Method for producing press-formed article

Abstract

A method of manufacturing a press-formed product according to the present invention is a method of manufacturing a press-formed product 100 having a target shape, the press-formed product 100 including a top plate portion 101 and a vertical wall portion 105 continuous from the top plate portion 101 via a ridgeline portion 103, a step portion 109 having a concave shape in a cross section orthogonal to the ridgeline portion being formed in an extending direction of the ridgeline portion 103 in the top plate portion 101, the method including a first forming step of press-forming a blank 110 into an intermediate formed product 120 including an intermediate top plate portion 121 and an intermediate vertical wall portion 125 continuous from the intermediate top plate portion 121 via an intermediate ridgeline portion 123 and a second forming step of forming the step portion 109 having the concave shape in the intermediate top plate portion 121 of the intermediate formed product 120 and press-forming the press-formed product 100 having the target shape.

Description

Field

[0001] The present invention relates to a method of manufacturing a press-formed product including: a top plate portion and a vertical wall portion continuous from the top plate portion via a ridgeline portion, a step portion having a concave shape or a convex shape being formed in the top plate portion in a direction in which the ridgeline portion extends.Background

[0002] As the improvement of collision safety of a vehicle body has been advanced according to the tightening of the automobile collision safety standard, in response to the recent carbon dioxide emission regulations, it is also necessary to reduce the weight of the vehicle body. Therefore, in order to achieve both pf the improvement of the collision safety performance and the weight reduction of the vehicle body, a metal plate having higher strength compared with the conventional metal plate is being adopted for the vehicle body. An ultra-high-tensile steel sheet having tensile strength of a 1.5 GPa class or higher has been applied most recently.

[0003] Such a metal plate generates large stress generated at a press-forming time. When the metal plate is released after the press-forming, large spring-back occurs and the metal plate tends to deviate from a target shape. In particular, in a press-formed product including a top plate portion and a vertical wall portion continuous from the top plate portion via a ridgeline portion, spring-back occurs in which an inner angle formed by the top plate portion and the vertical wall portion is opened.

[0004] Therefore, several techniques for reducing the spring-back in which the inner angle formed by the top plate portion and the vertical wall portion is opened have been proposed. For example, Patent Literature 1 discloses a method of, in press-forming a product to a predetermined product size in two or more times of press-forming, in the last press-forming of the second and subsequent times, widening a punch width more than a punch width in the first press-forming.

[0005] Patent Literature 2 discloses a method of press-forming a workpiece while pressing a die side pad against the workpiece in a state in which a punch side pad is projected further to the outer side than a pressurizing surface of a punch and press-forming the workpiece such that the punch side pad is at the same height as the pressurizing surface of the punch at a forming bottom dead center.Citation ListPatent Literature

[0006] Patent Literature 1: JP 2007-111725 A Patent Literature 2: JP 2010-082660 A SummaryTechnical Problem

[0007] In a press-formed product 100 in which a step portion 109 having a concave shape is formed in a top plate portion 101 as illustrated as an example in FIG. 12, when the press-formed product 100 is released, spring-back also occurs in which an inner angle formed by the top plate portion 101 and a vertical wall portion 105 is opened. Therefore, the method disclosed in Patent Literature 1 or Patent Literature 2 was applied to the press-formed product 100.

[0008] However, in the method of Patent Literature 1, a part where the vertical wall portion 105 (a wall portion) and the top plate portion 101 (a bottom portion) are bent and formed in the first time is bent back by the last forming of the second and subsequent times and spring-back that closes the inner angle between the vertical wall portion 105 and the top plate portion 101 is caused by the bending back. As a result, the spring-back in which the inner angle of the ridgeline portion is opened in the last forming of the second and subsequent times is suppressed. However, a bending angle between the vertical wall portion 105 and the top plate portion 101 in the first forming was larger than a bending angle of the ridgeline portion in the last forming of the second and subsequent times. For that reason, it has been found that the spring-back that closes the inner angle with the bending back is smaller than the spring-back in which the inner angle is opened by the last forming of the second and subsequent times and the spring-back after forming cannot be sufficiently suppressed.

[0009] In the method disclosed in Patent Literature 2, when a cross-sectional line length of the workpiece was excessively longer than the target shape, a break occurred at a punch shoulder portion (corresponding to the ridgeline portion 103 of the press-formed product 100 in FIG. 12). Further, when the cross-sectional line length of the press-formed product 100 was shorter than the target shape, the angle of the ridgeline portion 103 did not reach the target shape.

[0010] As explained above, in the methods disclosed in Patent Literature 1 and Patent Literature 2, there is a problem in that the spring-back is not sufficiently reduced and the appearance of the target shape is spoiled.

[0011] The present invention has been made in view of the problems described above, and an object of the present invention is to provide a method of manufacturing a press-formed product that can reduce spring-back without spoiling the appearance of a press-formed product having a target shape in which a step portion having a concave shape or a convex shape is formed in a top plate portion.Solution to Problem

[0012] In order to solve the problems described above and achieve the object, (1) a method of manufacturing a press-formed product according to the present invention is a method of manufacturing a press-formed product including a top plate portion and a vertical wall portion continuous from the top plate portion via a ridgeline portion, the press-formed product having a target shape in which a step portion having a concave shape or a convex shape in a cross section orthogonal to the ridgeline portion is formed in the top plate portion in an extending direction of the ridgeline portion, and includes the steps of: press-forming a blank into an intermediate formed product including an intermediate top plate portion and an intermediate vertical wall portion continuous from the intermediate top plate portion via an intermediate ridgeline portion and applying bending deformation to the intermediate ridgeline portion; and subsequently press-forming the intermediate formed product into the press-formed product having the target shape by forming the step portion having the concave shape or the convex shape in the intermediate top plate portion of the intermediate formed product, wherein when the step portion having the concave shape or the convex shape is formed, bending-back deformation is applied to the intermediate ridgeline portion by drawing the intermediate ridgeline portion to the intermediate top plate portion side. (2) In the above-described invention (1), the method of manufacturing the press-formed product according to the present invention includes: a first forming step of press-forming the blank into the intermediate formed product including the intermediate top plate portion and the intermediate vertical wall portion continuous from the intermediate top plate portion via the intermediate ridgeline portion and applying bending deformation to the intermediate ridgeline portion; and a second forming step of press-forming the intermediate formed product into the press-formed product having the target shape by forming the step portion having the concave shape or the convex shape in the intermediate top plate portion of the intermediate formed product, wherein in the second forming step, at a time of forming the step portion having the concave shape or the convex shape, bending-back deformation is applied to the intermediate ridgeline portion by drawing the intermediate ridgeline portion to the intermediate top plate portion side. (3) In the above-described invention (2), in the method of manufacturing, in the first forming step, a low step portion having a step height smaller than the target shape is formed in the intermediate top plate portion, and in the second forming step, the step portion is formed by setting the low step portion to a step height of the target shape. (4) In the above-described invention (1), in the method of manufacturing, the step of press-forming the blank into the intermediate formed product and subsequently press-forming the intermediate formed product into the press-formed product having the target shape by forming the step portion having the concave shape or the convex shape in the intermediate top plate portion of the intermediate formed product are performed in one step. (5) A method of manufacturing a press-formed product according to the present invention includes: a press-forming step of press-forming, by using the method of manufacturing the press-formed product according to any one of inventions (1) to (4), the top plate portion, a pair of the vertical wall portions continuous from both edges of the top plate portion via the ridgeline portion, and the press-formed product in which the step portion is formed in the top plate portion; and a dividing step of cutting the top plate portion of the press-formed product press-formed in the press-forming step in an extending direction of the ridgeline portion and dividing the press-formed product. Advantageous Effects of Invention

