Hollow member

Abstract

To reduce weight while suppressing a decrease in rigidity and strength. [Solution] The hollow member 1 is made of a raw pipe 100 in which both side edges 101 of a plate material are joined to form a closed cross section. The hollow member 1 includes a partition 20 in which a first contact portion 22 and a second contact portion 24, which are spaced apart from each other in the circumferential direction of the raw pipe 100, are in contact with each other to form a first hollow portion 30 and a second hollow portion 40 inside the raw pipe 100, and a first joint 70 in which a first circumferential wall portion 31 forming the first hollow portion 30 is joined to a second circumferential wall portion 41 or partition 20 forming the second hollow portion 40, and a third hollow portion 50 is formed outside the first hollow portion 30 and the second hollow portion 40.

Description

Technical Field

[0001] This disclosure relates to a hollow member made of metal.

Background Art

[0002] In automotive parts, weight reduction is always required. As a specific method of weight reduction, it is conceivable to reduce the usage amount of the material by thinning the plate thickness of the material, but there is a concern that the rigidity and strength may decrease. Therefore, it is conceivable to reduce the weight while suppressing the decrease in rigidity and strength by forming a cross-sectional shape incorporating a plurality of closed cross-sectional structures.

[0003] Patent Document 1 discloses a structural member (hollow member) having at least two hollow profiled chambers (hollow chambers) manufactured by roll forming.

[0004] The hollow chambers of the hollow member disclosed in Patent Document 1 are manufactured from a single metal plate (plate material). The hollow member has a flange shape protruding outward from the hollow chamber formed at the side edge portion of the plate material. The hollow member forms a closed cross-sectional shape by overlapping and joining the side edge portion of the plate material and the flange shape protruding outward from the hollow chamber. That is, the side edge portion of the plate material is disposed on the outer surface in the cross-section of the hollow member.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] By the way, in the hollow member disclosed in Patent Document 1, the side edges of the sheet material are located on the outer surface of the hollow chamber after the sheet material has been roll-formed, and are joined to the sheet material constituting the hollow chamber at the outer surface of the hollow chamber. Therefore, the side edges of the sheet material are exposed to the outside of the hollow member. As a result, water is more likely to come into contact with the side edges of the sheet material.

[0007] However, paint does not adhere as well to the side edges of the plate material compared to other parts, so rust is likely to occur if water gets on the side edges of the plate material. In addition, the material strength of the joints at the side edges of the plate material is easily reduced due to the heat effects during joining. Furthermore, stress concentration due to the discontinuity in shape of the joint may become the starting point of failure, and it is thought that if these structurally weak parts are located on the outer surface of the hollow member, it may be undesirable in terms of the functional properties of the hollow member.

[0008] This disclosure is made in view of the above, and its purpose is to provide a lightweight, highly rigid, and highly strong hollow member. [Means for solving the problem]

[0009] To achieve the above objective, this disclosure describes a method of forming a raw tube in which both side edges of a plate material are joined to form a closed cross-section, and by providing multiple hollow sections, the aim is to reduce weight while suppressing a decrease in rigidity and strength.

[0010] To achieve the above objective, the first disclosure relates to a hollow member consisting of a raw tube in which both side edges of a plate material are joined to form a closed cross-section. The hollow member comprises a partition portion in which a first contact portion and a second contact portion, which are spaced apart from each other in the circumferential direction of the raw tube, are in contact with each other to form a first hollow portion and a second hollow portion inside the raw tube, and a first joint portion in which a first circumferential wall portion forming the first hollow portion is joined to a second circumferential wall portion or partition portion forming the second hollow portion, forming a third hollow portion outside the first hollow portion and the second hollow portion.

[0011] According to the first disclosure, the hollow member is formed from a raw tube in which the side edges of a plate material are joined to form a closed cross-section. Therefore, since it is not necessary to join the side edges of the plate material after forming the hollow member, the side edges of the plate material and the joint can be placed at any point in the cross-section of the hollow member. In addition, a third hollow section is formed when the first peripheral wall is joined to the second peripheral wall or partition, thereby forming multiple closed cross-section structures. As a result, the section modulus of the hollow member can be increased. Thus, in the first disclosure, weight reduction can be achieved while suppressing a decrease in rigidity and strength.

[0012] The second disclosure states that, in the first disclosure, the joints to which the side edges of the plate material in the raw pipe are joined are located in the first circumferential wall portion, the second circumferential wall portion, or the partition portion that forms the third hollow portion.

[0013] According to the second disclosure, the joint is located in the first circumferential wall, the second circumferential wall, or the partition that forms the third hollow section. Since these are inside the hollow section, rust is less likely to occur and they are less likely to be the starting point of fracture. Therefore, rust or fracture can be suppressed without increasing the plate thickness. As a result, the second disclosure makes it possible to reduce weight while suppressing a decrease in rigidity and strength.

[0014] The third disclosure is that, in the first disclosure, the hollow member has a portion in the longitudinal direction that has a different circumference from the rest.

[0015] According to the third disclosure, the hollow member has a portion in its longitudinal direction where the circumference differs from the rest. Therefore, for example, by making the circumference of the cross-section in the central part of the longitudinal direction larger than the circumference of the cross-sections at both ends, the member can be efficiently arranged so that stress is less likely to occur locally in response to an input that causes bending deformation. As a result, the third disclosure makes it possible to reduce weight while suppressing a decrease in rigidity and strength.

[0016] The fourth disclosure is that, in the first disclosure, the hollow member has portions in the longitudinal direction where the thickness differs from the rest.

[0017] According to the fourth disclosure, the hollow member has a portion in the longitudinal direction where the plate thickness differs from the rest. Therefore, for example, by making the plate thickness of the central portion when the hollow member is divided into three parts in the longitudinal direction smaller than the plate thickness of the portions at both ends, it is possible to control the portion of the hollow member that buckles when subjected to a compressive load. As a result, the fourth disclosure makes it possible to reduce weight while suppressing a decrease in rigidity and strength.

[0018] The fifth disclosure is that, in the first disclosure, the hollow member has a portion in the circumferential direction in which the thickness of the plate differs from the rest.

[0019] According to the fifth disclosure, the hollow member has a portion in the circumferential direction where the plate thickness differs from the rest. Therefore, for example, by making the plate thickness of the portion provided in the first compartment of the hollow member smaller than the plate thickness of the other portions, the thickness of the compartment where the plate material overlaps and has excessive rigidity or strength can be reduced. As a result, the fifth disclosure makes it possible to reduce weight while suppressing a decrease in rigidity and strength.

[0020] The sixth disclosure is that, in the first disclosure, the hollow member has portions in which the cross-sectional shape of a portion in the longitudinal direction differs from that portion in other portions located longitudinally away from the said portion.

[0021] According to the sixth disclosure, the hollow member has portions in which the cross-sectional shape differs between a portion in the longitudinal direction and other portions located longitudinally away from that portion. Therefore, for example, by making the cross-sectional shape of the portion of the hollow member that is connected to the mating object have a larger section modulus than the cross-sectional shapes of other portions, the hollow member can be firmly connected to the mating object. As a result, the sixth disclosure makes it possible to reduce weight while suppressing a decrease in rigidity and strength.

[0022] In the seventh disclosure, in the first disclosure, a second peripheral wall portion forming a second hollow portion is joined to a first peripheral wall portion or a partitioning portion forming a first hollow portion, and a second joining portion forming a fourth hollow portion is provided outside the second hollow portion and the first hollow portion.

[0023] According to the seventh disclosure, in the hollow member, a plurality of closed cross-sectional structures are formed by joining the second peripheral wall portion to the first peripheral wall portion or the partitioning portion to form the fourth hollow portion. Therefore, the sectional coefficient of the hollow member can be increased. Thereby, in the seventh disclosure, weight reduction can be achieved while suppressing a decrease in rigidity and strength.

Effects of the Invention

[0024] As described above, a plain tube in which both side edge portions of a plate material are joined to form a closed cross-section is formed, and a plurality of hollow portions are provided. Therefore, weight reduction can be achieved while suppressing a decrease in rigidity and strength.

