Method for manufacturing press-formed article

Abstract

The present invention provides a press-forming method capable of reducing generation of wrinkles and stably obtaining a press-formed article with a simple die structure. Provided is a method for manufacturing a press-formed article having a target component shape (1) with a cross-section including a top plate part (1A) and a vertical wall part (1B), the top plate part (1A) having a curved part (2), which is curved to protrude toward the outer surface side of the top plate part (1A), at an intermediate portion in the longitudinal direction. The method comprises: a first step (11) for press-forming an intermediate component (13) using a die having a top plate forming surface (30A), a vertical wall upper part forming surface (30Ba) for forming an upper part of the vertical wall part (1B), and a vertical wall lower part forming surface (30Bb); and a second step (12) for press-forming the intermediate component (13) into the target component shape. An angle of the vertical wall lower part forming surface (30Bb) with respect to the top plate forming surface (30A) is larger than an angle of the vertical wall upper part forming surface (30Ba) with respect to the top plate forming surface (30A), and the top plate forming surface (30A) has a forming surface for forming the curved part (2), curved along the longitudinal direction at an intermediate portion in the longitudinal direction.

Description

Manufacturing method for press-molded products

[0001] The present invention relates to a method for manufacturing a press-formed product by press-forming a metal plate into a target part shape. The target part shape of the present invention has a cross section having a top plate portion and vertical wall portions connected to widthwise ends of the top plate portion. The target part shape of the present invention also has a curved portion midway along the longitudinal direction, which is a direction intersecting the cross section. The curved portion causes the top plate portion to be convexly curved toward the outer surface of the top plate portion along the longitudinal direction. The present invention is a technology particularly suitable for press-forming high-strength materials, such as steel plate with a material strength of 590 MPa or more.

[0002] In recent years, automobile bodies have been required to achieve both improved crashworthiness and weight reduction. For this reason, the use of high-tensile steels of 590 MPa or more, and even ultra-high-tensile steels of 980 MPa or more, has been increasing as materials for body structural parts. High-tensile steels and ultra-high-tensile steels have high yield strength and tensile strength, so forming defects such as wrinkles become an issue when they are press-formed.

[0003] One example of a press-formed product used in a vehicle body structural component is a part with a hat-shaped cross section. A hat-shaped cross section is a cross-sectional shape in which a top plate portion, a vertical wall portion, and a flange portion are continuous in the width direction. Furthermore, press-formed products used in vehicle body structural components include a part in which the top plate portion is convexly curved toward the outer surface (upper side) of the top plate portion along the longitudinal direction in a side view. Specifically, there is a part having a curved portion that is curved in a mountain shape in a side view. When a metal sheet is press-formed into such a part shape, the difference in line length between the top plate portion and the flange portion may cause wrinkles in the flange. In particular, when an ultra-high tensile steel is used as the metal sheet, the above-mentioned factors can cause more pronounced wrinkles. This is due to the high yield stress.

[0004] Patent Document 1 describes a press-forming method for manufacturing a curved press part having a hat-shaped cross section. The press-forming method includes a preforming step and a main forming step. The preforming step is a step of producing a preform having a bent portion extending along the longitudinal direction at the widthwise end of a flat blank. The main forming step is a step of forming a top surface portion and a side wall portion of the preform. Patent Document 1 describes that this forming method imparts high rigidity to the preform and can suppress wrinkles during main forming.

[0005] Patent Document 2 also describes a press-forming method for producing a press-formed product with a hat-shaped cross section. The press-formed product has a convexly curved portion that is convexly curved in the height direction along the longitudinal direction in a side view. The press-forming method includes an intermediate shape forming process and a target part shape forming process. The intermediate shape forming process is a process of press-forming a part into an intermediate shape. The intermediate shape has a shorter longitudinal length than the target part shape, and the convexly curved portion is more curved than the target part shape. Furthermore, the intermediate shape has a larger opening angle between the top plate portion and the vertical wall portion at the convexly curved portion, and a lower vertical wall height than the target part shape. The target part shape forming process is a process of press-forming the part into the intermediate shape into the target part shape. Patent Document 2 describes that this process suppresses material flow from the vertical wall portion to the flange portion and reduces wrinkles.

[0006] The press-forming method described in Patent Document 3 is a press-forming method in which a press-formed part having a drawn shape is formed by setting a shape of a press-formed part in a previous process from an intermediate shape obtained during development into a final part shape. Patent Document 3 describes that this allows the shape to be set so that there is substantially no change in cross-sectional line length when forming from the shape in the previous process into the final part shape, thereby suppressing the occurrence of cracks.

[0007] JP 2013-169578 A JP 2020-185591 A WO2017 / 010470

[0008] However, the press forming method described in Patent Document 1 does not form the ridgeline of the punch shoulder in the upstream process. As a result, the setting position of the upstream part in the downstream process and its behavior during forming become unstable, making it difficult to obtain a stable shape in mass production. Furthermore, the press forming method described in Patent Document 2 changes the shape of each part relative to the target part shape, resulting in a complex design. Furthermore, the upstream part shape is formed into a loose shape similar to a flat plate compared to the target part shape. As a result, there is a risk of unstable behavior during forming in the downstream process. Furthermore, the press forming method described in Patent Document 3 is effective for simple parts. However, there is a risk of cross-sectional line length variations occurring in actual parts with complex shapes. If cross-sectional line length variations occur, there is a risk that wrinkles occurring during forming in the downstream process cannot be sufficiently suppressed.

[0009] The present invention has been made with the above points in mind. The present invention is directed to a press-formed product having a cross section such as a hat-shaped cross section and a top plate portion that is curved in a mountain shape along the longitudinal direction. One of the objects of the present invention is to provide a method for press-forming such a press-formed product using a simple mold structure. Another object of the present invention is to provide a press-forming method that reduces the occurrence of wrinkles and can stably produce a press-formed product.

[0010] The inventors have investigated the manufacture of press-formed products having a cross-sectional shape, such as a hat-shaped cross section, with a top plate portion and vertical wall portions, in which the top plate portion has a convex curve toward the outer surface of the top plate portion along the longitudinal direction midway. Specifically, the inventors have investigated the manufacture of press-formed products having a curved portion that is curved in a mountain shape in side view. Furthermore, the inventors have investigated a press-forming method that can significantly reduce the occurrence of wrinkles with a simple die structure, even when a high-strength metal sheet, such as a high-tensile steel or ultra-high-tensile steel, is used as the blank. In this process, the inventors have also investigated a press-forming method that can consistently obtain a wrinkle-free target part shape. The inventors have discovered the following: For an intermediate part before final forming, first, the vertical wall portion is bent outward in a cross-sectional shape midway along the height direction of the vertical wall portion. Then, in the final forming process, the inventors have discovered that wrinkles in the flange portion and the lower end of the vertical wall portion can be consistently reduced by simply bending back the vertical wall portion of the intermediate part midway.