[0013] According to the present invention, it is possible to, while sufficiently reducing spring-back without spoiling the appearance, manufacture a press-formed product having a target shape, the press-formed product including the top plate portion and the vertical wall portion continuous from the top plate portion via the ridgeline portion, the step portion having the concave shape or the convex shape in the cross section orthogonal to the ridgeline portion being formed in the top plate portion in the extending direction of the ridgeline portion. Further, in the present invention, the press-formed product including top plate portion in which the step portion having the concave shape or the convex shape is formed and the pair of vertical wall portions continuous from both the edges of the top plate portion via the ridgeline portion is divided by cutting the top plate portion in the direction in which the ridgeline portion extends. Accordingly, it is possible to obtain two press-formed products having a Z cross-sectional shape or an L cross-sectional shape with reduced spring-back from a press-formed product having a hat cross-sectional shape or a U cross-sectional shape manufactured by one press-forming. This is preferable because production cost can be reduced.Brief Description of Drawings

[0014] [FIG. 1] FIG. 1 is a diagram for explaining a first forming step of press-forming into an intermediate formed product and a second forming step of press-forming into a press-formed product having a target shape in a method of manufacturing a press-formed product according to a first embodiment of the present invention ((a) the first forming step, (b) the second forming step). [FIG. 2] FIG. 2 is a cross-sectional view in a ridgeline portion orthogonal direction illustrating a process of forming the intermediate formed product in the first forming step and a process of forming the press-formed product having the target shape in the second forming step in the method of manufacturing the press-formed product according to the first embodiment of the present invention ((a) the first forming step, (b) the second forming step). [FIG. 3] FIG. 3 is a diagram for explaining a forming step of the related art of press-forming, in one step, into a press-formed product having a target shape in which a step portion having a concave shape is formed in a top plate portion. [FIG. 4] FIG. 4 is a cross-sectional view in a ridgeline portion orthogonal direction for explaining a method of the related art of press-forming, in one step, a press-formed product having a target shape in which a step portion having a concave shape is formed in a top plate portion. [FIG. 5] FIG. 5 is a contour diagram illustrating a stress distribution at a forming bottom dead center of the press-formed product by the method of the related art and a cross-sectional view in the ridgeline portion orthogonal direction of the press-formed product after being released and sprung back ((a) the stress distribution, (b) a cross section of the press-formed product at the forming bottom dead center and after the spring-back). [FIG. 6] FIG. 6 is a contour diagram illustrating a stress distribution at a forming bottom dead center of the press-formed product having the target shape obtained by press-forming, in the second forming step, the intermediate formed product press-formed in the first forming step in the method of manufacturing the press-formed product according to the first embodiment of the present invention and a cross-sectional view of the press-formed product in the ridgeline portion orthogonal direction of the press-formed product after being released and sprung back ((a) the stress distribution, (b) a cross section of the press-formed product at the forming bottom dead center and after the spring-back). [FIG. 7] FIG. 7 is a diagram for explaining a mechanism in which spring-back is suppressed in a press-formed product in which a step portion is formed in a top plate portion according to first and second embodiments of the present invention ((a) before the step portion formation, (b) after the step portion formation). [FIG. 8] FIG. 8 is a diagram in which a press-formed product having a target shape is press-formed in one step in a method of manufacturing a press-formed product according to the second embodiment of the present invention. [FIG. 9] FIG. 9 is a cross-sectional view in a ridgeline portion orthogonal direction for explaining a step of press-forming a press-formed product having a target shape in one step in the method of manufacturing the press-formed product according to the second embodiment of the present invention. [FIG. 10] FIG. 10 is a contour diagram illustrating a stress distribution at a forming bottom dead center of a press-formed product having a target shape press-formed in one step in the method of manufacturing the press-formed product according to the second embodiment of the present invention and a cross-sectional view in a ridgeline portion orthogonal direction of the press-formed product at a forming bottom dead center and after being released and sprung back ((a) the stress distribution, (b) a cross section the press-formed product at the forming bottom dead center and after the spring-back). [FIG. 11] FIG. 11 is a diagram illustrating dimensions of a press-formed product having a hat cross-sectional shape set as a forming target in an example. [FIG. 12] FIG. 12 is a diagram illustrating, as an example of a press-formed product targeted in the present invention, a press-formed product in which a step portion having a concave shape is formed in a top plate portion. Description of Embodiments

[0015] Before methods of manufacturing press-formed products according to first and second embodiments of the present invention, a press-formed product targeted in the present invention and circumstances leading to the present invention are explained.<Press-formed Product>

[0016] FIG. 12 illustrates an example of a press-formed product 100 targeted in the present invention. The press-formed product 100 has a hat cross-sectional shape including a top plate portion 101, a vertical wall portion 105 continuous from the top plate portion 101 via a ridgeline portion 103, and a flange portion 107 continuous from the vertical wall portion 105. In the press-formed product 100, a step portion 109 having a concave shape in a cross section orthogonal to the ridgeline portion is formed in an extending direction of the ridgeline portion 103 in top plate portion 101. Here, the step portion 109 is formed over the entire length in the extending direction of the ridgeline portion 103.<Circumstances leading to the present invention>

[0017] FIG. 3 illustrates an example of a method of press-forming the blank 110 into the press-formed product 100 (FIG. 12) by a die 30. A process of press-forming the press-formed product 100 in one step of the related art is explained based on a cross-sectional view in a ridgeline portion orthogonal direction illustrated in FIG. 4. First, the step portion 109 having the concave shape is formed in a part equivalent to the top plate portion 101 in a blank 110 (FIG. 4(i)) which is a metal plate (FIG. 4(ii)).

[0018] Subsequently, simultaneously with the formation of the step portion 109, both edge sides of the blank 110 are formed into the vertical wall portion 105 and the flange portion 107 (FIG. 4(iii) to FIG. 4(v)).

[0019] A result of analyzing, with a finite element method (FEM), the process of press-forming the press-formed product 100 in one step of the related art and calculating a stress distribution at a forming bottom dead center is illustrated in FIG. 5. FIG. 5(a) is a contour diagram in which a stress distribution on a plate thickness direction outer side is displayed in a perspective view of the press-formed product 100 having a target shape. FIG. 5(b) is a cross-sectional view in the ridgeline portion orthogonal direction in which the press-formed product 100 at the forming bottom dead center and the press-formed product 100 after being released and sprung back are superimposed and displayed. FIG. 5(a) illustrates stress in a direction orthogonal to the extending direction of the ridgeline portion 103.

