Method for manufacturing press-molded article

Abstract

The present invention reduces the gap generated between a first metal plate member and a second metal plate member in monolithic molding with the two metal plate members in an overlapped state. A method for manufacturing a press-molded article according to the present invention is characterized by performing press-molding using a punch 41 having a raised portion 42 on which a first metal plate member PL1 and a second metal plate member PL2 are positioned and fixed in an overlapped state, a die 31 having a recessed portion 31a into which the raised portion 42 of the punch 41 is to be inserted, and a pad 32 that applies a prescribed load to the first metal plate member PL1 and the second metal plate member PL2 when the raised portion 42 of the punch 41 is inserted into the recessed portion 31a of the die 31, wherein the load applied to the first metal plate member PL1 and the second metal plate member PL2 by the pad 32 is smaller than the load required to prevent uplift from the punch 41 in a top plate portion.

Description

Manufacturing method for press-molded products

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

[0002] Structural components used as automobile frames are required to suppress deformation of the vehicle body during a collision and to ensure internal space within the vehicle body. A skeletal component may include, for example, a main body member having a U-shaped or hat-shaped cross section with a top panel and two vertical walls, and a reinforcing member (hereinafter, "reinforcing member") overlapping and joined to the outside or inside of the main body member. By providing a skeletal component with a structure in which the main body member and the reinforcing member are overlapped, the strength and performance of the skeletal component can be increased.

[0003] A common method for manufacturing a component having the above-described overlapping structure is to overlap and weld a main body member and a reinforcing member that are manufactured separately. Recently, a method for integrally molding two overlapping metal plate members has also been proposed (see, for example, Patent Document 1). Patent Document 1 proposes a method for forming an extension of the first and second metal plate members by joining a second metal plate member that is smaller in area and thicker than the first metal plate member to the rear surface of the first metal plate member in the extension direction of the first metal plate member, which is the main body member.

[0004] Japanese Patent Application Laid-Open No. 2002-192245

[0005] The forming method of Patent Document 1 involves constraining the outer edge of a first metal plate member while leaving the second metal plate member unconstrained, thereby performing stretch forming. This method not only causes the top plate portion to bend (lift) during stretch forming, but also causes springback when removed from the mold. As a result, the shape of the formed part (hereinafter referred to as the molded product) is likely to deviate from the correct dimensions. Furthermore, gaps may occur between the first metal plate member and the second metal plate member in areas such as the vertical wall portion connected to the top plate portion and the bend between the top plate portion and the vertical wall portion. Gaps between the first metal plate member and the second metal plate member not only degrade the performance of the molded product itself, but also hinder its assembly with other parts.

[0006] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a molding technology that can reduce the gap that occurs between a first metal plate member and a second metal plate member when two metal plate members are stacked together and molded into a single piece.

[0007] A method for manufacturing a press-formed product according to one aspect is a method for manufacturing a long press-formed product having a U-shaped cross section with a top plate portion and two vertical wall portions, or a hat-shaped cross section with flange portions connected to each of the two vertical wall portions, by press-forming a first metal plate member and a second metal plate member while they are overlapped, wherein the press-forming is carried out using a punch having a convex portion that positions and fixes the first metal plate member and the second metal plate member while they are overlapped, a die having a concave portion into which the convex portion of the punch is inserted, and a pad that applies a predetermined load to the first metal plate member and the second metal plate member when the convex portion of the punch is inserted into the concave portion of the die, and wherein the load applied to the first metal plate member and the second metal plate member by the pad is smaller than the load required to prevent the top plate portion from lifting up from the punch.

[0008] Furthermore, the load applied to the top plate portion by the pad is preferably set to 1% or more and less than 30% of the load required to prevent the top plate portion from floating up from the punch.

[0009] Furthermore, the load required to prevent the top plate portion from lifting up from the punch is preferably a value determined by a press forming simulation.

[0010] Furthermore, it is preferable that the press-molded product is a long-shaped part having a hat-shaped cross section, and that the vertical wall portion has a first region provided at one end in the extension direction of the press-molded product, a second region provided at the other end in the extension direction and having a height lower than that of the first region, and a third region provided between the first and second regions and whose lower end slopes downward from the second region toward the first region, and that the flange portion is bent in a crank shape along the lower end of the vertical wall portion.

