Method for manufacturing press-formed product, intermediate formed product

Abstract

A method for manufacturing a press-formed product that suppresses springback of a press-formed product having a U-shaped or hat-shaped cross-sectional shape including a curved portion curved along the longitudinal direction and linear portions extending linearly from both longitudinal ends thereof, and an intermediate formed product are provided. 【Solution means】The method for manufacturing a press-formed product according to the present invention includes a step of press-forming an intermediate formed product 10 and a step of press-forming the intermediate formed product 10 into a press-formed product 20 having a target shape. The intermediate formed product 10 has an intermediate curved portion 10A corresponding to the curved portion 20A of the target shape, and a creep section 10B1 and an intermediate linear portion 10B2 corresponding to the linear portion 20B of the target shape. The bending ridge line 13a in the intermediate curved portion 10A is at the same position as or inside the width direction of the bending ridge line 23 of the curved portion 20A of the target shape, and the bending ridge line 13b2 in the intermediate linear portion 10B2 is located outside the width direction of the bending ridge line 23 of the linear portion 20B of the target shape via the bending ridge line 13b1 of the creep section 10B1.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a press-formed product including a hat cross-sectional shape or a U-shaped cross-sectional shape, having a curved portion that curves along the longitudinal direction in a top view, and straight portions that extend linearly from both ends of the curved portion, and an intermediate formed product of the press-formed product.

Background Art

[0002] Most of the body parts of automobiles are manufactured by press-forming a metal thin plate (such as a thin steel plate) into a part shape. In particular, in recent years, due to the demand for vehicle body weight reduction, the strengthening of metal thin plates has been promoted. The press formability of body parts varies depending on the target part shape, but the influence of material properties such as the ductility of metal thin plates is also significant. However, not only does the difficulty of press forming increase due to the decrease in ductility accompanying the strengthening of metal thin plates, but also dimensional accuracy defects due to springback after press forming have become a problem.

[0003] In a press-formed product having a U-shaped cross-sectional shape having a top plate portion and a vertical wall portion, or a hat cross-sectional shape having a top plate portion, a vertical wall portion, and a flange portion, springback (wall opening) occurs in which the angle (bending angle) formed by the top plate portion and the vertical wall portion increases. Further, in a press-formed product having a U-shaped cross-sectional shape or a hat cross-sectional shape having a portion curved along the longitudinal direction, three-dimensional springback such as bending and twisting occurs. Therefore, many techniques have been proposed so far to suppress these springbacks and improve the dimensional accuracy of press-formed products.

[0004] For example, Patent Document 1 discloses a technique for reducing springback (camber back) in a side view in a press-formed product having a hat-shaped cross section that is convex or concave on the top plate portion side along the longitudinal direction and having a top plate portion and a flange portion. Patent Document 2 discloses a technique for manufacturing a press-formed product without causing three-dimensional shape defects such as angular changes due to springback, warping of ridges (surface warping), and twisting after press-forming a press-formed product having a hat cross-sectional shape. Patent Document 3 discloses a technique for suppressing springback in which the angle between the faces at the connecting portion of a press-formed part having a U-shaped cross-sectional shape or a V-shaped cross-sectional shape in which the faces are connected via a connecting portion increases. Patent Document 4 discloses a technique for reducing three-dimensional springback such as twisting and bending without changing the product shape having a flange portion that curves along the longitudinal direction on at least one of the longitudinal walls of a groove-shaped portion extending in the longitudinal direction.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] Since the cost reduction effect by integrating body parts to reduce the number of parts is significant, a press forming technology that can manufacture much longer body parts than before is desired. However, in the press-formed product 20 having a hat cross-sectional shape as shown in FIG. 6, which has a curved portion 20A curved along the longitudinal direction in a top view and straight portions 20B extending linearly from both ends of the curved portion 20A, as shown in FIG. 7, not only springback such as wall opening and twisting occurs, but also springback (camber springback in top view) in which the bending angle of the curved portion 20A increases occurs. In FIG. 7, the white arrows indicate the displacement directions due to springback at each position of the press-formed product 20.

[0007] The techniques of Patent Documents 1, 3, and 4 press an intermediate formed product, which is an intermediate shape of a press-formed product, in the first step and press the intermediate formed product into a press-formed product having a target shape in the second step. Thereby, it is considered possible to suppress camber springback and wall opening of the press-formed product in a side view. In this case, although camber springback and wall opening in a side view are factors that reduce dimensional accuracy, even if camber springback and wall opening occur in the intermediate formed product press-formed in the first step, it was possible to press it into a press-formed product having a target shape without problems in the second step.

