Method for manufacturing press-formed product

Abstract

In the integral molding in a state where two metal plate members are overlapped, the gap generated between the first metal plate member and the second metal plate member is reduced. The manufacturing method of the press-formed product according to the present invention includes a punch 41 having a convex portion 42 that is positioned and fixed in a state where the first metal plate member PL1 and the second metal plate member PL2 are overlapped, a die 31 having a concave portion 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 concave portion 31a of the die 31. The press forming is performed using these components, and 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 the lifting of the top plate portion from the punch 41.

Description

Technical Field

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

Background Art

[0002] Skeletal components used as automobile frames are required to suppress deformation of the vehicle body during a collision and secure the interior space of the vehicle body. The skeletal component has, for example, a main body member having a top plate portion and two vertical wall portions and having a U-shaped or hat-shaped cross section, and a reinforcing member (hereinafter referred to as a reinforcing member) that is overlapped and joined to the outside or inside of the main body member. By adopting a stacked structure of the skeletal component including the main body member and the reinforcing member, the high strength and high performance of the skeletal component are achieved.

[0003] As a method for manufacturing a component having the above-described stacked structure, a method of overlapping and welding an individually manufactured main body member and a reinforcing member is generally used. In recent years, a method of integrally forming two metal plate members in a stacked state has also been proposed (see, for example, Patent Document 1). In Patent Document 1, a second metal plate member having a smaller area and a larger plate thickness than the first metal plate member is joined to the back surface of the first metal plate member in the overhanging direction of the first metal plate member serving as the main body component, and the joined first and second metal plate members are overhangingly formed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The forming method of Patent Document 1 is a method of performing overhanging forming while restraining the outer edge portion of the first metal plate member and leaving the second metal plate member in an unrestrained state. This method not only causes the top plate portion to curve (lift up) during overhanging forming but also causes springback when removed from the mold. As a result, the shape of the formed part (hereinafter referred to as the formed product) is likely to deviate from the correct dimensions. In addition, in regions such as the vertical wall portion continuous with the top plate portion and the bent portion between the top plate portion and the vertical wall portion, a gap may occur between the first metal plate member and the second metal plate member. The gap generated between the first metal plate member and the second metal plate member not only degrades the performance of the formed product itself but also becomes an obstacle during assembly with other parts.

[0006] The present invention has been made in view of the above problems, and when integrally forming two metal plate members in a stacked state, it aims to provide a forming technique capable of reducing the gap generated between the first metal plate member and the second metal plate member.

Means for Solving the Problems

[0007] A method for manufacturing a press-formed product from one perspective is a method for manufacturing a long-shaped press-formed product having a U-shaped cross-section including a top plate portion and two vertical wall portions, or a hat-shaped cross-section further including flange portions continuous with each of the two vertical wall portions, by press-forming the first metal plate member and the second metal plate member in a stacked state. The press-forming is performed using a punch having a convex portion that is positioned and fixed in a state where the first metal plate member and the second metal plate member are stacked, 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. The load applied to the first metal plate member and the second metal plate member by the pad is characterized by being smaller than the load required to prevent the lift-up from the punch at the top plate portion.

[0008] Further, the load applied to the top plate portion by the pad is preferably set to be 1% or more and less than 30% of the load necessary to prevent the top plate portion from lifting off from the punch.

[0009] Further, the load necessary to prevent the top plate portion from lifting off from the punch is preferably a value obtained by simulation of press forming.

[0010] Further, the press-formed product is a long-shaped part having a hat-shaped cross section, and the vertical wall portion includes a first region provided at one end in the extending direction of the press-formed product, and a second region provided at the other end in the extending direction and having a height lower than the height of the first region, and a third region provided between the first and second regions and having a lower end portion inclined downward from the second region toward the first region, and the flange portion is preferably bent in a crank shape along the lower end of the vertical wall portion.

Advantages of the Invention

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

Brief Description of the Drawings

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DETAILED DESCRIPTION OF THE INVENTION

[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 the X-axis direction, the vertical direction of the press-formed product 10 is the Y-axis direction, and the extending direction of the press-formed product 10 is the Z-axis direction.

[0014] The press-formed product 10 has a first metal plate member PL1 and a second metal plate member PL2, and is manufactured by superposing and press-forming these metal plate members PL1 and PL2. In the following description, an example is given in which the first metal plate member PL1 and the second metal plate member PL2 are joined by welding or the like in a superposed state before press-forming. Further, in the following description, the joined first metal plate member PL1 and second metal plate member PL2 may be referred to as a superposed member 20. Note that the joining of the first metal plate member PL1 and the second metal plate member PL2 is not necessarily limited to welding, and can be joined by an appropriate method.

