Manufacturing method for press-molded article

Abstract

This manufacturing method is for stably acquiring a press-molded article having high dimensional accuracy. The manufacturing method comprises, when manufacturing a press-molded article which has a cross section including a top plate part (1A) and vertical wall parts (1B) and which has a curved portion (2) curved toward the side of the top plate part (1A) at an intermediate position in the longitudinal direction thereof, a first step (10) for performing press-molding into an intermediate component (11) by using a first mold, and a second step (12) for press-molding the intermediate component (11) into a target component shape (1) by using a second mold. A molding surface of the first mold is set so that a first side viewing angle (θ1) formed between a first portion (3) and a second portion (4) positioned at both sides of the curved portion (2) in a side view is smaller than a top plate side viewing angle (θ0) in the target component shape (1). In addition, a molding surface of the second mold is set so that a second side viewing angle (θ2) formed between the first portion (3) and the second portion (4) which are positioned at both sides of the curved portion (2) in a side view is greater than or equal to the top plate side viewing angle (θ0).

Description

Manufacturing method for press-molded products

[0001] The present invention relates to a technique for manufacturing a press-formed product having a cross section including a top plate portion and a vertical wall portion, and having a curved portion in the longitudinal direction (extension direction) that is convex or concave toward the top plate portion in a side view. The press-formed product has a first portion and a second portion on either side of the curved portion. The first portion and the second portion extend along the longitudinal direction, but do not necessarily extend linearly.

[0002] In recent years, there has been a trend toward achieving both improved collision safety and reduced vehicle weight for automobile bodies. For this reason, the use of high-tensile steels with a strength of 590 MPa or more, and even ultra-high-tensile steels with a strength of 980 MPa or more, for automobile body structural parts is increasing. High-tensile steels and ultra-high-tensile steels have high yield strength and tensile strength. Therefore, forming defects such as dimensional accuracy due to springback become an issue for press-formed products manufactured by press forming.

[0003] One type of press-formed product used in vehicle body structural components is a part having a cross section with a top plate portion and a vertical wall portion. For example, in a side view, the part has a part shape that, along the longitudinal direction, is curved convexly or concavely toward the top plate portion midway along the longitudinal direction. When a press-formed product having such a part shape is manufactured by press forming, stress generated in the top plate portion or the vertical wall portion causes springback in the press-formed product in the longitudinal direction. In this case, if, for example, an ultra-high tensile steel is used as the material, the yield stress and tensile strength will be higher. Therefore, when the yield strength and tensile strength are high, a larger springback will occur.

[0004] Methods for addressing this issue include those described in, for example, Patent Document 1 and Patent Document 2. Patent Document 1 deals with a molded part having a top plate portion curved in the longitudinal direction and two side wall portions extending from both ends of the top plate portion along the longitudinal direction toward the inside of the curve. Patent Document 1 also discloses a method for changing the curvature of the top plate portion in a previous process and the angle between the top plate portion and the side wall portions. As a result, Patent Document 1 reduces stress generated in a subsequent process and suppresses springback.

[0005] Patent Document 2 deals with a formed part having a hat-shaped cross section curved along the longitudinal direction. Patent Document 2 also discloses a method in which, in a pre-process, the longitudinal radii of curvature of the top plate and flange are formed to be smaller than the radii of curvature of the target part shape, and then, in a post-process, the part is formed to the target part shape. This reduces stress generated in the post-process and suppresses springback.

[0006] JP 2011-206789 A

[0007] However, the method described in Patent Document 1 only changes the radius of curvature of the top plate in a side view. Therefore, the stress generated in the vertical wall portion and flange portion is not significantly improved. In particular, with high-tensile steel, which has a large amount of springback, there is a risk that springback will not be sufficiently suppressed.

[0008] In addition, it is assumed that the method described in Patent Document 2 is applied to a target part shape that has a curved portion midway in the longitudinal direction, and that a first portion and a second portion, each having a substantially straight shape, are continuous on both sides of the curved portion in the longitudinal direction. In this case, the method described in Patent Document 2 reduces stress only within the range of the curved portion, and therefore may not be able to sufficiently reduce springback.

[0009] The present invention has been made with the above points in mind. It is an object of the present invention to manufacture a press-formed product having a shape in which, in a side view, a portion along the longitudinal direction is curved convexly or concavely toward the top plate portion. It is also an object of the present invention to significantly reduce the occurrence of springback in the longitudinal direction with a simple die structure, even when high-tensile steel or the like is used for such a press-formed product. It is also an object of the present invention to provide a method for manufacturing a press-formed product that can stably obtain a target part shape with high dimensional accuracy.

[0010] In order to solve the problem, one aspect of the present invention provides a press-formed product of a target part shape by press-forming a metal plate into a part shape having a cross section with a top plate portion and a vertical wall portion continuing from a widthwise end of the top plate portion, extending along a longitudinal direction that is a direction intersecting the cross section, and having a curved portion at a midpoint in the longitudinal direction that is curved convexly or concavely toward the top plate portion in a side view, and having a first portion and a second portion continuing from both ends of the curved portion along the longitudinal direction, the press-formed product comprising: a first step of press-forming the metal plate into an intermediate part having a shape that imitates the target part shape using a first mold; and a second step of press-forming the intermediate part into the target part shape using a second mold, wherein the first mold has a tangent line along the longitudinal direction at a position where a forming surface that forms the top plate portion of the first portion continues to a forming surface that forms the top plate portion of the curved portion in a side view, and a first side view angle, which is the angle between the molding surface that molds the top plate portion of the second portion and a tangent along the longitudinal direction at a position continuous with the molding surface that molds the top plate portion of the curved portion, and a target top plate side view angle, which is the angle between the tangent to the top plate portion of the first portion, along the longitudinal direction at a position continuous with the molding surface that molds the top plate portion of the curved portion, in the target part shape, and a tangent to the top plate portion of the second portion, along the longitudinal direction, at a position continuous with the top plate portion of the curved portion; and the second mold is set so that, in a side view, a second side view angle, which is the angle between the tangent to the molding surface that molds the top plate portion of the first portion, along the longitudinal direction at a position continuous with the molding surface that molds the top plate portion of the curved portion, and a tangent to the molding surface that molds the top plate portion of the second portion, along the longitudinal direction, at a position continuous with the molding surface that molds the top plate portion of the curved portion, is greater than the target top plate side view angle.

[0011] According to an aspect of the present invention, in the manufacture of a press-formed product having a shape in which a portion of the press-formed product in the longitudinal direction is curved convexly or concavely toward the top plate portion, it is possible to significantly reduce the occurrence of springback in the longitudinal direction with a simple die structure. Therefore, according to an aspect of the present invention, even when high-tensile steel or the like is used as the material, it is possible to significantly reduce the occurrence of springback in the longitudinal direction with a simple die structure. As a result, according to an aspect of the present invention, it is possible to stably obtain a target part shape with high dimensional accuracy. Thus, according to one aspect of the present invention, even when high-tensile steel or ultra-high-tensile steel is used, parts with high dimensional accuracy can be obtained, leading to improved yield. Furthermore, when the press-formed product is used as a vehicle body structural part, it is possible to easily assemble the part.

