Manufacturing method for press-formed products

Abstract

The present invention provides a method for manufacturing press-formed products that can reduce wrinkles in the top plate without changing the final shape of the press-formed product. [Solution] The manufacturing method comprises a preparation step, a first molding step, and a second molding step. The intermediate molded product (30) includes a top plate (31), a ridge portion (32), and a vertical wall (33). The press-molded product (10) includes a top plate (11), a ridge portion (12), and a vertical wall (13). The ridge portion (12) includes a curved ridge portion (121). The curved ridge portion (121) curves inward in a concave shape when viewed from above and from the side of the press-molded product (10). The ridge portion (32) includes an intermediate-shaped ridge portion (321). The intermediate-shaped ridge portion (321) is molded into the curved ridge portion (121) in the second molding step. The curvature Cp of the curved ridge portion (121) of the press-formed product (10) in a side view, and the curvature Cm of the intermediate shaped ridge portion (321) of the intermediate-formed product (30) in a side view, are given by -1.40 × Cp ≤ Cm

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a press-formed product.

Background Art

[0002] For example, in automobiles, press-formed products are used as skeletal parts and the like. A press-formed product is manufactured by subjecting a metal plate (blank), which is a raw material, to press working.

[0003] Patent Document 1 discloses a method for manufacturing a press-formed product having a hat cross-sectional shape. The press-formed product has an L-shaped or T-shaped configuration including a vertical portion and a horizontal portion in a top view thereof. In Patent Document 1, the press-formed product is manufactured through an intermediate forming step and a final forming step. In the intermediate forming step, a bulging portion is formed from a shoulder portion (ridge line portion) to a top plate at a bending portion between the vertical portion and the horizontal portion. In the final forming step, the bulging portion is crushed to form a concave portion in the top plate. Patent Document 1 describes that the occurrence of wrinkles in the top plate of the final product is suppressed by crushing the bulging portion.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the press-formed product of Patent Document 1, the vertical walls and the ridges connecting the vertical walls to the top plate are provided with concave bends (curved ridges) on the inside when viewed from above. When such a press-formed product is formed by press-working a metal sheet, compressive stress, which is a cause of wrinkles, is generated in the vicinity of the curved ridges on the top plate. In particular, when the curved ridges have a concave shape on the inside of the press-formed product when viewed from both above and from the side, compressive stress concentrates on the top plate near the curved ridges, making it easy for wrinkles to occur.

[0006] As a measure to reduce wrinkles in the top plate, for example, as described in Patent Document 1, it is conceivable to provide recesses or protrusions on or near the curved ridges. Alternatively, it is conceivable to reduce wrinkles in the top plate by easing the curved shape of the ridges and the top plate in the top and / or side view of the press-formed product. However, when attempting to reduce wrinkles in the top plate by these measures, there is a problem in that it is necessary to change the final shape (product shape) of the press-formed product.

[0007] The object of this disclosure is to provide a method for manufacturing a press-formed product that can reduce wrinkles in the top plate without changing the final shape of the press-formed product. [Means for solving the problem]

[0008] The method for manufacturing a press-formed product according to this disclosure comprises a preparation step of preparing a metal sheet as a material, a first forming step of applying press processing to the metal sheet to obtain an intermediate molded product, and a second forming step of applying press processing to the intermediate molded product to obtain a press-formed product. The intermediate molded product includes a first top plate, a first ridge portion, and a first vertical wall. The first ridge portion is continuous with the first top plate. The first vertical wall is connected to the first top plate via the first ridge portion. The press-formed product includes a second top plate, a second ridge portion, and a second vertical wall. The second ridge portion is continuous with the second top plate. The second vertical wall is connected to the second top plate via the second ridge portion. The second ridge portion includes a curved ridge portion. The curved ridge portion curves inward in a concave shape when viewed from above and inward in a concave shape when viewed from the side. The first ridge section includes an intermediate ridge section. The intermediate ridge section is formed into a curved ridge section in the second molding process. When Cp is the curvature of the curved ridge section in a side view of the press-formed product, and Cm is the curvature of the intermediate ridge section in a side view of the intermediate-formed product, Cp and Cm satisfy the following equation (1). -1.40 × Cp ≤ Cm <Cp (1) However, Cp is the reciprocal of the minimum radius of curvature Rp in a side view of the press-formed product at the boundary between the second top plate and the curved ridge. If the intermediate ridge is curved concavely inward in a side view of the intermediate molded product, Cm is the reciprocal of the minimum radius of curvature Rm in a side view of the intermediate molded product at the boundary between the first top plate and the intermediate ridge. If the intermediate ridge is curved convexly outward in a side view of the intermediate molded product, Cm is the reciprocal of the minimum radius of curvature Rm multiplied by -1. If the intermediate ridge is straight in a side view of the intermediate molded product, Cm is 0. [Effects of the Invention]

[0009] According to the method for manufacturing press-formed products described herein, wrinkles in the top plate can be reduced without changing the final shape of the press-formed product. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic perspective view showing a press-formed product manufactured by the manufacturing method according to the embodiment. [Figure 2] Figure 2 is a cross-sectional view taken along line II-II of the press-formed product shown in Figure 1. [Figure 3] Figure 3 is a top view of the press-formed product shown in Figure 1. [Figure 4] Figure 4 is a side view of the press-formed product shown in Figure 1. [Figure 5A] Figure 5A is a schematic diagram illustrating the manufacturing method of a press-formed product according to the embodiment. [Figure 5B] Figure 5B is a schematic diagram illustrating the manufacturing method of a press-formed product according to the embodiment. [Figure 5C] Figure 5C is a schematic diagram illustrating the manufacturing method of a press-formed product according to the embodiment. [Figure 5D] Figure 5D is a schematic diagram illustrating the manufacturing method of a press-formed product according to the embodiment. [Figure 5E] Figure 5E is a schematic diagram illustrating the manufacturing method of a press-formed product according to the embodiment. [Figure 5F] Figure 5F is a schematic diagram illustrating the manufacturing method of a press-formed product according to the embodiment. [Figure 5G] Figure 5G is a schematic diagram illustrating the manufacturing method of a press-formed product according to the embodiment. [Figure 6] Figure 6 is a cross-sectional view of an intermediate molded product obtained in the first molding step of the manufacturing method according to this embodiment. [Figure 7] Figure 7 is a top view of the intermediate molded product. [Figure 8A] Figure 8A shows an example of the shape of an intermediate molded product in a side view. [Figure 8B] Figure 8B shows another example of the shape of an intermediate molded product in a side view. [Figure 8C] Figure 8C shows yet another example of the shape of an intermediate molded product in a side view. [Modes for carrying out the invention]

