Method for manufacturing a tubular member

Abstract

To suppress generation of a damage in a fragile portion of a workpiece when the workpiece is inflated.SOLUTION: Provided is a manufacturing method of a tubular member by inflating a tubular workpiece having a fragile portion. In this manufacturing method, first, the workpiece is arranged in a space surrounded by a molding surface of a mold. Then, in a state where a pressing portion presses the fragile portion in an outer peripheral surface of the workpiece, pressing of an inner peripheral surface of the workpiece is started to inflate the workpiece, and pressing of the fragile portion and the inner peripheral portion is continued until the outer peripheral surface of the workpiece contacts the molding surface of the mold.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a method for manufacturing a tubular member. By law Regarding. [Background technology]

[0002] When a tubular workpiece is expanded by hydroforming so that its cross section increases, damage such as cracks may occur in weak parts of the workpiece (e.g., weld beads, etc.). Therefore, when expanding the workpiece by hydroforming, both ends of the workpiece are pressed by punches. This allows the material that constitutes the workpiece to be sent toward the weak parts, suppressing damage to the weak parts.

[0003] However, in a curved workpiece having a double-tube structure, pressing both ends may change the relative position between the inner tube and the outer tube. Therefore, when expanding such a workpiece by hydroforming, it is not possible to press both ends, which may result in damage to the weak parts. In order to expand such a workpiece while avoiding damage to the weak parts, it is necessary, for example, to perform hydroforming on the workpiece in stages multiple times to expand the workpiece little by little.

[0004] In response to this, Patent Document 1 discloses a technique for adjusting the orientation of a workpiece before the start of hydroforming, in which a workpiece with a circular cross section is expanded by hydroforming to process the cross section into an ellipse, so that a weak part is located at the end of the minor axis of the elliptical cross section of the expanded workpiece. This allows the weak part to come into contact with the die early during the expansion of the workpiece, and is pressed by the die, thereby suppressing the occurrence of cracks in the welded part. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-171406 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, with the technique disclosed in Patent Document 1, there is a risk that the weak portion of the workpiece will stretch before it comes into contact with the die, causing damage to the welded portion. One aspect of the present disclosure aims to suppress damage to weak portions of a workpiece when the workpiece is expanded. [Means for solving the problem]

[0007] One aspect of the present disclosure is a method for manufacturing a tubular member by expanding a tubular workpiece having a fragile portion, in which the workpiece is placed in a space surrounded by a molding surface of a die, and while a pressing portion presses the fragile portion on the outer circumferential surface of the workpiece, pressing of the inner circumferential surface of the workpiece is started, and the workpiece is expanded while pressing of the fragile portion and pressing of the inner circumferential surface are continued until the outer circumferential surface of the workpiece abuts on the molding surface of the die.

[0008] According to the above configuration, while the workpiece is expanded by pressing the inner circumferential surface, the weak portion on the outer circumferential surface of the workpiece is pressed by the pressing portion, and the elongation of the weak portion can be suppressed. Therefore, damage to the weak portion of the workpiece can be suppressed when the workpiece is expanded.

[0009] In one aspect of the present disclosure, the weak portion may be a portion where a weld bead is formed. According to the above configuration, damage to the weld bead of the workpiece can be suppressed when the workpiece is expanded.

[0010] In one aspect of the present disclosure, the pressing portion may be made of an elastic material. According to the above-mentioned configuration, the weak portion on the outer circumferential surface of the workpiece can be pressed effectively, which further suppresses damage to the weak portion of the workpiece.

[0011] In one aspect of the present disclosure, the inner peripheral surface of the workpiece may be pressed by hydroforming. According to the above configuration, the workpiece can be expanded satisfactorily. In one embodiment of the present disclosure, the workpiece is configured as a multi-tube structure in which multiple tubes are arranged to overlap each other, and includes an outer tube and at least one inner tube. The outer tube is an outermost tubular member. The at least one inner tube is located inside the outer tube. The fragile portion is formed in the outer tube. The outer peripheral surface and inner peripheral surface of the workpiece are the outer peripheral surface and inner peripheral surface of the outer tube, respectively.

