Method for manufacturing a press-formed article, intermediate formed article

Abstract

The manufacturing method of the press-formed product of the present application includes a step of press-forming an intermediate formed product (10) and a step of press-forming the intermediate formed product (10) into a target shape of a press-formed product (20), the intermediate formed product (10) having an intermediate curved portion (10A) corresponding to a curved portion (20A) of the target shape and a gradual change interval (10B1) and an intermediate straight portion (10B2) corresponding to a straight portion (20B) of the target shape, a bend line (13a) in the intermediate curved portion (10A) being at the same position or a position inside in the width direction as a bend line (23) of the curved portion (20A) of the target shape, and a bend line (13b2) in the intermediate straight portion (10B) being at a position outside in the width direction than a bend line (23) of the straight portion (20B) of the target shape via a bend line (13b1) of the gradual change interval (10B1).

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a stamped article and an intermediate stamped article thereof, the stamped article being a hat-shaped cross section or a U-shaped cross section, having a curved portion that bends along the length direction when viewed from above and a straight portion extending in a straight line from both ends of the curved portion. Background Technology

[0002] Most automotive body components are manufactured by stamping thin metal sheets (such as sheet metal) into part shapes. In recent years, in particular, driven by the demand for lightweight vehicle bodies, the use of high-strength sheet metal has been continuously developed. The stamping formability of body components varies depending on the shape of the component, but material properties, primarily the ductility of the sheet metal, have a significant impact. However, due to the reduced ductility accompanying the increase in sheet metal strength, not only does stamping become more difficult, but springback after stamping also leads to dimensional inaccuracies.

[0003] In stamped products with a U-shaped cross section (hat-shaped cross section) and side wall portions, or in stamped products with a top plate, side wall portions, and a flange portion, springback (wall opening) occurs due to an increase in the angle (bending angle) between the top plate and side wall portions. Furthermore, in stamped products with U-shaped or hat-shaped cross sections that have portions that bend along their length, three-dimensional springback such as bending and torsion occurs. Therefore, many techniques have been proposed to date to suppress this springback and improve the dimensional accuracy of stamped products.

[0004] For example, Patent Document 1 discloses a technique for reducing the springback (camber-back) of a stamped article with a hat-shaped cross-section that bends or protrudes along the length direction towards the top plate portion when viewed from the side. Patent Document 2 discloses a technique for manufacturing stamped articles without producing three-dimensional shape defects such as angle changes, ridgeline warpage (surface warpage), and twisting caused by springback after stamping of a bent stamped article with a hat-shaped cross-section. Patent Document 3 discloses a technique for suppressing springback caused by increased angles of the face and face in the connecting portion of a stamped part with a face and face connected via a connecting portion. Patent Document 4 discloses a technique for reducing three-dimensional springback such as twisting and bending without changing the product shape in which at least one of the longitudinal wall portions of the groove-shaped portion extending along the length direction has a flange portion that bends along the length direction.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent No. 6176430

[0008] Patent Document 2: Japanese Patent No. 5380890

[0009] Patent Document 3: Japanese Patent No. 4992048

[0010] Patent Document 4: Japanese Patent No. 5664810 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] Integrating body parts into a single unit significantly reduces the number of components, leading to a strong demand for stamping technology capable of manufacturing much longer body parts than before. However, in Figure 6 In the stamped product 20 shown, which has a cap-shaped cross-section with a curved portion 20A that bends along its length when viewed from above and straight portions 20B extending linearly from both ends of the curved portion 20A, such as Figure 7 As shown, not only does it produce springback with wall opening and twisting, but it also produces springback with an increased bending angle at the bend 20A (top-view camber springback). Figure 7 In the diagram, hollow arrows indicate the direction of displacement caused by springback at various locations on the stamped part 20.

[0013] Patent documents 1, 3, and 4 describe a process where an intermediate-shaped part, serving as a stamped product, is stamped in a first step, and then stamped into a target-shaped stamped product in a second step. This is believed to suppress lateral camber springback and wall opening in the stamped product. While lateral camber springback and wall opening are major causes of reduced dimensional accuracy, even if lateral camber springback and wall opening occur in the intermediate-shaped part stamped in the first step, it can still be stamped into the target-shaped stamped product without problems in the second step.

[0014] Therefore, for Figure 6 The stamped article 20 shown, which has a curved portion 20A that bends along its length when viewed from above, is also believed to suppress springback by performing stamping in two processes using the techniques of Patent Documents 1, 3, and 4. However, if the intermediate formed part stamped in the first process exhibits springback with a camber when viewed from above, the amount of deformation in the horizontal direction varies depending on the position in the length direction. Therefore, it is impossible to insert the intermediate formed part into the stamping die used in the second process, and sometimes it is impossible to stamp the stamped article 20.