[0011] The method for manufacturing a press-formed product according to the embodiment includes a preparation step of preparing a metal plate as a material, a first forming step of performing press working on the metal plate to obtain an intermediate formed product, and a second forming step of performing press working on the intermediate formed product to obtain a press-formed product. The intermediate formed product includes a first top plate, a first ridge line portion, and a first vertical wall. The first ridge line portion is continuous with the first top plate. The first vertical wall is connected to the first top plate via the first ridge line portion. The press-formed product includes a second top plate, a second ridge line portion, and a second vertical wall. The second ridge line portion is continuous with the second top plate. The second vertical wall is connected to the second top plate via the second ridge line portion. The second ridge line portion includes a curved ridge line portion. The curved ridge line portion curves concave inward the press-formed product in a top view of the press-formed product and also curves concave inward the press-formed product in a side view of the press-formed product. The first ridge line portion includes an intermediate shape ridge line portion. The intermediate shape ridge line portion is formed into the curved ridge line portion in the second forming step. When the curvature of the curved ridge line portion in the side view of the press-formed product is Cp and the curvature of the intermediate shape ridge line portion in the side view of the intermediate formed product is Cm, Cp and Cm satisfy the following formula (1) (the first configuration). -1.40×Cp≦Cm<Cp (1) However, Cp is the reciprocal of the minimum radius of curvature Rp in the side view of the press-formed product of the boundary line between the second top plate and the curved ridge line portion. When the intermediate shape ridge line portion curves concave inward the intermediate formed product in the side view of the intermediate formed product, Cm is the reciprocal of the minimum radius of curvature Rm in the side view of the intermediate formed product of the boundary line between the first top plate and the intermediate shape ridge line portion. When the intermediate shape ridge line portion curves convex outward the intermediate formed product in the side view of the intermediate formed product, Cm is the value obtained by multiplying -1 by the reciprocal of the minimum radius of curvature Rm. When the intermediate shape ridge line portion is linear in the side view of the intermediate formed product, Cm is 0.

[0012] When forming a press-formed product including a concave curved ridge line portion in a side view from a metal plate as a material, compressive stress is generated in at least a portion of the top plate adjacent to the curved ridge line portion. Due to this compressive stress, the top plate undergoes out-of-plane deformation and wrinkles are generated on the top plate. Similarly, when forming a press-formed product including a concave curved ridge line portion in a top view from a metal plate as a material, compressive stress is generated in a portion of the top plate adjacent to the curved ridge line portion. This compressive stress also becomes a factor in generating wrinkles on the top plate.

[0013] In contrast, in the manufacturing method according to the first configuration, after obtaining an intermediate molded product from a metal plate in the first molding step, a press-molded product is obtained from the intermediate molded product in the second molding step. The curved ridge line portion of the press-molded product is formed from the intermediate shape ridge line portion of the intermediate molded product. The curvature Cm of the intermediate shape ridge line portion in the side view of the intermediate molded product is smaller than the curvature Cp of the curved ridge line portion in the side view of the press-molded product. By setting the shape of the intermediate shape ridge line portion in the side view of the intermediate molded product in this way, the compressive stress generated in the top plate (first top plate) of the intermediate molded product is relaxed, or a tensile stress is generated in the first top plate. As a result, when the curved ridge line portion is formed from the intermediate shape ridge line portion, the compressive stress generated in the top plate (second top plate) of the press-molded product due to the curved ridge line portion being concave in the side view of the press-molded product is more relaxed than the compressive stress generated in the second top plate when the curved ridge line portion is formed without passing through the intermediate shape ridge line portion. Therefore, wrinkles on the second top plate are likely to be reduced.

[0014] In the manufacturing method according to the first configuration, by molding a press-molded product through the first molding step and the second molding step, wrinkles on the top plate (second top plate) of the press-molded product are reduced. Therefore, there is no need to provide concave or convex portions on the press-molded product to reduce wrinkles, or to relax the shape of the final curved ridge line portion. Therefore, according to the manufacturing method according to the first configuration, wrinkles on the second top plate can be reduced without changing the final shape of the press-molded product.

[0015] In the manufacturing method according to the first configuration, the metal plate may have a tensile strength of 400 MPa or more and 1850 MPa or less (second configuration).

[0016] In the manufacturing method according to the first or second configuration, when the minimum radius of curvature in the top view of the press-molded product of the boundary line between the curved ridge line portion and the second vertical wall is Rv and the reciprocal of Rv is Cv, Cp, Cm, and Cv may satisfy the following formula (2) (third configuration). Cp - (Cp + Cv) × 0.46 ≤ Cm ≤ Cp - (Cp + Cv) × 0.10 (2)

[0017] Embodiments of this disclosure will be described below with reference to the drawings. In these drawings, the same or equivalent components are denoted by the same reference numerals, and the same description will not be repeated.

