according to a first embodiment.
[FIG. 2] FIG. 2 is a diagram illustrating an example of a target press-formed product of the present invention.
[FIG. 3] FIG. 3(a) is a diagram illustrating a ridge-orthogonal cross section near an intermediate ridge at a forming bottom dead center in a first step, and is an explanatory diagram illustrating a stress generated at a portion indicated by gray in the drawing. FIG. 3(b) is a diagram illustrating a cross section near the ridge at the forming bottom dead center in a second step, and is an explanatory diagram illustrating a material flow in the second step and a stress generated in a portion indicated by gray in the drawing.
[FIG. 4] FIG. 4 is a diagram illustrating a stress distribution on an outer side of the target press-formed product at the forming bottom dead center in the second step obtained by performing an FEM analysis on the manufacturing method according to the first embodiment, and is a diagram illustrating a ridge-orthogonal cross-sectional shape of the target press-formed product after a die release.
[FIG. 5] FIG. 5 is an explanatory diagram illustrating a press-formed product manufacturing method according to a second embodiment, and is a perspective view of an intermediate press-formed product and a target press-formed product when an L-shaped cross-section component is a target shape.
[FIG. 6] FIG. 6 is a diagram illustrating a press-forming method of forming the intermediate press-formed product in FIG. 5(a) into the L-shaped cross-section component in FIG. 5(b) in the second step according to the second embodiment.
[FIG. 7] FIG. 7 is a perspective view of the intermediate press-formed product and the target press-formed product when a Z-shaped cross-section component is a target shape according to the second embodiment.
[FIG. 8] FIG. 8 is a diagram illustrating a stress distribution on an outer side of the target press-formed product at the forming bottom dead center in the second step obtained by performing the FEM analysis on the manufacturing method according to the second embodiment, and is a diagram illustrating a ridge-orthogonal cross-sectional shape of the target press-formed product after a die release.
[FIG. 9] FIG. 9 is a diagram illustrating a stress distribution on the outer side of the target press-formed product at the forming bottom dead center obtained by performing the FEM analysis on a conventional manufacturing method, and is a diagram illustrating a ridge-orthogonal cross-sectional shape of the target press-formed product after a die release.

Description of Embodiments

(First embodiment)