[0011] In order to solve the problem, one aspect of the present invention is a method for manufacturing a press-molded product by press-molding a metal plate into a target part shape having a cross section with a top plate portion and a vertical wall portion connected to a width direction end of the top plate portion, and the top plate portion has a curved portion that is convexly curved toward the outer surface of the top plate portion along the longitudinal direction, which is a direction intersecting the cross section, the method comprising: a top plate molding surface that molds the top plate portion; a vertical wall upper molding surface that is continuous with the top plate molding surface and molds the upper part of the vertical wall portion; and a vertical wall portion that is continuous with the vertical wall upper molding surface and extends in a direction away from the top plate molding surface. The method comprises a first step of press-forming a metal plate into an intermediate part having a top plate portion and a vertical wall portion using a mold having a vertical wall lower molding surface that extends in a direction different from the extending direction of the upper molding surface, and a second step of press-forming the intermediate part into the target part shape, wherein the angle of the vertical wall lower molding surface relative to the top plate molding surface is greater than the angle of the vertical wall upper molding surface relative to the top plate molding surface and the angle of the vertical wall portion relative to the top plate portion of the target part shape, and the top plate molding surface has a molding surface that forms a curved portion that curves along the longitudinal direction midway along the longitudinal direction.

[0012] An aspect of the present invention relates to the manufacture of a press-formed product having a target part shape, a cross-sectional shape having a top plate portion and a vertical wall portion, and a curved portion in which the top plate portion has a mountain-like shape in side view along the longitudinal direction midway. According to this aspect of the present invention, even when high-tensile steel is used for the metal sheet, wrinkles that occur in a curved part in side view can be significantly reduced without requiring a complex mold shape. As a result, according to this aspect of the present invention, a part having a wrinkle-free target part shape can be obtained. That is, according to this aspect of the present invention, a press-formed product having the above-mentioned target part shape can be manufactured without wrinkles. As a result, according to this aspect of the present invention, even when high-tensile steel or ultra-high-tensile steel is used, wrinkle-free parts can be obtained, leading to improved yield. Furthermore, the absence of wrinkles reduces damage to the mold, leading to cost savings due to reduced repair costs. Furthermore, when used as a vehicle body structural part, the part can be easily assembled.

[0013] 1 is a diagram illustrating an example of a cross-sectional shape of a part to which the present invention can be applied; FIG. 2 is a diagram illustrating a target part shape according to an embodiment based on the present invention; (a) is a perspective view; (b) is a side view; FIG. 3 is a diagram illustrating steps of a method for manufacturing a press-formed part according to an embodiment based on the present invention; FIG. 4 is a diagram illustrating the cross-sectional shape of a part; (a) is an example of the cross-sectional shape of an intermediate part; (b) is an example of the cross-sectional shape of the target part shape at that time; FIG. 5 is a diagram illustrating an example of a longitudinal distribution pattern of bends; FIG. 6 is a diagram illustrating an example of a longitudinal distribution pattern of bends; FIG. 7 is a schematic cross-sectional view illustrating the forming surface of a mold used in a first step; FIG. 8 is a diagram illustrating a state during forming in a comparative forming method; FIG. 9 is a diagram illustrating the distribution of the sheet thickness change rate at the bottom dead center of forming in a comparative forming method; FIG. 10 is a schematic diagram illustrating the cause of wrinkles occurring in a comparative forming method; FIG. 11 is a diagram illustrating a state during forming in a first step; FIG. 12 is a diagram illustrating a state during forming in a second step; FIG. 13 is a schematic diagram for illustrating processing when the target part shape does not have a flange portion;

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The present embodiment relates to a method for manufacturing a press-formed product in which a metal plate is formed into a target part shape by press forming.

[0015] (Target Part Shape) In this embodiment, the target part shape 1 has a cross-sectional shape having a top plate portion 1A and a vertical wall portion 1B, as shown in FIG. 1 . Examples of the cross-section include a hat-shaped cross-section (see FIG. 1( a)) or a U-shaped cross-section (see FIG. 1( b)), in which vertical wall portions 1B are continuous on both widthwise sides of the top plate portion 1A. The cross-section may also be a Z-shaped cross-section (see FIG. 1( c)) or an L-shaped cross-section (see FIG. 1( d)), in which the vertical wall portion 1B is continuous on only one widthwise side of the top plate portion 1A. Note that the hat-shaped cross-section and Z-shaped cross-section are cross-sectional shapes in which a flange portion 1C is continuous with the end of the vertical wall portion 1B, as shown in FIG. 1 . In the following example, the cross-section of the target part shape 1 is a hat-shaped cross-section. The present invention achieves the same effects as those described below even when using other cross-sections.

[0016] Furthermore, as shown in Figure 2, the target part shape 1 of this embodiment is a part shape in which the top plate portion 1A has a curved portion 2 in the longitudinal direction, where the top plate portion 1A is curved convexly toward the outer surface side of the top plate portion 1A along the longitudinal direction. The longitudinal direction is a direction intersecting the cross section. "Convex toward the outer surface side of the top plate portion 1A" means that the top plate portion 1A has a shape that is convex upward (see Figure 2(b)). For example, in a side view, the top plate portion 1A has a mountain shape at the curved portion 2.

[0017] In this embodiment, as shown in FIG. 2 , the table comprises a curved portion 2 and left and right linear portions 3 and 4, respectively, provided on either side of the curved portion 2. In this embodiment, the table top portion 1A of the left linear portion 3 has a surface that extends substantially horizontally along the longitudinal direction. However, the table top portion 1A of the right linear portion 4 has an inclined surface that becomes lower as it moves away from the curved portion 2, i.e., toward the right in FIG. 2 . In this way, by having the curved portion 2 that is convexly curved on the outer surface of the table top portion 1A, the angle θ3 between the flange portion 1C (inner surface) between the left and right table top portions 1A sandwiching the curved portion 2 is less than 180 degrees. The angle θ3 between the left and right table top portions 1A sandwiching the curved portion 2 is, for example, between 160 degrees and 175 degrees.

[0018] Here, the curved portion 2 shown in FIG. 2 has a curved shape that is bent upward and convex. In this case, the curved portion 2 is formed in a portion along the longitudinal direction, and the range of the curved portion 2 in the longitudinal direction is shortened. Furthermore, the radius of curvature of the curved portion 2 may be larger or smaller than the radius of curvature shown in FIG. 2. Here, in this embodiment, as shown in FIG. 2, the left and right linear portions 3 and 4 connected via the curved portion 2 have a flat surface on the top plate 1A along the longitudinal direction. This portion may be formed with a curved shape along the longitudinal direction that is gentler than the curve of the curved portion 2. Furthermore, the top plate 1A of the linear portion 3 may have an inclined surface whose height changes toward the left side in FIG. 2.

[0019] In addition, in Fig. 2, the lower end of the vertical wall portion 1B and the flange portion 1C extend linearly along the longitudinal direction in a side view. These portions may be curved along the entire longitudinal direction in a side view. However, this embodiment is particularly effective when there is a locally curved portion 2 in a portion of the longitudinal direction. Furthermore, the dimensions shown in Fig. 2 are included to accompany the dimensions of the example and do not limit the present invention in any way.

