Method for manufacturing press-molded article

Abstract

The present invention suppresses cracking from occurring in a corner part during press molding. A method for manufacturing a press-molded article according to the present invention comprises: a pre-molding step for press-molding a blank material into a pre-molded article 40; and a main molding step for molding the pre-molded article 40 into a press-molded article that is a target molded article. The manufacturing method is characterized in that when a linear section 11', which is one from among two linear sections 11', 12 of the pre-molded article 14 and is provided with an outer vertical wall section 43, is such that the end, from among both ends in an extension direction D3 of the linear section 11', closest to the other linear section 12 is defined as a proximal end P2, the end on the opposite side from the proximal end P2 is defined as a distal end P1, and an angle formed by an outer vertical wall section of the press-molded article and the outer vertical wall section 43 of the pre-molded article 40 is defined as an opening angle, press molding is carried out during the pre-molding step such that the opening angle at the proximal end P2 is larger than the opening angle at the distal end P1 and is an opening angle having a positive value.

Description

Manufacturing method for press-molded products

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

[0002] In recent years, press-formed products using high-strength metal sheets have been used for automotive parts in order to simultaneously improve automobile crashworthiness and reduce the vehicle body weight. Press-forming using high-strength metal sheets poses challenges, such as cracking due to reduced ductility of the metal sheet and wrinkles due to increased yield strength. In particular, press-formed products with concavely curved portions not only suffer from cracking in the flanges of the curved portions, but also from wrinkles in the top plate and punch shoulders of the curved portions.

[0003] Cracks in the flanges of curved sections are caused by stresses that pull the flanges in the circumferential direction during press forming. Wrinkles in the top plate and punch shoulders are caused by the reaction force of the stresses. One proposed method for preventing such cracks and wrinkles is to increase the bending radius of the punch shoulders in the curved sections from the center toward both ends of the curved sections (see Patent Document 1). Another proposed method involves providing a bead on the top plate of one of the two straight sections in a press-formed product that has a substantially L-shaped cross section, for example, two straight sections whose extension directions intersect with each other and a curved section between the two straight sections (see Patent Document 2).

[0004] JP 2021-166997 A International Publication No. 2012 / 070623

[0005] Hereinafter, in a press-formed product having a substantially L-shape, the vertical wall on the side where the curved portion is provided may be referred to as the inner vertical wall, and the vertical wall on the back side of the curved portion may be referred to as the outer vertical wall. Also, the portion of the press-formed product opposite the curved portion may be referred to as the corner portion.

[0006] Among generally L-shaped press-formed products, there are some in which one of the straight portions does not have an outer vertical wall portion, or the outer vertical wall portions provided on the two straight portions are provided independently and not continuous near the corner portions. In such press-formed products, cracks and wrinkles occur not only in the curved portions but also in the corner portions. Cracks in the corner portions occur when the portions of the straight portions corresponding to the top plate portions are pulled toward the inner vertical wall portion during press forming. The manufacturing methods disclosed in Patent Documents 1 and 2 have difficulty preventing cracks in the corner portions. Therefore, new measures to prevent cracks in the corner portions are needed.

[0007] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a new molding technology that can suppress the occurrence of cracks in corner portions when manufacturing, for example, a press-molded product having an approximately L-shape, with two straight portions whose extension directions intersect and a curved portion provided between these straight portions.

[0008] A method for manufacturing a press-molded product according to one aspect is a method for manufacturing a press-molded product having a top plate portion that is L-shaped in top view by having two straight portions extending in different directions and a curved portion provided between the two straight portions, an inner vertical wall portion that is continuous with the top plate portion at one end where the curved portion is provided, of both end portions in the width direction of the top plate portion, and an outer vertical wall portion that is provided in at least one of the two straight portions and is continuous with the top plate portion at the other end opposite the one end where the curved portion is provided, of both end portions in the width direction of the top plate portion, The method includes a first forming step of press-molding the intermediate product into a target product, and a second forming step of molding the intermediate product into a target product, wherein, of two straight portions of the intermediate product, the end closest to the other straight portion in the extension direction of the straight portion where the outer vertical wall portion is provided is defined as the proximal end, and the end opposite the proximal end is defined as the distal end, and the press-molding is performed in the first forming step so that the opening angle at the proximal end is larger than the opening angle at the distal end and has a positive value, when the angle formed by the outer vertical wall portion of the target product and the outer vertical wall portion of the intermediate product is defined as the opening angle. Here, the width direction of the top plate portion refers to the direction perpendicular to the extension direction of the straight portion.