[0011] According to the present disclosure, when two metal plate members are integrally molded in a stacked state, the gap that occurs between the first metal plate member and the second metal plate member can be reduced.

[0012] FIG. 1 is a schematic perspective view showing an example of a press-formed product according to this embodiment. FIG. 2 is a schematic end view showing a state in which an overlapping member positioned on a punch is in contact with a pad at the location indicated by line B-B in FIG. 1 . FIG. 3 is a schematic end view showing a state in which both ends of the overlapping member are in contact with the lower surface of the die. FIG. 4 is a schematic end view showing a state in which the overlapping member is curved between the die and the punch. FIG. 5 is a schematic end view showing a state in which the overlapping member is clamped between the die and the punch. FIG. 6 is a schematic end view showing a state in which the punch is not lifted and a state in which the punch is lifted. FIG. 7 is a schematic graph showing the relationship between pad load and pad lift amount. FIG. 8 is a schematic end view showing the vicinity of an upper bent portion of a press-formed product. FIG. 9 is a schematic graph showing the relationship between pad load and gap. FIG. 10 is a schematic graph showing the relationship between the pad load ratio and pad lift amount. FIG. 11 is a schematic graph showing the relationship between the ratio of pad load and the ratio of gaps occurring near the upper bent portion.

[0013] A method for manufacturing a press-formed product according to the present embodiment will be described with reference to the drawings. Fig. 1 is a schematic perspective view showing an example of a press-formed product 10 according to the present embodiment. Hereinafter, in Fig. 1, the width direction of the press-formed product 10 is defined as the X-axis direction, the up-down direction of the press-formed product 10 is defined as the Y-axis direction, and the extension direction of the press-formed product 10 is defined as the Z-axis direction.

[0014] The press-formed product 10 includes a first metal plate member PL1 and a second metal plate member PL2, and is manufactured by overlapping and press-forming these metal plate members PL1 and PL2. In the following description, a case will be exemplified in which the first metal plate member PL1 and the second metal plate member PL2 are joined by welding or the like in an overlapping state before being press-formed. In the following description, the joined first metal plate member PL1 and second metal plate member PL2 may be referred to as an overlapping member 20. The joining of the first metal plate member PL1 and the second metal plate member PL2 does not have to be limited to welding, and they can be joined by any suitable method.

[0015] The press-formed product 10 has, for example, a substantially U-shaped or hat-shaped cross section in an XY cross section perpendicular to the Z-axis direction in FIG. 1 . FIG. 1 illustrates a press-formed product 10 having a hat-shaped XY cross section perpendicular to the Z-axis direction in FIG. 1 . The press-formed product 10 has a top plate portion 11, two vertical wall portions 12, 12 bent in the same direction relative to the top plate portion 11, and two flange portions 13, 13 bent outward from the vertical wall portions 12, 12. Upper bent portions 14, 14 are provided between the top plate portion 11 and the two vertical wall portions 12, 12. Lower bent portions 15, 15 are provided between the two vertical wall portions 12, 12 and the flange portions 13, 13. The press-formed product 10 is a part that is symmetrical with respect to a YZ plane passing through the midpoint of the top plate portion 11 in the X-axis direction.

[0016] The vertical wall portion 12 of the press-formed product 10 has a region A1 at the front end in the Z-axis direction in FIG. 1 , a region A2 at the rear end in the Z-axis direction in FIG. 1 , and a region A3 provided between the regions A1 and A2. The height (length) H1 of the region A1 is greater than the height (length) H2 of the region A2. Therefore, the lower end of the region A3 slopes downward from the region A2 toward the region A3, i.e., the region A3 is a substantially trapezoidal region. Note that, in the Z-axis direction in FIG. 1 , the length L1 of the region A1 and the length L2 of the region A2 provided on the vertical wall portion 12 may be the same length or may be different lengths.

