Manufacturing method of press-molded products

Abstract

Provided is a press molding method that can reduce the occurrence of wrinkles and can stably obtain products with a simple die structure.The method is a manufacturing method for a press-molded product of a target part shape (1) having a cross section with a top plate portion (1A) and a vertical wall portion (1B), and in the middle of the longitudinal direction, the top plate portion (1A) has a curved portion (2) where the top plate portion (1A) is curved convexly toward the outer surface side of the top plate portion (1A).The method includes a first step (11) of press-molding an intermediate part (13) using a die having a top plate molding surface (30A) and a vertical wall upper molding surface (30Ba) and a vertical wall lower molding surface (30Bb) that mold the upper part of the vertical wall portion (1B), and a second step (12) of press-molding the intermediate part (13) into the target part shape. The angle of the vertical wall lower molding surface (30Bb) relative to the top plate molding surface (30A) is larger than the angle of the vertical wall upper molding surface (30Ba) relative to the top plate molding surface (30A), and the top plate molding surface (30A) has a molding surface that molds a curved portion (2) that curves along the longitudinal direction midway along the longitudinal direction.

Description

[Technical field]

[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 a vertical wall portion connected to a width direction end of the top plate portion. The target part shape of the present invention also has a curved portion midway in the longitudinal direction, which is a direction intersecting the cross section. The curved portion is curved convexly toward the outer surface side of the top plate portion along the longitudinal direction. The present invention is a technology particularly suitable for press forming a high-strength material such as a steel plate having a material strength of 590 MPa or more. [Background technology]

[0002] In recent years, automobile bodies are required to be both lightweight and have improved crashworthiness. For this reason, the use of high tensile steel with a strength of 590 MPa or more, and even ultra-high tensile steel with a strength of 980 MPa or more, is becoming more common as materials for body structural parts. High tensile steel and ultra-high tensile steel have high yield strength and tensile strength, so forming defects such as wrinkles become an issue when they are press-formed.

[0003] One of the press-formed products used for the vehicle body structural parts is a part with a hat-shaped cross section. The 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 for the vehicle body structural parts include a part in which the top plate portion is curved convexly on the outer surface side (upper side) of the top plate portion along the longitudinal direction in a side view. Specifically, there is a part having a curved portion curved in a mountain shape in a side view. When a metal plate 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 to occur in the flange. In particular, when an ultra-high tensile steel is used as the metal plate, the above factors cause a problem of wrinkles occurring more significantly. The reason for this is that the yield stress is high.

[0004] Here, Patent Document 1 describes a press forming method for manufacturing a curved press part formed with a hat-shaped cross section. The press forming method includes a preliminary forming step and a main forming step. The preliminary forming step is a step of producing a preformed product having a bent portion extending along the longitudinal direction at the width direction 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 preformed product. Patent Document 1 describes that this forming method makes the preformed product highly rigid and can suppress wrinkles during main forming.

[0005] In addition, the press forming method described in Patent Document 2 describes a press forming method for manufacturing a press-formed product having 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 having an intermediate shape. The intermediate shape has a shorter longitudinal length than the target part shape, and the convexly curved portion is curved more than the target part shape. In addition, the intermediate shape has a larger opening angle between the top plate portion and the vertical wall portion at the convexly curved portion than the target part shape, and the vertical wall height of the vertical wall portion is lower. The target part shape forming process is a process of press forming the part having the intermediate shape into the target part shape. Patent Document 2 describes that this suppresses the flow of material from the vertical wall portion to the flange portion and suppresses wrinkles.

[0006] The press forming method described in Patent Document 3 is a press forming method in which the shape of a press-formed product in a previous process is set from the intermediate development shape obtained in the process of developing a final part shape for a press-formed part having a drawn shape. Patent Document 3 describes that this makes it possible to set a shape such that there is substantially no change in the cross-sectional line length when forming from the previous process shape to the final part shape. This makes it possible to suppress the occurrence of cracks. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2013-169578 A [Patent Document 2] JP 2020-185591 A [Patent Document 3] WO2017 / 010470 issue Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the press forming method described in Patent Document 1, the ridgeline of the punch shoulder is not formed in the front-end process. As a result, the setting position of the front-end product in the back-end process and its behavior during forming become unstable, making it difficult to obtain a stable shape in mass production. In addition, in the press forming method described in Patent Document 2, the shape of each part is changed relative to the target part shape. This makes the design complicated. Also, the shape in the previous process is formed into a loose shape close to a flat plate relative to the target part shape. This may cause the behavior during forming in the later process to become unstable. The press forming method described in Patent Document 3 is effective for simple parts. However, for actual parts with complex shapes, there is a risk of cross-sectional line length change. If cross-sectional line length change occurs, there is a risk that wrinkles occurring during forming in the subsequent process cannot be sufficiently suppressed.

