Press-molded product manufacturing method

Abstract

The object of the present invention is to provide a method for manufacturing a press-molded product, which can perform appropriate press molding while reducing the bending radius. [Solution] The manufacturing method of the press-molded product P includes an intermediate product preparation process (step S10) for preparing an intermediate product P1, a loading process (step S20) for loading the intermediate product P1 on a second lower mold 21, the second shoulder portion 21c of which is formed with a radius of curvature RC2 smaller than the bending radius RB1 of the first bending portion 80, a clamping process (step S30) for lowering an upper mold 22 including an upper mold shoulder portion 22c relative to the second lower mold 21 to clamp the side plate 82 of the intermediate product P1 between the side surface 21b and the upper mold recess side surface 22b and to restrain the bottom plate 81 in a direction along the bottom plate 81, and a press molding process (step S40) for lowering the upper mold 22 to press-mold the intermediate product P1.

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a press-molded product, a press-molded product, and a press molding die. [Background technology]

[0002] Conventionally, press molding methods and press molding dies for press-molded products including a bent portion having a cross section in a hat shape, etc. For example, Patent Document 1 discloses a press molding method for bending a metal plate with a plate thickness t to form a bent portion by moving a bending blade while contacting the metal plate at the shoulder of a punch, and a press-molded product manufacturing method, a press-molded product, and a press molding die, in which the bending blade moves so that the minimum distance L between the punch and the bending blade satisfies 1.0≦L / t≦1.2 when the bending blade passes through the center position of the bent portion. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-206836 A Summary of the Invention [Problem to be solved by the invention]

[0004] The press molding die described in Patent Document 1 requires many components, such as a slide mechanism for moving the bending blade in the horizontal direction and a spring for biasing the bending blade. Meanwhile, in recent years, press molding using high-tensile steel plates with a tensile strength of 590 MPa or more is required. And even in such high-tensile steel plates, it is required to reduce the bending radius. However, when the bending radius of a high-tensile steel plate is reduced, high tensile stress is generated on the outside of the bent portion, which causes cracks in the outer part of the bent portion, and there are cases where press molding cannot be performed properly.

[0005] An object of the present invention is to provide a method for manufacturing a press-molded product, a press-molded product, and a press-molding die that enable appropriate press molding while reducing the bending radius. [Means for solving the problem]

[0006] The press-molded product manufacturing method of the present invention includes an intermediate product preparation process for preparing an intermediate product including a first plate portion, a second plate portion, and a bending portion connecting the first plate portion and the second plate portion; a loading process for loading the intermediate product on a lower mold having an upper surface and a side surface, and a shoulder portion where the upper surface and the side surface are connected is formed with a radius of curvature smaller than the bending radius of the bending portion of the intermediate product so that the second plate portion is positioned on the side surface side; a clamping process for lowering an upper mold including an upper mold recess having an upper mold deep bottom surface corresponding to the upper surface of the lower mold, an upper mold recess side surface corresponding to the side surface of the lower mold, and an upper mold shoulder connecting the upper mold recess bottom surface and the upper mold recess side surface and arranged to correspond to the shoulder, to clamp the second plate portion of the intermediate product between the side surface of the lower mold and the upper mold recess side surface of the upper mold to restrict movement of the second plate portion and to restrain the first plate portion in a direction along the first plate portion; and a press molding process for lowering the upper mold to press-mold the intermediate product.

[0007] The press-molded product of the present invention is a press-molded product manufactured by the above-mentioned press-molded product manufacturing method, and is made of a high-tensile steel plate having a plate thickness t, and the ratio (R / t) of the bending radius R of the bent portion to the plate thickness t after the press molding process is greater than 0 and less than or equal to 1.

[0008] The press molding die of the present invention comprises: a lower die including an upper surface and a side surface connected by a shoulder portion, the shoulder portion being formed with a radius of curvature smaller than the bending radius of the bending portion in an intermediate product including a first plate portion, a second plate portion, and a bending portion connecting the first plate portion and the second plate portion; and an upper die including an upper die recess corresponding to the lower die, the upper die recess having an upper die recess bottom surface corresponding to the top surface of the lower die, an upper die recess side surface corresponding to the side surface of the lower die, and an upper die shoulder connecting the upper die recess bottom surface and the upper die recess side surface to correspond to the shoulder of the lower die, and includes a restraint structure that restrains the first plate portion in a direction along the first plate portion, and the side surface of the lower die and the upper die recess side surface of the upper die each include a plane provided at a distance sufficient to allow the second plate portion of the intermediate product to be sandwiched. Effect of the Invention