[0020] As illustrated in FIG. 5(a), large tensile stress in a direction orthogonal to the ridgeline portion 103 is generated on the plate thickness direction outer side in the ridgeline portion 103 between the top plate portion 101 and the vertical wall portion 105 and in the vicinity of the ridgeline portion 103. As a result, as illustrated in FIG. 5(b), when the press-formed product 100 is released after the press-forming, spring-back occurs and an inner angle between the top plate portion 101 and the vertical wall portion 105 of the press-formed product 100 becomes larger than an inner angle of the target shape.

[0021] Therefore, the inventor intensively studied a method of reducing such spring-back in the press-formed product 100. As a result, the order of press-forming is changed to form the step portion 109 in the top plate portion 101 after forming the ridgeline portion 103. Accordingly, the inventor conceived to draw the ridgeline portion 103 to the top plate portion 101 side, cause bending bending back in the part, and generate stress for offsetting the stress of the ridgeline portion 103 of the target shape. The present invention is based on such an idea and is specifically described in the following embodiments.[First Embodiment]

[0022] A method of manufacturing a press-formed product according to a first embodiment of the present invention is a method of manufacturing the press-formed product 100 illustrated in FIG. 12 as an example. As illustrated in FIG. 1, the method of manufacturing the press-formed product according to the first embodiment includes a first forming step and a second forming step. Each of the first forming step and the second forming step is explained below.<First forming step>

[0023] In the first forming step, as illustrated in FIG. 1(a) and FIG. 2(a), the blank 110 is press-formed into the intermediate formed product 120 with a first die 10. The intermediate formed product 120 has a hat cross-sectional shape including an intermediate top plate portion 121, an intermediate ridgeline portion 123, an intermediate vertical wall portion 125, and an intermediate flange portion 127. The intermediate formed product 120 has a shape before the step portion 109 (FIG. 2(b)) is formed in the intermediate top plate portion 121.<Second forming step>

[0024] As illustrated in FIG. 1(b) and FIG. 2(b), the second forming step is a step of forming the step portion 109 in the intermediate top plate portion 121 of the intermediate formed product 120 with a second die 20 and press-forming the press-formed product 100 having the target shape. In the second forming step, when the step portion 109 is formed, a part that has been the intermediate ridgeline portion 123 in the intermediate formed product 120 is drawn to the top plate portion 101 side, whereby bending back is caused in the part.

[0025] In the second forming step, the part drawn to the top plate portion 101 side is desirably the entire or a part of the part that has been the intermediate ridgeline portion 123 of the intermediate formed product 120.<Reason why spring-back decreases>

[0026] A reason why spring-back decreases in the press-formed product 100 manufactured by the method of manufacturing the press-formed product according to the first embodiment is explained below.

[0027] A process of press-forming was analyzed by a finite element method (FEM) for each of the first forming step and the second forming step in the first embodiment. A stress distribution at the forming bottom dead center in the second forming step is illustrated in FIG. 6. FIG. 6(a) is a contour diagram in which a stress distribution on a plate thickness direction outer side is displayed in a perspective view of the press-formed product 100 having the target shape. FIG. 6(b) is a cross-sectional view in a ridgeline portion orthogonal direction in which the press-formed product 100 at the forming bottom dead center and the press-formed product 100 after being released and sprung back are superimposed and displayed. FIG. 6(a) illustrates stress in a direction orthogonal to the extending direction of the ridgeline portion 103.

[0028] As illustrated in FIG. 6(a), it can be seen that tensile stress is generated in the ridgeline portion orthogonal direction on the plate thickness direction outer side of the ridgeline portion 103 and compressive stress is generated on the top plate portion 101 side on the plate thickness direction outer side near the ridgeline portion 103. Here, the tensile stress generated in the ridgeline portion 103 and the compressive stress generated in the top plate portion 101 are offset. Accordingly, spring-back does not occur even if the press-formed product 100 having the target shape is released. As a result, as illustrated in FIG. 6(b), the inner angle between the top plate portion 101 and the vertical wall portion 105 of the press-formed product 100 after the release is substantially the same as the inner angle at the forming bottom dead center.

[0029] The method according to the first embodiment is explained in detail with reference to FIG. 7.

[0030] In the first forming step, as illustrated in a cross section in the ridgeline portion orthogonal direction in FIG. 7(a), tensile stress due to bending is generated the plate thickness direction outer side in the intermediate ridgeline portion 123 and compressive stress is generated on the plate thickness direction inner side. In the subsequent second forming step, as illustrated in a cross section in the ridgeline portion orthogonal direction in FIG. 7(b), when the step portion 109 is formed in the intermediate top plate portion 121, the part that has been the intermediate ridgeline portion 123 is drawn to the intermediate top plate portion 121 side from the intermediate vertical wall portion 125 side. As a result, in the part that has been the intermediate ridgeline portion 123 in the top plate portion 101 of the press-formed product 100, compressive stress due to bending back occurs on the plate thickness direction outer side and tensile stress occurs on the plate thickness direction inner side.

[0031] As a result, the tensile stress on the plate thickness direction outer side of the ridgeline portion 103 is offset by the compressive stress (FIG. 7(b)) on the plate thickness direction outer side of the bent-back intermediate ridgeline portion 123 in the top plate portion 101. Further, the compressive stress on the plate thickness direction inner side of the ridgeline portion 103 is offset by the tensile stress (FIG. 7(b)) on the plate thickness direction inner side of the bent-back intermediate ridgeline portion 123 in the top plate portion 101. As explained above, in the press-formed product 100 having the target shape after being released, stress acting on the ridgeline portion 103 is offset by stress generated by formation of the step portion 109. Therefore, spring-back sufficiently decreases.

[0032] As explained above, according to the method of manufacturing the press-formed product according to the first embodiment, compared with Patent Literature 1, it is possible to more sufficiently reduce spring-back in which the inner angle between the top plate portion 101 and the vertical wall portion 105 in the press-formed product 100 in which the step portion 109 having the concave shape is formed is opened.

[0033] Further, in the method of manufacturing the press-formed product according to the first embodiment, a cross-sectional line length of the intermediate formed product 120 is not set excessively larger than the target shape unlike the method disclosed in Patent Literature 2. Therefore, the ridgeline portion 103 is not bent. Moreover, since the cross-sectional line length of the intermediate formed product 120 is not set excessively smaller than the target shape, the angle of the ridgeline portion 103 can be set to the target shape.

[0034] As another aspect of the first embodiment, in the first forming step, a low step portion having a step height smaller than the target shape may be formed in the intermediate top plate portion 121. In this case, in the subsequent second forming step, by setting the low step portion formed in the first forming step to the step height of the target shape, the step portion 109 can be formed to suppress spring-back.[Second Embodiment]

[0035] About a method of manufacturing a press-formed product according to a second embodiment, a process of press-forming, in one step, the press-formed product 100 having a target shape in which the step portion 109 is formed in the top plate portion 101 (see FIG. 8) is explained with reference to a cross-sectional view in a ridgeline portion orthogonal direction illustrated in FIG. 9.

