Press molding manufacturing method and intermediate molding

Abstract

To provide a press molding manufacturing method capable of suppressing springing-back of a press molding of a U cross section shape or a hat cross section shape provided with a bent part bent in a longitudinal direction and a linear part linearly extending from both ends in the longitudinal direction, and an intermediate molding.SOLUTION: This press molding manufacturing method comprises: a step of press-molding an intermediate molding 10; and a step of press-molding the intermediate molding 10 into a press molding 20 of a target shape. The intermediate molding 10 includes an intermediate bent part 10A corresponding to a bent part 20A of a target shape, and a gradually changing section 10B1 and an intermediate linear part 10B2 corresponding to a linear part 20B of a target shape. A bent ridgeline 13a in the intermediate bent part 10A is at the same position as that of a bent ridgeline 23 of the bent part 20A of the target shape or a position inside in a width direction. A bent ridgeline 13b2 in the intermediate linear part 10B2 is positioned closer to the outside in the width direction than the bent ridgeline 23 of the linear part 20B of the target shape beyond a bent ridgeline 13b1 of the gradually changing section 10B1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a press-molded product that produces a press-molded product having a hat cross-sectional shape or a U-shaped cross-sectional shape, a curved portion that curves along the longitudinal direction when viewed from above, and straight portions that extend linearly from both ends of the curved portion, and to an intermediate molded product of the press-molded product. [Background technology]

[0002] Most automobile body parts are manufactured by press-forming thin metal sheets (such as thin steel sheets) into the part shape. In particular, in recent years, there has been a push to increase the strength of thin metal sheets in response to demands for lighter car bodies. The press formability of auto body parts varies depending on the part shape, but is also greatly affected by material properties such as the ductility of the sheet metal. However, the decrease in ductility that accompanies the increase in strength of sheet metal not only makes press forming more difficult, but also leads to problems such as poor dimensional accuracy due to springback after press forming.

[0003] In press-formed products with a U-shaped cross section having a top plate portion and a vertical wall portion, or in press-formed products with a hat cross section having a top plate portion, a vertical wall portion, and a flange portion, springback (wall opening) occurs, in which the angle (bending angle) between the top plate portion and the vertical wall portion increases. Furthermore, in press-formed products with a U-shaped cross section or a hat cross section having a curved portion along the longitudinal direction, three-dimensional springback such as bending and twisting occurs. Therefore, many technologies have been proposed to suppress this springback and improve the dimensional accuracy of press-formed products.

[0004] For example, Patent Document 1 discloses a technology for reducing springback (camberback) in a side view of a press-formed product with a hat-shaped cross section that has a top plate portion and a flange portion and is curved convexly or concavely toward the top plate portion along the longitudinal direction. Patent document 2 discloses a technology for manufacturing press-formed products without causing three-dimensional shape defects such as angle changes due to springback, ridge warpage (surface warpage), and twisting after press-forming of curved press-formed products with a hat cross-section shape. Patent Document 3 discloses a technology for suppressing springback, which is an increase in the angle between face portions at the connecting portions of a press-molded part having a U-shaped or V-shaped cross-sectional shape in which face portions are connected via connecting portions. Patent Document 4 discloses a technology for reducing three-dimensional springback such as twisting and bending without changing the product shape, which has a flange portion that curves along the longitudinal direction on at least one of the vertical wall portions of a groove-shaped portion extending in the longitudinal direction. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6176430 [Patent Document 2] Patent No. 5380890 [Patent Document 3] Patent No. 4992048 [Patent Document 4] Patent No. 5664810 Summary of the Invention [Problem to be solved by the invention]

[0006] Because the cost reduction effect of integrating vehicle body parts and reducing the number of parts is significant, there is a demand for press-forming technology that can manufacture vehicle body parts that are much longer than conventional ones. However, in a press-formed product 20 with a hat-shaped cross section, which has a curved portion 20A that curves along the longitudinal direction when viewed from above and straight portions 20B that extend linearly from both ends of the curved portion 20A, as shown in Fig. 6, not only springback due to wall opening and twisting but also springback (camber back when viewed from above) in which the bending angle of the curved portion 20A increases occurs, as shown in Fig. 7. In Fig. 7, the white arrows indicate the displacement direction due to springback at each position on the press-formed product 20.