[0009] According to the present invention, it is possible to provide a method for manufacturing a press-molded product, a press-molded product, and a press-molding die that can perform appropriate press molding while reducing the bending radius. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic front view of a first die used in an intermediate product preparing step according to the first embodiment. [Diagram 2] FIG. 2 is a schematic front view of the second mold according to the first embodiment. [Diagram 3] FIG. 3 is a flow diagram showing steps of the method for manufacturing a press-formed product according to the embodiment. [Figure 4] FIG. 4 is a schematic front view of a first die performing press molding in the intermediate product preparation step according to the first embodiment. [Diagram 5] FIG. 5 is a schematic front view of the second mold in the placing step according to the first embodiment. [Figure 6] FIG. 6 is a schematic front view of the second mold in the clamping step according to the first embodiment. [Figure 7] FIG. 7 is a schematic front view of a second die in a press molding step according to the first embodiment. [Figure 8] FIG. 8 is a schematic front view of the second die showing a state after the press molding step according to the first embodiment is completed. [Figure 9] FIG. 9 is a schematic front view of the second mold in the placing step according to the second embodiment. [Figure 10] FIG. 10 is a schematic front view of the second mold in the clamping step according to the second embodiment. [Figure 11] FIG. 11 is a schematic front view of the second die in the press molding step according to the second embodiment. [Figure 12] FIG. 12 is a schematic front view of the second die showing a state after the press molding step according to the second embodiment is completed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to this embodiment. In addition, the components in the following embodiments include those that are replaceable and easy for a person skilled in the art, or those that are substantially the same.

[0012] [First embodiment] The press-molded product manufacturing method in this embodiment is for manufacturing a press-molded product P formed in a long shape having, for example, a substantially U-shaped cross section. The press-molded product manufacturing method in this embodiment uses a first die 10 shown in Fig. 1 and a second die 20 shown in Fig. 2.

[0013] In the following description, the upper side in Figures 1 and 2 is referred to as "up" and the lower side as "down," and the left side as viewed in the figures is referred to as "left" and the right side as viewed in the figures is referred to as "right." In addition, since the first mold 10 and the second mold 20 are bilaterally symmetrical, only the right half is shown in Figures 4 to 12.

[0014] The first die 10 shown in Fig. 1 is a die used in an intermediate product preparation step (step S10, see Fig. 3) in the press-molded product manufacturing method. The first die 10 has a first lower die 11, an upper pad 12, and two upper bending blades 13 provided on the left and right sides. The first lower die 11, the upper pad 12, and the upper bending blade 13 are formed in an elongated shape in a direction perpendicular to the paper surface. The first die 10 can be used, for example, by attaching it to a press machine (not shown), fixing the first lower die 11 to a bolster of the press machine, and attaching the upper pad 12 and the upper bending blade 13 to a slide of the press machine.

[0015] The first lower die 11 has an upper surface 11a and side surfaces 11b provided on the left and right sides. The upper surface 11a is formed on a plane along a horizontal plane (a plane including two directions (left-right direction and direction perpendicular to the paper surface) perpendicular to the up-down direction). The side surfaces 11b are formed on a plane perpendicular to the upper surface 11a, with a normal line directed in the left-right direction. The ridge portions connecting the upper surface 11a and the left and right side surfaces 11b are each formed as a first shoulder portion 11c. In this embodiment, the first shoulder portion 11c is formed with a curvature radius RC1 = 6 mm, for example.

[0016] The upper pad 12 has a width X2 in the left-right direction that is substantially the same as the width X1 of the first lower die 11 in the left-right direction (X2=X1). The upper side of the upper pad 12 is supported by an elastic member (not shown) such as a spring. The lower surface 12a of the upper pad 12 is formed as a flat surface along a horizontal plane. The lower surface 12a of the upper pad 12 and the upper surface 11a of the first lower die 11 face each other in the vertical direction and are flat surfaces parallel to each other. The upper bending blades 13 are disposed on the left and right sides of the upper pad 12 with a gap S1 between them. The upper bending blade 13 has a corner on the inside (upper pad 12 side) of the lower end that is rounded. The upper bending blade 13 is provided so that the gap S1 between the upper bending blade 13 and at least the side surface 11b of the first lower die 11 is substantially the same as the plate thickness t of the blank material B (S1=t).