[0015] The press-formed product 10 has, as an XY cross-section orthogonal to the Z-axis direction in FIG. 1, for example, a substantially U-shaped or hat-shaped cross-section. In FIG. 1, a press-formed product 10 having an XY cross-section orthogonal to the Z-axis direction in FIG. 1 and having a hat-shaped cross-section is illustrated. The press-formed product 10 has a top plate portion 11, two vertical wall portions 12, 12 bent in the same direction with respect to the top plate portion 11, and two flange portions 13, 13 bent outward from these vertical wall portions 12, 12. Further, upper bent portions 14, 14 are provided between the top plate portion 11 and the two vertical wall portions 12, 12. Furthermore, lower bent portions 15, 15 are provided between the two vertical wall portions 12, 12 and the flange portions 13, 13. Note that the press-formed product 10 is a component that is symmetric about a YZ plane passing through the midpoint of the top plate portion 11 in the X-axis direction.

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

[0017] The flange portion 13 is bent outward with respect to the vertical wall portion 12 at the lower end of the vertical wall portion 12. The flange portion 13 has a first flange component portion 13a continuous with the lower end of the region A1, a second flange component portion 13b continuous with the lower end of the region A2, and a third flange component portion 13c continuous with the lower end of the region A3. As described above, the lower end of the region A3 of the vertical wall portion 12 is inclined downward from the region A2 toward the region A1. Therefore, the third flange component portion 13c constituting the flange portion 13 is inclined downward from the second flange component portion 13b toward the first flange component portion 13a. Since the third flange component portion 13c is inclined downward from the second flange component portion 13b toward the first flange component portion 13a, the portion between the first flange component portion 13a and the third flange component portion 13c and the portion between the second flange component portion 13b and the third flange component portion 13c are bent.

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

[0019] On the other hand, the second metal plate member PL2 becomes a member having a U-shaped cross-sectional shape perpendicular to the Z-axis direction in FIG. 1 by press-forming. At this time, the second metal plate member PL2 that has become a U-shaped member is disposed on the back side of the first metal plate member PL1 that becomes the main body member, straddling the upper end sides of the top plate portion 11 and the two vertical wall portions 12, 12. That is, the second metal plate member PL2 becomes a reinforcing member for the main body member by press-forming.

[0020] Next, the press die used when manufacturing the above-described press-formed product will be described with reference to FIG. 2. Note that FIG. 2 is a schematic end view showing a state in which the superimposed member is in contact with the pad at the portion indicated by the B-B line shown in FIG. 1. As shown in FIG. 2, the press die includes an upper die 30 having a die 31 and a pad 32, and a lower die 40 having a punch 41.

[0021] Die 31 has two recesses 31a and 31b. These recesses 31a and 31b are provided in die 31 such that recess 31b is continuous above recess 31a. During press forming, a convex portion 42 formed on punch 41 is inserted into recess 31a. Further, during press forming, a pad 32 that moves upward (in the D direction in FIG. 2) against the biasing of biasing means 33 is inserted into recess 31b.

[0022] Pad 32 is biased downward (in the C direction in FIG. 2) by biasing means 33 such as a spring. In a state where press forming is not performed, pad 32 is held in a state of protruding downward from the lower surface 31c of die 31. When press forming is started, pad 32 abuts against the overlapping member 20 positioned and held by convex portion 42 of punch 41, and applies a predetermined load to the overlapping member 20. Hereinafter, the load applied to the overlapping member 20 is referred to as the pad load.

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

[0024] Punch 41 has a convex portion 42 that is inserted into recess 31a of die 31. The overlapping member 20 is positioned and held on convex portion 42 of punch 41. Although illustration is omitted, as a method of positioning and holding the overlapping member 20 on convex portion 42 of punch 41, for example, a plurality of positioning pins are provided on the upper surface 42a of convex portion 42 of punch 41, and the positioning pins are inserted into positioning holes provided at a plurality of positions of the overlapping member 20.

[0025] Next, the press forming using the above-described two molds (upper mold 30 and lower mold 40) will be described with reference to FIGS. 2 to 5. In performing the press forming, first, the overlapping member 20 is positioned and held on the convex portion 42 of the punch 41. With the overlapping member 20 positioned and held on the convex portion 42 of the punch 41, for example, the lower mold 40 moves toward the upper mold 30 (in the E direction in FIG. 2). It is also possible to perform the press forming by moving the upper mold 30 toward the lower mold 40.