[0020] (Metal Plate) The material of the metal plate 10 (blank 10) targeted in this embodiment is not particularly limited. However, the present invention is a technology suitable for a steel plate having a material strength (tensile strength) of 590 MPa or more for the metal plate 10.

[0021] (Manufacturing Method) As shown in FIG. 3 , the manufacturing method of the press-formed product of this embodiment includes a first step 11 and a second step 12 .

[0022] <First Step 11> The first step 11 is a step of press-forming the metal plate 10 into an intermediate part 13. The cross section of the intermediate part 13 has a top plate portion 13A and a vertical wall portion 13B. As shown in FIG. 4(a), the cross section of the intermediate part 13 is formed by connecting the top plate portion 13A and the upper portions 13Ba of the vertical wall portions 13B to the left and right ends of the top plate portion 13A in the width direction. Furthermore, the cross section of the intermediate part 13 has a bent portion 14 at a midpoint in the height direction, where the lower portions 13Bb of the vertical wall portions 13B are bent outward. As shown in FIG. 4(a), the cross section of the intermediate part 13 has a shape in which a flange portion 13C is connected to the lower end of the vertical wall portion 13B. Furthermore, the top plate portion 13A of the intermediate part 13 has a shape having a curved portion 21 midway along the longitudinal direction. The curved portion 21 is a portion of the top plate portion 13A that is curved convexly toward the outer surface of the top plate portion 13A along the longitudinal direction (see FIG. 5). Note that FIG. 4B shows the cross-sectional shape of the target part shape 1 for the intermediate part 13 having the cross section shown in FIG. 4A.

[0023] In the first step 11, the metal sheet 10 is formed by the upper vertical-wall forming surface and the lower vertical-wall forming surface, as described below. That is, when the metal sheet 10 is formed into the intermediate part 13, the boundary between the upper vertical-wall forming surface and the lower vertical-wall forming surface forms the vertical wall portion 13B of the intermediate part 13 into a shape that is bent outward at a midpoint in the height direction. This bent position is the bent portion 14. The outwardly opening bent portion 14 imparted to the vertical wall portion 1B in the first step 11 may be uniformly provided linearly along the longitudinal direction of the part, as shown in FIG. 5 . Note that in the example of FIG. 5 , the distance H from the top plate portion 13A to the bent portion 14 is constant in the linear portion on the left side. In contrast, in the bent portion 14 on the right side, the distance H from the top plate portion 13A to the bent portion 14 decreases toward the right side depending on the inclination of the top plate portion 13A. However, the position of the bent portion 14 is not limited thereto. As shown in FIG. 7( a ), the bent portion 14 may extend linearly in an oblique direction so that the right side (the side with a lower height) is relatively lower in side view.

[0024] As shown in FIG. 6 , the bent portion 14 may be formed to match the shape (inclination) of the top plate portion 13A along the longitudinal direction in a side view of the component. That is, the bent portion 14 along the longitudinal direction may be bent at a position where the top plate portion 13A curves in a side view. This allows the bent portion 14 to be formed so that the distance H (height H) from the top plate portion 13A to the bent portion 14 is constant. However, the height distance from the top plate portion 13A to the bent portion 14 does not necessarily need to be constant. For example, as shown in FIG. 7( a), the bent portion 14 may be linearly inclined in the longitudinal direction to match the inclination direction of the top plate portion 13A. As shown in FIG. 7( b), the bent portion 14 may be bent along the longitudinal direction at the curved portion 21 to match the curvature of the top plate portion 13A. In the case of FIG. 7( b), the ratio between the height length of the upper portion 13Ba of the vertical wall portion and the height length of the lower portion 13Bb of the vertical wall portion is constant in the longitudinal direction. The length in the height direction of the upper portion 13Ba of the vertical wall portion is the height direction distance H. Here, press forming of the bent portion 14 is easier when the bent portion 14 extends linearly.

[0025] Furthermore, the bent portion 14 does not necessarily have to be formed over the entire length of the part, from one end to the other in the longitudinal direction. The bent portion 14 may be provided only at the position of the curved portion 21 and its vicinity in a side view. Note that the position of the curved portion 21 in the longitudinal direction is aligned with the position of the curved portion 2 of the target part shape 1. Note that the convex shape of the curved portion 21 of the intermediate part 13 does not have to perfectly match the curved portion 2 of the target part shape 1. However, considering the stability of subsequent processes, it is better for the convex shape to match the curved portion 2 as closely as possible.

[0026] In addition, at the position of the curved portion 21 in a side view, the distance H is preferably in the range of 15% to 75% of the height of the vertical wall portion 1B in the target part shape 1. The distance H is the distance from the top plate portion 13A of the intermediate part 13 to the bent portion 14 along the vertical wall portion 13B of the intermediate part 13. If the distance H is less than 15% of the height of the vertical wall portion 1B in the target part shape 1, the amount of the flange portion 1C formed in the second forming step will be large. As a result, wrinkles may not be sufficiently reduced. On the other hand, if the distance H is more than 75% of the height of the vertical wall portion 1B in the target part shape 1, the amount of the flange portion 13C formed in the first forming step will be large. As a result, wrinkles may be large in the first forming step.

[0027] [Mold] The mold used in the first step 11 includes an upper mold 30 and a lower mold 31, as shown in FIG. 8. The upper mold 30 and the lower mold 31 are positioned opposite each other in the pressing direction. The molding surfaces of the upper mold 30 and the lower mold 31 have a surface shape that conforms to the shape of the intermediate part 13 to be manufactured, as shown in FIG. 8. The upper mold 30 includes a top plate molding surface 30A, a vertical wall upper molding surface 30Ba, a vertical wall lower molding surface 30Bb, and a flange molding surface 30C as molding surfaces. The top plate molding surface 30A is a molding surface that molds the top plate portion 13A. In this embodiment, the width of the top plate molding surface 30A is set to match the width of the top plate portion 1A of the target part shape 1. For example, the width is the same as or similar to the width of the top plate portion 1A of the target part shape 1. The top plate molding surface 30A also has a concave molding surface along the longitudinal direction that molds the curved portion 21.

[0028] In this embodiment, there are a pair of left and right vertical wall upper molding surfaces 30Ba. The left and right vertical wall upper molding surfaces 30Ba are formed continuously on both sides of the top plate molding surface 30A in the width direction. The vertical wall upper molding surfaces 30Ba are surfaces that mold the upper portion 13Ba of the vertical wall portion 13B that is continuous with the top plate portion 13A. In this embodiment, the angle of each vertical wall upper molding surface 30Ba relative to the top plate molding surface 30A is set to match the angle of the vertical wall portion 1B relative to the top plate portion 1A in the target part shape 1. For example, the angle relative to the top plate molding surface 30A is equal to the angle of the vertical wall portion 1B relative to the top plate portion 1A in the target part shape 1. The vertical wall lower molding surface 30Bb is continuous with the lower end of the vertical wall upper molding surface 30Ba. The vertical-wall lower molding surface 30Bb is a molding surface that extends in a direction away from the top-plate molding surface 30A, different from the extending direction of the vertical-wall upper molding surface 30Ba.