[0017] The second mold 20 shown in FIG. 2 is a mold (press forming mold) used in the placing step (step S20), the clamping step (step S30), and the press forming step (step S40) in the press formed product manufacturing method. The second mold 20 has a second lower mold 21 (lower mold) and an upper mold 22. The second lower mold 21 and the upper mold 22 are also formed in a long shape in a direction perpendicular to the paper surface, similar to the first mold 10. Further, the second mold 20 can be used by fixing the second lower mold 21 to a bolster of a press machine (not shown) and attaching the upper mold 22 to the slide of the press machine.

[0018] The second lower mold 21 has an upper surface 21a and side surfaces 21b provided on the left and right respectively. The upper surface 21a is formed in a plane along a horizontal plane. The side surface 21b is formed in a plane orthogonal to the upper surface 21a and having a normal line directed in the left - right direction. The width (distance X3) of the second lower mold 21 in the left - right direction is made substantially the same as the width X1 of the first lower mold 11 in the left - right direction (X3 = X1). The ridge line portions connecting the upper surface 21a and the left and right side surfaces 21b are respectively the second shoulders 21c (shoulders). The second shoulder 21c is formed with a curvature radius RC2 smaller than the bending radius RB1 of the first bending portion 80 of the intermediate product P1 to be described later (0 < RC2 < RB1). In the present embodiment, for example, the first bending portion 80 of the intermediate product P1 has a bending radius RB1 = 6 mm, and the curvature radius RC2 of the second shoulder 21c is 0.5 mm.

[0019] The upper mold 22 includes a concave upper mold recess 220 corresponding to the second lower mold 21. The upper mold recess 220 includes an upper mold recess bottom surface 22a corresponding to the upper surface 21a of the second lower mold 21, upper mold recess side surfaces 22b corresponding to the left and right side surfaces 21b of the second lower mold 21 respectively, and upper mold shoulders 22c provided so as to connect the upper mold recess bottom surface 22a and the upper mold recess side surfaces 22b on the left and right respectively and corresponding to the second shoulders 21c of the second lower mold 21. Further, the upper mold recess 220 includes lower corner portions 22d of the left and right upper mold recess side surfaces 22b which are chamfered in an R shape. Here, the upper mold recess bottom surface 22a includes a plane formed along a horizontal plane.

[0020] The upper mold recess side surface 22b includes a plane 22b1 perpendicular to the upper mold recess bottom surface 22a and with a normal line facing in the left-right direction. The upper mold recess side surface 22b is provided opposite to the left-right direction. Here, the side surface 21b of the second lower mold 21 includes a plane 21b1. The side surface 21b of the second lower mold 21 and the upper mold recess side surface 22b of the upper mold 22 include substantially parallel planes 21b1, 22b1 facing each other. Note that the upper mold recess bottom surface 22a of the upper mold recess 220 in the upper mold 22 and the upper surface 21a of the second lower mold 21 are parallel to each other. In addition, the planes 21b1, 22b1 on the side surface 21b of the second lower mold 21 and the upper mold recess side surface 22b of the upper mold 22 may be angled slightly in order to adjust the press-molded product.

[0021] A distance X4 between the left and right upper mold recess side surfaces 22b is longer than the left-right width of the second lower mold 21 (in other words, the distance X3 between the side surfaces 21b) by twice the plate thickness t of a side plate 82 of an intermediate product P1 (that is, the plate thickness t of a blank material B) described later. In other words, a distance S2 between the side surfaces 21b and the upper mold recess side surfaces 22b is approximately the same as the plate thickness t (S2=t).

[0022] Furthermore, the radius of curvature RC3 of the upper die shoulder 22c can be set to, for example, a value obtained by adding the radius of curvature RC2 of the second shoulder 21c to the thickness t of the blank material B. In this embodiment, since the radius of curvature RC2 of the second shoulder 21c=0.5 mm and the thickness t of the blank material B (intermediate product P1)=2 mm, the radius of curvature RC3 can be set to 2.5 mm.

