Manufacturing method for press-formed products

Abstract

A method for manufacturing a press-formed product is a method for manufacturing a press-formed product obtained by press-forming a metal sheet, comprising: a first pressing step of press-forming an intermediate molded product having a first bend and an intermediate bend that is continuous with the first bend and has a different radius of curvature from the first bend, with the first bend or the intermediate bend positioned at its end; and a second pressing step of bending the intermediate bend into a second bend and press-forming the intermediate molded product into the press-formed product.

Description

Technical Field

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

Background Art

[0002] There is a press forming method that suppresses wall warpage of the vertical wall portion due to springback of a press-formed product having a top plate portion, a vertical wall portion, and a flange portion (see, for example, Japanese Patent No. 7047890).

[0003] Further, there is a press forming method for forming a press-formed product, which has a top plate portion, a vertical wall portion continuous from the top plate portion, and a flange portion continuous from the vertical wall portion via a ridge portion, and at least the flange portion is convexly or concavely curved in the height direction, into a target shape (see, for example, Japanese Patent No. 6841271).

[0004] Furthermore, there is a method for manufacturing a press-formed product, in which a top plate portion and a flange portion are continuous in the width direction via a side wall portion, and the metal plate is press-formed into a product shape having a hat-shaped cross section in which the top plate portion and the flange portion are convexly curved toward the top plate portion side along the longitudinal direction (see, for example, Japanese Patent No. 6504130).

[0005] Furthermore, in a metal plate press forming process that reaches the final press-formed product shape through a plurality of press forming steps, a portion where residual tensile stress occurs near a ridge line having a predetermined radius of curvature in the formed shape is press-formed in the preceding step of the plurality of press forming steps using a die with a radius of curvature 1 mm or more smaller than the final shape of that portion (see, for example, Japanese Patent No. 4879588).

Summary of Invention

Problems to be Solved by the Invention

[0006] Incidentally, in press-formed products made by press-forming metal sheets, for example, residual stress tends to be high in the bent areas. In particular, at the edges of press-formed products, stress is generated, for example, during the trimming (cutting) process of the metal sheet, so the residual stress at the edges of the bent areas tends to be relatively high, which can cause delayed fracture at the edges of the bent areas.

[0007] This disclosure aims to suppress delayed fracture at the bent portion of the end portion of a press-formed product obtained by press-forming a metal sheet. [Means for solving the problem]

[0008] The method for manufacturing a press-formed product according to the first embodiment is: In a method for manufacturing press-formed products, in which a metal sheet is press-formed to produce a press-formed product, A first pressing step involves press-forming an intermediate molded product having a first bend and an intermediate bend that is continuous with the first bend and has a different radius of curvature from the first bend, with the first bend or the intermediate bend positioned at the end. A second pressing step in which the intermediate bend is bent into a second bend, and the intermediate molded product is press-formed into the press-formed product, It is equipped with.

[0009] According to the method for manufacturing a press-formed product according to the first embodiment, in the first pressing step, an intermediate molded product is press-formed having a first bend and an intermediate bend that is continuous with the first bend and has a different radius of curvature from the first bend, with the first bend or the intermediate bend positioned at the end.

[0010] Next, in the second pressing process, the intermediate bend is bent into the second bend, and the intermediate molded product is press-formed into a press-formed product.

[0011] Here, if the radius of curvature of the intermediate bend is smaller than the radius of curvature of the second bend, the intermediate bend is compressed in the neutral axis direction (circumferential direction of the second bend) during the second pressing process. At this time, compressive stress is generated in the second bend and the first bend that is continuous with the second bend, so that the residual stress in the first and second bends is reduced.

[0012] On the other hand, if the radius of curvature of the intermediate bend is greater than that of the second bend, the intermediate bend is stretched in the neutral axis direction during the second pressing process. In this case, tensile stress is generated in the second bend and the first bend that is continuous with the second bend, thus reducing the residual stress in the first and second bends.

[0013] Therefore, by positioning a first bend or intermediate bend at the end of the intermediate molded product in the first pressing process, and then bending the intermediate bend into a second bend in the second pressing process, the residual stress in the first or second bend positioned at the end of the press-formed product is reduced. As a result, delayed fracture of the bend (first or second bend) at the end of the press-formed product can be suppressed.

[0014] Furthermore, in the method for manufacturing press-formed products according to this disclosure, in the bending deformation of the intermediate bend in the second pressing step, whether compressive stress or tensile stress is predominantly generated in the intermediate bend and the first bend continuous therewith may vary depending on the relationship between the radius of curvature of the intermediate bend and the second bend after final forming.

[0015] However, in all cases, the common point is that the stress difference between the outer and inner sides of the second bend is reduced, and the technical significance of the manufacturing method according to this disclosure lies in the fact that the residual stress in the second bend is reduced by this reduction in stress difference.

[0016] Preferably, the second bent portion is curved convexly in the same direction as the first bent portion. However, this configuration is only one embodiment, and the essence of the method for manufacturing a press-formed product according to this disclosure is not limited thereto. The technical significance of the method for manufacturing a press-formed product according to this disclosure lies in the fact that by bending the intermediate bent portion formed in the first pressing step into a second bent portion in the second pressing step, the stress difference between the outer and inner sides of the bend of the second bent portion is reduced, and as a result, the residual stress of the second bent portion and the first bent portion continuous with the second bend portion is reduced.

[0017] Furthermore, the shape, radius of curvature relationship, and bending direction of the bent portions (first bend, intermediate bend, second bend) described in the manufacturing method of press-formed products according to this disclosure are examples in each embodiment, and the technology according to this disclosure is not limited to these specific shapes or conditions.

[0018] The method for manufacturing a press-formed product according to the second embodiment is, in the method for manufacturing a press-formed product according to the first embodiment, In the first pressing step, the intermediate bent portion is formed on the end of the intermediate molded product.

[0019] According to the method for manufacturing a press-formed product according to the second embodiment, in the first pressing step, an intermediate bend is formed at the end of the intermediate molded product.

[0020] In this way, an intermediate bend is formed at the end of the intermediate molded product in the first pressing process, and then in the second pressing process, the intermediate bend is bent into a second bend. This reduces the residual stress in the second bend located at the end of the press-formed product. Therefore, delayed fracture of the bend (second bend) at the end of the press-formed product can be suppressed.

[0021] The method for manufacturing a press-formed product according to the third embodiment is, in the method for manufacturing a press-formed product according to the first embodiment, In the first pressing step, the first bent portion is formed on the end of the intermediate molded product.

[0022] According to the method for manufacturing a press-formed product according to the third aspect, in the first press step, a first bent portion is formed at an end portion of an intermediate formed product.

[0023] Thereby, in the second press step, by bending and deforming the intermediate bent portion into a second bent portion, the residual stress of the first bent portion formed at the end portion of the press-formed product is reduced. Therefore, delayed fracture of the bent portion (first bent portion) at the end portion of the press-formed product can be suppressed.

[0024] The method for manufacturing a press-formed product according to the fourth aspect is the method for manufacturing a press-formed product according to the third aspect, wherein In the first press step, the first bent portion is formed at the end portion of the intermediate formed product, and the intermediate bent portion is formed on the end portion side of the intermediate formed product.

[0025] According to the method for manufacturing a press-formed product according to the fourth aspect, in the first press step, the first bent portion is formed at the end portion of the intermediate formed product, and the intermediate bent portion is formed on the end portion side of the intermediate formed product.

