Manufacturing method of structural member

Abstract

A structural member having a closed cross section can be manufactured by press molding in a simpler method. The structural member is press molded into a target part shape (1) having a top plate portion (1A) and left and right vertical wall portions (1B), in which recesses (1Bc) protruding toward the other vertical wall portion (1B) are formed, and an inner surface (2) of the recesses (1Bc) is capable of surface contact with the inner surface of the other vertical wall portion (1B). The method includes a first shaping step (5A) of shaping a metal plate (10) into a first intermediate part (11) having a recess (1Bc); a second shaping step (5B) of producing a second intermediate part (12) by imparting bending deformation to a region (11A) that will become the top plate portion (1A) of the first intermediate part (11) in a direction in which the recesses (1Bc) approach each other; and a third shaping step (5C) of further imparting bending deformation to the region (11A) that will become the top plate portion (1A) of the second intermediate part (12) while pressing the left and right vertical wall portions (1B) in a direction in which they approach each other.

Description

[Technical field]

[0001] The present invention relates to a manufacturing technique for structural members. The present invention relates to a technique suitable for a manufacturing method for manufacturing structural members by press molding, which are mainly used for automobile parts, home appliance parts, etc. The present invention is also a technique suitable for manufacturing structural members having a closed cross-sectional shape. [Background technology]

[0002] When high strength is required for structural members using steel plates, such as in automobiles, it is common to use high-strength steel plates as the material. In addition, in order to increase the strength of structural members, it is common to configure them with a structure having a closed cross-sectional shape. This type of structure is seen in many parts of automobile bodies, such as side sills and front side members.

[0003] Here, in press forming of metal sheets, the metal sheet is sandwiched between a pair of dies to form the sheet. Therefore, in principle, it is not possible to create parts with uneven cross-sectional shapes on the vertical surface perpendicular to the die stroke direction or parts with closed cross sections in one process. Therefore, for example, the side sills and front side members mentioned above are composed of two hat-shaped parts, or a combination of a hat-shaped part and a flat part. In other words, it is common to form multiple parts individually by press forming and then combine these formed parts by welding or other methods to form a skeleton with a closed cross section.

[0004] However, manufacturing and combining two parts requires the preparation of separate dies for the two types of parts, as well as the separate press molding required to manufacture the two types of parts, and then the work of assembling the two parts. Therefore, if it were possible to manufacture parts with closed cross sections from a single metal plate, the above-mentioned work could be significantly reduced. To achieve this, various efforts have been made.

[0005] For example, roll forming may be used to manufacture parts with closed cross sections. Roll forming is excellent for forming long parts with a constant cross-sectional shape as described above. In addition, roll forming can easily be multi-staged, making it possible to produce parts with complex cross sections. Furthermore, joining can be performed in the forming line. For this reason, roll forming is also relatively easy for forming parts that can form a closed cross section when in use. In addition, various methods for producing closed cross-section parts by press molding have been proposed in the past. For example, Patent Document 1 discloses a method for forming a cylindrical closed cross-section part having different diameters in the longitudinal direction. Furthermore, Patent Documents 2 and 3 disclose press molding methods for a closed cross-section part in which both ends of the cross section are bent and fastened to prevent the shape from opening after molding. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2014-004626 A [Patent Document 2] JP 2013-244511 A [Patent Document 3] JP 2013-244512 A Summary of the Invention [Problem to be solved by the invention]

[0007] As mentioned above, roll forming is good at producing parts with a constant cross section. However, there are various restrictions and difficulties when forming products whose cross-sectional shapes change at each part. In addition, it is necessary to have production equipment specialized for roll forming. However, roll forming is not as widespread as press machines. Therefore, there is great significance in producing structural components by press forming using widely used press machines.

[0008] On the other hand, Patent Document 1 describes that the cross section opens after press forming. In particular, high tensile steel sheets are used for automobile frames. When manufacturing parts by press forming these high tensile steel sheets, there is a problem that the elastic return (springback) is large and the opening after demolding is also large. Furthermore, when joining the molded parts, a dedicated reworking jig is required to close the open cross section again, which increases costs.

[0009] To address this issue, Patent Documents 2 and 3 show a method of fastening by bending both ends of the cross section. This is an effective method when both ends are to be joined. However, this method cannot be applied to joining other parts. In particular, press molding using a core as shown in Patent Document 3 has the following issue. That is, in order to remove the core from the molded product after molding, a mechanism for moving the core or the molded product in a direction different from the operating direction of the press machine and the operating time for removal are required. This results in increased costs in terms of equipment costs and production time.

[0010] The present invention has been made in light of the above-mentioned points, and has an object to provide a manufacturing method capable of producing a structural member having a closed cross-section by press molding in a simpler manner. [Means for solving the problem]

[0011] In order to solve the problem, one aspect of the present invention is a manufacturing method for a structural member, comprising: a top plate portion; left and right vertical wall portions connected to both widthwise ends of the top plate portion via ridge portions and facing each other in the width direction of the top plate portion; and a recess is formed in one or both of the left and right vertical wall portions at a midpoint in the height direction of the vertical wall portion, protruding toward the other opposing vertical wall portion, and an inner surface of the recess is in surface contact with an inner surface of the other vertical wall portion, the manufacturing method comprising press-forming a metal plate into a target part shape having a cross section, the target part shape including a first intermediate portion having the recess, a second shaping step of producing a second intermediate part by applying bending deformation to the region that will become the top plate portion, or to the region that will become the top plate portion and the region that will become the ridge line portion, in a direction in which the inner surface of the recess approaches the region that will become the other vertical wall portion, and a third shaping step of pressing the regions that will become the left and right vertical wall portions of the second intermediate part in a direction in which the regions that will become the left and right vertical wall portions approach each other, and further applying bending deformation to the region that will become the top plate portion. Effect of the Invention

[0012] According to an aspect of the present invention, it is possible to manufacture a press-formed product having a closed cross section from a single metal plate by press working. When the target part shape has a flange portion, the manufactured structural member becomes a closed cross-sectional part whose joint portion is not an end portion of the cross-sectional surface. In addition, according to the present invention, a general-purpose press machine can be used, and a die structure that is typical for automotive parts can be used. Therefore, according to the present invention, production is possible without reducing the production speed in the conventional press process for automotive parts. Therefore, according to the present invention, it is possible to inexpensively produce parts with closed cross sections that have traditionally been produced using roll forming or a combination of multiple parts. [Brief description of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view of a target part shape according to an embodiment of the present invention; [Diagram 2]FIG. 2 is a perspective view of a target part shape according to an embodiment of the present invention. [Diagram 3] FIG. 11 is a diagram showing another example of the cross-sectional shape of the target part shape. [Figure 4] 3A to 3C are diagrams illustrating a manufacturing process of a structural member according to the present embodiment. [Diagram 5] FIG. 2 is a schematic diagram showing a configuration of a mold used in a first molding step. [Figure 6] FIG. 2 is a schematic diagram showing a state at the bottom dead point in the first compacting step. [Figure 7] 1A and 1B are schematic diagrams illustrating a second molding step, in which (a) shows the shape of a first intermediate part, and (b) shows an example of the configuration of a mold used in the second molding step. [Figure 8] FIG. 4 is an enlarged schematic view of the molding surface of a lower die used in the second molding step. [Figure 9] FIG. 4 is a schematic diagram illustrating a third molding step. [Figure 10] 13 is a schematic diagram showing another example of the molding surface 41A. FIG. [Figure 11] FIG. 11 is a schematic diagram illustrating another example of the third molding step. [Figure 12] 13 is a conceptual diagram illustrating the shaping of a region that will become a top plate portion in a third shaping step. FIG. [Figure 13] 13 is a schematic diagram showing another example of the molding surface 41A. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Next, an embodiment of the present invention will be described with reference to the drawings. This embodiment relates to a method for manufacturing a target structural member by press-forming a metal plate into a target part shape. In the present invention, there is no particular restriction on the material of the metal plate to be processed. The metal plate may be, for example, a steel plate having a tensile strength of about 270 MPa to 2000 MPa. The present invention is a suitable technique for processing a high-strength steel plate having a tensile strength of 980 MPa or more.

[0015] (Target part shape 1) As shown in FIG. 1, the target part shape 1 in this embodiment has a cross-sectional shape including a top plate portion 1A and left and right vertical wall portions 1B. The left and right vertical wall portions 1B are connected to both widthwise ends of the top plate portion 1A via ridge portions 1D. The left and right vertical wall portions 1B are disposed opposite each other in the widthwise direction of the top plate portion 1A. The ridge portion 1D has an outwardly convex arc-shaped cross section, and is a joint that joins (connects) the top plate portion 1A and the vertical wall portions 1B. This ridge portion 1D may be considered as part of the top plate portion 1A. Figure 1 shows an example in which the top surface of the top plate portion 1A is flat.

[0016] Furthermore, in the cross section of the target part shape 1, at least one of the left and right vertical wall portions 1B has a recess 1Bc formed at a midpoint in the height direction of the vertical wall portion. The recess 1Bc protrudes toward the other opposing vertical wall portion 1B. The inner surface of the recess 1Bc is capable of surface contact with the inner surface of the other vertical wall portion 1B. FIG. 1 shows an example in which the above-mentioned recess 1Bc is provided on both the left and right vertical wall portions 1B. This results in an example in which the target part shape 1 is symmetrical. The dimensions shown in FIG. 1 and other figures are merely examples and are not intended to limit the present invention in any way.