[0036] First, the blank 110 is held by pads 59 and a punch 57 of a die 50 (FIG. 9(i)). Subsequently, both edge sides of the blank 110 are held and bent by cams 61 (FIG. 9(ii)).

[0037] Subsequently to the forming of the ridgeline portion 103, the vertical wall portion 105 and the flange portion 107 are formed and the step portion 109 is formed in the top plate portion 101 (FIG. 9(iii) to FIG. 9(iv)).

[0038] In the second embodiment, the process of press-forming, in one step, the press-formed product 100 having the target shape is analyzed by the finite element method (FEM) and a stress distribution at a forming bottom dead center is illustrated in FIG. 10.

[0039] FIG. 10(a) is a contour diagram in which a stress distribution on a plate thickness direction outer side is displayed in a perspective view of the press-formed product 100. FIG. 10(b) is a cross-sectional view in the ridgeline portion orthogonal direction in the press-forming process. FIG. 10(a) illustrates stress in a direction orthogonal to the extending direction of the ridgeline portion 103. As illustrated in FIG. 10(a), tensile stress is generated on the plate thickness direction outer side of the ridgeline portion 103 and the vicinity of the ridgeline portion 103 and compressive stress is generated on the top plate portion 101 side adjacent to the ridgeline portion 103. As a result, as illustrated in FIG. 10(b), these stresses offset each other and spring-back does not occur. The inner angle between the top plate portion 101 and the vertical wall portion 105 of the press-formed product 100 is substantially the same as the inner angle at the forming bottom dead center.

[0040] A reason why the spring-back decreases is the same as the reason explained with reference to FIG. 7 above. That is, halfway in press-forming before the step portion 109 is formed, as illustrated in FIG. 7(a), tensile stress due to bending is generated in the plate thickness direction outer side and compressive stress is generated in a plate thickness direction inner side. Thereafter, when the step portion 109 is formed near the forming bottom dead center, a part that has been the intermediate ridgeline portion 123 in the intermediate formed product 120 is drawn from the ridgeline portion 103 to the top plate portion 101. Accordingly, as illustrated in FIG. 7(b), compressive stress due to bending bending back is generated on the plate thickness direction outer side and tensile stress is generated on the plate thickness direction inner side.

[0041] As a result, the tensile stress on the plate thickness direction outer side of the ridgeline portion 103 is offset by the compressive stress (FIG. 7(b)) on the plate thickness direction outer side of the bent-back ridgeline portion 103 in the top plate portion 101. Further, the compressive stress (FIG. 7(a)) on the plate thickness direction inner side of the ridgeline portion 103 is offset by the tensile stress (FIG. 7(b)) on the plate thickness direction inner side of the ridgeline portion 103 unbent in the top plate portion 101. Accordingly, in the press-formed product 100 having the target shape after being released, spring-back sufficiently decreases.

[0042] As explained above, with the method of manufacturing the press-formed product according to the second embodiment, it is possible to sufficiently reduce spring-back in which the inner angle between the top plate portion 101 and the vertical wall portion 105 is opened in the press-formed product 100 in which the step portion 109 having the concave shape is formed. Furthermore, the method of manufacturing the press-formed product according to the second embodiment does not deteriorate the appearance of the press-formed product 100 having the target shape as in the first embodiment explained above.

[0043] In the second embodiment explained above, the step portion 109 may be formed immediately before the forming of the ridgeline portion 103 is completed or the step portion 109 may be formed after the forming of the ridgeline portion 103 is completed.

[0044] In the present invention, a step height (depth to the bottom surface of the step portion) of the step portion having the concave shape formed in the top plate portion is preferably set in a range of 1 / 5 to two times a cross-sectional length in the ridgeline portion orthogonal direction. Here, the cross-sectional length in the ridgeline portion orthogonal direction refers to length from a bending start part with the top plate portion to a bending stop part with the vertical wall portion in the ridgeline portion.

[0045] If the step height of the step portion is as excessively small as 1 / 5 or less of the cross-sectional length in the ridgeline portion orthogonal direction, an amount of drawing in and bending back the vertical wall portion when forming the step portion deceases. Expansion of the inner angle between the top plate portion and the vertical wall portion due to spring-back after release cannot be sufficiently offset. On the other hand, if the step height of the step portion is as excessively large as exceeding two times of the cross-sectional length in the ridgeline portion orthogonal direction, an amount of drawing the vertical wall portion 105 when forming the step portion is too large and the vertical wall portion is draw-formed to cause warpage. Therefore, the press-formed product 100 less easily formed in the target shape.

[0046] Both of the first and second embodiments target a press-formed product in which a step portion recessed in a press-forming direction is formed. However, the present invention may target a press-formed product in which a step portion having a convex shape in a cross section orthogonal to the ridgeline portion is formed in a top plate portion in an extending direction of a ridgeline portion.

[0047] In a press-formed product in which a step portion having a convex shape is formed, the step portion having the convex shape only has to be formed by the same method as the method in the first or second embodiment. In this case as well, a material is drawn from the vertical wall portion toward the top plate portion side when the step portion having the convex shape is formed. At this time, bending-back occurs a part that has been the intermediate ridgeline portion. As a result, in the press-formed product having the target shape after being released, it is possible to sufficiently reduce spring-back in which the inner angle between the top plate portion and the vertical wall portion expands.

[0048] The present invention can reduce spring-back in which the inner angle between the top plate portion and the vertical wall portion is opened not only in the press-formed product having the hat cross-sectional shape but also in a press-formed product having a U cross-sectional shape, a Z cross-sectional shape, or an L cross-sectional shape.

[0049] The press-formed product having the Z cross-sectional shape and including the top plate portion, the vertical wall portion, and the flange portion can be manufactured by a press-forming step and a dividing step as explained below.

[0050] The press-forming step is a step of press-forming the press-formed product 100 having the hat cross-sectional shape illustrated in FIG. 12 by the method according to the first or second embodiment explained above. The dividing step is a step of cutting the top plate portion 101 of the press-formed product 100 in the extending direction of the ridgeline portion and dividing the press-formed product 100. Accordingly, two press-formed products having the Z cross-sectional shape can be obtained.

[0051] In the press-formed product having the hat cross-sectional shape press-formed in the press-forming step, spring-back can be reduced as explained above. For that reason, in the press-formed product having the Z cross-sectional shape obtained by dividing the press-formed product having the hat cross-sectional shape in the subsequent dividing step, spring-back is sufficiently reduced. As explained above, two press-formed products having the Z cross-sectional shape with reduced spring-back can be obtained from the press-formed product having the hat cross-sectional shape manufactured by one press-forming. This is preferable because production cost can be reduced.