[0008] Therefore, it was thought that springback might be suppressed by press-forming in two steps using the techniques of Patent Documents 1, 3, and 4 for the press-formed product 20 having a curved portion 20A curved along the longitudinal direction in a top view as shown in FIG. 6. However, when camber springback in a top view occurs in the intermediate formed product press-formed in the first step, since the amount of horizontal deformation varies depending on the position in the longitudinal direction, it may not be possible to fit the intermediate formed product into the press die used in the second step, and in some cases, the press-formed product 20 cannot be press-formed.

[0009] In addition, since the technology of Patent Document 2 performs press forming into the target shape in one step, it is considered that problems such as press forming in two steps as described above can be avoided. However, the technology of Patent Document 2 forms a surplus bead or emboss on the flange immediately before the forming bottom dead center, thereby reducing the bending moment due to the stress difference between the top plate portion and the flange portion and suppressing the camber back in side view. Therefore, it could not be applied to press-formed products having a U-shaped cross-sectional shape without a flange or a hat cross-sectional shape with a narrow flange width.

[0010] The present invention has been made to solve the above problems, and suppresses springback of a press-formed product having a curved portion that curves along the longitudinal direction in a top view and straight portions extending from both ends thereof, and improves dimensional accuracy. An object is to provide a method for manufacturing a press-formed product and an intermediate formed product of the press-formed product.

Means for Solving the Problems

[0011] (1) The method for manufacturing a press-formed product according to the present invention has a U-shaped cross-sectional shape or a hat cross-sectional shape having a top plate portion and a pair of vertical wall portions continuous from both ends in the width direction of the top plate portion via bending ridges, and has a curved portion that curves along the longitudinal direction in a top view, and a straight portion that linearly extends from both longitudinal ends of the curved portion. A first forming step of press-forming an intermediate formed product; A second forming step of press-forming the intermediate formed product into a press-formed product having a target shape, and includes The intermediate formed product has an intermediate curved portion corresponding to the curved portion of the target shape, and a creep section and an intermediate straight portion corresponding to the straight portion of the target shape, The bending ridge in the intermediate curved portion is located at the same position as the bending ridge in the curved portion of the target shape or at a position inside in the width direction, The bending ridge in the intermediate straight portion is located outside in the width direction than the bending ridge in the straight portion of the target shape via the bending ridge in the creep section, and is characterized by this.

[0012] (2) The intermediate molded product according to the present invention has a U-shaped cross-sectional shape or a hat cross-sectional shape having a top plate portion and a pair of vertical wall portions continuous from both ends in the width direction of the top plate portion via bending ridge lines, and is a press-molded product including a curved portion that curves along the longitudinal direction in a top view and linear portions that extend linearly from both ends in the longitudinal direction of the curved portion. The intermediate molded product has an intermediate curved portion corresponding to the curved portion of the target shape, and a creep section and an intermediate linear portion corresponding to the linear portion of the target shape. The bending ridge line in the intermediate curved portion is located at the same position as the bending ridge line in the curved portion of the target shape or at a position inside in the width direction. The bending ridge line in the intermediate linear portion is located outside in the width direction of the bending ridge line in the linear portion of the target shape via the bending ridge line in the creep section. It has an intermediate curved portion corresponding to the curved portion of the target shape, and a creep section and an intermediate linear portion corresponding to the linear portion of the target shape. The bending ridge line in the intermediate curved portion is located at the same position as the bending ridge line in the curved portion of the target shape or at a position inside in the width direction. The bending ridge line in the intermediate linear portion is located outside in the width direction of the bending ridge line in the linear portion of the target shape via the bending ridge line in the creep section. This is the gist of the present invention.

Effect of the Invention

[0013] In the present invention, in a press-molded product having a hat cross-sectional shape or a U-shaped cross-sectional shape, and including a curved portion that curves along the longitudinal direction in a top view and linear portions that extend linearly from both ends of the curved portion, camber back, wall opening, and torsional spring back in the top view can be suppressed, and dimensional accuracy can be ensured.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0015] FIG. 6 shows an example of a press-formed product 20 that is the object to be manufactured in the present invention. The press-formed product 20 has a hat cross-sectional shape including a top plate portion 21, a pair of vertical wall portions 25 continuous from both ends in the width direction of the top plate portion 21 via bending ridge lines 23, and a flange portion 27 continuous from the lower ends of the respective vertical wall portions 25. Further, the press-formed product 20 includes a curved portion 20A that curves along the longitudinal direction in a top view, and straight portions 20B that extend linearly from both ends in the longitudinal direction of the curved portion 20A. Hereinafter, the embodiment of the present invention will be described with the press-formed product 20 as the object to be manufactured. The numerical values shown in FIG. 6 are described to represent the specific dimensions of the press-formed product 20 that was the object to be manufactured in the example described later, and do not limit the dimensions and shapes of the press-formed products that are the objects to be manufactured in the present invention.