A press-formed product manufacturing method according to a first embodiment of the present invention is a method of manufacturing a press-formed product having a top plate and a vertical wall continuous with the top plate via a ridge. FIG. 2 illustrates an example of the press-formed product applicable to the present invention.
FIG. 2(a) is a diagram illustrating an example of a hat-shaped cross-section component 9 including a top plate 1 and a pair of vertical walls 5 each continuous with both sides of the top plate 1 via a ridge 3. Each of the pair of the vertical walls 5 has a flange 7 at a lower end. FIG. 2(b) is a diagram illustrating an example of a U-shaped cross-section component 11 including the top plate 1 and the pair of vertical walls 5 each continuous with both sides of the top plate 1 via the ridge 3. Each of the pair of vertical walls 5 does not have the flange 7 at the lower end.
FIG. 2(c) is a diagram illustrating an example of a Z-shaped cross-section component 13 as a press-formed product having the top plate 1 and one vertical wall 5 continuous with one side of the top plate 1 via the ridge 3. FIG. 2(d) is a diagram illustrating an example of an L-shaped cross-section component 15 as a press-formed product having the top plate 1 and one vertical wall 5 continuous with one side of the top plate 1 via the ridge 3. The press-formed product manufacturing method of the present invention is applicable to any of the press-formed products illustrated in FIGS. 2(a) to 2(d).
Prior to the description of the present embodiment, problems in manufacturing each press-formed product illustrated in FIG. 2 will be described with reference to FIG. 9. FIG. 9 illustrates only a half of the top plate 1 of the hat-shaped cross-section component 9 or the U-shaped cross-section component 11 obtained by dividing the top plate 1 into two along the extending direction of the ridge 3. FIG. 9(a-1) is a diagram illustrating a stress distribution on an outer side at a forming bottom dead center by performing an FEM analysis of the press-forming of the hat-shaped cross-section component 9 illustrated in FIG. 2(a). The stress illustrated here is a stress in a direction orthogonal to the extending direction of the ridge 3 of the hat-shaped cross-section component 9, and also in a direction along an outer surface. FIG. 9(a-2) is a diagram of the hat-shaped cross-section component 9 in FIG. 9(a-1), illustrating a ridge-orthogonal cross-sectional shape after a die release by a solid line and a ridge-orthogonal cross-sectional shape at the forming bottom dead center by a broken line.
Similarly, FIG. 9(b-1) is a diagram illustrating a stress distribution on the outer side at the forming bottom dead center by performing the FEM analysis of the press-forming of the U-shaped cross-section component 11 illustrated in FIG. 2(b). The stress illustrated here is a stress in a direction orthogonal to the extending direction of the ridge 3 of the U-shaped cross-section component 11 and in a direction along the outer surface. FIG. 9(b-2) is a diagram of the U-shaped cross-section component 11, illustrating a ridge-orthogonal cross-sectional shape after a die release by a solid line and a ridge-orthogonal cross-sectional shape at the forming bottom dead center by a broken line.
In FIGS. 9(a-1) and 9(b-1), a tensile stress is generated in a light-colored portion, and a compressive stress is generated in a dark-colored portion. As illustrated in FIGS. 9(a-1) and 9(b-1), when the hat-shaped cross-section component 9 and the U-shaped cross-section component 11 are press-formed, the tensile stress is generated on an outer side of the ridge 3 in line with bending deformation, and the compressive stress is generated on an inner side of the ridge 3.
Therefore, when the press-formed component is released from the die, the tensile stress generated on the outer side of the ridge 3 and the compressive stress generated on the inner side act to cause spring-back. As illustrated in FIGS. 9(a-2) and 9(b-2), an inner angle θ₂ of the ridge 3 after the die release becomes larger than a target angle θ₁.
Therefore, in order to bring the inner angle θ₂ of the ridge 3 after the die release close to the target angle θ₁, the inventor of the present invention has studied to apply an equivalent stress to the vicinity of the ridge 3 to offset the stress caused by the bending deformation of the ridge 3. By applying the compressive stress to the outer side and the tensile stress to the inner side in the vicinity of the ridge 3, it is considered that the spring-back can be suppressed by offsetting the tensile stress on the outer side and the compressive stress on the inner side caused by bending. For this reason, the inventor has conceived that by pushing out a material of the ridge 3 bent toward the vertical wall 5, the stress as described above can be generated in a pushed-out portion.
In other words, by pushing out the material of the ridge 3, after bending, toward the flat vertical wall 5, the bent portion is bent back. In this bent-back portion, the compressive stress on the outer side and the tensile stress on the inner side are generated. Therefore, since stresses opposite to the stresses (tensile stress on outer side and compressive stress on inner side) generated in the ridge 3 can be generated in the vicinity of the ridge 3 (upper part of the vertical wall 5), both stresses are offset and the spring-back hardly occurs.
Hereafter, a method of manufacturing the hat-shaped cross-section component or the U-shaped cross-section component by press-forming will be described. FIGS. 1(a) and 1(b) illustrate an example of a manufacturing process when the hat-shaped cross-section component is press-formed.
As illustrated in FIGS. 1(a) and 1(b), the press-formed product manufacturing method according to the first embodiment includes a first step of forming a metal sheet blank into an intermediate press-formed product 17, and a second step of forming the intermediate press-formed product 17 into a hat-shaped cross-section component 19.