[0052] In the press-formed product having the L cross-sectional shape, the press-formed product having the U cross-sectional shape may be press-formed and the top plate portion may be cut in the subsequent dividing step to be divided into two press-formed products having the L cross-sectional shape.Examples

[0053] Since the action effects of the present invention are verified above, the action effects are explained below. A steel sheet having a plate thickness of 1.0 mm and tensile strength of a 1470 MPa class or a 980 MPa class was used to manufacture press-formed products having a hat cross-sectional shape, a U cross-sectional shape, a Z cross-sectional shape, and an L cross-sectional shape.

[0054] As dimensions of the target shape of the press-formed product 100 having the hat cross-sectional shape, as illustrated in FIG. 11, length was set to 50 mm, the width of the top plate portion 101 was set to 150 mm, the vertical wall height of the vertical wall portion 105 was set to 55 mm, the inner angle between the vertical wall portion and the top plate portion was set to 95°, and the bending radiuses of the ridgeline portion 103 and the step portion 109 were respectively set to R 4 mm on the inside of bending. Further, the width of the step portion 109 was set to 80 mm and the step height of the step portion 109 was set to 9 mm (1.4 times the cross-sectional length in the ridgeline portion orthogonal direction). The step height of a step portion having a shallow concave shape and a shallow convex shape (hereinafter referred to as low step portion) was set to 5 mm.

[0055] The press-formed product having the U cross-sectional shape is obtained by removing the flange portion 107 from the press-formed product 100 having the hat cross-sectional shape illustrated in FIG. 11. Dimensions of the parts were set equal to the dimensions of the press-formed product 100 illustrated in FIG. 11.

[0056] The press-formed product having the Z cross-sectional shape is obtained by removing the vertical wall portion 105 and the flange portion 107 on one side from the press-formed product 100 having the hat cross-sectional shape illustrated in FIG. 11. Then, the widths of the top plate portion and the step portion were respectively set to 75 mm and 40 mm, which were halves of the widths in the press-formed product 100 and the dimensions of the other parts were set equal to the dimensions of the press-formed product 100.

[0057] The press-formed product having the L cross-sectional shape is obtained by removing the vertical wall portion 105 on one side and the flange portions 107 on both sides from the press-formed product 100 having the hat cross-sectional shape illustrated in FIG. 11. The widths of the top plate portion and the step portion were set to halves of the widths in the press-formed product 100 and the dimensions of the other parts were set equal to the dimensions of the press-formed product 100.

[0058] In the example, the press-formed products press-formed by the methods explained in the first and second embodiments explained above were inventive examples. In the invention examples, the shape of the step portion formed in the top plate portion in the target shape explained above, the number of steps, and timing for forming the step portion in the top plate portion were changed. The number of steps of the press-formed product was set to two as the method according to the first embodiment explained above and was set to one as the method according to the second embodiment explained above.

[0059] Then, an inner angle between the top plate portion and the vertical wall portion after the press-formed product having the target shape is released and sprung-back was measured and evaluated as a spring-back amount. Further, a press-formed product press-formed in one step in which a step portion having a concave shape or a convex shape is formed in a top plate portion is press-formed in one step by the method of the related art illustrated in FIG. 3 explained above was set as a related art example. In conventional example, as in the invention example, the inner angle between the top plate portion and the vertical wall portion after the press-formed product having the target shape was released and sprung back was measured. Results of the invention example and conventional example are collectively illustrated in Table 1. [TABLE 1]Sectional shape of press-formed product, shape of step portionNumber of stepsTiming for forming step portion having concave shape or convex shape in top plate portionNo.Inner angle (degrees) between top plate portion and vertical wall portion 1470 MPa classNo.Inner angle (degrees) between top plate portion and vertical wall portion 980 MPa classRemarksHat cross section, concave shapeOne stepForm step portion having concave shape from initial stage of forming111151103Conventional example↑One stepForm step portion having concave shape near forming bottom dead center21025299Invention example↑Two stepsForm step portion having concave shape in second step31005397Invention example↑Two stepsForm low step portion having concave shape in first step* Step height of target shape in second step41015497Invention exampleU-shaped cross section, concave shapeOne stepForm step portion having concave shape from initial stage of forming510855101Conventional example↑One stepForm step portion having concave shape near forming bottom dead center6985696Invention example↑Two stepsForm step portion having concave shape in second step7985796Invention example↑Two stepsForm low step portion having concave shape in first step* Step height of target shape in second step8995896Invention exampleHat cross section, convex shapeOne stepForm step portion having convex shape from initial stage of forming911559110Conventional example↑One stepForm step portion having convex shape near forming bottom dead center101016099Invention example↑Two stepsForm step portion having convex shape in second step111016198Invention example↑Two stepsForm low step portion having convex shape in first step* Step height of target shape in second step121046299Invention exampleU-shaped cross section, convex shapeOne stepForm step portion having convex shape from initial stage of forming1311363107Conventional example↑One stepForm step portion having convex shape near forming bottom dead center141016499Invention example↑Two stepsForm step portion having convex shape in second step151016598Invention example↑Two stepsForm low step portion having convex shape in first step* Step height of target shape in second step161016699Invention exampleZ-shaped cross section, concave shape / convex shapeOne step-1711367106Conventional example↑One stepForm step portion having concave shape near forming bottom dead center181026899Invention example↑One stepForm step portion having convex shape near forming bottom dead center1910169100Invention example↑Two stepsForm step portion having concave shape in second step201007097Invention example↑Two stepsForm step portion having convex shape in second step211017199Invention exampleL-shaped cross section, concave shape / convex shapeOne step-2210872101Conventional example↑One stepForm step portion having concave shape near forming bottom dead center23987396Invention example↑One stepForm step portion having convex shape near forming bottom dead center241017499Invention example↑Two stepsForm step portion having concave shape in second step25987596Invention example↑Two stepsForm step portion having convex shape in second step261017698Invention example*Step height of low step portion: 5 mm

[0060] In Table 1, for No. 1 to No. 26, a steel sheet having tensile strength of 1470 MPa was used as a blank. In No. 1 to No. 4, the press-formed product 100 (FIG. 11) having the hat cross-sectional shape in which the step portion 109 having the concave shape was formed in the top plate portion 101 was press-formed.

[0061] In No. 1, press-forming was performed in one step of the related art and the step portion 109 having the concave shape was formed from an initial stage of forming. The inner angle between the top plate portion 101 and the vertical wall portion 105 in No. 1 was 111 degrees, and spring-back greatly occurred.

[0062] In No. 2, press-forming was performed in one step according to the present invention and the step portion 109 having the concave shape was formed near the forming bottom dead center. The inner angle between the top plate portion 101 and the vertical wall portion 105 in No. 2 was 102 degrees and spring-back satisfactorily decreased more than the spring-back in No. 1 of conventional example.

[0063] In No. 3, press-forming was performed in two steps including the first forming step and the second forming step according to the present invention and the step portion 109 having the concave shape was formed in the second forming step. The inner angle between the top plate portion 101 and the vertical wall portion 105 in No. 3 was 100 degrees and spring-back satisfactorily deceased more than the spring-back in No. 1 of conventional example and No. 2 of the invention example.