[0012] 1A and 1B are diagrams showing a target part shape according to an embodiment of the present invention; (a) is a perspective view; (b) is a side view; and (c) is a cross section in the width direction; (a) is a side view showing a curved portion and its state before and after; (b) is a view showing another cross section of the target part shape; (c) is a view showing a curved portion and its state before and after; (d) is a view showing another cross section of the target part shape; (d) is a view showing a process of a method for manufacturing a press-formed product according to an embodiment of the present invention; (a) is a view explaining the molding surface of a first mold used in a first process; (b) is a view explaining the shape around the curved portion on the top plate molding surface of the first mold; (c) is a view explaining the shape around the curved portion on the top plate molding surface of the second mold; (d) is a perspective view showing the stress distribution around the curved portion in a comparative molding method; (d) is a perspective view showing the stress distribution around the curved portion in an example of this embodiment; (d) is a view showing an example of a hat-shaped target part shape; (a) is a side view; and (b) is a cross section in the width direction; (c) is a view explaining another molding surface of the first mold used in the first process; (d) is a view explaining the shape around the curved portion on the flange portion molding surface of the first mold; and (d) is a view explaining the shape around the curved portion on the flange portion molding surface of the second mold.

[0013] Next, an embodiment of the present invention will be described with reference to the drawings. (Target Part Shape) In this embodiment, the target part shape (target part shape 1) of the part (press-molded product) to be manufactured is as follows. That is, in this embodiment, the cross section is U-shaped, as shown in FIG. 1, having a top plate portion 1A and left and right vertical wall portions 1B continuing from both sides of the top plate portion 1A in the width direction. Note that the dimensions shown in FIG. 1 are for illustrative purposes only and do not limit the present invention. Furthermore, the present invention can be applied to a part shape having an L-shaped cross section (see FIG. 3(a)) in which the vertical wall portion 1B is present only on one side of the top plate portion 1A in the width direction. Furthermore, the present invention can be applied to a part shape in which a flange portion 1C is connected to the lower end of the vertical wall portion 1B. In these cases, the cross section can be, for example, a hat-shaped (see FIG. 3(b)) or a substantially Z-shaped (see FIG. 3(c)).

[0014] Furthermore, the target part shape 1 in this embodiment is a longitudinal member extending along the longitudinal direction, which is a direction intersecting the above-mentioned cross section. As shown in FIGS. 1 and 2 , the target part shape 1 is a part shape having a curved portion 2 that is curved convexly or concavely toward the top plate portion 1A in a side view. The example shown in FIGS. 1 and 2 is an example in which the curved portion 2 is curved convexly toward the top plate portion 1A. There may be two or more curved portions 2 along the longitudinal direction. In this example, the curved portion 2 is provided midway along the longitudinal direction, and therefore has other portions on both sides of the curved portion 2. In this example, the other portions are referred to as a first portion 3 and a second portion 4.

[0015] FIG. 1 illustrates an example in which the first and second regions 3 and 4 on either side of the curved region 2 are non-curved regions, i.e., linear portions extending linearly in the longitudinal direction. That is, the first and second regions 3 and 4 are, for example, portions with zero or nearly zero curvature along the longitudinal direction of the tabletop 1A. However, the first and second regions 3 and 4 do not need to be entirely linear along the longitudinal direction. In this embodiment, it is sufficient that at least the continuous portion continuing to the curved region 2 is linear. Furthermore, the target part shape 1 may include a continuous shape of the curved region 2. In this case, the adjacent curved region 2 for one curved region 2 is the first region 3 or the second region 4. The radius of curvature of the curved region 2 along the longitudinal direction does not need to be a constant radius of curvature. In this case, when comparing the two radii of curvature, for example, the average or maximum value of the radius of curvature along the longitudinal direction may be compared. Alternatively, the curved region 2 may be divided into multiple sections, and the two radii of curvature may be compared for each section.

[0016] (Manufacturing Method) The manufacturing method of this embodiment is a method for manufacturing a target press-formed product by press-forming a metal plate (blank material) into the target part shape 1 having the part shape described above. The present invention is particularly suitable when the material is a high-tensile steel (steel plate with a tensile strength of 590 MPa or more) or an ultra-high-tensile steel. However, the present invention is also applicable to metal plates such as mild steel plate and aluminum plate. One of the objectives of this embodiment is to reduce fluctuations in the dimensional accuracy of a part when manufacturing a press-formed product having the target part shape 1. The fluctuations in dimensional accuracy occur due to camber back, which is springback along the longitudinal direction.

[0017] As shown in FIG. 4 , the method for manufacturing a press-formed product according to this embodiment includes a first step 10 and a second step 12. In the first step 10, a metal plate is press-formed into an intermediate part 11 using a first die (described later). The intermediate part 11 has a shape that follows a target part shape 1, which is a desired part shape. The intermediate part 11 according to this embodiment has a cross-sectional shape that is the same as the target part shape 1. The intermediate part 11 also has a curved portion along its longitudinal direction that is curved in the same direction as the target part shape 1 at the same position as the target part shape 1. However, the cross-sectional shape of the intermediate part 11 does not have to be exactly the same as the target part shape 1. For example, the angle of the vertical wall portion relative to the top plate portion may be different.

[0018] Here, the part shape of the intermediate part 11 is a shape that follows the target part shape 1. For this reason, in this specification, the names and symbols of the parts of the intermediate part 11 will be described using the same names and symbols as those of the target part shape 1. The intermediate part 11 of this embodiment has a U-shaped cross section with a top plate portion 1A, and has a curved portion 2 midway along the longitudinal direction. Note that the intermediate part 11 may have a portion that will be cut in a subsequent trimming process. For example, draw forming or form forming is used for the press forming in the first process 10.

[0019] The second process 12 is a process for producing a press-formed product of the target part shape 1. The second process 12 is performed by press-forming an intermediate part 11 using a second die described below. The press forming of the second process 12 is performed, for example, by a restriking process. As shown in FIG. 2 , a first tangent line S1 is defined as a tangent line along the longitudinal direction of the top plate portion 1A of the first portion 3 in the target part shape 1 at a continuous position 3A between the top plate portion 1A of the curved portion 2 and the top plate portion 1A of the curved portion 2. Furthermore, a second tangent line S2 is defined as a tangent line along the longitudinal direction of the top plate portion 1A of the second portion 4 in the target part shape 1 at a continuous position 4A between the top plate portion 1A of the curved portion 2 and the top plate portion 1A of the curved portion 2.

[0020] The first tangent line S1 and the second tangent line S2 are indicators that define the longitudinal extension directions of the first region 3 and the second region 4 relative to the curved region 2. Therefore, as shown in FIG. 2 , when at least the portions of the first region 3 and the second region 4 in the tabletop 1A that are continuous with the curved region 2 are straight, extending linearly along the longitudinal direction, they may be defined as follows. That is, the first tangent line S1 and the second tangent line S2 may be defined as follows. The extension directions S1′ and S2′ of the straight portions can be considered to be the directions of the tangent lines S1 and S2, respectively. The straight portions correspond to the first region 3 and the second region 4 in FIG. 2 . FIG. 2 shows an example in which the extension directions S1′ and S2′ are set at the vertical wall portion 1B position. The extension directions S1′ and S2′ may also be set at the tabletop 1A position.

[0021] In addition, the angle θ0 formed by the first tangent S1 and the second tangent S2 in the side view is the side view angle in the target part shape 1. This side view angle is defined as the target top plate side view angle θ0. The target top plate side view angle θ0 is also simply referred to as the top plate side view angle θ0. In addition, the radius of curvature of the curved portion 2 along the longitudinal direction of the top plate portion 1A in the target part shape 1 is defined as the reference radius of curvature R0.