[0015] Furthermore, Patent Document 2's technology is a technique for stamping to the target shape in a single process, thus avoiding the problem of stamping in two processes as described above. However, Patent Document 2's technology reduces the bending moment caused by the stress difference between the top plate and the flange by forming an excess metal bead or emboss on the flange just before reaching the bottom dead center, thereby suppressing camber springback when viewed from the side. Therefore, it cannot be applied to stamped products with a U-shaped cross-section without a flange or a hat-shaped cross-section with a narrow flange width.

[0016] The present invention was made to solve the above-mentioned problems, and its object is to provide a method for manufacturing a stamped article that improves dimensional accuracy by suppressing springback of the stamped article and an intermediate stamped article of the stamped article, the stamped article having a curved portion that bends along the length direction when viewed from above and straight portions extending from both ends of the curved portion.

[0017] Methods for solving problems

[0018] In the manufacturing method of the stamped article of the present invention, the stamped article is a U-shaped or hat-shaped cross-section having a top plate portion and a pair of longitudinal wall portions that are continuous from both ends of the top plate portion in the width direction via curved ridges, and has a curved portion that bends along the length direction when viewed from above and a straight portion that extends in a straight line from both ends of the curved portion in the length direction. The manufacturing method of the stamped article includes: a first forming step of stamping an intermediate formed article; and a second forming step of stamping the intermediate formed article into a stamped article of a target shape. The intermediate formed article has an intermediate curved portion corresponding to the curved portion of the target shape, a gradually changed area corresponding to the straight portion of the target shape, and an intermediate straight portion. The curved ridge in the intermediate curved portion is located at the same position as the curved ridge in the curved portion of the target shape or at a position inside the width direction of the curved ridge in the curved portion of the target shape. The curved ridge in the intermediate straight portion passes through the curved ridge in the gradually changed area and is located outside the width direction of the curved ridge in the straight portion of the target shape.

[0019] The intermediate formed article of the present invention is an intermediate formed article of a stamped article. The stamped article has a U-shaped or hat-shaped cross-section shape having a top plate portion and a pair of longitudinal wall portions that are continuous from both ends of the top plate portion in the width direction via curved ridges. It also has a curved portion that bends along the length direction when viewed from above and a straight portion that extends in a straight line from both ends of the curved portion in the length direction. The intermediate formed article has an intermediate curved portion corresponding to the curved portion of the target shape, a gradient section corresponding to the straight portion of the target shape, and an intermediate straight portion. The curved ridge in the intermediate curved portion is located at the same position as the curved ridge in the curved portion of the target shape or at a position inside the width direction of the curved ridge in the curved portion of the target shape. The curved ridge in the intermediate straight portion passes through the curved ridge of the gradient section and is located outside the width direction of the curved ridge in the straight portion of the target shape.

[0020] Invention Effects

[0021] In this invention, springback of top-view camber, wall opening, and twisting in stamped products with a hat-shaped or guilloché cross-section and having a curved portion that bends along the length direction when viewed from above and a straight portion that extends in a straight line from both ends of the curved portion can be suppressed, thereby ensuring dimensional accuracy. Attached Figure Description

[0022] Figure 1 The figures illustrate the manufacturing method of the stamped article according to this embodiment ((a) a stamped article with an intermediate shape, (b) a stamped article with a target shape).

[0023] Figure 2 This is a diagram illustrating an example of the manufacturing method of the stamped article in this embodiment and an example of the stamping die used in the first forming process and the stamping die used in the second forming process.

[0024] Figure 3 It is a diagram showing the stress distribution at the bottom dead center of a stamped part formed in a single process using conventional methods.

[0025] Figure 4 This is a diagram showing the stress distribution at the bottom dead center of a stamped article formed by the stamping manufacturing method of this embodiment.

[0026] Figure 5 It is a graph showing the offset and gradient of the intermediate molded article formed by stamping in the first forming process in the embodiment.

[0027] Figure 6 This is a diagram showing a stamped article, which is the subject of manufacture in the present invention and embodiments, and has a curved portion that bends along the length direction when viewed from above.

[0028] Figure 7 This diagram illustrates the springback, i.e., top-view camber springback, wall opening, and twisting, that occurs in the stamped product being formed in this invention. Detailed Implementation

[0029] Figure 6 This illustrates an example of a stamped article 20, which is the object of manufacture in this invention. The stamped article 20 has a hat-shaped cross-section having a top plate portion 21, a pair of longitudinal wall portions 25, and a flange portion 27. The pair of longitudinal wall portions 25 are continuous from both ends of the top plate portion 21 in the width direction via curved ridges 23, and the flange portion 27 is continuous from the lower end of each longitudinal wall portion 25. Furthermore, the stamped article 20 includes a curved portion 20A that bends along the length direction when viewed from above, and a straight portion 20B that extends linearly from both ends of the curved portion 20A in the length direction. Hereinafter, embodiments of the present invention will be described using the stamped article 20 as the object of manufacture. Figure 6 The values ​​shown are recorded to indicate the specific dimensions of the stamped article 20 to be manufactured in the embodiments described later, and do not limit the size or shape of the stamped article to be manufactured in this invention.