[0017] In addition, as shown in FIG. 2, the target part shape 1 of this embodiment is a part shape in which the cross section extends along the longitudinal direction. The longitudinal direction is a direction intersecting the cross section. The recesses 1Bc are also formed to extend along the longitudinal direction. The recesses 1Bc may be formed intermittently along the longitudinal direction. However, it is preferable that the shape of each recess 1Bc is such that the longitudinal dimension is longer than the height dimension of the vertical wall portion 1B. The target part shape 1 of this embodiment is not limited to the cross-sectional shape shown in Fig. 1. The cross-section of the target part shape 1 may have a cross-sectional shape in which at least one of the left and right vertical wall portions 1B has a recess 1Bc formed therein that can come into surface contact with the inner surface of the other vertical wall portion 1B.

[0018] Another example of the cross-sectional shape of the target part shape 1 is shown in Fig. 3. Note that the cross-sectional shape of the target part shape 1 is not limited to the example in Fig. 3. Fig. 3(a) shows an example in which the shape of the top plate 1A is changed from the cross-sectional shape of Fig. 1 to a cross-section of an arc convex upward. In this specification, the term "arc" or "arc-like" is not limited to a part of a perfect circle. The term "arc" or "arc-like" described in this specification includes curved shapes that have a rounded convex shape on one side, such as an elliptical shape or a part of a parabola. "Rounded" means that there is no sharp curvature along the curve. Figures 3(b) and (c) show examples in which the position of the inner surface of the recess 1Bc is offset from the center position in the width direction. Figure 3(b) shows an example in which the left and right recesses 1Bc have different shapes. Figure 3(c) shows a recess 1Bc provided only on one vertical wall portion 1B, with the inner surface 2 of the recess 1Bc shaped to be in surface contact with the inner surface 3 of the other vertical wall portion 1B.

[0019] 3(d) and (e) show an example in which the left and right recesses 1Bc have different ranges and positions in the up-down direction. The left and right recesses 1Bc may be arranged so that they do not completely overlap in the up-down direction. In this case, the inner surface 2 of each recess 1Bc is in surface contact with the inner surface 3 of the corresponding vertical wall portion 1B other than the recess 1Bc. Fig. 3(f) shows an example in which the width above the recess 1Bc is different from the width below the recess 1Bc, and Fig. 3(g) shows an example in which there is no flange portion 1C.

[0020] In this embodiment, the cross-sectional shape of the vertical wall portion 1B other than the recessed portion 1Bc is a straight line. However, the vertical wall portion 1B other than the recessed portion 1Bc may have a curved portion in whole or in part. However, this is limited to the case where the left and right vertical wall portions 1B are shaped so as to be in surface contact with each other at the recessed portion 1Bc.

[0021] The following describes an example in which the target part shape 1 of the structural member to be manufactured is the shape shown in Fig. 1. The target part shape 1 shown in Fig. 1 has a flat top plate portion 1A, and recesses 1Bc are formed in both left and right vertical wall portions 1B, and the inner surfaces of the left and right recesses 1Bc are shaped to be in surface contact with each other. 1, outward flange portions 1C are connected to the lower ends of the left and right vertical wall portions 1B, respectively. In this specification, the outward flange portions 1C are also simply referred to as flange portions 1C. Before the manufactured part is assembled, the structural member of the target part shape 1 may have a gap between the inner surfaces 2 of the left and right recesses 1Bc. However, in consideration of the effort required for assembly, it is preferable that the gap is small.

[0022] (Manufacturing method) As shown in Fig. 4, the method for manufacturing a structural member of this embodiment includes a first shaping step 5A, a second shaping step 5B, a third shaping step 5C, and a joining process step 5D. In this embodiment, the method manufactures a structural member (formed part 13) having a target part shape 1 by pressing a metal plate 10 through the steps 5A to 5C. The joining process step 5D may not be included. The metal plate 10 to be pressed is also called a blank 10.

[0023] <1st molding process 5A> The first forming step 5A is a step of press-forming the metal plate 10 into a first intermediate part 11. The first intermediate part 11 has a shape in which the recess 1Bc and the flange portion 1C are formed in the metal plate 10 (see FIGS. 6 and 7(a)). The first molding step 5A is carried out using a pair of dies 20 and 21 opposed to each other with a metal plate 10 therebetween, as shown in FIG.

[0024] A concave shape 20Ba for forming the recess 1Bc of the vertical wall portion 1B is formed on the molding surface of one mold 20. A convex shape 21Ca corresponding to the concave shape 20Ba is formed on the molding surface of the other mold 21. In this example, one mold 20 is a lower mold 20, and the other mold 21 is an upper mold 21. In addition, the first forming step 5A of this embodiment has left and right bending blades 20C. The bending blades 20C bend and deform the metal plate 10 at the ridge line position connecting the vertical wall portion 1B and the outward flange portion 1C to form the left and right outward flange portions 1C. The outward flange portions 1C are formed to rise in the opposite direction to the concave direction of the recess 1Bc. In this example, the bending blades 20C are provided on the lower mold 20.

[0025] The mold of this embodiment will now be described more specifically. The lower die 20 of this example has a lower die pad 20B and left and right bending blades 20C. The lower die pad 20B and the left and right bending blades 20C are provided on the main body 20A. A lower die gas cushion 20D is interposed between the lower die pad 20B and the main body 20A. The lower die gas cushion 20D is a component that allows the lower die pad 20B to move in the pressing direction and biases the lower die pad 20B toward the metal plate 10.

[0026] A concave shape 20Ba is formed on the upper surface of the lower pad 20B at a position where the concave portion 1Bc is to be formed. A bending blade 20C is disposed on each side of the lower pad 20B. The bending blade 20C has a surface 20Ca facing the lower pad 20B side that raises each end of the metal plate 10 to form the left and right flange portions 1C. The lower die pad 20B is supported by a lower die gas cushion 20D so as to be movable below the upper portion of the bending blade 20C.

[0027] The upper die 21 is disposed so that its molding surface faces the upper surface of the metal plate 10 . The upper mold 21 includes a main body 21A, left and right upper dies 21C, and upper mold pads 21B. The lower surfaces (molding surfaces) of the left and right upper dies 21C face the upper surface (molding surface) of the lower pad 20B, and are formed with convex shapes 21Ca corresponding to the concave shapes 20Ba of the lower pad 20B. The upper pad 21B is disposed between the left and right upper dies 21C. An upper gas cushion 21D is interposed between the upper pad 21B and the main body 21A. The upper gas cushion 21D is a component that allows the upper pad 21B to move in the pressing direction and biases the upper pad 21B toward the metal plate 10.

[0028] Moreover, the position of the widthwise outer end of each upper die 21C is located outward from the outer end of the lower pad 20B in a top view. The lower corners 21Cb of the outer end of each upper die 21C are rounded to form a radius. This forms a shoulder that forms a ridge line formed at the connection position between the vertical wall portion 1B and the flange portion 1C. In addition, a step portion 20Cb is formed at the lower part of the bending blade 20C. The upper surface of the step portion 20Cb faces the above-mentioned shoulder portion 21Cb from above and below. In addition, a radius corresponding to the radius of the shoulder portion 21Cb of the upper die 21C is formed on the upper surface of the step portion 20Cb. Here, the upper surface of the lower pad 20B, and the lower surface of the upper die 21C and the upper pad 21B form a forming surface for forming the metal plate 10.

[0029] In this embodiment, the vertical wall portion 1B has a flat portion on the top plate portion 1A side and a flat portion on the flange portion 1C side from the recessed portion 1Bc (see FIG. 1). Therefore, the molded surface other than the recessed shape 20Ba corresponding to the recessed portion 1Bc is flat. The vertical wall portion 1B has a flat portion on the top plate portion 1A side above the recessed portion 1Bc, which is also called an upper vertical wall portion 1Ba. The vertical wall portion 1B has a flat portion on the flange portion side below the recessed portion 1Bc, which is also called a lower vertical wall portion 1Bb. If the shape of part or all of the upper vertical wall portion 1Ba or the lower vertical wall portion 1Bb is not flat, a shape corresponding to the shape of that part can be formed on the corresponding parts of the upper surface (molding surface) of the lower pad 20B and the upper surfaces (molding surfaces) of the upper die 21C and upper pad 21B. That is, in this embodiment, in the first forming step 5A, the surface shape of the region that will become the vertical wall portion is formed into the surface shape of the vertical wall portion 1B in the target part shape, as necessary. Therefore, in the following description, the region that will become the vertical wall portion is also referred to as the vertical wall portion 1B.

[0030] Next, the operation of the mold will be described. As shown in Fig. 5, when no load is applied, the metal plate 10 is placed on the lower die pad 20B located above the bending blade 20C. In this state, the upper die 21 is relatively lowered toward the metal plate 10, i.e., toward the lower die 20. Then, the upper die pad 21B is brought into contact with the metal plate 10, and the lower die pad 20B and the upper die pad 21B hold (sandwich) the metal plate 10. This prevents the metal plate 10 from shifting in position during forming.

[0031] Subsequently, by lowering the upper die 21 toward the lower die 20, the upper die gas cushion 21D is compressed, and the recess 1Bc is formed in the metal plate 10 by the lower die pad 20B and the upper die 21C. Furthermore, as the upper die 21C descends, the lower gas cushion 20D contracts. Then, both ends of the metal sheet 10 are bent by the outer end of the upper die 21C and the lower bending blade 20C to form the left and right flanges 1C.

[0032] FIG. 6 is a schematic diagram illustrating a state at the bottom dead point of press molding using an upper mold 21 and a lower mold 20. As shown in FIG. The metal plate 10 is formed into the shape of the first intermediate part 11 by this first forming step 5A. As shown in Fig. 6 and Fig. 7(a), the first intermediate part 11 has a shape in which left and right recesses 1Bc and left and right flanges 1C are formed. In addition, in the target part shape 1, the upper vertical wall portion 1Ba and the lower vertical wall portion 1Bb may not be flat along the cross-sectional direction. For example, these portions may not be linear in the cross-sectional direction but may be curved. In that case, the first forming process 5A forms the regions that will become the upper vertical wall portion 1Ba and the lower vertical wall portion 1Bb into the curved shape. The flange portion 1C may be formed in a separate process.