[0009] The intermediate shape of the outer vertical wall portion preferably has an opening angle that gradually increases from the distal end to the proximal end, and the opening angle at the proximal end is preferably 2 to 20 degrees.

[0010] In addition, it is preferable that the second forming step presses the intermediate shape of the outer vertical wall portion from the outside using a cam member, thereby forming the intermediate shape of the outer vertical wall portion into the outer vertical wall portion of the target formed product.

[0011] According to the present disclosure, it is possible to suppress the occurrence of cracks in corner areas.

[0012] FIG. 1 is a schematic perspective view showing an example of a press-formed product shown in this embodiment. FIG. 2 is a schematic flowchart showing an example of a manufacturing process of a press-formed product. FIG. 3 is a schematic perspective view showing an example of a preformed product. FIG. 4(a) is an end view showing the configuration of the preformed product at a distal end P1, and FIG. 4(b) is an end view showing the configuration of the preformed product at a proximal end P2 in the extension direction D3. FIG. 5 is an end view showing an example of a mold used in the preforming step. FIG. 6 is an end view showing an example of a mold used in the main forming step. FIG. 7(a) is an end view showing an example of a force acting at a proximal end P2 when the preforming step is performed, and FIG. 7(b) is an end view showing an example of a force acting at a distal end P1 when the preforming step is performed.

[0013] The press-formed product shown in this embodiment will be described below with reference to the drawings. As shown in FIG. 1 , the press-formed product 10 is a generally L-shaped part having two straight portions 11, 12 that extend in different directions and whose ends intersect. The press-formed product 10 is manufactured by performing a pre-forming step S100 and a main forming step S200 shown in FIG. 2 . Here, the press-formed product 10 corresponds to a target formed product as claimed. The pre-forming step corresponds to a first forming step as claimed, and the main forming step corresponds to a second forming step as claimed.

[0014] The press-formed product 10 has a curved portion 13 that is concavely curved between the straight portions 11 and 12. Hereinafter, at the intersection of the straight portions 11 and 12, the portion opposite the curved portion 13 (the portion indicated by reference numeral 14 in FIG. 1 ) may be referred to as a corner portion. In addition, in the press-formed product 10, the direction perpendicular to the extension direction of the straight portions 11 and 12 is defined as the width direction of the top plate portion 21. In addition, in the width direction of the top plate portion 21, the side where the curved portion 13 is provided is defined as the inner side, and the side where the corner portion 14 is provided is defined as the outer side.

[0015] The press-formed product 10 is provided on the inside with an inner vertical wall portion 23 that continues from the top plate portion 21 via an upper bent portion 22, and an inner flange portion 25 that continues from the inner vertical wall portion 23 via a lower bent portion 24. Hereinafter, the upper bent portion 22, the inner vertical wall portion 23, the lower bent portion 24, and the inner flange portion 25 may be collectively referred to as an inner component E1.

[0016] On the outside of the straight portion 11 of the press-formed product 10, there are provided an outer vertical wall portion 28 that continues from the top plate portion 21 via an upper bent portion 27, and an outer flange portion 30 that continues from the outer vertical wall portion 28 via a lower bent portion 29. Hereinafter, the upper bent portion 27, the outer vertical wall portion 28, the lower bent portion 29, and the outer flange portion 30 may be collectively referred to as outer constituent element E2.

[0017] Furthermore, an extension portion 33 that is continuous with the top plate portion 21 and extends outward is provided on the outside of the straight portion 12 of the press-formed product 10. The extension portion 33 is located on approximately the same plane as the top plate portion 21. The extension portion 33 is provided independently of and not continuous with the outer vertical wall portion 28 that is continuous with the straight portion 11. A bead 34 is provided on the extension portion 33 along the extension direction D2 of the straight portion 12. The bead 34 is provided to prevent material from being drawn toward the curved portion 13 during press forming, which will be described later.

[0018] In this embodiment, a press-formed product 10 is illustrated that includes an inner component E1 having an inner flange portion 25, an outer component E2 having an outer flange portion 30, and an extension portion 33. However, the inner flange portion 25, the outer flange portion 30, and the extension portion 33 are not necessarily required components of the press-formed product 10. Therefore, any of these components may be omitted.