Brief Description of the Drawings

[0025] [Figure 1] FIG. 1 is a plan view showing a hollow member according to Embodiment 1 of the present disclosure. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1 according to Embodiment 1 of the present disclosure. [Figure 3A] FIG. 3A is a view corresponding to a cross-sectional view taken along line II-II of FIG. 1, showing a molding die and an intermediate molded body in the middle pressing process. [Figure 3B] FIG. 3B is a view corresponding to FIG. 2, showing a molding die and an intermediate molded body in the outer bending process. [Figure 3C] FIG. 3C is a view corresponding to FIG. 2, showing a molding die and a hollow member in the trimming process. [Figure 3D] FIG. 3D is a view corresponding to FIG. 2, showing a hollow member in the joining process. [Figure 4A] FIG. 4A is a view corresponding to FIG. 2, showing a molding die and a plate material in the U-bending process. [Figure 4B] FIG. 4B is a view corresponding to FIG. 2, showing a molding die and a plate material in the O-bending process. [Figure 4C] Figure 10 is a diagram equivalent to Figure 2, showing the raw pipe in the pipe manufacturing process. [Figure 5A] Figure 5A is a diagram equivalent to Figure 3A, showing the mold and intermediate molded body in the intermediate pressing process according to Embodiment 2 of this disclosure. [Figure 5B] Figure 5B is a diagram equivalent to Figure 3C, showing the mold and hollow member in the restrike process according to Embodiment 2 of the present disclosure. [Figure 6A] Figure 6A is a diagram corresponding to Figure 3A in Embodiment 3 of this disclosure. [Figure 6B] Figure 6B is a diagram corresponding to Figure 3C in Embodiment 3 of this disclosure. [Figure 7A] Figure 7A is a perspective view showing a hollow member according to Embodiment 4 of the present disclosure. [Figure 7B] Figure 7B is a plan view showing a hollow member according to Embodiment 4 of the present disclosure. [Figure 7C] Figure 7C is a cross-sectional view taken along line VII-VII of Figure 7B relating to Embodiment 4 of the present disclosure. [Figure 7D] Figure 7D is a perspective view showing the raw tube before molding the hollow member according to Embodiment 4 of this disclosure. [Figure 8A] Figure 8A is a plan view showing a hollow member according to Embodiment 5 of the present disclosure. [Figure 8B] Figure 8B is a cross-sectional view taken along line VIII-VIII of Figure 8A relating to Embodiment 5 of the present disclosure. [Figure 9] Figure 9 is a diagram corresponding to Figure 2 in Embodiment 6 of this disclosure. [Figure 10A] Figure 10A is a plan view showing a hollow member according to Embodiment 7 of the present disclosure. [Figure 10B] Figure 10B is a cross-sectional view taken along line XX of Figure 10A according to Embodiment 7 of this disclosure. [Figure 11A] Figure 11A is a diagram corresponding to Figure 2 in Embodiment 8 of this disclosure. [Figure 11B] Figure 11B is a diagram corresponding to Figure 3A in Embodiment 8 of this disclosure. [Figure 11C]Figure 11C is a diagram corresponding to Figure 3C in Embodiment 8 of this disclosure. [Figure 12A] Figure 12A is a diagram corresponding to Figure 2 in Embodiment 9 of this disclosure. [Figure 12B] Figure 12B is a diagram corresponding to Figure 3C in Embodiment 9 of this disclosure. [Figure 13A] Figure 13A is a diagram corresponding to Figure 2 in Embodiment 10 of this disclosure. [Figure 13B] Figure 13B shows the pre-molding state in the restrike process according to Embodiment 10 of this disclosure. [Figure 13C] Figure 13C is a diagram corresponding to Figure 3C in Embodiment 10 of this disclosure. [Figure 14A] Figure 14A is a diagram corresponding to Figure 2 in Embodiment 11 of this disclosure. [Figure 14B] Figure 14B shows the state during the molding process in the flange forming process according to Embodiment 11 of this disclosure. [Figure 14C] Figure 14C shows the completed state of the flange forming process according to Embodiment 11 of this disclosure. [Figure 15A] Figure 15A is a plan view showing a hollow member according to Embodiment 12 of the present disclosure. [Figure 15B] Figure 15B is a cross-sectional view taken along the line XVB-XVB in Figure 15A relating to Embodiment 12 of the present disclosure. [Figure 15C] Figure 15C is a cross-sectional view taken along the XVC-XVC line of Figure 15A according to Embodiment 12 of this disclosure. [Figure 15D] Figure 15D is a side view showing a hollow member according to Embodiment 12 of the present disclosure. [Figure 15E] Figure 15E is a plan view showing a sheet material before forming the hollow member according to Embodiment 12 of this disclosure. [Modes for carrying out the invention]

[0026] Embodiments of the present disclosure will be described in detail below with reference to the drawings. The following description of preferred embodiments is illustrative in nature and is not intended to limit the present disclosure, its applications, or its uses.

[0027] [Embodiment 1] (Hollow member) Figures 1 and 2 show a hollow member 1 according to Embodiment 1 of the present disclosure. The hollow member 1 can be applied to members subjected to bending forces or compressive forces. For example, it can be applied to automotive parts such as bumper reinforcements, door impact beams, or side sills.

[0028] As shown in Figures 1 and 2, the hollow member 1 is a long member having a uniform closed cross-sectional shape. The hollow member 1 extends along a line segment connecting the centroids of the cross-sections located at both ends in the longitudinal direction. The outer shape of the cross-section of the hollow member 1 is formed to be approximately rectangular. The two opposing long sides of the approximately rectangular shape have one long side bulging inward towards the center of the cross-section and in contact with the other long side. As a result, multiple hollow sections are formed in the cross-section of the hollow member 1.

[0029] (Partitioned area) As shown in Figure 2, the hollow member 1 is provided with a partition 20. The partition 20 has a first contact portion 22 and a second contact portion 24 that are spaced apart from each other in the circumferential direction of the raw pipe 100, which will be described later, and these contact portions are in contact with each other. The first contact portion 22 is the inner surface of the first partition portion 21. The second contact portion 24 is the inner surface of the second partition portion 23. The first partition portion 21 and the second partition portion 23 are provided on the circumferential walls of the raw pipe 100, facing each other across the center of the cross-section. The first contact portion 22 and the second contact portion 24 are in contact over a range of approximately 1 / 3 to 1 / 4 of the circumference of the raw pipe 100. The partition portion 20 may be formed by joining the first partition portion 21 and the second partition portion 23 together.

[0030] (1st hollow part) As shown in Figure 2, the partitioned section 20 forms a first hollow section 30 within the raw pipe 100. The first hollow section 30 is surrounded by a first circumferential wall section 31. The first circumferential wall section 31 is provided with a first bulge section 32. The first bulge section 32 is located near the center of the upper long side of the rectangle formed by the cross-sectional shape of the hollow member 1. The first bulge section 32 is a part of the first circumferential wall section 31 that bulges toward the second hollow section 40.

[0031] As shown in Figure 2, the first hollow section 30 is located on the left side of the cross-section of the hollow member 1. The first hollow section 30 is formed in a substantially trapezoidal shape, with the left sides of a pair of opposing long sides in the rectangular outer shape of the cross-section of the hollow member 1 serving as the upper and lower bases. The cross-sectional area of ​​the first hollow section 30 accounts for approximately 1 / 3 of the cross-sectional area of ​​the hollow member 1.

[0032] (2nd hollow part) As shown in Figure 2, the partitioned section 20 forms a second hollow section 40 within the raw pipe 100. The second hollow section 40 is surrounded by a second circumferential wall section 41. The second circumferential wall section 41 is provided with a second bulge section 42. The second bulge section 42 is located near the center of the upper long side of the rectangle formed by the cross-sectional shape of the hollow member 1. The second bulge section 42 is a part of the second circumferential wall section 41 that bulges toward the first hollow section 30.

[0033] As shown in Figure 2, the second hollow section 40 is located on the right side of the cross-section of the hollow member 1. The second hollow section 40 is formed in a substantially trapezoidal shape, with the right sides of a pair of opposing long sides in the rectangular outer shape of the cross-section of the hollow member 1 serving as the upper and lower bases. The second hollow section 40 is formed substantially symmetrically with respect to the first hollow section 30. The cross-sectional area of ​​the second hollow section 40 accounts for approximately 1 / 3 of the cross-sectional area of ​​the hollow member 1.