[0017] The flange portion 13 is bent outward at the lower end of the vertical wall portion 12 relative to the vertical wall portion 12. The flange portion 13 has a first flange component 13a connected to the lower end of the region A1, a second flange component 13b connected to the lower end of the region A2, and a third flange component 13c connected to the lower end of the region A3. As described above, the lower end of the region A3 of the vertical wall portion 12 slopes downward from the region A2 toward the region A1. Therefore, the third flange component 13c constituting the flange portion 13 slopes downward from the second flange component 13b toward the first flange component 13a. Because the third flange component 13c slopes downward from the second flange component 13b toward the first flange component 13a, there is a bend between the first flange component 13a and the third flange component 13c, and between the second flange component 13b and the third flange component 13c.

[0018] As described above, the press-formed product 10 is obtained by press-forming the overlapping member 20, which is formed by overlapping and joining the first metal plate member PL1 and the second metal plate member PL2. The first metal plate member PL1 is press-formed into a main body member having the top plate portion 11, two vertical wall portions 12, 12, and two flange portions 13, 13, which are essential parts of the press-formed product 10.

[0019] On the other hand, the second metal plate member PL2 is press-formed into a member having a U-shaped cross section perpendicular to the Z-axis direction in Fig. 1. At this time, the U-shaped second metal plate member PL2 is disposed on the back surface side of the first metal plate member PL1, which will be the main body member, straddling the top plate portion 11 and the upper end sides of the two vertical wall portions 12, 12. In other words, the second metal plate member PL2 becomes a reinforcing member for the main body member through press forming.

[0020] Next, the press mold used in producing the above-mentioned press-molded product will be described with reference to Fig. 2. Fig. 2 is a schematic end view showing a state in which the overlapping member is in contact with the pad at the portion indicated by line B-B in Fig. 1. As shown in Fig. 2, the press mold is composed of an upper mold 30 having a die 31 and a pad 32, and a lower mold 40 having a punch 41.

[0021] The die 31 has two recesses 31a and 31b. These recesses 31a and 31b are provided on the die 31 so that the recess 31b is continuous with the upper side of the recess 31a. A protrusion 42 formed on a punch 41 is inserted into the recess 31a during press forming. Furthermore, a pad 32 that moves upward (in the direction D in FIG. 2 ) against the biasing force of a biasing means 33 during press forming is inserted into the recess 31b.

[0022] The pad 32 is biased downward (in the direction C in FIG. 2 ) by a biasing means 33 such as a spring. When press forming is not being performed, the pad 32 is held in a state in which it protrudes downward from the lower surface 31 c of the die 31. When press forming is started, the pad 32 comes into contact with the overlapping members 20, which are positioned and held by the protrusion 42 of the punch 41, and applies a predetermined load to the overlapping members 20. Hereinafter, the load applied to the overlapping members 20 will be referred to as the pad load.

[0023] Here, the pad load is set to, for example, 1% or more and less than 30% of the maximum pad load when the amount of lift of the top plate portion 11 of the press-molded product 10 becomes 0.

[0024] The punch 41 has a protrusion 42 that is inserted into the recess 31 a of the die 31. The overlapping member 20 is positioned and held by the protrusion 42 of the punch 41. Although not shown in the drawings, one method for positioning and holding the overlapping member 20 on the protrusion 42 of the punch 41 is to provide a plurality of positioning pins on the upper surface 42 a of the protrusion 42 of the punch 41 and insert the positioning pins into positioning holes provided at a plurality of positions on the overlapping member 20.

[0025] Next, press molding using the above-mentioned two dies (upper die 30, lower die 40) will be described with reference to Figures 2 to 5. When performing press molding, first, the overlapping member 20 is positioned and held by the convex portion 42 of the punch 41. With the overlapping member 20 positioned and held by the convex portion 42 of the punch 41, for example, the lower die 40 moves toward the upper die 30 (in the direction E in Figure 2). It is also possible to perform press molding by moving the upper die 30 toward the lower die 40.

[0026] When the lower die 40 moves toward the upper die 30, the central portion of the overlapping member 20 positioned on the convex portion 42 of the punch 41 (the portion that will become the top plate portion 11 of the press-formed product 10) comes into contact with the lower surface 32 a of the pad 32. At this time, both end portions of the overlapping member 20 positioned on the convex portion 42 of the punch 41 have not yet come into contact with the lower surface 31 c of the die 31.