[0030] The method for manufacturing a stamped article according to an embodiment of the present invention includes: stamping. Figure 1 The first forming process of the intermediate molded article 10 shown in (a) involves stamping the intermediate molded article 10 into... Figure 1 The second forming process of the stamped article 20 with the target shape shown in (b).

[0031] The intermediate molded article 10 has a hat-shaped cross-sectional shape, having an intermediate top plate portion 11, a pair of intermediate longitudinal wall portions 15 that are continuous from both ends of the intermediate top plate portion 11 in the width direction via curved ridges 13, and an intermediate flange portion 17 that is continuous from the lower end of each intermediate longitudinal wall portion 15. Furthermore, the intermediate molded article 10 has an intermediate curved portion 10A corresponding to the target shape's curved portion 20A, a gradient section 10B1 corresponding to the target shape's straight portion 20B, and an intermediate straight portion 10B2. The gradient section 10B1 refers to the section that gradually expands outward in the width direction from both ends of the intermediate curved portion 10A in the length direction to the intermediate straight portion 10B2.

[0032] The intermediate curved portion 10A corresponding to the curved portion 20A of the target shape means that, in the second forming process, the intermediate curved portion 10A becomes the curved portion 20A of the target shape. Similarly, the gradient section 10B1 and the intermediate straight portion 10B2 corresponding to the straight portion 20B of the target shape means that, in the second forming process, the gradient section 10B1 and the intermediate straight portion 10B2 become the straight portion 20B of the target shape.

[0033] When viewed from above, the curved ridge 13a in the intermediate curved portion 10A is located inside the width direction compared to the curved ridge 23 in the curved portion 20A of the target shape. Furthermore, when viewed from above, the curved ridge 13b2 in the intermediate straight portion 10B2, via the curved ridge 13b1 of the gradient section 10B1, is located outside the width direction compared to the curved ridge 23 in the curved portion 20A of the target shape. Also, when viewed from above, the curved ridge 13b1 in the gradient section 10B1 gradually widens outwards in the width direction from the curved ridge 13a in the intermediate curved portion 10A toward the curved ridge 13b2 in the intermediate straight portion 10B2.

[0034] Thus, compared to the curved edge 23 of the stamped product 20 of the target shape, the curved edge 13 of the intermediate molded product 10 is offset inward and outward in the width direction. Therefore, in plan view, the intermediate curved portion 10A has a shape that necks inward in the width direction. Furthermore, in the intermediate molded product 10, the intermediate longitudinal wall portion 15 on the inner side of the curve is formed by the deformation of the stretch flange, and the intermediate longitudinal wall portion 15 on the outer side of the curve is formed by the deformation of the shrinkage flange. The inner side of the curve refers to the side that is the same as the center of curvature of the curve when viewed from above, and the outer side of the curve refers to the side that is opposite to the center of curvature of the curve when viewed from above.

[0035] In the first forming process, for example, it is possible to use Figure 2The stamping die 110 shown in (a) stamps an intermediate formed article 10. The stamping die 110 includes a punch 111, a die 113, and a blank holder 115. The punch 111 has: a punch-side intermediate curved section forming section 111A, forming an intermediate curved section 10A; a punch-side gradient section forming section 111B1, forming a gradient section 10B1; and a punch-side intermediate straight section forming section 111B2, forming an intermediate straight section 10B2. The die 113 includes: a die-side intermediate bending portion forming portion 113A, which cooperates with the punch-side intermediate bending portion forming portion 111A to form an intermediate bending portion 10A; a die-side gradient section forming portion 113B1, which cooperates with the punch-side gradient section forming portion 111B1 to form a gradient section 10B1; and a die-side intermediate straight portion forming portion 113B2, which cooperates with the punch-side intermediate straight portion forming portion 111B2 to form an intermediate straight portion 10B2. Furthermore, in the first forming process, while the blank is being pressed by the punch 111 and the pressure plate 115, the die 113 is moved relative to the punch 111 to stamp and form an intermediate molded product 10.