[0019] In the press-formed product 10 of this embodiment, an example is shown in which the linear portion 12 is provided with an extension portion 33 that is continuous with the top plate portion 21. However, the press-formed product may be provided with a linear portion 12 that has an outer vertical wall portion that is not continuous with the outer vertical wall portion 28 and is independent of the outer vertical wall portion 28.

[0020] As shown in Fig. 2, the above-mentioned press-formed product 10 is manufactured by a manufacturing process including, for example, a preforming step S100 and a main forming step S200. As will be described in detail later, the preforming step S100 is a step in which a metal plate processed into a predetermined shape (hereinafter referred to as a blank B) is press-formed to manufacture a preformed product 40. The main forming step S200 is a step in which the preformed product 40 is press-formed or cam-bent to manufacture the press-formed product 10 shown in Fig. 1. Here, the preformed product 40 corresponds to an intermediate product as defined in the claims.

[0021] First, the configuration of the preformed product 40 will be described with reference to Fig. 3. As shown in Fig. 3, the preformed product 40 has formed therein an inner constituent element E1 of the press-formed product 10 and an intermediate shape of an outer constituent element E2 of the press-formed product 10. Hereinafter, the intermediate shape of the outer constituent element E2 of the press-formed product 10 may be referred to as an outer constituent element E2'.

[0022] The outer structural element E2' of the preformed product 40 is configured to include an outer vertical wall portion 43 that continues from the top plate portion 41 via an upper bend portion 42, and an outer flange portion 45 that continues from the outer vertical wall portion 43 via a lower bend portion 44.

[0023] Hereinafter, the extension direction of the straight portion 11' of the preformed product 40 will be referred to as D3. Of both end portions of the straight portion 11' in the extension direction D3, the end portion that does not intersect with the straight portion 12 will be referred to as the distal end P1. Furthermore, of both end portions of the straight portion 11' in the extension direction D3, the end portion opposite the distal end P1, i.e., the end portion where the straight portion 11' and the straight portion 12 intersect, will be referred to as the proximal end P2.

[0024] In the example of the preformed product 40 shown in Fig. 3, the outer vertical wall portion 43 of the straight portion 11' at the distal end P1 is formed at the same angle as the outer vertical wall portion 28 of the straight portion 11 (see Fig. 4(a)). On the other hand, the outer vertical wall portion 43 of the straight portion 11' at the proximal end P2 opens outward from the outer vertical wall portion 28 of the straight portion 11 at a predetermined angle θ (see Fig. 4(b)).

[0025] Hereinafter, the angle θ of the outer vertical wall portion 43 of the preformed product 40 relative to the outer vertical wall portion 28 of the press-formed product 10 will be referred to as the opening angle θ. Note that the counterclockwise direction in FIG. 4 is the positive direction of the opening angle θ. The opening angle at the distal end P1 will be referred to as θ1, and the opening angle at the proximal end P2 will be referred to as θ2. In the preformed product 40, the opening angle θ1 at the distal end P1 and the opening angle θ2 at the proximal end P2 are set as follows:

[0026] The opening angle θ1 at the distal end P1 is set to, for example, θ1 = 0°. However, it is preferable that the opening angle θ1 at the distal end P1 be appropriately set taking into consideration springback in press forming, forming loads in the preforming step and the main forming step, etc. Therefore, the opening angle θ1 may be a positive value or a negative value.

[0027] Furthermore, the opening angle θ2 at the proximal end P2 is preferably set so that θ2 > θ1 relative to the opening angle θ1 at the distal end P1. However, if the opening angle θ2 at the proximal end P2 is set, for example, to θ2 < 2°, the effect of suppressing cracking during press molding may be too small. Furthermore, if the opening angle θ2 at the proximal end P2 is set too large, the amount of deformation during the main molding process increases, requiring careful consideration of the dimensional and shape accuracy of the press-molded product. The effect of suppressing cracking during press molding is sufficiently achieved when the opening angle θ2 is set to θ2 = 20°. Therefore, the opening angle θ2 at the proximal end P2 is preferably set to, for example, θ2 = 2 to 20°, and more preferably, θ2 = 5 to 15°.