[0027] The lower die 40 moves toward the upper die 30 while the convex portion 42 of the punch 41 presses the pad 32. At this time, the pad 32 is urged downward (in the direction C in FIG. 2 ) by the urging means 33. Therefore, the pad 32 moves upward (in the direction D in FIG. 2 ) while applying a load to the central portion of the overlapping member 20 positioned on the convex portion 42 of the punch 41.

[0028] As the pad 32 moves while being pressed by the punch 41, both ends of the overlapping member 20 positioned on the punch 41 (more specifically, both ends of the first metal plate member PL1) come into contact with the lower surface 31c of the die 31. Even after both ends of the overlapping member 20 come into contact with the lower surface 31c of the die 31, the punch 41 continues to move toward the die 31 (in the direction E in FIG. 3 ).

[0029] At this time, the left end of the overlapping member 20 is supported by the shoulder 31d of the die 31 and the shoulder 42b of the punch 41. At the same time, the right end of the overlapping member 20 is supported by the shoulder 31e of the die 31 and the shoulder 42c of the punch 41. As a result, as the punch 41 moves toward the die 31, both ends of the overlapping member 20 are curved between the die 31 and the punch 41. At this time, the central portion of the overlapping member 20 (the portion that will become the top plate portion 11 of the press-formed product 10), which is positioned on the convex portion 42 of the punch 41, rises from the upper surface 42a of the convex portion 42 of the punch 41 and presses the pad 32 in the direction D in FIG. 3 (see FIG. 4). The lower mold 40 moves toward the upper mold 30 until both ends of the overlapping member 20 are sandwiched between the die 31 and the punch 41 (top dead center). When the lower die 40 moves to the top dead center, the lower die 40 moves in a direction (downward) away from the upper die 30. The overlapping member 20 is molded into the press-molded product 10 described above and is removed from the lower die 40.

[0030] Next, the pad load applied by the pad 32 to the overlapping member 20 during press molding will be described. For example, when the pad load reaches the maximum pad load, the pad 32 is held in place during press molding without floating up. As a result, floating up of the top plate portion 11 of the press-molded product 10 is suppressed.

[0031] On the other hand, when the pad load becomes smaller than the maximum pad load, the pad 32 is lifted by the curved overlapping member 20. That is, in press molding in which the pad load is smaller than the maximum pad load, lifting of the top plate portion 11 of the press-molded product 10 occurs. Note that the smaller the pad load, the greater the lifting of the top plate portion 11.

[0032] In Figure 6, the top panel 11 where no lift occurs is indicated by a solid line, and the top panel 11' where lift occurs is indicated by a dotted line. For example, when the upper surface of the top panel 11 when no lift occurs is used as a reference, the amount of lift of the top panel 11' where lift occurs is denoted as La. Note that the amount of lift of the top panel 11 and the amount of lift of the pad 32 are the same. In the following description, the amount of lift of the top panel 11 and the amount of lift of the pad 32 will be referred to as the amount of lift of the pad 32.

[0033] FIG. 7 is a schematic graph showing the relationship between the pad load and the amount of pad lift. As shown in FIG. 7, when the pad load is set to, for example, 260 kN, the amount of pad lift La of the pad 32 is 0. Furthermore, when the pad load is set to 60 kN or less, the amount of pad lift La of the pad 32 exceeds 1 mm. Furthermore, as the pad load approaches 0, the amount of pad lift La of the pad 32 increases. It was found that the amount of pad lift La of the pad 32 when the pad load is 0 is approximately 13.5 mm. The relationship between the amount of pad lift La of the pad 32 and the pad load is a value obtained, for example, by performing a simulation.

[0034] 8, in the press-formed product 10 manufactured by press forming, the pad load during press forming may cause the first metal plate member PL1 and the second metal plate member PL2 constituting the vertical wall portion 12 to separate from each other in the vicinity of the upper bent portion 14. Hereinafter, the distance from the back surface of the first metal plate member PL1 to the front surface of the second metal plate member PL2 will be referred to as the gap G.