[0016] The method for manufacturing a press-formed product according to the embodiment of the present invention includes a first forming step of press-forming an intermediate formed product 10 shown in FIG. 1(a), and a second forming step of press-forming the intermediate formed product 10 into a press-formed product 20 having a target shape shown in FIG. 1(b).

[0017] The intermediate molded product 10 has a hat cross-sectional shape including an intermediate top plate portion 11, a pair of intermediate vertical wall portions 15 continuous from both ends in the width direction of the intermediate top plate portion 11 via bending ridge lines 13, and an intermediate flange portion 17 continuous from the lower ends of the respective intermediate vertical wall portions 15. And the intermediate molded product 10 includes an intermediate curved portion 10A corresponding to the curved portion 20A of the target shape, and a creep section 10B1 and an intermediate straight portion 10B2 corresponding to the straight portion 20B of the target shape. The creep section 10B1 is a section that gradually expands outward in the width direction from both longitudinal ends of the intermediate curved portion 10A to the intermediate straight portion 10B2.

[0018] That the intermediate curved portion 10A corresponds to the curved portion 20A of the target shape means that in the second molding step, the intermediate curved portion 10A becomes the curved portion 20A of the target shape. Similarly, that the creep section 10B1 and the intermediate straight portion 10B2 correspond to the straight portion 20B of the target shape means that in the second molding step, the creep section 10B1 and the intermediate straight portion 10B2 become the straight portion 20B of the target shape.

[0019] The bending ridge line 13a in the intermediate curved portion 10A is located inward in the width direction than the bending ridge line 23 in the curved portion 20A of the target shape in a top view. Furthermore, the bending ridge line 13b2 in the intermediate straight portion 10B2 is located outward in the width direction than the bending ridge line 23 in the curved portion 20A of the target shape via the bending ridge line 13b1 of the creep section 10B1 in a top view. And the bending ridge line 13b1 in the creep section 10B1 gradually expands outward in the width direction from the bending ridge line 13a in the intermediate curved portion 10A toward the bending ridge line 13b2 in the intermediate straight portion 10B2 in a top view.

[0020] Thus, since the intermediate molded product 10 has the bending ridge line 13 shifted inward and outward in the width direction compared to the bending ridge line 23 of the press-molded product 20 of the target shape, the intermediate curved portion 10A has a constricted shape inward in the width direction in a top view. In the intermediate molded product 10, the intermediate vertical wall portion 15 on the inner side of the curve is formed by receiving an elongation flange deformation, and the intermediate vertical wall portion 15 on the outer side of the curve is formed by receiving a shrinkage flange deformation. Note that the inner side of the curve is the same side as the center of curvature of the curve in top view, and the outer side of the curve is the opposite side of the center of curvature of the curve in top view.

[0021] In the first molding step, for example, the intermediate molded product 10 can be press-molded using the press die 110 shown in FIG. 2(a). The press die 110 includes a punch 111, a die 113, and a pad 115. The punch 111 has a punch-side intermediate curved portion forming portion 111A for forming the intermediate curved portion 10A, a punch-side creep section forming portion 111B1 for forming the creep section 10B1, and a punch-side intermediate straight portion forming portion 111B2 for forming the intermediate straight portion 10B2. The die 113 has a die-side intermediate curved portion forming portion 113A that cooperates with the punch-side intermediate curved portion forming portion 111A to form the intermediate curved portion 10A, a die-side creep section forming portion 113B1 that cooperates with the punch-side creep section forming portion 111B1 to form the creep section 10B1, and a die-side intermediate straight portion forming portion 113B2 that cooperates with the punch-side intermediate straight portion forming portion 111B2 to form the intermediate straight portion 10B2. In the first molding step, with the blank held by the punch 111 and the pad 115, the die 113 is relatively moved toward the punch 111 side to press-mold the intermediate molded product 10.

[0022] Also, in the second molding step, for example, using the press die 120 shown in FIG. 2(b), the press-molded product 20 with the target shape can be press-molded. The press die 120 includes a punch 121, a die 123, and a pad 125. The punch 121 has a punch-side curved portion forming portion 121A for forming the curved portion 20A and a punch-side straight portion forming portion 121B for forming the straight portion 20B. The die 123 has a die-side curved portion forming portion 123A that cooperates with the punch-side curved portion forming portion 121A to form the curved portion 20A, and a die-side straight portion forming portion 123B that cooperates with the punch-side straight portion forming portion 121B to form the straight portion 20B. Then, in the second forming step, with the intermediate top plate portion 11 of the intermediate molded product 10 being held by the punch 121 and the pad 125, the die 123 is relatively moved toward the punch 121 side, and the intermediate molded product 10 is press-formed into the press-molded product 20 having the target shape.