[0007] The technologies of Patent Documents 1, 3, and 4 involve press-forming an intermediate product, which is an intermediate shape of the press-formed product, in a first process, and then press-forming the intermediate product into a press-formed product of the target shape in a second process. This is thought to make it possible to suppress camber back and wall splay in a press-formed product in a side view. In this case, although camber back and wall splay in a side view are factors that reduce dimensional accuracy, even if camber back and wall splay in a side view occur in the intermediate product press-formed in the first process, it was possible to press-form the press-formed product into the target shape without any problems in the second process.

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

[0009] Furthermore, the technology of Patent Document 2 involves press-forming to a target shape in one process, which is thought to avoid the problems associated with press-forming in two processes. However, the technology of Patent Document 2 reduces the bending moment due to the stress difference between the top plate and flange by forming an excess bead or embossment on the flange just before the bottom dead center of the forming, thereby suppressing camber back in a side view. Therefore, it could not be applied to press-formed products with a U-shaped cross section without a flange or a hat-shaped cross section with a narrow flange width.

[0010] The present invention has been made to solve the above-mentioned problems, and aims to provide a method for manufacturing a press-formed product that suppresses springback and improves dimensional accuracy in a press-formed product that has a curved portion that curves along the longitudinal direction when viewed from above and straight portions extending from both ends of the curved portion, and an intermediate molded product of the press-formed product. [Means for solving the problem]

[0011] (1) The manufacturing method of the press-molded product of the present invention is a U-shaped or hat-shaped cross-sectional shape having a top plate portion and a pair of vertical wall portions continuing from both widthwise ends of the top plate portion via bending ridges, and is provided with a curved portion that curves along the longitudinal direction when viewed from above, and a straight portion that extends linearly from both longitudinal ends of the curved portion. a first forming step of press-forming the intermediate formed product; A second forming step of press-forming the intermediate formed product into a press-formed 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 located 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, The bending ridgeline in the intermediate straight section is located widthwise outside the bending ridgeline in the straight section of the target shape, passing through the bending ridgeline in the gradually changing section.

[0012] (2) The intermediate molded product according to the present invention is a press-molded product having a U-shaped cross section or a hat-shaped cross section, which has a top plate portion and a pair of vertical wall portions that are continuous from both ends of the top plate portion in the width direction via bending ridges, and which has a curved portion that curves along the longitudinal direction in top view, and linear portions that extend linearly from both ends of the curved portion in the longitudinal direction, 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 located 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, The bending ridgeline in the intermediate straight section is located widthwise outside the bending ridgeline in the straight section of the target shape, passing through the bending ridgeline in the gradually changing section. [Effects of the Invention]

[0013] In the present invention, it is possible to suppress top-view camber back, wall opening, and torsional springback in a press-formed product that has a hat cross-sectional shape or a U-shaped cross-sectional shape and that has a curved portion that curves along the longitudinal direction when viewed from above, and straight portions that extend linearly from both ends of the curved portion, thereby ensuring dimensional accuracy. [Brief explanation of the drawings]