[0036] Additionally, in the second forming process, for example, it is possible to use Figure 2 The stamping die 120 shown in (b) stamps and forms a stamped product 20 of the target shape. The stamping die 120 includes a punch 121, a die 123, and a pressure plate 125. The punch 121 has a punch-side curved portion forming portion 121A for forming a curved portion 20A and a punch-side straight portion forming portion 121B for forming a straight portion 20B. The die 123 has a die-side curved portion forming portion 123A for forming a curved portion 20A in cooperation with the punch-side curved portion forming portion 121A and a die-side straight portion forming portion 123B for forming a straight portion 20B in cooperation with the punch-side straight portion forming portion 121B. Furthermore, in the second forming process, while the intermediate top plate portion 11 of the intermediate product 10 is pressed by the punch 121 and the pressure plate 125, the die 123 is moved relative to the punch 121 to stamp the intermediate product 10 into a stamped product 20 of the target shape.

[0037] based on Figure 3 and Figure 4 The stress distribution shown explains why springback can be suppressed in the stamped article 20 manufactured by the stamping article manufacturing method of this embodiment.

[0038] Figure 3 This refers to the distribution of stress along the length at the bottom dead center of the stamped part 20, which was formed in a previous stamping process. Figure 4 This refers to the stress distribution along the length of the stamped product 20 formed in the first and second forming processes of this embodiment, specifically the stress distribution at the bottom dead center of the stamping process. Figure 3 and Figure 4In the diagram, positive stress values ​​represent tensile stress, and negative stress values ​​represent compressive stress. Additionally, the X-axis represents the length direction, the Y-axis represents the width direction, and the Z-axis represents the stamping direction.

[0039] In a previous process, the stamped part 20 produced by stamping generates tensile stress in the longitudinal wall portion 25a on the stretch flange side (bent inner side). Figure 3 (b) and the compressive stress of the longitudinal wall portion 25b on the shrink flange side (bending outer side). Figure 3 The stress difference of (a)).

[0040] Therefore, when the stamped part 20 is demolded from the stamping die, as Figure 3 As shown in (c), a bending moment is generated due to the stress difference between the longitudinal wall portion 25a on the tension flange side and the longitudinal wall portion 25b on the contraction flange side, resulting in... Figure 7 The camber rebound shown in (a) is a top-view image. Furthermore, the bending moment differs in magnitude between the curved section 20A and the straight section 20B, thus also becoming... Figure 7 The main cause of the twisting springback shown in (c) is the plan view camber springback and twisting springback of the stamped part 20. Therefore, in order to suppress the plan view camber springback and twisting springback, it is effective to reduce the tensile stress generated in the longitudinal wall portion 25a on the stretch flange side and the compressive stress generated in the longitudinal wall portion 25b on the shrink flange side.

[0041] In the second forming process of this embodiment, the intermediate longitudinal wall portion 15 on the shrinkage flange side (bending outer side) of the intermediate straight portion 10B2 undergoes shrinkage flange deformation following the first forming process. Conversely, the intermediate longitudinal wall portion 15 on the stretch flange side (bending inner side) undergoes stretch flange deformation following the first forming process. Therefore, in the straight portion 20B formed in the second forming process, as... Figure 3 and Figure 4 As shown, the longitudinal wall portion 25 generates stress equivalent to that of a conventional stamped product 20 formed in a single process without causing the curved edge 23 to deviate.

[0042] On the other hand, the intermediate curved portion 10A has a curved ridge 13a formed on both the shrink flange side and the stretch flange side, which is closer to the inside of the curved ridge 23 of the target shape in the width direction. Therefore, during the second forming process, as the intermediate curved portion 10A becomes the curved portion 20A of the target shape, the curved ridge 13a bends back in the opposite direction.

[0043] That is, in the second forming process, the longitudinal wall portion 25b on the shrinkage flange side (outer side of the bend) is subjected to the stretch flange deformation, while the longitudinal wall portion 25a on the stretch flange side (inner side of the bend) is subjected to the shrinkage flange deformation. Thus, as... Figure 4As shown, for the longitudinal wall portion 25b on the contraction flange side and the longitudinal wall portion 25a on the tension flange side in the bending portion 20A, the stresses of both are reversed or reduced (see reference). Figure 3 (b) and Figure 4 (b) is the region enclosed by the dashed ellipse.

[0044] Furthermore, the intermediate molded part 10 has a curved ridge 13b1 with a gradient section 10B1, thereby suppressing metal flow during the process of the intermediate curved part 10A becoming the curved part 20A of the target shape in the second molding process. Therefore, the material of the curved part 20A will not flow to the straight part 20B side, and the stress in the longitudinal wall part 25 of the curved part 20A can be effectively reversed or reduced.

[0045] As a result, the stress difference between the tensile stress of the longitudinal wall portion 25a on the tension flange side and the compressive stress of the longitudinal wall portion 25b on the contraction flange side can be reduced, thereby reducing the bending moment and suppressing the rebound of the camber and the rebound of the torsion.