[0026] Here, when the intermediate bent portion is formed at the end portion of the intermediate formed product, in the second press step, when the intermediate bent portion is bent and deformed into the second bent portion, the peripheral portion of the intermediate bent portion in the intermediate formed product is not restrained by the die, and the deformation amount (compression amount or elongation amount) of the intermediate bent portion in the neutral axis direction may become small.

[0027] In contrast, in the present aspect, as described above, the first bent portion is formed at the end portion of the intermediate formed product, and the intermediate bent portion is formed on the end portion side of the intermediate formed product. Thereby, in the present aspect, when the intermediate bent portion is bent and deformed into the second bent portion in the second press step, the peripheral portion of the intermediate bent portion in the intermediate formed product is restrained by the die over the entire circumference. As a result, since the intermediate bent portion can be deformed in the neutral axis direction, the residual stress of the first bent portion can be further reduced.

[0028] Therefore, delayed fracture of the bent portion (first bent portion) at the end portion of the press-formed product can be suppressed.

[0029] The method for manufacturing a press-formed product according to the fifth embodiment is a method for manufacturing a press-formed product according to the third or fourth embodiment, The press-formed product has a cross-bend portion that intersects with the second bend portion and reaches the widthwise end or heightwise end of the press-formed product. In the first pressing step, the intersecting bend portion that intersects the intermediate bend portion is formed into the intermediate molded product.

[0030] According to the manufacturing method of a press-formed product according to the fifth embodiment, the press-formed product has a cross-bend portion that intersects with the second bend portion and reaches the widthwise end or heightwise end of the press-formed product. Then, in the first pressing step, the cross-bend portion that intersects with the intermediate bend portion and reaches the widthwise end or heightwise end of the press-formed product is formed into the intermediate molded product.

[0031] In press-formed products, residual stress tends to be high at the cross-bend sections. In particular, at the widthwise or heightwise ends of press-formed products reached by the cross-bend sections, stress is generated, for example, during the trimming (cutting) process of the metal sheet. As a result, the residual stress at the cross-bend sections tends to be relatively high, and these ends of the cross-bend sections can become the starting point (location of occurrence) of delayed fracture.

[0032] In contrast, in this embodiment, as described above, in the first pressing process, a cross-bend portion intersecting the intermediate bend portion is formed in the intermediate molded product. Then, in the second pressing process, the intermediate bend portion is bent into a second bend portion, thereby reducing the residual stress in the cross-bend portion intersecting the intermediate bend portion. Therefore, delayed fracture of the bend portion (cross-bend portion) can be suppressed at the widthwise end or heightwise end of the press-formed product reached by the cross-bend portion.

[0033] The method for manufacturing a press-formed product according to the sixth embodiment is a method for manufacturing a press-formed product according to any one of the first to fifth embodiments, In the first pressing process, the first bent portion and the intermediate bent portion are connected, and a gradually changing portion is formed in the intermediate molded product in which the radius of curvature changes gradually from the first bent portion toward the intermediate bent portion. In the second pressing step, the intermediate bend and the gradually deforming section are bent and deformed into the second bend, and the intermediate molded product is press-formed into the press-formed product.

[0034] According to the manufacturing method for press-formed products of the sixth embodiment, in the first pressing step, the first bent portion and the intermediate bent portion are connected, and a gradually changing portion in which the radius of curvature changes gradually from the first bent portion to the intermediate bent portion is formed into the intermediate molded product. Furthermore, in the second pressing step, the intermediate bent portion and the gradually changing portion are bent and deformed into a second bent portion, and the intermediate molded product is press-formed into a press-formed product.

[0035] By forming an intermediate molded product with a gradually changing radius of curvature, where the radius of curvature changes gradually from the first bend to the intermediate bend, the moldability of the intermediate bend can be improved.

[0036] The method for manufacturing a press-formed product according to the seventh aspect is a method for manufacturing a press-formed product according to any one of the first to sixth aspects, In the first pressing step, the intermediate bent portion, which curves convexly in the same direction as the first bent portion, is formed into the intermediate molded product.

[0037] According to the manufacturing method for press-formed products of the seventh embodiment, by curving the intermediate bend portion in a convex shape in the same direction as the first bend portion, the formability of the second bend portion can be improved in the second pressing step.

[0038] The method for manufacturing a press-formed product according to the eighth aspect is, in the method for manufacturing a press-formed product according to the seventh aspect, The radius of curvature of the intermediate bend is smaller than the radius of curvature of the second bend.

[0039] According to the manufacturing method for press-formed products according to the eighth embodiment, the radius of curvature of the intermediate bend is smaller than the radius of curvature of the second bend.

[0040] In this case, when the intermediate bend is bent into a second bend by the punch shoulder, if the radius of curvature of the intermediate bend is larger than the radius of curvature of the second bend, it becomes difficult to position the intermediate bend along the punch shoulder, for example.

[0041] In contrast, in this embodiment, as described above, the radius of curvature of the intermediate bend is smaller than the radius of curvature of the second bend. Therefore, for example, when the intermediate bend is bent into the second bend by the punch shoulder, it becomes easier to position the intermediate bend along the punch shoulder. Consequently, in this embodiment, the formability of the second bend by the punch shoulder can be improved.

[0042] The method for manufacturing a press-formed product according to the ninth aspect is a method for manufacturing a press-formed product according to any one of the first to eighth aspects, The press-formed product comprises a top plate portion, a side plate portion connected to the widthwise end of the top plate portion via a bent portion, and a flange portion connected to the heightwise end of the side plate portion via a bent portion. At least one of the bent portion on the top plate side and the bent portion on the flange side includes the first bent portion and the second bent portion.

[0043] According to the manufacturing method for press-formed products of the ninth embodiment, the press-formed product has a top plate portion, a side plate portion connected to the widthwise end of the top plate portion via a bent portion, and a flange portion connected to the heightwise end of the side plate portion via a bent portion. At least one of the bent portion on the top plate portion side and the bent portion on the flange portion side includes a first bent portion and a second bent portion.

[0044] Therefore, in this embodiment, delayed fracture occurring at the end of the press-formed product can be suppressed in at least one of the bent sections (first bend or second bend) connecting the top plate section and the side plate section, and the bent section (first bend or second bend) connecting the side plate section and the flange section.

[0045] The method for manufacturing a press-formed product according to the tenth embodiment is a method for manufacturing a press-formed product according to any one of the first to ninth embodiments, wherein the press-formed product has a tensile strength of 1300 MPa or more.

[0046] According to the manufacturing method for press-formed articles of the 10th embodiment, delayed fracture of the bent portion can be suppressed at the end of a press-formed article with a tensile strength of 1300 MPa or more. [Effects of the Invention]

[0047] According to this disclosure, delayed fracture of the bent portion can be suppressed at the end of a press-formed product obtained by press-forming a metal sheet. [Brief explanation of the drawing]

[0048] [Figure 1] This is a cross-sectional view showing a press-formed product manufactured by the method for manufacturing a press-formed product according to the first embodiment. [Figure 2] Figure 1 is a perspective view showing a portion of the press-formed product. [Figure 3] This is a perspective view corresponding to Figure 2, showing an intermediate molded product formed in the manufacturing process of a press-formed product according to the first embodiment. [Figure 4A] This is a cross-sectional view taken along line 4A-4A in Figure 3. [Figure 4B] This is a cross-sectional view taken along line 4B-4B in Figure 2. [Figure 5A] This is a cross-sectional view taken along the line 5A-5A in Figure 3. [Figure 5B] This is a cross-sectional view taken along the line 5B-5B in Figure 2. [Figure 6] This is a perspective view corresponding to Figure 2, showing an intermediate molded product formed in the manufacturing process of a press-formed product according to the second embodiment. [Figure 7A] This is a cross-sectional view taken along line 7A-7A in Figure 6. [Figure 7B] This is a cross-sectional view taken along line 7B-7B in Figure 2. [Figure 8A] This is a cross-sectional view taken along the line 8A-8A in Figure 6. [Figure 8B]This is a cross-sectional view taken along line 8B-8B in Figure 2. [Figure 9] This is a perspective view showing a press-formed product manufactured by the press-formed product manufacturing method according to the third embodiment. [Figure 10] Figure 9 is a side view of the press-formed product as seen from the width direction. [Figure 11] This is a perspective view corresponding to Figure 9, showing an intermediate molded product formed in the manufacturing process of a press-formed product according to the third embodiment. [Figure 12A] This is a cross-sectional view taken along the line 12A-12A in Figure 11. [Figure 12B] This is a cross-sectional view taken along line 12B-12B in Figure 9. [Figure 13A] This is a cross-sectional view taken along the line 13A-13A in Figure 11. [Figure 13B] This is a cross-sectional view taken along line 13B-13B in Figure 9. [Modes for carrying out the invention]

[0049] (First Embodiment) First, I will describe the first embodiment.