[0014] [Figure 1] 1A and 1B are diagrams illustrating a method for manufacturing a press-formed product according to the present embodiment ((a) press-formed product in an intermediate shape, (b) press-formed product in a target shape). [Figure 2] 1A and 1B are diagrams showing an example of a press die used in a first forming step and a press die used in a second forming step in a manufacturing method and examples of a press-formed product according to the present embodiment. [Figure 3] FIG. 1 is a diagram showing the stress distribution at the bottom dead center of a press-formed product press-formed in one step by a conventional method. [Figure 4]1 is a diagram showing a stress distribution at the bottom dead center of a press-molded product press-molded by a method for manufacturing a press-molded product according to the present embodiment. FIG. [Figure 5] FIG. 10 is a diagram showing the amount of shift and the amount of gradual change in an intermediate formed product press-formed in a first forming step in an example. [Figure 6] FIG. 1 is a diagram showing a press-formed product having a curved portion curved along the longitudinal direction when viewed from above, which was the subject of manufacture in the present invention and examples. [Figure 7] 1 is a diagram showing top view camber back, wall opening, and twist, which are springbacks that occur in a press-formed product that is the object of forming in the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] FIG. 6 shows an example of a press-molded product 20 to be manufactured in accordance with the present invention. The press-formed product 20 has a hat-shaped cross section including a top plate portion 21, a pair of vertical wall portions 25 continuing from both widthwise ends of the top plate portion 21 via bending ridge lines 23, and flange portions 27 continuing from the lower ends of each vertical wall portion 25. Furthermore, the press-formed product 20 includes a curved portion 20A that curves along the longitudinal direction in a top view, and linear portions 20B that extend linearly from both longitudinal ends of the curved portion 20A. Hereinafter, an embodiment of the present invention will be described, with the press-formed product 20 being the manufacturing target. Note that the numerical values ​​shown in Fig. 6 are provided to indicate the specific dimensions of the press-formed product 20 that is the manufacturing target in the examples described below, and do not limit the dimensions or shape of the press-formed product that is the manufacturing target in the present invention.

[0016] A manufacturing method for a press-molded product according to an embodiment of the present invention includes a first molding process of press-molding an intermediate molded product 10 shown in Figure 1(a) and a second molding process of press-molding the intermediate molded product 10 into a press-molded product 20 having a target shape shown in Figure 1(b).

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

[0018] The middle curved portion 10A corresponds to the curved portion 20A of the target shape means that the middle curved portion 10A becomes the curved portion 20A of the target shape in the second forming step. Similarly, the gradual change section 10B1 and the intermediate straight section 10B2 corresponding to the straight section 20B of the target shape means that in the second forming step, the gradual change section 10B1 and the intermediate straight section 10B2 become the straight section 20B of the target shape.

[0019] The bending ridge line 13a of the intermediate curved portion 10A is located more inward in the width direction than the bending ridge line 23 of the curved portion 20A of the target shape in a top view. Furthermore, in top view, the bending ridge line 13b2 in the intermediate straight portion 10B2 is located widthwise outward of the bending ridge line 13b1 in the gradually-changing section 10B1 and the bending ridge line 23 in the curved portion 20A of the target shape. In top view, the bending ridge line 13b1 in the gradually-changing section 10B1 gradually widens outward in the widthwise 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.

[0020] In this way, the intermediate molded product 10 has bending ridge lines 13 shifted inward and outward in the width direction compared to the bending ridge lines 23 of the press-molded product 20 of the target shape, so that when viewed from above, the intermediate curved portion 10A has a shape that is narrowed inward in the width direction. In the intermediate molded product 10, the intermediate vertical wall portion 15 on the inside of the curve is formed by stretch flange deformation, and the intermediate vertical wall portion 15 on the outside of the curve is formed by shrink flange deformation. Note that the inside of the curve is the same side as the center of curvature of the curve when viewed from above, and the outside of the curve is the opposite side to the center of curvature of the curve when viewed from above.

[0021] In the first molding step, the intermediate molded product 10 can be press-molded using, for example, a 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 that forms the intermediate curved portion 10A, a punch-side gradual change section forming portion 111B1 that forms the gradual change section 10B1, and a punch-side intermediate straight portion forming portion 111B2 that forms 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 gradual change section forming portion 113B1 that cooperates with the punch-side gradual change section forming portion 111B1 to form the gradual change 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 forming step, the die 113 is moved relatively toward the punch 111 while the blank is held down by the punch 111 and the pad 115, and the intermediate formed product 10 is press-formed.