[0046] According to the manufacturing method of the stamped article of this embodiment, the springback of the top view camber and the springback of the twist of the stamped article 20 can be suppressed, ensuring dimensional accuracy. Therefore, without using a stamping die with a cam mechanism to form ribs, the stress difference between the longitudinal wall portion 25b on the shrink flange side and the longitudinal wall portion 25a on the stretch flange side can be reduced. Furthermore, it can prevent the risk of cracking caused by forming ribs in the longitudinal wall portion 25, the increase in forming load, and the residue of de-beadmarks / flattened bead marks.

[0047] Furthermore, in this embodiment, the curved edge 13 of the intermediate formed article 10 is formed to be offset outward or inward in the width direction compared to the curved edge 23 of the target shape, so it is bent back to the shape of the curved edge 23 of the target shape in the second forming process. Therefore, for the stamped article 20 of the target shape, the bending moment induced in the wall-shrinking direction can also be suppressed ( Figure 7 (b)) The rebound effect.

[0048] The above description refers to a stamped article 20 with a hat-shaped cross-section. However, the present invention can also be applied to stamped articles with a U-shaped cross-section that do not have a flange.

[0049] In addition, Figure 1In the intermediate molded article 10 shown in (a), the bending ridge 13a of the intermediate curved portion 10A is located inside the bending ridge 23 of the target shape in the width direction. However, the bending ridge of the intermediate curved portion of the present invention may also be located at the same position as the bending ridge of the target shape. In this case, the bending ridge of the intermediate straight portion is also located outside the bending ridge in the width direction from both ends of the bending ridge of the intermediate curved portion via the bending ridge of the gradient section.

[0050] Even with such intermediate formed products, during the second forming process where the intermediate curved portion is formed into the target curved portion, the stress reversal between the longitudinal wall portion on the shrink flange side and the longitudinal wall portion on the stretch flange side can be effectively achieved, thus reducing the stress difference. This suppresses the springback of the top-view camber and the springback of the twist in the stamped product of the target shape. Furthermore, since the curved ridge of the intermediate straight portion bends back towards the curved ridge of the target shape, the springback of the wall opening at the straight portion can also be suppressed.

[0051] As described above, the present invention targets stamped articles with a U-shaped or hat-shaped cross-section, comprising a curved portion that bends along its length when viewed from above and a straight portion extending linearly from both ends of the straight portion along its length. In particular, the present invention is preferably applicable to the manufacture of long automotive parts. Examples of long automotive parts include the A-pillar upper, front side member, and rear side member.

[0052] [Example]

[0053] Since an analysis was conducted to verify the effectiveness of the present invention, it will be described below. In the embodiment, stamping was performed using two processes: a first forming process and a second forming process as described in the foregoing embodiments. Figure 6 The forming analysis and springback analysis of the stamped product 20 with the hat-shaped cross-section shown.

[0054] The stamped part 20 is designed to have a length of 1000 mm in the longitudinal direction, and the radius of curvature R of the bent part 20A is 600 mm. Figure 5 As shown in the diagram (R), the width of the top plate portion 21 is 80 mm (= W), the forming height is 80 mm, and the bending angle of the bent portion 20A is 19.2°. Figure 5(θ shown in the figure). Furthermore, the stamped product 20 is configured such that the radius of curvature R of the curved edge 23 is 10 mm, the bending angle is 120°, the radius of curvature R of the die shoulder 29 connecting the longitudinal wall portion 25 and the flange portion 27 is 10 mm, the bending angle is 120°, and the width of the flange portion 27 is 40 mm. When stamping the stamped product 20, a high-strength steel sheet with a tensile strength of 1470 MPa and a thickness of 1.4 mm is used as the blank. Table 1 shows the mechanical property values ​​of the high-strength steel sheet used for the blank.

[0055] [Table 1]

[0056] In the forming analysis, both the first and second forming processes are set as pad foaming. Figure 2 The stamping die 110 (first forming process) shown in (a) and Figure 2 The stamping die 120 shown in (b) is for the second forming process. In both the first and second forming processes, the pressure of the blank holder is 50 tonf.

[0057] like Figure 1 As shown in (a), the intermediate molded article 10 has an intermediate curved portion 10A corresponding to the curved portion 20A of the target shape, and a gradient section 10B1 and an intermediate straight portion 10B2 corresponding to the straight portion 20B of the target shape. Furthermore, as an example of the invention, the curved ridge 13 in the intermediate curved portion 10A is located at the same position as the curved ridge 23 of the curved portion 20A of the target shape, or is located inside in the width direction. Moreover, the curved ridge 13b in the intermediate straight portion 10B2 is located outside in the width direction compared to the curved ridge 23 of the straight portion 20B of the target shape, via the curved ridge 13b of the gradient section 10B1.