[0050] (Press-formed product) Figures 1 and 2 show a press-formed product 20 manufactured by the manufacturing method of a press-formed product according to this embodiment. The press-formed product 20 is manufactured by press-forming a metal sheet (blank) 10 that has been trimmed to a predetermined shape. This press-formed product 20 is used, for example, as an automobile part and is formed from steel sheets such as high-strength steel sheets and ultra-high-strength steel sheets with a tensile strength of 1300 MPa or more. The tensile strength can be measured by taking a tensile test specimen in accordance with JIS Z 2241:2011 from the top plate portion 22 of the press-formed product 20 and performing a tensile test in accordance with JIS Z 2241:2011. The tensile strength test specimen (tensile test specimen) is taken from the top plate portion 22 along the longitudinal direction of the press-formed product 20. The tensile strength is measured by taking a No. 5 test specimen, as specified in Annex B of JIS Z 2241:2011, from a position on the top plate portion 22 of the press-formed product 20 that is not affected by the edges, along the longitudinal direction, and performing a tensile test in accordance with JIS Z 2241:2011.

[0051] If a tensile test specimen cannot be taken from the top plate portion 22 of the press-formed product 20, the top plate portion 22 is cut, and the Vickers hardness (test force 0.5 kgf) is measured at five locations at 1 / 4 of the thickness direction on the obtained cut surface. The average value of the five measured Vickers hardnesses is converted to tensile strength based on SAE J417 (1983) and is taken as the tensile strength of the top plate portion 22. The Vickers hardness is determined as follows. First, a test specimen is cut from the center of the top plate portion 22, in a position unaffected by the edges, so that a cut surface perpendicular to the surface can be observed. The cut surface is wet-polished using #600 to #1500 silicon carbide sandpaper. Next, a mirror finish is achieved using a liquid in which diamond powder with a particle size of 1 to 6 μm is dispersed in a diluent such as alcohol or pure water, and this cut surface is used as the measurement surface. Next, the Vickers hardness is measured using a micro Vickers hardness tester with a load of 0.5 kgf at intervals of three times or more the indentation. The hardness (Vickers hardness) of the press-formed product 20 is, for example, 402 HV or higher.

[0052] The arrow X direction shown in each figure indicates the axial direction (longitudinal direction) of the press-formed product 20 (intermediate molded product 20M). The arrow Y direction shown in each figure indicates the width direction of the press-formed product 20 (intermediate molded product 20M). Furthermore, the arrow Z direction shown in each figure indicates the height direction of the press-formed product 20 (intermediate molded product 20M).

[0053] In this specification, unless otherwise specified, "end" refers to the end of the press-formed product 20 or the intermediate-formed product 20M in the axial direction (arrow X direction). On the other hand, when referring to the end in the width direction (arrow Y direction) or height direction (arrow Z direction), it shall be clearly indicated as "width direction end" or "height direction end".

[0054] The cross-sectional shape of the press-formed product 20 is, for example, a hat shape. This press-formed product 20 has a top plate portion 22, a pair of side plate portions (side wall portions) 24, and a pair of flange portions 26.

[0055] The top plate portion 22 is positioned along the width direction (arrow Y direction) of the press-formed product 20. A pair of side plate portions 24 are connected to both ends of the top plate portion 22 in the width direction (arrow Y direction) via bent portions 30. The pair of bent portions 30 extend in the axial direction (arrow X direction) of the press-formed product 20 and also extend to the axial ends 20E on both sides of the press-formed product 20.

[0056] Note that the axial direction of the press-formed product 20 is just one example of a predetermined direction.

[0057] A pair of side plate portions 24 extend from both ends in the width direction of the top plate portion 22 to one side in the height direction (arrow Z direction) of the press-formed product 20 via a pair of bent portions 30, and face each other in the width direction of the top plate portion 22. A pair of flange portions 26 are connected to the ends of the pair of side plate portions 24 opposite to the top plate portion 22 via bent portions 40. The pair of bent portions 40 extend in the axial direction of the press-formed product 20 and extend to both ends 20E in the axial direction of the press-formed product 20.

[0058] The pair of flange portions 26 extend from the height-direction ends of the pair of side plate portions 24 along the width direction of the press-formed product 20 to opposite sides. Other components, not shown, are joined to the width-direction ends of this pair of flange portions 26 by welding or other means.

[0059] (Method of manufacturing press-formed products) Next, an example of a method for manufacturing a press-formed product according to this embodiment will be described.

[0060] In this embodiment, a press-formed product 20 is manufactured by press-forming (pad bending) a metal sheet using a mold (second mold) (not shown) equipped with a punch, die, and pad. At this time, a pair of bent portions (punch shoulder bends) 30 are formed (bent) by the shoulder portion of the punch (punch shoulder). In addition, a pair of bent portions (die shoulder bends) 40 are formed (bent) by the shoulder portion of the die (die shoulder).

[0061] Furthermore, the press-formed product 20 (intermediate molded product 20M) may be manufactured not only by the pad bending molding described above, but also by other methods such as draw molding using a blank holder or foam molding without a blank holder.

[0062] As shown in Figure 2, residual stress tends to be high at each bent portion 30 and 40. In particular, residual stress is generated at the end portion 20E of the press-formed product 20 during the trimming (cutting) process of the metal plate 10. Therefore, the residual stress at each bent portion 30 and 40 tends to be relatively high at the end portion 20E of the press-formed product 20, and these ends 30E and 40E of the bent portions 30 and 40 may cause delayed fracture.

[0063] As a countermeasure, in this embodiment, in the first pressing process, the metal sheet 10 is press-formed into an intermediate molded product 20M (see Figure 3), and in the second pressing process, the intermediate molded product 20M is press-formed into a press-formed product 20. In other words, in this embodiment, in the second pressing process, the intermediate molded product 20M is restrked into the press-formed product 20. This reduces the residual stress in the bent portion 30 at the end 20E of the press-formed product 20, and suppresses delayed fracture of the end 30E of the bent portion 30.

[0064] The first and second pressing processes will be described in detail below. The method for suppressing delayed fracture of the end portion 40E of the bent portion 40 will be described later in the second embodiment.

[0065] Furthermore, for the sake of explanation, in the bent portion 30 of the press-formed product 20, the portion that is not restripped in the second pressing process is designated as the first bent portion 30A, and the portion that is restripped is designated as the second bent portion 30B.