[0023] The reason why springback can be suppressed in the press-molded product 20 manufactured by the method for manufacturing a press-molded product according to the present embodiment will be described based on the stress distributions shown in FIGS. 3 and 4.

[0024] FIG. 3 shows the distribution of the longitudinal stress at the bottom dead center of the press-molded product 20 press-molded in a conventional single step, and FIG. 4 shows the longitudinal stress distribution at the bottom dead center of the press-molded product 20 press-molded in two steps of the first forming step and the second forming step of the present embodiment. In FIGS. 3 and 4, a positive stress value indicates a tensile stress, a negative stress value indicates a compressive stress, the X-axis indicates the longitudinal direction, the Y-axis indicates the width direction, and the Z-axis indicates the press-forming direction.

[0025] In the press-molded product 20 press-molded in a conventional single step, a stress difference occurs between the tensile stress (FIG. 3(b)) in the vertical wall portion 25a on the elongation flange side (inner side of the curve) and the compressive stress (FIG. 3(a)) in the vertical wall portion 25b on the shrinkage flange side (outer side of the curve).

[0026] Therefore, when the press-molded product 20 is released from the press mold, as shown in FIG. 3(c), a bending moment is generated due to the stress difference between the vertical wall portion 25a on the elongation flange side and the vertical wall portion 25b on the shrinkage flange side, resulting in the upper surface view camber back shown in FIG. 7(a). Further, since the magnitude of this bending moment is different between the curved portion 20A and the straight portion 20B, it also becomes a factor of the torsional springback shown in FIG. 7(c). Therefore, in order to suppress the camber back and torsional springback in the top view of the press-formed product 20, it is effective to reduce the tensile stress generated in the vertical wall portion 25a on the elongation flange side and the compressive stress generated in the vertical wall portion 25b on the shrinkage flange side.

[0027] In the second forming step of the present embodiment, the intermediate vertical wall portion 15 on the shrinkage flange side (outer side of the curve) in the intermediate straight portion 10B2 undergoes shrinkage flange deformation following the first step. On the other hand, the intermediate vertical wall portion 15 on the elongation flange side (inner side of the curve) undergoes elongation flange deformation following the first forming step. Therefore, in the straight portion 20B formed in the second forming step, as shown in FIGS. 3 and 4, the same stress as that in the conventional press-formed product 20 press-formed in one step without shifting the bending ridge line 23 is generated in the vertical wall portion 25.

[0028] On the other hand, in the intermediate curved portion 10A, the bending ridge line 13a is formed on the inner side in the width direction from the bending ridge line 23 of the target shape on both the shrinkage flange side and the elongation flange side. Therefore, in the process of the intermediate curved portion 10A becoming the curved portion 20A of the target shape in the second forming step, the bending ridge line 13a is bent back in the reverse direction.

[0029] That is, in the second forming step, the vertical wall portion 25b on the shrinkage flange side (outer side of the curve) undergoes elongation flange deformation, while the vertical wall portion 25a on the elongation flange side (inner side of the curve) undergoes shrinkage flange deformation. As a result, as shown in FIG. 4, the stress in both the vertical wall portion 25b on the shrinkage flange side and the vertical wall portion 25a on the elongation flange side in the curved portion 20A is reversed or reduced (refer to the region surrounded by the broken-line ellipse in FIGS. 3(b) and 4(b)).

[0030] Furthermore, due to the presence of the bending ridge line 13b1 in the creep section 10B1 in the intermediate formed product 10, the material flow is suppressed in the process of the intermediate curved portion 10A becoming the curved portion 20A of the target shape in the second forming step. Therefore, the stress in the vertical wall portion 25 of the curved portion 20A can be efficiently reversed or reduced without the material of the curved portion 20A escaping to the straight portion 20B side.

[0031] As a result, the stress difference between the tensile stress of the vertical wall portion 25a on the stretching flange side and the compressive stress of the vertical wall portion 25b on the shrinking flange side can be reduced, and the bending moment can be reduced. Therefore, the camber back and the torsional springback in the top view can be suppressed.