[0034] (3rd hollow part) As shown in Figure 2, the first joint 70 forms a third hollow section 50 outside the first hollow section 30 and the second hollow section 40. The third hollow section 50 is surrounded by a first circumferential wall section 31, a second circumferential wall section 41, and a partition section 20. The third hollow section 50 shares the first circumferential wall section 31 with the first hollow section 30 and the second circumferential wall section 41 with the second hollow section 40. The first circumferential wall section 31, which is shared with the first hollow section 30, extends to the left as it proceeds downward from the first bulge section 32. The second circumferential wall section 41, which is shared with the second hollow section 40, extends to the right as it proceeds downward from the second bulge section 42.

[0035] The third hollow section 50 is formed in the shape of an approximately isosceles triangle, with the peripheral walls of the first hollow section 30 and the peripheral walls of the second hollow section 40 being equal sides and the partition section 20 as the base. The cross-sectional area of ​​the third hollow section 50 accounts for approximately 1 / 3 of the cross-sectional area of ​​the hollow member 1.

[0036] (1st joint) As shown in Figure 2, the hollow member 1 is provided with a first joint 70. The first joint 70 is a joint where the first peripheral wall portion 31 forming the first hollow portion 30 is joined to the second peripheral wall portion 41 forming the second hollow portion 40. The first joint 70 is where the first bulge portion 32 and the second bulge portion 42 are joined. The joining method will be described later.

[0037] (Method of manufacturing hollow components) Next, the manufacturing method for the hollow member 1 will be described. Figures 3A to 3D show the process for manufacturing the hollow member 1. The manufacturing process for the hollow member 1 includes an internal pressing process, an external bending process, a restrike process, and a joining process. By performing these processes, it becomes possible to form a cross-sectional shape incorporating multiple closed cross-sectional structures when forming the hollow member 1 from the raw pipe 100 by press working. Note that the manufacturing method for the hollow member 1 may include processes other than those listed above.

[0038] (Plain pipe) The hollow member 1 consists of a pipe 100. As will be described later, the pipe 100 has a closed cross-section formed by joining the edges 101 on both sides of a plate material.

[0039] As shown in Figures 3A to 3D, the pipe 100 is provided with a joint 102. The joint 102 is where the side edges 101 of the plate material in the pipe 100 are joined. The side edges 101 of the plate material are joined by butt joints. As shown in Figures 3A to 3D, the joint 102 is located in the partition 20 that forms the third hollow section 50. The joint 102 may also be located in the first circumferential wall section 31 or the second circumferential wall section 41 that forms the third hollow section 50.

[0040] (Medium pushing process) Figure 3A is a cross-sectional view illustrating the procedure for the internal pressing process that forms the compartment 20, and shows the completed molding state. The internal pressing process uses a lower mold 210 for forming the compartment and an upper mold 220 for forming the compartment. The lower mold 210 for forming the compartment is a fixed mold, and the upper mold 220 for forming the compartment is a movable mold. The upper mold 220 for forming the compartment is driven vertically (in the direction of approaching and moving away from the lower mold 210 for forming the compartment) by a mold drive device (not shown), and is switched between an open mold position (not shown) and a closed mold position (molding completed position) as shown in Figure 4.

[0041] The upper surface of the lower mold 210 for forming the partition is a molding surface, and a concave surface 211 for forming the partition is formed on this molding surface. The concave surface 211 has a roughly symmetrical V-shape. The lower surface of the upper mold 220 for forming the partition is a molding surface, and a convex surface 221 for forming the partition 20 is formed on this molding surface. The convex surface 221 has a roughly symmetrical U-shape.

[0042] After raising the upper mold 220 for forming the partitioned section to the open position, the raw pipe 100, which will be the material for the hollow member 1, is placed between the lower mold 210 for forming the partitioned section and the upper mold 220 for forming the partitioned section. At this time, the joint portion 102 of the raw pipe 100 is located above and faces the lower end of the convex surface 221.

[0043] As shown in Figure 3A, when the upper mold 220 for forming the partition is lowered, the raw pipe 100 is formed into an intermediate molded body 10 by the concave surface 211 of the lower mold 210 for forming the partition and the convex surface 221 of the upper mold 220 for forming the partition. As a result, a partition 20 is formed along the longitudinal direction of the raw pipe 100, and a first hollow section 30 and a second hollow section 40 are formed on both sides of the partition 20. The first hollow section 30 and the second hollow section 40 are approximately symmetrical. After that, the intermediate molded body 10 is demolded.

[0044] As shown in Figure 3A, the first hollow section 30 and the second hollow section 40 have a pointed teardrop shape in the portion adjacent to the partitioned section 20. The bending radius of the portions of the first hollow section 30 and the second hollow section 40 that are separated from the partitioned section 20 is smaller than the bending radius of the outer shape of the raw pipe 100.

[0045] (External bending process) After the internal molding process, the external molding process is performed. Figure 3B is a cross-sectional view illustrating the procedure for the external molding process that forms the intermediate molded body 10, and shows the completed molding state. The external molding process uses a lower mold 230 for forming the intermediate molded body and an upper mold 240 for forming the intermediate molded body. The lower mold 230 for forming the intermediate molded body is a fixed mold, and the upper mold 240 for forming the intermediate molded body is a movable mold. The upper mold 240 for forming the intermediate molded body is driven vertically (in the direction of approaching and moving away from the lower mold 230 for forming the intermediate molded body) by a mold drive device (not shown), and is switched between a mold open position (not shown) and a mold closed position (molding completed position) shown in Figure 5.

[0046] The upper surface of the lower mold 230 for forming the intermediate molded body is a molding surface, and a concave surface 231 for forming the intermediate molded body 10 is formed on this molding surface. The lower surface of the upper mold 240 for forming the intermediate molded body is a molding surface, and a concave surface 241 for forming the intermediate molded body 10 is formed on this molding surface.

[0047] After raising the upper mold 240 for forming the intermediate molded body to the open position, the intermediate molded body 10 is placed between the lower mold 230 for forming the intermediate molded body and the upper mold 240 for forming the intermediate molded body.

[0048] As shown in Figure 3B, when the upper mold 240 for forming the intermediate molded body is lowered, the first hollow section 30 and the second hollow section 40 are molded together by the concave surface 231 of the lower mold 230 for forming the intermediate molded body and the concave surface 241 of the upper mold 240 for forming the intermediate molded body. After that, the intermediate molded body 10 is demolded.

[0049] (Restriking process) After the external curving process, a restriking process is performed. Figure 3C is a cross-sectional view illustrating the procedure for the restriking process that forms the external shape of the hollow member 1, and shows the completed molding state. The restriking process uses a lower mold 250 for external shape formation and an upper mold 260 for external shape formation. The lower mold 250 for external shape formation is a fixed mold, and the upper mold 260 for external shape formation is a movable mold. The upper mold 260 for external shape formation is driven vertically (in the direction of approaching and moving away from the lower mold 250 for external shape formation) by a mold drive device (not shown), and is switched between a mold open position (not shown) and a mold closed position (molding completed position) shown in Figure 3C.

[0050] The upper surface of the lower mold 250 for forming the outer shape is a molding surface, and a concave surface 251 for forming the lower outer shape of the hollow member 1 is formed on this molding surface. The concave surface 251 is roughly rectangular in shape, following the cross-sectional shape of the lower part of the hollow member 1. The lower surface of the upper mold 260 for forming the outer shape is a molding surface, and a concave surface 261 for forming the upper outer shape of the hollow member 1 is formed on this molding surface. The concave surface 261 follows the cross-sectional shape of the upper part of the hollow member 1, with the central part of the cross-section bulging toward the concave surface 251.

[0051] After raising the upper mold 260 for forming the outer shape to the open position, the intermediate molded body 10 is placed between the lower mold 250 for forming the outer shape and the upper mold 260 for forming the outer shape.

[0052] As shown in Figure 3C, when the upper mold 260 for forming the outer shape is lowered, the intermediate molded body 10 is formed into a hollow member 1 by the concave surface 251 of the lower mold 250 for forming the outer shape and the concave surface 261 of the upper mold 260 for forming the outer shape. As a result, a first bulge 32 is formed in the first hollow section 30 along the longitudinal direction of the hollow member 1, and a second bulge 42 is formed in the second hollow section 40 along the longitudinal direction of the hollow member 1. After that, the hollow member 1 is demolded.

[0053] (Joining process) After the restriking process, a joining process is performed. Figure 3D is a cross-sectional view illustrating the procedure for joining the first bulge 32 and the second bulge 42, showing the joining process. In the joining process, the first bulge 32 of the first hollow section 30 and the second bulge 42 of the second hollow section 40 are butted together and welded by irradiating them with laser light L. This creates the first joint 70 and forms the third hollow section 50 on the outside of the first hollow section 30 and the second hollow section 40. Existing joining methods such as laser welding or arc welding can be used for joining.