[0066] (First pressing process) In the first pressing process, the metal sheet 10 is press-formed (pad-bent) using a first mold (intermediate mold) (not shown) equipped with a punch, die, and pad to form the intermediate molded product 20M shown in Figure 3. The intermediate molded product 20M differs from the press-formed product 20 in that it has an intermediate bend portion 32 and a gradually changing portion 34 that are restrked in the second pressing process. These intermediate bend portion 32 and gradually changing portion 34 are formed into the second bend portion 30B of the bend portion 30 in the second pressing process.

[0067] Furthermore, the configuration of the intermediate molded product 20M, other than the intermediate bend portion 32 and the gradually changing portion 34, is the same as that of the press-formed product 20. Therefore, the first mold used in the first pressing process differs from the second mold used in the second pressing process described later in the shape of the punch and die that form the intermediate bend portion 32 and the gradually changing portion 34, while the shape of the other parts is the same as that of the second mold.

[0068] The intermediate bend 32 is formed (bent) by the punch shoulder (punch shoulder) of the first die. The intermediate bend 32 is formed on one end 20E of the intermediate molded product 20M, along the axial direction (arrow X direction) of the intermediate molded product 20M. Note that one end 20E of the intermediate molded product 20M is an example of an end of the intermediate molded product 20M.

[0069] As shown in Figure 4A, the intermediate bend 32 is, for example, curved convexly in the same direction as the first bend 30A. The radius of curvature of this intermediate bend 32 is smaller than the radius of curvature of the first bend 30A. Furthermore, the radius of curvature of the intermediate bend 32 is, for example, constant in the longitudinal direction of the intermediate bend 32. In other words, the cross-sectional shape and size of the intermediate bend 32 are, for example, constant in the longitudinal direction of the intermediate bend 32.

[0070] Furthermore, the radius of curvature of the intermediate bend 32 is not limited to being constant in the longitudinal direction of the intermediate bend 32, but may vary.

[0071] Furthermore, the ratio of the radius of curvature of the intermediate bend 32 to the radius of curvature of the second bend 30B is preferably, for example, 0.3 or more and 0.7 or less. Here, the radius of curvature refers to the minimum radius of curvature of the curved portion on the inside of the bend, measured in a cross section perpendicular to the extending direction of the bend.

[0072] Here, if the radius of curvature of the intermediate bend 32 is excessively small compared to the radius of curvature of the second bend 30B, excessive plastic deformation is likely to occur in the intermediate bend 32 during the second pressing process, which may lead to a decrease in molding accuracy and variations in shape. On the other hand, if the radius of curvature of the intermediate bend 32 is excessively close to the radius of curvature of the second bend 30B, it may be difficult to ensure sufficient deformation in the neutral axis direction of the intermediate bend 32 during the second pressing process, which may reduce the effect of reducing the stress difference in the bend.

[0073] Therefore, in this embodiment, from the viewpoint of achieving both formability and residual stress reduction effect, it is preferable that the ratio of the radius of curvature of the intermediate bend portion 32 to the radius of curvature of the second bend portion 30B be 0.3 or more and 0.7 or less.

[0074] In this specification, "the direction of the neutral axis of the bend" refers to the direction corresponding to the circumferential direction of the bend, not the direction along the neutral axis.

[0075] As shown in Figure 3, the intermediate bend 32 is formed, for example, to be continuous with the first bend 30A and the intermediate molded product 20M in the axial direction (arrow X direction). The intermediate bend 32 is also connected to the first bend 30A via a gradual change section (section gradual change section) 34.

[0076] In this specification, "continuous" means not only when two parts are directly connected, but also when the two parts are connected via another part (for example, a variable section).

[0077] The gradually changing section 34 is curved convexly in the same direction as the first bending section 30A. Furthermore, the radius of curvature of the gradually changing section 34 gradually changes from the first bending section 30A towards the intermediate bending section 32. More specifically, the radius of curvature of the gradually changing section 34 increases from the intermediate bending section 32 towards the first bending section 30A. In other words, the radius of curvature of the gradually changing section 34 decreases from the first bending section 30A towards the intermediate bending section 32. This gradually changing section 34 connects the intermediate bending section 32 and the first bending section 30A in a smooth, continuous manner.

[0078] (Second pressing process) In the second pressing process, the intermediate bent portion 32 and the gradually deformed portion 34 are bent into a second bent portion 30B using a second mold (not shown) which includes a punch, die, and pad, thereby press-forming (restrike) the intermediate molded product 20M into a press-formed product 20.

[0079] Specifically, as shown in Figures 4A and 4B, the intermediate bend 32 is press-formed, for example, so that its radius of curvature is increased. As a result, the intermediate bend 32 is compressed in the direction of its neutral axis (circumferential direction of the second bend 30B, arrow R direction) and formed into the second bend 30B. Also, as shown in Figures 2 and 3, the end 32E of the intermediate bend 32 is formed into the end 30E of the second bend 30B (bend 30).

[0080] Furthermore, in the second pressing process, similar to the intermediate bending section 32, the gradually changing section 34 is press-formed (bent) so that its radius of curvature increases. As a result, the gradually changing section 34 is compressed in the direction of its neutral axis (the circumferential direction of the second bending section 30B) and formed into the second bending section 30B.

[0081] As shown in Figures 5A and 5B, in the second pressing process, the intermediate molded product 20M is press-formed in such a way that the radius of curvature of the first bent portion 30A does not change. This forms the bent portions 30 (first bent portion 30A and second bent portion 30B) that extend across both axial ends 20E of the press-formed product 20.

[0082] Furthermore, in this embodiment, as an example, in the second pressing step, the intermediate bending section 32 and the gradually changing section 34 are press-formed so that the radius of curvature of the second bending section 30B is the same as the radius of curvature of the first bending section 30A. However, in the second pressing step, the intermediate bending section 32 and the gradually changing section 34 may be press-formed so that the radius of curvature of the second bending section 30B is different from the radius of curvature of the first bending section 30A.

[0083] (effect) Next, the effects of the first embodiment will be described.

[0084] As described above, according to the manufacturing method of a press-formed product according to this embodiment, in the first pressing step, an intermediate molded product 20M having a first bent portion 30A and an intermediate bent portion 32 that is continuous with the first bent portion 30A and has a different radius of curvature from the first bent portion 30A is press-formed. In addition, the intermediate bent portion 32 is formed on one end 20E of the intermediate molded product 20M.

[0085] Next, in the second pressing process, the intermediate bend portion 32 is bent into a second bend portion 30B, and the intermediate molded product 20M is press-formed into a press-formed product 20. In other words, in the second pressing process, the second bend portion 30B is formed on one end 20E of the press-formed product 20.

[0086] Here, as shown in Figures 4A and 4B, the radius of curvature of the intermediate bend 32 is smaller than the radius of curvature of the first bend 30A (second bend 30B). In this case, during the second pressing process, the intermediate bend 32 is compressed in the direction of its neutral axis (arrow R direction). At this time, compressive stress P is generated in the intermediate bend 32, and the stress difference (compressive stress difference) between the outer and inner sides of the bend in the second bend 30B is reduced, thereby reducing the residual stress in the second bend 30B.

[0087] In this way, an intermediate bend 32 is formed at one end 20E of the intermediate molded product 20M in the first pressing process, and then in the second pressing process, the intermediate bend 32 is bent into a second bend 30B. This reduces the residual stress in the second bend 30B at one end 20E of the press-formed product 20. Therefore, delayed fracture of the bend 30 (second bend 30B) at one end 20E of the press-formed product 20 can be suppressed.