[0023] As shown in Fig. 3, the press-molded product manufacturing method in this embodiment includes an intermediate product preparation step (step S10) for obtaining an intermediate product P1, a placement step (step S20) for setting the intermediate product P1 in the second die 20, a clamping step (step S30) for clamping the side plate 82 of the intermediate product P1, and a press molding step (step S40) for obtaining a press-molded product P as a product. The placement step (step S20) includes a locking step for locking a connection portion 83 (described later) of the intermediate product P1 to the second shoulder portion 21c. Here, the blank material B (see Fig. 1) is a plate material made of a high-tensile steel plate having a tensile strength of 590 MPa or more, and in this embodiment, the plate thickness t is 2 mm. Each step will be described below with reference to Figs. 3 to 8.

[0024] Intermediate product preparation process (step S10): The intermediate product P1 can be obtained by press-molding the blank material B with the first die 10. In the press-molding of the intermediate product P1, the upper pad 12 and the upper bending blade 13 are lowered onto the blank material B (see FIG. 1) placed on the upper surface 11a of the first lower die 11. Then, as shown in FIG. 4, the blank material B is bent at both left and right ends by the upper bending blade 13 while the central portion in the left-right direction is clamped between the lower surface 12a of the upper pad 12 and the upper surface 11a of the first lower die 11. The blank material B is bent from the first shoulder portion 11c along the side surface 11b of the first lower die 11. In this way, the intermediate product P1 having a substantially U-shaped cross section perpendicular to the longitudinal direction can be obtained by press-molding using the first die 10.

[0025] Intermediate product P1 prepared in the intermediate product preparation step (step S10) has a bottom plate 81 (first plate portion), side plates 82 (second plate portions) rising from both ends of the bottom plate 81, and a first bent portion 80 (bent portion) connecting the bottom plate 81 and the side plates 82. The bottom plate 81 and the side plates 82 are disposed perpendicular to each other. In this embodiment, for example, the first bent portion 80 formed along the first shoulder portion 11c having a curvature radius RC1 = 6 mm has a bending radius RB1 = 6 mm.

[0026] Placement step (step S20): The intermediate product P1 is set in the second lower die 21 of the second die 20 as shown in FIG. 5. The intermediate product P1 is placed on the second lower die 21 so that the bottom plate 81 is disposed on the upper surface 21a side of the second lower die 21 and the side plate 82 is disposed on the side surface 21b side. At this time, since the curvature radius RC2 of the second shoulder 21c is sufficiently smaller than the bending radius RB1 of the first bent portion 80, the connection portion 83 between the first bent portion 80 and the side plate 82 is engaged with the second shoulder 21c. In other words, the curvature radius RC2 of the second shoulder 21c is set smaller than the bending radius RB1 sufficiently to the extent that the first bent portion 80 (connection portion 83) of the intermediate product P1 is engaged. Thus, the placement step (step S20) includes an engagement step in which the first bent portion 80 (connection portion 83) of the intermediate product P1 is engaged with the second shoulder 21c. The locking process allows the bottom plate 81 to be easily restrained in a direction along the bottom plate 81 in a subsequent process without using a complicated restraining structure. Meanwhile, the inner surfaces of the side plates 82 opposing each other in the left-right direction of the intermediate product P1 abut against the side surfaces 21b of the second lower die 21. Therefore, when the intermediate product P1 is placed on the second lower die 21, the movement of the intermediate product P1, particularly the bottom plate 81, in the normal direction of the side surfaces 21b (movement in the left-right direction in FIG. 5) is restricted. The intermediate product P1 is placed with the bottom plate 81 and the upper surface 21a of the second lower die 21 spaced apart from each other.

[0027] Clamping step (step S30): After the placing step (step S20), when the upper die 22 is lowered, the side plate 82 of the intermediate product P1 is sandwiched between the side surface 21b of the second lower die 21 and the upper die recess side surface 22b of the upper die 22, as shown in FIG. 6. More specifically, the side plate 82 is sandwiched between the flat surface 21b1 of the side surface 21b and the flat surface 22b1 of the upper die recess side surface 22b. That is, the flat surface 21b1 of the side surface 21b and the flat surface 22b1 of the upper die recess side surface 22b are provided at a distance S2 in the left-right direction so that the side plate 82 can be sandwiched. The side plate 82 of the intermediate product P1 is sandwiched between the flat surfaces 21b1, 22b1 of the side surface 21b of the second lower die 21 and the upper die recess side surface 22b of the upper die 22, thereby restricting the vertical movement of the side plate 82. Furthermore, since the side plate 82 is sandwiched between the side surface 21b and the upper die recess side surface 22b, the relative movement of the side plate 82 with respect to the side surface 21b of the second lower die 21 in the vertical direction is restricted.