[0064] In No. 4, press-forming was performed in two steps including the first forming step and the second forming step according to the present invention and a low step portion having a shallow concave shape was formed in the first forming step and was set to a step height of the target shape in the second forming step. The inner angle between the top plate portion 101 and the vertical wall portion 105 in No. 4 was 101 degrees and spring-back satisfactorily decreased more than the spring-back in No. 1 of conventional example.

[0065] In Table 1, in No. 5 to No. 8, a press-formed product (not illustrated) having a U cross-sectional shape in which a step portion having a concave shape was formed in a top plate portion was press-formed.

[0066] In No. 5, press-forming was performed in one step of the related art and a step portion having a concave shape was formed from the initial stage of forming. The inner angle between the top plate portion and the vertical wall portion in No. 5 was 108 degrees and spring-back greatly occurred.

[0067] In No. 6, press-forming was performed in one step according to the present invention and a step portion having a concave shape was formed near the forming bottom dead center. The inner angle between the top plate portion and the vertical wall portion in No. 6 was 98 degrees and spring-back satisfactorily decreased more than the spring-back in No. 5 of conventional example.

[0068] In No. 7, press-forming was performed in two steps including the first forming step and the second forming step according to the present invention and a step portion having a concave shape was formed in the second forming step. The inner angle between the top plate portion 101 and the vertical wall portion 105 in No. 7 was 98 degrees and, as in No. 6 of the invention example, spring-back satisfactorily decreased more than No. 5 of conventional example.

[0069] In No. 8, press-forming was performed in two steps including the first forming step and the second forming step according to the present invention and a low step portion having a shallow concave shape was formed in the first forming step and set to the step height of the target shape in the second forming step. The inner angle between the top plate portion and the vertical wall portion in No. 8 was 99 degrees and spring-back satisfactorily decreased more than the spring-back in No. 5 of conventional example.

[0070] In Table 1, in No. 9 to No. 12, a press-formed product (not illustrated) having a hat cross-sectional shape in which a step portion having a convex shape was formed in a top plate portion was press-formed.

[0071] In No. 9, press-forming was performed in one step of the related art and a step portion having a convex shape was formed from the initial stage of forming. The inner angle between the top plate portion and the vertical wall portion in No. 9 was 115 degrees and spring-back greatly occurred.

[0072] In No. 10, press-forming was performed in one step according to the present invention and a step portion having a convex shape was formed near the forming bottom dead center. The inner angle between the top plate portion and the vertical wall portion in No. 10 was 101 degrees and spring-back satisfactorily decreased more than the spring-back in No. 9 of conventional example.

[0073] In No. 11, press-forming was performed in two steps including the first forming step and the second forming step according to the present invention and a step portion having a convex shape was formed in the second forming step. The inner angle between the top plate portion 101 and the vertical wall portion 105 in No. 11 was 101 degrees and, as in No. 10, spring-back satisfactorily deceases more than the spring-back in No. 9 of conventional example.

[0074] In No. 12, press-forming was performed in two steps including the first forming step and the second forming step according to the present invention and a low step portion having a low convex shape was formed in the first forming step and was set to the step height of the target shape in the second forming step. The inner angle between the top plate portion and the vertical wall portion in No. 12 was 104 degrees and spring-back satisfactorily decreased more than the spring-back in No. 9 of conventional example.

[0075] In Table 1, in No. 13 to No. 16, a press-formed product (not illustrated) having a U cross-sectional shape in which a step portion having a convex shape was formed in a top plate portion was press-formed.

[0076] In No. 13, press-forming was performed in one step of the related art and a step portion having a convex shape was formed from the initial stage of forming. The inner angle between the top plate portion and the vertical wall portion in No. 13 was 113 degrees and spring-back greatly occurred.

[0077] In No. 14, press-forming was performed in one step according to the present invention and a step portion having a convex shape was formed near the forming bottom dead center. The inner angle between the top plate portion and the vertical wall portion in No. 14 was 101 degrees and spring-back satisfactorily decreased more than the spring-back in No. 13 of conventional example.

[0078] In No. 15, press-forming was performed in two steps including the first forming step and the second forming step according to the present invention and a step portion having a convex shape was formed in the second forming step. The inner angle between the top plate portion and the vertical wall portion in No. 15 was 101 degrees and, as in No. 14 of the invention example, spring-back satisfactorily decreased more than the spring-back in No. 13 of conventional example.

[0079] In No. 16, press-forming was performed in two steps including the first forming step and the second forming step according to the present invention and a low step portion having a convex shape was formed in the first forming step and set to the step height of the target shape in the second forming step. The inner angle between the top plate portion and the vertical wall portion in No. 16 was 101 degrees and, as in No. 14 and No. 15 of the invention example, spring-back satisfactorily decreased more than the spring-back in No. 13 of conventional example.

[0080] In Table 1, in No. 17 to No. 21, a press-formed product (not illustrated) having a Z cross-sectional shape was press-formed.

[0081] In No. 17, press-forming was performed without a step portion being formed in the top plate portion in one step of the related art. The inner angle between the top plate portion and the vertical wall portion in No. 17 was 113 degrees and spring-back greatly occurred.

[0082] In No. 18, press-forming was performed in one step according to the present invention and a step portion having a concave shape was formed in the top plate portion near the forming bottom dead center. The inner angle between the top plate portion and the vertical wall portion in No. 18 was 102 degree and spring-back satisfactorily decreased more than the spring-back in No. 17 of conventional example.

[0083] In No. 19, press-forming was performed in one step according to the present invention and a step portion having a convex shape was formed in the top plate portion near the forming bottom dead center. The inner angle between the top plate portion and the vertical wall portion in No. 19 was 101 degrees and spring-back satisfactorily decreased more than the spring-back in No. 17 of conventional example.

[0084] In No. 20, press-forming was performed in two steps including the first forming step and the second forming step according to the present invention and a step portion having a concave shape was formed in the top plate portion in the second forming step. The inner angle between the top plate portion and the vertical wall portion in No. 20 was 100 degrees and spring-back satisfactorily decreased more than the spring-back in No. 17 of conventional example.

[0085] In No. 21, press-forming was performed in two steps including the first forming step and the second forming step according to the present invention and a step portion having a convex shape was formed in the top plate portion in the second forming step. The inner angle between the top plate portion and the vertical wall portion in No. 21 was 101 degrees and, as in No. 19 of the invention example, spring-back satisfactorily decreased more than the spring-back in No. 17 of conventional example.

[0086] In Table 1, in No. 22 to No. 26, a press-formed product (not illustrated) having an L cross-sectional shape was press-formed.

[0087] In No. 22, press-forming was performed without a step portion being formed in the top plate portion in one step of the related art. The inner angle between the top plate portion and the vertical wall portion in No. 22 was 108 degrees and spring-back greatly occurred.