[0029] Specifically, the angle of the vertical wall lower molding surface 30Bb relative to the top plate molding surface 30A is set to be larger than the angle of the vertical wall upper molding surface 30Ba relative to the top plate molding surface 30A. The angle of the vertical wall lower molding surface 30Bb relative to the top plate molding surface 30A is also set to be larger than the angle of the vertical wall portion 1B relative to the top plate portion 1A in the target part shape 1. As a result, compared to the target part shape 1, the intermediate part 13 is formed with a shape in which the lower portion 13Bb of the vertical wall portion 13B opens outward (see FIG. 4(a)). The surface shape of the vertical wall lower molding surface 30Bb follows the surface shape of the lower side of the vertical wall portion 1B in the target part shape 1. The flange molding surface 30C is a molding surface that molds the flange portion 13C. The flange molding surface 30C is continuous with the lower end of the vertical wall lower molding surface 30Bb via an arc-shaped connecting surface.

[0030] 8, the lower mold 31 also has molding surfaces including a top plate molding surface 31A, an upper vertical wall molding surface 31Ba, a lower vertical wall molding surface 31Bb, and a flange molding surface 31C. The top plate molding surface 31A, together with the top plate molding surface 30A of the upper mold 30, is a surface that molds the top plate portion 13A of the intermediate part 13. The upper vertical wall molding surface 31Ba and the lower vertical wall molding surface 31Bb, together with the upper vertical wall molding surface 30Ba and the lower vertical wall molding surface 30Bb of the upper mold 30, are surfaces that mold the vertical wall portion 13B of the intermediate part 13. The flange molding surface 31C, together with the flange molding surface 30C of the upper mold 30, is a surface that molds the flange portion 13C of the intermediate part 13.

[0031] Each molding surface of the lower mold 31 has a shape that follows the corresponding molding surface of the opposing upper mold 30. This is synonymous with each molding surface of the lower mold 31 following the shape of the inner surface of the intermediate part 13. By using a mold consisting of this upper mold 30 and lower mold 31, it is possible to manufacture the intermediate part 13 as shown in Figure 4(a). The relationship between each part of the molding surfaces of the upper mold 30 and lower mold 31 can be considered to be the same as the relationship between each part of the intermediate part 13.

[0032] Here, as shown in Fig. 4(b), the flange angle between the vertical wall portion 1B and the flange portion 1C in the target part shape 1 is defined as θ0. Also, the angle of the flange molding surface 30C relative to the vertical wall lower molding surface 30Bb in the intermediate part 13 is defined as θ1. The angle of the flange molding surface 30C relative to the vertical wall lower molding surface 30Bb is synonymous with the flange angle θ1 between the lower side 13Bb of the vertical wall portion in the intermediate part 13 and the flange portion 13C (see Fig. 4(a)).

[0033] The angle θ1 of the flange molding surface 30C relative to the vertical wall lower molding surface 30Bb is preferably set to satisfy the following formula (1): θ1 ≦ θ0 (1) In general, in the target part shape 1, the angle γ0 of the vertical wall portion 1B relative to the top plate portion 1A and the flange angle θ0 of the flange portion 1C relative to the vertical wall portion 1B are greater than 90 degrees.

[0034] In contrast, by setting the angle θ1 to be equal to or less than the angle θ0, the rigidity of the ridgeline between the vertical wall portion 13B and the flange portion 13C during molding is increased accordingly. As a result, in this embodiment, it is possible to further suppress the occurrence of wrinkles at the lower end of the vertical wall portion 13B and the flange portion 13C in the second step 12. Note that if the angle θ1 is greater than the angle θ0, sufficient part rigidity may not be obtained, and wrinkles may not be sufficiently suppressed in the second step 12.

[0035] Furthermore, it is preferable that angle θ1 be equal to or greater than θ0 / 2. If angle θ1 is smaller than θ0 / 2, the flange angle will be a negative angle in first step 11, which may prevent molding into target part shape 1. Furthermore, the radius of curvature of the ridgeline connecting vertical wall portion 1B and flange portion 1C in target part shape 1 is defined as R0 (see FIG. 4( b)). Furthermore, the radius of curvature of the ridgeline forming surface joining vertical wall lower forming surface 30Bb and flange forming surface 30C in intermediate part 13 is defined as R1. This radius of curvature R1 is synonymous with the radius of curvature of the ridgeline between vertical wall portion 13B and flange B13C in intermediate part 13 (see FIG. 4( a)).

[0036] It is preferable to set the value of the radius of curvature R1 so as to satisfy the following formula (2). The radius of curvature R1 is the radius of curvature of the ridge forming surface joining the vertical wall lower forming surface 30Bb and the flange forming surface 30C. R1 ≦ Ro (2) Here, if R1 is larger than Ro, sufficient part rigidity cannot be obtained, and wrinkles may not be sufficiently suppressed in the second step 12. It is preferable that R1 be 0.5 times or more the plate thickness. If R1 is set to less than 0.5 times the plate thickness, bending cracks may occur.

[0037] Furthermore, it is preferable that the angle α1 between the top plate forming surface 30A and the vertical wall lower forming surface 30Bb is 160 degrees or less. The angle α1 between the top plate portion 1A of the intermediate part 13 and the portion 13Bb below the bent portion 14 of the vertical wall portion 13B is α1 (see FIG. 4(a)). If the angle α1 exceeds 160 degrees, an extreme increase in plate thickness may occur in the second forming step 12, and wrinkles may not be sufficiently suppressed. The specifications for each part of the forming surface of the mold used in the first step 11 are synonymous with the specifications for each part of the shape of the intermediate part 13. For this reason, the shape of the intermediate part 13 shown in FIG. 4(a) will be described.

[0038] The angle γ1 between the top plate portion 13A and the vertical wall portion 13B of the intermediate part 13 may be larger than the angle γ0 between the top plate portion 13A and the vertical wall portion 13B in the target part shape. However, for stable molding in the second step 12, the following setting is preferable. That is, it is preferable to align the angle γ1 with the angle γ0 and provide a bent portion 14 that serves as a base point for opening outward midway in the height direction of the vertical wall portion 13B of the intermediate part 13. Note that the outward-opening portion 13Bb below this bent portion 14 is bent back in the second step 12.

[0039] Furthermore, the curvature radius ρ1 of the bent portion 14 is preferably 0.5 times or more the plate thickness. Setting the curvature radius ρ1 to less than 0.5 times the plate thickness may result in cracks during bending. There is no particular upper limit for the curvature radius ρ1. It is sufficient to ensure a predetermined opening amount or opening angle for the portion of the vertical wall portion 1B below the bent portion 14. Furthermore, it is preferable that the line length L1 in the height direction of the vertical wall portion 1B in the intermediate part 13 be the same as the line length L0 in the height direction of the vertical wall portion 1B in the target part shape 1. The reason for this is as follows: If the line length changes, the rigidity improvement effect is not sufficiently achieved, which may result in wrinkles. Furthermore, the position of the die R portion changes between the first and second steps. Therefore, the bending tendency of the die R portion in the first step may result in a deterioration in dimensional accuracy after forming in the second step.