[0022] In the second forming step, a press mold 120 shown in FIG. 2(b) can be used to press-form a press-formed product 20 having a target shape. 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 that forms the curved portion 20A, and a punch-side straight portion forming portion 121B that forms 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. In the second molding process, the die 123 is moved relative to the punch 121 while the punch 121 and pad 125 are pressing the intermediate top plate portion 11 of the intermediate molded product 10, and the intermediate molded product 10 is press-molded into a press-molded product 20 of the target shape.

[0023] The reason why springback can be suppressed in the press-formed product 20 manufactured by the method for manufacturing a press-formed product according to this embodiment will be explained based on the stress distributions shown in FIGS.

[0024] Fig. 3 shows the longitudinal stress distribution at the bottom dead center of a press-formed product 20 press-formed in a conventional single step, and Fig. 4 shows the longitudinal stress distribution at the bottom dead center of a press-formed product 20 press-formed in two steps, a first forming step and a second forming step, according to this embodiment. In Fig. 3 and Fig. 4, positive stress values ​​indicate tensile stress and negative stress values ​​indicate compressive stress, and 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 that is press-molded in a conventional single process, a stress difference occurs between the tensile stress (Figure 3(b)) in the vertical wall portion 25a on the stretch flange side (inside the curve) and the compressive stress (Figure 3(a)) in the vertical wall portion 25b on the contraction flange side (outside the curve).

[0026] Therefore, when the press-formed product 20 is released from the press die, a bending moment is generated due to the difference in stress between the vertical wall portion 25a on the stretch flange side and the vertical wall portion 25b on the contraction flange side, as shown in Fig. 3(c), resulting in camber back as seen from above as shown in Fig. 7(a). Furthermore, because the magnitude of this bending moment differs between the curved portion 20A and the straight portion 20B, it also causes torsional spring back as shown in Fig. 7(c). Therefore, in order to suppress top-view camber back and torsional springback in the press-formed product 20, it is effective to reduce the tensile stress generated in the vertical wall portion 25a on the stretch flange side and the compressive stress generated in the vertical wall portion 25b on the contraction flange side.

[0027] In the second forming step of this embodiment, the intermediate vertical wall portion 15 on the contracted flange side (outer side of the curve) of the intermediate straight portion 10B2 undergoes contracted flange deformation following the first forming step. In contrast, the intermediate vertical wall portion 15 on the stretched flange side (inner side of the curve) undergoes stretch flange deformation following the first forming step. Therefore, in the straight portion 20B formed in the second forming step, stress equivalent to that in a conventional press-formed product 20 press-formed in one step without shifting the bend ridgeline 23 is generated in the vertical wall portion 25, as shown in Figures 3 and 4.

[0028] On the other hand, in the intermediate curved portion 10A, the bending ridge line 13a is formed on both the contracted flange side and the stretched flange side, more inward in the width direction than the bending ridge line 23 of the target shape. Therefore, in the process in which the intermediate curved portion 10A becomes the curved portion 20A of the target shape in the second forming step, the bending ridge line 13a is bent back in the opposite direction.

[0029] That is, in the second forming step, the vertical wall portion 25b on the contracted flange side (outer side of the curve) undergoes stretch flange deformation, while the vertical wall portion 25a on the stretch flange side (inner side of the curve) undergoes contracted flange deformation. As a result, as shown in Fig. 4, the stress in both the vertical wall portion 25b on the contracted flange side and the vertical wall portion 25a on the stretch flange side in the curved portion 20A is reversed or reduced (see the areas surrounded by dashed ellipses in Figs. 3(b) and 4(b)).