[0009] The present invention has been made with attention to the above points. The present invention is directed to a press-formed product having a cross section such as a hat-shaped cross section and a curved portion in which the top plate portion 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 die structure. Another object of the present invention is to provide a press-forming method that reduces the occurrence of wrinkles and can stably obtain the product. [Means for solving the problem]

[0010] The inventors have studied the manufacture of press-formed products having a cross-sectional shape with a top plate portion and a vertical wall portion, such as a hat-shaped cross section, in which the top plate portion has a convex curve on the outer surface side of the top plate portion along the longitudinal direction midway. Specifically, the inventors have studied the manufacture of press-formed products having a curved portion that is curved in a mountain shape when viewed from the side. Furthermore, the inventors have studied a press-formed method that can greatly reduce the occurrence of wrinkles with a simple die structure, even when a high-strength metal plate such as a high-tensile material or an ultra-high-tensile material is used as a blank. In this regard, the inventors have also studied a press-formed method that can stably obtain a target part shape without wrinkles. As a result, the following discovery was made: First, the vertical wall portion of the intermediate part before the main molding is bent to have a cross-sectional shape that spreads outward at a midpoint in the height direction of the vertical wall portion. Then, in the main molding, the vertical wall portion of the intermediate part is simply bent back at a midpoint, and wrinkles at the flange portion and the lower end of the vertical wall portion can be stably reduced.

[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 having a curved portion in which the top plate portion is curved convexly toward an outer surface side of the top plate portion along the longitudinal direction, which is a direction intersecting the cross section, the method comprising the steps of: forming a top plate forming surface that forms the top plate portion; a vertical-wall upper forming surface that is continuous with the top plate forming surface and forms an upper portion of the vertical wall portion; 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 die having a vertical wall lower molding surface extending 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. Effect of the Invention

[0012] An aspect of the present invention relates to the manufacture of a press-formed product having a target part shape, which has 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 shape in side view along the longitudinal direction midway. According to this aspect of the present invention, even when a high tensile material is applied to the metal plate, wrinkles that occur in a curved part in side view can be significantly reduced without making the mold shape complicated. As a result, according to this aspect of the present invention, a part having a target part shape without wrinkles can be obtained. In other words, according to this aspect of the present invention, it is possible to manufacture a press-formed product having the above target part shape without wrinkles. As a result, according to the present invention, even when high tensile steel or ultra-high tensile steel is used, wrinkle-free parts can be obtained, leading to improved yields. Furthermore, the absence of wrinkles reduces damage to the mold, leading to reduced repair costs and therefore cost savings. Furthermore, when used as a body structural part, the parts can be easily assembled. [Brief description of the drawings]

[0013] [Figure 1] 1A to 1C are diagrams showing examples of cross-sectional shapes of parts to which the present invention can be applied; [Diagram 2] 1A and 1B are diagrams illustrating a target part shape according to an embodiment of the present invention, in which (a) is a perspective view and (b) is a side view. [Diagram 3] 1A to 1C are diagrams illustrating steps of a method for manufacturing a press-molded product according to an embodiment of the present invention. [Figure 4] 1A is an example of the cross-sectional shape of an intermediate part, and FIG. 1B is an example of the cross-sectional shape of a target part at that time. [Diagram 5] 11A and 11B are diagrams illustrating examples of longitudinal distribution patterns of bent portions. [Figure 6] 11A and 11B are diagrams illustrating examples of longitudinal distribution patterns of bent portions. [Figure 7] 11A and 11B are diagrams illustrating examples of longitudinal distribution patterns of bent portions. [Figure 8] FIG. 2 is a schematic cross-sectional view illustrating a molding surface of a mold used in a first step. [Figure 9]FIG. 13 is a diagram showing a state during molding in a comparative molding method. [Figure 10] FIG. 13 is a diagram showing the distribution of sheet thickness change rates at the bottom dead center in a comparative forming method. [Figure 11] FIG. 13 is a schematic diagram for explaining the cause of wrinkles in a comparative molding method. [Figure 12] FIG. 2 is a diagram showing a state during molding in a first step. [Figure 13] FIG. 11 is a diagram showing a state during molding in a second step. [Figure 14] 13 is a schematic diagram for explaining a process when a target part shape does not have a flange portion. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The present embodiment is an invention relating 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) The target part shape 1 of this embodiment has a cross-sectional shape having a top plate portion 1A and a vertical wall portion 1B as shown in FIG. 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 sides of the width direction 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 vertical wall portion 1B is only on one side of the width direction of the top plate portion 1A. Note that the hat-shaped cross section and the Z-shaped cross section are cross-sectional shapes in which flange portions 1C are continuous with the ends of the vertical wall portions 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. However, the present invention achieves the same effects as those described below even when other cross sections are used.