[0032] As described above, according to the method for manufacturing a press-formed product according to the present embodiment, the camber back and the torsional springback in the top view of the press-formed product 20 can be suppressed, and dimensional accuracy can be ensured. As a result, the stress difference between the vertical wall portion 25b on the shrinking flange side and the vertical wall portion 25a on the stretching flange side can be reduced without forming beads using a press die equipped with a cam mechanism. In addition, it is also possible to prevent the risk of cracking due to forming beads on the vertical wall portion 25, an increase in the forming load, and the remaining of bead removal marks.

[0033] Furthermore, in the present embodiment, since the bending ridge line 13 of the intermediate formed product 10 is formed by being shifted outward or inward in the width direction from the bending ridge line 23 of the target shape, it is bent back so as to become the bending ridge line 23 of the target shape in the second forming step. As a result, the press-formed product 20 of the target shape induces a bending moment in the wall closing direction, and an effect of suppressing the springback of the wall opening (Fig. 7(b)) can also be obtained.

[0034] Note that the above description was directed to the press-formed product 20 having a hat cross-sectional shape. However, the present invention may be directed to a press-formed product having a U-shaped cross-sectional shape without a flange portion.

[0035] Also, although the bending ridge line 13a of the intermediate bending portion 10A of the intermediate formed product 10 shown in Fig. 1(a) is located inward in the width direction from the bending ridge line 23 of the target shape, in the present invention, the bending ridge line of the intermediate bending portion may be at the same position as the bending ridge line of the target shape. Even in this case, the bending ridge line of the intermediate straight portion is located outward in the width direction from the bending ridge line of the target shape through the bending ridge line of the gradual change section from both ends of the bending ridge line of the intermediate bending portion.

[0036] Even for such an intermediate molded product, in the process of forming the intermediate curved portion into the curved portion of the target shape in the second forming step, the stress reversal between the vertical wall portion on the shrink flange side and the vertical wall portion on the stretch flange side is efficiently performed, so that the stress difference is reduced. As a result, it is possible to suppress the camber back or torsional spring back in the top view of the press-molded product having the target shape. Further, since the bending ridge line of the intermediate straight portion is bent back to the bending ridge line of the target shape, it is also possible to suppress the spring back of the wall opening in the straight portion.

[0037] As described above, the present invention is directed to a press-molded product having a U-shaped cross-sectional shape or a hat-shaped cross-sectional shape, including a curved portion that curves along the longitudinal direction in a top view, and straight portions that extend linearly from both longitudinal ends of the straight portion. In particular, the present invention can be preferably applied to the manufacture of long automotive parts. Examples of the long automotive parts include an A-pillar upper, a front side member, and a rear side member.

Example

[0038] In order to verify the effects of the present invention, an analysis was performed, and this will be described below. In the example, a forming analysis of press-molding a press-molded product 20 having a hat-shaped cross-sectional shape shown in FIG. 6 in two steps of the first forming step and the second forming step according to the above-described embodiment, and a spring back analysis of the press-molded product 20 were performed.

[0039] The press-molded product 20 had a longitudinal length of 1000 mm, a radius of curvature R of 600 mm for the curved portion 20A (R shown in FIG. 5), a width of 80 mm (=W) for the top plate portion 21, a forming height of 80 mm, and a bending angle of 19.2° for the curved portion 20A (θ shown in FIG. 5). Further, the press-molded product 20 had a radius of curvature R of 10 mm for the bending ridge line 23, a bending angle of 120°, a radius of curvature R of 10 mm for the die shoulder portion 29 connecting the vertical wall portion 25 and the flange portion 27, a bending angle of 120°, and a width of 40 mm for the flange portion 27. When press-forming the press-formed product 20, a high-strength steel sheet with a tensile strength of 1470 MPa and a thickness of 1.4 mm was used as the blank. Table 1 shows the mechanical property values of the high-strength steel sheet used for the blank.

[0040]

Table 1

[0041] In the forming analysis, in both the first forming step and the second forming step, pad forming was performed, and the press die 110 shown in Fig. 2(a) (first forming step) and the press die 120 shown in Fig. 2(b) (second forming step) were used. In the first forming step and the second forming step, the pad pressure was set to 50 tonf in both cases.

[0042] As shown in Fig. 1(a), the intermediate formed product 10 was assumed to have an intermediate curved portion 10A corresponding to the curved portion 20A of the target shape, and a creep section 10B1 and an intermediate straight portion 10B2 corresponding to the straight portion 20B of the target shape. Then, as an inventive example, the bending ridge line 13 in the intermediate curved portion 10A was set at the same position as the bending ridge line 23 in the curved portion 20A of the target shape, or was located inside in the width direction. Further, the bending ridge line 13b2 in the intermediate straight portion 10B2 was located outside in the width direction than the bending ridge line 23 in the straight portion 20B of the target shape via the bending ridge line 13b1 in the creep section 10B1.