[0058] like Figure 5 As shown, the offset of the curved edge 13b2 in the middle straight section 10B2 is set as Wa, and the offset of the curved edge 13a in the middle curved section 10A is set as Wb. Figure 5 It is a diagram showing the intermediate formed product 10 overlapping with the stamped formed product 20 of the target shape. The offsets Wa and Wb are set to positive when they are outside the target shape in the width direction and negative when they are inside the target shape in the width direction.

[0059] Furthermore, in the invention examples, for Figure 5 The length of the gradient interval 10B1 (hereinafter referred to as "gradient H") in the intermediate molded article 10 shown is modified in various ways to stamp the article 20 into the target shape.

[0060] In the stamped product 20, as described above Figure 7As shown, springback results in top-view camber springback, wall opening, and twisting. Therefore, the top-view camber springback, wall opening, and twisting are calculated as the springback amount of the stamped product 20.

[0061] The top-view camber springback is defined as the amount of movement at the front end of the stamped product 20 in a direction orthogonal to the length direction. The wall opening is defined as the change in the angle between the top plate portion 21 at the center of the stamped product 20 in the length direction and the longitudinal wall portion 25. The torsion is defined as the change in the angle between the top plate portion 21 at the center of the stamped product 20 in the length direction and the top plate portions 21 at both ends of the length direction.

[0062] Furthermore, in this embodiment, the wrinkles of the stamped article 20, which is stamped into the target shape, are determined. The wrinkles are calculated based on the sheet thickness and curvature during the stamping process of the stamped article 20.

[0063] Furthermore, as a comparison, a conventional example is used where the bending edges are stamped into the target shape in a single process without any deviation (Wa=0, Wb=0). Additionally, a comparative example is used where the bending edges of the intermediate straight portion and intermediate curved portion of the intermediate formed article stamped in the first forming process are offset outward in the width direction (Wa>0, Wb>0) or inward in the width direction (Wa<0, Wb<0) compared to the bending edges 23 of the target shape. Then, forming analysis and springback analysis are performed on both the conventional example and the comparative example, and the springback amount and wrinkles are determined in the same manner as in the inventive example.

[0064] Table 2 shows the offset and gradual change of the intermediate molded article 10, the top view camber springback, wall opening and twist, and the wrinkle results of the stamped article 20 in the existing examples, comparative examples and inventive examples.

[0065] [Table 2]

[0066] In Table 2, No. 1 is a prior art example, No. 2 and No. 3 are comparative examples, and No. 4 to No. 11 are inventive examples. The top view camber rebound, wall opening and twist, and wrinkle results of the comparative examples and inventive examples are expressed as ratios relative to the results of the prior art examples.

[0067] In Comparative Example No. 2, both the curved edges of the straight section and the curved sections of the middle section are offset outward in the width direction from the target shape (Wa = 20 mm, Wb = 20 mm), making the gradient H = 0 mm. The wall opening is significantly reduced to 0.20 compared to the existing example, the top-view camber rebound is 0.68, which, although reduced compared to the existing example, remains, and the twist is worse at 1.88. Furthermore, the wrinkles are 0.69, which is better than the existing example.

[0068] In Comparative Example No. 3, both the curved edges of the straight section and the curved edges of the curved section in the middle are offset inward in the width direction compared to the target shape (Wa = -20mm, Wb = -20mm), making the gradient H = 0mm. The wall opening is 0.30, and the twist is 0.38, which are significantly reduced compared to existing examples, but the top-view camber rebound is 0.67, which remains. In addition, the wrinkle is 0.79, which is better than existing examples.

[0069] In Inventive Example No. 4, the offset Wa of the curved edge 13b of the middle straight section 10B2 is set to 20mm, the offset Wb of the curved edge 13a of the middle curved section 10A is set to -20mm, and the gradient is set to H = 80mm. The top-view camber rebound is 0.01, the wall opening is 0.26, and the twist is 0.28, all of which are better than the existing examples and comparative examples. However, the wrinkle is 1.79, which is worse than the comparative examples No. 2 and No. 3.

[0070] Compared to Invention No. 4, the absolute values ​​of offsets Wa and Wb in Invention No. 5 are reduced, set to Wa = 15mm and Wb = -15mm. The top-view camber rebound is 0.14, the wall opening is 0.19, and the twist is 0.41, all of which are good. In addition, the wrinkle is 1.57, which is reduced compared to Invention No. 4.