[0022] <First Mold> The first mold used in the first step 10 is a mold for press-forming a metal plate into a predetermined part shape to produce an intermediate part 11. The part shape has a U-shaped cross section with a top plate portion 1A and a curved portion 2 midway along the longitudinal direction. As shown in Fig. 5 , the first mold includes an upper mold 20 and a lower mold 120 that face each other in the pressing direction. The first mold of this embodiment also has a pad (not shown) for pressing the metal plate against the lower mold 120.

[0023] The upper mold 20 of the first mold has a top plate molding surface 21 and a vertical wall molding surface 22 as molding surfaces for press molding. The top plate molding surface 21 is the surface that molds the top plate portion 1A. The vertical wall molding surface 22 continues from the top plate molding surface 21 in the width direction and is the surface that molds the vertical wall portion 1B. Furthermore, as shown in FIG. 6 , the top plate molding surface 21 has a curved molding surface 21A midway along its length that molds a curved portion 2 that is convex upward along the length. Furthermore, the top plate molding surface 21 has left and right molding surfaces on either side of the curved molding surface 21A that mold the first portion 3 and the second portion 4 of the top plate portion 1A, respectively. In FIG. 6 , the left and right molding surfaces are the first portion molding surface 21B and the second portion molding surface 21C.

[0024] Here, a third tangent line S3 is defined as a tangent line along the longitudinal direction of the first-part molding surface 21B that molds the first part 3 at a continuous position 21Ba (boundary position) with the molding surface for the curved part 2. A fourth tangent line S4 is defined as a tangent line along the longitudinal direction of the second-part molding surface 21C that molds the second part 4 at a continuous position 21Ca (boundary position) with the molding surface for the curved part 2. As shown in Figure 6, the angle between the third tangent line S3 and the fourth tangent line S4 in a side view is defined as a first side view angle θ1.

[0025] As shown in Figures 5 and 6, the molding surface of the lower mold 120 of the first mold is shaped to match the molding surface of the upper mold 20 that faces it in the pressing direction. That is, as shown in Figure 5, the lower mold 120 of the first mold has a top plate molding surface 121 and a vertical wall molding surface 122 as molding surfaces for press molding. The top plate molding surface 121 is the surface that molds the top plate portion 1A. The vertical wall molding surface 122 continues from the top plate molding surface 121 in the width direction and is the surface that molds the vertical wall portion 1B. Furthermore, as shown in Figure 6, the top plate molding surface 121 has a curved molding surface 121A midway in the longitudinal direction that molds the curved portion 2. Furthermore, the top plate molding surface 121 has left and right molding surfaces on either side of the curved molding surface 121A that mold the first portion 3 and the second portion 4 of the top plate portion 1A, respectively. In Fig. 6, the left and right molding surfaces are a first-section molding surface 121B and a second-section molding surface 121C. Furthermore, as shown in Fig. 6, the side view angle formed by the first-section molding surface 121B for molding the first section 3 and the second-section molding surface 121C for molding the second section 4 in a side view is a first side view angle θ1, similar to that of the upper mold 20. In the first mold of this embodiment, the first side view angle θ1 is set to be smaller than the target top plate side view angle θ0. This first side view angle θ1 corresponds to the side view angle of the intermediate part 11 at the bottom dead center of the press in the first process 10.

[0026] Furthermore, it is preferable to set the value of the first side view angle θ1 in the first step 10 so as to satisfy the following formula (1): 0.83≦θ1 / θ0<1.0 (1) Here, if "θ1 / θ0" is less than 0.83, the amount of unbending in the second step will be large, and there is a possibility that large springback will occur in the opposite direction. Also, if "θ1 / θ0" is 1.0 or more, there is a possibility that unbending deformation will not occur in the second step, and the stress reduction effect will not be obtained.

[0027] Furthermore, it is preferable to set the first side view angle θ1 so that the side view angle of the intermediate part 11 after release from the mold is smaller than the top plate side view angle θ0. If the side view angle of the intermediate part 11 after springback exceeds the side view angle of the target part shape 1, bending back deformation will not occur in the second step 12, and the stress reduction effect may not be achieved. These settings may be adjusted to satisfy the conditions, for example, by performing forming analysis such as CAE analysis using a computer.

[0028] Here, in this specification, the line length along the longitudinal direction of the top plate portion in the curved portion of the above-mentioned part shape is defined as the curved portion line length. In this case, it is preferable that the curved portion line length L1 of the intermediate part 11 (after demolding) produced in the first step 10 is longer than the curved portion line length L0 of the target part shape 1 and the curved portion line length L2 of the press-formed product produced in the second step. The curved portion line length L2 is manufactured to be the same as or similar to the curved portion line length L0. It is preferable to set the press conditions, etc., of the first step 10 so as to satisfy the above-mentioned line length conditions. When the intermediate part 11 produced under these conditions is press-formed in the second step 12, stress is reduced over a wider range of the curved portion 2 along the longitudinal direction, resulting in a springback reduction effect.

[0029] Furthermore, the radius of curvature R1 in the longitudinal direction of the curved forming surfaces 21A, 121A in the first mold of this embodiment is defined as the first radius of curvature R1. It is preferable to specify the forming surface of the first mold so that this first radius of curvature R1 is equal to or greater than the reference radius of curvature R0. In other words, it is preferable to set the value of R1 as the radius of curvature of the top plate in side view in the first step 10 so as to satisfy the following formula (2). When formula (2) is satisfied, it is possible to make "curved portion line length L1 > curved portion line length L0". R0 ≦ R1 (2)

[0030] If R0 > R1, the longitudinal range in which stress is reduced in the second step 12 will be narrowed, and there is a possibility that a sufficient springback reduction effect will not be obtained. Here, the first radius of curvature R1 corresponds to the radius of curvature of the intermediate part 11 at the bottom dead center of pressing in the first step 10. Therefore, the definition of formula (2) indicates that the radius of curvature of the curved portion of the intermediate part 11 after demolding is larger than the reference radius of curvature R0.

[0031] <Second Mold> The second mold used in the second step 12 is a mold for press-molding the intermediate part 11 into the target part shape 1. The second mold includes an upper mold 30 and a lower mold 130. The upper mold 30 and the lower mold 130 have top plate molding surfaces 31, 131 and vertical wall molding surfaces as molding surfaces for press molding. The top plate molding surfaces 31, 131 are surfaces that mold the top plate portion 1A. The vertical wall molding surfaces are continuous with the top plate molding surfaces 31, 131 in the width direction and are surfaces that mold the vertical wall portion 1B. In addition, as shown in FIG. 7 , the top plate molding surfaces 31, 131 have curved molding surfaces 31A, 131A midway along the longitudinal direction that mold the curved portion 2 that is convex upward along the longitudinal direction. The top plate forming surfaces 31, 131 have forming surfaces on both sides of the curved forming surfaces 31A, 131A that form the top plate portion 1A of the first region 3 and the second region 4. In Fig. 7, these forming surfaces are the first region forming surfaces 31B, 131B and the second region forming surfaces 31C, 131C.

[0032] Here, a fifth tangent line S5 is defined as a tangent line along the longitudinal direction of the first-part molding surface 31B, 131B that molds the first part 3 at a position (boundary position) where the curved molding surface 31A, 131A joins the first part 3. A sixth tangent line S6 is defined as a tangent line along the longitudinal direction of the second-part molding surface 31C, 131C that molds the second part 4 at a position (boundary position) where the curved molding surface 31A, 131A joins the second part 3. As shown in FIG. 7 , the angle between the fifth tangent line S5 and the sixth tangent line S6 in a side view is defined as a second side view angle θ2. In the second mold of this embodiment, the second side view angle θ2 is set to be equal to or greater than the target top plate side view angle θ0. This setting can be adjusted to satisfy the conditions, for example, by CAE analysis. As a result, in this embodiment, the relationship "θ1 < θ0 ≦ θ2" is established.