[0035] FIG. 9 is a schematic graph showing the relationship between the pad load and the gap G. As shown in FIG. 9, when the pad load exceeds 80 kN, the gap G fluctuates within a range of more than 0.8 mm and less than 1.0 mm. On the other hand, when the pad load is 80 kN or less, the smaller the pad load, the smaller the value of the gap G. It was also found that when the pad load is 0, the gap G is approximately 0.1 mm. Note that the gap G is a value measured, for example, by cutting the press-molded product 10, or a value measured by shape scanning using X-ray CT.

[0036] In this embodiment, in order to prevent the first metal plate member PL1 and the second metal plate member PL2 from separating (to reduce the gap G) near the upper bend portion 14 of the vertical wall portion 12, it is preferable to set the pad load to 30% or less of the maximum pad load.

[0037] In the overlapping member 20 to be press-formed, the first metal plate member PL1 and the second metal plate member PL2 were changed, and the floating amount La of the pad 32 and the gap G were measured.

[0038] As shown in Table 1, Example 1 is a case in which a hot-dip galvanized steel plate with a tensile strength of 980 MPa and a plate thickness of 1.4 mm is used as the first metal plate member PL1, and a cold-rolled steel plate with a tensile strength of 1470 MPa and a plate thickness of 1.6 mm is used as the second metal plate member PL2.

[0039] In addition, Example 2 is a case in which a hot-dip galvanized steel plate with a tensile strength of 980 MPa and a thickness of 0.8 mm is used as the first metal plate member PL1, and a cold-rolled steel plate with a tensile strength of 1470 MPa and a thickness of 1.2 mm is used as the second metal plate member PL2.

[0040]

[0041] Fig. 10 is a schematic graph showing the relationship between the pad load ratio and the amount of pad lift. Fig. 11 is a schematic graph showing the relationship between the pad load ratio and the ratio of the gap that occurs near the upper bent portion. Here, the pad load ratio refers to the ratio of the pad load actually applied relative to the maximum pad load. Furthermore, the ratio of the gap G that occurs near the upper bent portion 14 refers to the ratio of the gap G that actually occurs relative to the gap that occurs near the upper bent portion 14 when the maximum pad load is applied.

[0042] 10 and 11, the solid line indicates Example 1 and the dotted line indicates Example 2. As shown in Fig. 10, when the ratio of the actual pad load to the maximum pad load exceeds 30%, there is no significant change in the amount of pad lift La in both Examples 1 and 2. On the other hand, it was found that when the ratio of the actual pad load to the maximum pad load becomes 30% or less, the amount of pad lift La changes significantly.

[0043] 11 , in Example 1, when the ratio of the actual pad load to the maximum pad load exceeds 30%, there is no significant change in the ratio of the gap that actually occurs. On the other hand, when the ratio of the actual pad load to the maximum pad load is less than 30%, the ratio of the gap that actually occurs becomes smaller. Furthermore, in Example 2, when the ratio of the actual pad load to the maximum pad load exceeds 20%, there is no significant change in the ratio of the gap that actually occurs. On the other hand, when the ratio of the actual pad load to the maximum pad load is less than 20%, the ratio of the gap that actually occurs becomes smaller.

[0044] Thus, in Example 1, it was found that the gap G generated between the first metal plate member PL1 and the second metal plate member PL2 during press forming can be reduced if the ratio of the actual pad load to the maximum pad load is less than 30%. Also, in Example 2, it was found that the gap G generated between the first metal plate member PL1 and the second metal plate member PL2 during press forming can be reduced if the ratio of the actual pad load to the maximum pad load is less than 20%.

[0045] <Summary of Effects> According to the manufacturing method of a press-formed product of this embodiment, by press-forming the first metal plate member PL1 and the second metal plate member PL2 in a state where they are stacked together, a long press-formed product 10 having a U-shaped cross section including a top plate portion 11 and two vertical wall portions 12, 12, or a hat-shaped cross section including flange portions 13, 13 connected to each of the two vertical wall portions 12, 12 is manufactured. In this method, the protrusions 4 are positioned and fixed in place in a state where the first metal plate member PL1 and the second metal plate member PL2 are stacked together. 2, a die 31 having a recess 31a into which the convex portion 42 of the punch 41 is inserted, and a pad 32 that applies a predetermined load to the first metal plate member PL1 and the second metal plate member PL2 when the convex portion 42 of the punch 41 is inserted into the recess 31a of the die 31, and is characterized in that the load applied by the pad 32 to the first metal plate member PL1 and the second metal plate member PL2 is smaller than the load required to prevent the top plate portion from lifting up from the convex portion 42 of the punch 41.