[0030] Furthermore, the presence of the bending ridge 13b1 of the gradually changing section 10B1 in the intermediate formed product 10 suppresses material flow in the process in which the intermediate curved portion 10A becomes the curved portion 20A of the target shape in the second forming step. This prevents the material of the curved portion 20A from escaping to the straight portion 20B side, and allows the stress in the vertical wall portion 25 of the curved portion 20A to be efficiently reversed or reduced.

[0031] As a result, the stress difference between the tensile stress of the vertical wall portion 25a on the stretch flange side and the compressive stress of the vertical wall portion 25b on the contraction flange side can be reduced, thereby reducing the bending moment, thereby suppressing camber back and torsional spring back when viewed from above.

[0032] As described above, the method for manufacturing a press-formed product according to this embodiment can suppress top-view camber back and torsional springback in the press-formed product 20, ensuring dimensional accuracy. This reduces the stress difference between the vertical wall portion 25b on the contraction flange side and the vertical wall portion 25a on the stretch flange side without using a press die equipped with a cam mechanism to form a bead. It also prevents the risk of cracking due to the formation of a bead on the vertical wall portion 25, an increase in forming load, and the remaining of bead removal marks.

[0033] Furthermore, in this embodiment, the bending ridge line 13 of the intermediate product 10 is formed so as to be shifted outward or inward in the width direction relative to the bending ridge line 23 of the target shape, and therefore is bent back to the bending ridge line 23 of the target shape in the second forming step. As a result, a bending moment in the wall closing direction is induced in the press-formed product 20 of the target shape, which also has the effect of suppressing springback at the wall opening (FIG. 7(b)).

[0034] The above description has been directed to the press-formed product 20 having a hat-shaped cross section. However, the present invention may also be directed to a press-formed product having a U-shaped cross section that does not have a flange portion.

[0035] 1(a), the bending ridge line 13a of the intermediate curved portion 10A is located more inward in the width direction than the bending ridge line 23 of the target shape, but in the present invention, the bending ridge line of the intermediate curved portion may be located in 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 more outward in the width direction than the bending ridge line of the straight portion of the target shape, passing from both ends of the bending ridge line of the intermediate curved portion through the bending ridge line of the gradually changing section.

[0036] Even with such an intermediate formed product, the stress difference between the vertical wall portion on the contracted flange side and the vertical wall portion on the stretched flange side is efficiently reversed during the second forming process, as the intermediate curved portion is formed into the curved portion of the target shape. This reduces the stress difference. This makes it possible to suppress top-view camber back and torsional springback in the press-formed product of the target shape. Furthermore, because the bending ridgeline of the intermediate straight portion is bent back to the bending ridgeline of the target shape, it is also possible to suppress wall-opening springback in the straight portion.

[0037] As described above, the present invention is directed to a press-formed product having a U-shaped or hat-shaped cross section, a curved portion that curves along the longitudinal direction in top view, and straight portions that extend linearly from both longitudinal ends of the straight portion. In particular, the present invention is preferably applicable to the manufacture of long automobile parts. Examples of long automobile parts include A-pillar uppers, front side members, and rear side members. [Example]

[0038] An analysis was carried out to verify the effects of the present invention, which will be described below. In the example, a forming analysis was performed on a press-formed product 20 having a hat cross-sectional shape as shown in Figure 6, using two steps, the first forming step and the second forming step, according to the embodiment described above, and a springback analysis was also performed on the press-formed product 20.

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

[0040] [Table 1]

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

[0042] As shown in Figure 1(a), the intermediate molded product 10 has an intermediate curved portion 10A corresponding to the curved portion 20A of the target shape, and a gradually changing section 10B1 and an intermediate straight portion 10B2 corresponding to the straight portion 20B of the target shape. In the example of the invention, the bending ridge line 13 in the intermediate curved portion 10A is located at the same position as the bending ridge line 23 in the curved portion 20A of the target shape or is located on the inner side in the width direction. Furthermore, the bending ridge line 13b2 in the intermediate straight portion 10B2 is located on the outer side in the width direction of the bending ridge line 23 in the straight portion 20B of the target shape, passing through the bending ridge line 13b1 in the gradually changing section 10B1.