[0043] Here, as shown in Fig. 5, the displacement amount of the bending ridge line 13b2 in the intermediate straight portion 10B2 was defined as Wa, and the displacement amount of the bending ridge line 13a in the intermediate curved portion 10A was defined as Wb. Fig. 5 is a figure showing the intermediate formed product 10 and the press-formed product 20 of the target shape superimposed, and the displacement amounts Wa and Wb are positive on the outside in the width direction than the target shape and negative on the inside in the width direction.

[0044] Furthermore, in the inventive example, the length of the creep section 10B1 (hereinafter referred to as "creep amount H") in the intermediate formed product 10 shown in Fig. 5 was variously changed and press-formed into the press-formed product 20 of the target shape.

[0045] In the press-formed product 20, as shown in FIG. 7 described above, camber back, wall opening, and torsional springback occur in top view. Therefore, as the springback amount of the press-formed product 20, the camber back amount, wall opening amount, and torsional amount in top view were determined.

[0046] The camber back amount in top view was defined as the amount of movement in the direction orthogonal to the longitudinal direction at the longitudinal end of the press-formed product 20. The wall opening amount was defined as the amount of change in the angle formed between the top plate portion 21 and the vertical wall portion 25 at the center in the longitudinal direction of the press-formed product 20. The torsional amount was defined as the amount of change in the angle formed between the top plate portion 21 at the center in the longitudinal direction of the press-formed product 20 and the top plate portions 21 at both longitudinal ends.

[0047] Furthermore, in the examples, the wrinkles in the press-formed product 20 press-formed into the target shape were determined. The wrinkles were calculated from the plate thickness and curvature during the press-forming of the press-formed product 20.

[0048] Also, as a comparison target, a conventional example was a product press-formed into the target shape in one step without shifting the bending ridge line (Wa = 0, Wb = 0). Furthermore, a comparative example was a product in which the bending ridge lines of the intermediate straight portion and the intermediate curved portion of the intermediate formed product press-formed in the first forming step were shifted to the outside (Wa > 0, Wb > 0) or the inside (Wa < 0, Wb < 0) in the width direction from the bending ridge line 23 of the target shape. Then, for each of the conventional example and the comparative example, a forming analysis and a springback analysis were performed, and similar to the inventive example, the springback amount and the wrinkles were determined.

[0049] Table 2 shows the shift amount and creep amount of the intermediate formed product 10, the camber back amount, wall opening amount, and torsional amount in top view of the press-formed product 20, and the results of the wrinkles in the conventional example, comparative example, and inventive example.

[0050]

Table 2

[0051] In Table 2, No. 1 is a conventional example, No. 2 and No. 3 are comparative examples, and No. 4 to No. 11 are invention examples. The camberback amount, wall opening amount, and twist amount in the top view of the comparative examples and invention examples, as well as the wrinkle results, are shown as ratios to the results of the conventional example.

[0052] In the comparative example of No. 2, both the bending ridge line of the intermediate straight part and the bending ridge line of the intermediate curved part are shifted outward in the width direction from the target shape (Wa = 20 mm, Wb = 20 mm), and the creep amount is set to H = 0 mm. The wall opening amount was significantly reduced to 0.20 compared to the conventional example. The camberback amount in the top view was 0.68, which decreased compared to the conventional example but remained. The twist amount deteriorated to 1.88. Also, the wrinkle was 0.69, which was better than the conventional example.

[0053] In the comparative example of No. 3, both the bending ridge line of the intermediate straight part and the bending ridge line of the intermediate curved part are shifted inward in the width direction from the target shape (Wa = -20 mm, Wb = -20 mm), and the creep amount is set to H = 0 mm. The wall opening amount was 0.30 and the twist amount was 0.38, which were significantly reduced compared to the conventional example. However, the camberback amount in the top view was 0.67 and remained. Also, the wrinkle was 0.79, which was better than the conventional example.

[0054] In the invention example of No. 4, the shift amount Wa of the bending ridge line 13b2 of the intermediate straight part 10B2 is 20 mm, the shift amount Wb of the bending ridge line 13a of the intermediate curved part 10A is -20 mm, and the creep amount is set to H = 80 mm. The camberback amount in the top view was 0.01, the wall opening amount was 0.26, and the twist amount was 0.28, all of which were better than the conventional example and the comparative examples. Also, the wrinkle was 1.79, which deteriorated compared to the comparative examples of No. 2 and No. 3.

[0055] In the invention example of No. 5, the absolute values of the shift amounts Wa and Wb were made smaller than those of No. 4, and Wa = 15 mm and Wb = -15 mm. The camber back amount in top view was 0.14, the wall opening amount was 0.19, and the twist amount was 0.41, all of which were good. Also, the wrinkle was 1.57, which was reduced compared to the invention example of No. 4.