[0033] Furthermore, it is preferable to set the value of the first side view angle θ1 in the first step 10 and the value of the second side view angle θ2 in the second step 12 so as to satisfy the following formula (A): 0.83≦θ1 / θ2<1.0 (A) Here, if "θ1 / θ2" is less than 0.83, the amount of unbending in the second step will be large, and there is a possibility that large springback will occur in the reverse direction. Also, if "θ1 / θ2" is 1.0 or more, there is a possibility that unbending deformation will not occur in the second step, and the stress reduction effect will not be obtained.

[0034] Furthermore, the relationship between the curved portion line length L1 and the curved portion line length L2 may be set to satisfy the following formula (B): 1.00< L1 / L2< 2.00 (B) In this case, the amount of springback can be kept within the target range even when the first curvature radius R1 is set closer to the second curvature radius R2. For example, the first curvature radius R1 is set closer to the second curvature radius R2 when the relationship between the first curvature radius R1 and the second curvature radius R2 is set to 0.7< R1 / R2≦1.0. By bringing the curvature radii R1 and R2 closer together, the intermediate part 11 (a one-step molded product) can be stably molded without being carried by a mold in the second step 12, which is the second step. The first curvature radius R1 is the radius of curvature R1 in the longitudinal direction of the curved molding surfaces 21A and 121A in the first mold. The second curvature radius R2 is the radius of curvature R2 in the longitudinal direction of the curved molding surfaces 31A and 131A in the second mold.

[0035] In the above description, the curved portion 2 is convex toward the tabletop 1A. The side view angle is defined as the angle on the inner surface (lower side) of the tabletop 1A. This definition is reversed when the curved portion 2 is concave toward the tabletop 1A. That is, when the curved portion 2 is concave toward the tabletop 1A, the side view angles, such as the first side view angle θ1, are defined as the angle on the outer surface (upper side) of the tabletop 1A so that they are smaller than 180 degrees. In this example, the first side view angle θ1 is the angle that is smaller than 180 degrees in side view.

[0036] (Operation and Others) Next, the operation and other aspects of this embodiment will be described. The inventors studied the manufacture of a press-formed product consisting of a longitudinal member with a U-shaped cross section, as shown in FIG. 1 . The press-formed product has a curved portion 2 that is curved convexly toward the top plate portion 1A in side view, located midway along the longitudinal direction. In the example of a press-formed product having a target part shape 1 shown in FIG. 1 , a first portion 3 and a second portion 4, each having a straight shape, are continuous on both sides of the curved portion 2 along the longitudinal direction. The inventors then studied the springback that occurs when a press-formed product having the target part shape 1 shown in FIG. 1 is manufactured by press forming. In this example, the press-formed product has a U-shaped cross section in which the top plate portion 1A and the vertical wall portion 1B are continuous in the width direction.

[0037] Here, θ is the angle between the portions on both sides of the curved portion 2 in the target part shape. The top plate side view angle θ0 was set to 170 degrees. In this example, the top plate side view angle θ0 corresponds to the side view angle between the first portion 3 and the second portion 4. The material used was a steel plate with a tensile strength of 1470 MPa. Then, press forming analysis was performed under these conditions. As a comparative forming method, a metal plate was formed into the target part shape 1 in a single press forming operation. Padded form forming was used for this comparative forming method. Padded form forming has a pad that presses the entire top plate surface. The analysis results showed that with the comparative forming method, springback occurred, with each longitudinal end bouncing up by 2.9 mm when viewed from the side.

[0038] Figure 8 shows the distribution of longitudinal stress when formed using the comparative forming method. This longitudinal stress distribution is the distribution at the center of the plate thickness at the bottom dead center of the press. As can be seen from Figure 8, tensile stress occurs in the top plate portion and compressive stress occurs in the vertical wall portion in the curved region 2 and its surrounding area. These stresses then cause longitudinal springback. Furthermore, as the material strength increases, these generated stresses also increase, resulting in a larger amount of springback. For these reasons, the comparative forming method may encounter issues such as not being able to achieve the target dimensional accuracy. As such, it can be seen that measures not only for the curved region 2 but also for the vicinity of the curved region 2 are effective in reducing springback.

[0039] To reduce this springback, the press-forming method of this embodiment performs the above-described first step 10 and second step 12. That is, in the first step 10, the top plate portion 1A is formed into a part shape in which, in side view, the first side view angle θ1 between the first portion 3 and the second portion 4 located on both sides of the curved portion 2 is bent to an angle smaller than the top plate side view angle θ0 of the target part shape 1. Note that the top plate curvature radius R1 in side view in the first step 10 is set to a value equal to the reference curvature radius R0 in side view of the target part shape 1. Then, in the second step 12, the part is press-formed to a side view angle equal to or larger than the target part shape 1.

[0040] In the example shown in FIG. 1 , the first and second regions 3 and 4 on either side of the curved region 2 are straight. However, the side view angle is not affected by the extension shapes of the first and second regions 3 and 4 at the portions away from the continuity with the curved region 2. The side view angle determines the continuity of the first and second regions 3 and 4 to the longitudinal end of the curved region 2. This continuity affects the springback. Therefore, the first and second regions 3 and 4 are not affected by the extension shapes of the first and second regions 3 and 4 at the portions away from the continuity with the curved region 2. As an example, the intermediate part 11 is formed in the first step 10 by setting the first side view angle θ1 to 168 degrees, which is smaller than the top plate side view angle θ0. Note that R1 = R0. In the first step 10, the part shape conditions other than the side view angle are the same as those for the target part shape 1.

[0041] Next, in the second process 12, which was a process subsequent to the first process 10, the intermediate part 11 was bent back to 170 degrees, the target part shape 1. In other words, the second side view angle θ2 was set to 170 degrees. The analysis results showed that the springback behavior in this example was -0.1 mm. Thus, it was found that the application of the forming method of this embodiment significantly reduced the amount of springback compared to the comparative forming method.

[0042] Figure 9 shows the longitudinal stress distribution at the center of the plate thickness at the bottom dead center of the press in the second step when the press forming method of this embodiment is applied. Compared to Figure 8, Figure 9 shows that the tensile stress generated in the top plate portion 1A around the curved portion 2 has been reduced, and compressive stress has been generated on both sides of the curved portion 2. In addition, the compressive stress generated in the vertical wall portion around the curved portion 2 before the countermeasure was taken has been reduced. It can be seen that these stress reduction effects have reduced springback in the longitudinal direction.

[0043] As described above, in this embodiment, the first side view angle θ1 in the first step 10 is set smaller than the target top plate side view angle θ0. Furthermore, in this embodiment, in the second step 12, the intermediate part 11 is bent back to a second side view angle θ2 that is equal to or greater than the top plate side view angle θ0 in the target part shape 1. In this case, in the second step 12, both sides of the curved portion of the intermediate part 11 are bent back as a structure. This reduces the stresses that contribute to springback. As such, in this embodiment, even when using high-tensile steel with a tensile strength of 440 PMa or higher or ultra-high-tensile steel with a strength of 980 MPa or higher, springback can be significantly reduced with a simple mold structure. This allows for the production of a part with the target part shape 1 with high dimensional accuracy.