[0018] [Press-formed product] Figure 1 is a schematic perspective view showing a press-formed product 10 manufactured by the manufacturing method according to this embodiment. The press-formed product 10 is used, for example, in a vehicle such as an automobile. The press-formed product 10 may also be a structural component of an automobile.

[0019] The press-formed product 10 includes a top plate 11, a ridge portion 12, and a vertical wall 13. In this embodiment, the press-formed product 10 further includes a ridge portion 14 and a vertical wall 15. The press-formed product 10 may further include flanges 16 and 17.

[0020] The top plate 11 extends in the longitudinal direction of the press-formed product 10. The top plate 11 may have recesses, protrusions, through holes, etc. The ridge line 12 is continuous with the top plate 11. The ridge line 12 extends along the top plate 11 in the longitudinal direction of the press-formed product 10. The vertical wall 13 is continuous with the ridge line 12. The vertical wall 13 is provided along the ridge line 12. The flange 16 is connected to the vertical wall 13 on the opposite side of the top plate 11. The flange 16 is provided along the vertical wall 13.

[0021] The ridge section 14, vertical wall 15, and flange 17 are positioned on the opposite side of the top plate 11 from the ridge section 12, vertical wall 13, and flange 16. The ridge section 14 is continuous with the top plate 11 on the opposite side of the ridge section 12. The ridge section 14 extends along the top plate 11 in the longitudinal direction of the press-formed product 10. The vertical wall 15 is continuous with the ridge section 14. The vertical wall 15 is provided along the ridge section 14. The flange 17 is connected to the vertical wall 15 on the opposite side of the top plate 11. The flange 17 is provided along the vertical wall 15.

[0022] Figure 2 is a cross-sectional view taken along line II-II of the press-formed product 10 shown in Figure 1. Figure 2 shows a cross-section (transverse plane) of the press-formed product 10 perpendicular to its longitudinal direction. In this embodiment, the press-formed product 10 has a substantially hat-shaped transverse plane.

[0023] Referring to Figure 2, the vertical wall 13 is connected to the top plate 11 via a ridge portion 12, which acts as a corner. The ridge portion 12 has a curved shape that is convex outward from the press-formed product 10 in a cross-sectional view. In the cross-section of the press-formed product 10, at least the area of ​​the top plate 11 adjacent to the ridge portion 12 is substantially straight. Similarly, in the cross-section of the press-formed product 10, at least the area of ​​the vertical wall 13 adjacent to the ridge portion 12 is substantially straight. The top plate 11 and the vertical wall 13 may be straight as a whole in a cross-sectional view of the press-formed product 10.

[0024] The vertical wall 15 is connected to the top plate 11 on the opposite side of the vertical wall 13 via a ridge portion 14 that acts as a corner. The ridge portion 14 has a curved shape that is convex outward in a cross-sectional view of the press-formed product 10. In a cross-section of the press-formed product 10, at least the area of ​​the top plate 11 adjacent to the ridge portion 14 is substantially straight. Similarly, in a cross-section of the press-formed product 10, at least the area of ​​the vertical wall 15 adjacent to the ridge portion 12 is substantially straight. The vertical wall 15 may be entirely straight in a cross-sectional view of the press-formed product 10.

[0025] Flange 16 is connected to vertical wall 13 via ridge portion 18, which acts as a corner. Flange 17 is connected to vertical wall 15 via ridge portion 19, which acts as a corner. The ridge portions 18 and 19 may have a curved shape that is convex in the opposite direction to the ridge portions 12 and 14 when viewed in cross-section of the press-formed product 10. Flanges 16 and 17 protrude from the ridge portions 18 and 19 to the opposite side of the vertical walls 13 and 15, respectively.

[0026] Figure 3 is a top view of the press-formed product 10. Referring to Figure 3, the ridge portion 12 includes the curved ridge portion 121. The curved ridge portion 121 curves inward in a concave shape when viewed from above. Because the ridge portion 12 includes the curved ridge portion 121, the vertical wall 13 also includes the curved vertical wall 131. The curved vertical wall 131 is continuous with the curved ridge portion 121. The curved vertical wall 131 is the portion of the vertical wall 13 that curves inward in a concave shape when viewed from above. The top view of the press-formed product 10 with respect to the curved ridge portion 121 and the curved vertical wall 131 refers to viewing the curved ridge portion 121 and the curved vertical wall 131 from the top plate 11 side along the pressing direction of the second forming process, which will be described later.

[0027] The boundary line A1 between the curved ridge portion 121 and the curved vertical wall 131 extends with a radius of curvature of 80 mm to 4000 mm when viewed from above the press-formed product 10. The boundary line A1 may have a constant radius of curvature when viewed from above the press-formed product 10, or its radius of curvature may change along its extension direction. The boundary line A1 can be specified, for example, as follows.

[0028] Evaluation points are placed at equal intervals (e.g., 1 mm intervals) on boundary line A0 between the ridge section 12 and the vertical wall 13, and for each evaluation point, the radius of curvature [mm] of the arc passing through that evaluation point and the evaluation points on both sides thereof is measured in a top view of the press-formed product 10. Boundary line A1 is the portion of boundary line A0 where evaluation points with a radius of curvature of 80 mm or more and 4000 mm or less are continuous. The minimum value of the radius of curvature of the evaluation points located within boundary line A1 is the minimum radius of curvature Rv [mm] in a top view of the press-formed product 10 at boundary line A1 between the curved ridge section 121 and the vertical wall 13. Boundary line A0 between the ridge section 12 and the vertical wall 13 corresponds to the R-end of the ridge section 12 on the vertical wall 13 side on the outer surface of the press-formed product 10. The R-end of the ridge section 12 on the vertical wall 13 side is the boundary between the curved ridge section 12 and the straight section of the vertical wall 13 in a cross-sectional view of the press-formed product 10.