[0028] The bottom plate 81 is constrained in a direction along the bottom plate 81 by sandwiching the side plates 82 on both the left and right sides of the bottom plate 81 between the side surfaces 21b and the upper mold recess side surfaces 22b. That is, the first bent portion 80 is constrained in the left-right direction along the bottom plate 81 and the up-down direction along the side plates 82. Here, in the second mold 20, the two side surfaces 21b facing each other in the left-right direction and the two upper mold recess side surfaces 22b provided corresponding to each side surface 21b form a constraining structure Y that constrains the bottom plate 81 in a direction along the bottom plate 81. The timing at which the upper mold recess bottom surface 22a of the upper mold recess 220 abuts against the bottom plate 81 of the intermediate product P1 is set to be simultaneous with the sandwiching of the side plates 82 between the side surfaces 21b and the upper mold recess side surfaces 22b, or slightly later than that.

[0029] Press forming process (step S40): After the clamping process (step S30), when the upper die 22 is further lowered, the bottom plate 81 has a central portion in the left-right direction recessed toward the upper surface 21a of the second lower die 21, as shown in FIG. 7. The bottom plate 81 is restrained in a direction along the bottom plate 81, so that almost no plastic deformation occurs, and the side plate 82 is sandwiched between the side surface 21b and the upper die recess side surface 22b, so that the movement is restricted. Therefore, in this process, the first bent portion 80 is mainly plastically deformed. The first bent portion 80 is subjected to compressive stress on both the inside and outside of the first bent portion 80 due to the reaction force from the bottom plate 81 and the reaction force from the side plate 82. Here, the restraining structure Y is a structure that restrains the bottom plate 81 so that the bottom plate 81 can apply a reaction force to the first bent portion 80. In other words, the restraint of the bottom plate 81 is a restraint that allows the bottom plate 81 to apply a reaction force to the first bent portion 80. Similarly, restricting the movement of the side plate 82 means restricting the movement so that the side plate 82 can apply a reaction force to the first bent portion 80.

[0030] Then, when the upper mold 22 further descends, the plane 22b1 of the side surface of the upper mold recess 22b is in sliding contact with the outer surface 82a of the side plate 82 of the intermediate product P1 while restricting the movement of the side plate 82 together with the plane 21b1 of the side surface 21b. When the upper mold 22 descends to the bottom dead center, as shown in FIG. 8, the intermediate product P1 is press-formed following the second lower mold 21 and the upper mold recess 220 of the upper mold 22. In this way, the press-forming process (step S40) is completed, and the press-formed product P is formed. After the completion of the press-forming, the upper mold 22 and the second lower mold 21 are opened, and the press-formed product P can be taken out from the second mold 20. Here, the press-formed product P includes a second bending portion 85 (bending portion) that connects the bottom plate 81 and the side plate 82. The second bending portion 85 is formed after the first bending portion 80 is formed through the press-forming process (step S40).

[0031] The second bending portion 85 after the press-forming process (step S40) is formed following the second shoulder portion 21c and the upper mold shoulder portion 22c. For example, in the forming of the intermediate product P1 in the above example where the plate thickness t = 2 mm and the radius of curvature RC2 of the second shoulder portion 21c = 0.5 mm, the bending radius R of the second bending portion 85 can be set to about R = 1 mm to 1.5 mm. Therefore, the ratio (R / t) of the bending radius R to the plate thickness t of the second bending portion 85 of the press-formed product P can be set to 1 or less (0 < R / t ≤ 1). Note that since the bending radius R is considered to be at least the same as the radius of curvature RC2 of the second shoulder portion 21c, which is R = 0.5 mm, the ratio (R / t) of the bending radius R to the plate thickness t is greater than 0 and at least 0.25 or more (0.25 < R / t ≤ 1).