[0016] Furthermore, the target part shape 1 in this embodiment is a part shape in which, midway along the longitudinal direction, the top plate portion 1A has a curved portion 2 that is curved convexly toward the outer surface side of the top plate portion 1A along the longitudinal direction, as shown in Figure 2. The longitudinal direction is a direction that intersects with the cross section. "Convex toward the outer surface side of the top plate portion 1A" refers to the top plate portion 1A having a convex shape facing upward (see Figure 2(b)). For example, when viewed from the side, the top plate portion 1A has a mountain shape at the curved portion 2.

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

[0018] Here, the curved portion 2 shown in Fig. 2 has a curved shape that is bent so as to be convex upward. In this case, the curved portion 2 is formed at a portion along the longitudinal direction, and the range of the curved portion 2 in the longitudinal direction is short. The radius of curvature of the curved portion 2 may be larger or smaller than the radius of curvature in Fig. 2. Here, in this embodiment, as shown in Fig. 2, the left and right straight sections 3, 4 connected via the curved section 2 have a flat surface along the longitudinal direction of the tabletop section 1A. This portion may be formed in a curved shape along the longitudinal direction that is gentler than the curve of the curved section 2. In addition, the tabletop section 1A of the straight section 3 may be an inclined surface whose height changes toward the left side of Fig. 2.

[0019] In addition, in Fig. 2, the lower end of the vertical wall portion 1B and the flange portion 1C extend linearly in the longitudinal direction in side view. These portions may be curved over the entire longitudinal direction in side view. However, this embodiment is particularly effective when the vertical wall portion 1B has a locally curved portion 2 in a part of the longitudinal direction. Moreover, the dimensions shown in FIG. 2 are merely examples and are not intended to limit the present invention in any way.

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

[0021] (Manufacturing method) The method for manufacturing a press-molded product of this embodiment includes a first step 11 and a second step 12, as shown in FIG.

[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 intermediate part 13 has a cross section in which the top plate portion 13A and the upper portion 13Ba of the vertical wall portion 13B are connected 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 in which the vertical wall portion 13B is bent at a midpoint in the height direction so that the lower portion 13Bb of the vertical wall portion 13B spreads outward. As shown in FIG. 4(a), the cross section of the intermediate part 13 has a shape in which the flange portion 13C is connected to the end of the lower portion 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 in the middle in the longitudinal direction. The curved portion 21 is a portion where the top plate portion 13A is curved convexly toward the outer surface side of the top plate portion 13A along the longitudinal direction (see FIG. 5). FIG. 4(b) shows a cross-sectional shape of a target part shape 1 for an intermediate part 13 having the cross section shown in FIG. 4(a).

[0023] In the first step 11, the metal plate 10 is formed by the vertical-wall upper molding surface and the vertical-wall lower molding surface, which will be described later, as follows. That is, when the metal plate 10 is formed into the intermediate part 13, the vertical wall part 13B of the intermediate part 13 is formed into a shape that is bent outward at a midpoint in the height direction by the boundary between the vertical-wall upper molding surface and the vertical-wall lower molding surface. This bending position is the bent part 14. The outwardly opening bent portion 14 imparted to the vertical wall portion 1B in the first process 11 may be uniformly provided in a straight line along the longitudinal direction of the part as shown in Fig. 5. In the example of Fig. 5, in the straight line portion on the left side, the distance H from the top plate portion 13A to the bent portion 14 is constant. 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 becomes smaller toward the right in accordance with the inclination of the top plate portion 13A. However, the position of the bent portion 14 is not limited to this. 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] Also, as shown in FIG. 6, the bent portion 14 may be provided so as 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 is curved in a side view. In this way, the bent portion 14 may be provided so that the distance H (height H) from the top plate portion 13A to the bent portion 14 is constant. However, it is not necessary to set the height distance from the top plate portion 13A to the bent portion 14 constant. For example, as shown in FIG. 7(a), the bent portion 14 may be linearly inclined in the longitudinal direction in accordance with the inclination direction of the top plate portion 13A. Also, as shown in FIG. 7(b), the bent portion 14 may be bent in a shape that matches the curvature of the top plate portion 13A at the curved portion 21 along the longitudinal direction. 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 a distance H in the height direction. Here, press forming of the bent portion 14 becomes easier if 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 end in the longitudinal direction. The bent portion 14 may be provided only at the position of the curved portion 21 and in its vicinity when viewed from the side. In addition, in the longitudinal direction, the position of the curved portion 21 is set to a position that matches the position of the curved portion 2 of the target part shape 1. The convex shape of the curved portion 21 of the intermediate part 13 does not have to completely match the curved portion 2 of the target part shape 1. However, in consideration of the stability of the subsequent processes, it is better for the convex shape to match the curved portion 2 as closely as possible.

[0026] 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 curved 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 will be large when formed in the second step, and wrinkles may not be sufficiently reduced. On the other hand, if the distance H exceeds 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 step becomes large, which may cause large wrinkles in the first 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 disposed opposite each other in the pressing direction. The molding surfaces of the upper mold 30 and the lower mold 31 have a surface shape following the shape of the intermediate part 13 to be manufactured as shown in Fig. 8. The upper mold 30 has, as molding surfaces, 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. The top plate forming surface 30A is a forming surface that forms the top plate portion 13A. The width of the top plate forming surface 30A in this embodiment 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 close to the width of the top plate portion 1A of the target part shape 1. In addition, the top plate forming surface 30A has a concave forming surface that forms the curved portion 21 along the longitudinal direction.