[0028] In this embodiment, the opening angle θ of the outer vertical wall portion 43 of the preformed product 40 gradually increases from the distal end P1 toward the proximal end P2, and the opening angle θ2 at the proximal end P2 is maximum. However, if the opening angle θ2 at the proximal end P2 is a positive value (e.g., θ2 = 2° to 20°), the opening angle θ does not need to be maximum at the proximal end P2, and the opening angle θ may be maximum between the distal end P1 and the proximal end P2, for example.

[0029] The outer flange portion 45 is continuous with the outer vertical wall portion 43 via the lower bent portion 44. The outer flange portion 45 and the lower bent portion 44 form a certain angle. At the distal end P1, the outer flange portion 45 is parallel to, for example, the horizontal plane. At the proximal end P2, the outer flange portion 45 is inclined, for example, at an opening angle θ2 with respect to the horizontal plane.

[0030] Next, the mold used in the preforming step S100 will be described. As shown in Figures 5(a) and 5(b), the mold 50 used in the preforming step S100 is composed of, for example, a lower mold 51 and an upper mold 52. The lower mold 51 has, for example, a punch 53.

[0031] As shown in Figures 5(a) and 5(b), at the distal end P1 in the extension direction D3 (the direction perpendicular to the paper surface in Figure 5), the angle θ3 of the inclined surface 53c relative to the upper surface 53a of the punch 53 is set to the same angle as the inclination angle of the outer vertical wall portion 28 relative to the top plate portion 21 of the press-formed product 10.

[0032] At the proximal end P2 in the extension direction D3, the angle θ4 of the inclined surface 53c with respect to the upper surface 53a of the punch 53 opens outward by the above-mentioned opening angle θ2 with respect to the inclination angle of the outer vertical wall portion 28 of the press-formed product 10. In other words, the inclined surface 53c of the punch 53 is inclined so that the opening angle θ gradually increases from the distal end P1 toward the proximal end P2.

[0033] The bottom surface 53e of the punch 53 maintains a constant angle with respect to the inclined surface 53c. That is, as the opening angle θ of the inclined surface 53c increases, the inclination angle of the bottom surface 53e with respect to the horizontal plane also increases. The inclination angle of the bottom surface 53e with respect to the horizontal plane is the same angle as the opening angle θ.

[0034] The upper mold 52 includes a die 54 and a pad 55. The die 54 has an inclined surface 54c that continues via a die shoulder 54b that connects to the lower surface 54a. For example, at the distal end P1 in the extension direction D3, the inclination angle θ5 of the inclined surface 54c relative to the lower surface 54a of the die 54 is set to the same angle as the angle θ3 of the inclined surface 53c relative to the upper surface 53a of the punch 53. Furthermore, the inclined surface 54c at the proximal end P2 in the extension direction D3 is inclined at an angle θ6 relative to the inclined surface 54c at the distal end P1 in the extension direction D3. Note that the angle θ6 is the same as the opening angle θ2. In other words, the inclined surface 54c is inclined such that the opening angle θ gradually increases from the distal end P1 toward the proximal end P2.

[0035] The lower surface 54a of the die 54 maintains a constant angle with respect to the inclined surface 54c. As described above, the inclined surface 54c is inclined so that the opening angle θ gradually increases from the distal end P1 toward the proximal end P2. Therefore, the lower surface 54a is inclined from the distal end P1 toward the proximal end P2.

[0036] The pad 55 is biased toward the lower mold 51 by a biasing means (not shown). When the upper mold 52 moves toward the lower mold 51, the pad 55 comes into contact with the blank B before the die 54 of the upper mold 52 comes into contact with the blank B, thereby sandwiching the blank B between the pad 55 and the lower mold 51.

[0037] Next, the mold used in the main molding step will be described. As shown in Figure 6, the mold 60 used in the main molding step is composed of, for example, a lower mold 61 and an upper mold 62. The lower mold 61 has, for example, a punch 63 and a cam slider 64 arranged at a processing distance from the punch 63. An insertion space 65 is provided between the punch 63 and the cam slider 64, into which a cam 68, described later, is inserted.

[0038] The punch 63 has an upper surface 63a, a punch shoulder 63b connected to the upper surface 63a, an inclined surface 63c connected to the upper surface 63a via the punch shoulder 63b, a curved surface 63d connected to the lower end of the inclined surface 63c, and a bottom surface 63e connected to the curved surface 63d.