[0044] (Modification) The press-forming method of the above embodiment can also be applied to reduce springback in the longitudinal direction when the target part shape 1 has a hat-shaped cross section with a flange portion 1C. In this case, in the first step 10 and the second step 12, it is recommended to make similar adjustments to the side view angle for the flange portion 1C as well as for the top plate portion 1A. An example of such adjustment is shown below. Figure 10 shows an example of a target part shape 1 with a hat cross section having a flange portion 1C. In this case, the upper mold 20 and lower mold 120 of the first mold used in the first step 10 have flange portion forming surfaces 23, 123 for forming the flange portion 1C, as shown in Figure 11.

[0045] As shown in Fig. 12, the flange portion molding surface 23, 123 has a flange curve molding surface 23A, 123A midway along the longitudinal direction. The flange curve molding surface 23A, 123A is a surface for molding the flange portion 1C of the curved portion that convex upward along the longitudinal direction. The flange portion molding surface 23, 123 also has left and right molding surfaces on both sides of the flange curve molding surface 23A, 123A that mold the flange portion 1C of the first portion 3 and the second portion 4, respectively. In Fig. 12, the left and right molding surfaces are the first portion molding surface 23B, 123B and the second portion molding surface 23C, 123C.

[0046] Here, a seventh tangent line S7 is defined as a tangent line along the longitudinal direction at a boundary position (boundary position) between the first-part molding surfaces 23B, 123B that form the first part 3 and the flange curve molding surfaces 23A, 123A. Furthermore, an eighth tangent line S8 is defined as a tangent line along the longitudinal direction at a boundary position (boundary position) between the second-part molding surfaces 23C, 123C that form the second part 4 and the flange curve molding surfaces 23A, 123A. The angle formed by the seventh tangent line S7 and the eighth tangent line S8 in a side view is defined as a third side view angle θ5. In the first mold of this embodiment, the third side view angle θ5 is set smaller than the side view angle θ10 at the flange portion of the target part shape 1. The third side view angle θ5 corresponds to the side view angle at the flange portion 1C of the intermediate part 11 at the bottom dead center of press in the first step 10.

[0047] Furthermore, it is preferable to set the third side view angle θ5 so that the side view angle of the flange portion after the intermediate part 11 is released from the mold is smaller than the target side view angle θ10. If the side view angle after springback of the intermediate part 11 becomes equal to or larger than the side view angle of the target part shape 1, bending back deformation may not occur in the second step 12, and the stress reduction effect may not be obtained. These settings may be adjusted to satisfy the conditions, for example, by performing forming analysis such as CAE analysis using a computer.

[0048] Furthermore, in the first mold of this embodiment, it is preferable to define the molding surface of the first mold as follows. That is, it is preferable to define the radius of curvature R3 in the longitudinal direction of the flange curved molding surface 23A, 123A to be equal to or greater than the radius of curvature R4 of the flange portion 1C at the curved portion 2 in the target part shape 1. Specifically, it is preferable to set the value of R3, which is the radius of curvature in a side view in the first step 10, so as to satisfy the following formula (3): R4 ≦ R3 (3)

[0049] By satisfying this condition, the length of the curve in the longitudinal direction in the first process is longer than the length of the curve in the longitudinal direction of the target part shape 1. When the second process is formed under this condition, stress is reduced over a wider range of the curved portion 2 along the longitudinal direction, resulting in a springback reduction effect. Furthermore, if R4 > R3, the longitudinal range in which stress is reduced in the second process 12 is narrowed, and there is a possibility that the sufficient springback reduction effect will be reduced.

[0050] The second mold has flange portion molding surfaces 33, 133 that mold the flange portion 1C as molding surfaces for press molding. Furthermore, as shown in Fig. 13 , the flange portion molding surfaces 33, 133 have curved molding surfaces 33A, 133A midway along the longitudinal direction that mold the flange portion of the curved portion 2 that is convex upward along the longitudinal direction. The flange portion molding surfaces 33, 133 have molding surfaces on both sides of the curved molding surfaces 33A, 133A that mold the flange portion 1C of the first portion 3 and the second portion 4, respectively. In Fig. 13 , these molding surfaces are first portion molding surfaces 33B, 133B and second portion molding surfaces 33C, 133C.

[0051] Here, the tangent line along the longitudinal direction at the boundary position (boundary position) between the first-part molding surface 33B, 133B and the curved molding surface 33A, 133A that molds the first part 3 is defined as the ninth tangent line S9. Furthermore, the tangent line along the longitudinal direction at the boundary position (boundary position) between the second-part molding surface 33C, 133C and the curved molding surface 33A, 133A that molds the second part 4 is defined as the tenth tangent line S10. The angle between the ninth tangent line S9 and the tenth tangent line S10 in a side view is defined as the fourth side view angle θ6. This fourth side view angle θ6 is set to be equal to or greater than the target side view angle θ10. The action and effect of the flange portion are the same as those for the top plate portion. According to the above configuration, by adjusting the flange portion 1C in addition to the top plate portion 1A, it is possible to more effectively suppress springback in the hat-shaped target part shape 1. The same applies to a substantially Z-shaped cross section.

[0052] (Other) The present disclosure may also have the following configurations: (1) Disclosure 1 provides a method for producing a press-formed product having a target part shape by press-forming a metal plate into a part shape that has a cross section including a top plate portion and vertical wall portions continuing from widthwise ends of the top plate portion, extends along a longitudinal direction that is a direction intersecting the cross section, and has, at a midpoint in the longitudinal direction, a curved portion that is curved convexly or concavely toward the top plate portion in a side view, and has a first portion and a second portion that continue from both ends of the curved portion along the longitudinal direction, the method comprising: a first step of press-forming the metal plate into an intermediate part having a shape that follows the target part shape using a first die; and a second step of press-forming the intermediate part into the press-formed product having the target part shape using a second die. In a side view, the first mold has a first side view angle, which is the angle formed by a tangent line along the longitudinal direction of the molding surface that molds the top plate portion of the first section at a position continuous with the molding surface that molds the top plate portion of the curved section, and a tangent line along the longitudinal direction of the molding surface that molds the top plate portion of the second section at a position continuous with the molding surface that molds the top plate portion of the curved section, and is smaller than a target top plate side view angle, which is the angle formed by a tangent line along the longitudinal direction of the top plate portion of the first section at a position continuous with the top plate portion of the curved section, in the target part shape, and a tangent line along the longitudinal direction of the top plate portion of the second section at a position continuous with the top plate portion of the curved section, a second mold, when viewed from the side, having a second side view angle, which is an angle between a tangent line along the longitudinal direction of the molding surface that molds the top plate portion of the first section at a position continuous with the molding surface that molds the top plate portion of the curved section, and a tangent line along the longitudinal direction of the molding surface that molds the top plate portion of the second section at a position continuous with the molding surface that molds the top plate portion of the curved section, set to be equal to or greater than the target top plate side view angle. (2) Disclosure 2 provides a method for manufacturing a press-molded product, wherein, when a line length along the longitudinal direction of the top plate portion of the curved section of the part shape is defined as a curved portion line length, in the first step, the intermediate part is molded so that the curved portion line length is longer than the curved portion line length in the target part shape.(3) Disclosure 3 is a method for manufacturing a press-molded product, in which the first mold has a radius of curvature (R1) along the longitudinal direction of a molding surface that molds the top plate portion of the curved portion, set to be equal to or greater than the radius of curvature (R0) along the longitudinal direction of the top plate portion of the curved portion in the target part shape. (4) Disclosure 4 discloses a method for manufacturing a molded product, wherein the cross section includes a flange portion continuing from a lower end of the vertical wall portion, and the first mold has a third side view angle, which is an angle formed by a tangent line of a molding surface that molds the flange portion of the first portion, along the longitudinal direction at a position continuous with the molding surface that molds the flange portion of the curved portion, and a tangent line of a molding surface that molds the flange portion of the second portion, along the longitudinal direction, at a position continuous with the molding surface that molds the flange portion of the curved portion, in a side view, that is smaller than a target flange side view angle, which is an angle formed by a tangent line of a flange portion of the first portion, along the longitudinal direction at a position continuous with the flange portion of the curved portion, in the target part shape, and a tangent line of a flange portion of the second portion, along the longitudinal direction, at a position continuous with the flange portion of the curved portion, a fourth side view angle, which is an angle between a tangent line of a molding surface that molds the flange portion of the first portion, along a longitudinal direction at a position continuous with the molding surface that molds the flange portion of the curved portion, and a tangent line of a molding surface that molds the flange portion of the second portion, along a longitudinal direction at a position continuous with the molding surface that molds the flange portion of the curved portion, is set to be equal to or greater than the target flange side view angle. (5) Disclosure 5 provides a method for manufacturing a press-molded product, wherein, when a first side view angle is defined as θ1 and a second side view angle is defined as θ2, the first side view angle θ1 and the second side view angle θ2 are set to values ​​that satisfy the following formula (A): 0.83≦θ1 / θ2<1.00 (A) (6) Disclosure 6 discloses a method for manufacturing a press-formed product, in which, when the line length of the curved portion in the intermediate part in the first step is defined as L1 and the line length of the curved portion in the formed part in the second step is defined as L2, L1 and L2 are set so that the values ​​satisfy the following formula (B): 1.00<L1 / L2<2.00 (B).