[0032] When press-forming a press-formed product having a bent portion with 0 < R / t ≤ 1 using a high-tensile steel sheet with a mold having a configuration such as the first mold 10, for example, compressive stress is applied to the inside of the bent portion, and a strong tensile stress is applied to the outside of the bent portion. Therefore, cracks may occur on the outside of the bent portion. On the other hand, in the press-forming method according to the present invention, in the press-forming of the step of forming the bent portion, the bottom plate 81 is restrained in the direction along the bottom plate 81, and the movement of the side plate 82 along the side plate 82 is restricted. Therefore, the first bent portion 80 of the intermediate product P1 plastically flows between the upper die concave portion bottom surface 22a and the upper die shoulder portion 22c of the upper die concave portion 220 and the second lower die 21 while compressive stress is applied to both the inside and the outside, and is press-formed. Since the second bent portion 85 is formed while compressive stress is applied to both the outside and the inside, almost no tensile stress that is likely to cause cracks is applied. Therefore, by using the press-forming product manufacturing method according to the present embodiment and the second mold 20 as a press-forming mold, the bending process with 0 < R / t ≤ 1 using a high-tensile steel sheet can be performed well.

[0033] [Second Embodiment] Based on FIGS. 9 to 12, a second embodiment of the present invention will be described. Note that the same reference numerals are given to members and parts equivalent to those described in the first embodiment above, and the description thereof will be omitted or simplified.

[0034] In the second embodiment, instead of the second lower die 21 of the second mold 20 in the first embodiment, a second lower die 21E having a lower pad 300 is provided. In addition to the configuration of the second lower die 21 described above, the second lower die 21E is provided with a lower pad 300 that faces the upper die recess bottom surface 22a in the vertical direction. The lower pad 300 is accommodated inside a lower die body 301 having a second shoulder portion 21c. The lower pad 300 is supported by a plurality of springs 302 provided inside the lower die body 301 so as to be movable in the vertical direction. A step portion 303 is provided inside the lower die body 301. When no load is applied, the lower pad 300 protrudes from the upper surface 301f of the lower die body 301 with a lower surface 300d of the lower pad 300 and the step portion 303 separated from each other. When the lower pad 300 descends against the elastic force of the spring 302 and the lower surface 300d comes into contact with the step portion 303, the upper surface 300f of the lower pad 300 becomes flush with the upper surface 301f of the lower die body 301 (see FIG. 12). In other words, the upper surface 21a of the second lower die 21 includes the upper surface 300f of the lower pad 300 at the lowest position and the upper surface 301f of the lower die body 301.

[0035] 9 shows a state in which the intermediate product P1 obtained in the intermediate product preparation step (step S10) is placed on the second lower die 21E of the second die 20 in the placement step (step S20). At this time, the first bent portion 80 (connection portion 83) of the intermediate product P1 is engaged with the second shoulder portion 21c. In addition, the upper surface 300f of the lower pad 300 is in contact with the bottom plate 81.

[0036] 10 shows a state in which the upper die 22 is lowered and the side plate 82 of the intermediate product P1 is sandwiched between the side surface 21b (flat surface 21b1) of the second lower die 21E and the upper die recess side surface 22b (flat surface 22b1) of the upper die 22 in the clamping step (step S30), thereby restricting the vertical movement of the side plate 82. At this time, the bottom plate 81 is sandwiched between the upper surface 300f of the lower pad 300 and the upper die recess bottom surface 22a. The bottom plate 81 is restrained in a direction along the bottom plate 81 by the side plates 82 on both the left and right sides being sandwiched between the side surface 21b and the upper die recess side surface 22b, and furthermore, the bottom plate 81 is restrained in a direction along the bottom plate 81 by the bottom plate 81 being sandwiched between the upper surface 300f of the lower pad 300 and the upper die recess bottom surface 22a of the upper die recess 220. The plastic deformation of the bottom plate 81 is reduced by being sandwiched between the lower pad 300 and the upper mold recess bottom surface 22a. That is, in the second mold 20 including the second lower mold 21E, the two side surfaces 21b facing each other in the left-right direction, the two upper mold recess side surfaces 22b provided corresponding to the respective side surfaces 21b, and the upper surface 300f of the lower pad 300 and the upper mold recess bottom surface 22a of the upper mold recess 220 form a restraining structure Y that restrains the bottom plate 81 in a direction along the bottom plate 81.

[0037] Fig. 11 shows a state in which the upper die 22 has been further lowered from the state shown in Fig. 10 in the press forming process (step S40). The first bent portion 80 of the intermediate product P1 is subjected to compressive stress on both the inside and outside due to reaction forces from the bottom plate 81 and the side plate 82 during plastic deformation. The bottom plate 81 remains sandwiched between the upper surface 300f of the lower pad 300 and the bottom surface 22a of the upper die recess. Fig. 12 shows a state in which the press forming is completed.