[0039] Although not shown, the inclination angle θ7 of the inclined surface 63c relative to the upper surface 63a of the punch 63 is the same as the inclination angle of the outer vertical wall portion 28 relative to the top plate portion 21 of the press-formed product 10.

[0040] The cam slider 64 has a guide surface 64 a that slopes downward toward the punch 63. A cam 68 is in sliding contact with the guide surface 64 a of the cam slider 64, and moves the cam 68 toward the punch 63.

[0041] When the lower mold 61 moves relatively toward the upper mold 62, the pad 67 abuts against the preformed product 40 positioned in the punch 63 held by the lower mold 61, and clamps the preformed product 40 between the punch 63.

[0042] When the lower mold 61 moves relatively toward the upper mold 62, the cam 68 moves along the guide surface 64a of the cam slider 64, clamping the outer component E2' of the preformed product 40 between it and the punch 63, thereby generating the outer component E2 in the press-molded product 10.

[0043] The cam 68 has an inclined surface 68 a, a curved portion 68 b, and a lower surface 68 c. Although not shown, the inclination angle θ8 of the inclined surface 68 a with respect to the lower surface 68 c of the cam 68 is the same as the inclination angle θ7 of the inclined surface 63 c with respect to the upper surface 63 a of the punch 63.

[0044] Finally, a description will be given of a method for manufacturing the press-formed product 10. In a preforming step S100, the blank B is press-formed using, for example, a die 50 shown in Fig. 5. This produces a preformed product 40 (see Fig. 3) in which the inner constituent element E1 of the press-formed product 10 and the outer constituent element E2' of the press-formed product 10 are formed.

[0045] As described above, the opening angle θ of the inclined surface 53c of the punch 53 of the mold 50 and the inclined surface 54c of the die 54 increases from the distal end P1 to the proximal end P2 in the extension direction D3. As a result, as shown in FIG. 7( a), the height H2 of the outer vertical wall portion 43 at the proximal end P2 is lower than the height H1 of the outer vertical wall portion 43 at the distal end P1. That is, when forming the outer vertical wall portion 43, the distance over which the material is pulled from the upper bent portion 42 to the lower bent portion 44 is shortened. That is, the force F1 pulling the corner region 14′ on the upper bent portion 42 is reduced, and cracking of the corner region 14′ is suppressed.

[0046] Furthermore, when the inner vertical wall portion 23 is formed, the portion 41a of the top plate portion 41 on the distal end P1 side is pulled into the inner vertical wall portion 23. As a result, material movement occurs in the portion 41a on the distal end P1 side in the direction M1 in FIG. 3 . This material movement also occurs in the portion 41b on the proximal end P2 side in the direction M2 in FIG. 3 . As the material movement in the direction M1 in FIG. 3 increases, the material movement in the direction M2 in FIG. 3 also increases. This can cause cracking in the corner region 14'. As shown in FIG. 7(b), by reducing the opening angle θ1 at the distal end P1 and increasing the force F2 pulling the material from the upper bent portion 42 to the lower bent portion 44, a force can be exerted in a direction that prevents material movement in the direction M1 in FIG. 7(b). As a result, material movement in the direction M2 in FIG. 3 is reduced, thereby suppressing cracking in the corner region 14'.

[0047] After the preforming step S100, the main forming step S200 is performed. In the main forming step S200, press forming or cam bending is performed on the preformed product 40 produced in the preforming step S100. For example, cam bending is performed using a mold 60 shown in FIG. 6. Cam bending is a process in which the upper curved portion 2 formed in the preforming step S100 is opened and bent by an angle θ. In the main forming step S200, the force pulling the upper bent portion 42 toward the lower bent portion 44 is smaller than in the preforming step S100. As a result, cracks can be prevented from occurring in the corner region 14. Note that although cam bending is used in the main forming step, similar effects can be obtained by using press forming.

[0048] When manufacturing the above-described press-formed product 10, it is preferable to use a metal plate having a thickness of 0.6 to 4.0 mm and a tensile strength of 270 to 1800 MPa as the blank material B. The reasons for this include the fact that metal plates having a tensile strength of less than 270 MPa and a thickness of less than 0.6 mm are rarely used in parts for general automobiles, home appliances, etc., that metal plates exceeding 1800 MPa generally have poor ductility and are prone to cracking, and that press forming of metal plates having a thickness of more than 4.0 mm tends to increase the press load and easily damage the mold.