[0054] (Bottom tube forming) As shown in Figures 4A to 4C, in this embodiment, the raw pipe 100 may be formed by sequentially performing a U-bending process, an O-bending process, and a pipe-making process before the pressing process.

[0055] (plate material) The sheet material is flat and may be pre-cut to a predetermined size, or it may be cut from coil material at the manufacturing plant of the hollow member 1. By using sheet material for the hollow member 1, transportation costs can be reduced compared to transporting pipes. The sheet material may be slightly curved or bent.

[0056] Metal materials such as steel or aluminum can be used for the plate material. For the steel material, a grade sufficient to perform the required functions of the hollow member 1 can be selected, such as mild steel, high-tensile steel, or ultra-high-tensile steel. Heat treatments such as quenching or annealing may be applied. Plating may also be applied to the surface. Furthermore, a combination of these can be used.

[0057] (U-bending process) Figure 4A is a cross-sectional view illustrating the procedure for the U-bending process, which forms a U-shaped plate material 120 from a flat plate material, and shows the completed state of molding. The U-bending process uses a lower mold 310 for U-bending and an upper mold 320 for U-bending. The lower mold 310 is a fixed mold, and the upper mold 320 is a movable mold. The upper mold 320 is driven vertically (in the direction of approaching and moving away from the lower mold 310) by a mold drive device (not shown), and is switched between an open mold position (not shown) and a closed mold position (molding completed position) as shown in Figure 4A.

[0058] The upper surface of the lower mold 310 for U-bending is a molding surface, and a concave surface 311 for forming the curved portion 121 is formed on this molding surface. The concave surface 311 has a roughly U-shape that is symmetrical. The lower surface of the upper mold 320 for U-bending is a molding surface, and a convex surface 321 for forming the curved portion 121 is formed on this molding surface. The convex surface 321 has a roughly U-shape that is symmetrical.

[0059] After raising the upper mold 320 for U-bending to the open position, the sheet material that will become the raw pipe 100 is placed between the lower mold 310 for U-bending and the upper mold 320 for U-bending.

[0060] As shown in Figure 4A, when the upper mold 320 for U-bending is lowered, the plate material is formed into a U-shape in cross-section by the concave surface 311 of the lower mold 310 for U-bending and the convex surface 321 of the upper mold 320 for U-bending. This forms the shape of the lower side of the raw pipe 100. After that, the U-shaped plate material 120 is demolded. The resulting U-shaped plate material 120 has an expanded shape due to springback, where the distance between the opposing side walls 122 widens towards the side edges 101.

[0061] (Bending process) After the U-bending process, the O-bending process is performed. Figure 4B is a cross-sectional view illustrating the procedure for the O-bending process, which forms an O-shaped plate material 110 from a U-shaped plate material 120, and shows the completed molding state. The O-bending process uses a lower mold 330 for O-bending and an upper mold 340 for O-bending. The lower mold 330 for O-bending is a fixed mold, and the upper mold 340 for O-bending is a movable mold. The upper mold 340 for O-bending is driven vertically (in the direction of approaching and moving away from the lower mold 330 for O-bending) by a mold drive device (not shown), and is switched between an open mold position (not shown) and a closed mold position (molding completed position) as shown in Figure 9.

[0062] The upper surface of the lower mold 330 for forming the O-bend is a molding surface, and a concave surface 331 for forming the O-bend is formed on this molding surface. The lower surface of the upper mold 340 for forming the O-bend is a molding surface, and a concave surface 341 for forming the O-bend is formed on this molding surface.

[0063] After raising the upper mold 340 for O-bend formation to the open position, the U-shaped plate material 120 is placed between the lower mold 330 for O-bend formation and the upper mold 340 for O-bend formation.

[0064] The curved portion 121 of the U-shaped plate material 120 is received by the concave surface 331 of the lower mold 330 for O-bend formation, and when the upper mold 340 for O-bend formation is lowered, the concave surface 341 of the upper mold 340 for O-bend formation comes into contact with the side edges 101 of the opposing side walls 122 of the U-shaped plate material 120. Further lowering of the upper mold 340 for O-bend formation causes the opposing side walls 122 to bulge outwards on both sides, and as shown in Figure 4B, the upper mold 340 for O-bend formation and the lower mold 330 for O-bend formation come together to form the O-shaped plate material 110. After that, the O-shaped plate material 110 is demolded.

[0065] (Pipe making process) After the bending process, the pipe-making process is carried out. Figure 4C shows how a laser beam L is irradiated onto the butted side edges 101 of the O-shaped plate material 110 to join them and create a joint 102. To prevent the side edges 101, 101 from separating during joining, the O-shaped plate material 110 is pressed and fixed from both sides in the radial direction of the cross-section. The side edges 101, 101 of the plate material may overlap. In addition to laser welding, existing methods such as arc welding or riveting can be used for joining.

[0066] [Embodiment 2] In Embodiment 1 described above, an example was shown in which the hollow member 1 has a symmetrical cross-sectional shape with a first hollow section 30 and a second hollow section 40 on both sides of the partitioned section 20, but the embodiment is not limited to this form. In Embodiment 2 shown below, the same reference numerals are used for parts that are the same as in Embodiment 1 and their descriptions are omitted, while the different parts will be described in detail.

[0067] (Hollow member) As shown in Figure 5A, the first section 21 and the second section 23 are located on the peripheral wall of the pipe 100, slightly to the left of the center of the cross-section.

[0068] (Medium pushing process) Figure 5A is a cross-sectional view illustrating the procedure for the internal pressing process that forms the partitioned section 20, and shows the completed state of molding.

[0069] The upper surface of the lower mold 210 for forming the partition is a molding surface, and a concave surface 211 for forming the partition is formed on this molding surface. The bottom surface of the concave surface 211 has long flat sections on the left and right, corresponding to the long side of the cross-sectional shape of the hollow member 1. The lower surface of the upper mold 220 for forming the partition is a molding surface, and a convex surface 221 for forming the partition 20 is formed on this molding surface. The convex surface 221 is positioned slightly to the left of the plane of the concave surface 211. This creates a difference in size between the first hollow section 30 and the second hollow section 40.

[0070] After raising the upper mold 220 for forming the partitioned section to the open position, the raw pipe 100, which will be the material for the hollow member 1, is placed between the lower mold 210 for forming the partitioned section and the upper mold 220 for forming the partitioned section. At this time, the joint portion 102 of the raw pipe 100 is located slightly to the left from above.

[0071] (Restriking process) Figure 5B is a cross-sectional view illustrating the procedure for the restriking process that forms the outer shape of the hollow member 1, and shows the completed state of molding.

[0072] The lower surface of the upper mold 260 for forming the outer shape is a molding surface, and a concave surface 261 for forming the upper outer shape of the hollow member 1 is formed on this molding surface. The concave surface 261 bulges outwards from the center to the left of the cross-sectional shape of the upper part of the hollow member 1 toward the concave surface 251. As a result, the first hollow section 30 is molded to be smaller than the second hollow section 40.

[0073] [Embodiment 3] In Embodiment 1 described above, an example was shown in which the third hollow portion 50 is provided between the first hollow portion 30 and the second hollow portion 40, but the embodiment is not limited to this form. In Embodiment 3 shown below, the same reference numerals are used for parts that are the same as in Embodiment 1 and their descriptions are omitted, while the different parts will be described in detail.

[0074] (1st hollow part) As shown in Figure 6A, the partitioned section 20 forms a first hollow section 30 within the raw pipe 100. The first hollow section 30 is surrounded by a first circumferential wall section 31. The first circumferential wall section 31 is provided with a first bulge section 32. As shown in Figure 6B, the first hollow section 30 is located in the upper left side of the cross-section of the hollow member 1. The first bulge section 32 is a part of the first circumferential wall section 31 that bulges toward the partitioned section 20.

[0075] (3rd hollow part) As shown in Figure 6B, the third hollow section 50 is formed outside the first hollow section 30 and the second hollow section 40. The third hollow section 50 is surrounded by the first circumferential wall section 31 and the partition section 20. The third hollow section 50 shares the first circumferential wall section 31 with the first hollow section 30.