[0029] Figure 4 shows the press-formed product 10 as seen from the vertical wall 13 side. Referring to Figure 4, the curved ridge portion 121 also curves concavely inward when viewed from the side of the press-formed product 10. The side view of the press-formed product 10 with respect to the curved ridge portion 121 refers to viewing the curved ridge portion 121 from a direction perpendicular to the pressing direction of the second forming process described later, and perpendicular to the extension direction vector at the center of the extension direction of the boundary line B1 between the top plate 11 and the curved ridge portion 121.

[0030] The boundary line B1 between the top plate 11 and the curved ridge portion 121 extends with a radius of curvature of 200 mm to 4000 mm in a side view of the press-formed product 10. The boundary line B1 may have a constant radius of curvature in a side view of the press-formed product 10, or its radius of curvature may change along its extension direction. The boundary line B1 can be specified, for example, as follows.

[0031] Evaluation points are placed at equal intervals (e.g., 1 mm intervals) on the boundary line B0 between the top plate 11 and the ridge section 12. For each evaluation point, the radius of curvature [mm] of the arc passing through that evaluation point and the evaluation points on both sides of it is measured in a side view of the press-formed product 10. The portion of boundary line B0 where evaluation points with a radius of curvature of 200 mm or more and 4000 mm or less are continuous is boundary line B1. The minimum value of the radius of curvature of the evaluation points located within boundary line B1 is the minimum radius of curvature Rp [mm] in a side view of the press-formed product 10 at boundary line B1 between the top plate 11 and the curved ridge section 121. The boundary line B0 between the top plate 11 and the ridge section 12 corresponds to the R-end of the ridge section 12 on the top plate 11 side on the outer surface of the press-formed product 10. The R-end of the ridge section 12 on the top plate 11 side is the boundary between the curved ridge section 12 and the straight section of the top plate 11 in a cross-sectional view of the press-formed product 10.

[0032] In the longitudinal direction of the press-formed product 10, the area of ​​boundary line B1 (Figure 4) between the top plate 11 and the curved ridge portion 121 overlaps with the area of ​​boundary line A1 (Figure 3) between the curved ridge portion 121 and the vertical wall 13. The areas of boundary lines A1 and B1 in the longitudinal direction of the press-formed product 10 generally coincide. However, the areas of boundary lines A1 and B1 in the longitudinal direction of the press-formed product 10 do not need to coincide perfectly.

[0033] [Method for manufacturing press-formed products] Next, the method for manufacturing the press-formed product 10 according to this embodiment will be described with reference to Figures 5A to 5G. The method for manufacturing the press-formed product 10 comprises a preparation step, a first molding step, and a second molding step.

[0034] (preparation process) Referring to Figure 5A, the preparation step involves preparing a metal sheet (blank) 20 as the material. The metal sheet 20 may have a thickness of, for example, 0.6 mm or more and 3.2 mm or less. The metal sheet 20 is typically a steel sheet. The metal sheet 20 may have a tensile strength of 400 MPa or more and 1850 MPa or less.

[0035] (1st molding process) As shown in Figures 5B to 5D, in the first forming step, an intermediate molded product 30 is obtained by press working on the metal sheet 20. The intermediate molded product 30 is typically formed by drawing the metal sheet 20. In the first forming step, a mold set 40 including a punch 41, a die 42, and holders 43 and 44 is used.

[0036] Referring to Figure 5B, the punch 41 has a convex forming surface. In this embodiment, the punch 41 includes a punch top surface 411, punch shoulders 412, 414, and punch sides 413, 415. The punch shoulders 412, 414 are positioned on either side of the punch top surface 411. The punch sides 413, 415 are connected to the punch top surface 411 via the punch shoulders 412, 414, respectively.

[0037] The die 42 is able to move closer to and further away from the punch 41 in the pressing direction P. The die 42 has a concave forming surface that corresponds to the convex forming surface of the punch 41. More specifically, the die 42 includes a die bottom surface 421, die shoulders 422, 424, die sides 423, 425, and die flange surfaces 426, 427. The die bottom surface 421 faces the punch top surface 411 in the pressing direction P. The die sides 423, 425 are connected to the die bottom surface 421 via the die shoulders 422, 424, respectively. The die flange surfaces 426, 427 face the holders 43, 44 in the pressing direction P, respectively. The die flange surface 426 is connected to the die side surface 423 via a corner portion 428. The die flange surface 427 is connected to the die side surface 425 via a corner portion 429.

[0038] Continuing with Figure 5B, in the first forming step, first, the metal plate 20 as the material is placed between the punch 41 and holders 43, 44 and the die 42. The metal plate 20 may be placed on the top surface 411 of the punch or on the holders 43, 44. Then, the punch 41 and holders 43, 44 and the die 42 are brought relatively closer together in the pressing direction P.

[0039] As shown in Figure 5C, a portion of the metal plate 20 is held between the die flange surfaces 426, 427 and the holders 43, 44. When the punch 41 and die 42 are brought relatively closer in the pressing direction P, as shown in Figure 5D, the remaining portion of the metal plate 20 is pressed into the die 42 by the punch 41. This forms an intermediate molded product 30 from the metal plate 20.

[0040] Figure 6 is a cross-sectional view of the intermediate molded product 30 obtained in the first molding process. Referring to Figure 6, the intermediate molded product 30 has a substantially hat-shaped cross-section, similar to the press-formed product 10 (Figure 2). The intermediate molded product 30 includes a top plate 31, a ridge portion 32, and a vertical wall 33. In this embodiment, the intermediate molded product 30 further includes a ridge portion 34, a vertical wall 35, and flanges 36, 37.