[0043] Here, as shown in Fig. 5, the shift amount of the bending ridge line 13b2 in the intermediate straight portion 10B2 is set to Wa, and the shift amount of the bending ridge line 13a in the intermediate curved portion 10A is set to Wb. Note that Fig. 5 is a diagram showing the intermediate product 10 and the press-formed product 20 of the target shape superimposed on each other, and the shift amounts Wa and Wb are set to be positive on the outer side in the width direction from the target shape and negative on the inner side in the width direction.

[0044] Furthermore, in the invention examples, the length of the gradually changing section 10B1 (hereinafter referred to as "gradual change amount H") in the intermediate formed product 10 shown in FIG. 5 was changed in various ways, and the press-formed product 20 having the target shape was press-formed.

[0045] 7, springback occurs in the press-formed product 20 in the form of camber back when viewed from above, wall opening, and torsion. Therefore, the amount of camber back when viewed from above, wall opening, and torsion were determined as the amount of springback of the press-formed product 20.

[0046] The amount of camber back as viewed from above was defined as the amount of movement of the longitudinal tip of the press-formed product 20 in a direction perpendicular to the longitudinal direction. 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 of the press-formed product 20 in the longitudinal direction. The amount of twist was determined 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 portion 21 at both ends in the longitudinal direction.

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

[0048] For comparison, a conventional example was prepared by press-forming into the target shape in one step without shifting the bending ridgeline (Wa = 0, Wb = 0). Furthermore, a comparative example was prepared by shifting the bending ridgelines of the intermediate straight and curved portions of the intermediate formed product press-formed in the first forming step to the outside in the width direction (Wa > 0, Wb > 0) or the inside in the width direction (Wa < 0, Wb < 0) from the bending ridgeline 23 of the target shape. Forming analysis and springback analysis were then performed on each of the conventional example and comparative example, and the springback amount and wrinkles were determined in the same way as for the inventive example.

[0049] Table 2 shows the shift amount and gradual change amount of the intermediate molded product 10 in the conventional example, comparative example, and invention example, the top view camber back amount, wall opening amount, twist amount, and wrinkle results of the press-molded product 20.

[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 examples of the invention. The top view camber back amount, wall opening amount, twist amount, and wrinkle results for the comparative examples and examples of the invention are shown as a ratio to the results for the conventional example.

[0052] In the comparative example No. 2, the bending ridgeline of the intermediate straight section and the bending ridgeline of the intermediate curved section are both shifted outward in the width direction from the target shape (Wa=20 mm, Wb=20 mm), and the gradual change amount H=0 mm. The wall opening was significantly reduced to 0.20 compared to the conventional example, the top view camber back was 0.68, which was lower than the conventional example but remained, and the twist amount was 1.88, which was worse. In addition, the wrinkles were 0.69, which was better than the conventional example.

[0053] In the comparative example No. 3, the bending ridgeline of the intermediate straight section and the bending ridgeline of the intermediate curved section are both shifted inward in the width direction from the target shape (Wa=-20 mm, Wb=-20 mm), and the gradual change amount H=0 mm. The wall opening was 0.30 and the twist was 0.38, which were significantly reduced compared to the conventional example, but the top view camber back remained at 0.67. In addition, the wrinkles were 0.79, which were better than the conventional example.

[0054] In Example No. 4, the shift amount Wa of the bending ridge 13b2 of the intermediate straight portion 10B2 is 20 mm, the shift amount Wb of the bending ridge 13a of the intermediate curved portion 10A is -20 mm, and the gradual change amount H is 80 mm. The top view camber back amount 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 example. The wrinkle amount was 1.79, which was worse than the comparative examples No. 2 and No. 3.