As illustrated in FIG. 1(a), the first step is a step of forming the metal sheet blank into the intermediate press-formed product 17 having an intermediate top plate 21, an intermediate vertical wall 25 continuous with the intermediate top plate 21 via an intermediate ridge 23, and an intermediate flange 27 continuous with the intermediate vertical wall 25.
On the intermediate top plate 21 of the intermediate press-formed product 17, a convex/concave portion 29 having a curved shape projected upward in a cross-section orthogonal to the ridge is formed and extended in the same direction as the extending direction of the intermediate ridge 23. An overall shape of the intermediate press-formed product 17 is the same as the hat-shaped cross-section component 19, which is the target shape in the second step, except that the intermediate top plate 21 is provided with the convex/concave portion 29. Note that the convex/concave portion 29 may have a curved shape recessed upward in the cross section orthogonal to the ridge, or may have a curved shape projected and recessed in the cross section orthogonal to the ridge.
In the example in FIG. 1, the convex/concave portion 29 is formed at an intermediate position of the intermediate top plate 21. By forming the convex/concave portion 29 at the intermediate position of the intermediate top plate 21, a material easily flows uniformly to both sides when the convex/concave portion 29 is crushed in the second step described later.
Still more, the intermediate top plate 21 of the intermediate press-formed product 17 in FIG. 1 is formed according to the target shape by cutting out both sides, in the extending direction of the intermediate ridge 23, of a portion where the convex/concave portion 29 is provided. However, only one side of the intermediate top plate 21 may be cut out or may not be cut out.

As illustrated in FIG. 1(b), the second step is a step of crushing the convex/concave portion 29 of the intermediate press-formed product 17 formed in the first step to form the hat-shaped cross-section component 19.
As described above, the overall shape of the intermediate press-formed product 17 is the same as the hat-shaped cross-section component 19, which is the target shape in the second step, except for the convex/concave portion 29 to be crushed. Therefore, in the second step, it is preferable to use a die in which a top plate portion of a die used in the first step is flattened.
When the intermediate press-formed product 17 is press-formed using the die as described above, the convex/concave portion 29 is crushed while maintaining the outer shape, and a material flows from the convex/concave portion 29 toward the intermediate vertical walls 25 on both sides as indicated by a broken line arrow in FIG. 1(b). When the material flows as described above, the material of the intermediate ridge 23 is pushed out toward the vertical wall 5. As a result, a portion that has been the intermediate ridge 23 or a part thereof is bent back from the bent shape to a flat shape. Movement of the material of the intermediate ridge 23 at this time and the stress generated in the portion will be described with reference to FIG. 3.
FIG. 3(a) is a diagram illustrating a ridge-orthogonal cross-section of the intermediate ridge 23 and the vicinity thereof at the forming bottom dead center in the first step. FIG. 3(b) is a diagram illustrating a ridge-orthogonal cross-section of the ridge 3 and the vicinity thereof at the forming bottom dead center in the second step. When the intermediate press-formed product 17 is press-formed in the first step, as illustrated in FIG. 3(a), the tensile stress is generated on the outer side and the compressive stress is generated on the inner side of the intermediate ridge 23 bent (portion indicated by gray in FIG. 3(a)).
When the convex/concave portion 29 of the intermediate press-formed product 17 is crushed in the second step, a material flows as indicated by a white arrow in FIG. 3(b), and a part or all of the material of the intermediate ridge 23 is pushed out toward the vertical wall 5 (portion indicated by gray in FIG. 3(b)). As described above, when the portion that has been the intermediate ridge 23 is pushed out toward the vertical wall 5, a bent portion or a part thereof is bent back flat, so that the compressive stress is generated on the outer side and the tensile stress is generated on the inner side of the bent-back portion. Since the above stress is a stress opposite to the stress generated in the ridge 3 of the hat-shaped cross-section component 19, both stresses are offset, and the stress acting at the time of the die release is reduced. This point will be described with reference to FIG. 4.
FIG. 4(a-1) illustrates a stress distribution on the outer side of the hat-shaped cross-section component 19 at the forming bottom dead center in the second step. Note that FIG. 4(a-1) illustrates only a half of the top plate 1 of the hat-shaped cross-section component 19 obtained by dividing the top plate 1 into two along the extending direction of the ridge 3. FIG. 4(a-2) is a diagram of the hat-shaped cross-section component 19 in FIG. 4(a-1), illustrating a ridge-orthogonal cross-sectional shape after the die release by a solid line and a ridge-orthogonal cross-sectional shape at the forming bottom dead center by a broken line. Note that the stress illustrated here is a stress in a direction orthogonal to the extending direction of the ridge 3 of the hat-shaped cross-section component 19 and in a direction along the outer surface.
As described above, in the second step, the material of the portion that has been the intermediate top plate 21 flows into the ridge 3 by the material flow generated by crushing the convex/concave portion 29, and the material of the portion that has been the intermediate ridge 23 is pushed out to the vertical wall 5 by the material flowing into the ridge 3. Therefore, a part of the flat intermediate top plate 21 is bent and formed into the ridge 3, and thus a tensile stress is generated on the outer side of the ridge 3 as illustrated in FIG. 4(a-1). Although not illustrated, the compressive stress due to bending is generated on the inner side of the ridge 3. On the other hand, the portion that has been the intermediate ridge 23 flows to the upper end of the vertical wall 5, and the bent portion is bent back, so that the compressive stress is generated on the outer side of an upper end of the vertical wall 5 as illustrated in FIG. 4(a-1). Although not illustrated, the tensile stress generated by reverse bending occurs on the inner side of the upper end of the vertical wall 5.
As described above, at the forming bottom dead center in the second step, a stress for increasing the inner angle of the ridge 3 is generated at the ridge 3 of the hat-shaped cross-section component 19 at the time of the die release, but a stress opposite to the stress is generated in the vicinity of the ridge 3 (upper end of the vertical wall 5). Therefore, both stresses offset each other at the time of the die release, and the stress acting at the time of the die release is reduced. As illustrated in FIG. 4(a-2), the inner angle θ₂ of the ridge 3 after the die release can be brought closer to the target angle θ₁ as compared with the conventional press-forming illustrated in FIG. 9.
Note that, although the above is an example in which the hat-shaped cross-section component 19 is formed, a similar effect can be obtained even in the U-shaped cross-section component not having the flange 7 at a lower end of the vertical wall 5. FIG. 4(b-1) illustrates only a half of the top plate 1 of a U-shaped cross-section component 31 obtained by dividing the top plate 1 into two along the extending direction of the ridge 3. FIG. 4(b-1) illustrates a stress distribution on an outer side of the plate at the forming bottom dead center when the target press-formed product in the second step is the U-shaped cross-section component 31. The stress illustrated here is a stress in a direction orthogonal to the extending direction of the ridge 3 of the U-shaped cross-section component 31 and in a direction along the outer surface. FIG. 4(b-2) is a diagram of the U-shaped cross-section component 31, illustrating a ridge-orthogonal cross-sectional shape after the die release by a solid line and a ridge-orthogonal cross-sectional shape at the forming bottom dead center by a broken line.
Even when the target press-formed product in the second step is the U-shaped cross-section component 31, the action described in FIG. 3 causes, as illustrated in FIG. 4(b-1), the tensile stress on the outer side and the compressive stress on the inner side of the ridge 3, and the compressive stress on the outer side and the tensile stress on the inner side of an upper end of the vertical wall 5. Therefore, the stress generated in the ridge 3 and the stress generated in the upper end of the vertical wall 5 offset each other to reduce the stress acting at the time of the die release. Thus, as illustrated in FIG. 4(b-2), the spring-back at the time of the die release is suppressed, and the inner angle θ₂ of the ridge 3 after the die release becomes close to the target angle θ₁.