[0046] This makes it possible to reduce the gap that occurs between the first metal plate member PL1 and the second metal plate member PL2 in the vertical wall portion 12 near the upper bent portion 14.

[0047] Furthermore, the load applied to the top plate portion 11 by the pad 32 is preferably set to 1% to 30% of the load required to prevent the top plate portion 11 from floating up from the punch 41 .

[0048] For example, when the load applied to the top plate portion 11 by the pad 32 is 30% or more of the load necessary to prevent the top plate portion 11 from lifting up, the gap that occurs when the first metal plate member PL1 and the second metal plate member PL2 are separated is large. On the other hand, when the load applied to the top plate portion 11 by the pad 32 is 30% or less of the load necessary to prevent the top plate portion 11 from lifting up, the gap becomes smaller as the load decreases. In other words, when the load is 30% or less of the load necessary to prevent the top plate portion 11 from lifting up, the gap that occurs when the first metal plate member PL1 and the second metal plate member PL2 are separated can be made smaller.

[0049] In addition, the press-formed product 10 is a long-shaped part having a hat-shaped cross section, and the vertical wall portions 12, 12 have a first region A1 provided at one end in the extension direction of the press-formed product 10, a second region A2 provided at the other end in the extension direction and having a height lower than the height of the first region A1, and a third region A3 provided between the first and second regions A1, A2 and whose lower end slopes downward from the second region A2 toward the first region A1, and the flange portions 13, 13 are bent in a crank shape along the lower ends of the vertical wall portions 12, 12.

[0050] According to this, when molding is performed using a die 31 having a pad 32 and a punch 41, the molding conditions are adjusted so that a gap is created between the punch 41 and the pad 32 that squeeze the top plate portion 11 during press molding, thereby inducing a curved deformation of the top plate portion 11, thereby dispersing the bending moment that occurs near the upper bend portion 14 and making it possible to reduce the gap that occurs between the main body member and the reinforcing member after demolding.

[0051] REFERENCE SIGNS LIST 10 Press-molded product 11 Top plate portion 12, 12 Vertical wall portion 13, 13 Flange portion 20 Overlapping member 30 Upper die 31 Die 32 Pad 33 Pressing means 40 Lower die 41 Punch 42 Convex portion A1, A2, A3 Region PL1 First metal plate member PL2 Second metal plate member

Claims

1. A method for manufacturing a long press-formed product having a U-shaped cross section with a top plate portion and two vertical wall portions, or a hat-shaped cross section with flange portions continuing to each of the two vertical wall portions, by press-forming a first metal plate member and a second metal plate member while they are overlapped, wherein the press-forming is carried out using a punch having a convex portion that positions and fixes the first metal plate member and the second metal plate member while they are overlapped, a die having a concave portion into which the convex portion of the punch is inserted, and a pad that applies a predetermined load to the first metal plate member and the second metal plate member when the convex portion of the punch is inserted into the concave portion of the die, wherein the load applied to the first metal plate member and the second metal plate member by the pad is smaller than the load required to prevent the top plate portion from lifting up from the punch.

2. A method for manufacturing a press-formed product as described in claim 1, characterized in that the load applied to the top plate portion by the pad is set to be greater than 1% and less than 30% of the load required to prevent the top plate portion from lifting off the punch.

3. The method for manufacturing a press-formed product according to claim 2, characterized in that the load required to prevent the top plate portion from lifting off the punch is a value determined by simulating the press forming.

4. A method for manufacturing a press-formed product according to any one of claims 1 to 3, characterized in that the press-formed product is an elongated part having a hat-shaped cross section, the vertical wall portion has a first region provided at one end in the extension direction of the press-formed product, a second region provided at the other end in the extension direction and having a height lower than that of the first region, and a third region provided between the first and second regions and having a lower end that slopes downward from the second region toward the first region, and the flange portion is bent in a crank shape along the lower end of the vertical wall portion.

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