[0033] <Second forming process 5B> The second forming step 5B is a step of press-forming the first intermediate part 11 into the second intermediate part 12. Specifically, in the second forming process 5B, the first intermediate part 11 is bent in the region 11A that will become the top plate portion 1A in a direction in which the inner surface 2 of the recess 1Bc approaches the region that will become the other vertical wall portion 1B. Alternatively, in the second forming process 5B, the first intermediate part 11 is bent in the region 11A that will become the top plate portion 1A and the region that will become the ridge portion 1D in a direction in which the inner surface 2 of the recess 1Bc approaches the region that will become the other vertical wall portion 1B. Then, the second intermediate part 12 is produced by this press forming. In this embodiment, the region 11A that will become the top plate portion 1A in the first intermediate part 11 is bent in a direction in which the recesses 1Bc of the left and right vertical wall portions 1B approach each other (see FIG. 7(b)).

[0034] At this time, it is preferable that by applying bending deformation in the second forming process 5B, the second intermediate part 12 has a curved portion (convex portion) with a cross-sectional shape that is convex in the outward bending direction in the region 11A that will become the top plate portion 1A and the region that will become the ridge portion 1D. In this embodiment, as the cross-sectional shape convex in the bending outward direction, a first convex cross-sectional shape and a second convex cross-sectional shape are exemplified as follows. Note that the cross-sectional shape convex in the bending outward direction is not limited to the first convex cross-sectional shape and the second convex cross-sectional shape.

[0035] The cross-sectional shape of the first protrusion is a curved cross-sectional shape that is convex in the outward bending direction, as shown in FIG. 9(a). The cross-sectional curved shape may be a shape of a part of a circular arc, or may be a rounded shape, such as an ellipse or a parabola. It is preferable that the cross-sectional shape of the region 11A that becomes the top plate portion 1A has a curved cross-sectional shape with a smaller radius of curvature than the cross-sectional shape of the top plate portion 1A in the target part shape 1.

[0036] The cross-sectional shape of the second convexity is a curved cross-sectional shape that is convex in the outward bending direction, as shown in FIG. 11(a). The cross-sectional shape of the second convexity includes a top plate flat portion 12Aa formed in the region 11A that becomes the top plate portion 1A, and left and right inclined portions 12Ab that join the top plate flat portion 12Aa and the vertical wall portion 1B. The left and right inclined portions 12Ab are arranged in a V-shape, sandwiching the top plate flat portion 12Aa. That is, the cross-sectional shape of the convexity is a trapezoidal shape without a base, as shown in the enlarged view of FIG. 12(a). The top plate flat portion 12Aa and the inclined portion 12Ab are joined via a first ridge portion 12Ac. The inclined portion 12Ab and the vertical wall portion 1B are joined via a second ridge portion 12Ad. The first ridge portion 12Ac and the second ridge portion 12Ad are bent portions, and have an arc-shaped cross-sectional shape that is convex outward.

[0037] The inclined portions 12Ab are connected to both ends of the top plate flat portion 12Aa in the width direction. The inclined portions 12Ab extend obliquely from the top plate flat portion 12Aa toward the vertical wall portion. The lower ends of the inclined portions 12Ab in the extending direction are joined to the vertical wall portion 1B via the second ridge portion 12Ad. A virtual straight line passing through the first ridge portion 12Ac and the second ridge portion 12Ad that defines the left and right inclined portions 12Ab is inclined so as to extend downward and outward in the width direction of the top plate portion. The cross-sectional shape of the inclined portion 12Ab in this embodiment is a straight line shape. However, the cross-sectional shape of the inclined portion 12Ab is not limited to a straight line shape. The cross-sectional shape of the inclined portion 12Ab may be, for example, a curved cross-sectional shape that bulges outwardly at a midpoint in the extension direction. The cross-sectional curved shape of the inclined portion 12Ab may be a shape that is a part of a circular arc, or may be a rounded shape, such as an elliptical shape or a parabolic shape.

[0038] The second molding step 5B is carried out using a pair of dies 30, 31 opposed to each other with the metal plate 10 interposed therebetween, as shown in FIG. The pair of dies includes a lower die 30 and an upper die 31 as shown in FIG. 7(b). A recessed concave surface 30A is formed on the upper surface (molding surface) of the lower die 30 at a position facing the region 11A that will become the top plate portion 1A of the first intermediate part 11. The concave surface 30A has a shape following the curved portion that constitutes the above-mentioned convex portion.

[0039] When the curved portion constituting the above-mentioned convex portion has the cross-sectional shape of the second convex portion, the molding surface 30A of the lower die 30 has a cross-section with a curved shape following the cross-sectional shape of the second convex portion. Furthermore, when the curved portion constituting the above-mentioned convex portion has the cross-sectional shape of the second convex portion, the molding surface 30A of the lower die 30 has a shape as shown in the enlarged schematic diagram of Fig. 8. That is, as shown in Fig. 8, the concave surface 30A has a shape following the cross-sectional shape constituting the above-mentioned convex portion on the top plate side of the second intermediate part.

[0040] In the case of the cross-sectional shape of the second convex portion, the cross-sectional shape of the concave surface 30A constituting the molding surface includes a top plate flat portion molding surface 30Aa, left and right inclined portion molding surfaces 30Ab, and left and right vertical wall portion upper molding surfaces 30Ac, as shown in the enlarged view of Fig. 8. Here, the angle of the inclined portion molding surface 30Ab relative to the top plate flat portion molding surface 30Aa is less than 180 degrees. Also, the angle of the vertical wall portion upper molding surface 30Ac relative to the inclined portion molding surface 30Ab is less than 180 degrees. The top plate flat portion molding surface 30Aa and the inclined portion molding surface 30Ab are connected by a first ridge portion molding surface having an arc-shaped cross section. The inclined portion molding surface 30Ab and the vertical wall portion upper portion molding surface 30Ac are connected by a second ridge portion molding surface having an arc-shaped cross section. 8, the molding surface 30A of the lower die 30 has a shape that is synonymous with the shape of the top plate side of the second intermediate part before demolding (see FIG. 7(b)). That is, the molding surface 30Aa has the same shape as the top plate flat portion 12Aa.

[0041] Also, the cross-sectional line length of the top plate flat portion 12Aa of the second intermediate part before release is w1 [mm]. The cross-sectional line length of the flat portion of the top plate portion 1A in the target part shape is Tf [mm]. In this case, it is preferable to design it so as to satisfy the following formula (1). The flat portion of the top plate portion 1A in the target part shape corresponds to, for example, the portion indicated by the symbol 12Aa in FIG. 12(d). 1 / 3 Tf ≦ w1 ≦ Tf (1) Furthermore, the top plate flat portion 12Aa is disposed within the region that will become the top plate portion 1A, and is preferably disposed at an equal position in the width direction, i.e., at the center position, of the region that will become the top plate portion 1A. However, if the product has asymmetry in the width direction, the top plate flat portion 12Aa may be disposed biased to one side in the width direction within the region that will become the top plate portion 1A.

[0042] Also, the angle of the inclined portion 12Ab relative to the top plate flat portion 12Aa is set to, for example, 120 degrees or more and 165 degrees or less on the inner surface side. Also, the angle of the upper portion of the vertical wall portion relative to the inclined portion 12Ab may be less than 180 degrees. In other words, it is preferable that there is an angle between the inclined portion 12Ab and the upper portion of the vertical wall portion. Furthermore, it is preferable that the angle of the upper portion of the vertical wall portion relative to the inclined portion 12Ab is less than 180 degrees on the inner surface side. In addition, the total cross-sectional line length of the top plate flat portion 12Aa, the left and right first ridge portions 12Ac, the left and right inclined portions 12Ab, and the left and right second ridge portions 12Ad is preferably equal to the total cross-sectional line length of the top plate portion 1A and the ridge portion 1D, for example. Alternatively, it is preferably a value slightly larger than the total cross-sectional line length. The slightly larger value corresponds to the line length portion of the upper end portion of the vertical wall portion 1B in the product. For example, at least a part of the cross-sectional line of the second ridge portion 12Ad may constitute the upper end portion of the vertical wall portion 1B.

[0043] The upper die 31 has a punch 31A that protrudes toward the concave surface 30A of the lower die 30. The tip 31Aa of the punch 31A is set so as to be able to press the region 11A that will become the top plate portion 1A toward the concave surface 30A of the lower die 30. The cross-sectional shape of the tip 31Aa of the punch 31A follows the cross-sectional shape of the second intermediate part 12 on the top plate portion side.

[0044] Next, the operation of the mold in the second molding step 5B will be described. The first intermediate part 11 is placed on the lower die 30 with the protrusion of the recess 1Bc of the first intermediate part 11 facing upward (see Figure 7(b)). That is, the first intermediate part 11 after the first molding step 5A is inverted and the first intermediate part 11 is set on the upper surface of the lower die 30. However, the above-mentioned inversion is not essential. If the die 30 is used as the upper die and the die 31 as the lower die, and further if a jig that can stably position the first intermediate part 11 is used, the above-mentioned inversion is not necessarily required. Moreover, the first intermediate part 11 has a shape as shown in Figure 7(a).

[0045] Then, the upper die 31 is lowered toward the lower die 30, and the first intermediate part 11 is sandwiched between the lower die 30 and the punch 31A of the upper die 31. Then, the region 11A that will become the top plate portion 1A is bent into a shape having a greater curvature than the intended shape of the top plate portion 1A, thereby producing a second part shape. The second intermediate component 12 is bent in the region 11A that will become the top plate portion 1A and in the region that will become the ridge line portion 1D. Therefore, compared to the first intermediate component 11, the second intermediate component 12 is bent in a V-shape with the regions that will become the left and right vertical wall portions 1B closer together.