[0076] (Medium pushing process) Figure 6A is a cross-sectional view illustrating the procedure for the internal pressing process that forms the partitioned section 20, and shows the completed state of molding.

[0077] The upper surface of the lower mold 210 for forming the partition is a molding surface, and a concave surface 211 for forming the partition is formed on this molding surface. The bottom surface of the concave surface 211 has long flat sections on the left and right, corresponding to the long side of the cross-sectional shape of the hollow member 1. The lower surface of the upper mold 220 for forming the partition is a molding surface, and a convex surface 221 for forming the partition 20 is formed on this molding surface. The convex surface 221 is positioned close to the left vertical wall of the concave surface 211. Therefore, the first hollow section 30 is formed to extend upward.

[0078] After raising the upper mold 220 for forming the partitioned section to the open position, the raw pipe 100, which will be the material for the hollow member 1, is placed between the lower mold 210 for forming the partitioned section and the upper mold 220 for forming the partitioned section. At this time, the joint portion 102 of the raw pipe 100 is located above and faces the lower end of the convex surface 221.

[0079] (Restriking process) Figure 6B is a cross-sectional view illustrating the procedure for the restriking process that forms the outer shape of the hollow member 1, and shows the completed state of molding.

[0080] The upper surface of the lower mold 250 for forming the outer shape is a molding surface, and a concave surface 251 for forming the lower outer shape of the hollow member 1 is formed on this molding surface. The lower surface of the upper mold 260 for forming the outer shape is a molding surface, and a concave surface 261 for forming the upper outer shape of the hollow member 1 is formed on this molding surface. The concave surface 261 bulges outwards from the center to the right of the cross-sectional shape of the upper part of the hollow member 1. As a result, the first hollow portion 30 is bent back from the central portion toward the second hollow portion 40 and formed to contact the partition portion 20.

[0081] [Embodiment 4] In Embodiment 1 described above, an example was shown in which the circumference of the hollow member 1 is uniformly distributed along the longitudinal direction, but the embodiment is not limited to this form. In Embodiment 4 shown below, the same reference numerals are used for parts that are the same as in Embodiment 1 and their descriptions are omitted, while the different parts will be described in detail.

[0082] Figures 7A to 7C show a hollow member 1 according to Embodiment 4. The hollow member 1 has a portion 90 in its longitudinal direction that has a different circumference from the rest. As shown in Figures 7A to 7B, the circumference of the cross-section of the central part of the hollow member 1 in the longitudinal direction is greater than the circumference of the cross-sections at both ends. Between the central part and the ends, there is a gradually changing section in which the circumference of the cross-section decreases from the central part to the ends. Therefore, the hollow member 1 has a shape in which the central part in the longitudinal direction bulges out. The cross-sectional shape of the central part (Figure 7C) and the cross-sectional shape of the ends (Figure 2) are similar.

[0083] Figure 7D shows the raw pipe 100 before forming the hollow member 1. The circumference of both ends of the raw pipe 100 in the longitudinal direction is smaller than the circumference of the central part. The cross-sectional shape of the raw pipe 100 may be formed into a polygonal shape such as a triangle, square, pentagon, or hexagon to match the outer cross-sectional shape of the hollow member 1. Pre-forming the raw pipe 100 makes it easier to form the hollow member 1.

[0084] [Embodiment 5] In Embodiment 1 described above, a configuration in which the hollow member 1 is formed with the same plate thickness was illustrated, but the embodiment is not limited to this configuration. In Embodiment 5 shown below, the same parts as in Embodiment 1 are denoted by the same reference numerals and their descriptions are omitted, while the different parts will be described in detail.

[0085] Figures 8A to 8B show the hollow member 1 according to Embodiment 5. The hollow member 1 has a substantially uniform cross-section along its longitudinal direction. As shown in Figures 8A to 8B, the hollow member 1 differs from the above embodiment in that it has portions 91B, 91B at both ends in the longitudinal direction, where the plate thickness differs from that of the central portion. The plate thickness of the portions 91B, 91B at both ends when the hollow member 1 is divided into three parts in the longitudinal direction is greater than the plate thickness of the central portion 91C.

[0086] In Embodiment 5, the difference in plate thickness between the central portion 91B and the portions 91C, 91C at both ends is provided by joining plate materials with different thicknesses together (tailored blank), but it can also be provided by a layered structure (patchwork).

[0087] Furthermore, three or more different plate thicknesses may be used. The plate thickness may also be set to increase from one end to the other.

[0088] Furthermore, three or more different plate thicknesses may be used. The materials of each part may also be different from each other.

[0089] [Embodiment 6] Figure 9 shows a hollow member 1 according to Embodiment 6. The hollow member 1 has the same cross-section along its longitudinal direction. As shown in Figure 9, the hollow member 1 differs from the above embodiment in that it has a portion 92B in the circumferential direction where the plate thickness differs from the rest. In the hollow member 1, the plate thickness of the portion 92B provided in the first compartment 21 is smaller than the plate thickness of the other portions.

[0090] In Embodiment 6, the difference in plate thickness between the portion 92B provided in the first section 21 and other portions is provided by joining plate materials with different thicknesses together (tailored blank), but it can also be provided by a layered structure (patchwork).

[0091] Three or more different plate thicknesses may be used. The materials of each part may be different from each other.

[0092] [Embodiment 7] In Embodiment 1 described above, an example was shown in which the hollow member 1 is formed with the same cross-sectional shape, but the embodiment is not limited to this. In Embodiment 7 shown below, the same parts as in Embodiment 1 are denoted by the same reference numerals and their descriptions are omitted, while the different parts will be described in detail.

[0093] Figures 10A to 10B show the hollow member 1 according to Embodiment 7. The hollow member 1 has different cross-sectional shapes at both ends 93B, 93B in the longitudinal direction and at the central part 93C. As shown in Figures 10A to 10B, the hollow member 1 differs from the above embodiment in that it has a portion in the longitudinal direction and a portion located further longitudinally from that portion with a different cross-sectional shape.

[0094] As shown in Figure 10B, the cross-sectional shape of both ends 93B, 93B has a partitioned section 20, a first hollow section 30, and a second hollow section 40. The first hollow section 30 and the second hollow section 40 extend upward from the end of the partitioned section 20 in the figure. The vertical dimension H of the cross-sectional shape of both ends 93B, 93B in Figure 10B is greater than the vertical dimension h of the cross-sectional shape of the central section 93C.

[0095] Between the end portion 93B and the longitudinal central portion 93C, there is a gradually changing section in which the cross-section gradually expands toward the tip of the hollow member 1. In the cross-section of the gradually changing section, the distance between the first bulge portion 32 and the second bulge portion 42 increases as it moves toward the end portion 93C of the hollow member 1.

[0096] [Embodiment 8] In Embodiment 1 described above, an example was shown in which three hollow sections are provided, but the embodiment is not limited to this form. In Embodiment 8 shown below, the same parts as in Embodiment 1 are denoted by the same reference numerals and their descriptions are omitted, while the different parts will be described in detail.

[0097] (1st hollow part) As shown in Figure 11A, the partitioned section 20 forms a first hollow section 30 within the raw pipe 100. The first hollow section 30 is surrounded by a first peripheral wall section 31. The first peripheral wall section 31 is provided with a first bulge section 32. The first bulge section 32 is a part of the first peripheral wall section 31 that bulges toward the partitioned section 20. The first hollow section 30 is located in the upper left side of the cross-section of the hollow member 1.

[0098] (2nd hollow part) As shown in Figure 11A, the partitioned section 20 forms a second hollow section 40 within the raw pipe 100. The second hollow section 40 is surrounded by a second peripheral wall section 41. The second hollow section 40 is located in the upper right side of the cross-section of the hollow member 1.

[0099] (3rd hollow part) As shown in Figure 11A, the third hollow section 50 is surrounded by the first peripheral wall section 31 and the partition section 20. The third hollow section 50 shares the first peripheral wall section 31 with the first hollow section 30. The third hollow section 50 is located in the lower left side of the cross-section of the hollow member 1.

[0100] (4th hollow part) As shown in Figure 11A, the fourth hollow section 60 is formed outside the second hollow section 40 and the first hollow section 30. The fourth hollow section 60 is surrounded by the second circumferential wall section 41, the first circumferential wall section 31, and the partition section 20. The fourth hollow section 60 shares the first circumferential wall section 31 with the first hollow section 30 and the second circumferential wall section 41 with the second hollow section 40. The fourth hollow section 60 is located in the lower right side of the cross-section of the hollow member 1.