[0056] The invention example of No. 6 further reduced the absolute values of the displacement amounts Wa and Wb compared to No. 5, and set Wa = 10 mm and Wb = -10 mm. The camber back amount in top view was 0.33, the wall opening amount was 0.22, and the twist amount was 0.47, all of which were good. Also, the wrinkle was 1.50, which was worse than the conventional example but reduced compared to the invention example of No. 5, and was within the allowable range assuming spot welding joining of the press-formed product 20.

[0057] The invention example of No. 7 set the bending ridge line 13a of the intermediate curved portion 10A at the same position as the target shape (Wb = 0 mm), and shifted the bending ridge line 13b2 of the intermediate straight portion 10B2 outward in the width direction from the target shape (Wb = 20 mm). The camber back amount in top view was 0.40, the wall opening amount was 0.45, which was better than the conventional example. Also, the twist amount was 1.02, which was equivalent to the conventional example. Furthermore, the wrinkle was 1.36, which was worse than the conventional example but within the allowable range and reduced compared to the invention example of No. 4 with the same displacement amount Wb.

[0058] The invention example of No. 8 increased the creep amount to H = 150 mm while keeping the same displacement amounts Wa and Wb as those of No. 4. The camber back amount in top view was 0.09, the wall opening amount was 0.24, and the twist amount was 0.08, all of which were good. Also, the wrinkle was 1.36, which was worse than the conventional example but within the allowable range and reduced compared to the invention examples of No. 4 and No. 5.

[0059] The invention example of No. 9 increased the creep amount more than No. 8 to H = 200 m. The camber back amount in top view was 0.16, the wall opening amount was 0.25, and the twist amount was -0.11, all of which were good. Also, the wrinkle was 1.29, which was within the allowable range although it deteriorated compared to the conventional example and was reduced compared to the invention example of No. 8.

[0060] The invention example of No. 10 further increased the creep amount to H = 250 mm compared to No. 9. The camber back amount in top view was 0.26, the wall opening amount was 0.32, and the twist amount was -0.08, all of which were good. Also, the wrinkle was 0.86, which was reduced compared to the conventional example.

[0061] From the results of No. 4 to No. 6, it can be seen that when the displacement amounts Wa and Wb are reduced, the suppression effects of the camber back in top view and the twist both become smaller. Furthermore, it can be seen that No. 5 with the displacement amount of the bending ridge line 13 being Wa = 15 mm and Wb = -15 mm has less wrinkles compared to No. 4 with Wa = 20 mm and Wb = -20 mm. From this, it was found that Wa = 15 mm and Wb = -15 mm are preferable for reducing the camber back in top view while suppressing the increase in wrinkles.

[0062] Also, from the results of No. 7 to No. 10, it can be seen that a larger creep amount H can suppress the increase in wrinkles, but the reduction effect of the camber back in top view becomes smaller. On the other hand, there was no significant influence on the twist. From this, in order to achieve both suppression of the camber back in top view and wrinkles, it is considered that the creep amount in the creep section 10B1 is preferably between H = 80 mm and 150 mm.

[0063] Therefore, as conditions enabling the upper surface view camber back, torsional spring back, and wrinkle suppression, an example of Invention No. 11 was a case where the displacement amounts were Wa = 15 mm and Wb = -15 mm, and the creep amount was H = 100 mm, and the upper surface view camber back amount, torsional amount, and wrinkles were determined. As a result, the upper surface view camber back amount was 0.19, the wall opening amount was 0.20, and the torsional amount was 0.26, all of which were significantly reduced compared to the conventional examples. Also, the wrinkle was 1.43, which was larger than that of the conventional examples but lower than those of Invention Examples Nos. 4 to 6.

[0064] The results related to the invention examples shown in Table 2 indicate that when the displacement amounts Wa and Wb are large, that is, when the difference between the width of the intermediate straight portion 10B2 and the width of the intermediate curved portion 10A is large, the effect of improving the dimensional accuracy of the press-formed product 20 is significant. On the other hand, when the gradient of the spread of the width of the creep section 10B1 from the intermediate curved portion 10A to the intermediate straight portion 10B is large, the wrinkles in the intermediate vertical wall portion 15 of the creep section 10B1 deteriorate. From this, it can be seen that there is a suitable range for the displacement amounts Wa and Wb. Also, when the creep amount H of the creep section 10B1 is long, the reverse stress (the stress in the vertical wall portion 25a on the inner side of the curve and the stress in the vertical wall portion 25b on the outer side of the curve shown in FIG. 4) generated in the vertical wall portion 25 of the press-formed product 20 press-formed into the target shape spreads toward the straight portion 20B side, so the suppression effect of the upper surface view camber back becomes small. From this point, it can be seen that there is also a suitable range for the creep amount H of the creep section 10B1.