[0049] Finally, the thickness reduction rate was measured in the pre-forming process and the main forming process when a press-formed product was manufactured using a 1180 MPa-class steel sheet. An example of the measurement results of the thickness reduction rate is shown in Table 1 below. In measuring the thickness reduction rate, a steel material with a thickness of 1.2 mm, a yield stress of 820 MPa, a tensile strength of 1230 MPa, and an elongation rate of 10% was used as blank material B.

[0050]

[0051] First, Comparative Example 1 was a case in which press forming was performed in the main forming step with the opening angle θ between the distal end P1 and the proximal end P2 in the preforming step set to θ = 0°. Comparative Example 2 was a case in which press forming was performed in the main forming step with the opening angle θ between the distal end P1 and the proximal end P2 in the preforming step set to θ = 15°. Comparative Example 3 was a case in which cam bending was performed in the main forming step with the opening angle θ between the distal end P1 and the proximal end P2 in the preforming step set to θ = 0°.

[0052] In addition, cases where press forming was performed in the main forming process with the opening angle θ of the proximal end in the preforming process set to θ = 2, 5, 15, or 20° are designated as invention examples 1 to 4. Furthermore, cases where cam bending forming was performed in the main forming process with the opening angle θ of the proximal end in the preforming process set to θ = 2, 5, 10, 15, or 20° are designated as invention examples 5 to 9.

[0053] In this case, in Comparative Example 1, the thickness reduction rate was 11.2% in the curved region 13 and 10.7% in the corner region. In Comparative Example 2, the thickness reduction rate in the corner region when the preforming process was performed was 11.6%, and the thickness reduction rate in the corner region when the main forming process was performed was 12.2%. Furthermore, in Comparative Example 3, the thickness reduction rate in the corner region when the main forming process was performed was 11.2%. However, when the thickness reduction rate is 10% or more, cracks are likely to occur. In other words, the results obtained in each of Comparative Examples 1 to 3 showed that cracks are likely to occur.

[0054] On the other hand, in Examples 1 to 9, even when the preforming step and the main forming step were performed, the sheet thickness reduction rate was 10% or less. Therefore, it can be seen that Examples 1 to 9 can suppress the occurrence of cracks more effectively than Comparative Examples 1 to 3.

[0055] In this embodiment, the preforming step is performed to form the inner constituent elements of the preformed product into the same shape as the inner constituent elements of the press-formed product. However, in the preforming step, press forming may be performed multiple times to form the inner constituent elements of the preformed product 40 into the same shape as the inner constituent element E1 of the press-formed product 10.

[0056] Furthermore, although no specific explanation has been given regarding the radius of the upper bend 22 of the curved portion 13 in each of the preformed product 40 and the press-formed product 10, the radius may be the same diameter at the center in the curved direction Cd of the curved portion 13 and at both ends in the curved direction Cd, or may increase from the center to both ends in the curved direction Cd of the curved portion 13.

[0057] For example, if the radius of the upper bent portion 22 is increased from the center to both ends in the curvature direction Cd of the curved portion 13, material moves from both ends of the upper bent portion 22 in the ridge direction toward the center of the curved portion 13 during press forming, and at the inner flange portion 25, material is drawn toward the midpoint (center portion) of the curved portion 13. Furthermore, as described above, by forming the curved portion 13 with material moved from both ends of the upper bent portion 22, material located adjacent to the top plate portion 21 at the center of the upper bent portion 22 in the curved portion 13 does not need to be moved from the upper bent portion 22 when the curved portion 13 is formed. Therefore, if the radius of the upper bent portion 22 is increased from the center to both ends in the curvature direction Cd of the curved portion 13, it is possible to effectively prevent cracks from occurring in the inner flange portion 25 of the curved portion 13 and wrinkles from occurring in the top plate portion 21 and upper bent portion 22 of the curved portion 13.