[0101] As shown in Figure 11A, the joint 102 where the side edges 101 of the plate material of the raw pipe 100 are joined is located in the partition 20 that forms the third hollow section 50. The joint 102 is located in the first partition 21, but it may also be located in the first peripheral wall 31 or the second peripheral wall 41 that form the third hollow section 50.

[0102] (2nd joint) As shown in Figure 11A, the hollow member 1 is provided with a second joint 80. The second joint 80 is a joint where the second circumferential wall portion 41 forming the second hollow portion 40 is joined to the first circumferential wall portion 31 forming the first hollow portion 30. The second joint 80 is where the second bulge portion 42 and the first circumferential wall portion 31 are joined. The joining method can be the same as that used for the first joint 70.

[0103] (Medium pushing process) Figure 11B is a cross-sectional view illustrating the procedure for the internal pressing process that forms the partitioned section 20, and shows the completed state of molding.

[0104] The upper surface of the lower mold 210 for forming the partition is a molding surface, and a concave surface 211 for forming the partition is formed on this molding surface. The bottom surface of the concave surface 211 has long flat sections on the left and right, corresponding to the long side of the cross-sectional shape of the hollow member 1. The lower surface of the upper mold 220 for forming the partition is a molding surface, and a convex surface 221 for forming the partition 20 is formed on this molding surface. The convex surface 221 is positioned close to the left vertical wall of the concave surface 211. Therefore, the first hollow section 30 is formed to extend upward.

[0105] After raising the upper mold 220 for forming the partitioned section to the open position, the raw pipe 100, which will be the material for the hollow member 1, is placed between the lower mold 210 for forming the partitioned section and the upper mold 220 for forming the partitioned section. At this time, the joint portion 102 of the raw pipe 100 is located above and faces the lower end of the convex surface 221.

[0106] (Restriking process) Figure 11C is a cross-sectional view illustrating the procedure for the restriking process that forms the outer shape of the hollow member 1, and shows the completed state of molding.

[0107] The upper surface of the lower mold 250 for forming the outer shape is a molding surface, and a concave surface 251 for forming the lower outer shape of the hollow member 1 is formed on this molding surface. The lower surface of the upper mold 260 for forming the outer shape is a molding surface, and a concave surface 261 for forming the upper outer shape of the hollow member 1 is formed on this molding surface. The concave surface 261 bulges outwards from the center to the left of the cross-sectional shape of the upper part of the hollow member 1. As a result, the first hollow portion 30 is bent back from the central portion toward the second hollow portion 40 and formed to contact the partition portion 20, and the second hollow portion 40 is bent back from the central portion toward the first hollow portion 30 and formed to contact the first peripheral wall portion 31.

[0108] [Embodiment 9] In Embodiment 1 described above, an example was shown in which the first hollow portion 30 and the second hollow portion 40 are bent back toward the first partitioned portion 21, but the embodiment is not limited to this form. In Embodiment 9 shown below, the same reference numerals are used for parts that are the same as in Embodiment 1 and their descriptions are omitted, while the different parts will be described in detail.

[0109] (1st hollow part) As shown in Figure 12A, the partitioned section 20 forms a first hollow section 30 within the raw pipe 100. The first hollow section 30 is surrounded by a first circumferential wall section 31. The first circumferential wall section 31 is provided with a first bulge section 32. The first bulge section 32 is a part of the first circumferential wall section 31 that bulges toward the partitioned section 20. The first hollow section 30 is located in the hollow member 1, with its left end wrapped around from the upper left to the lower left side of the cross-section.

[0110] (2nd hollow part) As shown in Figure 12A, the partitioned section 20 forms a second hollow section 40 within the raw pipe 100. The second hollow section 40 is surrounded by a second peripheral wall section 41. The second peripheral wall section 41 is provided with a second bulge section 42. The second bulge section 42 is a part of the second peripheral wall section 41 that bulges out toward the partitioned section 20. The second hollow section 40 is located in the hollow member 1, with its right end wrapped around from the lower right side to the upper right side of the cross-section.

[0111] (4th hollow part) As shown in Figure 12A, the fourth hollow section 60 is formed outside the second hollow section 40 and the first hollow section 30. The fourth hollow section 60 is surrounded by the second peripheral wall section 41 and the partition section 20. The fourth hollow section 60 shares the second peripheral wall section 41 with the second hollow section 40.

[0112] (2nd joint) As shown in Figure 12A, the hollow member 1 is provided with a second joint 80. The second joint 80 is a joint where the second peripheral wall portion 41, which forms the second hollow portion 40, is joined to the partition portion 20. The second joint 80 is where the second bulge portion 42 and the second partition portion 23 are joined.

[0113] (Restriking process) Figure 12B is a cross-sectional view illustrating the procedure for the restriking process that forms the outer shape of the hollow member 1, and shows the completed state of molding.

[0114] The upper surface of the lower mold 250 for forming the outer shape is a molding surface, and a concave surface 251 for forming the lower outer shape of the hollow member 1 is formed on this molding surface. The concave surface 251 bulges outwards from the center to the left of the cross-section, following the cross-sectional shape of the lower part of the hollow member 1. The lower surface of the upper mold 260 for forming the outer shape is a molding surface, and a concave surface 261 for forming the upper outer shape of the hollow member 1 is formed on this molding surface. The concave surface 261 bulges outwards from the center to the left of the cross-section, following the cross-sectional shape of the upper part of the hollow member 1. As a result, the first hollow section 30 is formed to be bent back from the center toward the second hollow section 40 and to contact the partition section 20, and the second hollow section 40 is formed to be bent back from the center toward the first hollow section 30 and to contact the partition section 20.

[0115] [Embodiment 10] In Embodiment 1 described above, an example was given in which the cross-sectional outer shape of the hollow member 1 is formed to be approximately rectangular, but the embodiment is not limited to this form. In Embodiment 10 shown below, the same parts as in Embodiment 1 are denoted by the same reference numerals and their descriptions are omitted, while the different parts will be described in detail.

[0116] As shown in Figure 13A, the hollow member 1 has a first flange 33 and a second flange 43 that project in the short direction, extending along the longitudinal direction, on the first joint portion 70 side in the thickness direction. The first flange 33 is formed by a first extension portion 33a, a first flange portion 33b, and a first curved portion 33c. The first extension portion 33a is provided with a first circumferential wall portion 31 that forms the upper circumferential wall of the hollow member 1, extending straight toward the short direction of the hollow member 1. The first flange portion 33b is provided with the first extension portion 33a side of the first circumferential wall portion 31 that forms the left circumferential wall of the hollow member 1, bent in an L-shape toward the short direction of the hollow member 1 along the first extension portion 33a. The first curved portion 33c connects the first extension portion 33a and the first flange portion 33b.

[0117] As shown in Figure 13A, the second flange 43 is formed by a second extension 43a, a second flange 43b, and a second curved portion 43c. The second extension 43a is provided by a second circumferential wall portion 41 that forms the upper circumferential wall of the hollow member 1, extending straight outwards from the cross-section. The second flange 43b is provided by bending the second extension 43a side of the second circumferential wall portion 41 that forms the right circumferential wall of the hollow member 1 in an L-shape outwards from the cross-section along the second extension 43a. The second curved portion 43c connects the second extension 43a and the second flange 43b.

[0118] (Plain pipe) As shown in Figure 13A, the joint 102 is located in the second compartment 23 of the compartment 20. Alternatively, the joint 102 may be located in the first compartment 21.

[0119] (Restriking process) The manufacturing process for the hollow member 1 according to Embodiment 10 comprises an internal pressing process, an external bending process, a restriking process, and a joining process. In Embodiment 10, the restriking process differs from that of Embodiment 1. Figures 13B and 13C are cross-sectional views illustrating the procedure for the restriking process that forms the first flange 33 and the second flange 43 of the hollow member 1. Figure 13B shows the pre-molding state in which the intermediate molded body 10 is set between the lower mold 250 for forming the outer shape and the upper mold 260 for forming the outer shape. Figure 13C shows the completed molding state.