[0026] When the lower mold 40 moves toward the upper mold 30, the central portion of the overlapping member 20 (the portion that will become the top plate portion 11 of the press-formed product 10) positioned on the convex portion 42 of the punch 41 abuts against the lower surface 32a 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 abutted against the lower surface 31c of the die 31.

[0027] The lower mold 40 moves toward the upper mold 30 while the convex portion 42 of the punch 41 presses the pad 32. At this time, the pad 32 is biased downward (in the C direction in FIG. 2) by the biasing means 33. Therefore, the pad 32 moves upward (in the D direction 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] In the process of the pad 32 being pressed by the punch 41 and moving, both end portions of the overlapping member 20 positioned on the punch 41 (specifically, both end portions of the first metal plate member PL1) abut against the lower surface 31c of the die 31. Even after both end portions of the overlapping member 20 have abutted against the lower surface 31c of the die 31, the punch 41 moves toward the die 31 (in the E direction in FIG. 3).

[0029] At this time, the left end of the overlapping member 20 is supported by the shoulder portion 31d of the die 31 and the shoulder portion 42b of the punch 41. At the same time, the right end of the overlapping member 20 is supported by the shoulder portion 31e of the die 31 and the shoulder portion 42c of the punch 41. As a result, when the punch 41 moves toward the die 31, both ends of the overlapping member 20 are bent between the die 31 and the punch 41. At this time, the central portion of the overlapping member 20 (the portion that becomes the top plate portion 11 of the press-formed product 10) 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 D direction in FIG. 3. (See FIG. 4). The lower die 40 moves toward the upper die 30 until the both ends of the overlapping member 20 are clamped 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 formed into the above-described press-formed product 10 and removed from the lower die 40.

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

[0031] On the other hand, when the pad load is smaller than the maximum pad load, the pad 32 rises due to the bent overlapping member 20. That is, in the press forming in which the pad load is made smaller than the maximum pad load, the top plate portion 11 of the press-formed product 10 is lifted. Note that the smaller the pad load, the greater the lifting of the top plate portion 11.

[0032] In FIG. 6, the top plate portion 11 without lifting is shown by a solid line, and the top plate portion 11' with lifting is shown by a dotted line. For example, when taking the upper surface of the top plate portion 11 when no lifting occurs as a reference, the lifting amount of the top plate portion 11' with lifting is defined as La. Note that the lifting amount of the top plate portion 11 and the lifting amount of the pad 32 are the same amount. Hereinafter, the lifting amount of the top plate portion 11 and the lifting amount of the pad 32 will be described by referring to them as the lifting amount of the pad 32.

[0033] FIG. 7 is a schematic graph showing the relationship between the pad load and the lifting amount of the pad. As shown in FIG. 7, when the pad load is set to, for example, 260 kN, the lifting amount La of the pad 32 becomes 0. Also, when the pad load is set to 60 kN or less, the lifting amount La of the pad 32 exceeds 1 mm. Further, when the pad load approaches 0, the lifting amount La of the pad 32 increases. It has been found that the lifting amount La of the pad 32 when the pad load becomes 0 is approximately 13.5 mm. Note that the relationship between the lifting amount La of the pad 32 and the pad load is a value obtained, for example, by performing a simulation or the like.

[0034] Also, as shown in FIG. 8, in the press-formed product 10 manufactured by press forming, due to the pad load during press forming, the first metal plate member PL1 and the second metal plate member PL2 constituting the vertical wall portion 12 may be separated 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 changes in the range exceeding 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. Also, when the pad load becomes 0, it was found that the gap G is about 0.1 mm. Note that the gap G is a value actually measured by cutting the press-formed product 10, for example, or a value measured by shape scanning using X-ray CT.

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

[0037] Hereinafter, in the overlapping member 20 that undergoes press forming, the first metal plate member PL1 and the second metal plate member PL2 were changed, and the amount of lift La of the pad 32 and the gap G were measured.

[0038] As shown in Table 1, Example 1 is a case where a hot-dip galvanized steel sheet 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 sheet 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] Also, Example 2 is a case where a hot-dip galvanized steel sheet with a tensile strength of 980 MPa and a plate thickness of 0.8 mm is used as the first metal plate member PL1, and a cold-rolled steel sheet with a tensile strength of 1470 MPa and a plate thickness of 1.2 mm is used as the second metal plate member PL2.