[0046] <Third molding process 5C> The third forming step 5C is a step of forming the top plate portion 1A of the second intermediate part 12 and bending the ridge portion 1D, which is the connection portion between the top plate portion 1A and the vertical wall portion 1B. In the third forming step 5C, this processing forms the top plate portion 1A into a target shape and also brings the left and right vertical wall portions 1B closer to each other to form them into the target part shape.

[0047] Specifically, in the third forming step 5C, a process is performed to further impart bending deformation to the region 11A that will become the top plate portion 1A while the second intermediate part 12 is pressed in a direction in which the regions that will become the left and right vertical wall portions 1B approach each other, as shown in Fig. 9. The bending deformation may be imparted while the left and right cams are pressing the left and right vertical wall portions 1B in the direction in which they approach each other. At this time, it is preferable that the bending deformation in the third shaping step 5C deforms the convex portion of the region 12A that will become the top plate portion 1A in a direction that increases the radius of curvature of the cross section. Here, the second intermediate part 12 before being formed in the third forming step 5C has a recess 1Bc and a flange portion 1C, as shown in FIG. 9(a), and has a generally mountain-like shape as a whole.

[0048] 9, the third forming step 5C is performed using a pair of dies facing each other with the metal plate 10 interposed therebetween, and left and right cams 42. The pair of dies includes a lower die 40 and an upper die 41. The upper surface of the lower die 40 is a flat surface that can be contacted by the flange portion 1C, which is the lower portion of the second intermediate part 12. A positioning protrusion 40A protrudes from the upper surface. The protrusion 40A has a width that matches the width between the lower vertical wall portions 1Bb in the target part shape 1. In addition, the side surface facing the lower vertical wall portion 1Bb has a shape that follows the shape of the lower vertical wall portion 1Bb in the target part shape 1. In this example, since the lower vertical wall portion 1Bb is flat, the side surface of the protrusion 40A facing the lower vertical wall portion 1Bb is a flat surface. In addition, the height of the protrusion 40A is equal to the height of the lower vertical wall portion 1Bb. The height of the protrusion 40A may be lower than the height of the lower vertical wall portion 1Bb.

[0049] The upper die 41 has a forming surface 41A on its lower surface for press-forming the cross section of the top plate portion 1A. The forming surface 41A has a surface shape following the target top plate portion 1A. The left and right cams 42 are configured to be able to approach and separate from each other with the second intermediate part 12 sandwiched therebetween. The opposing surfaces of the left and right cams 42 are shaped to follow the shape of the target vertical wall part 1B (see FIG. 9(c)). The upper surface of the cam 42 is at approximately the same height as or slightly lower than the upper end of the vertical wall part 1B of the part placed on the lower die 40. The slightly lower position is, for example, a position that is five times lower than the upper end of the vertical wall part 1B by the thickness of the molded product. In other words, the top plate part 1A and the part that becomes the ridge part connecting the top plate part 1A and the vertical wall part 1B are set to be located above the upper surface of the cam 42. In this embodiment, the lower end surface of the cam 42 is set to have a gap with the upper surface of the lower die 40 so that the flange part 1C does not come into contact with the wall surface (pressing surface) of the cam 42.

[0050] Next, the operation of the mold shown in FIG. 9 in the third molding step 5C will be described. In the third molding step 5C, first, as shown in Fig. 9(a), the second intermediate part 12 is placed on the lower die 40. In this state, as shown in Fig. 9(a), the ridge portion of the second intermediate part 12 connecting the vertical wall portion 1B and the flange portion 1C is in contact with the upper surface of the lower die 40.

[0051] From this state, as shown in Fig. 9(b), the left and right cams 42 are brought closer to each other, and the second intermediate component 12 is deformed so that the areas that will become the left and right vertical wall portions 1B come closer to each other. Then, as shown in Fig. 9(c), the left and right cams 42 are brought closer to each other until the inner surfaces 2 of the recesses 1Bc of the left and right vertical wall portions 1B come into contact with each other. The gap distance between the inner surfaces 2 of the recesses 1Bc of the left and right vertical wall portions 1B is preferably 0 mm or more and half the width of the top plate portion 1A or less. The smaller this gap distance, the easier it is to align the inner surfaces 2 of the recesses 1Bc of the left and right vertical wall portions 1B. At this time, the position of the part is determined by the protrusion 40A. In addition, by clamping the lower vertical wall portion 1Bb between the protrusion 40A and the lower side of the cam 42, the shape of the lower vertical wall portion 1Bb can be further formed into the shape of the target part shape 1.

[0052] In this manner, by bending and deforming the second intermediate component 12 by the left and right cams 42, the region 12A which becomes the top plate portion 1A is deformed in a direction in which the radius of curvature becomes smaller. Then, the left and right cams 42 are brought close to each other to restrain the left and right vertical wall portions 1B in the state where they are brought close to each other, or the next process is executed in synchronization with the completion of the approach of the left and right cams 42. That is, as shown in FIG. 9(c), the upper die 41 is lowered, and the upper die 41 bends and deforms the region 12A that will become the top plate portion 1A in a direction in which the radius of curvature increases. The direction in which the radius of curvature increases is the direction in which the surface becomes flat. At this time, it is preferable that the stroke amount of the upper die 41 is regulated by bringing both side portions of the lower surface of the upper die 41 into contact with the upper surfaces of the left and right cams 42.

[0053] Here, the region 12A that will become the top plate portion 1A is formed in a direction from a convex shape with a small radius of curvature to a flat shape. This causes springback in the direction of closing the cross section at the ridge line connecting the top plate portion 1A and the vertical wall portion 1B. In other words, springback occurs in the direction of approaching the left and right vertical wall portions 1B. This springback also acts to increase the radius of curvature of the cross section of the top plate portion 1A, that is, to flatten the shape of the top plate portion. Therefore, if the top plate portion 1A is molded using an upper die 41 with a completely flat molding surface 41A, a convex shape remains on the top plate portion 1A after demolding. Therefore, if a flat top plate portion 1A is required after springback, it is desirable to set the molding surface 41A of the upper die 41 to a mold shape (molding surface shape) with a convex shape, for example, as shown in FIG. 10, which compensates for the deformation due to springback.

[0054] Here, the line length of each side after the third forming process 5C may be set to be slightly longer or shorter than the line length of each side up to the second forming process 5B. In this case, tensile or compressive deformation occurs in the metal sheet 10, respectively, and it becomes possible to reduce the amount of springback at the bend ridgeline.

[0055] <Another example of the third molding process 5C> Next, another example of the third molding step 5C suitable for the case where the curved portion constituting the convex portion has the cross-sectional shape of the second convex portion will be described. Note that even when the curved portion constituting the convex portion has the cross-sectional shape of the second convex portion, the above-mentioned third molding step 5C performed with a mold as shown in FIG. 9 may be applied. Similar to the above-described third forming process 5C, another example of the third forming process 5C is a process for forming the top plate portion 1A and bending the ridge portion 1D, which is the connection portion between the top plate portion 1A and the vertical wall portion 1B, of the second intermediate part 12. In this example of the third forming process 5C, when forming the top plate portion 1A into the target shape, the left and right vertical wall portions 1B are brought closer to each other and formed into the target part shape by this processing.

[0056] Another example of the third forming process 5C is a process in which, similar to the above-mentioned third forming process 5C, the second intermediate part 12 is pressed in a direction in which the areas that will become the left and right vertical wall portions 1B approach each other, and a further bending deformation is imparted to the area 11A that will become the top plate portion 1A. This other example of the third shaping step 5C is performed by the same process and mechanism as the above-mentioned third shaping step 5C, except for the specific processing method for bending and deforming the region 12A that becomes the top plate portion 1A. In another example of the third forming step 5C, the convex portion on the side of the region 12A that will become the top plate portion 1A has a trapezoidal cross-sectional shape having a flat top plate flat portion 12Aa and inclined portions 12Ab on both the left and right sides, as shown in Fig. 12(a). The top plate flat portion 12Aa is the highest position (top surface). 11, another example of the third molding step 5C is performed using a pair of dies 40, 41 facing each other with the second intermediate part 12 in between, and left and right cams 42. The pair of dies includes a lower die 40 and an upper die 41.

[0057] The upper surface of the lower die 40 is a flat surface that can be contacted by the flange portion 1C, which is the lower portion of the second intermediate part 12. A positioning protrusion 40A protrudes from the upper surface. The protrusion 40A has a width that matches the width between the lower vertical wall portions 1Bb in the target part shape 1. In addition, the side surface facing the lower vertical wall portion 1Bb has a shape that follows the shape of the lower vertical wall portion 1Bb in the target part shape 1. In this example, the lower vertical wall portion 1Bb is flat. Therefore, the side surface of the protrusion 40A facing the lower vertical wall portion 1Bb is a flat surface. In addition, the height of the protrusion 40A is equal to the height of the lower vertical wall portion 1Bb. The height of the protrusion 40A may be lower than the height of the lower vertical wall portion 1Bb.

[0058] As shown in FIG. 12(a), the upper die 41 has a molding surface 41A that presses the top plate flat portion 12Aa against the lower surface. The molding surface 41A has a surface shape that follows the target top plate portion 1A. A concave relief portion 41B is formed at each end in the width direction of the molding surface 41A. The width T of the molding surface 41A is equal to or slightly smaller than the width of the top plate flat portion 12Aa. The molding surface 41A faces the top plate flat portion 12Aa from above and below, and may apply a downward pressing force to the top plate flat portion 12Aa. It is preferable that the surface of the top plate flat portion 12Aa is a surface perpendicular to the pressing direction.