[0120] As shown in Figures 13B and 13C, the upper surface of the lower mold 250 for forming the outer shape is a molding surface, and a concave surface 251 for forming the lower outer shape of the hollow member 1 is formed on this molding surface. The concave surface 251 is substantially rectangular in shape, following the cross-sectional shape of the lower part of the hollow member 1. The concave surface 251 of the lower mold 250 for forming the outer shape is provided with a bottom wall portion 251a that extends along the longitudinal direction of the lower mold 250 for forming the outer shape, and a pair of side wall portions 251b, 251b that extend from both ends of the bottom wall portion 251a in the short direction to the middle of the concave surface 251 in the vertical direction. The upper ends of the side wall portions 251b, 251b of the concave surface 251 are provided with lower flange forming surfaces 251c, 251c that extend outward from the cross-section along the short direction of the lower mold 250 for forming the outer shape, and also extend along the longitudinal direction of the lower mold 250 for forming the outer shape.

[0121] The lower surface of the upper mold 260 for forming the outer shape is provided with a convex portion 262 for forming the upper outer shape of the hollow member 1. The convex portion 262 is formed to fit into the portion above the lower flange forming surface 251c of the concave surface 251. The lower surface of the convex portion 262 is a forming surface, and the forming surface is formed flat.

[0122] As the upper mold 260 for forming the outer shape is lowered, the first circumferential wall portion 31 and the second circumferential wall portion 41 are positioned between the lower flange molding surfaces 251c, 251c of the lower mold 250 for forming the outer shape and the molding surface of the upper mold 260 for forming the outer shape. As shown in Figure 13C, when the upper mold 260 for forming the outer shape is lowered to its bottom dead center, the first circumferential wall portion 31 and the second circumferential wall portion 41 are sandwiched between the lower flange molding surfaces 251c, 251c of the lower mold 250 for forming the outer shape and the lower surface of the convex portion 262 of the upper mold 260 for forming the outer shape, thereby forming the first flange 33 and the second flange 43.

[0123] [Embodiment 11] In Embodiment 1 described above, a form was shown in which the cross-sectional outer shape of the hollow member 1 is formed to be approximately rectangular, but the embodiment is not limited to this form. In Embodiment 11 shown below, the same parts as in Embodiment 1 are denoted by the same reference numerals and their descriptions are omitted, while the different parts will be described in detail.

[0124] As shown in Figure 14A, the hollow member 1 has a first flange 33 and a second flange 43 that project in the short direction toward the partition portion 20 in the thickness direction, and these flanges are continuous along the longitudinal direction. The first flange 33 is formed by a first extension 33a, a first flange portion 33b, and a first curved portion 33c. The first extension 33a is provided with a first circumferential wall portion 31 that forms the lower circumferential wall of the hollow member 1 and extends straight toward the short direction of the hollow member 1. The first flange portion 33b is provided with the first extension 33a side of the first circumferential wall portion 31 that forms the left circumferential wall of the hollow member 1 bent in an L-shape toward the short direction of the hollow member 1 along the first extension 33a. The first curved portion 33c connects the first extension 33a and the first flange portion 33b.

[0125] As shown in Figure 14A, the second flange 43 is formed by a second extension 43a, a second flange 43b, and a second curved portion 43c. The second extension 43a is provided by a second circumferential wall portion 41 that forms the lower circumferential wall of the hollow member 1, extending straight outwards from the cross-section. The second flange 43b is provided by bending the second extension 43a side of the second circumferential wall portion 41 that forms the right circumferential wall of the hollow member 1 in an L-shape outwards from the cross-section along the second extension 43a. The second curved portion 43c connects the second extension 43a and the second flange 43b.

[0126] (Plain pipe) As shown in Figure 14A, the joint 102 is located in the second compartment 23 of the compartment 20. Alternatively, the joint 102 may be located in the first compartment 21.

[0127] (Flange forming process) The manufacturing process for the hollow member 1 according to Embodiment 11 differs from that of Embodiment 1 in that it includes a flange forming process between the restrike process and the joining process of the manufacturing process for the hollow member 1 according to Embodiment 1. Figures 14B and 14C are cross-sectional views illustrating the procedure for the flange forming process that forms the first flange 33 and the second flange 43 of the hollow member 1. Figure 14B shows the state during forming. Figure 14C shows the state after forming is complete.

[0128] The lower mold 410 for flange formation includes a base portion 411 and a left molding die 412 and a right molding die 415 positioned on the base portion 411 and moving toward and away from each other in the short-side direction of the lower mold 410 for flange formation. The left molding die 412 is provided with a left sliding portion 413 that moves vertically along the left wall surface 412a extending in the vertical direction. The upper end surface of the left sliding portion 413 is provided with an upper mold support left surface 413a. The lower end surface of the left sliding portion 413 is provided with a first flange pressing surface 413b. The right molding die 415 is provided with a right sliding portion 416 that moves vertically along the right wall surface 415a extending in the vertical direction. The upper end surface of the right sliding portion 416 is provided with an upper mold support right surface 416a. The lower end surface of the right sliding portion 416 is provided with a second flange pressing surface 416b.

[0129] The lower surface of the upper flange-forming mold 420 protrudes toward the lower flange-forming mold 410 along the longitudinal direction of the upper flange-forming mold 420, and a molding surface 421 is provided at the lowest point. The molding surface 421 is formed flat. Above the molding surface 421, slide pressing surfaces 422, 422 are provided that extend outward along the cross-section in the short direction of the hollow member 1 and also extend along the longitudinal direction of the hollow member 1.

[0130] When the hollow member 1 is set in the lower flange forming mold 410, where the left molding die 412 and the right molding die 415 are separated from each other, and molding is started, the left molding die 412 and the right molding die 415 move closer to each other, as shown in Figure 14B. As the left molding die 412 and the right molding die 415 move closer to each other, the upper part of the first circumferential wall portion 31 that forms the left circumferential wall of the hollow member 1 is pushed by the left sliding portion 413, causing the left circumferential wall in the roughly rectangular cross-section of the hollow member 1 to deform inward, and the upper part of the second circumferential wall portion 41 that forms the right circumferential wall of the hollow member 1 is pushed by the right sliding portion 416, causing the right circumferential wall in the roughly rectangular cross-section of the hollow member 1 to deform inward.

[0131] As the left and right peripheral walls deform, first protrusions 34 and second protrusions 44 are formed at both ends of the lower edge of the roughly rectangular cross-section of the hollow member 1. Furthermore, as the upper flange-forming mold 420 is lowered, the left sliding portion 413 and the right sliding portion 416 of the lower flange-forming mold 410 are pushed downward by the sliding pressing surfaces 422, 422 provided on the upper flange-forming mold 420. Subsequently, the first protrusions 34 and second protrusions 44 are sandwiched between the upper surface of the base portion 411 and the first flange pressing surface 413b and the second flange pressing surface 416b, respectively. This forms the first flange 33 and the second flange 43.

[0132] [Embodiment 12] In Embodiment 1 described above, the hollow member 1 is shown as having a closed cross-sectional shape along its entire longitudinal direction, but the embodiment is not limited to this form. In Embodiment 12 shown below, the same parts as in Embodiment 1 are denoted by the same reference numerals and their descriptions are omitted, while the different parts are described in detail. Note that the manufacturing process for the hollow member 1 in Embodiment 12 is the same as the manufacturing process for the hollow member 1 in Embodiment 1, so a detailed description is omitted.

[0133] Figures 15A to 15D show the hollow member 1 according to Embodiment 12. The hollow member 1 has different cross-sectional shapes at both ends 94B, 94B in the longitudinal direction and at the central part 94C. The outer shape of the cross section of the central part 94C is formed into a roughly rectangular shape. The pair of opposing long sides of the roughly rectangular shape have one long side bulging inward towards the center of the cross section and in contact with the other long side.

[0134] As shown in Figures 15A to 15D, the hollow member 1 is provided with a bottom wall portion 25, a first rib 35, and a second rib 45 at both longitudinal ends 94B, 94B. The bottom wall portion 25 extends from the longitudinal ends of the first peripheral wall portion 31, which forms the left side of the lower peripheral wall of the hollow member 1, the second peripheral wall portion 41, which forms the right side of the lower peripheral wall of the hollow member 1, and the second compartment portion 23, which forms the middle part of the lower peripheral wall of the hollow member 1. The first rib 35 extends from the longitudinal end of the first peripheral wall portion 31, which forms the left side of the peripheral wall of the hollow member 1. The height dimension of the first rib 35 increases as it moves from the tip of the bottom wall portion 25 toward the longitudinal center of the hollow member 1. The second rib 45 extends along the longitudinal end of the second peripheral wall portion 41, which forms the right side of the peripheral wall of the hollow member 1. The second rib 45 is formed so that its height increases as it moves from the tip of the bottom wall portion 25 toward the longitudinal center of the hollow member 1.