[0088] Furthermore, as shown in Figure 3, in the first pressing process, a gradually changing section 34 connecting the first bent section 30A and the intermediate bent section 32 is formed into the intermediate molded product 20M. The radius of curvature of the gradually changing section 34 gradually decreases as it moves from the first bent section 30A towards the intermediate bent section 32. By connecting the first bent section 30A and the intermediate bent section 32 via this gradually changing section 34, the moldability of the intermediate bent section 32 can be improved.

[0089] Furthermore, in the second pressing process, the gradually changing section 34 is bent into the second bending section 30B, thereby making the first bending section 30A and the second bending section 30B smoothly continuous.

[0090] Furthermore, by curving the intermediate bend 32 in a convex shape in the same direction as the first bend 30A, the formability of the second bend 30B can be improved in the second pressing process.

[0091] In this embodiment, during the first pressing process, an intermediate bent portion 32 and a gradually changing portion 34 are formed on the bent portion 30 of the intermediate molded product 20M. However, the intermediate bent portion 32 and the gradually changing portion 34 are not limited to the bent portion 30 of the intermediate molded product 20M; they may also be formed on the bent portion 40, or on the bent portions 30 and 40 respectively.

[0092] Furthermore, in this embodiment, the radius of curvature of the intermediate bend 32 is smaller than the radius of curvature of the first bend 30A (second bend 30B). However, the radius of curvature of the intermediate bend 32 may be larger than the radius of curvature of the first bend 30A (second bend 30B).

[0093] The second bent portion 30B is formed, for example, by bending and deforming the intermediate bent portion 32 with the punch shoulder. In this case, if the radius of curvature of the intermediate bent portion 32 is larger than the radius of curvature of the second bent portion 30B, it becomes difficult to position the intermediate bent portion 32 along the punch shoulder. Therefore, it is preferable that the radius of curvature of the intermediate bent portion 32 be smaller than the radius of curvature of the second bent portion 30B.

[0094] (Second embodiment) Next, a second embodiment will be described. In the second embodiment, components and the like that have the same configuration as in the first embodiment will be denoted by the same reference numerals, and their descriptions will be omitted as appropriate.

[0095] In the method for manufacturing a press-formed product according to the second embodiment, the residual stress of the bent portion 40 at one end 20E of the press-formed product 20 is reduced, thereby suppressing delayed fracture of the end 40E of the bent portion 40.

[0096] For the sake of explanation, in the bent portion 40 of the press-formed product 20, the portion that is not restripped in the second pressing process is referred to as the first bent portion 40A, and the portion that is restripped is referred to as the second bent portion 40B.

[0097] (First pressing process) Specifically, in the first pressing process, the metal sheet 10 is press-formed (pad-bent) using a first mold (intermediate mold) (not shown) equipped with a punch, die, and pad, thereby forming the intermediate molded product 20M shown in Figure 6. The intermediate molded product 20M differs from the press-formed product 20 in that it has an intermediate bend portion 42 and two gradual deformation portions 44 that are restrike in the second pressing process. These intermediate bend portion 42 and the two gradual deformation portions 44 are formed into a second bend portion 40B in the second pressing process.

[0098] Furthermore, the configuration of the intermediate molded product 20M, other than the intermediate bend portion 42 and the two gradual deformation portions 44, is the same as that of the press-formed product 20. Therefore, the first mold used in the first pressing process differs from the second mold used in the second pressing process described later in the shape of the punch and part of the die that form the intermediate bend portion 42 and the two gradual deformation portions 44, while the shape of the other parts is the same as that of the second mold.

[0099] Furthermore, similar to the first embodiment, the press-formed product 20 (intermediate molded product 20M) may be manufactured not only by pad bending, but also by, for example, draw forming using a blank holder or form forming without a blank holder.

[0100] In this embodiment, a first bend 40A is formed at one end 20E of the intermediate molded product 20M. Furthermore, an intermediate bend 42 is formed on the end 20E side of the intermediate molded product 20M, which is continuous with the first bend 40A in the axial direction of the intermediate molded product 20M. Additionally, a first bend 40A is formed in the axial middle portion of the intermediate molded product 20M, which is continuous with the intermediate bend 42 in the axial direction of the intermediate molded product 20M. In other words, the first bend 40A is formed on both sides of the intermediate bend 42 in the longitudinal direction.

[0101] As shown in Figures 7A and 7B, the intermediate bend 42 is, for example, curved convexly in the same direction as the first bend 40A. The radius of curvature of this intermediate bend 42 is larger than the radius of curvature of the first bend 40A. Furthermore, the radius of curvature of the intermediate bend 42 is, for example, constant in the longitudinal direction of the intermediate bend 42. In other words, the cross-sectional shape and size of the intermediate bend 42 are, for example, constant in the longitudinal direction of the intermediate bend 42.

[0102] Furthermore, the radius of curvature of the intermediate bend 42 is not limited to being constant in the longitudinal direction of the intermediate bend 42, but may vary.

[0103] Furthermore, the ratio of the radius of curvature of the intermediate bend 42 to the radius of curvature of the second bend 40B is preferably, for example, 1.4 or more and 3.0 or less.

[0104] Here, if the radius of curvature of the intermediate bend 42 is excessively large compared to the radius of curvature of the second bend 40B, it may be difficult to obtain sufficient bending deformation in the second pressing process, and the effect of reducing the stress difference generated in the bend may be reduced. On the other hand, if the radius of curvature of the intermediate bend 42 is excessively close to the radius of curvature of the second bend 40B, the shape difference between the first pressing process and the second pressing process will be reduced, and it may be difficult to obtain the stress redistribution effect by re-bending. Therefore, in this embodiment, from the viewpoint of ensuring bending deformation and reducing residual stress, it is preferable that the ratio of the radius of curvature of the intermediate bending portion 42 to the radius of curvature of the second bending portion 40B be 1.4 or more and 3.0 or less.

[0105] As shown in Figure 6, the intermediate bend 42 and the first bends 40A on both sides of the intermediate bend 42 are molded to be continuous in the axial direction (arrow X direction) of the intermediate molded product 20M. Furthermore, the intermediate bend 42 is connected to the first bends 40A on both sides of the intermediate bend 42 and to the intermediate molded product 20M in the axial direction via the gradual change section (section gradual change section) 44.

[0106] The gradually changing section 44 is curved convexly in the same direction as the first bend section 40A. Furthermore, the radius of curvature of the gradually changing section 44 changes as it moves from the intermediate bend section 42 toward the first bend section 40A. More specifically, the radius of curvature of the gradually changing section 44 decreases as it moves from the intermediate bend section 42 toward the first bend section 40A. In other words, the radius of curvature of the gradually changing section 44 increases as it moves from the first bend section 40A toward the intermediate bend section 42. This gradually changing section 44 connects the intermediate bend section 42 and the first bend sections 40A on both sides of the intermediate bend section 42 so that they are smoothly continuous in the axial direction of the intermediate molded product 20M.

[0107] (Second pressing process) In the second pressing process, the intermediate bend portion 42 and the two deformable portions 44 are bent into a second bend portion 40B using a second mold (not shown) which includes a punch, die, and pad, thereby press-forming (restrike) the intermediate molded product 20M into a press-formed product 20.

[0108] Specifically, as shown in Figures 7A and 7B, the intermediate bend 42 is press-formed (bent) so that its radius of curvature is reduced. As a result, the intermediate bend 42 is stretched in the neutral axis direction (circumferential direction of the second bend 40B, arrow R direction), and the second bend 40B is formed on one end 20E side of the intermediate molded product 20M.

[0109] Furthermore, in the second pressing process, similar to the intermediate bend 42, the two gradually changing sections 44 are press-formed (bent) so that their radii of curvature become smaller. As a result, the two gradually changing sections 44 are stretched in the direction of their neutral axis (circumferential direction of the second bend 40B), and are formed into the second bend 40B at one end 20E of the intermediate molded product 20M.