[0071] Compared to No. 5, the absolute values ​​of the offsets Wa and Wb in Invention Example No. 6 are further reduced, with Wa = 10 mm and Wb = -10 mm. The top-view camber springback is 0.33, the wall opening is 0.22, and the twist is 0.47, all of which are good. In addition, the wrinkle is 1.50, which is worse than the existing example, but less than that of Invention Example No. 5, and is within an acceptable range if spot welding of the stamped product 20 is considered.

[0072] In Invention Example No. 7, the curved ridge 13a of the intermediate curved portion 10A is positioned at the same location as the target shape (Wb = 0 mm), and the curved ridge 13b of the intermediate straight portion 10B2 is offset outward in the width direction from the target shape (Wb = 20 mm). The top-view camber rebound is 0.40, and the wall opening is 0.45, which is better than the prior art. In addition, the twist is 1.02, the same as the prior art. Furthermore, the wrinkles are 1.36, which is worse than the prior art, but within an acceptable range, and is reduced compared to Invention Example No. 4, which has an equal offset Wb.

[0073] Invention example No. 8 is an example where the offsets Wa and Wb are the same as in invention example No. 4, but a gradual change is added and H is set to 150 mm. The top-view camber rebound is 0.09, the wall opening is 0.24, and the twist is 0.08, all of which are good. In addition, the wrinkle is 1.36, which is worse than the existing example, but within the acceptable range, and is reduced compared to invention examples No. 4 and No. 5.

[0074] In Invention Example No. 9, the gradual change is increased compared to No. 8, resulting in H = 200m. The top-view camber rebound is 0.16, the wall opening is 0.25, and the twist is -0.11, all of which are good. In addition, the wrinkle is 1.29, which is worse than the existing example, but within the acceptable range, and is reduced compared to Invention Example No. 8.

[0075] In Invention Example No. 10, the gradient variable is further increased compared to No. 9, with H = 250 mm. The top-view camber rebound is 0.26, the wall opening is 0.32, and the torsion is -0.08, all of which are good. In addition, the wrinkle is 0.86, which is reduced compared to existing examples.

[0076] According to the results of No.4 to No.6, reducing the offsets Wa and Wb reduces the suppression effect on camber rebound and twisting when viewed from above. Furthermore, it is found that No.5, with an offset of Wa = 15mm and Wb = -15mm, exhibits less wrinkling compared to No.4, with Wa = 20mm and Wb = -20mm. Therefore, to suppress the increase in wrinkles while reducing camber rebound when viewed from above, it is preferable to have Wa = 15mm and Wb = -15mm.

[0077] Furthermore, according to the results of No. 7 to No. 10, a larger gradient variable H is more effective in suppressing the increase of wrinkles, but the effect of reducing the camber rebound in the top view is smaller. On the other hand, it has no significant effect on distortion. Therefore, it can be considered that, in order to balance the suppression of camber rebound in the top view and wrinkles, the gradient variable of the gradient range 10B1 is preferably between H = 80mm and 150mm.

[0078] Therefore, as conditions for suppressing top-view camber rebound and torsion rebound, as well as wrinkles, an example was set as Invention Example No. 11, with offsets of Wa = 15mm, Wb = -15mm, and gradient of H = 100mm. The top-view camber rebound, torsion, and wrinkles were calculated. The results showed that the top-view camber rebound was 0.19, the wall opening was 0.20, and the torsion was 0.26, all significantly lower than existing examples. Furthermore, the wrinkle value was 1.43, which, although larger than existing examples, was lower than Invention Examples No. 4 to No. 6.

[0079] The results of the invention examples shown in Table 2 indicate that when the offsets Wa and Wb are large, i.e., when the difference between the width of the intermediate straight portion 10B2 and the width of the intermediate curved portion 10A is large, the dimensional accuracy of the stamped product 20 is greatly improved. On the other hand, when the gradient of the expansion trend of the width of the transition interval 10B1 from the intermediate curved portion 10A to the intermediate straight portion 10B is large, the wrinkles in the intermediate longitudinal wall portion 15 of the transition interval 10B1 will worsen. Therefore, it can be seen that there is an appropriate range for the offsets Wa and Wb. Furthermore, when the gradient H of the transition interval 10B1 is long, the reverse stress generated in the longitudinal wall portion 25 of the stamped product 20, which is stamped into the target shape, ( Figure 4 The stress at the inner longitudinal wall portion 25a of the bend and the stress at the outer longitudinal wall portion 25b of the bend extend towards the straight portion 20B, thus reducing the suppression effect of the camber rebound when viewed from above. Based on this, it can be concluded that there is also an appropriate range for the gradient variable H of the gradient interval 10B1.