[0135] (Plain pipe) The hollow member 1 is formed from a base tube 100 which has a joint 102 formed by joining the two side edges 101, 101 of a plate material 130 (shown in Figure 15E) that has notches 131 at both ends 94B, 94B. As shown in Figure 15C, the joint 102 in embodiment 12 is located in the second compartment 23.

[0136] As shown in Figure 15E, the rectangular plate material 130 is provided with a notch 131 formed by cutting out the center of one short side toward the other short side. The dimension of the notch 131 along the short side of the plate material 130 decreases as it moves toward the other short side. The other end of the notch 131 is parallel to the tip 135 of the plate material 130. The notch 131 has a first inclined portion 133, a second inclined portion 134, and a straight portion 132. The first inclined portion 133 is provided at the longitudinal end 94B of the plate material 130, which corresponds to the longitudinal end 94B of the hollow member 1. The first inclined portion 133 is provided so as it moves from the tip 135 of the plate material 130 toward the longitudinal center of the plate material 130, it is located toward the center in the width direction of the plate material 130. The second inclined portion 134 is provided at the longitudinal end 94B of the plate material 130, which corresponds to the longitudinal end 94B of the hollow member 1. The second inclined portion 134 is provided so as you move from the tip 135 of the plate material 130 toward the longitudinal center of the plate material 130, it will be located toward the center in the width direction of the plate material 130. The straight portion 132 is formed between the end of the first inclined portion 133 toward the center in the width direction of the plate material 130 and the end of the second inclined portion 134 toward the center in the width direction of the plate material 130. The longitudinal center portion 94C of the plate material 130 corresponds to the longitudinal center portion 94C of the hollow member 1.

[0137] The tip portion 135 shown in Figure 15E corresponds to the longitudinal tip portion of the bottom wall portion 25 shown in Figures 15A to 15D. The first inclined portion 133 corresponds to the height-direction tip portion of the first rib 35 shown in Figures 15A to 15D. The second inclined portion 134 corresponds to the height-direction tip portion of the second rib 45 shown in Figures 15A to 15D.

[0138] [Other variations] The hollow member 1 may have a center of gravity in the cross-sectional shape of the intermediate portion that is located away from a line segment connecting the center of gravity in the cross-sectional shapes of both ends in the longitudinal direction. Furthermore, the cross-sectional shape of any part along the longitudinal direction may be rotated in any direction with the line segment as the axis of rotation.

[0139] (Effects of the embodiment) As described above, according to this embodiment, the hollow member 1 is formed from a raw tube 100 in which both side edges 101, 101 of the plate material are joined to form a closed cross section. Therefore, since it is not necessary to join both side edges 101, 101 of the plate material after forming the hollow member 1, both side edges 101, 101 of the plate material and the joint portion 102 can be placed at any part of the cross section of the hollow member 1. In addition, a third hollow section 50 is formed when the first circumferential wall portion 31 is joined to the second circumferential wall portion 41 or the partition portion 20, thereby forming multiple closed cross section structures. As a result, the section modulus of the hollow member 1 can be increased. This makes it possible to reduce weight while suppressing a decrease in rigidity and strength.

[0140] Furthermore, the joint portion 102 is located in the first peripheral wall portion 31, the second peripheral wall portion 41, or the partition portion 20 that form the third hollow portion 50. Since these are inside the hollow cross-section, rust is less likely to occur and they are less likely to be the starting point of fracture. Therefore, rust or fracture can be suppressed without increasing the plate thickness. This makes it possible to reduce weight while suppressing a decrease in rigidity and strength.

[0141] Furthermore, the hollow member 1 has a portion in its longitudinal direction where its circumference differs from the rest. Therefore, for example, by making the circumference of the cross-section of the central part (part 90) in the longitudinal direction larger than the circumference of the cross-sections at both ends, the member can be efficiently arranged so that stress is less likely to occur locally in response to an input that causes bending deformation. This makes it possible to reduce weight while suppressing a decrease in rigidity and strength.

[0142] Furthermore, the hollow member 1 has a portion in its longitudinal direction where the plate thickness differs from the rest. Therefore, for example, by making the plate thickness of the central portion 91B, obtained by dividing the longitudinal hollow member 1 into three parts, smaller than the plate thickness of the portions 91C at both ends, it is possible to control the portion of the hollow member 1 that buckles when subjected to a compressive load. This makes it possible to reduce weight while suppressing a decrease in rigidity and strength.

[0143] Furthermore, the hollow member 1 has a portion in the circumferential direction where the plate thickness differs from the rest. Therefore, for example, by making the plate thickness of the portion 92B provided in the first compartment 21 of the hollow member 1 smaller than the plate thickness of the other portions, the thickness of the compartment 20, which has excessive rigidity or strength due to overlapping plate materials, can be reduced. This makes it possible to reduce weight while suppressing a decrease in rigidity and strength.

[0144] Furthermore, the hollow member 1 has portions where the cross-sectional shape differs between a portion in the longitudinal direction and other portions located further in the longitudinal direction from that portion. Therefore, for example, by making the cross-sectional shape of the portion of the hollow member that is connected to the mating object (the central portion 93C in the longitudinal direction) larger than the cross-sectional shape of the other portions (the ends 93B in the longitudinal direction), the hollow member can be firmly connected to the mating object. This makes it possible to reduce weight while suppressing a decrease in rigidity and strength.

[0145] Furthermore, the hollow member 1 has multiple closed cross-sectional structures formed when the second peripheral wall portion 41 is joined to the first peripheral wall portion 31 or the partition portion 20 to form a fourth hollow portion 60. Therefore, the section modulus of the hollow member 1 can be increased. This makes it possible to reduce weight while suppressing a decrease in rigidity and strength. [Industrial applicability]

[0146] As explained above, this disclosure is industrially applicable as a hollow component. [Explanation of symbols]

[0147] 1 Hollow member 20 sections 22 1st contact part 24 Second contact part 30 1st hollow part 31 First peripheral wall part 40 Second hollow part 41 Second peripheral wall part 50 3rd hollow part 60 4th hollow part 70 1st joint 80 Second joint 90. Areas with different circumferences from others (at least a portion in the longitudinal direction) 91B Areas where the plate thickness differs from the rest (at least a portion in the longitudinal direction) 92B Areas where the plate thickness differs from the rest (at least a portion in the circumferential direction) 93B Areas with a different cross-sectional shape from others (a portion in the longitudinal direction and other portions located longitudinally away from that portion) 100 tubes 101 Side edge 102 Joint

Claims

1. A hollow member consisting of a raw tube in which both side edges of a plate material are joined to form a closed cross-section, The first contact portion and the second contact portion, which are separated from each other in the circumferential direction of the tube, are in contact with each other, forming a partition portion that creates a first hollow portion and a second hollow portion within the tube, A hollow member comprising: a first peripheral wall portion forming the first hollow portion, which is joined to a second peripheral wall portion or the partition portion forming the second hollow portion; and a first joining portion forming a third hollow portion on the outside of the first hollow portion and the second hollow portion.

2. In the hollow member according to claim 1, The joint portion where both side edges of the plate material in the raw pipe are joined is a hollow member arranged in the first peripheral wall portion, the second peripheral wall portion, or the partition portion that forms the third hollow portion.

3. In the hollow member according to claim 1, The hollow member is a hollow member having a portion in its longitudinal direction in which the circumference differs from that of the rest.

4. In the hollow member according to claim 1, The hollow member is a hollow member having a portion in the longitudinal direction in which the plate thickness differs from the rest.

5. In the hollow member according to claim 1, The hollow member is a hollow member having a portion in the circumferential direction in which the plate thickness differs from the rest.

6. In the hollow member according to claim 1, The hollow member is a hollow member having a portion in the longitudinal direction and another portion located longitudinally away from that portion, in which the cross-sectional shape of that portion differs from the rest.

7. In the hollow member according to claim 1, A hollow member comprising a second circumferential wall portion forming the second hollow portion, which is joined to the first circumferential wall portion or the partition portion forming the first hollow portion, and a second joining portion forming a fourth hollow portion on the outside of the second hollow portion and the first hollow portion.

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