[0110] As shown in Figures 8A and 8B, in the second pressing step, the intermediate molded product 20M is press-formed so that the radius of curvature of the first bent portions 40A on both sides of the intermediate bent portion 42 does not change. This forms the bent portions 40 (first bent portion 40A, second bent portion 40B) that extend across both ends of the press-formed product 20 in the axial direction.

[0111] Furthermore, in this embodiment, as an example, in the second pressing step, the intermediate bending section 42 and the gradually changing section 44 are press-formed so that the radius of curvature of the second bending section 40B is the same as the radius of curvature of the first bending section 40A. However, the intermediate bending section 42 and the gradually changing section 44 may also be press-formed so that the radius of curvature of the second bending section 40B is different from the radius of curvature of the first bending section 40A.

[0112] Furthermore, the second pressing process only needs to reduce the residual stress in the first bending portion 40A at one end 20E of the press-formed product 20 by bending the intermediate bending portion 42 into the second bending portion 40B.

[0113] (effect) Next, the effects of the second embodiment will be described.

[0114] As described above, according to the manufacturing method of press-formed products according to this embodiment, in the first pressing step, an intermediate molded product 20M having a first bent portion 40A and an intermediate bent portion 42 that is continuous with the first bent portion 40A and has a different radius of curvature from the first bent portion 40A is press-formed. Furthermore, the first bent portion 40A is formed on one end 20E of the intermediate molded product 20M, and the intermediate bent portion 42 is formed on the end 20E side of the intermediate molded product 20M.

[0115] Next, in the second pressing process, the intermediate bend portion 42 is bent into a second bend portion 40B, and the intermediate molded product 20M is press-formed into a press-formed product 20. In other words, in the second pressing process, the intermediate bend portion 42 is formed into a second bend portion 40B on one end 20E side of the press-formed product 20.

[0116] Here, as shown in Figures 7A and 7B, the radius of curvature of the intermediate bend 42 is greater than the radius of curvature of the first bend 40A (second bend 40B). In this case, during the second pressing process, the intermediate bend 42 is stretched in the neutral axis direction (arrow R direction) and formed into the second bend 40B. At this time, tensile stress S is generated not only in the second bend 40B but also in the first bend 40A which is continuous with the second bend 40B, and the stress difference (tensile stress difference) between the outer and inner sides of the bend in the first bend 40A is reduced, so the residual stress at the end 40E of the first bend 40A is also reduced.

[0117] In this way, in the first pressing process, an intermediate bend 42 continuous with the first bend 40A is formed on one end 20E of the intermediate molded product 20M, and in the second pressing process, the intermediate bend 42 is bent into a second bend 40B. This reduces the residual stress at the end 40E of the first bend 40A at one end 20E of the press-formed product 20. Therefore, delayed fracture of the end 40E of the bend 40 (first bend 40A) can be suppressed at one end 20E of the press-formed product 20.

[0118] In pad bending or foam forming, depending on the forming conditions and mold structure, the flange portion 26 may not be sufficiently constrained by the mold, and in the second pressing process, the flange portion 26 may be more likely to move (slide) relative to the mold. On the other hand, in draw forming, the flange portion 26 is constrained by the blank holder, so the movement of the flange portion 26 relative to the mold tends to be suppressed, but depending on the forming conditions, the flange portion 26 may still move relative to the mold. Therefore, for example, if an intermediate bend portion 42 is formed on one end 20E of an intermediate molded product 20M, in the second pressing process, when the intermediate bend portion 42 is bent, the flange portion 26 may slide relative to the second mold, and the amount of deformation (elongation) of the intermediate bend portion 42 in the neutral axis direction may be reduced.

[0119] In contrast, in this embodiment, as described above, a first bent portion 40A is formed on one end 20E of the intermediate molded product 20M, and an intermediate bent portion 42 is formed on the end 20E side of the intermediate molded product 20M. As a result, in this embodiment, when the intermediate bent portion 42 is bent and deformed in the second pressing process, the peripheral portion of the intermediate bent portion 42 is constrained by the second mold around its entire circumference, making it difficult for the flange portion 26 to move relative to the second mold.

[0120] As a result, the amount of deformation in the neutral axis direction of the intermediate bend portion 42 increases, reducing the residual stress at the end 40E of the first bend portion 40A at one end 20E of the press-formed product 20. Therefore, delayed fracture of the end 40E of the bend portion 40 (first bend portion 40A) at one end 20E of the press-formed product 20 can be further suppressed.

[0121] Furthermore, an intermediate bend 42 may be formed at one end 20E of the intermediate molded product 20M, not limited to the first bend 40A. Also, if the flange portion 26 is wide, it becomes difficult for the flange portion 26 to slide relative to the first mold when press-forming the first bend 40A. Therefore, when the flange portion 26 is wide, it is preferable to form an intermediate bend 42 at one end 20E of the intermediate molded product 20M.

[0122] Furthermore, in the first pressing process, the intermediate bent section 42 and the two gradually changing sections 44 are formed into the intermediate molded product 20M. The radius of curvature of each gradually changing section 44 gradually increases from the first bent section 40A toward the intermediate bent section 42. By connecting the intermediate bent section 42 to the first bent sections 40A on both sides of the intermediate bent section 42 via these gradually changing sections 44, the moldability of the intermediate bent section 42 can be improved.

[0123] Furthermore, in the second pressing process, the gradually changing section 44 is bent into the second bending section 40B, thereby making the first bending section 40A and the second bending section 40B smoothly continuous.

[0124] Furthermore, by curving the intermediate bend portion 42 in a convex shape in the same direction as the first bend portion 40A, the formability of the second bend portion 40B can be improved in the second pressing process.

[0125] In this embodiment, an intermediate bent portion 42 and a gradually changing portion 44 are formed in the bent portion 40 of the intermediate molded product 20M during the first pressing process. However, the intermediate bent portion 42 and the gradually changing portion 44 are not limited to the bent portion 40 of the intermediate molded product 20M, but may also be formed in the bent portion 30, or in the bent portions 30 and 40, respectively.

[0126] Furthermore, in this embodiment, the radius of curvature of the intermediate bend 42 is larger than the radius of curvature of the first bend 40A (second bend 40B). However, the radius of curvature of the intermediate bend 42 may be smaller than the radius of curvature of the first bend 40A (second bend 40B).

[0127] (Third embodiment) Next, a third embodiment will be described. In the third embodiment, components and the like that have the same configuration as in the first and second embodiments will be denoted by the same reference numerals, and their descriptions will be omitted as appropriate.

[0128] As shown in Figures 9 and 10, the flange portion 26 of the press-formed product 20 according to the third embodiment has a stepped portion 50 press-formed (bent). The stepped portion 50 has a plurality (four in this embodiment) intersecting bent portions 52 that intersect with the bent portion 40. Note that there may be one intersecting bent portion 52 or a plurality of them may be provided.

[0129] As shown in Figure 9, the multiple intersecting bends 52 extend in the width direction (arrow Y direction) of the press-formed product 20 and are spaced apart in the axial direction of the press-formed product 20. Each intersecting bend 52 extends across both ends of the flange portion 26 in the width direction. In other words, one end of each intersecting bend 52 reaches the bend 40 and intersects with the bend 40. The other end 52E of the intersecting bend 52 reaches the tip 26T of the flange portion 26.