[0040]

Table 1

[0041] FIG. 10 is a schematic graph showing the relationship between the ratio of the pad load and the amount of pad lift. Further, FIG. 11 is a schematic graph showing the relationship between the ratio of the pad load and the ratio of the gap generated near the upper bent portion. Here, the ratio of the pad load indicates the ratio of the actually applied pad load based on the maximum pad load. Also, the ratio of the gap G generated near the upper bent portion 14 is the ratio of the actually generated gap G based on the gap generated near the upper bent portion 14 when the maximum pad load is applied.

[0042] In each of FIGS. 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 Example 1 and Example 2. On the other hand, when the ratio of the actual pad load to the maximum pad load is 30% or less, it was found that the amount of pad lift La changes significantly.

[0043] Also, as shown in FIG. 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 actually generated gap. On the other hand, when the ratio of the actual pad load to the maximum pad load is less than 30%, it was found that the ratio of the actually generated gap becomes smaller. Also, 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 actually generated gap. On the other hand, when the ratio of the actual pad load to the maximum pad load is less than 20%, it was found that the ratio of the actually generated gap becomes smaller.

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

[0045] <Summary of Effects> According to the method for manufacturing a press-formed product of the present embodiment, by press-forming the first metal plate member PL1 and the second metal plate member PL2 in a stacked state, a U-shaped cross-section including a top plate portion 11 and two vertical wall portions 12, 12, or a hat-shaped cross-section further including flange portions 13, 13 continuous with each of the two vertical wall portions 12, 12 is provided. A method for manufacturing a long press-formed product 10, wherein the press-forming is performed using a punch 41 having a convex portion 42 that is positioned and fixed in a state where the first metal plate member PL1 and the second metal plate member PL2 are stacked, a die 31 having a concave portion 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 concave portion 31a of the die 31. 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 the convex portion 42 of the punch 41 from lifting off the top plate portion.

[0046] According to this, the gap generated between the first metal plate member PL1 and the second metal plate member PL2 can be reduced in the vertical wall portion 12 in the vicinity of the upper bent portion 14.

[0047] Further, it is preferable that the load applied to the top plate portion 11 by the pad 32 is set to be 1% or more and 30% or less of the load required to prevent the top plate portion 11 from lifting off 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, the gap generated by the separation of the first metal plate member PL1 and the second metal plate member PL2 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, as the load decreases, the gap also decreases. That is, if the load is 30% or less of the load necessary to prevent the top plate portion 11 from lifting, the gap generated by the separation of the first metal plate member PL1 and the second metal plate member PL2 can be reduced.

[0049] Further, the press-formed product 10 is a long-shaped part having a hat-shaped cross section, and the vertical wall portions 12, 12 include a first region A1 provided at one end in the extending direction of the press-formed product 10, a second region A2 provided at the other end in the extending direction and having a height lower than that of the first region A1, and a third region A3 provided between the first and second regions A1, A2 and having a lower end portion inclined downward from the second region A2 toward the first region A1. 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 forming using the die 31 having the pad 32 and the punch 41, by adjusting the forming conditions so that a gap is generated between the punch 41 and the pad 32 that narrowly presses the top plate portion 11 during press forming to induce bending deformation of the top plate portion 11, the bending moment generated in the vicinity of the upper bent portion 14 can be dispersed, and the gap generated between the main body member and the reinforcing member after mold release can be reduced.

Explanation of Reference Numerals

[0051] 10 Press-formed product 11 Top plate portion 12, 12 Vertical wall portions 13, 13 Flange portions 20 Overlay member 30 Upper mold 31 Die 32 pads 33 biasing means 40 lower mold 41 punch 42 convex portion Regions A1, A2, A3 PL1 First metal plate member PL2 Second metal plate member

Claims

1. A method for manufacturing a long-shaped press-formed product having a U-shaped cross section including a top plate portion and two vertical wall portions, or a hat-shaped cross section including 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 in a stacked state, the press forming is performed using a punch having a convex portion that is positioned and fixed in a state in which the first metal plate member and the second metal plate member 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, A manufacturing method for a press-molded product, characterized in that 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. The method for manufacturing a press-molded product according to claim 1, characterized in that the load applied to the top plate portion by the pad is set to be greater than or equal to 1% and less than 30% of the load required to prevent the top plate portion from lifting up from the punch.

3. 3. The method for manufacturing a press-formed product according to claim 2, wherein a load required to prevent the top plate portion from floating up from the punch is a value obtained by simulating the press forming.

4. The press-molded product is an elongated part having the hat-shaped cross section, 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 the height 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, The method for manufacturing a press-formed product according to any one of claims 1 to 3, wherein the flange portion is bent in a crank shape along a lower end of the vertical wall portion.

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