[0038] In this way, according to the second mold 20 equipped with the second lower mold 21E, in the press molding process (step S40), the central portion of the bottom plate 81 is not deformed so as to be concave, for example as shown in Figure 7 in the second mold 20 of the first embodiment, so that the stability of the press molding process (step S40) can be improved and the flatness of the bottom plate 81 in the press-molded product P can be increased.

[0039] The manufacturing method of the press-molded product P described above includes an intermediate product preparation step (step S10) of preparing an intermediate product P1 including a bottom plate 81 as a first plate portion, a side plate 82 as a second plate portion, and a first bent portion 80 which is a bent portion connecting the bottom plate 81 and the side plate 82, a placement step (step S20) of placing the intermediate product P1 on a second lower mold 21, 21E which is a lower mold having an upper surface 21a and a side surface 21b and a second shoulder portion 21c which is a shoulder portion where the upper surface 21a and the side surface 21b are connected, the second shoulder portion 21c being formed with a curvature radius RC2 which is smaller than the bending radius RB1 of the first bent portion 80 of the intermediate product P1, and a recessed portion of the upper mold corresponding to the upper surface 21a of the second lower mold 21, 21E. The method includes a clamping process (step S30) in which an upper mold 22 including an upper mold recess 220 having a bottom surface 22a, an upper mold recess side surface 22b corresponding to the side surface 21b of the second lower mold 21, 21E, and an upper mold shoulder 22c connecting the upper mold recess bottom surface 22a and the upper mold recess side surface 22b and arranged to correspond to the second shoulder 21c is lowered to clamp a side plate 82 of the intermediate product P1 between the side surface 21b of the second lower mold 21, 21E and the upper mold recess side surface 22b of the upper mold 22 to restrict movement of the side plate 82 and restrain the bottom plate 81 in a direction along the bottom plate 81, and a press molding process (step S40) in which the upper mold 22 is lowered to press mold the intermediate product P1.

[0040] The second die 20 as a press molding die includes an upper surface 21a and a side surface 21b connected by a second shoulder portion 21c which is a shoulder portion, and the second shoulder portion 21c includes a second lower die 21, 21E formed with a curvature radius RC2 smaller than a bending radius RB1 of a first bent portion 80 in an intermediate product P1 including a bottom plate 81 as a first plate portion, a side plate 82 as a second plate portion, and a first bent portion 80 as a bent portion connecting the bottom plate 81 and the side plate 82, and an upper die recess 220 corresponding to the second lower die 21, 21E, and the upper die recess 220 corresponds to the upper surface 21a of the second lower die 21, 21E. The upper mold 22 has an upper mold recess bottom surface 22a, an upper mold recess side surface 22b corresponding to the side surface 21b of the second lower mold 21, 21E, and an upper mold shoulder 22c connecting the upper mold recess bottom surface 22a and the upper mold recess side surface 22b and arranged to correspond to the second shoulder 21c of the second lower mold 21, 21E, and includes a restraining structure Y that restrains the bottom plate 81 in a direction along the bottom plate 81, and the side surface 21b of the second lower mold 21, 21E and the upper mold recess side surface 22b of the upper mold 22 include planes 21b1, 22b1 that are spaced apart to an extent (e.g., distance S2) that allows the side panel 82 of the intermediate product P1 to be sandwiched therebetween.

[0041] As a result, the first bent portion 80 of the intermediate product P1 is press-formed into the second bent portion 85 of the press-formed product. In this press-formation, compressive stress is mainly applied to the inside and outside of the bent portion (first bent portion 80), so cracks and the like are reduced compared to the outside of the bent portion of the press-formed product, where tensile stress is large. Therefore, according to the above-mentioned manufacturing method of the press-formed product P and the second die 20, which is a die for press-formation, the press-formed product P having the bent portion is appropriately press-formed. The side plate 82 is sandwiched between the side surface 21b of the second lower die 21, 21E and the flat surfaces 21b1, 22b1 on the upper die recess side surface 22b of the upper die 22, so that a frictional force is applied to the side plate 82, and the vertical movement of the side plate 82 can be reliably restricted.