[0088] In No. 23, press-forming was performed in one step according to the present invention and a step portion having a concave shape was formed near the forming bottom dead center. The inner angle between the top plate portion and the vertical wall portion in No. 23 was 98 degrees and spring-back satisfactorily decreased more than the spring-back in No. 22 of conventional example.

[0089] In No. 24, press-forming was performed in one step according to the present invention and a step portion having a convex shape was formed near the forming bottom dead center. The inner angle between the top plate portion and the vertical wall portion in No. 24 was 101 degrees and spring-back satisfactorily decreased more than the spring-back in No. 22 of conventional example.

[0090] In No. 25, press-forming was performed in two steps including the first forming step and the second forming step according to the present invention and a step portion having a concave shape was formed in the second forming step. The inner angle between the top plate portion and the vertical wall portion in No. 25 was 98 degrees and, as in No. 23 of the invention example, spring-back satisfactorily decreased more than the spring-back in No. 22 of conventional example.

[0091] In No. 26, press-forming was performed in two steps including the first forming step and the second forming step according to the present invention and a step portion having a convex shape was formed in the second forming step. The inner angle between the top plate portion and the vertical wall portion in No. 26 was 101 degrees and, as in to No. 24 of the invention example, spring-back satisfactorily decreased more than the spring-back in No. 22 of conventional example.

[0092] In Table 1, in No. 51 to No. 76, a steel sheet having tensile strength of 980 MPa was used as a blank. In No. 51 to No. 54, the press-formed product 100 (FIG. 11) having the hat cross-sectional shape in which the step portion 109 having the concave shape was formed in the top plate portion 101 was press-formed.

[0093] In No. 51, press-forming was performed in one step of the related art and the step portion 109 having the concave shape was formed from the initial stage of forming. The inner angle between the top plate portion 101 and the vertical wall portion 105 in No. 51 was 103 degrees and spring-back greatly occurred.

[0094] In No. 52, press-forming was performed in one step according to the present invention and the step portion 109 having the concave shape was formed near the forming bottom dead center. The inner angle between the top plate portion 101 and the vertical wall portion 105 in No. 52 was 99 degrees and spring-back satisfactorily decreased more than the spring-back in No. 51 of conventional example.

[0095] In No. 53, press-forming was performed in two steps including the first forming step and the second forming step according to the present invention and the step portion 109 having the concave shape was formed in the second forming step. The inner angle between the top plate portion 101 and the vertical wall portion 105 in No. 53 was 97 degrees and spring-back satisfactorily decreased more than the spring-back in No. 51 of conventional example.

[0096] In No. 54, press-forming was performed in two steps including the first forming step and the second forming step according to the present invention and a low step portion was formed in the first forming step and set to the step height of the target shape in the second forming step. The inner angle between the top plate portion 101 and the vertical wall portion 105 in No. 54 was 97 degrees and, as in No. 53 of the invention example, spring-back satisfactorily decreased more than the spring-back in No. 51 of conventional example.

[0097] In Table 1, in No. 55 to No. 58, a press-formed product (not illustrated) having a U cross-sectional shape in which a step portion having a concave shape was formed in a top plate portion as press-formed.

[0098] In No. 55, press-forming was performed in one step of the related art and a step portion having a concave shape was formed from the initial stage of forming. The inner angle between the top plate portion and the vertical wall portion in No. 55 was 101 degrees and spring-back greatly occurred.

[0099] In No. 56, press-forming was performed in one step according to the present invention and a step portion having a concave shape was formed near the forming bottom dead center. The inner angle between the top plate portion and the vertical wall portion in No. 56 was 96 degrees and spring-back satisfactorily decreased more than the spring-back in No. 55 of conventional example.

[0100] In No. 57, press-forming was performed in two steps including a first forming step and a second forming step according to the present invention and a step portion having a concave shape was formed in the second forming step. The inner angle between the top plate portion 101 and the vertical wall portion 105 in No. 57 was 96 degrees and, as in No. 56 of the invention example, spring-back satisfactorily decreased more than the spring-back in No. 55 of conventional example.

[0101] In No. 58, press-forming was performed in two steps including the first forming step and the second forming step according to the present invention and a low step portion was formed in the first forming step and the low step portion was set to the step height of the target shape in the second forming step. The inner angle between the top plate portion and the vertical wall portion in No. 58 was 96 degrees and, as in No. 56 and No. 57 of the invention example, spring-back satisfactorily decreased more than the step-back in No. 55 of conventional example.

[0102] In Table 1, in No. 59 to No. 62, a press-formed product (not illustrated) having a hat cross-sectional shape in which a step portion having a convex shape was formed in a top plate portion was press-formed.

[0103] In No. 59, press-forming was performed in one step of the related art and a step portion having a convex shape was formed from the initial stage of forming. The inner angle between the top plate portion and the vertical wall portion in No. 59 was 110 degrees and spring-back greatly occurred.

[0104] In No. 60, press-forming was performed in one step according to the present invention and a step portion having a convex shape was formed near the forming bottom dead center. The inner angle between the top plate portion and the vertical wall portion in No. 60 was 99 degrees and spring-back satisfactorily decreased more than the spring-back in No. 59 of conventional example.

[0105] In No. 61, press-forming was performed in two steps including the first forming step and the second forming step according to the present invention and a step portion having a convex shape was formed in the second forming step. The inner angle between the top plate portion 101 and the vertical wall portion 105 in No. 61 was 98 degrees and spring-back satisfactorily decreased more than the spring-back in No. 59 of conventional example.

[0106] In No. 62, press-forming was performed in two steps including the first forming step and the second forming step according to the present invention and a low step portion was formed in the first forming step and a step portion was formed with height set to the step height of the target shape in the second forming step. The inner angle between the top plate portion and the vertical wall portion in No. 62 was 99 degrees and spring-back satisfactorily decreased more than the spring-back in No. 59 of conventional example.

[0107] In Table 1, in No. 63 to No. 66, a press-formed product (not illustrated) having a U cross-sectional shape in which a step portion having a convex shape was formed in a top plate portion was press-formed.

[0108] In No. 63, press-forming was performed in one step of the related art and a step portion having a convex shape was formed from the initial stage of forming. The inner angle between the top plate portion and the vertical wall portion in No. 63 was 107 degrees and spring-back greatly occurred.

[0109] In No. 64, press-forming was performed in one step according to the present invention and a step portion having a convex shape was formed near the forming bottom dead center. The inner angle between the top plate portion and the vertical wall portion in No. 64 was 99 degrees and spring-back satisfactorily decreased more than the spring-back in No. 63 of conventional example.

[0110] In No. 65, press-forming was performed in two steps including the first forming step and the second forming step according to the present invention and a step portion having a convex shape was formed in the second forming step. The inner angle between the top plate portion and the vertical wall portion in No. 65 was 98 degrees and spring-back satisfactorily decreased more than the spring-back in No. 63 of conventional example.