[0040] <Second Step 12> The second step 12 is a step of press-forming the intermediate part 13 into the target part shape. In the second step 12, the vertical wall portion 13B bent at the bend portion 14 of the intermediate part 13 is bent back into the shape of the vertical wall portion 1B of the target part shape 1. The molding surface of the mold used in the second step 12 has a shape that follows the target part shape. The mold used in the second step 12 includes an upper mold and a lower mold. The molding surface of the upper mold 30 has a shape that follows the outer surface of the target part shape. The molding surface of the lower mold 31 has a shape that follows the inner surface of the target part shape.

[0041] (Functions and Others) <Comparative Forming Method> As a comparative forming method, consider the case where a metal sheet 10 is pressed into a target part shape 1 shown in FIG. 2 in a single press forming operation. The metal sheet 10 used was a steel sheet with a tensile strength of 1470 MPa, and had the dimensions shown in FIG. 2. In the comparative forming method, upper and lower molds having forming surfaces conforming to the target part shape 1 were used as molds. Padded form forming was applied to the comparative forming method. Specifically, the surface of the lower mold that would form the top plate portion 1A of the metal sheet 10 was pressed with a pad and the forming surface of the top plate portion 1A of the lower mold, and the upper mold was moved in the pressing direction toward the lower mold to the bottom dead center of the forming, and press forming was performed.

[0042] Figure 9 shows the side view of the shape during forming using the comparative forming method. As can be seen from Figure 9, wrinkles were found to have occurred 20 mm above the bottom dead center (Figure 9(a)) of the forming bottom of the top plate portion 1A, at the position that would become the curved portion 2. Specifically, wrinkles were found to have occurred in the flange portion 1C. As forming progressed, these wrinkles were found to be flattened, resulting in surface defects such as wrinkle marks and wrinkle patterns. Note that, in this specification, surface defects such as wrinkle marks and wrinkle patterns are collectively referred to as "wrinkles." Figure 10 shows the thickness change rate at the bottom dead center of forming using the comparative forming method. A maximum thickness increase of 20.4% occurred in the flange portion 1C, which is located at the lower end of the curved portion 2. Higher material strength makes the material more susceptible to buckling. Therefore, the higher the material strength, the more pronounced the flange wrinkle problem becomes.

[0043] The mechanism by which these flange wrinkles occur will be explained with reference to Figure 11. In the comparative forming method, as forming progresses, the material of the metal plate 10 moves downward in a direction perpendicular to the surface of the top plate portion 1A. Furthermore, considering the longitudinal line length, the line length of the flange portion 1C becomes shorter than the line length of the curved portion 2 in the top plate portion 1A. As a result, excess material appears in the flange portion 1C, resulting in wrinkles. As the material strength increases, these flange wrinkles become larger. As a result, important issues arise, such as not being able to achieve the desired product shape and the wrinkles damaging the mold.

[0044] In the press-forming method of this embodiment, in order to reduce wrinkles in the flange portion 1C, the intermediate part 13 is first manufactured into the shape described above. That is, in this embodiment, first, in a first step 11, the intermediate part 13 is manufactured into the target part shape 1 or a part shape similar to the target part shape 1, except for the shape of the vertical wall portion 1B. Then, in a second step 12, the intermediate part 13 is manufactured into the target part shape 1. That is, in the first step 11, the metal plate 10 is formed into the intermediate part 13. As shown in FIG. 4( a), the vertical wall portion 13B of the intermediate part 13 is bent so as to open outward at a midpoint in the height direction. Next, in a second step 12, the intermediate part 13 is press-formed into a press-formed product having the target part shape 1, as shown in FIG. 4( b).

[0045] Here, consider the case where the bent portion 14 of the intermediate part 13 is uniformly formed linearly in the longitudinal direction of the part in a side view, as shown in FIG. 5 . The state of wrinkles during forming in the first step 11 and the second step 12 in this case is shown in FIGS. 12 and 13 . The numerical values ​​in FIGS. 12 and 13 refer to the distance to the bottom dead center of forming. Also, FIG. 12 shows the state in the first step 11. FIG. 13 shows the state in the second step 12. In this example, the angle γ0 between the top plate portion 1A and the vertical wall portion 1B in the target part shape 1 is set to 90 degrees (see FIG. 4( b)). The angle α1 of the vertical-wall lower forming surface 30Bb relative to the top plate forming surface 30A is set to 150 degrees (see FIG. 4( a)). That is, the opening angle β1 of the vertical-wall lower forming surface 30Bb relative to the vertical-wall upper forming surface 30Ba is set to 60 degrees.

[0046] As can be seen from Figure 12, in the first process 11, the flange portion 13C reached the bottom dead center without any significant wrinkles. Furthermore, as can be seen from Figure 13, in the second process 12, wrinkles were dispersed over a wide area starting 10 mm above the bottom dead center and continued to the bottom dead center. Thus, according to this embodiment, widespread dispersion of wrinkles reduces mold damage. Furthermore, wrinkles are easily eliminated and flattened near the bottom dead center. Furthermore, the thickness change rates at the bottom dead center in the first process 11 and the second process 12 were calculated using CAE analysis. As a result, in the first process 11, the flange portion 13C at the curved portion 21 increased by a maximum of 4.7%. Furthermore, in the second process 12, the thickness increased by a maximum of 5.8% at the curved portion 2 and its vicinity. It was found that the thickness change rate was significantly reduced compared to 20.4% in the case without countermeasures (comparative forming method).

[0047] Next, the mechanisms for reducing the dispersion of wrinkles and the increase in sheet thickness will be described. First, in the first step 11, forming is performed on a flat blank 10. At this time, an outwardly opening portion 13Bb is formed on the vertical wall portion 13B of the intermediate part 13. This reduces the amount of deformation in the vertical wall portion 13B and the flange portion 13C compared to when the flat blank 10 is formed into the target part shape 1 in a single press. Therefore, the occurrence of wrinkles and the increase in sheet thickness are significantly reduced.

[0048] The flange portion 13C is also formed in the first step 11. This also improves the rigidity of the intermediate part 13. When the intermediate part 13 manufactured in the first step 11 is molded in the second step 12, the main process is bending back the vertical wall portion 13B. This improved part rigidity reduces the likelihood of large localized wrinkles. Similarly to the first step 11, the second step 12 also mainly involves bending back the bent portions, such as the bent portion 14, of the vertical wall portion 13B. As a result, the amount of deformation is reduced compared to molding in one step. Therefore, wrinkles are also less likely to occur in the second step 12. Regarding the above-mentioned improvement in rigidity, the first step 11 forms the bent portion 14 in the vertical wall portion 13B, which serves as the base point for opening outward. At the same time, a ridgeline between the vertical wall portion 13B and the flange portion 13C is formed. By forming this ridgeline, the rigidity of the intermediate part 13 molded in the first step 11 is improved.

[0049] As described above, this embodiment can significantly reduce flange wrinkles with a simple die structure. In particular, this effect can be achieved even when high-tensile steel with a strength class of 590 PMa or higher or ultra-high-tensile steel with a strength class of 980 MPa or higher is used as the material. This makes it more possible to obtain a part with a wrinkle-free target part shape 1. As described above, the present invention primarily targets high-tensile steel and ultra-high-tensile steel with a strength class of 590 PMa or higher as the metal sheet 10. However, the present invention may also use mild steel sheet, aluminum sheet, or the like as the material.