[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 in the width direction of the top plate molding surface 30A. 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, which is 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. Also, 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 portion 1B relative to the top plate portion 1A in the target part shape 1. As a result, the intermediate part 13 is formed into a shape in which the lower part 13Bb side of the vertical wall part 13B opens outward compared to the target part shape 1 (see FIG. 4(a)). The surface shape of the vertical-wall lower molding surface 30Bb is a shape following the surface shape of the lower side of the vertical wall portion 1B of 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 connection surface.

[0030] As shown in FIG. 8, the lower mold 31 also has, as molding surfaces, a top plate molding surface 31A, a vertical wall upper molding surface 31Ba, a vertical wall lower 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 die 30, is a surface that molds the top plate portion 13A of the intermediate part 13. The vertical wall upper molding surface 31Ba and the vertical wall lower molding surface 31Bb, together with the vertical wall upper molding surface 30Ba and the vertical wall lower molding surface 30Bb of the upper die 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 die 30, is a surface that molds the flange portion 13C of the intermediate part 13.

[0031] Each molding surface of the lower die 31 has a shape following the corresponding molding surface of the opposing upper die 30. This is synonymous with each molding surface of the lower die 31 having a shape following the surface shape of the inner surface of the intermediate part 13. 4(a) can be manufactured by using a mold consisting of the upper mold 30 and the lower mold 31. The relationship between the various parts of the molding surfaces of the upper mold 30 and the lower mold 31 can be considered to be the same as the relationship between the various parts 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 so as to satisfy the following formula (1). That is, it is preferable to set the flange angle θ1 of the intermediate part 13 to be equal to or smaller than the flange angle θ0 of the target part shape 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 portion of the vertical wall portion 1B and the flange portion 1C in the second step 12. Note that if the angle θ1 is greater than the angle θ0, sufficient part rigidity cannot be obtained, and wrinkles may not be sufficiently suppressed in the second step 12.

[0035] Also, it is preferable that the angle θ1 is equal to or larger than θ0 / 2. If the angle θ1 is smaller than θ0 / 2, the flange angle will be a negative angle in the first step 11, and it may not be possible to form the target part shape 1. The radius of curvature of the ridgeline portion connecting the vertical wall portion 1B and the flange portion 1C in the target part shape 1 is defined as R0 (see FIG. 4(b)). The radius of curvature of the ridgeline forming surface joining the vertical wall lower molding surface 30Bb and the flange molding surface 30C in the intermediate part 13 is defined as R1. This radius of curvature R1 is synonymous with the radius of curvature of the ridgeline portion between the vertical wall portion 13B and the flange B13C in the 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 that joins the vertical wall lower molding surface 30Bb and the flange molding surface 30C. R1 ≦ R0 ····(2) Here, R1 is R0If R1 is larger than this, sufficient part rigidity cannot be obtained, and wrinkles may not be sufficiently suppressed in the second step 12. R1 is preferably set to 0.5 times the plate thickness or more. If R1 is set to less than 0.5 times the plate thickness, bending cracks may occur.

[0037] In addition, the angle α1 between the top plate forming surface 30A and the vertical wall lower forming surface 30Bb is preferably 160 degrees or less. The angle α1 is the angle of the portion 13Bb below the bent portion 14 of the vertical wall portion 13B with respect to the top plate portion 1A of the intermediate part 13 (see FIG. 4(a)). If the angle α1 exceeds 160 degrees, an extreme increase in plate thickness occurs in the second step 12 of the main forming, and wrinkles may not be sufficiently suppressed. The specifications of each part of the molding surface of the metal mold used in the first step 11 are the same as the specifications of 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 1A and the vertical wall portion 1B in the target part shape. However, in order to ensure stable molding in the second step 12, the following setting is preferable. That is, it is preferable to match the angle γ1 with the angle γ0, and to 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, it is preferable that the radius of curvature ρ1 of the bent portion 14 is 0.5 times or more the plate thickness. If the radius of curvature ρ1 is set to less than 0.5 times the plate thickness, bending cracks may occur. There is no particular restriction on the upper limit of the radius of curvature ρ1. It is sufficient that a predetermined opening amount or opening angle is ensured 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 is 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 is as follows. If the line length changes, the effect of improving rigidity is not sufficiently obtained, which may cause wrinkles. Also, 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 cause a deterioration in dimensional accuracy after molding in the second step.