[0059] Furthermore, by pressing the top plate flat portion 12Aa with the forming surface 41A, the left and right inclined portions 12Ab are deformed to be outwardly convex (see FIG. 12(c)). The above-mentioned relief portion 41B is formed to prevent interference with this deformation. However, FIG. 12(c) shows the deformation in an exaggerated manner, and it is not necessary to deform the first ridge portion 12Ac and the second ridge portion 12Ad to the extent that they are reversely bent.

[0060] The left and right cams 42 are configured to be able to move toward and away from each other, sandwiching the second intermediate part 12. The opposing surfaces of the left and right cams 42 are shaped to conform to the shape of the target vertical wall portion 1B (see FIG. 11(c)). The upper surfaces of the cams 42 are at approximately the same height as or slightly lower than the upper end of the area that will become the vertical wall portion 1B in the part placed on the lower die 40. A slightly lower position is, for example, a position that is five times the plate thickness of the molded product lower than the upper end of the vertical wall portion 1B.

[0061] As a result, the second intermediate part 12 is set so that the top plate portion 1A and a portion that becomes the ridge portion 1D connecting the top plate portion 1A and the vertical wall portion 1B are positioned above the upper surface of the cam 42. In this embodiment, the lower end surface of the cam 42 is set so as to have a gap with the upper surface of the lower die 40. As a result, the flange portion 1C does not come into contact with the wall surface (pressing surface) of the cam 42 (see FIG. 11(a)).

[0062] Next, the operation of the mold in another example of the third molding step 5C will be described. In the third molding step 5C, first, as shown in Fig. 11(a), the second intermediate part 12 is placed on the lower die 40. In this state, as shown in Fig. 11(a), the ridge portion of the second intermediate part 12 that connects the vertical wall portion 1B and the flange portion 1C is in contact with the upper surface of the lower die 40.

[0063] From this state, as shown in Fig. 11(b), the left and right cams 42 are brought closer to each other, and the second intermediate component 12 is deformed so that the areas that will become the left and right vertical wall portions 1B come closer to each other. Then, as shown in Fig. 11(c), the left and right cams 42 are brought closer to each other until the inner surfaces 2 of the recesses 1Bc of the left and right vertical wall portions 1B come into contact with each other. At this time, the positioning of the part is performed by the protrusion 40A. In addition, by clamping the lower vertical wall portion 1Bb between the protrusion 40A and the lower side of the cam 42, the shape of the lower vertical wall portion 1Bb can be further formed into the shape of the target part shape 1. In this way, by bending and deforming the second intermediate part 12 by the left and right cams 42, as shown in FIG. 12(a) to FIG. 12(b), the radius of curvature of the region 12A that becomes the top plate portion 1A is deformed in a direction that decreases.

[0064] Then, the left and right cams 42 are brought close to each other to restrain the left and right vertical wall portions 1B, or pressing is performed in synchronization with the completion of the approach of the left and right cams 42, as shown in FIG. 11(c). That is, the upper die 41 is lowered and the molding surface 41A of the upper die 41 presses the top plate flat portion 12Aa downward. Pressing downward means pressing in the direction in which the top plate flat portion 12Aa approaches the vertical wall portion. By pressing the top surface of the top plate flat portion 12Aa, the surface of the top plate flat portion 12Aa comes into contact with the molding surface 41A of the upper die 41, so that even if the top plate flat portion 12Aa is tilted at the time of initial setting, it is automatically adjusted to a horizontal surface.

[0065] As the flat portion 12Aa of the top plate is pressed downward, the left and right inclined portions 12Ab are deformed so as to bulge outward, as shown in Fig. 12(b) to Fig. 12(c). That is, the radius of curvature of the cross-sectional shape of the inclined portions 12Ab is deformed to become smaller when viewed from the inner surface side. With this deformation of the inclined portions 12Ab, the cross-sections of the first ridge portion 12Ac and the second ridge portion 12Ad, which are bent portions continuing to the ends of the inclined portions 12Ab, are both deformed in a direction in which the radius of curvature becomes larger.

[0066] Here, it is desirable to set the overall width W of the upper die 41 from left to right to greater than the target width of the target part shape at that height position. The stroke amount of the upper die 41 is regulated by adjusting the distance between both side portions of the lower surface of the upper die 41 and the upper surfaces of the left and right cams 42 . In Fig. 12(c), the bulging left and right inclined portions 12Ab are in contact with the relief portions 41B. However, it is not necessary for the bulging left and right inclined portions 12Ab to be in contact with the relief portions 41B. The amount of outward bulging of the left and right inclined portions 12Ab may be adjusted by adjusting the depth D of the relief portions.

[0067] When the top plate flat portion 12Aa is pressed downward to the bottom dead center and then released from the mold, springback occurs in the region 12A that will become the top plate portion, resulting in a shape as shown in the schematic diagram of FIG. 12(d). This demolding causes springback mainly at the left and right inclined portions 12Ab, the first edge portion 12Ac, and the second edge portion 12Ad. In the left and right inclined portions 12Ab, springback occurs in the direction in which the radius of curvature increases. In other words, in the left and right inclined portions 12Ab, springback acts in the direction in which the inclined portions 12Ab become flat. In other words, springback occurs in the direction in which the left and right vertical wall portions 1B open from each other when the mold is released. On the other hand, the first ridgeline portion 12Ac and the second ridgeline portion 12Ad act as springback in a direction from a state in which the radius of curvature is large to a state in which the radius of curvature is small. In other words, at the time of demolding, springback occurs in a direction in which the left and right vertical wall portions B approach each other.

[0068] That is, by forming with the left and right cams 42 and the upper die 41, all or part of the top plate flat portion 12Aa is bent slightly convexly from the flat shape before forming, and then bent in a direction that stretches the convex bend. At this time, all or part of the first ridge portion 12Ac and the second ridge portion 12Ad are deformed to stretch the convex bend formed in the second forming process, or are deformed to bend concavely. All or part of the inclined portion 12Ab is bent convexly outward. As a result of these forming processes, at the bottom dead center of forming, the top plate flat portion 12Aa, the first ridge portion 12Ac, and the second ridge portion 12Ad are subjected to bending moments mainly in the direction of closing the walls on both sides, and the inclined portion 12Ab is subjected to bending moments mainly in the direction of opening the vertical wall portions. After that, even after springback due to demolding, these are offset or the closing direction becomes dominant. As a result, a molded product with a closed cross section can be produced. Furthermore, the order in which the left and right cams 42 and the upper die 41 come into contact with the molded product or reach the bottom dead center position may be any of the following: the left and right cams 42 first, the left and right cams 42 and the upper die 41 simultaneously, or the upper die 41 first.

[0069] As described above, in another example of the third forming step 5C, the region 12A including the top plate portion 1A and the ridge portion 1D is formed from the convex shapes 12Aa and 12Ad with a small radius of curvature toward a flattened direction. This causes springback in the direction of closing the cross section of the ridge portion 1D and part of the vertical wall portion 1B connecting the top plate portion 1A and the vertical wall portion 1B. In other words, springback is generated in the direction of approaching the left and right vertical wall portions 1B. As a result, it is possible to achieve a more firmly closed shape for the surfaces to be joined of the left and right vertical wall portions 1B.

[0070] The molding surface of the upper mold may not have a relief portion, as shown in FIG. Here, the line length of each side after the alternative example of the third forming process 5C may be set to be slightly longer or shorter than the line length of each side up to the second forming process 5B. In this case, tensile or compressive deformation occurs in the metal sheet 10, respectively, and it becomes possible to reduce the amount of springback at the bent ridgeline.

[0071] <Joining process step 5D> In the joining process 5D, the left and right vertical wall portions 1B are joined at the positions of the recesses 1Bc to the part that has become the target part shape after the third forming process 5C. The joining process is performed by spot welding at 50 mm intervals along the longitudinal direction, for example. However, there are no particular restrictions on the joining method. Known joining processes such as adhesion and riveting other than welding may be used. The joining process makes it possible to more reliably form a structural member with a closed cross-sectional shape. However, the joining process does not necessarily have to be performed. When the manufactured structural members are assembled, the structural members are assembled so that the recesses 1Bc are in surface contact with each other, resulting in a structure with a closed cross-sectional shape.

[0072] (Operation etc.) According to this embodiment, it is possible to produce a press-formed product having a closed cross section from one metal plate 10 by a multi-step press forming process using a combination of a press machine and a die having a general structure. That is, in this embodiment, a general-purpose press machine can be used, and the die structure is a general structure for automobile parts, so that it is possible to produce the product in the conventional press process for automobile parts without reducing the production speed. Therefore, it is possible to inexpensively produce parts having a closed cross section that would have been conventionally produced by roll forming or by combining multiple parts.

[0073] In this embodiment, in the third forming step 5C, bending deformation is applied to the region 11A that will become the top plate portion 1A while the left and right vertical wall portions 1B are brought close to each other. This makes it possible to set the gap between the recesses 1Bc of the left and right vertical wall portions 1B to zero or to a small gap. As a result, the metal plate 10 is made of a high-strength material, and a structural member having a closed cross-sectional shape can be easily manufactured by press forming.

[0074] In this case, when the curved portion constituting the convex portion has the cross-sectional shape of the second convex portion, the following advantageous effects are achieved. That is, according to this embodiment, the surfaces of the left and right vertical wall portions 1B to be joined to each other can be made into a more closed shape by the modified third molding step 5C. According to this embodiment, when forming the top plate portion 1A side in another example of the third forming process 5C, a flat top plate portion 12Aa is formed in advance in the region that will become the top plate portion in a previous process. As a result, a flat portion with high flatness and better dimensional accuracy can be provided for the top plate portion 1A.