In order to improve a component manufacturing efficiency, the hat-shaped cross-section component 9 in FIG. 2(a) may be press-formed, and the top plate 1 of the hat-shaped cross-section component 9 may be cut in the extending direction of the ridge, so as to manufacture two Z-shaped cross-section components 13. Alternatively, the U-shaped cross-section component 11 in FIG. 2(b) may be press-formed, and the top plate 1 of the U-shaped cross-section component 11 may be cut in the extending direction of the ridge, so as to manufacture two L-shaped cross-section components 15. As illustrated in FIG. 1(c), the dividing step is a step of cutting and dividing the top plate 1 of the hat-shaped cross-section component 19 formed in the second step to obtain two Z-shaped cross-section components 13. For example, the top plate 1 may be cut at two positions indicated by broken lines in FIG. 1(c) to remove a cut-out portion of the top plate 1 and form two Z-shaped cross-section components 13 as illustrated in FIG. 1(d).
The dividing method in the dividing step is not limited thereto. For example, the hat-shaped cross-section component 9 whose top plate 1 is not cut out, as illustrated in FIG. 2(a), may be formed, and the hat-shaped cross-section component 9 may be divided into two by cutting the top plate 1 at one position at the center in the extending direction of the ridge 3, so as to acquire two Z-shaped cross-section components 13.
As described above, the hat-shaped cross-section component 19 formed through the first step and the second step has a favorable shape in which the spring-back is reduced and the inner angle θ₂ of the ridge 3 (angle between the top plate 1 and the vertical wall 5) is close to the target angle θ₁. Therefore, by dividing the above the hat-shaped cross-section component 19, it is possible to acquire two Z-shaped cross-section components 13 favorable shape.
In addition, when the U-shaped cross-section component 11 is press-formed in the first step and the second step by the same method as that of the hat-shaped cross-section component 19 described with reference to FIG. 1, and then the U-shaped cross-section component 11 is divided, two L-shaped cross-section components 15 (FIG. 2(d)) can be manufactured.
As described above, according to the present embodiment, the stress opposite to the stress generated in the ridge 3 of the press-formed product is generated in the vicinity of the ridge 3, and thus the spring-back at the time of the die release can be reduced by offsetting the both stresses. As a result, the hat-shaped cross-section component 9, the hat-shaped cross-section component 19, or the U-shaped cross-section component 11 having a favorable shape close to the target shape can be manufactured. Further, by dividing the hat-shaped cross-section component 9, the hat-shaped cross-section component 19, or the U-shaped cross-section component 11 having the favorable shape, the Z-shaped cross-section component 13 (FIG. 2(c)) or the L-shaped cross-section component 15 having a favorable shape can be manufactured.
In the first embodiment described above, the intermediate top plate 21 of the intermediate press-formed product 17 is provided with the convex/concave portion 29 having the curved shape projected upward in the cross section orthogonal to the ridge. However, the present invention is not limited thereto. For example, the convex/concave portion 29 having a curved shape recessed upward may be provided. Also in this case, by crushing the convex/concave portion 29 in the second step, the same action as in the first embodiment is generated to reduce the spring-back. Still more, the intermediate top plate 21 of the intermediate press-formed product 17 may be provided with the convex/concave portion 29 having the curved shape recessed and projected upward in both directions in the cross section orthogonal to the ridge. Still more, the convex/concave portion 29 may also be provided entirely in a width direction of the intermediate top plate 21. In any case, by crushing and flattening the convex/concave portion 29 in the second step, the same action as in the first embodiment is generated, and thus the spring-back can be reduced.