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

[0041] (Actions and others) <Comparative molding methods> As a comparative forming method, a case will be considered in which a metal plate 10 is pressed into a target part shape 1 shown in Fig. 2 in a single press forming operation. Note that a metal plate 10 made of a steel plate having a tensile strength of 1470 MPa and having the dimensions shown in Fig. 2 is used as the metal plate 10. In the comparative molding method, an upper mold and a lower mold having molding surfaces following the target part shape 1 were used as molds. In addition, the comparative molding method applied a padded foam molding. Specifically, the surface of the lower mold that forms the top plate portion 1A of the metal sheet 10 was pressed with a pad and the surface that forms 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 point of molding to perform press molding.

[0042] Fig. 9 shows the side view of the shape during forming by the comparative forming method. As can be seen from Fig. 9, wrinkles were found to have occurred 20 mm above the bottom dead point of forming (Fig. 9(a)) at the bottom of the position that will become the curved portion 2 of the top plate portion 1A. Specifically, wrinkles were found to have occurred in the flange portion 1C. Then, as forming progressed, it was found that these wrinkles were smoothed out, causing surface defects such as wrinkle marks and wrinkle patterns. In this specification, surface defects such as wrinkle marks and wrinkle patterns are collectively referred to as "wrinkles". Figure 10 shows the rate of change in sheet thickness at the bottom dead point in the comparative forming method. A maximum thickness increase of 20.4% occurred in flange portion 1C, which is the lower end side of the curved portion 2. As the material strength increases, it becomes more prone to buckling. For this reason, the issue of flange wrinkles becomes more pronounced as the material strength increases.

[0043] The mechanism by which these flange wrinkles occur will be described with reference to FIG. 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. Also, considering the line length in the longitudinal direction, the line length of the flange portion 1C is shorter than the line length of the curved portion 2 in the top plate portion 1A. This results in excess material in the flange portion 1C, which appears as wrinkles. As the material strength increases, these flange wrinkles become larger. As a result, important issues include the failure to form the target 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. The vertical wall portion 13B of the intermediate part 13 is bent so as to open outward at a midpoint in the height direction as shown in FIG. 4(a). 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 a case where the bent portion 14 of the intermediate part 13 is uniformly provided in a straight line in the longitudinal direction of the part when viewed from the side, 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 ​​shown in Figs. 12 and 13 indicate the distance to the bottom dead center of forming. Fig. 12 shows the state in the first step 11, and 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)). Also, the angle α1 of the vertical-wall lower molding surface 30Bb relative to the top plate molding surface 30A is set to 150 degrees (see FIG. 4(a)). In other words, the opening angle β1 of the vertical-wall lower molding surface 30Bb relative to the vertical-wall upper molding surface 30Ba is set to 60 degrees.

[0046] As can be seen from Fig. 12, in the first step 11, the flange portion 13C reached the bottom dead point without any large wrinkles. Furthermore, as can be seen from Fig. 13, in the second step 12, wrinkles were dispersed over a wide range starting 10 mm above the bottom dead point of the forming, and the part continued to reach the bottom dead point in this state. Thus, according to this embodiment, the wrinkles are dispersed over a wide range, reducing damage to the mold. Also, the wrinkles are eliminated near the bottom dead point of the forming, making it easier to flatten the part. Additionally, the rate of change in thickness at the bottom dead center of forming in the first process 11 and the second process 12 was obtained by CAE analysis. As a result, in the first process 11, the plate thickness increased by a maximum of 4.7% at the flange portion 13C at the curved portion 21. Additionally, in the second process 12, the plate thickness increased by a maximum of 5.8% at the curved portion 2 and its vicinity. It was also found that the rate of change in thickness was significantly reduced compared to 20.4% in the case where no countermeasures were taken (comparative forming method).

[0047] Next, the mechanism of the dispersion of wrinkles and the reduction of the increase in plate thickness will be described. First, in the first process 11, a flat blank 10 is formed. At this time, an outwardly opening portion 13Bb is formed in 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 an increase in plate thickness are significantly reduced.

[0048] Also, the flange portion 13C is 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 formed in the second step 12, bending back the vertical wall portion 13B is the main process. The improvement in part rigidity makes it difficult for large localized wrinkles to occur. Also, like the first step 11, bending back the bent portions such as the bent portion 14 of the vertical wall portion 13B is the main process in the second step 12. As a result, the amount of deformation is reduced compared to when forming in one step. As a result, wrinkles are also less likely to occur in the second step 12. Regarding the above-mentioned improvement in rigidity, in the first step 11, the bent portion 14 that serves as the base point for opening outward is formed in the vertical wall portion 13B. At the same time, the 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 formed in the first step 11 is improved.

[0049] From the above, in this embodiment, flange wrinkles can be significantly reduced with a simple die structure. In particular, in this embodiment, this effect can be obtained even when high tensile steel with a strength class of 590 PMa or more or ultra-high tensile steel with a strength class of 980 MPa or more is used as the material. This makes it possible to obtain a part having the target part shape 1 without wrinkles. Thus, the present invention is primarily intended for high tensile steel and ultra-high tensile steel with a strength class of 590 PMa or more as the metal plate 10. However, the present invention may also use mild steel plate, aluminum plate, or the like as the material.