[0075] As described above, according to this embodiment, even if the metal plate 10 is a high-strength steel plate, it is possible to provide a flat portion with good dimensional accuracy on the top plate portion 1A while suppressing the gap between the left and right vertical wall portions 1B. In other words, this embodiment is a suitable technique for high-strength materials with large springback.

[0076] Here, a closed cross-section part, such as the part shape targeted by the present invention, is often used by joining it to another part. At that time, it is desirable that the joint with the other part is flat. Therefore, high flatness and dimensional accuracy may be required for the top plate portion 1A in order to attach another part. Simply, if the top plate portion 1A side is bent in the second forming process 5B, a cross-sectional curvature larger than the target part shape is given to the area that will become the top plate portion 1A. In this case, it is necessary to reduce the curvature to form the top plate portion 1A in the subsequent third forming process 5C, and adjustment of the mold for this purpose is required. In particular, when it is desired to form a flat surface on the top plate portion 1A, the following problem arises. That is, when a curvature is given to the top plate portion 1A in an intermediate process and then the top plate portion 1A is molded to return to a flat shape in the third forming process 5C, it may be difficult to adjust the dimensional accuracy of the flat surface. In contrast, in this embodiment, when another example of the third forming process 5C is adopted, a flat top plate flat portion 12Aa is provided in the area that will become the top plate portion 1A in the second forming process 5B. Therefore, the top plate flat portion 12Aa can be molded as it is in the third molding step 5C without changing its shape as a part of the top plate portion 1A. Therefore, when another example of the third molding step 5C is adopted, according to this embodiment, it becomes easier to obtain a molded product having a top plate shape with a flat portion with high dimensional accuracy.

[0077] In addition, the structural member manufactured in this embodiment has a closed cross section, and the mounting portion is formed by the flange portion 1C that is continuous with the lower vertical wall portion 1Bb extending downward. In the case where the flange portion 1C is not present, for example, the lower end portion or the longitudinal end portion of the lower vertical wall portion 1Bb is assembled, so that the manufactured structural member is used in a state having a closed cross section.

[0078] (others) The present disclosure may have the following configurations. (1) Disclosure 1 is a manufacturing method for a structural member, comprising: a top plate portion; and left and right vertical wall portions that are connected to both widthwise ends of the top plate portion via ridge portions and that face each other in the width direction of the top plate portion, and a recess is formed in one or both of the left and right vertical wall portions at a midpoint in the height direction of the vertical wall portion, protruding toward the other opposing vertical wall portion, and an inner surface of the recess is in surface contact with an inner surface of the other vertical wall portion, the manufacturing method comprising press-forming a metal plate into a target part shape having a cross section; a first forming step of press-forming the metal plate into a first intermediate part having the recess; a second forming step of bending the first intermediate component in a direction in which an inner surface of the recess approaches a region that will become the other vertical wall portion, in a region that will become the top plate portion, or in a region that will become the top plate portion and a region that will become the ridge line portion, to produce a second intermediate component; a third forming step of further bending the region that will become the top plate portion while pressing the regions that will become the left and right vertical wall portions of the second intermediate part in a direction in which the regions approach each other; A manufacturing method of a structural member comprising: (2) In the second forming step, a convex portion having a cross-sectional curved shape that is convex in an outward bending direction is formed in the region that will become the top plate portion by applying the bending deformation, In the third forming step, the bending deformation is applied to the protruding portion so that the radius of curvature of the cross section increases. A method for manufacturing a structural member. (3) Disclosure 3 discloses that the cross-sectional shape of the second intermediate component on the side of the region that will become the top plate portion has a top plate flat portion formed within the region that will become the top plate portion and having a flat surface shape, and left and right inclined portions that are connected to both ends of the top plate flat portion in the width direction, extend obliquely toward the vertical wall portion, and connect the top plate flat portion and the region that will become the vertical wall portion, The bending deformation in the third forming step is performed by pressing the flat portion of the top plate in a direction in which the flat portion of the top plate approaches the vertical wall portion. A method for manufacturing a structural member. (4) In the third forming step, the flat portion of the top plate is pressed to deform the left and right inclined portions in a direction in which the radius of curvature of the cross section becomes smaller. A method for manufacturing a structural member. (5) Disclosure 5 discloses the first forming step, which is carried out by press-forming the metal plate with a pair of dies facing each other in a plate thickness direction of the metal plate; a concave shape for forming the recess is formed on a molding surface of one of the molds, and a convex shape corresponding to the concave shape is formed on a molding surface of the other mold; A method for manufacturing a structural member. (6) Disclosure 6 discloses that the target part shape includes an outward flange portion connected to an end of the vertical wall portion, The first forming step is to bend and deform the outward flange portion at a ridge line position connecting the vertical wall portion and the outward flange portion so that the outward flange portion rises in a direction opposite to a protruding direction of the recessed portion. A method for manufacturing a structural member. (7) Disclosure 7 discloses that the second forming step is a bending process using a die having a recess on a forming surface facing the region that will become the top plate portion of the first intermediate part, and a punch that presses the region that will become the top plate portion toward the recess of the die, thereby forming the first intermediate part into the shape of the second intermediate part. A method for manufacturing a structural member. (8) Disclosure 8 states that the third molding step is performed using left and right cams that press the regions that will become the left and right vertical wall portions of the second intermediate part in a direction in which the regions approach each other, and a die that presses the region that will become the top plate portion to have a top plate shape in a target part shape while being pressed by the left and right cams. A method for manufacturing a structural member. (9) Disclosure 9 discloses that the surfaces of the left and right cams that come into contact with the second intermediate part have a shape that follows the shape of the vertical wall portion. A method for manufacturing a structural member. (10) Disclosure 10 sets the approach of the regions that will become the left and right vertical wall portions by the pressing in the third molding step so that the distance between the inner surface of the recess in the second intermediate part and the surface of the region that will become the other vertical wall portion that faces the recess is 0 mm or more and 1 / 2 the width of the top plate portion or less. A method for manufacturing a structural member. (11) Disclosure 11 discloses a method for manufacturing a molded product, the method comprising the steps of: forming a molded product having a molded product having a molded product; forming the outward flange portion, A method for manufacturing a structural member. (12) Disclosure 12 includes, as a step after the third molding step, a joining process in which the concave surface of the recess is brought into surface contact with the inner surface of the other vertical wall portion to join the inner surface of the recess and the inner surface of the other vertical wall portion to form a closed cross section. A method for manufacturing a structural member. EXAMPLES

[0079] Next, examples based on this embodiment will be described. "First embodiment" First, the first embodiment will be described. (Target part shape 1) In this embodiment, the target part shape 1 of the target structural member (press-molded product) is the shape shown in FIG. 1 and FIG. 2. That is, the target part shape 1 of this embodiment has a top plate portion 1A, left and right vertical wall portions 1B, and left and right flange portions 1C. Furthermore, the target part shape 1 of this embodiment is a shape in which recesses 1Bc are formed in the left and right vertical wall portions 1B, and the inner surfaces 2 of the left and right recesses 1Bc can be in surface contact with each other. By making the inner surfaces 2 of the left and right recesses 1Bc in surface contact with each other, the structural member has a closed cross section formed above the recesses 1Bc, and the lower flange portion 1C has a mounting portion for another component. In addition, when the structural member is in an upright position, the left and right flange portions 1C extend horizontally to form feet. In addition, the connections of each portion are configured to be continuous by forming an arc-shaped arc.

[0080] The metal sheet 10 to be press-formed was a cold-rolled steel sheet having a thickness of 1.4 mm and a yield strength of 1200 to 1300 MPa. The dimensions of the structural member to be manufactured are as shown in Figures 1 and 2. That is, the target structural member has a height of 100 mm, a width of the top plate portion 1A of 15 mm, a longitudinal length of 600 mm, and a vertical length at the bottom portion (vertical wall joint) of the recess 1Bc of 15.1 mm. The depth (step) of the recess 1Bc is 6.1 mm. Also, the connection portions of each side in the cross section are configured to be continuous, forming an arc-shaped R. Specifically, the sides are connected by a curve with an inner radius of curvature of 4.2 mm.

[0081] (Manufacturing) In this example, similarly to the embodiment, press molding was carried out in the order of the first molding step 5A, the second molding step 5B, and the third molding step 5C to manufacture a structural member.

[0082] <1st molding process 5A> In the first forming step 5A of this example, the metal plate 10 was press-formed by the method described in the embodiment using the die shown in Fig. 5 to produce the first intermediate part 11. That is, left and right recesses 1Bc and left and right flange portions 1C were formed in the metal plate 10 (see Fig. 7(a)).

[0083] <Second forming process 5B> In the second forming step 5B of this example, the first intermediate part 11 was press-formed by the method described in the embodiment using the die shown in Fig. 7(b) to produce a second intermediate part 12. However, the shape of the forming surface of the die used in the second forming step 5B was a forming surface having an arc-shaped cross section. In this example, the tip 31Aa of the punch 31A provided on the upper die 41 is shaped to have a width of 20.8 mm and a tip R of 8.5 mm. The punch 31A is bent using a metal mold so that the angle between the left and right vertical wall portions 1B is approximately 30 degrees.

[0084] <Third molding process 5C> In the third forming step 5C of this example, the second intermediate part 12 was press-formed by the method described in the embodiment using the mold shown in FIG. 9, to produce a part having the target part shape 1. Here, the protrusion 40A provided on the lower die 40 was set to match the target part shape 1, with a width of 12.2 mm and an arc shape with a rounded tip having a radius of 4.2 mm. The recessed shape 20Ba of the molding surface formed on the lower surface of the upper die 41 was an arc-shaped recessed portion 1Bc having a width of 15 mm and a radius of curvature of 5 mm. In this embodiment, the minimum approach distance between the left and right cams 42 was changed, and the third forming step 5C was performed under three conditions, the first example to the third example, as described below. However, the conditions for the first forming step 5A and the second forming step 5B in the first example to the third example were the same.