[0041] The ridge portion 32 is continuous with the top plate 31. The vertical wall 33 is continuous with the ridge portion 32. The vertical wall 33 is connected to the top plate 31 via the ridge portion 32, which acts as a corner. In a cross-sectional view of the intermediate molded product 30, the ridge portion 32 has a curved shape that is convex outward from the intermediate molded product 30. In a cross-sectional view of the intermediate molded product 30, at least the region of the top plate 31 adjacent to the ridge portion 32 is substantially straight. Similarly, in a cross-sectional view of the intermediate molded product 30, at least the region of the vertical wall 33 adjacent to the ridge portion 32 is substantially straight. The top plate 31 and the vertical wall 33 may be straight as a whole in a cross-sectional view of the intermediate molded product 30.

[0042] The ridge portion 34 is continuous with the top plate 31 on the opposite side of the ridge portion 32. The vertical wall 35 is continuous with the ridge portion 34. The vertical wall 35 is connected to the top plate 31 via the ridge portion 34 as a corner portion. The ridge portion 34 has a curved shape that is convex outward from the intermediate molded product 30 in a cross-sectional view of the intermediate molded product 30. In the cross-section of the intermediate molded product 30, at least the area of ​​the top plate 31 adjacent to the ridge portion 34 is substantially straight. Similarly, in the cross-section of the intermediate molded product 30, at least the area of ​​the vertical wall 35 adjacent to the ridge portion 34 is substantially straight. The vertical wall 35 may be straight as a whole in a cross-sectional view of the intermediate molded product 30.

[0043] The flanges 36 and 37 are connected to the vertical walls 33 and 35, respectively, on the opposite side of the top plate 31. Flange 36 is connected to the vertical wall 33 via a ridge portion 38 which serves as a corner. Flange 37 is connected to the vertical wall 35 via a ridge portion 39 which serves as a corner. The ridge portions 38 and 39 may have a curved shape that is convex in the opposite direction to the ridge portions 32 and 34 when viewed in cross-section of the intermediate molded product 30. The flanges 36 and 37 protrude from the ridge portions 38 and 39, respectively, to the opposite side of the vertical walls 33 and 35.

[0044] Figure 7 is a top view of the intermediate molded product 30. The top view of the intermediate molded product 30 refers to viewing the intermediate molded product 30 from the top plate 31 side along the pressing direction P (Figures 5B to 5D).

[0045] Referring to Figure 7, the ridges 32 and 34 extend along the top plate 31 in the longitudinal direction of the intermediate molded product 30. The vertical walls 33 and 35 are provided along the ridges 32 and 34, respectively. The flanges 36 and 37 are provided along the vertical walls 33 and 35, respectively.

[0046] The ridge portion 32 includes an intermediate-shaped ridge portion 321. The intermediate-shaped ridge portion 321 is the portion of the ridge portion 32 that is formed into a curved ridge portion 121 (Figures 3 and 4) in the second molding process described later. The intermediate-shaped ridge portion 321 curves inward in a concave shape when viewed from above in the intermediate molded product 30. The shape of the intermediate-shaped ridge portion 321 in the top view of the intermediate molded product 30 may be substantially equal to the shape of the curved ridge portion 121 in the top view of the press-formed product 10 after the second molding process (Figure 3). In this case, the vertical wall 33 may include a curved vertical wall 331. The curved vertical wall 331 is the portion of the vertical wall 33 that curves inward in a concave shape when viewed from above in the intermediate molded product 30. The curved vertical wall 331 is formed into a curved vertical wall 131 (Figures 3 and 4) in the second molding process described later.

[0047] Figures 8A to 8C are side views of the intermediate molded product 30. As shown in Figure 8A, the intermediate ridge portion 321 may be concave inward when viewed from the side of the intermediate molded product 30. As shown in Figure 8B, the intermediate ridge portion 321 may be convex outward when viewed from the side of the intermediate molded product 30. The intermediate ridge portion 321 has a minimum radius of curvature Rm when viewed from the side of the intermediate molded product 30. The portion of the flange 36 corresponding to the intermediate ridge portion 321 may or may not be curved when viewed from the side of the intermediate molded product 30. The portion of the flange 36 corresponding to the intermediate ridge portion 321 may be curved in the same direction as the intermediate ridge portion 321, or in the opposite direction. As shown in Figure 8C, the intermediate ridge portion 321 may also be substantially straight when viewed from the side of the intermediate molded product 30.

[0048] A side view of the intermediate molded product 30 with respect to the intermediate ridge portion 321 means viewing the intermediate ridge portion 321 from a direction perpendicular to the pressing direction P (Figures 5B to 5D) and perpendicular to the extension direction vector at the center of the extension direction of the boundary line C1 between the top plate 31 and the intermediate ridge portion 321.

[0049] The minimum radius of curvature Rm can be measured as follows. Of the boundary line C0 between the top plate 31 and the ridge portion 32, the portion corresponding to the boundary line B1 (Figure 4) between the top plate 11 and the curved ridge portion 121 in the press-formed product 10 is defined as the boundary line C1 between the top plate 31 and the intermediate shaped ridge portion 321. Then, evaluation points are placed at equal intervals (e.g., 1 mm intervals) on the boundary line C1, and for each evaluation point, the radius of curvature [mm] of the arc passing through the evaluation point and the evaluation points on both sides thereof is measured in a side view of the intermediate molded product 30. The minimum value of the radius of curvature of the evaluation points located within the boundary line C1 is the minimum radius of curvature Rm [mm] of the boundary line C1 between the top plate 31 and the intermediate shaped ridge portion 321 in a side view of the intermediate molded product 30. The boundary line C0 between the top plate 31 and the ridge portion 32 corresponds to the end of the R on the top plate 31 side of the ridge portion 32 on the outer surface of the intermediate molded product 30. The R-end of the ridge portion 32 on the top plate 31 side is the boundary between the curved ridge portion 32 of the intermediate molded product 30 and the straight portion of the top plate 31 in a cross-sectional view.