(Second embodiment)

In the second embodiment, a method of manufacturing a Z-shaped cross-section component or an L-shaped cross-section component alone in the first step and the second step will be described. Hereinafter, the manufacturing method of the present embodiment will be described with an example of manufacturing the L-shaped cross-section component alone.
The press-formed product manufacturing method according to the second embodiment includes a first step of forming a metal sheet blank as illustrated in FIG. 5(a) into an intermediate press-formed product, and a second step of forming the intermediate press-formed product into the L-shaped cross-section component as illustrated in FIG. 5(b). In FIGS. 5(a) and 5(b), parts corresponding to FIGS. 1(a) and 1(b) are denoted by the same reference signs. Hereinafter, each step will be described in detail.

As illustrated in FIG. 5(a), the first step is a step of forming a metal sheet blank into an intermediate press-formed product 33 having an intermediate top plate 21 and one intermediate vertical wall 25 continuous with one side of the intermediate top plate 21 via an intermediate ridge 23. On the intermediate top plate 21 of the intermediate press-formed product 33, the convex/concave portion 29 having a curved shape projected upward in a cross section orthogonal to the ridge is formed, and the convex/concave portion 29 extends in the extending direction of the intermediate ridge 23. An overall shape of the intermediate press-formed product 33 is the same as that of an L-shaped cross-section component 35, which is a target shape in the second step, except that the intermediate top plate 21 is provided with the convex/concave portion 29.