[0053] Next, an example based on this embodiment will be described. In order to confirm the springback reduction effect of the manufacturing method for a press-formed product according to this embodiment, a press forming analysis was performed using the finite element method (FEM). The results are described below. In this example, the shape shown in FIG. 1 was used as target part shape 1. That is, in this example, target part shape 1 is a shape having a first part and a second part each having a straight shape on both sides of a curved portion 2 in the longitudinal direction when viewed from the side.

[0054] The dimensions are as shown in Figure 1. Specifically, as shown in Figure 1, the target part shape 1 in this example had a length of 300 mm, a vertical wall height of 20 mm, a cross-sectional punch shoulder R (the radius of curvature on the outer surface of the ridge line portion) of 5 mm, and a flat portion width of the top plate of 10 mm (the overall width of the top plate portion 1A including the ridge line portion was 20 mm). The angle between the top plate portion 1A and the vertical wall portion 1B was 95 degrees. The metal plate used for press forming had a thickness t of 1.4 mm and was a steel plate with a tensile strength of 1470 MPa.

[0055] Then, press molding analysis was performed under molding conditions in which the side view angle in the first step 10 was set smaller than the side view angle in the second step 12. The amount of springback was measured through this analysis. For this shape, the side view R and angle of the curved portion 2 of the top plate were changed and the analysis was performed. In the following example, an absolute value of the difference in height of the longitudinal end of the press-formed product after demolding from the target part shape 1 after the second step 12 of less than 2.5 mm was deemed acceptable. In the following tables and descriptions, the difference in height of the longitudinal end of the press-formed product after demolding from the second step 12 is also referred to as the amount of springback.

[0056] Example 1 In target part shape 1, the radius of curvature (outer surface side) in side view of top plate portion 1A was set to 20 mm, and the top plate side view angle θ0 was selected and set within the range of 160 degrees to 175 degrees. Then, the first side view angle θ1 in first step 10 was changed within the range of 157 degrees to 175 degrees. Under the above conditions, FEM analysis of press forming was performed. The results are shown in Table 1.

[0057] In the following tables, the curved portion line length L1 indicates the curved portion line length of the intermediate part 11 (after demolding). The curved portion line length L2 indicates the curved portion line length of the press-molded product after molding in the second process. The top plate R1 indicates the radius of curvature (outer surface side) of the curved portion in the first process. The top plate R2 indicates the radius of curvature (outer surface side) of the curved portion in the second process. The top plate R1, the top plate R2, the first side view angle θ1, and the second side view angle θ2 are values ​​on the molding surface of the mold (the part shape at the bottom dead center of molding).

[0058]

[0059] <Nos. 1 to 7> Nos. 1 to 7 are cases where the top plate side view angle θ0 was set to 175 degrees. No. 1 is a conventional example formed using the comparative forming method described above. In other words, this conventional example is one in which a metal plate is press-formed into the target part shape 1 in a single process. In this conventional example, the side view angle in the die was set to 175 degrees. The amount of springback when formed using conventional example No. 1 was 3.2 mm.

[0060] No. 2 is an example of a case where the mold was manufactured using two press-forming steps, consisting of a first step and a second step, as in the present invention. However, the first side view angle θ1 in the first step 10 and the second side view angle θ2 in the second step 12 were both set to 175 degrees. The springback amount was 2.6 mm, a slight improvement compared to the springback amount in No. 1. However, No. 2 did not meet the target condition of an absolute value of less than 2.5 mm. In addition, in Nos. 3 to 7, which are examples of the present invention, the first side view angle θ1 in the first step 10 was set in the range of 171 to 174 degrees, and the second side view angle θ2 in the second step 12 was set to 175 degrees. Nos. 3 to 7 represent the results of press-forming under these conditions.

[0061] As can be seen from Table 1, when the first side view angle θ1 was 173 degrees, the springback amount after the second step 12 (after demolding) was the smallest, at 0.3 mm. No. 5 corresponds to the case where the first side view angle θ1 was 173 degrees. Furthermore, as in Nos. 6 and 7, when the side view angle θ1 in the first step 10 was set to 172 degrees or less, springback tended to occur in the opposite direction. However, the absolute values ​​of the springback amounts in Nos. 3 to 7 were smaller than those of the conventional example, satisfying the target absolute value of less than 2.5 mm. Furthermore, No. 3 is an example of the invention in which the curved portion line length L1 in the first step was shorter than the curved portion line length L2 in the second step. In No. 3, the springback amount was 1.5 mm. No. 3 also satisfied the target absolute value of less than 2.5 mm. In this way, if the angle θ1 of the first step 10 is smaller than the angle θ2 of the second step 12, it is not necessarily necessary to make the curved portion line length L1 of the first step 10 longer than the curved portion line length L2 of the second step 12.

[0062] <Nos. 8-12> Next, Nos. 8-12 are cases where the target top plate side view angle θ0 was set to 170 degrees. No. 8 is a conventional example formed in one process. The springback amount in No. 8 was 2.9 mm. Therefore, No. 8 does not meet the target condition of an absolute value of less than 2.5 mm. Nos. 9-12 are inventive examples. In Nos. 9-12, the first side view angle θ1 of the mold in the first process 10 was changed to 166-169 degrees. Furthermore, in Nos. 9-12, the second side view angle θ2 in the second process 12 was set to 170 degrees.

[0063] As can be seen from Table 1, when θ1 = 168 degrees in No. 10, the amount of springback after demolding in the second step 12 was the smallest. The amount of springback was -0.1 mm. Furthermore, when the first side view angle θ1 in the first step 10 was set to 168 degrees or less, springback tended to occur in the opposite direction. The absolute values ​​of the amount of springback in Nos. 9 to 12 were smaller than those of the conventional example, and met the target condition of an absolute value of less than 2.5 mm.