[0050] (Modifications) (1) In the above embodiment, the target part shape 1 has a flange portion 1C in cross section. When the target part shape 1 does not have a flange portion 1C in cross section, such as a U-shaped or L-shaped cross section, the following procedure is used. As in the above embodiment, the mold used in the first step 11 has flange molding surfaces 30C, 31C that mold the flange portion 1C continuously with the vertical wall lower molding surfaces 30Bb, 31Bb. Therefore, as shown by the solid line in FIG. 14 , the intermediate part 13 has a flange portion 13C that is continuous with the vertical wall portion 13B, as in the above embodiment. However, the combined line length of the vertical wall portion 13B and the flange portion 13C in the intermediate part 13 is set to be equivalent to the line length of the vertical wall portion 1B in the target part shape 1.

[0051] Then, in a second process 12, the bent portion 14 formed in the intermediate part 13 is bent back. At the same time, the flange portion 13C of the intermediate part 13 is bent back so that the flange portion 13C of the intermediate part 13 becomes part of the lower end of the vertical wall portion 1B in the target part shape 1. The remaining configuration may be the same as that of the above embodiment. The effects are the same as those of the above embodiment.

[0052] (Other) The present disclosure may also have the following configurations: (1) Disclosure 1 is a manufacturing method for a press-formed product produced by press-forming a metal plate into a target part shape having a cross section with a top plate portion and vertical wall portions connected to widthwise ends of the top plate portion, and in which the top plate portion has a curved portion that is convexly curved toward an outer surface of the top plate portion along the longitudinal direction, which is a direction intersecting the cross section, the method comprising: a first step of press-forming the metal plate into an intermediate part having the top plate portion and vertical wall portions using a mold having a top plate forming surface that forms the top plate portion, an upper vertical wall forming surface that is continuous with the top plate forming surface and forms upper portions of the vertical wall portions, and a lower vertical wall forming surface that is continuous with the upper vertical wall forming surface and extends in a direction away from the top plate forming surface, different from the extending direction of the upper vertical wall forming surface; and a second step of press-forming the intermediate part into the target part shape. A method for manufacturing a press-formed product, wherein an angle of the vertical-wall lower forming surface relative to the top plate forming surface is greater than an angle of the vertical-wall upper forming surface relative to the top plate forming surface and an angle of the vertical wall portion relative to the top plate portion in the target part shape, and the top plate forming surface has a forming surface that forms a curved portion that curves along the longitudinal direction midway along the longitudinal direction. (2) Disclosure 2 describes a method in which the target part shape has a flange portion connected to an end of the vertical wall portion, and a mold used in the first step has a flange forming surface that forms the flange portion contiguous with the vertical-wall lower forming surface. (3) Disclosure 3 describes a method in which the target part shape does not have a flange portion connected to an end of the vertical wall portion, and a mold used in the first step has a flange forming surface that forms the flange portion contiguous with the vertical-wall lower forming surface, and in the second step, the flange portion formed in the intermediate part is bent back to form it into a part of the vertical wall portion of the target part shape. (4) Disclosure 4 provides a manufacturing method for a press-molded product according to Disclosure 2, in which, when a flange angle between a vertical wall portion and a flange portion in the target part shape is defined as θ0 and an angle of the flange molding surface relative to the vertical wall lower molding surface is defined as θ1, the value of the angle θ1 is set so as to satisfy the following formula (1):θ1 ≦ θ0 (1) (5) Disclosure 5 discloses a method for manufacturing a press-formed product according to Disclosure 2 or 4, wherein, when a radius of curvature of a ridge line portion connecting a vertical wall portion and a flange portion in the target part shape is defined as R0, and a radius of curvature of a molding surface connecting the vertical-wall lower molding surface and the flange molding surface is defined as R1, the value of R1 is set so as to satisfy the following formula (2): R1 ≦ Ro (2) (6) Disclosure 6 discloses a method for manufacturing a press-formed product according to any one of Disclosures 1 to 5, wherein, at a position of the curved portion of the intermediate part, a length H of the vertical-wall upper molding surface in a direction away from a top-plate molding surface is set to a length in a range of 15% to 75% of a length of the vertical wall portion in the target part shape in a direction away from the top-plate portion. (7) Disclosure 7 discloses a method for manufacturing a press-formed product according to any one of Disclosures 1 to 6, wherein a boundary between the vertical-wall upper molding surface and the vertical-wall lower molding surface extends linearly along a longitudinal direction of the intermediate part. (8) Disclosure 8 provides a method for manufacturing a press-molded product according to any one of Disclosures 1 to 7, wherein a boundary between the vertical wall upper molding surface and the vertical wall lower molding surface extends along the longitudinal direction of the intermediate part and is curved to match the shape of a top plate portion of the intermediate part at a position that forms a curved portion of the intermediate part. (9) Disclosure 9 is a manufacturing method of a press-molded product manufactured by press-molding a metal plate into a target part shape having a cross section with a top plate portion and vertical wall portions connected to widthwise ends of the top plate portion, and wherein the top plate portion has a curved portion that is convexly curved toward the outer surface of the top plate portion along the longitudinal direction, which is a direction intersecting the cross section, midway along the longitudinal direction, the method comprising: a first step of press-molding a metal plate into an intermediate part having a cross section that has a top plate portion and vertical wall portions connected to widthwise ends of the top plate portion, and the vertical wall portions are bent outward at a midpoint in the height direction; and a second step of press-molding the intermediate part into the target part shape, wherein the top plate portion of the intermediate part has a shape that has a curved portion that is convexly curved toward the outer surface of the top plate portion along the longitudinal direction, midway along the longitudinal direction. (10) Disclosure 10 relates to the method for manufacturing a press-molded product according to Disclosure 9, wherein the target part shape has a flange portion connected to an end of the vertical wall portion, and the intermediate part molded in the first step has a flange portion at a lower part of the vertical wall portion.(11) Disclosure 11 relates to the method for manufacturing a press-formed product according to Disclosure 9, wherein the target part shape does not have a flange portion connected to an end of the vertical wall portion, the intermediate part formed in the first step has a flange portion at a lower part of the vertical wall portion of the intermediate part, and in the second step, the flange portion of the intermediate part is bent back and formed into a part of the vertical wall portion of the target part shape. (12) Disclosure 12 relates to the method for manufacturing a press-formed product according to Disclosures 9 to 11, wherein, at the curved portion, a height direction distance from a top plate portion of the intermediate part to the bent portion of the vertical wall portion of the intermediate part is 15% to 75% of a height direction length of the vertical wall portion of the target part shape. (13) Disclosure 13 relates to the method for manufacturing a press-formed product according to any one of Disclosures 9 to 12, wherein the position of the bend extends linearly along the longitudinal direction of the intermediate part. (14) Disclosure 14 provides the method for manufacturing a press-molded product according to any one of Disclosures 9 to 12, wherein the bending position extends along the longitudinal direction of the intermediate part and is bent at a curved portion position of the intermediate part in a side view to match the shape of the top plate portion of the intermediate part.