As illustrated in FIG. 5(b), the second step is a step of crushing the convex/concave portion 29 of the intermediate press-formed product 33 formed in the first step to form the L-shaped cross-section component 35. A forming method in the second step according to the second embodiment will be described with reference to FIG. 6.
FIG. 6 is a cross-sectional view illustrating a state in the middle of forming in the second step. As illustrated in FIG. 6, in the second step, the intermediate press-formed product 33 is formed into the L-shaped cross-section component 35 using a punch 37, a die 39, and a pad 41.
As described in the first embodiment, in the present invention, the material of the intermediate ridge is pushed out to the vertical wall by a material flow generated by crushing the convex/concave portion 29, and a pushed out portion is bent back, thereby reducing a stress that causes a spring-back. Therefore, when the target shape has the vertical wall 5 only on one side as in the L-shaped cross-section component 35 of the present embodiment, it is preferable to perform the second step such that the material flows toward a side having the intermediate vertical wall 25.
Therefore, in the second step of the present embodiment, as illustrated in FIG. 6, forming is performed in a state where a restraining portion 37a is provided in the punch 37 to restrain an end of the intermediate top plate 21. By performing the second step as described above, it is easy to push out a part of the intermediate ridge 23 toward the vertical wall 5. The method of restraining one end of the intermediate top plate 21 is not limited to the example in FIG. 6, and the end may be fixed with a pin or the like.
In the above description, the L-shaped cross-section component 35 is manufactured alone, but the same applies to a case where the Z-shaped cross-section component is manufactured alone. In this case, an intermediate press-formed product 43 having the convex/concave portion 29 illustrated in FIG. 7(a) may be formed in the first step, and the convex/concave portion 29 may be crushed and formed into a Z-shaped cross-section component 45 illustrated in FIG. 7(b) in the second step.
FIG. 8(a-1) is a diagram of the Z-shaped cross-section component 45, illustrating a stress distribution at the forming bottom dead center in the second step of the press-formed product manufacturing method according to the second embodiment. The stress illustrated here is a stress in a direction orthogonal to the extending direction of the ridge 3 of the Z-shaped cross-section component 45 and in a direction along the outer surface. FIG. 8(b-1) is a diagram of the L-shaped cross-section component 35, illustrating a stress distribution at the forming bottom dead center in the second step of the press-formed product manufacturing method according to the second embodiment. The stress illustrated here is a stress in a direction orthogonal to the extending direction of the ridge 3 of the L-shaped cross-section component 35 and in a direction along the outer surface. FIG. 8(a-2) is a diagram of the Z-shaped cross-section component 45, illustrating a ridge-orthogonal cross-sectional shape after a die release by a solid line and a ridge-orthogonal cross-sectional shape at the forming bottom dead center by a broken line. FIG. 8(b-2) is a diagram of the L-shaped cross-section component 35, illustrating a ridge-orthogonal cross-sectional shape after a die release by a solid line and a ridge-orthogonal cross-sectional shape at the forming bottom dead center by a broken line.
As illustrated in FIGS. 8(a-1) and 8(b-1), in the Z-shaped cross-section component 45 and the L-shaped cross-section component 35 manufactured by the press-formed product manufacturing method according to the second embodiment, the tensile stress is generated on the outer side of the ridge 3 at the forming bottom dead center in the second step, and the compressive stress is generated on the outer side of the upper end of the vertical wall 5, similarly to the first embodiment. Although not illustrated, the compressive stress is generated on the inner side of the ridge 3 and the tensile stress is generated on the inner side of the upper end of the vertical wall 5 of the Z-shaped cross-section component 45 and the L-shaped cross-section component 35.
As described above, also in the press-formed product manufacturing method according to the second embodiment, similarly to the first embodiment, a stress opposite to the stress of the ridge 3 is generated in the vicinity of the ridge 3, and both stresses are offset to reduce the stress acting at the time of the die release. As a result, as illustrated in FIGS. 8(a-2) and 8(b-2), the spring-back at the time of die release is suppressed, and the inner angle θ₂ of the ridge 3 after the die release becomes close to the target angle θ₁.