[0064] <Nos. 13 to 16> Next, Nos. 13 to 16 are cases where the top plate side view angle θ0 was set to 160 degrees. No. 13 is a conventional example formed in one process. The springback amount in No. 13 was 2.5 mm. Therefore, No. 13 does not meet the target condition of an absolute value of less than 2.5 mm. Nos. 14 to 16 are inventive examples. In Nos. 14 to 16, the first side view angle θ1 in the first process 10 was selected and set from 157 to 159 degrees.

[0065] As can be seen from Table 1, when θ1 = 158 degrees in No. 15, the amount of springback after demolding from the second step 12 was the smallest. The amount of springback was -0.4 mm. Furthermore, when the angle in the first step 10 was set to 158 degrees or less, springback tended to occur in the opposite direction. The absolute values ​​of the amount of springback in Nos. 14 to 16 were smaller than those of the conventional example, and met the target condition of an absolute value of less than 2.5 mm.

[0066] Example 2 This example examines the change in springback amount when the top plate R2 and the curved portion line length L2 after the second process are fixed and the top plate R1 of the intermediate part is changed. The results are shown in Table 2. In this example, the first side view angle θ1 in the first process 10 is fixed to 166 degrees. Furthermore, the second side view angle θ2 in the second process 12 is fixed to 170 degrees. This example shows the results when the top plate R1 and the curved portion line length L1 of the curved portion of the intermediate part are changed. Note that the radius of curvature R2 (= R20) and the curved portion line length L2 (= 3.49 mm) of the top plate portion of the curved portion in the second process 12 are fixed constant.

[0067]

[0068] As can be seen from Table 2, the larger the top plate R1 of the intermediate part is relative to the top plate R2, the more the amount of springback is reduced.

[0069] In this example, the radius of curvature of the curved portion 2 at the top plate portion 1A in the side view of the target part shape 1 was set to 200 mm. The second side view angle θ2 was selected and set from the range of 145 to 175 degrees. The results are shown in Table 3.

[0070]

[0071] <Nos. 31 to 35> Nos. 31 to 35 are cases where the target top plate side view angle θ0 was set to 175 degrees. In the first process 10, the first side view angle θ1 was selected and set from 170 to 175 degrees. In the second process 12, the second side view angle θ2 was set to 175 degrees. FEM analysis was performed under these molding conditions.

[0072] No. 31 is a conventional example formed in one process. The springback amount in No. 31 was 3.3 mm. No. 32 is a conventional example. The first side view angle θ1 in the first process 10 and the second side view angle θ2 in the second process 12 were both set to 175 degrees. The springback amount in No. 32 was 2.6 mm. No. 32 has a slightly improved springback amount compared to No. 31, but does not meet the target absolute value of less than 2.5 mm. Nos. 33 to 35 are inventive examples. The first side view angle θ1 of the mold in the first process 10 was set within the range of 170 to 173 degrees. In the second process 12, the second side view angle θ2 was set to 175 degrees.

[0073] When θ1 = 173 degrees, as in No. 33, the springback amount after the second step 12 (after demolding) was the smallest. The springback amount was 0.4 mm. Furthermore, when the angle θ1 measured in the first step 10 was set to 170 degrees, springback tended to occur in the opposite direction. The absolute values ​​of the springback amounts in Nos. 33 to 35 were smaller than those of the conventional example, satisfying the target absolute value of less than 2.5 mm. Furthermore, No. 33 is an example of the invention in which the curved portion line length L1 in the first step 10 was shorter than the curved portion line length L2 in the second step. The springback amount was 0.4 mm, satisfying the target absolute value of less than 2.5 mm. Thus, as long as the angle θ1 in the first step 10 is smaller than the angle θ2 in the second step 12, it is not necessarily necessary to make the curved portion line length L1 in the first step longer than the curved portion line length L2 in the second step.

[0074] <Nos. 36-40> Nos. 36-40 represent cases where the target top plate side view angle θ0 was 150 degrees. No. 36 is a conventional example formed in a single process. The springback amount for No. 36 was 5.5 mm, which does not meet the target condition of an absolute value of less than 2.5 mm. No. 37 is a conventional example. No. 37 is an example manufactured by setting both the first side view angle θ1 in the first process 10 and the second side view angle θ2 in the second process 12 to 150 degrees. The springback amount for No. 37 was 4.4 mm. No. 37 is a slight improvement over No. 36, but does not meet the target condition of an absolute value of less than 2.5 mm.

[0075] In Examples Nos. 38 to 40, which are examples of the present invention, the first side view angle θ1 of the mold in the first step 10 was selected from the range of 140 to 145 degrees. In the second step 12, it was set to 150 degrees. In this case, when θ1 = 143 degrees in Example No. 39, the springback amount after the second step 12 (after demolding) was the smallest. The springback amount was 0.0 mm. Furthermore, when the first side view angle θ1 in the first step 10 was set to 140 degrees or less, springback tended to occur in the opposite direction. The absolute values ​​of the springback amounts in Examples Nos. 38 to 40 were smaller than those of the conventional examples, meeting the target absolute value of less than 2.5 mm.

[0076] <Nos. 41 to 46> Nos. 41 to 46 are examples where the target top plate side view angle θ0 was 145 degrees. No. 41 is a conventional example formed in one process. The springback amount for No. 41 was 6.1 mm. No. 41 does not meet the target condition of an absolute value of less than 2.5 mm. No. 42 is a conventional example. No. 42 is an example manufactured by setting both the first side view angle θ1 in the first process 10 and the second side view angle θ2 in the second process 12 to 145 degrees. The springback amount was 5.8 mm. No. 42 is a slight improvement over No. 41, but does not meet the target condition of an absolute value of less than 2.5 mm.

[0077] In Examples Nos. 43 to 46, the first side view angle θ1 of the die in the first step 10 was selected from the range of 120 to 135 degrees. In the second step 12, the second side view angle θ2 was set to 145 degrees. In this case, as can be seen from Table 3, the springback amount in the second step was reduced most significantly to -0.1 mm when θ1 = 130 degrees, as in Example No. 44. Furthermore, when the angle in the first step 10 was set to 130 degrees or less, springback tended to occur in the opposite direction. The absolute values ​​of the springback amounts in Examples Nos. 43 to 46 were smaller than those of the conventional example, satisfying the target absolute value of less than 2.5 mm. Furthermore, as can be seen from Tables 1 and 2, in the present invention, the springback amount could be reduced even when the relationship between the curved portion line length L1 and the curved portion line length L2 was set to 1.00 < L1 / L2 < 2.00.

[0078] Example 4 This example examines the change in springback amount when the curved portion line length L2 after the second process is fixed and the top plate R1 of the intermediate part is changed. The results are shown in Table 4. In this example, the first side view angle θ1 in the first process 10 was fixed to 170 degrees. Furthermore, the second side view angle θ2 in the second process 12 was fixed to 175 degrees. This example shows the results when the top plate R1 and curved portion line length L1 of the intermediate part were changed. Note that the radius of curvature R2 (= R200) ​​and the curved portion line length L2 (= 17.45 mm) of the top plate portion of the curved portion in the second process 12 were fixed constant.

[0079]

[0080] As shown in Table 4, it was found that the larger the top plate R1 of the intermediate part was relative to the top plate R2, the more the amount of springback was reduced.