[0050] (Modification) (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-shape or an L-shape, the following is performed. 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 continuous with the vertical wall lower molding surfaces 30Bb, 31Bb. Therefore, as shown by the solid line in Fig. 14, as in the above embodiment, the intermediate part 13 has a flange portion 13C that is continuous with the vertical wall portion 13B. However, the combined line length of the vertical wall portion 13B and the flange portion 13C in the intermediate part 13 is set to correspond 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 to form a part of the lower end portion of the vertical wall portion 1B in the target part shape 1. The rest of the configuration may be the same as in the above embodiment. The effects are the same as in the above embodiment.

[0052] (others) The present disclosure may also have the following configuration. (1) Disclosure 1 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 including a top plate portion and a vertical wall portion connected to a width direction end portion of the top plate portion, and having a curved portion in which the top plate portion is curved convexly toward an outer surface side of the top plate portion along the longitudinal direction, which is a direction intersecting the cross section, 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 for molding the top plate portion, a vertical wall upper molding surface that is continuous with the top plate molding surface and molds an upper portion 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 different from the extension direction of the vertical wall upper molding surface in a direction away from the top plate molding surface; a second step of press-molding the intermediate part into the target part shape; an angle of the vertical-wall lower molding surface relative to the top plate molding surface is greater than an angle of the vertical-wall upper molding surface relative to the top plate molding surface and an angle of the vertical wall portion relative to the top plate portion in the target part shape; 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. A manufacturing method for press-molded products. (2) In disclosure 2, the target part shape has a flange portion connected to an end portion of the vertical wall portion, The mold used in the first step has a flange molding surface for molding a flange portion continuous with the vertical wall lower molding surface. (3) Disclosure 3 discloses that 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 forming surface for forming a flange portion continuous with the vertical wall lower forming surface, In the second step, the flange portion formed on the intermediate part is bent back to form a part of the vertical wall portion of the target part shape. (4) Disclosure 4 defines the flange angle between the vertical wall portion and the flange portion in the target part shape as θ0 and the angle of the flange molding surface relative to the vertical wall lower molding surface as θ1, The value of the angle θ1 is set so as to satisfy the following formula (1). A method for producing the press-molded product according to Disclosure 2. θ1 ≦ θ0 (1) (5) Disclosure 5 defines the radius of curvature of the ridge line connecting the vertical wall portion and the flange portion in the target part shape as R0, and the radius of curvature of the molding surface connecting the vertical wall lower molding surface and the flange molding surface as R1, The value of R1 is set so as to satisfy the following formula (2). A method for producing a press-molded product according to Disclosure 2 or 4. R1 ≦ Ro (2) (6) Disclosure 6 sets the length H of the vertical wall upper forming surface in the direction away from the top plate forming surface at the position of the curved portion of the intermediate part 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. A method for producing a press-molded product according to any one of claims 1 to 5. (7) Disclosure 7 discloses that the boundary between the vertical wall upper molding surface and the vertical wall lower molding surface extends linearly along the longitudinal direction of the intermediate part. A method for producing a press-molded product according to any one of claims 1 to 6. (8) Disclosure 8 discloses that the 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 the top plate portion of the intermediate part at a position that forms the curved portion of the intermediate part. A method for producing a press-molded product according to any one of claims 1 to 7. (9) Disclosure 9 is a method for producing a press-molded product, which is produced by press-molding a metal plate into a target part shape having a cross section including a top plate portion and a vertical wall portion connected to a width direction end portion of the top plate portion, and having a curved portion in which the top plate portion is curved convexly toward an outer surface side of the top plate portion along the longitudinal direction, which is a direction intersecting the cross section, A first step of press-forming a metal plate into an intermediate part having a top plate portion and a vertical wall portion connected to a width direction end portion of the top plate portion, the vertical wall portion being bent outward at a midpoint in the height direction; a second step of press-molding the intermediate part into the target part shape; The top plate portion of the intermediate part has a curved portion that is curved convexly toward the outer surface side of the top plate portion along the longitudinal direction, in the middle of the longitudinal direction. A manufacturing method for press-molded products. (10) Disclosure 10 discloses a method for manufacturing a molded product, the method comprising the steps of: forming a molded product having a target part shape; and forming a molded product having 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 portion of the vertical wall portion. A method for manufacturing a press-molded product according to Disclosure 9. (11) Disclosure 11 discloses that 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 portion of a vertical wall portion of the intermediate part, In the second step, the flange portion of the intermediate part is bent back to form a part of the vertical wall portion of the target part shape. A method for manufacturing the press-molded product according to Disclosure 9. (12) Disclosure 12 is such that, in 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 in the target part shape. A method for producing a press-molded product according to any one of claims 9 to 11. (13) Disclosure 13 relates to a bending position that extends linearly along the longitudinal direction of the intermediate part. A method for producing a press-molded product according to any one of claims 9 to 12. (14) Disclosure 14 discloses that the bending position extends along the longitudinal direction of the intermediate part, and is bent at the curved portion of the intermediate part in a side view according to the shape of the top plate portion of the intermediate part. A method for producing a press-molded product according to any one of claims 9 to 12. EXAMPLES