[0058] <Summary of Effects> The method for manufacturing a press-formed product of the present invention is a method for manufacturing a press-formed product 10 having a top plate portion 21 that is L-shaped in top view by having two straight portions 11, 12 extending in different directions and a curved portion 13 provided between the two straight portions 11, 12, an inner vertical wall portion 23 that is continuous with the top plate portion 21 at one end portion where the curved portion 13 is provided, of both end portions in the width direction of the top plate portion 21, and an outer vertical wall portion 28 that is provided in at least one straight portion of the two straight portions 11, 12 and that is continuous with the top plate portion 21 at the other end portion opposite the one end portion where the curved portion 13 is provided, of both end portions in the width direction of the top plate portion 21, the method comprising the steps of: a preforming step of press-forming a blank B to generate a preformed product 40; and a main forming process for forming the preformed product into a formed product. Of the two straight portions 11′, 12 in the preformed product 40, of both ends in the extension direction of the straight portion 11′ where the outer vertical wall portion 43 is provided, the end closest to the other straight portion is defined as the proximal end P2, and the end opposite the proximal end P2 is defined as the distal end P1. When the angle formed by the outer vertical wall portion 28 in the press-formed product 10, which is the target formed product, and the outer vertical wall portion 43 in the preformed product 40 is defined as the opening angle, the preformed product 40 is characterized by generating an outer vertical wall portion 43 in the preformed product 40 that is an intermediate shape of the outer vertical wall portion 28, which is inclined outward with respect to the outer vertical wall portion 28 of the press-formed product 10, which is the target formed product, and whose opening angle θ with respect to the outer vertical wall portion 28 of the press-formed product 10, which is the target formed product, increases from the distal end P1 to the proximal end P2.

[0059] In the preforming step S100, the force F1 pulling the corner region 14' and the material movement M2 are reduced, so that stress concentration in the corner region 14' is suppressed, and the occurrence of cracks in the corner region 14' is suppressed.

[0060] In addition, this forming process involves using a cam 68 to press the outer vertical wall portion 43 of the preformed product 40 from the outside, thereby forming the outer vertical wall portion 43 of the preformed product 40 into the outer vertical wall portion 28 of the press-formed product 10, which is the target formed product.

[0061] Since the main forming process S200 is a process of bending the upper bent portion 42 formed in the pre-forming process S100 by an opening angle θ, it does not promote stress concentration in the corner portion 14, and therefore cracks are prevented from occurring in the corner portion 14 even in the main forming process.

[0062] 10 Press-formed product 11, 11', 12 Straight portion 13 Curved portion 21 Top plate portion 23 Inner vertical wall portion 28 Outer vertical wall portion 40 Preformed product 43 Outer vertical wall portion 68 Cam P1 Distal end P2 Proximal end θ Opening angle θ1 Opening angle on the distal end side θ2 Opening angle on the proximal end side B Blank material

Claims

1. A method for manufacturing a press-formed product having a top plate portion having two straight portions extending in different directions and a curved portion provided between the two straight portions, thereby forming an L-shape in top view; an inner vertical wall portion that is continuous with the top plate portion at one end where the curved portion is provided, of both end portions in the width direction of the top plate portion; and an outer vertical wall portion that is provided in at least one of the two straight portions and that is continuous with the top plate portion at the other end opposite the one end where the curved portion is provided, of both end portions in the width direction of the top plate portion, the method comprising: a first forming step of press-forming a blank material into an intermediate formed product; and a second forming step of forming the intermediate formed product into a target formed product, wherein of both end portions in the extension direction of the straight portion where the outer vertical wall portion is provided, the end closest to the other straight portion is defined as a proximal end, and the end opposite the proximal end is defined as a distal end, A method for manufacturing a press-molded product, characterized in that, when the angle formed by the outer vertical wall portion of the target molded product and the outer vertical wall portion of the intermediate molded product is defined as an opening angle, in the first molding process, press molding is performed so that the opening angle at the proximal end is larger than the opening angle at the distal end and is an opening angle with a positive value.

2. A method for manufacturing a press-formed product as described in claim 1, characterized in that the intermediate shape of the outer vertical wall portion is a shape in which the opening angle gradually increases as it approaches the proximal end from the distal end.

3. A method for manufacturing a press-formed product according to claim 1 or claim 2, characterized in that the opening angle is 2 to 20 degrees at the proximal end.

4. A method for manufacturing a press-formed product as described in claim 1 or claim 2, characterized in that the second forming process uses a cam material to press the intermediate shape of the outer vertical wall portion from the outside, thereby forming the intermediate shape of the outer vertical wall portion into the outer vertical wall portion of the target formed product.

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