[0050] When the intermediate ridge portion 321 of the intermediate molded product 30 is curved concavely inward in a side view (Figure 8A), the curvature Cm of the intermediate ridge portion 321 in a side view of the intermediate molded product 30 is the reciprocal of the minimum radius of curvature Rm (Cm = 1 / Rm). When the intermediate ridge portion 321 is curved convexly outward in a side view of the intermediate molded product 30 (Figure 8B), the curvature Cm of the intermediate ridge portion 321 is the value obtained by multiplying the reciprocal of the minimum radius of curvature Rm by -1 (Cm = -1 / Rm). When the intermediate ridge portion 321 is not curved in a side view of the intermediate molded product 30, in other words, when the intermediate ridge portion 321 is substantially straight in a side view of the intermediate molded product 30 (Figure 8C), the curvature Cm of the intermediate ridge portion 321 is 0 (Cm = 0). If the minimum radius of curvature Rm is 20,000 mm or more, the intermediate ridge line portion 321 of the intermediate molded product 30 can be considered to be straight in a side view, and Cm can be set to 0.

[0051] The curvature Cm[1 / mm] of the intermediate ridge section 321 is set, together with the curvature Cp[1 / mm], to satisfy the following equation (1). -1.40 × Cp ≤ Cm <Cp (1)

[0052] Preferably, the curvature Cm[1 / mm] is set together with the curvatures Cp[1 / mm] and Cv[1 / mm] to satisfy the following equation (2). Cp-(Cp+Cv)×0.46≦Cm≦Cp-(Cp+Cv)×0.10 (2)

[0053] In equations (1) and (2), the curvature Cp is the curvature of the curved ridge portion 121 in a side view of the press-formed product 10, and is the reciprocal of the minimum radius of curvature Rp (Figure 4) in a side view of the press-formed product 10 at the boundary line B1 between the top plate 11 and the curved ridge portion 121 (Cp = 1 / Rp). In equation (2), the curvature Cv is the reciprocal of the minimum radius of curvature Rv (Figure 3) in a top view of the press-formed product 10 at the boundary line A1 between the curved ridge portion 121 and the vertical wall 13 (Cv = 1 / Rv).

[0054] (Second molding process) As shown in Figures 5E and 5F, in the second molding process, the intermediate molded product 30 is subjected to press working to obtain the press-molded product 10. In the second molding process, for example, a mold set 50 including a punch 51, a die 52, and a pad 53 is used.

[0055] Referring to Figure 5E, the punch 51 has a convex forming surface. In this embodiment, the punch 51 includes a punch top surface 511, punch shoulders 512, 514, punch sides 513, 515, and punch flange surfaces 516, 517. The punch shoulders 512, 514 are positioned on either side of the punch top surface 511. The punch sides 513, 515 are connected to the punch top surface 511 via the punch shoulders 512, 514, respectively. The punch flange surface 516 is connected to the punch side surface 513 via a corner portion 518. The punch flange surface 517 is connected to the punch side surface 515 via a corner portion 519.

[0056] The die 52 is able to move closer to and further away from the punch 51 in the pressing direction P. The die 52 has a forming surface that corresponds to the punch 51. More specifically, the die 52 includes die shoulders 522, 524, die sides 523, 525, and die flange surfaces 526, 527. The die shoulders 522, 524 have shapes that correspond to the punch shoulders 512, 514, respectively. The die sides 523, 525 are continuous with the die shoulders 522, 524, respectively. The die sides 523, 525 have shapes that correspond to the punch sides 513, 515, respectively. The die flange surface 526 is connected to the die side surface 523 via a corner portion 528. The die flange surface 527 is connected to the die side surface 525 via a corner portion 529. The die flange surfaces 526, 527 have shapes that correspond to the punch flange surfaces 516, 517, respectively. The pad 53 faces the punch top surface 511 in the pressing direction P.

[0057] Continuing with Figure 5E, in the second molding process, first, the intermediate molded product 30 is placed between the punch 51 and the die 52 and pad 53. Then, as shown in Figure 5F, the top plate 31 of the intermediate molded product 30 is clamped between the top surface 511 of the punch and the pad 53. In this state, the die 52 is brought relatively closer to the punch 51 in the pressing direction P, and the intermediate molded product 30 is clamped between the punch 51 and the die 52. As a result, as shown in Figure 5G, the press-molded product 10 is formed from the intermediate molded product 30.

[0058] In the second molding process, the top plate 31, ridge portion 32, and vertical wall 33 of the intermediate molded product 30 are formed into the top plate 11, ridge portion 12, and vertical wall 13 of the press-formed product 10. In this embodiment, the ridge portion 34, vertical wall 35, and flanges 36, 37 of the intermediate molded product 30 are formed into the ridge portion 14, vertical wall 15, and flanges 16, 17 of the press-formed product 10. The intermediate shaped ridge portion 321 (Figures 7 and 8A to 8B) is deformed by the press working in the second molding process and formed into a curved ridge portion 121 (Figures 3 and 4). In addition, at least the portions of the top plate 31 and vertical wall 33 adjacent to the intermediate shaped ridge portion 321 are deformed by the press working in the second molding process. Other portions of the intermediate molded product 30 may be deformed by the press working in the second molding process, or their shape may be maintained.

[0059] [effect] In the manufacturing method according to this embodiment, an intermediate molded product 30 including an intermediate shaped ridge portion 321 is formed from a metal sheet 20 in the first molding step, and a press-formed product 10 including a curved ridge portion 121 is formed from the intermediate molded product 30 in the second molding step. The curved ridge portion 121 has a concave shape on the inside of the press-formed product 10 in both a top view and a side view. In the second molding step, the intermediate shaped ridge portion 321 is formed into the curved ridge portion 121. The curvature Cm of the intermediate shaped ridge portion 321 in a side view of the intermediate molded product 30 is smaller than the curvature Cp of the curved ridge portion 121 in a side view of the press-formed product 10. This makes it possible to suppress the occurrence of wrinkles on the top plate 11 of the press-formed product 10.