[0053] In order to confirm the effect of reducing flange wrinkles by the press forming method of this embodiment, press forming analysis and springback analysis were performed by the finite element method (FEM). The results are described below. In each of the following examples, the target part shape 1 is the shape shown in Fig. 2. That is, the target part shape 1 is a part having a hat-shaped cross section and a curved portion 2 in which a top plate portion 1A is curved along the longitudinal direction.

[0054] Then, in the first step (first step 11), a press forming analysis was carried out for forming the blank into an intermediate part 13 having a bent portion 14 that opens outward. Then, the sheet thickness increase rate at the vertical wall portion 13B was obtained. The metal plate 10 used for press forming had a plate thickness t of 1.2 mm and was a steel plate with a tensile strength of 1470 MPa. In this embodiment, the angle α1 between the top plate molding surface and the vertical wall lower molding surface of the mold in the first process was changed in the range of 100 degrees to 160 degrees. The vertical wall angle γ0 of the mold in the second process (second process 12) was unified to 90 degrees. The FEM analysis was performed under these conditions.

[0055] <Example 1> Example 1 is an example in which the bent portion 14 provided on the vertical wall portion 13B of the intermediate part 13 is uniformly provided linearly in the longitudinal direction of the part as viewed from the side (see FIG. 7(a)). The evaluation results are shown in Tables 1 and 2. Table 1 shows the case where 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 where 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 curved portion 2 position.

[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, the "maximum thickness increase in the first process" is the "maximum thickness increase rate after one process". The "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] [Table 1]

[0058] [Table 2]

[0059] [evaluation] The evaluation was based on the conventional method, No. 1, and a product was deemed to have passed if the maximum plate thickness increase rate was 18% or less, compared to 20.4% when formed using No. 1. Nos. 2 to 8 are the results when H=15 mm and the angle α1 between the top plate molding surface and the vertical wall lower molding surface of the mold in the first process is changed in the range of 100 degrees to 160 degrees. Furthermore, these are the results when the vertical wall angle γ0 of the mold in the second process is molded to 90 degrees. As can be seen from Table 1, the maximum thickness increase rate in the first process decreased with an increase in the first process angle α1. 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 set to 150 degrees.

[0060] Nos. 9 to 15 are the results when H=30 mm and the angle α1 between the top plate molding surface and the vertical wall lower molding surface of the mold in the first process is changed in the range of 100 degrees to 160 degrees. Furthermore, these are the results when the vertical wall angle γ0 of the mold in the second process is molded to 90 degrees. As can be seen from Table 2, the maximum thickness increase rate in the first process decreased with an increase in the first process angle α1. 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 150 degrees. This maximum thickness increase rate value in the second process is smaller than the result of No. 7.

[0061] From the above results, it was found that the following effects can be obtained 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. That is, it was found that the sheet thickness increase rate can be further reduced by increasing the first process angle α1 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 bent portion 14 is uniformly provided along the shape of the top plate in the longitudinal direction of the part 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 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] [Table 3]

[0064] [Table 4]

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

[0066] In addition, Nos. 23 to 29 are the results when H was 30 mm, the angle α1 between the top plate molding surface and the lower vertical wall molding 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 molded to 90 degrees. As can be seen from Table 4, the maximum thickness increase rate in the first process decreased with an increase in the first process angle α1. On the other hand, in the second process, the maximum thickness increase rate decreased to a minimum of 8.5% when the first process angle was 140 degrees.

[0067] <Example 3> 7(b), in Example 3, the ratio of height H is set uniformly in the longitudinal direction in accordance with the shape of the top plate in the longitudinal direction as viewed from the side of the part. The ratio of height H is the ratio of height H from top plate portion 1A to 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 ratio of height H is 15% (height H at the left end is 12 mm), and Table 6 shows the results when the ratio of height H is 75% (height H at the left end is 60 mm).

[0068] [Table 5]

[0069] [Table 6]

[0070] [evaluation] The evaluation was based on the conventional method, No. 1, and a product was deemed to have passed if the maximum plate thickness increase rate was 18% or less, compared to 20.4% when formed using No. 1. Nos. 30 to 36 and 37 to 43 are the results when the angle α1 between the top plate molding surface and the vertical wall lower molding surface of the mold in the first process was changed in the range of 100 degrees to 160 degrees. Furthermore, these are the results when the vertical wall angle γ0 of the mold in the second process was molded at 90 degrees. As can be seen from Table 5, in Nos. 30 to 36, where the ratio of height H is 15%, the maximum sheet thickness increase rate in the first process decreased with an increase in the first process angle (α1). On the other hand, in the second process, the maximum sheet thickness increase rate decreased to a minimum of 10.2% when forming with a first process angle of 150 degrees.