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

[0056] In Example No. 6, the absolute values ​​of the shift amounts Wa and Wb are smaller than those in Example No. 5, with Wa=10 mm and Wb=-10 mm. The top view camber back amount was 0.33, the wall opening amount was 0.22, and the twist amount was 0.47, all of which were good. In addition, the wrinkles were 1.50, which was worse than the conventional example, but less than the invention example No. 5, and were within the acceptable range when assuming spot welding of the press-formed product 20.

[0057] In the invention example No. 7, the bending ridge 13a of the intermediate curved portion 10A is positioned at the same position as the target shape (Wb = 0 mm), and the bending ridge 13b2 of the intermediate straight portion 10B2 is shifted outward in the width direction from the target shape (Wb = 20 mm). The top view camber back amount was 0.40, and the wall opening amount was 0.45, both of which were better than the conventional example. The twist amount was 1.02, which was the same as the conventional example. Furthermore, the wrinkles were 1.36, which was worse than the conventional example but within the acceptable range, and were lower than the No. 4 invention example, which had the same shift amount Wb.

[0058] In Example No. 8, the amount of gradual change is increased to H=150 mm while the amounts of shift Wa and Wb are kept the same as in Example No. 4. The top view camber back amount was 0.09, the wall opening amount was 0.24, and the twist amount was 0.08, all of which were good. In addition, the wrinkles amounted to 1.36, which was worse than the conventional example but still within the acceptable range and was lower than the invention examples No. 4 and No. 5.

[0059] In the invention example No. 9, the amount of gradual change was increased from No. 8 to H=200 m. The top view camber back was 0.16, the wall opening was 0.25, and the twist was -0.11, all of which were good. In addition, the wrinkles were 1.29, which was worse than the conventional example but still within the acceptable range and was lower than the No. 8 example of the invention.

[0060] In the invention example No. 10, the amount of gradual change is increased even more than in No. 9, to H=250 mm. The top view camber back was 0.26, the wall opening was 0.32, and the twist was -0.08, all of which were good results. In addition, the wrinkles were 0.86, which was reduced compared to the conventional example.

[0061] From the results of Nos. 4 to 6, it can be seen that when the shift amounts Wa and Wb are reduced, the effects of suppressing both the top view camber back and the torsion are reduced. Furthermore, it can be seen that No. 5, in which the shift amounts of the bending ridgeline 13 were Wa = 15 mm and Wb = -15 mm, had fewer wrinkles than No. 4, in which Wa = 20 mm and Wb = -20 mm. This shows that Wa = 15 mm and Wb = -15 mm are suitable for reducing camber back in a top view while suppressing an increase in wrinkles.

[0062] Furthermore, from the results of No. 7 to No. 10, it was found that a larger gradual change amount H could suppress an increase in wrinkles, but the effect of reducing the camber back in a top view was smaller. On the other hand, there was no significant effect on torsion. From this, it is considered that in order to simultaneously achieve camber back when viewed from above and suppress wrinkles, the gradual change amount H of the gradual change section 10B1 is preferably between 80 mm and 150 mm.

[0063] Therefore, to suppress top-view camber back, torsional springback, and wrinkles, the shift amounts Wa = 15 mm, Wb = -15 mm, and the gradual change amount H = 100 mm were set as Example No. 11 of the present invention, and the top-view camber back, torsion, and wrinkles were calculated. The top-view camber back, torsion, and wrinkles were calculated as follows: the top-view camber back was 0.19, the wall opening was 0.20, and the torsion was 0.26, all of which were significantly reduced compared to the conventional example. Furthermore, the wrinkles were 1.43, which was larger than the conventional example, but lower than the invention examples Nos. 4 to 6.