[0085] [Conditions for the first example] In the first example, the minimum approach distance between the left and right cams 42 was set to 4.2 mm (three times the plate thickness). In other words, the left and right cams 42 restrained the second intermediate part 12 so that the gap (spacing) between the left and right recesses 1Bc was 1.4 mm (corresponding to the plate thickness). In this state, the region 11A that would become the top plate portion 1A was bent by the upper die 41. The minimum approach distance between the left and right cams 42 is the distance between the faces that come into contact with the recesses 1Bc.

[0086] [Conditions for the second example] In the second example, the minimum approach distance between the left and right cams 42 was set to 2.8 mm (twice the plate thickness). In other words, the left and right cams 42 restrained the second intermediate part 12 so that the gap (spacing) between the left and right recesses 1Bc was 0.0 mm (surface contact state). However, bending of the region 11A that would become the top plate portion 1A by the upper die 41 was not performed.

[0087] [Conditions for the third example] In the third example, the minimum approach distance between the left and right cams 42 was set to 2.8 mm (twice the plate thickness). In other words, the left and right cams 42 restrained the second intermediate part 12 so that the gap (distance) between the left and right recesses 1Bc was 0.0 mm (surface contact state). Then, in this state, the region 11A that would become the top plate portion 1A was bent by the upper die 41.

[0088] (evaluation) Structural members were manufactured under the conditions of the first to third examples above, and the gap distance between the inner surfaces 2 of the recesses 1Bc provided in the left and right vertical wall portions 1B after release from the mold in the third molding step 5C was measured. The value at the center position in the height direction of the inner surfaces 2 of the recesses 1Bc was used as the gap distance. The results of the evaluation are shown below. First example: Gap distance = 1.5mm Second example: Gap distance = 5.3mm Third example: Gap distance = 0mm (no gap)

[0089] As can be seen from the first and third examples, in the third forming step 5C, the region 11A that will become the top plate portion 1A is bent and formed by the upper die 41, and the following was found. That is, it was found that the above-mentioned gap distance after demolding can be set to a value equivalent to the separation distance in the restrained state by the left and right cams 42. In other words, it was found that the manufacturing method based on the present invention can easily control the gap distance between the recesses 1Bc after demolding, and further, can set the separation distance small.

[0090] On the other hand, the second example has revealed the following: Even if the left and right cams 42 are used to restrict the separation distance to be small, if the region 11A that will become the top plate portion 1A in the upper die 41 is not bent in the third forming step 5C, the separation distance after release becomes wider than the width of the top plate portion 1A. In other words, the distance between the left and right vertical wall portions 1B widens in an inverted V shape, and the higher the strength of the material of the metal plate 10, the more likely it is that the joining process between the left and right recesses 1Bc cannot be easily performed.

[0091] Next, for the structural materials manufactured under the conditions of each of the first to third examples, the left and right recesses 1Bc were joined together by spot welding at a pitch of 50 mm along the longitudinal direction. Then, it was investigated whether the final target product shape could be formed. In the case of the structural members manufactured in the first and second examples, it was confirmed that the final target product shape could be achieved by spot welding while pressing and holding the lower vertical wall portion 1Bb from the left and right. However, the structural member manufactured in the second example required setting a larger pressing force from the left and right. Moreover, in the case of the structural member manufactured in the third example, it was confirmed that spot welding was possible without the need to press the lower vertical wall portion 1Bb, and the intended target part shape 1 could be easily formed.

[0092] "Second embodiment" Next, a second embodiment will be described. In the second example, an evaluation is performed for the case where the curved portion constituting the convex portion has the cross-sectional shape of the second convex portion (see FIG. 12(a)). (Target part shape 1) In this embodiment, the target part shape 1 of the target structural member (press-molded product) is the shape shown in FIG. 1 and FIG. 2. That is, the target part shape 1 of this embodiment has a top plate portion 1A, left and right vertical wall portions 1B connected to the top plate portion 1A via a ridge portion 1D, and left and right flange portions 1C. Furthermore, the target part shape 1 of this embodiment is a shape in which recesses 1Bc are formed in the left and right vertical wall portions 1B, and the inner surfaces 2 of the left and right recesses 1Bc can be in surface contact with each other. By making the inner surfaces 2 of the left and right recesses 1Bc in surface contact with each other, the structural member has a closed cross section formed above the recesses 1Bc, and the lower flange portion 1C has an attachment portion to another component. In addition, it is assumed that the top plate portion 1A is a joint portion with another component, and the top plate portion 1A is a flat surface. In addition, when the structural member is in an upright position, the left and right flange portions 1C extend horizontally to form feet. In addition, the connection of each portion is configured to be continuous by forming an arc-shaped arc.

[0093] The metal sheet 10 to be press-formed was a cold-rolled steel sheet having a thickness of 1.4 mm and a tensile strength of 1470 MPa. It was confirmed that the same evaluation as above was obtained when a metal sheet having a tensile strength of 1570 MPa was used. The dimensions of the structural member to be manufactured are as shown in Figures 1 and 2. That is, the target structural member has a height of 100 mm, a width of the top plate portion 1A of 15 mm, a longitudinal length of 600 mm, and a vertical length at the bottom portion (vertical wall joint) of the recess 1Bc of 15.1 mm. The depth (step) of the recess 1Bc is 6.1 mm. Also, the connection portions of each side in the cross section are configured to be continuous, forming an arc-shaped R. Specifically, the sides are connected by a curve with an inner radius of curvature of 4.2 mm.

[0094] (Manufacturing) In this example, similarly to the embodiment, press molding was carried out in the order of the first molding step 5A, the second molding step 5B, and the third molding step 5C to manufacture a structural member. At this time, the target structural members were manufactured by two methods: an example based on the present invention, and a reference example for comparison. In the inventive example, as described later, the molding surface shape of the mold used in the second molding step 5B was based on the molding surface of this embodiment. In the reference example, as described later, the molding surface shape of the mold used in the second molding step 5B was a molding surface having an arc-shaped cross section.

[0095] (Example of the invention) <1st molding process 5A> In the first forming step 5A of this example, the metal plate 10 was press-formed by the method described in the embodiment using the die shown in Fig. 5 to produce the first intermediate part 11. That is, left and right recesses 1Bc and left and right flange portions 1C were formed in the metal plate 10 (see Fig. 7(a)).

[0096] <Second forming process 5B> In the second molding process 5B of this embodiment, a mold having a lower die 30 having the shape of the molding surface 30A shown in Figure 11 was used to press-mold the first intermediate part 11 as shown in Figure 7(b) using the method described in the embodiment, to produce a second intermediate part 12. In this embodiment of the present invention, the shape of the tip 31Aa of the punch 31A provided in the upper die 41 was made to have the same surface shape as that of the lower die 30.

[0097] In the example of the invention, the cross-sectional shape of the molding surface 30A of the lower die 30, which forms the shape of the area that will become the top plate portion 1A, is set as follows. Here, the cross-sectional shape of the molding surface 30A is synonymous with the shape of the area that will become the top plate portion 1A in the second intermediate part 12. For this reason, it will be described according to the names of each part of the second intermediate part 12.

[0098] [Settings] The settings are as follows (see Figure 8): Angle between the flat top portion 12Aa and the left and right vertical wall portions 1B: 30 degrees Length of top plate flat part 12Aa w1: 7.8mm - Radius of curvature r1 of the first ridge 12Ac: 4.1 mm Distance between left and right second ridges 12Ad d1: 20.8mm - Radius of curvature of the second joint r2: 4.1mm

[0099] <Third molding process 5C> In the third forming process 5C of this example, a second intermediate part 12 was press-formed by the method described in the embodiment using the mold shown in Figures 11 and 12. Then, a part having the target part shape 1 was produced. Here, the protrusion 40A provided on the lower die 40 was set to match the target part shape 1, with a width of 12.2 mm and an arc shape with a rounded tip having a radius of 4.2 mm. The molding surface of the upper die 41 was shaped as shown in FIG. 12(a).

[0100] The dimensions are as follows: Overall width W of the molding surface of the upper die 41: 16 mm Width T of the convex molding surface 41A that contacts the top plate flat portion 12Aa: 5.2 mm Depth of relief D: 1.0mm - Radius of curvature R of the bottom of the arc-shaped part located on the left and right outer sides of the relief: 4.0 mm

[0101] (Reference example) In the reference example, as in the invention example, press molding was carried out in the order of the first forming step 5A, the second forming step 5B, and the third forming step 5C to manufacture a structural member. In the first molding step 5A, the processing was carried out under the same molding conditions as in the invention example. Next, the second molding step 5B was carried out under the same molding conditions as in the example of the invention, except that the shape of the molding surface of the mold was different.

[0102] The molding surface shape of the mold in the reference example is as follows. The shape of tip 31Aa of punch 31A provided on upper die 41 of the reference example was set to a width of 20.8 mm, with a tip radius of 8.5 mm. Regarding the shape of the bottom portion of concave forming surface 30A of lower die 30, the shape of the forming surfaces 30Aa, 30Ab, which are trapezoidal in the invention example (see FIG. 8), was made to match the shape of tip 31Aa of punch 31A, with a circular arc-shaped cross section with a radius of curvature of 8.5 mm. Then, using a die having the above-mentioned molding surface shape, the product was bent so that the angle between the left and right vertical wall portions 1B was about 30 degrees. The top portion of the second intermediate part manufactured in the reference example on the side of the region that becomes the top plate portion has an arc-shaped cross section.