[0053] To confirm the flange wrinkle reduction effect of the press forming method of this embodiment, press forming analysis and springback analysis were performed using the finite element method (FEM). The results are described below. In each of the following examples, the target part shape 1 was the shape shown in Figure 2. That is, the target part shape 1 was a part with a hat-shaped cross section and a curved portion 2 in which the top plate portion 1A curves along the longitudinal direction.

[0054] Then, in the first process (first process 11), a press forming analysis was performed in which the blank was formed into an intermediate part 13 having a bent portion 14 that opens outward. The sheet thickness increase rate at the vertical wall portion 13B was then calculated. The metal sheet 10 used for press forming was a steel sheet with a sheet thickness t of 1.2 mm and a tensile strength of 1470 MPa. In this example, the angle α1 between the top plate forming surface and the vertical wall lower forming surface of the die in the first process was varied within a range of 100 to 160 degrees. The vertical wall angle γ0 of the die in the second process (second process 12) was standardized to 90 degrees. An FEM analysis was then performed under these conditions.

[0055] Example 1 Example 1 is an example in which the position of the bent portion 14 provided on the vertical wall portion 13B of the intermediate component 13 is uniformly and linearly arranged in the longitudinal direction of the component when viewed from the side (see FIG. 7A ). The evaluation results are shown in Tables 1 and 2. Table 1 shows the case in which the height H from the top plate portion 13A to the bent portion 14 at the left end is 15 mm, and the height H from the top plate portion 13A to the bent portion 14 at the right end is 5 mm. Table 2 shows the case in which the height H from the top plate portion 13A to the bent portion 14 at the left end is 30 mm, and the height H from the top plate portion 13A to the bent portion 14 at the right end is 10 mm. Note that the height H from the top plate portion 13A to the bent portion 14 at the left and right ends is synonymous with the height from the top plate portion 13A to the bent portion 14 at the position of the curved portion 2.

[0056] Here, the "first process angle" in the table refers to the "angle α1" (see FIG. 4). Also, the "second process angle" is the "angle γ0" (see FIG. 4). "Maximum thickness increase" is the "maximum thickness increase rate". And, "maximum thickness increase in the first process" is the "maximum thickness increase rate after one process". "Maximum thickness increase in the second process" is the "maximum thickness increase rate after two processes". This is the same in each of the following examples.

[0057]

[0058]

[0059] [Evaluation] The evaluation was based on the conventional method, No. 1, and a maximum thickness increase rate of 20.4% when formed using No. 1 was evaluated as passing. A maximum thickness increase rate of 18% or less was evaluated as passing. Nos. 2 to 8 represent the results when H = 15 mm and the angle α1 between the top plate forming surface and the lower vertical wall forming surface of the mold in the first process was changed between 100 and 160 degrees. Furthermore, the results represent the results when the vertical wall angle γ0 of the mold in the second process was formed to 90 degrees. As can be seen from Table 1, the maximum thickness increase rate in the first process decreased as the first process angle α1 increased. On the other hand, the maximum thickness increase rate in the second process decreased to a minimum of 10.1% when the first process angle was formed at 150 degrees.

[0060] Additionally, Nos. 9 to 15 show the results when H = 30 mm and the angle α1 between the top plate forming surface of the mold and the lower vertical wall forming surface of the first process was changed between 100 and 160 degrees. Furthermore, these show the results when the vertical wall angle γ0 of the mold was formed at 90 degrees in the second process. As can be seen from Table 2, the maximum thickness increase rate in the first process decreased as the first process angle α1 increased. On the other hand, in the second process, the maximum thickness increase rate decreased to a minimum of 5.8% when the first process angle was formed at 150 degrees. This maximum thickness increase rate in the second process is smaller than the result of No. 7.

[0061] From the above results, it was found that the following effect can be achieved when the bent portion 14, which is the base point that opens outward and is given to the vertical wall portion 13B in the first process 11, is uniformly provided linearly in the longitudinal direction of the part when viewed from the side: In other words, it was found that the rate of increase in plate thickness can be further reduced by increasing the angle α1 in the first process to about 150 degrees and increasing the height H from the top plate portion 1A to the bent portion 14.

[0062] Example 2 Example 2 is an example in which the bent portion 14 is uniformly provided along the shape of the top plate in the longitudinal direction of the component as viewed from the side, as shown in Fig. 6. The evaluation results are shown in Tables 3 and 4. Table 3 shows the results when the height H from the top plate portion 1A to the bent portion 14 at the left and right ends is 15 mm. Table 4 shows the results when the height H at the left and right ends is 30 mm.

[0063]

[0064]

[0065] [Evaluation] The evaluation was based on the conventional method, No. 1, and a maximum thickness increase rate of 20.4% when formed using No. 1 was evaluated as passing if the maximum thickness increase rate was 18% or less. Nos. 16 to 22 represent the results when H = 15 mm and the angle α1 between the top plate forming surface and the lower vertical wall forming surface of the mold in the first process was changed between 100 and 160 degrees. Furthermore, these results represent the results when the vertical wall angle γ0 of the mold in the second process was formed to 90 degrees. As can be seen from Table 3, the maximum thickness increase rate in the first process decreased as the first process angle α1 increased. On the other hand, in the second process, the maximum thickness increase rate decreased to a minimum of 10.3% when formed with a first process angle of 140 degrees.

[0066] In addition, Nos. 23 to 29 show the results when H = 30 mm, the angle α1 between the top plate forming surface and the vertical wall lower forming surface of the mold in the first process was changed in the range of 100 degrees to 160 degrees, and the vertical wall angle γ0 of the mold in the second process was formed to 90 degrees. As can be seen from Table 4, the maximum thickness increase rate in the first process decreased as the first process angle α1 increased. On the other hand, in the second process, the maximum thickness increase rate decreased to a minimum of 8.5% when forming with a first process angle of 140 degrees.

[0067] Example 3 In Example 3, as shown in FIG. 7B , the height H ratio was set uniformly in the longitudinal direction to match the shape of the top plate in the longitudinal direction when viewed from the side of the part. The height H ratio is the ratio of the height H from the top plate portion 1A to the bent portion 14 to the length of the vertical wall portion in the target part shape in the direction away from the top plate portion. The evaluation results are shown in Tables 5 and 6. Table 5 shows the results when the height H ratio was 15% (height H at the left end was 12 mm). Table 6 shows the results when the height H ratio was 75% (height H at the left end was 60 mm).

[0068]

[0069]

[0070] [Evaluation] The evaluation was based on the conventional method, No. 1, and a maximum thickness increase rate of 20.4% when formed using No. 1 was evaluated as passing if the maximum thickness increase rate was 18% or less. Nos. 30-36 and Nos. 37-43 represent the results when the angle α1 between the top plate forming surface and the lower vertical wall forming surface of the mold in the first process was changed between 100 and 160 degrees. Furthermore, these results represent the results when the vertical wall angle γ0 of the mold in the second process was formed to 90 degrees. As can be seen from Table 5, for Nos. 30-36, where the height H ratio was 15%, the maximum thickness increase rate in the first process decreased as the first process angle (α1) increased. On the other hand, in the second process, the maximum thickness increase rate was reduced to a minimum of 10.2% when formed using a first process angle of 150 degrees.