[0080] Based on the results of No. 6, No. 8 to No. 11, which exhibit good top-view camber return, wall opening, twist, and wrinkles, if the preferred ranges of the offsets Wa and Wb and the gradient H in the intermediate formed part 10 are generalized, the preferred ranges for the offsets Wa and Wb are 0.08 ≤ Wa / H ≤ 0.15 and -0.15 ≤ Wb / H ≤ -0.08, respectively, and the preferred range for the gradient H is 0.40 ≤ H / L ≤ 1.24. In generalizing the preferred ranges, the gradient H in the gradient interval 10B1 is used for the offsets Wa and Wb, and the length L of the bend along the curved portion 20A (refer to...) is used for the gradient H. Figure 5 ).

[0081] If the size of the stamped part of the target shape increases, the preferred offset and gradient also increase, and vice versa. Therefore, by setting the offset and gradient of the intermediate part within the generalized preferred range as described above, regardless of the size of the stamped part of the target shape, it is possible to suppress the increase of wrinkles while suppressing springback (arch springback, wall opening, and twisting when viewed from above).

[0082] Industrial utilization potential

[0083] According to the present invention, a method for manufacturing a stamped article and an intermediate stamped article thereof can be provided, thereby improving dimensional accuracy by suppressing springback of a stamped article having a curved portion that bends along the length direction in plan view and a straight portion extending from both ends of the curved portion.

[0084] Explanation of reference numerals in the attached figures

[0085] 10 Intermediate molded products

[0086] 10A intermediate bend

[0087] 10B1 Gradient Range

[0088] 10B2 Middle Straight Section

[0089] 11. Middle Top Plate

[0090] 13 curved edges

[0091] 13a Curved edge

[0092] 13b1 curved edge

[0093] 13b2 curved edge

[0094] 15. Intermediate longitudinal wall section

[0095] 17. Middle flange portion

[0096] 20 stamped parts

[0097] 20A Bending Section

[0098] 20B Straight Section

[0099] 21 Top Plate Section

[0100] 23 Curved edge

[0101] 25 Longitudinal Wall Section

[0102] 25a Longitudinal Wall

[0103] 25b longitudinal wall section

[0104] 27 Flange portion

[0105] 29 Stamping Die Shoulder

[0106] 110 stamping die

[0107] 111 punch

[0108] 111A punch side middle bending section forming part

[0109] 111B1 Punch Side Gradient Section Forming Part

[0110] 111B2 punch side middle straight section forming part

[0111] 113 stamping die

[0112] 113A Die Side Middle Bending Section Forming Section

[0113] 113B1 Die Side Gradient Section Forming Part

[0114] 113B2 die side center straight section forming part

[0115] 115 pressure plate

[0116] 120 stamping die

[0117] 121 punch

[0118] 121A punch side bending section forming part

[0119] 121B punch side straight section forming part

[0120] 123 Die

[0121] 123A Die Side Bending Forming Section

[0122] 123B die side straight section forming part

[0123] 125 pressure plate.

Claims

1. A method for manufacturing a stamped article, said stamped article having a U-shaped or hat-shaped cross-section having a top plate portion and a pair of longitudinal wall portions continuous from both ends of the top plate portion in the width direction via curved ridges, and having a curved portion that bends along the length direction when viewed from above and a straight portion extending linearly from both ends of the curved portion in the length direction, wherein, The method for manufacturing the stamped product includes: The first forming process of stamping intermediate formed products; and The second forming process involves stamping the intermediate molded article into a stamped article of the target shape. The intermediate molded article has an intermediate curved portion corresponding to the curved portion of the target shape and a gradient section and an intermediate straight portion corresponding to the straight portion of the target shape. The curved edge in the intermediate curved portion is located at the same position as the curved edge in the curved portion of the target shape, or at a position inside the width direction of the curved edge in the curved portion of the target shape. The curved edge in the middle straight section passes through the curved edge in the gradient section and is located on the outer side in the width direction than the curved edge in the straight section of the target shape.

2. An intermediate formed article, which is an intermediate formed article of a stamped article, wherein the stamped article has a U-shaped or hat-shaped cross-section having a top plate portion and a pair of longitudinal wall portions that are continuous from both ends of the top plate portion in the width direction via curved ridges, and has a curved portion that bends along the length direction when viewed from above and a straight portion that extends in a straight line from both ends of the curved portion in the length direction, wherein, The intermediate molded article has an intermediate curved portion corresponding to the curved portion of the target shape and a gradient section and an intermediate straight portion corresponding to the straight portion of the target shape. The curved edge in the intermediate curved portion is located at the same position as the curved edge in the curved portion of the target shape, or at a position inside the width direction of the curved edge in the curved portion of the target shape. The curved edge in the middle straight section passes through the curved edge in the gradient section and is located on the outer side in the width direction than the curved edge in the straight section of the target shape.

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