[0042] In addition, the second lower die 21E has a lower pad 300 provided opposite to the upper die recess bottom surface 22a of the upper die 22, and in the press molding process (step S40), the upper die 22 is lowered while the bottom plate 81 of the intermediate product P1 is sandwiched between the lower pad 300 and the upper die recess bottom surface 22a. This makes it possible to increase the precision of the flatness, etc. of the bottom plate 81 of the press-molded product P.

[0043] Moreover, the press-formed product P is made of a high-tensile steel plate having a plate thickness t, and the ratio (R / t) of the bending radius R of the second bent portion 85 connecting the bottom plate 81 and the side plate 82 after the press forming process (step S40) to the plate thickness t is greater than 0 and equal to or less than 1. This makes it possible to provide a press-formed product P having a small bending radius at the bent portion by using a high-tensile steel plate.

[0044] As described above, the present invention is not limited to the present embodiment, and can be embodied in various forms. For example, in the present embodiment, the press-molded product P has a symmetrical U-shaped cross section, but it is also possible to press-mold a press-molded product having an asymmetric U-shaped cross section, such as by lengthening one of the left and right side plates, or an L-shaped cross section (that is, a shape in which a U-shaped cross section is divided in the middle). When press-molding a press-molded product having an L-shaped cross section, a restraining structure that restrains the bottom plate in a direction along the bottom plate can be provided on the side surface of the lower mold and the side surface of the upper mold recess of the upper mold recess, as well as on the opposite side of the side plate in the left-right direction, which is made of a restraining member or the like that restrains the bottom plate from moving to the opposite side of the side plate. In the present embodiment, the intermediate product P1 including the bottom plate 81, the side plate 82, and the first bent portion 80 is prepared by press molding using the first mold 10, but it may be prepared by other means. [Explanation of symbols]

[0045] 10: First mold 21, 21E: Second lower mold (press molding mold) 21a:Top 21b:Side 21b1: Plane 21c: Second shoulder (shoulder) 22: Upper mold 22a: Bottom surface of upper mold recess 22b: Upper mold recess side surface 22b1: Flat surface 22c: Upper die shoulder 80: First bending section 81: Bottom plate (1st plate part) 82: Side plate (2nd plate part) 85: Second bending portion 220: Upper mold recess 300: Lower pad 300f: Upper surface P: Press-molded products P1: Intermediate product R: bending radius (of the second bend) RB1: Bending radius (of the first bending part) RC2: Radius of curvature (at shoulder) t: plate thickness Y: Restraint structure

Claims

1. An intermediate product preparation process for preparing an intermediate product including a first plate portion, a second plate portion, and a first bent portion connecting the first plate portion and the second plate portion, the first plate portion being made of a high tensile steel plate having a thickness t; a placing step of placing the second plate portion on a lower mold having an upper surface and a side surface, the shoulder portion where the upper surface and the side surface are connected being formed with a curvature radius smaller than the bending radius of the first bent portion of the intermediate product, and placing the intermediate product such that a connecting portion between the first bent portion and the second plate portion engages with the shoulder portion; a clamping process in which an upper mold includes an upper mold recess having an upper mold recess bottom surface corresponding to the upper surface of the lower mold, an upper mold recess side surface corresponding to the side surface of the lower mold, and an upper mold shoulder connecting the upper mold recess bottom surface and the upper mold recess side surface and provided to correspond to the shoulder, and an upper mold having a radius of curvature of the upper mold shoulder set to a value obtained by adding the plate thickness t to the radius of curvature of the shoulder, thereby clamping the second plate portion of the intermediate product between the side surface of the lower mold and the upper mold recess side surface of the upper mold to restrict movement of the second plate portion and to restrain the first plate portion in a direction along the first plate portion; a press molding process in which the upper mold is lowered to apply compressive stress to the inside and outside of the first bent portion by a reaction force from the first plate portion and a reaction force from the second plate portion, thereby forming a second bent portion having a ratio (R / t) of a bending radius R to the plate thickness t that is greater than 0 and less than or equal to 1, following the upper mold shoulder and the shoulder, and press-molding the intermediate product to obtain a press-molded product in which the first plate portion and the second plate portion are connected by the second bent portion; A method for manufacturing a press-molded product comprising the steps of:

2. the lower mold has a lower pad provided opposite to a bottom surface of the upper mold recess, The method for manufacturing a press-molded product according to claim 1 , wherein the press molding step comprises lowering the upper die while sandwiching the first plate portion of the intermediate product between the lower pad and a bottom surface of the upper die recess.

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