[0071] Furthermore, as can be seen from Table 6, in Nos. 37 to 43, where the ratio of height H was 75%, the maximum thickness increase rate in the first process decreased as the first process angle α1 increased. On the other hand, in the second process, the maximum thickness increase rate decreased to a minimum of 7.1% when forming was performed at a first process angle of 160 degrees.

[0072] As described above, it was found that the evaluation was pass when the ratio of height H was in the range of 15% and 75%. Here, for Examples No. 30 to 36 and Examples No. 37 to 43, FEM analysis was performed under similar conditions except for the ratio of height H. In these examples, as can be seen from Tables 5 and 6, the effect was greater when the ratio of height H was 15% than when the ratio of height H was 75%, except for the cases where the first-step angle was 110 degrees and 160 degrees.

[0073] The results of the above examples demonstrate that the following effects can be achieved when the outward-opening curved portion 21 provided on the vertical wall portion 1B in the first process 11 is uniformly formed along the shape of the top plate in the longitudinal direction of the part in a side view. Specifically, it was found that the rate of increase in plate thickness can be further reduced by increasing the angle α1 in the first process to approximately 140 degrees and increasing the height H from the top plate portion 1A to the bent portion 14. Furthermore, the height H from the top plate portion 1A to the bent portion 14 at the position of the bent portion 2 was varied and evaluated. The evaluation also confirmed that the evaluation was acceptable under the conditions of the above examples 1 and 2 when the ratio of the height H of the vertical wall portion 1B of the target part shape 1 was in the range of 15% to 75%.

[0074] The entire contents of Japanese Patent Application No. 2023-211532 (filed December 14, 2023), from which this application claims priority, are incorporated herein by reference. While the present invention has been described with reference to a limited number of embodiments, the scope of the invention is not limited thereto, and modifications of each embodiment based on the above disclosure will be obvious to those skilled in the art.

[0075] 1 Target part shape 1A Top plate portion 1B Vertical wall portion 1C Flange portion 2 Curved portion 3, 4 Straight portion 10 Metal plate (blank) 11 First process 12 Second process 13 Intermediate part 13A Top plate portion 13B Vertical wall portion 13Ba Upper portion of vertical wall portion 13Bb Lower portion of vertical wall portion 13C Flange portion 14 Bent portion 21 Curved portion 30 Upper mold 30A Top plate forming surface 30Ba Upper vertical wall forming surface 30Bb Lower vertical wall forming surface 30C Flange forming surface 31 Lower mold 31A Top plate forming surface 31Ba Upper vertical wall forming surface 31Bb Lower vertical wall forming surface 31C Flange forming surface

Claims

1. A method for manufacturing a press-molded product by press-molding a metal plate into a target part shape having a cross section with a top plate portion and a vertical wall portion connected to a widthwise end of the top plate portion, and in which the top plate portion has a curved portion that is convexly curved toward the outer surface of the top plate portion along the longitudinal direction, which is a direction intersecting the cross section, the method comprising: a first step of press-molding a metal plate into an intermediate part having a top plate portion and a vertical wall portion using a die having a top plate molding surface that molds the top plate portion, a vertical-wall upper molding surface that is continuous with the top plate molding surface and molds the upper part of the vertical wall portion, and a vertical-wall lower molding surface that is continuous with the vertical-wall upper molding surface and extends in a direction away from the top plate molding surface, different from the extension direction of the vertical-wall upper molding surface; and a second step of press-molding the intermediate part into the target part shape. a manufacturing method for a press-molded product, wherein an angle of the lower vertical wall molding surface relative to the top plate molding surface is greater than an angle of the upper vertical wall molding surface relative to the top plate molding surface and an angle of the vertical wall portion relative to the top plate portion of the target part shape, and the top plate molding surface has a molding surface that molds a curved portion that curves along the longitudinal direction, midway along the longitudinal direction.

2. A method for manufacturing a press-molded product as described in claim 1, wherein the target part shape has a flange portion connected to an end portion of the vertical wall portion, and the die used in the first process has a flange molding surface that molds the flange portion continuous with the vertical wall lower molding surface.

3. A method for manufacturing a press-molded product as described in claim 1, wherein the target part shape does not have a flange portion connected to the end of the vertical wall portion, the die used in the first step has a flange molding surface that molds a flange portion continuous with the vertical wall lower molding surface, and in the second step, the flange portion formed in the intermediate part is bent back and molded into a part of the vertical wall portion of the target part shape.

4. The method for manufacturing a press-formed product according to claim 2, wherein, when a flange angle between a vertical wall portion and a flange portion in the target part shape is defined as θ0, and an angle of the flange forming surface relative to the vertical wall lower forming surface is defined as θ1, the value of the angle θ1 is set so as to satisfy the following formula (1): θ1 ≦ θ0 (1) 5. The method for manufacturing a press-formed product according to claim 2 or 4, wherein, when the radius of curvature of a ridge line portion connecting the vertical wall portion and the flange portion in the target part shape is defined as R0, and the radius of curvature of a forming surface connecting the vertical wall lower forming surface and the flange forming surface is defined as R1, the value of R1 is set so as to satisfy the following formula (2): R1 ≦ Ro ... (2) 6. A method for manufacturing a press-molded product as described in any one of claims 1 to 5, wherein, at the position of the curved portion of the intermediate part, the length H of the vertical wall upper molding surface in the direction away from the top plate molding surface is set to a length in the range of 15% to 75% of the length of the vertical wall portion in the direction away from the top plate portion of the target part shape.

7. A method for manufacturing a press-molded product according to any one of claims 1 to 6, wherein the boundary between the upper vertical wall molding surface and the lower vertical wall molding surface extends linearly along the longitudinal direction of the intermediate part.

8. A method for manufacturing a press-molded product as described in any one of claims 1 to 6, wherein the boundary between the upper vertical wall molding surface and the lower vertical wall molding surface extends along the longitudinal direction of the intermediate part and is curved to match the shape of the top plate portion of the intermediate part at a position that forms the curved portion of the intermediate part.

9. A manufacturing method for a press-molded product produced by press-molding a metal plate into a target part shape having a cross-section with a top plate portion and a vertical wall portion connected to the widthwise end portion of the top plate portion, and wherein the top plate portion has a curved portion that is convexly curved toward the outer surface of the top plate portion along the longitudinal direction, which is a direction intersecting the cross-section, the method comprising: a first step of press-molding a metal plate into an intermediate part having a cross-section with a top plate portion and a vertical wall portion connected to the widthwise end portion of the top plate portion, the vertical wall portion being bent outward at a midpoint in the height direction; and a second step of press-molding the intermediate part into the target part shape, wherein the top plate portion of the intermediate part has a shape having a curved portion that is convexly curved toward the outer surface of the top plate portion along the longitudinal direction, midway along the longitudinal direction.

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