[0065] Based on the results of Invention Examples Nos. 6, 8 to 11, where the upper surface view camber amount, wall opening amount, torsional amount, and wrinkles were all good, generalizing the suitable ranges of the displacement amounts Wa and Wb and the creep amount H in the intermediate formed product 10, the suitable ranges of the displacement amounts Wa and Wb are 0.08 ≦ Wa / H ≦ 0.15 and -0.15 ≦ Wb / H ≦ -0.08, and the suitable range of the creep amount H is 0.40 ≦ H / L ≦ 1.24. Here, in generalizing the suitable ranges, for the displacement amounts Wa and Wb, the creep amount H of the creep section 10B1 was used, and for the creep amount H, the length L (see FIG. 5) along the curve of the curved portion 20A was used.

[0066] As the size of the press-formed product with the target shape increases, the suitable amount of displacement and the amount of creep also increase, and vice versa. Therefore, by setting the amount of displacement and the amount of creep of the intermediate formed product within the suitable range generalized as described above, regardless of the size of the press-formed product with the target shape, it is possible to suppress an increase in wrinkles while suppressing springback (camber back, wall opening, and twist) when viewed from above.

Explanation of Symbols

[0067] 10 Intermediate formed product 10A Intermediate curved part 10B1 Creep section 10B2 Intermediate straight part 11 Intermediate top plate part 13 Bending ridge line 13a Bending ridge line 13b1 Bending ridge line 13b2 Bending ridge line 15 Intermediate vertical wall part 17 Intermediate flange part 20 Press-formed product 20A Curved part 20B Straight part 21 Top plate part 23 Bending ridge line 25 Vertical wall part 25a Vertical wall part 25b Vertical wall part 27 Flange part 29 Die shoulder part 110 Press mold 111 Punch 111A Punch-side intermediate curved part forming part 111B1 Punch-side creep section forming part 111B2 Punch-side intermediate straight part forming part 113 Die 113A Die-side intermediate curved part forming part 113B1 Die-side creep section forming part 113B2 Die-side intermediate straight part forming part 115 Pad 120 Press mold 121 Punch 121A Punch-side Curved Part Forming Section 121B Punch-side Straight Part Forming Section 123 Die 123A Die-side Curved Part Forming Section 123B Die-side Straight Part Forming Section 125 Pad

Claims

1. A method for manufacturing a press-molded product having a U-shaped cross-sectional shape or a hat-shaped cross-sectional shape including a top plate portion and a pair of vertical wall portions continuing from both ends of the top plate portion in the width direction via bending ridges, the cross-sectional shape including a curved portion curved along the longitudinal direction when viewed from above, and a straight portion extending linearly from both ends of the curved portion in the longitudinal direction, a first molding step of press-molding the intermediate molded product; A second molding step of press-molding the intermediate product into a press-molded product having a target shape, The intermediate molded product is An intermediate curved portion corresponding to the curved portion of the target shape, and a gradually changing section and an intermediate straight portion corresponding to the straight portion of the target shape, A bending ridgeline in the intermediate curved portion is at the same position as the bending ridgeline in the curved portion of the target shape or at a position on the inner side in the width direction, A method for manufacturing a press-molded product, characterized in that a bending ridgeline in the intermediate straight portion is located widthwise outside the bending ridgeline in the straight portion of the target shape, passing through the bending ridgeline in the gradual change section.

2. The intermediate molded product is an intermediate molded product before being press molded into the target shape, the intermediate molded product being a U-shaped cross-sectional shape or a hat-shaped cross-sectional shape having a top plate portion and a pair of vertical wall portions continuing from both ends of the width direction of the top plate portion via bending ridges, the intermediate molded product being a target shape and including a curved portion that curves along the longitudinal direction when viewed from above, and a straight portion that extends linearly from both ends of the longitudinal direction of the curved portion, The curved portion has an intermediate curved portion formed in the curved portion of the target shape, and a gradually changing section and an intermediate straight portion formed in the straight portion of the target shape, A bending ridgeline in the intermediate curved portion is at the same position as the bending ridgeline in the curved portion of the target shape or at a position inside in the width direction, An intermediate molded product, characterized in that a bending ridgeline in the intermediate straight portion is located widthwise outside the bending ridgeline in the straight portion of the target shape, passing through the bending ridgeline in the gradual change section.

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