[0060] For example, when the intermediate-shaped ridge line portion 321 is curved convexly outward in a side view of the intermediate molded product 30 (Cm = -1 / Rm < Cp), when the intermediate molded product 30 is formed from the metal plate 20, tensile stress can be generated in the top plate 31 according to the shape of the intermediate-shaped ridge line portion 321 in the side view of the intermediate molded product 30. In this case, even when the intermediate-shaped ridge line portion 321 has a concave shape inside the intermediate molded product 30 in a top view of the intermediate molded product 30 and compressive stress is generated in the top plate 31 according to the shape of the intermediate-shaped ridge line portion 321 in the top view of the intermediate molded product 30, the compressive stress generated in the portion of the top plate 31 adjacent to the intermediate-shaped ridge line portion 321 can be relaxed by the sum with the tensile stress according to the shape of the intermediate-shaped ridge line portion 321 in the side view of the intermediate molded product 30. Therefore, even in the press-molded product 10 formed from the intermediate molded product 30, the compressive stress in the portion of the top plate 11 adjacent to the curved ridge line portion 121 does not easily increase. Thus, wrinkles in the top plate 11 can be reduced.

[0061] For example, when the intermediate-shaped ridge line portion 321 is curved concavely inward in a side view of the intermediate molded product 30 but has a gentler curved shape than the curved ridge line portion 121 of the press-molded product 10 (Cm = 1 / Rm < Cp), or when the intermediate-shaped ridge line portion 321 is not curved in a side view of the intermediate molded product 30 (Cm = 0 < Cp), the line length of the boundary line C1 between the top plate 31 and the intermediate-shaped ridge line portion 321 in the intermediate molded product 30 is shorter than the line length of the boundary line B1 between the top plate 11 and the curved ridge line portion 121 in the press-molded product 10. Thereby, when forming the press-molded product 10 from the intermediate molded product 30 in the second forming step, since the portion of the boundary line C1 and the top plate 31 adjacent to the boundary line C1 is stretched, wrinkles in the top plate 11 of the press-molded product 10 can be reduced. Similarly, when the intermediate-shaped ridge line portion 321 is curved convexly outward in a side view of the intermediate molded product 30 (Cm = -1 / Rm < Cp) and the line length of the boundary line C1 is shorter than the line length of the boundary line B1, in the second forming step, since the portion of the boundary line C1 and the top plate 31 adjacent to the boundary line C1 is stretched, wrinkles in the top plate 11 of the press-molded product 10 can be reduced.

[0062] When the intermediate shape ridge line portion 321 curves convexly outward in the side view of the intermediate molded product 30 (Cm = -1 / Rm < Cp), even if the boundary line C1 is longer than the boundary line B1, tensile stress can be generated in the top plate 31 with respect to the shape of the intermediate shape ridge line portion 321 in the side view of the intermediate molded product 30. In this case, in the portion of the top plate 31 adjacent to the intermediate shape ridge line portion 321, the compressive stress is relaxed by the sum of the shape of the intermediate shape ridge line portion 321 in the side view of the intermediate molded product 30 and the shape of the intermediate shape ridge line portion 321 in the top view, and wrinkles are less likely to occur. By relaxing the compressive stress of the top plate 31 in the intermediate molded product 30, a large compressive stress is less likely to be generated in the top plate 11 of the press-molded product 10 formed from the intermediate molded product 30, and the wrinkles of the top plate 11 are reduced.

[0063] However, if the boundary line C1 is too long, wrinkles will occur on the top plate 11. Therefore, in the manufacturing method according to the present embodiment, the curvature Cm of the intermediate shape ridge line portion 321 in the side view of the intermediate molded product 30 is set to be -1.40 times or more of the curvature Cp of the curved ridge line portion 121 in the side view of the press-molded product 10 so that the boundary line C1 does not become too long with respect to the boundary line B1. Thereby, the boundary line C1 does not become too long with respect to the boundary line B1, and wrinkles are less likely to occur on the top plate 11.

[0064] In the manufacturing method according to the present embodiment, by forming the press-molded product 10 through the first molding step and the second molding step, the wrinkles of the top plate 11 are reduced. Therefore, there is no need to provide concave or convex portions for reducing wrinkles in the press-molded product 10 or to relax the shape of the final curved ridge line portion 121. Therefore, according to the manufacturing method according to the present embodiment, the wrinkles of the top plate 11 can be reduced without changing the final shape of the press-molded product 10.

[0065] In the manufacturing method according to the present embodiment, the curvature Cm of the intermediate shape ridge line portion 321 in the side view of the intermediate molded product 30 satisfies the above formula (1). The curvature Cm may further satisfy the above formula (2). By setting the curvature Cm so as to satisfy the formula (2), the occurrence of wrinkles on the top plate 11 in the press-molded product 10 can be further reduced.

[0066] While embodiments relating to this disclosure have been described above, this disclosure is not limited to the embodiments described above, and various modifications are possible as long as they do not deviate from its spirit.

[0067] For example, in the above embodiment, in the second molding step, a mold set 50 including a punch 51, a die 52, and a pad 53 is used, and the press-formed product 10 is formed from the intermediate molded product 30 by so-called pad bending. However, the mold set 50 does not have to include the pad 53. In the second molding step, the press-formed product 10 may be formed from the intermediate molded product 30 by so-called stamping using a mold set 50 consisting of a punch 51 and a die 52. [Examples]

[0068] The present disclosure will be further described below with reference to examples. However, the present disclosure is not limited to the following examples.

[0069] To confirm the effects of this disclosure, CAE analysis was performed on the molding (two-step molding) of press-formed product 10 using the same manufacturing method as in the above embodiment, using general-purpose analysis software (Ansys LS-DYNA, ANSYS, Inc.), and the wrinkles on the top plate 11 were evaluated. The conditions and evaluations for each example and comparative example are shown in Table 1.