[0111] In No. 66, press-forming was performed in two steps including the first forming step and the second forming step according to the present invention and a low step portion is formed in the first forming step and a step portion is formed with height set to the step height of the target shape in the second forming step. The inner angle between the top plate portion and the vertical wall portion in No. 66 was 99 degrees and, as in No. 64 of the invention example, spring-back satisfactorily decreased more than the spring-back in No. 63 of conventional example.

[0112] In Table 1, in No. 67 to No. 71, a press-formed product (not illustrated) having a Z cross-sectional shape was press formed.

[0113] In No. 67, press-forming was performed without a step portion being formed in the top plate portion in one step of the related art. The inner angle between the top plate portion and the vertical wall portion in No. 67 was 106 degrees and spring-back greatly occurred.

[0114] In No. 68, press-forming was performed in one step according to the present invention and a step portion having a concave shape was formed near the forming bottom dead center. The inner angle between the top plate portion and the vertical wall portion in No. 68 was 99 degrees and spring-back satisfactorily decreased more than the spring-back in No. 67 of conventional example.

[0115] In No. 69, press-forming was performed in one step according to the present invention and a step portion having a convex shape was formed near the forming bottom dead center. The inner angle between the top plate portion and the vertical wall portion in No. 69 was 100 degrees and spring-back satisfactorily decreased more than the spring-back in No. 67 of conventional example.

[0116] In No. 70, press-forming was performed in two steps including the first forming step and the second forming step according to the present invention and a step portion having a concave shape was formed in the second forming step. The inner angle between the top plate portion and the vertical wall portion in No. 70 was 97 degrees and spring-back satisfactorily decreased more than the spring-back in No. 67 of conventional example.

[0117] In No. 71, press-forming was performed in two steps including the first forming step and the second forming step according to the present invention and a step portion having a convex shape was formed in the second forming step. The inner angle between the top plate portion and the vertical wall portion in No. 71 was 99 degrees and spring-back satisfactorily decreased more than the spring-back in No. 67 of conventional example.

[0118] In Table 1, in No. 72 to No. 76, a press-formed product (not illustrated) having an L cross-sectional shape was press-formed.

[0119] In No. 72, press-forming was performed without a step portion being formed in the top plate portion in one step of the related art. The inner angle between the top plate portion and the vertical wall portion in No. 72 was 101 degrees and spring-back greatly occurred.

[0120] In No. 73, press-forming was performed in one step according to the present invention and a step portion having a concave shape was formed near the forming bottom dead center. The inner angle between the top plate portion and the vertical wall portion in No. 73 was 96 degrees and spring-back satisfactorily decreased more than the spring-back in No. 72 of conventional example.

[0121] In No. 74, press-forming was performed in one step according to the present invention and a step portion having a convex shape was formed near the forming bottom dead center. The inner angle between the top plate portion and the vertical wall portion in No. 74 was 99 degrees and spring-back satisfactorily decreased more than the spring-back in No. 72 of conventional example.

[0122] In No. 75, press-forming was performed in two steps including the first forming step and the second forming step according to the present invention and a step portion having a concave shape was formed in the second forming step. The inner angle between the top plate portion and the vertical wall portion in No. 75 was 96 degrees and, as in 73 of the invention example, spring-back satisfactorily decreased more than the spring-back in No. 72 of conventional example.

[0123] In No. 76, press-forming was performed in two steps including the first forming step and the second forming step according to the present invention and a step portion having a convex shape was formed in the second forming step. The inner angle between the top plate portion and the vertical wall portion in No. 76 was 98 degrees and spring-back satisfactorily decreased more than the spring-back in No. 72 of conventional example.Industrial Applicability

[0124] As explained above, the present invention can provide a method of manufacturing a press-formed product that can reduce spring-back without spoiling the appearance of a press-formed product having a target shape in which a step portion having a concave shape or a convex shape is formed in a top plate portion.Reference Signs List

[0125] 10FIRST DIE 20SECOND DIE 30DIE 50DIE 59PAD 61CAM 100PRESS-FORMED PRODUCT 101TOP PLATE PORTION 103RIDGELINE PORTION 105VERTICAL WALL PORTION 107FLANGE PORTION 109STEP PORTION 110BLANK 120INTERMEDIATE FORMED PRODUCT 121INTERMEDIATE TOP PLATE PORTION 123INTERMEDIATE RIDGELINE PORTION 125INTERMEDIATE VERTICAL WALL PORTION 127INTERMEDIATE FLANGE PORTION

Claims

1. A method of manufacturing a press-formed product including a top plate portion and a vertical wall portion continuous from the top plate portion via a ridgeline portion, the press-formed product having a target shape in which a step portion having a concave shape or a convex shape in a cross section orthogonal to the ridgeline portion is formed in the top plate portion in an extending direction of the ridgeline portion, the method comprising the steps of: press-forming a blank into an intermediate formed product including an intermediate top plate portion and an intermediate vertical wall portion continuous from the intermediate top plate portion via an intermediate ridgeline portion and applying bending deformation to the intermediate ridgeline portion; and subsequently press-forming the intermediate formed product into the press-formed product having the target shape by forming the step portion having the concave shape or the convex shape in the intermediate top plate portion of the intermediate formed product, wherein when the step portion having the concave shape or the convex shape is formed, bending-back deformation is applied to the intermediate ridgeline portion by drawing the intermediate ridgeline portion to the intermediate top plate portion side.

2. The method of manufacturing the press-formed product according to claim 1, comprising: a first forming step of press-forming the blank into the intermediate formed product including the intermediate top plate portion and the intermediate vertical wall portion continuous from the intermediate top plate portion via the intermediate ridgeline portion and applying bending deformation to the intermediate ridgeline portion; and a second forming step of press-forming the intermediate formed product into the press-formed product having the target shape by forming the step portion having the concave shape or the convex shape in the intermediate top plate portion of the intermediate formed product, wherein in the second forming step, at a time of forming the step portion having the concave shape or the convex shape, bending-back deformation is applied to the intermediate ridgeline portion by drawing the intermediate ridgeline portion to the intermediate top plate portion side.

3. The method of manufacturing the press-formed product according to claim 2, wherein in the first forming step, a low step portion having a step height smaller than the target shape is formed in the intermediate top plate portion, and in the second forming step, the step portion is formed by setting the low step portion to a step height of the target shape.

4. The method of manufacturing the press-formed product according to claim 1, wherein the step of press-forming the blank into the intermediate formed product and subsequently press-forming the intermediate formed product into the press-formed product having the target shape by forming the step portion having the concave shape or the convex shape in the intermediate top plate portion of the intermediate formed product are performed in one step.

5. A method of manufacturing a press-formed product comprising: a press-forming step of press-forming, by using the method of manufacturing the press-formed product according to any one of claims 1 to 4, the top plate portion, a pair of the vertical wall portions continuous from both edges of the top plate portion via the ridgeline portion, and the press-formed product in which the step portion is formed in the top plate portion; and a dividing step of cutting the top plate portion of the press-formed product press-formed in the press-forming step in an extending direction of the ridgeline portion and dividing the press-formed product.

Images