[0103] Next, another example of the third molding step 5C was carried out under the same molding conditions as the example of the invention, except that the shape of the molding surface of the upper die 41 was different. The molding surface shape of the upper die 41 in the reference example does not have a convex portion (molding surface 41A in Fig. 12(a)) in the center. The rest of the molding surface is a concave molding surface similar to the molding surface shape of the invention example (see Fig. 12(a)). The concave molding surface has an overall width W of 15 mm and a circular arc shape with a bottom curvature radius R of 5 mm.

[0104] (evaluation) A structural member was manufactured under each of the conditions of the above-mentioned invention example and reference example, and the gap distance between the inner surfaces 2 of the recesses 1Bc provided in the left and right vertical wall portions 1B after the structural member was released from the mold in another example of the third molding process 5C was measured. The value at the center position in the height direction of the inner surfaces 2 of the recesses 1Bc was used as the gap distance. The results of the evaluation are shown below. Example of the invention: Gap distance = 0 mm (no gap) Reference example: Gap distance = 2.0 mm

[0105] From this evaluation, it was found that the manufacturing method according to the present invention can easily control the gap distance between the recesses 1Bc after demolding. Moreover, it was found that the gap distance can be set small. In the example of the invention, the top shape of the second intermediate part is formed into a trapezoidal shape. As a result, compared to the reference example in which the top shape of the second intermediate part is simply bent in the second forming step to form an arc-shaped cross section, the following was found: In the example of the invention in which the top shape of the second intermediate part is formed into a trapezoidal shape, it was found that the gap between the left and right vertical wall portions after the third forming step can be controlled to be small.

[0106] Here, whether the second intermediate part of the invention example or the reference example was used, in the case where the region 12A to become the top plate portion 1A was not bent in the alternative example of the third forming step 5C, the separation distance after demolding was wider than the width of the top plate portion 1A. That is, even if the left and right vertical wall portions were restrained by the left and right cams 42 so as to reduce the separation distance, in the case where the region 12A to become the top plate portion 1A in the upper die 41 was not bent in the alternative example of the third forming step 5C, the separation distance after demolding was wider than the width of the top plate portion 1A. That is, the distance between the left and right vertical wall portions 1B widens in a V-shape, and the higher the strength of the material of the metal plate 10, the more likely it is that the joining process between the left and right recesses 1Bc cannot be easily performed.

[0107] Next, for the structural materials manufactured under each of the conditions of the invention example and the reference example, it was investigated whether the left and right recesses 1Bc could be joined together by spot welding at a pitch of 50 mm along the longitudinal direction to form the final target product shape. It was confirmed that the structural members manufactured in both the invention and reference examples could be formed into the final target product shape by spot welding the lower vertical wall portion 1Bb while pressing it from the left and right. However, the structural member manufactured in the reference example required a stronger pressing force from the left and right. Furthermore, in the case of the structural member manufactured according to the invention example, it was confirmed that spot welding was possible without the need to press the lower vertical wall portion 1Bb, and the desired target part shape 1 could be easily formed.

[0108] The entire contents of Japanese Patent Application No. 2023-220210 (filed December 27, 2023) and Japanese Patent Application No. 2024-035651 (filed March 8, 2024), from which this application claims priority, are incorporated herein by reference. Although the present application has been described with reference to a limited number of embodiments, the scope of the rights is not limited thereto, and modifications of each embodiment based on the above disclosure would be obvious to those skilled in the art. [Explanation of symbols]

[0109] 1 Target part shape 1A Top plate 1B Vertical wall section 1Ba Upper vertical wall 1Bb Lower vertical wall 1Bc Recess 1C Outward flange 1D Ridge 2. Inner surface of recess 5A 1st molding process 5B 2nd molding process 5C 3rd molding process 5D bonding process 10 Metal plate (blank) 11 First intermediate part 11A Top plate area 12 Second intermediate part 12A Top plate area 12Aa Flat top 12Ab Inclined section 12Ac 1st ridgeline section 12Ad 2nd ridgeline section 20 Upper mold 20 Lower mold 20B Lower Pad 20Ba concave shape 20C bending blade 21 Upper mold 21B Upper pad 21C Upper die 30 Lower die 30A concave 31 Upper die 31A Punch 31Aa Tip 40 Lower die 40A protrusion 41 Upper die 41A Molding surface 42 Cam

Claims

1. A method for manufacturing a structural member, comprising press-forming a metal plate into a target part shape comprising: a top plate portion; and left and right vertical wall portions connected to both widthwise ends of the top plate portion via ridge portions and opposing each other in the widthwise direction of the top plate portion; and a recess formed in one or both of the left and right vertical wall portions at a midpoint in the height direction of the vertical wall portion, the recess protruding toward the other opposing vertical wall portion, and the inner surface of the recess being in surface contact with the inner surface of the other vertical wall portion, a first forming step of press-forming the metal plate into a first intermediate part having the recess; a second forming step of producing a second intermediate part by applying bending deformation to the first intermediate part in a region that will become the top plate portion, or in a region that will become the top plate portion and a region that will become the ridge line portion, in a direction in which an inner surface of the recess approaches a region that will become the other vertical wall portion; a third forming step of further bending the region that will become the top plate portion while pressing the regions that will become the left and right vertical wall portions of the second intermediate part in directions in which the regions that will become the left and right vertical wall portions approach each other; Equipped with In the second forming step, by applying the bending deformation, a convex portion having a cross-sectional curved shape that is convex in an outward bending direction is formed in the region that will become the top plate portion, In the third forming step, the bending deformation is applied to the convex portion, thereby deforming the convex portion in a direction in which the radius of curvature of the cross section increases. Manufacturing method of structural members.

2. A method for manufacturing a structural member, comprising: a top plate portion; and left and right vertical wall portions connected to both widthwise ends of the top plate portion via ridge portions and opposing each other in the widthwise direction of the top plate portion, wherein a recess is formed in one or both of the left and right vertical wall portions at a midpoint in the height direction of the vertical wall portion, protruding toward the other opposing vertical wall portion, and the inner surface of the recess is in surface contact with the inner surface of the other vertical wall portion, wherein the method comprises press-forming a metal plate into a target part shape, a first forming step of press-forming the metal plate into a first intermediate part having the recess; a second forming step of producing a second intermediate part by applying bending deformation to the first intermediate part in a region that will become the top plate portion, or in a region that will become the top plate portion and a region that will become the ridge line portion, in a direction in which an inner surface of the recess approaches a region that will become the other vertical wall portion; a third forming step of further bending the region that will become the top plate portion while pressing the regions that will become the left and right vertical wall portions of the second intermediate part in directions in which the regions that will become the left and right vertical wall portions approach each other; Equipped with The cross-sectional shape of the second intermediate component on the side of the region that will become the top plate portion has a top plate flat portion that is formed within the region that will become the top plate portion and has a flat surface shape, and left and right inclined portions that are connected to both widthwise end portions of the top plate flat portion and extend obliquely toward the vertical wall portion to connect the top plate flat portion and the region that will become the vertical wall portion, The bending deformation in the third forming step is performed by pressing the flat portion of the top plate in a direction in which the flat portion of the top plate approaches the vertical wall portion. Manufacturing method of structural members.

3. In the third forming step, the flat portion of the top plate is pressed to deform the left and right inclined portions in directions in which the curvature radii of the cross sections become smaller. A method for manufacturing a structural member according to claim 2.

4. the first forming step is performed by press-forming the metal plate with a pair of dies facing each other in a plate thickness direction of the metal plate, a concave shape for forming the recess is formed on a molding surface of one of the molds, and a convex shape corresponding to the concave shape is formed on a molding surface of the other mold; A method for manufacturing a structural member according to any one of claims 1 to 3.

5. the target part shape includes an outward flange portion connected to an end of the vertical wall portion; the first forming step bending and deforming the outward flange portion at a ridge line position connecting the vertical wall portion and the outward flange portion so that the outward flange portion rises in a direction opposite to a protruding direction of the recessed portion, A method for manufacturing a structural member according to any one of claims 1 to 3.

6. the second forming step forms the first intermediate part into the shape of the second intermediate part by bending using a die having a recess on a forming surface facing the region that will become the top plate portion of the first intermediate part, and a punch that presses the region that will become the top plate portion toward the recess of the die; A method for manufacturing a structural member according to any one of claims 1 to 3.

7. The third molding step is performed using left and right cams that press the regions that will become the left and right vertical wall portions of the second intermediate part in directions in which the regions approach each other, and a mold that presses the region that will become the top plate portion into the shape of the top plate portion of the target part shape while being pressed by the left and right cams. A method for manufacturing a structural member according to any one of claims 1 to 3.

8. The surfaces of the left and right cams that come into contact with the second intermediate component have a shape that follows the shape of the vertical wall portion. A method for manufacturing a structural member according to claim 7.

9. The approach of the regions that will become the left and right vertical wall portions by the pressing in the third molding step is set so that the distance between the inner surface of the recess in the second intermediate part and the surface of the region that will become the other vertical wall portion, facing the recess, is 0 mm or more and ½ of the width of the top plate portion or less. A method for manufacturing a structural member according to claim 7.

10. the target part shape includes an outward flange portion connected to an end of the vertical wall portion; forming the outward flange portion, A method for manufacturing a structural member according to any one of claims 1 to 3.

11. a joining process for joining the inner surface of the recess and the inner surface of the other vertical wall portion by bringing the recessed surface into surface contact with the inner surface of the other vertical wall portion, thereby forming a closed cross section, as a process after the third molding process; A method for manufacturing a structural member according to any one of claims 1 to 3.

Images