[0130] Here, residual stress is generated in the cross-bend portion 52 during press forming. In addition, residual stress is generated in the tip portion 26T of the flange portion 26 during the trimming process of the metal plate 10. Therefore, the residual stress in the cross-bend portion 52 tends to be relatively large at the tip portion (end portion 26T) of the flange portion 26, and the end portion (end portion 26T side) of the cross-bend portion 52 can become the starting point (location of occurrence) of delayed fracture.

[0131] As a countermeasure, in this embodiment, in the first pressing process, the intersecting bend portion 52 that intersects with the intermediate bend portion 42 is formed into the intermediate molded product 20M.

[0132] (First pressing process) Specifically, in the first pressing process, the metal sheet 10 is press-formed (pad-bent) using a first mold (intermediate mold) (not shown) equipped with a punch, die, and pad, thereby forming the intermediate molded product 20M shown in Figure 11. The intermediate molded product 20M differs from the press-formed product 20 in that it has an intermediate bend portion 42 and two gradual deformation portions 44 that are restrike in the second pressing process. These intermediate bend portion 42 and the two gradual deformation portions 44 are formed into a second bend portion 40B in the second pressing process.

[0133] Furthermore, the configuration of the intermediate molded product 20M, other than the intermediate bend portion 42 and the two gradual deformation portions 44, is the same as that of the press-formed product 20. Therefore, the first mold used in the first pressing process differs from the second mold used in the second pressing process described later in the shape of the punch and part of the die that form the intermediate bend portion 42 and the two gradual deformation portions 44, while the shape of the other parts is the same as that of the second mold.

[0134] Furthermore, similar to the first embodiment, the press-formed product 20 (intermediate molded product 20M) may be manufactured not only by pad bending, but also by, for example, draw forming using a blank holder or form forming without a blank holder.

[0135] The intermediate bend 42 is formed along the axial direction (arrow X direction) of the intermediate molded product 20M in the middle of the intermediate molded product 20M. On both sides of the longitudinal direction of this intermediate bend 42, first bends 40A that are continuous with the intermediate bend 42 are formed. In addition, of the multiple intersecting bends 52, one intersecting bend 52 intersects with the intermediate bend 42 at intersection G and reaches the tip 26T of the flange portion 26.

[0136] In this embodiment, as an example, one of the multiple intersecting bends 52 intersects with the intermediate bend 42. However, multiple intersecting bends 52 may intersect with the intermediate bend 42.

[0137] As shown in Figures 12A and 12B, the radius of curvature of the intermediate bend 42 is larger than the radius of curvature of the first bend 40A (second bend 40B).

[0138] As shown in Figure 11, the intermediate bend 42 and the first bends 40A on both sides of the intermediate bend 42 are molded to be continuous in the axial direction (arrow X direction) of the intermediate molded product 20M. Furthermore, the intermediate bend 42 is connected to the first bends 40A on both sides of the intermediate bend 42 and to the intermediate molded product 20M in the axial direction via the gradual deformation section 44.

[0139] The radius of curvature of the gradually changing section 44 decreases as it moves from the intermediate bend 42 toward the first bend 40A. In other words, the radius of curvature of the gradually changing section 44 increases as it moves from the first bend 40A toward the intermediate bend 42. This gradually changing section 44 connects the intermediate bend 42 and the first bends 40A on both sides of the intermediate bend 42 in a smooth, continuous manner.

[0140] (Second pressing process) In the second pressing process, the intermediate bend portion 42 and the two deformable portions 44 are bent into a second bend portion 40B using a second mold (not shown) which includes a punch, die, and pad, thereby press-forming (restrike) the intermediate molded product 20M into a press-formed product 20.

[0141] Specifically, as shown in Figures 12A and 12B, the intermediate bent portion 42 is press-formed (bent) so that its radius of curvature is reduced. As a result, the intermediate bent portion 42 is stretched in the direction of its neutral axis (arrow R direction) and formed into the second bent portion 40B.

[0142] Furthermore, similar to the intermediate bend section 42, the two gradually changing sections 44 are press-formed (bent) so that their radii of curvature become smaller. As a result, the two gradually changing sections 44 are stretched in the direction of their neutral axis and formed into the second bend section 40B.

[0143] As shown in Figures 13A and 13B, in the second pressing process, the intermediate molded product 20M is press-formed in such a way that the radius of curvature of the first bent portions 40A on both sides of the intermediate bent portion 42 does not change. This forms the bent portions 40 (first bent portion 40A, second bent portion 40B) that extend across both ends of the press-formed product 20 in the axial direction.

[0144] Furthermore, in this embodiment, as an example, in the second pressing step, the intermediate bending section 42 and the gradually changing section 44 are press-formed so that the radius of curvature of the second bending section 40B is the same as the radius of curvature of the first bending section 40A. However, the intermediate bending section 42 and the gradually changing section 44 may also be press-formed so that the radius of curvature of the second bending section 40B is different from the radius of curvature of the first bending section 40A.

[0145] (effect) Next, the effects of the third embodiment will be described.

[0146] As described above, according to the manufacturing method of a press-formed product according to this embodiment, in the first pressing step, an intermediate molded product 20M having a first bent portion 40A, an intermediate bent portion 42, and a plurality of intersecting bent portions 52 is formed. One intersecting bent portion 52 intersects with the intermediate bent portion 42 at the intersection G and reaches the tip (end) 26T of the flange portion 26.

[0147] Next, in the second pressing process, the intermediate bend portion 42 is bent into the second bend portion 40B, and the intermediate molded product 20M is press-formed into the press-formed product 20.

[0148] Here, as shown in Figures 12A and 12B, the radius of curvature of the intermediate bend 42 is greater than the radius of curvature of the first bend 40A (second bend 40B). In this case, during the second pressing process, the intermediate bend 42 is stretched in the neutral axis direction (arrow R direction) and formed into the second bend 40B. At this time, tensile stress S is generated not only in the intermediate bend 42 but also in the intersecting bend 52 that intersects the intermediate bend 42, and the stress difference (tensile stress difference) between the outer and inner sides of the bend in the intersecting bend 52 is reduced, so the residual stress at the end 52E of the intersecting bend 52 is also reduced.

[0149] Thus, in the first pressing process, an intermediate bend 42 is formed in the intermediate molded product 20M, and in the second pressing process, the intermediate bend 42 is bent into a second bend 40B. As a result, residual stress at the end 52E of the cross bend 52 is reduced in the press-formed product 20. Therefore, delayed fracture of the end 52E of the cross bend 52 can be suppressed at the tip 26T of the flange portion 26 in the press-formed product 20.

[0150] Furthermore, in the first pressing process, the intermediate bent section 42 and the two gradually changing sections 44 are formed into the intermediate molded product 20M. The radius of curvature of each gradually changing section 44 gradually increases from the first bent section 40A toward the intermediate bent section 42. By connecting the intermediate bent section 42 to the first bent sections 40A on both sides of the intermediate bent section 42 via these gradually changing sections 44, the moldability of the intermediate bent section 42 can be improved.

[0151] Furthermore, in the second pressing process, the gradually changing section 44 is bent into the second bending section 40B, thereby making the first bending section 40A and the second bending section 40B smoothly continuous.

[0152] Furthermore, by curving the intermediate bend portion 42 in a convex shape in the same direction as the first bend portion 40A, the formability of the second bend portion 40B can be improved in the second pressing process.

[0153] In this embodiment, the cross-bend portion 52 is formed on the flange portion 26. However, the cross-bend portion 52 is not limited to the flange portion 26; for example, it may be formed on the side plate portion 24. Note that when the cross-bend portion 52 is formed on the side plate portion 24, although not shown in the figure, a stepped portion 50 is press-formed (bent) on the side plate portion 24 of the press-formed product 20, and the press-formed product 20 does not have a flange portion 26. The cross-bend portion 52 formed on the side plate portion 24 reaches the height end of the press-formed product 20.