[0081] From the above results, it can be seen that the amount of springback is reduced when the second side view angle θ2 in the first process 10 is formed smaller than the side view angle θ0 of the target part shape 1. It can also be seen that the amount of springback can be further reduced by making the curved portion line length L1 of the intermediate part larger than the curved portion line length L2. It can also be seen that the amount of springback can be further reduced by making the curvature radius R1 of the top plate portion of the curved portion of the intermediate part larger than the curvature radius R2 of the top plate portion of the curved portion of the target part shape 1.

[0082] Furthermore, the above example is a case where the second side view angle θ2 is set equal to the top plate side view angle θ0 in the target part shape 1. There is a possibility that the amount of springback can be further suppressed by making the second side view angle θ2 larger than the top plate side view angle θ0 in the target part shape 1. Furthermore, Tables 2 and 4 show that by increasing the radius of curvature of the top plate portion of the curved portion of the intermediate part, the amount of springback is reduced as the curved portion line length L1 of the intermediate part is increased relative to the curved portion line length L2.

[0083] The entire contents of Japanese Patent Application No. 2024-122587 (filed July 29, 2024), from which this application claims priority, are incorporated herein by reference. While the present invention has been described with reference to a limited number of embodiments, the scope of the invention is not limited thereto, and modifications of each embodiment based on the above disclosure will be obvious to those skilled in the art.

[0084] 1 Target part shape 1A Top plate portion 1B Vertical wall portion 1C Flange portion 2 Curved portion 3 First portion 4 Second portion 10 First process 11 Intermediate part 12 Second process 20 Upper mold (first mold) 120 Lower mold (first mold) 30 Upper mold (second mold) 130 Lower mold (second mold) R0 Reference radius of curvature R1 Top plate radius of curvature θ0 Top plate side view angle θ1 First side view angle θ2 Second side view angle

Claims

1. When press-forming a metal sheet into a part shape having a cross-section with a top plate portion and vertical wall portions continuous from the widthwise end of the top plate portion, extending along the longitudinal direction which intersects the cross-section, and having a curved portion at an intermediate position in the longitudinal direction that, in a side view, curves in a convex or concave shape toward the top plate portion, and having a first portion and a second portion that are continuous from both ends of the curved portion along the longitudinal direction, in order to manufacture a press-formed product of the target part shape, The first step involves press-forming a metal sheet into an intermediate part with a shape that conforms to the target part shape using a first mold, A second step involves press-forming the above-mentioned intermediate part into a press-formed product having the shape of the above-mentioned target part using a second mold, Equipped with, In a side view, the first mold described above has a first side view angle, which is the angle formed by the longitudinal tangent of the molding surface that forms the top plate portion of the first part at a continuous position with the molding surface that forms the top plate portion of the curved part, and the longitudinal tangent of the molding surface that forms the top plate portion of the second part at a continuous position with the molding surface that forms the top plate portion of the curved part, and the angle formed by the longitudinal tangent of the molding surface that forms the top plate portion of the second part at a continuous position with the molding surface that forms the top plate portion of the curved part, in the target part shape, and the angle formed by the longitudinal tangent of the top plate portion of the second part at a continuous position with the top plate portion of the curved part. The second mold described above has a second side view angle, which is the angle formed by the longitudinal direction of the tangent line between the molding surface for forming the top plate portion of the first part and the molding surface for forming the top plate portion of the curved part at a continuous position, and the longitudinal direction of the tangent line between the molding surface for forming the top plate portion of the second part and the molding surface for forming the top plate portion of the curved part at a continuous position, set to be greater than or equal to the target side view angle of the top plate. A method for manufacturing press-formed products.

2. When the length of the curved portion of the above-mentioned part shape along the longitudinal direction of the top plate is defined as the curved portion length, In the first step described above, the curved portion length in the intermediate part is formed to be longer than the curved portion length in the target part shape. A method for manufacturing a press-formed product as described in claim 1.

3. The first mold described above has a radius of curvature (R1) along the longitudinal direction of the molding surface that forms the top plate portion of the curved part set to be greater than or equal to the radius of curvature (R0) along the longitudinal direction of the top plate portion of the curved part in the target part shape. A method for manufacturing a press-formed product as described in claim 1.

4. The first mold is configured such that the radius of curvature (R1) along the longitudinal direction of the molding surface that forms the top plate portion of the curved portion is greater than or equal to the radius of curvature (R0) along the longitudinal direction of the top plate portion of the curved portion in the target part shape. A method for manufacturing a press-formed product as described in claim 2.

5. The above cross-section includes a flange portion that is continuous with the lower end of the vertical wall portion, In a side view, the first mold described above has a third side view angle, which is the angle formed by the longitudinal tangent of the molding surface that forms the flange portion of the first portion at a continuous position with the molding surface that forms the flange portion of the curved portion, and the longitudinal tangent of the molding surface that forms the flange portion of the second portion at a continuous position with the molding surface that forms the flange portion of the curved portion, and is smaller than the target flange side view angle, which is the angle formed by the longitudinal tangent of the flange portion of the first portion at a continuous position with the flange portion of the curved portion, and the longitudinal tangent of the flange portion of the second portion at a continuous position with the flange portion of the curved portion, in the target part shape. The second mold described above has a fourth side view angle, which is the angle formed by the longitudinal tangent of the molding surface that forms the flange portion of the first portion at a continuous position with the molding surface that forms the flange portion of the curved portion, and the longitudinal tangent of the molding surface that forms the flange portion of the second portion at a continuous position with the molding surface that forms the flange portion of the curved portion, set to be greater than or equal to the target flange side view angle. A method for manufacturing a press-formed article as described in any one of claims 1 to 4.

6. When the first side view angle is defined as θ1 and the second side view angle as θ2, the first side view angle θ1 and the second side view angle θ2 are set to satisfy the following equation (A). A method for manufacturing a press-formed article as described in any one of claims 1 to 4. 0.83 ≦ θ1 / θ2 <1.00 ... (A)

7. When the curved portion length in the intermediate part in the first process is defined as L1, and the curved portion length in the molded part in the second process is defined as L2, the following value is obtained to satisfy equation (B): Set L1 and L2. A method for manufacturing a press-formed article as described in any one of claims 1 to 4. 1.00 < L1 / L2 <2.00...(B)

8. When the first side view angle is defined as θ1 and the second side view angle is defined as θ2, the first side view angle θ1 and the second side view angle θ2 are set to satisfy the following equation (A): A method for manufacturing a press-formed product as described in claim 5. 0.83 ≦ θ1 / θ2 <1.00 ... (A)

9. When the curved portion length of the intermediate part in the first step is defined as L1 and the curved portion length of the molded part in the second step is defined as L2, the value satisfying the following equation (B) is obtained. Set L1 and L2. A method for manufacturing a press-formed product as described in claim 5. 1.00 < L1 / L2 <2.00...(B)

10. When the curved portion length of the intermediate part in the first step is defined as L1 and the curved portion length of the molded part in the second step is defined as L2, the value satisfying the following equation (B) is obtained. Set L1 and L2. A method for manufacturing a press-formed product as described in claim 6. 1.00 < L1 / L2 <2.00...(B)

11. When the first side view angle is defined as θ1 and the second side view angle is defined as θ2, the first side view angle θ1 and the second side view angle θ2 are set to satisfy the following equation (A): When the curved portion length in the intermediate part in the first process is defined as L1, and the curved portion length in the molded part in the second process is defined as L2, the following value is obtained to satisfy equation (B): Set L1 and L2. A method for manufacturing a press-formed product as described in claim 5. 0.83 ≦ θ1 / θ2 <1.00 ... (A) 1.00 < L1 / L2 <2.00...(B)