[Examples]

An effect of reducing the spring-back by the press-formed product manufacturing method of the present invention will be described based on specific examples. In the examples, a 1470 MPa-class steel sheet having a sheet thickness of 1.0 mm was used as a blank, and a hat-shaped cross-section component or a U-shaped cross-section component was press-formed. The top plate of the press-formed component was cut to manufacture two Z-shaped cross-section components or L-shaped cross-section components. The target angle θ₁ of the inner angle of the ridge in the Z-shaped cross-section component or the L-shaped cross-section component was set to 100°, and an allowable upper limit angle was set to 108°.
As a conventional example, a blank was press-formed in the first step using a punch and a die having a flat forming surface for the top plate when the blank was press-formed into the hat-shaped cross-section component or the U-shaped cross-section component.
Further, as an example of the present invention, a blank was press-formed in two steps and then divided into two components as in the first embodiment described with reference to FIG. 1 when the blank was press-formed into the hat-shaped cross-section component or the U-shaped cross-section component. Specifically, the intermediate press-formed product in which the convex/concave portion was provided to the intermediate top plate was formed in the first step, and the convex/concave portion was crushed to form the hat-shaped cross-section component or the U-shaped cross-section component in the second step. The convex/concave portion is provided in the intermediate top plate at the center in the ridge direction of the intermediate press-formed product, and a length thereof was set to 1/5 of the entire length of the intermediate top plate. Then, the component was divided into two pieces.
The inner angle θ₂ of the ridge, after the die release, of the Z-shaped cross-section component or the L-shaped cross-section component manufactured in the conventional example and the invention example was measured and compared. Results are illustrated in Table 1.

[Table 1]

Table 1

No.	Component cross-sectional shape	Shape provided to top plate in first step	Convex/concave height (mm)	Inner angle θ₂(°) between top plate and vertical wall after second step	Remarks
1	Z-shaped	-	-	115	Conventional example
2	↑	Convex	8	105	Invention example
3	↑	Concave	8	105	Invention example
4	L-shaped	-	-	111	Conventional example
5	↑	Convex	8	101	Invention example
6	↑	Concave	8	102	Invention example

In Table 1, the "component cross-sectional shape" indicates whether the manufactured component is the Z-shaped cross-section component or the L-shaped cross-section component. The "shape provided to top plate in first step" indicates whether the convex/concave portion provided to the intermediate top plate of the intermediate press-formed product in the invention example has a convex shape projected upward or a concave shape recessed upward. The "convex/concave height" indicates a height at the tip of the convex shape or a depth at the bottom of the concave shape from the outer surface of the intermediate top plate. The "inner angle between top plate and vertical wall after second step" indicates the inner angle θ₂ of the ridge of the Z-shaped cross-section component or the L-shaped cross-section component obtained by dividing the hat-shaped cross-section component or the U-shaped cross-section component after the die release.
Conventional example No. 1 is an example in which the hat-shaped cross-section component is formed in the first step and divided to manufacture the Z-shaped cross-section component. The inner angle θ₂ of the ridge of the Z-shaped cross-section component manufactured was 115°. When the Z-shaped cross-section component was manufactured by the conventional manufacturing method, an increase in the inner angle of the ridge was large with respect to the target angle θ₁ of 100°, and resulted in deviating from an allowable upper limit angle of 108°.
On the other hand, invention examples No. 2 and No. 3 are examples of forming the intermediate press-formed product in which the convex/concave portion is provided to the intermediate top plate, crushing the convex/concave portion to form the hat-shaped cross-section component, and dividing the hat-shaped cross-section component to manufacture the Z-shaped cross-section component. In the invention examples No. 2 and No. 3, the inner angle θ₂ of the ridge of both of the Z-shaped cross-section components manufactured was 105°. The spring-back was reduced as compared with the conventional example No. 1, and the angle was within the allowable range.
Conventional example No. 4 is an example of forming the U-shaped cross-section component in the first step and dividing the U-shaped cross-section component to manufacture the L-shaped cross-section component. The inner angle θ₂ of the ridge of the L-shaped cross-section component manufactured was 111°. When the L-shaped cross-section component was manufactured by the conventional manufacturing method, similarly to the Z-shaped cross-section component, an increase in the inner angle of the ridge was large with respect to the target angle θ₁ of 100°, and the allowable upper limit angle deviated from 108°.
On the other hand, invention examples No. 5 and No. 6 are examples of forming the intermediate press-formed product in which the convex/concave portion is provided to the intermediate top plate, crushing the convex/concave portion to form the U-shaped cross-section component, and dividing the U-shaped cross-section component to manufacture the L-shaped cross-section component. In the invention examples No. 5 and No. 6, the inner angles θ₂ of the ridge of the L-shaped cross-section component manufactured were 101° and 102°, and the spring-back was reduced as compared with the conventional example No. 4. The angles were within the allowable range.
As described above, it has been confirmed in the present examples that the spring-back that increases the inner angle of the ridge (inner angle formed between the top plate and the vertical wall) can be reduced by using the press-formed product manufacturing method of the present invention.