[0070] [Table 1]

[0071] In the column of Formula (1) in Table 1, when the curvature Cm of the intermediate shape ridge line portion 321 in the side view of the intermediate molded product 30 and the curvature Cp of the curved ridge line portion 121 in the side view of the press-formed product 10 satisfy Formula (1): -1.40×Cp≦Cm<Cp, "〇" is displayed; when not satisfied, "×" is displayed. Similarly, in the column of Formula (2), when the curvatures Cm, Cp, and the curvature Cv of the curved ridge line portion 121 in the top view of the press-formed product 10 satisfy Formula (2): Cp-(Cp+Cv)×0.46≦Cm≦Cp-(Cp+Cv)×0.10, "〇" is displayed; when not satisfied, "×" is displayed. The wrinkles of the top plate 11 were evaluated by the wrinkle height. Specifically, when the wrinkle height on the top plate 11 is 0.10 mm or more, it is evaluated as "not acceptable"; when the wrinkle height is 0.07 mm or more and less than 0.10 mm, it is evaluated as "good"; when the wrinkle height is less than 0.07 mm, it is evaluated as "excellent".

[0072] In Comparative Example 1, the curvature Cm of the intermediate shape ridge line portion 321 in the side view of the intermediate molded product 30 is larger than the curvature Cp of the curved ridge line portion 121 in the side view of the press-formed product 10. In Comparative Example 2, the curvature Cm is smaller than the curvature Cp, but the curvature Cm is less than -1.40 times the curvature Cp. That is, Comparative Examples 1 and 2 do not satisfy Formula (1). In Comparative Example 1, wrinkles with a wrinkle height of 0.16 mm occurred on the top plate 11, and the evaluation of the wrinkles was "not acceptable". In Comparative Example 2, wrinkles with a wrinkle height of 0.10 mm occurred on the top plate 11. In Comparative Example 2, although the wrinkles on the top plate 11 were reduced compared to Comparative Example 1, the evaluation of the wrinkles was still "not acceptable".

[0073] Examples 1 to 5 all satisfy Formula (1). That is, in Examples 1 to 5, the curvature Cm is -1.40 times or more the curvature Cp and smaller than the curvature Cp. In Examples 1 to 5, the wrinkles on the top plate 11 were improved compared to Comparative Examples 1 and 2. Particularly in Examples 2 to 4 that satisfy both Formulas (1) and (2), the wrinkle height of the wrinkles on the top plate 11 was suppressed to 0.05 mm or less, and the wrinkles on the top plate 11 were significantly reduced compared to Comparative Examples 1 and 2.

[0074] This analysis confirmed that wrinkles in the top plate 11 are reduced by forming the press-molded product 10 using the first and second molding processes and setting the curvatures Cm and Cp to satisfy equation (1). It was also confirmed that wrinkles in the top plate 11 are further reduced by setting the curvatures Cm, Cp, and Cv to satisfy equation (2) in addition to equation (1). [Explanation of Symbols]

[0075] 10: Press-formed product 11: Top plate (second top plate) 12: Ridge section (Second ridge section) 121: Curved ridge section 13: Vertical wall (Second vertical wall) 20: Metal plate 30: Intermediate molded product 31: Top plate (first top plate) 32: Ridge section (First ridge section) 321: Intermediate ridge section 33: Vertical wall (First vertical wall) A1,B1,C1:Border line

Claims

1. A method for manufacturing press-formed products, The preparation process involves preparing the metal sheet as the raw material, A first molding step involves press-forming the metal plate to obtain an intermediate molded product including a first top plate, a first ridge portion continuous with the first top plate, and a first vertical wall connected to the first top plate via the first ridge portion. A second molding step involves press-forming the aforementioned intermediate molded product to obtain a press-formed product including a second top plate, a second ridge portion continuous with the second top plate, and a second vertical wall connected to the second top plate via the second ridge portion. Equipped with, The second ridge portion includes a curved ridge portion that curves inward in a concave shape when viewed from above the press-formed product and also curves inward in a concave shape when viewed from the side of the press-formed product. The first ridge portion includes an intermediate shaped ridge portion that is formed into the curved ridge portion in the second molding step, A manufacturing method in which, when Cp is the curvature of the curved ridge portion in a side view of the press-formed product and Cm is the curvature of the intermediate shaped ridge portion in a side view of the intermediate-formed product, Cp and Cm satisfy the following formula (1). -1.40×Cp≦Cm<Cp (1) However, Cp is the reciprocal of the minimum radius of curvature Rp in a side view of the press-formed product at the boundary line between the second top plate and the curved ridge portion, and if the intermediate shaped ridge portion is curved concavely inward in a side view of the intermediate molded product, Cm is the reciprocal of the minimum radius of curvature Rm in a side view of the intermediate molded product at the boundary line between the first top plate and the intermediate shaped ridge portion, and if the intermediate shaped ridge portion is curved convexly outward in a side view of the intermediate molded product, Cm is the value obtained by multiplying the reciprocal of the minimum radius of curvature Rm by -1, and if the intermediate shaped ridge portion is straight in a side view of the intermediate molded product, Cm is 0.

2. A manufacturing method according to claim 1, A method for manufacturing the aforementioned metal plate having a tensile strength of 400 MPa or more and 1850 MPa or less.

3. A manufacturing method according to claim 1 or 2, A manufacturing method wherein, when Rv is the minimum radius of curvature of the boundary line between the curved ridge portion and the second vertical wall in a top view of the press-formed product, and Cv is the reciprocal of Rv, Cp, Cm, and Cv satisfy the following equation (2). Cp-(Cp+Cv)×0.46≦Cm≦Cp-(Cp+Cv)×0.10 (2)

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