[0071] Also, as can be seen from Table 6, in Nos. 37 to 43, where the ratio of height H is 75%, the maximum sheet thickness increase rate in the first process decreased with an increase in the first process angle α1. On the other hand, in the second process, the maximum sheet thickness increase rate decreased to a minimum of 7.1% when forming was performed with 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, the FEM analysis was carried out for Examples No. 30 to 36 and Examples No. 37 to 43 under similar conditions except for the condition of the ratio of height H. In this example, as can be seen from Tables 5 and 6, except for the first step angles of 110 degrees and 160 degrees, the effect was greater when the height H ratio was 15% than when the height H ratio was 75%.

[0073] From the results of each of the above examples, it was found that the following effects can be obtained when the outwardly opening curved portion 21 provided on the vertical wall portion 1B in the first process 11 is uniformly provided along the shape of the top plate in the longitudinal direction of the part as viewed from the side: In other words, it was found that the sheet thickness increase rate can be further reduced by increasing the first process angle α1 to about 140 degrees and increasing the height H from the top plate portion 1A to the bent portion 14. Furthermore, the evaluation was performed by changing the height H from the top plate portion 1A to the bent portion 14 at the position of the curved portion 2. In the evaluation, it was confirmed that the evaluation was passed under the conditions of the above-mentioned Example 1 and Example 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 on December 14, 2023), from which this application claims priority, are incorporated herein by reference. Although the present invention has been described with reference to a limited number of embodiments, the scope of the rights is not limited thereto, and modifications of each embodiment based on the above disclosure would be obvious to one skilled in the art. [Explanation of symbols]

[0075] 1 Target part shape 1A Top plate 1B Vertical wall section 1C Flange part 2 Curved section 3, 4 Straight section 10 Metal plate (blank) 11 First step 12 The second step 13 Intermediate parts 13A Top plate 13B Vertical wall section 13Ba Upper part of vertical wall 13Bb Lower part of vertical wall 13C Flange 14 Bend 21 Curved section 30 Upper mold 30A Top plate molding surface 30Ba vertical wall upper molding surface 30Bb Vertical wall lower molding surface 30C flange forming surface 31 Lower mold 31A Top plate molding surface 31Ba Vertical wall upper molding surface 31Bb Vertical wall lower molding surface 31C Flange molding surface

Claims

1. A method for producing a press-molded product, which is produced by press-molding a metal plate into a target part shape having a cross section including a top plate portion and a vertical wall portion connected to a width direction end portion of the top plate portion, and having a curved portion in which the top plate portion is curved convexly toward an outer surface side of the top plate portion along a longitudinal direction, which is a direction intersecting the cross section, 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 for molding the top plate portion, a vertical wall upper molding surface that is continuous with the top plate molding surface and molds an upper portion 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 different from the extension direction of the vertical wall upper molding surface in a direction away from the top plate molding surface; a second step of press-molding the intermediate part into the target part shape; an angle of the vertical-wall lower molding surface relative to the top plate molding surface is greater than an angle of the vertical-wall upper 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; 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. A manufacturing method for press-molded products.

2. the target part shape has a flange portion connected to an end of the vertical wall portion, The mold used in the first step has a flange molding surface that molds a flange portion continuously with the vertical wall lower molding surface. A method for producing a press-molded product according to claim 1.

3. the target part shape does not have a flange portion connected to an end of the vertical wall portion; The mold used in the first step has a flange forming surface for forming a flange portion continuous with the vertical wall lower forming surface, In the second step, the flange portion formed on the intermediate part is bent back to form a part of the vertical wall portion of the target part shape. A method for producing a press-molded product according to claim 1.

4. When the flange angle between the vertical wall portion and the flange portion in the target part shape is defined as θ0 and the angle of the flange molding surface with respect 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): A method for producing the press-molded product according to claim 2. θ1 ≦ θ0 (1)

5. When the radius of curvature of the 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 the 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): The method for producing a press-molded product according to claim 2 or 4. R1 ≦ R0 (2)

6. At the position of the curved portion of the intermediate part, a length H of the vertical wall upper forming surface in a direction away from the top plate forming surface is set to a length in a range of 15% to 75% of a length of the vertical wall part in the target part shape in a direction away from the top plate portion. The method for producing a press-molded product according to any one of claims 1 to 4.

7. The boundary between the vertical wall upper molding surface and the vertical wall lower molding surface extends linearly along the longitudinal direction of the intermediate part. The method for producing a press-molded product according to any one of claims 1 to 4.

8. The 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 in accordance with the shape of the top plate part of the intermediate part at a position that forms the curved part of the intermediate part. The method for producing a press-molded product according to any one of claims 1 to 4.

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

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