Industrial Applicability

The present invention can provide the press-formed product manufacturing method capable of efficiently obtaining a press-formed product having a good appearance by suppressing the spring-back that occurs in the press-forming of a vehicle body part.

Reference Signs List

1 TOP PLATE
3 RIDGE
5 VERTICAL WALL
7 FLANGE
9 HAT-SHAPED CROSS-SECTION COMPONENT
11 U-SHAPED CROSS-SECTION COMPONENT
13 Z-SHAPED CROSS-SECTION COMPONENT
15 L-SHAPED CROSS-SECTION COMPONENT
17 INTERMEDIATE PRESS-FORMED PRODUCT (FIRST EMBODIMENT)
19 HAT-SHAPED CROSS-SECTION COMPONENT (FIRST EMBODIMENT)
21 INTERMEDIATE TOP PLATE
23 INTERMEDIATE RIDGE
25 INTERMEDIATE VERTICAL WALL
27 INTERMEDIATE FLANGE
29 CONVEX/CONCAVE PORTION
31 U-SHAPED CROSS-SECTION COMPONENT (FIRST EMBODIMENT)
33 INTERMEDIATE PRESS-FORMED PRODUCT (SECOND EMBODIMENT)
35 L-SHAPED CROSS-SECTION COMPONENT (SECOND EMBODIMENT)
37 PUNCH
37a RESTRAINING PORTION
39 DIE
41 PAD
43 INTERMEDIATE PRESS-FORMED PRODUCT (SECOND EMBODIMENT)
45 Z-SHAPED CROSS-SECTION COMPONENT (SECOND EMBODIMENT)

Claims

A press-formed product manufacturing method for manufacturing a press-formed product including a top plate and a vertical wall continuous with the top plate via a ridge, the method comprising:
a first step of forming a metal sheet blank into an intermediate press-formed product including an intermediate top plate, and an intermediate vertical wall continuous with the intermediate top plate via an intermediate ridge, the intermediate top plate being provided with a convex/concave portion extending in a direction same as an extending direction of the intermediate ridge, the convex/concave portion having at least a convex or concave ridge-orthogonal cross-sectional shape; and

a second step of crushing the convex/concave portion of the intermediate press-formed product to form the press-formed product, wherein

the crushing of the convex/concave portion in the second step generates a material flow, and the material flow pushes out a material corresponding to the intermediate ridge toward the vertical wall to cause reverse bending of a portion that has been the intermediate ridge.
The press-formed product manufacturing method according to claim 1, wherein the press-formed product is a hat-shaped cross-section component or a U-shaped cross-section component having a pair of vertical walls on both sides of the top plate.
The press-formed product manufacturing method according to claim 2, further comprising a dividing step of cutting and dividing the top plate of the hat-shaped cross-section component or the U-shaped cross-section component formed in the second step in an extending direction of the ridge to acquire two Z-shaped cross-section components or two L-shaped cross-section components.
The press-formed product manufacturing method according to claim 3, wherein
the top plate is cut out at one side or both sides, in a ridge direction, of a portion where the convex/concave portion is provided, and

the dividing step includes dividing the top plate by cutting and removing a cut-out portion of the top plate.
The press-formed product manufacturing method according to claim 1, wherein
the press-formed product is a Z-shaped cross-section component or an L-shaped cross-section component having the vertical wall only on one side of the top plate, and

the second step includes restraining, during forming, an end of the intermediate top plate of the intermediate press-formed product on a side without the intermediate vertical wall.