[0064] The results for the examples of the invention shown in Table 2 indicate that the greater the shift amounts Wa and Wb, i.e., the greater the difference between the width of the intermediate straight portion 10B2 and the width of the intermediate curved portion 10A, the greater the effect of improving the dimensional accuracy of the press-formed product 20. On the other hand, if the gradient of the increase in width of the gradually changing section 10B1 from the intermediate curved portion 10A to the intermediate straight portion 10B is large, wrinkles in the intermediate vertical wall portion 15 of the gradually changing section 10B1 worsen. This shows that there are suitable ranges for the shift amounts Wa and Wb. Furthermore, if the gradual change amount H of the gradual change section 10B1 is long, the reversal 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 to the target shape spreads toward the straight section 20B, thereby reducing the effect of suppressing camber back in a top view. From this point of view, it can be seen that there is also a suitable range for the gradual change amount H of the gradual change section 10B1.

[0065] From the results of Nos. 6 and 8 to 11, in which the top view camber, wall opening, twist, and wrinkles were all good, the preferred ranges of the shift amounts Wa and Wb and the gradual change amount H for the intermediate molded product 10 can be generalized as follows: 0.08≦Wa / H≦0.15, −0.15≦Wb / H≦−0.08, and the preferred range of the gradual change amount H is 0.40≦H / L≦1.24. Here, in generalizing the preferred ranges, the gradual change amount H of the gradual change section 10B1 was used for the shift amounts Wa and Wb, and the length L along the curve of the curved portion 20A (see FIG. 5) was used for the gradual change amount H.

[0066] As the size of the press-formed product of the target shape increases, the preferable shift amount and gradual change amount also increase, and vice versa. Therefore, by setting the shift amount and gradual change amount of the intermediate formed product within the generalized preferable range as described above, it is possible to suppress the increase in wrinkles and to suppress springback (camber back when viewed from above, wall opening, and twisting) regardless of the size of the press-formed product of the target shape. [Explanation of symbols]

[0067] 10 Intermediate molded products 10A Intermediate curved section 10B1 Gradual change section 10B2 Intermediate straight section 11 Intermediate top plate 13 Bent ridge 13a Bent ridge 13b1 Bending ridge 13b2 Bent ridge 15 Intermediate vertical wall 17 Intermediate flange 20 Press-molded products 20A curved section 20B Straight section 21 Top plate 23 Bent ridge 25 Vertical wall section 25a Vertical wall section 25b Vertical wall section 27 Flange 29 Die shoulder 110 Press mold 111 Punch 111A Punch side intermediate curved part forming part 111B1 Punch side gradual change section forming part 111B2 Punch side intermediate straight section forming section 113 Die 113A Die side intermediate curved part forming part 113B1 Die side gradual change section forming part 113B2 Die side intermediate straight section forming section 115 Pad 120 Press mold 121 Punch 121A Punch side curved part forming part 121B Punch side straight section forming section 123 Die 123A Die side curved part forming part 123B Die side straight section forming section 125 pads

Claims

1. A method for manufacturing a press-formed product having a U-shaped cross section or a hat-shaped cross section including a top plate portion and a pair of vertical wall portions that are continuous from both widthwise ends of the top plate portion via bending ridges, the press-formed product having a curved portion that curves along the longitudinal direction in top view, and linear portions that extend linearly from both longitudinal ends of the curved portion, a first forming step of press-forming the intermediate formed product; a second forming step of press-forming the intermediate product into a press-formed 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 inside in the width direction; A method for manufacturing a press-formed product, characterized in that the bending ridge line in the intermediate straight section is located widthwise outside the bending ridge line in the straight section of the target shape, passing through the bending ridge line in the gradually changing section.

2. An intermediate press-molded product having a U-shaped cross section or a hat-shaped cross section having a top plate portion and a pair of vertical wall portions that are continuous from both ends of the top plate portion in the width direction via bending ridge lines, and a curved portion that curves along the longitudinal direction in a top view, and a linear portion that extends linearly from both ends of the curved portion in the longitudinal direction. 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 inside in the width direction; An intermediate molded product, characterized in that the bending ridge line in the intermediate straight section is located widthwise outside the bending ridge line in the straight section of the target shape, passing through the bending ridge line in the gradually changing section.

Images