[0154] Furthermore, in this embodiment, the radius of curvature of the intermediate bend 42 is larger than the radius of curvature of the first bend 40A (second bend 40B). However, the radius of curvature of the intermediate bend 42 may be smaller than the radius of curvature of the first bend 40A (second bend 40B).

[0155] (modified version) Next, modifications of the first to third embodiments described above will be explained. In the following explanation, various modifications will be described using the first embodiment as an example, but these modifications can also be appropriately applied to the second and third embodiments.

[0156] In the first embodiment described above, an intermediate bend 32 is formed on one end 20E of the intermediate molded product 20M during the first pressing process. However, the intermediate bend 32 can be formed on at least one of the two ends of the intermediate molded product 20M.

[0157] Furthermore, in the first embodiment described above, the cross-sectional shape of the press-formed product 20 is a hat shape. However, the press-formed product 20 only needs to have at least a bent portion, and the shape of the press-formed product 20 can be changed as appropriate. Therefore, the cross-sectional shape of the press-formed product 20 is not limited to a hat shape, but may be an L-shape, a Z-shape, or the like.

[0158] Furthermore, in the first embodiment described above, the bent portion 30 extends in the axial direction of the press-formed product 20, for example. However, the bent portion 30 is not limited to the axial direction of the press-formed product 20, but may also extend in the width direction or height direction of the press-formed product 20, for example, as a predetermined direction. Also, the bent portion 30 may be curved.

[0159] Furthermore, in the first embodiment described above, the bent portion 30 on the top plate portion 22 side of the press-formed product 20 includes a first bent portion 30A and a second bent portion 30B. However, at least one of the bent portion 30 on the top plate portion 22 side and the bent portion 40 on the flange portion 26 side of the press-formed product 20 may include a first bent portion and a second bent portion.

[0160] Furthermore, the intermediate molded product 20M and the press-formed product 20 in the first embodiment described above have the same configuration except for the intermediate bent portion 32 and the gradually changing portion 34. However, the intermediate molded product 20M and the press-formed product 20 may have other different configurations, such as those resulting from processing, in addition to the intermediate bent portion 32 and the gradually changing portion 34.

[0161] While embodiments of the present disclosure have been described above, the present disclosure is not limited to these embodiments, and embodiments and various modifications may be used in appropriate combinations, and the disclosure can be implemented in various ways without departing from the gist of the present disclosure.

[0162] Furthermore, the disclosure of Japanese Patent Application No. 2025-094390, filed on 5 June 2025, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

[0163] (Note) The following additional information is disclosed regarding the embodiments described above.

[0164] (Note 1) In a method for manufacturing press-formed products, in which a metal sheet is press-formed to produce a press-formed product, A first pressing step for press-forming an intermediate molded product having a bent portion extending in a predetermined direction, and an intermediate bent portion that is continuous with the bent portion in the predetermined direction and has a different radius of curvature from the bent portion, A second pressing step in which the intermediate bent portion is deformed and the intermediate molded product is press-formed into the press-formed product so that the intermediate bent portion becomes part of the bent portion, A method for manufacturing press-formed products. (Note 2) In the first pressing step, the intermediate bent portion is formed at the end of the intermediate molded product in the predetermined direction. The method for manufacturing press-formed products as described in Appendix 1. (Note 3) The press-formed product has the bent portion extending from both ends of the press-formed product, In the first pressing step, the intermediate bend is formed in the middle of the bend that extends from both ends of the intermediate molded product. The method for manufacturing press-formed products as described in Appendix 1. (Note 4) In the first pressing step, the bent portion is formed at one end of the intermediate molded product, and an intermediate bent portion continuous with the bent portion is formed on the end side of the intermediate molded product. The method for manufacturing press-formed products as described in Appendix 3. (Note 5) The press-formed product has a cross-bend portion that intersects with the bent portion, In the first pressing step, the intersecting bent portion that intersects the bent portion is formed into the intermediate molded product, and the intermediate bent portion is formed in at least one of the intersection of the bent portion and the intersecting bent portion and the peripheral portion of the intersection in the intermediate molded product. The method for manufacturing press-formed products as described in Appendix 3. (Note 6) In the first pressing process, the bent portion and the intermediate bent portion are connected, and a gradually changing portion is formed in the intermediate molded product in which the radius of curvature changes gradually from the bent portion toward the intermediate bent portion. In the second pressing step, the intermediate bent portion and the gradually changing portion are deformed, and the intermediate molded product is press-formed into the press-formed product such that the intermediate bent portion and the gradually changing portion become part of the bent portion. A method for manufacturing a press-formed product as described in any one of the appendices 1 to 5. (Note 7) The press-formed product comprises a top plate portion, a side plate portion connected to the end of the top plate portion via the bent portion, and a flange portion connected to the end of the side plate portion via the bent portion. A method for manufacturing a press-formed product as described in any one of the appendices 1 to 6.

Claims

1. In a method for manufacturing press-formed products, in which a metal sheet is press-formed to produce a press-formed product, A first pressing step for press-forming an intermediate molded product having a first bent portion extending in a predetermined direction, and an intermediate bent portion continuous with the first bent portion in the predetermined direction and having a different radius of curvature from the first bent portion, with the first bent portion or the intermediate bent portion positioned at the end; A second pressing step in which the intermediate bend is bent into a second bend, and the intermediate molded product is press-formed into the press-formed product, A method for manufacturing press-formed products.

2. In the first pressing step, the intermediate bent portion is formed at the end of the intermediate molded product. A method for manufacturing a press-formed article according to claim 1.

3. In the first pressing step, the first bent portion is formed on the end of the intermediate molded product. A method for manufacturing a press-formed article according to claim 1.

4. In the first pressing step, the first bent portion is formed on the end of the intermediate molded product, and the intermediate bent portion is formed on the end side of the intermediate molded product. The method for manufacturing a press-formed article according to claim 3.

5. The press-formed product has a cross-bend portion that intersects with the second bend portion and reaches the widthwise end or heightwise end of the press-formed product. In the first pressing step, the intersecting bend portion that intersects the intermediate bend portion is formed into the intermediate molded product. The method for manufacturing a press-formed article according to claim 3.

6. In the first pressing process, the first bent portion and the intermediate bent portion are connected, and a gradually changing portion is formed in the intermediate molded product in which the radius of curvature changes gradually from the first bent portion toward the intermediate bent portion. In the second pressing step, the intermediate bend portion and the gradually deforming portion are bent and deformed into the second bend portion, and the intermediate molded product is press-formed into the press-formed product. A method for manufacturing a press-formed article according to any one of claims 1 to 5.

7. In the first pressing step, the intermediate bent portion, which curves convexly in the same direction as the first bent portion, is formed into the intermediate molded product. A method for manufacturing a press-formed article according to any one of claims 1 to 5.

8. The radius of curvature of the intermediate bend is smaller than the radius of curvature of the second bend. The method for manufacturing a press-formed article according to claim 7.

9. The press-formed product comprises a top plate portion, a side plate portion connected to the widthwise end of the top plate portion via a bent portion, and a flange portion connected to the heightwise end of the side plate portion via a bent portion. At least one of the bent portion on the top plate side and the bent portion on the flange side includes the first bent portion and the second bent portion, A method for manufacturing a press-formed article according to any one of claims 1 to 5.

10. The aforementioned press-formed product has a tensile strength of 1300 MPa or more. A method for manufacturing a press-formed article according to any one of claims 1 to 5.

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