[0012] When both ends of a workpiece configured as a multi-tube are pressed, there is a risk that the relative positions of the multiple tubes included in the workpiece may change. In contrast, with the above configuration, when the outer tube of the workpiece is expanded by hydroforming, damage to the weak parts can be suppressed by pressing the weak parts without pressing both ends of the workpiece. Therefore, when the outer tube of the workpiece, which is a multi-tube, is expanded, damage to the weak parts can be suppressed while suppressing changes in the relative positions of the multiple tubes included in the workpiece.

[0013] One aspect of the present disclosure is a die used to expand a tubular workpiece having a fragile portion by pressing the inner peripheral surface of the workpiece, the die comprising a molding surface and a pressing portion. The molding surface is configured so that the outer peripheral surface of the workpiece expanded by pressing the inner peripheral surface comes into contact with the molding surface. The pressing portion is provided on the molding surface. The pressing portion is provided so as to protrude from the molding surface, and is configured to press the fragile portion of the outer peripheral surface and to be displaceable to the position of the molding surface.

[0014] According to the above configuration, while the workpiece arranged inside the molding surface of the die is expanded by pressing the inner circumferential surface, the weak portion on the outer circumferential surface of the workpiece is pressed by the pressing portion, thereby suppressing elongation of the weak portion, thereby suppressing damage to the weak portion of the workpiece when the workpiece is expanded.

[0015] In one aspect of the present disclosure, the pressing portion is made of an elastic material. According to the above-mentioned configuration, the weak portion on the outer circumferential surface of the workpiece can be pressed effectively, which further suppresses damage to the weak portion of the workpiece.

[0016] In one aspect of the present disclosure, the device may further include a biasing portion configured to bias the pressing portion toward the weakened portion. According to the above-mentioned configuration, the weak portion on the outer circumferential surface of the workpiece can be pressed effectively, which further suppresses damage to the weak portion of the workpiece. [Brief description of the drawings]

[0017] [Figure 1] FIG. 2 is an explanatory diagram of a workpiece according to the first embodiment. [Diagram 2] FIG. 2 is an explanatory diagram of a double-layered pipe produced by hydroforming in the first embodiment. [Diagram 3] 3 is an explanatory view showing a first member of the die of the first embodiment and an outer tube of a workpiece placed in a groove of the first member. FIG. [Figure 4] 4 is an explanatory view showing a second member of the die of the first embodiment and an outer tube of a workpiece placed in a groove of the second member. FIG. [Diagram 5] FIG. 2 is an explanatory view transparently illustrating a pressing mechanism for a first member of the mold according to the first embodiment, and also illustrating a closing member and a sealing punch. [Figure 6] 6 is a cross-sectional view taken along line VI-VI in FIG. 3 when the pressing portion protrudes from the storage portion (in other words, the molding surface). [Figure 7] 6 is a cross-sectional view taken along line VI-VI in FIG. 3 when the pressing portion is disposed in the storage portion. [Figure 8] FIG. 4 is an explanatory diagram of a first end of a closing member and a workpiece according to the first embodiment. [Figure 9] 4 is an explanatory diagram of a second end of the seal punch and the workpiece according to the first embodiment. FIG. [Figure 10] FIG. 11 is an explanatory diagram of a workpiece according to a second embodiment. [Figure 11] FIG. 11 is an explanatory diagram of a double-layered pipe produced by hydroforming in the second embodiment. [Figure 12] 13 is an explanatory view showing a first member of a die according to a second embodiment and an outer tube of a workpiece placed in a groove of the first member. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the embodiments of the present disclosure are not limited to the following embodiments, and various forms may be adopted as long as they fall within the technical scope of the present disclosure.

[0019] [First embodiment] [1. Work configuration] The workpiece 1 of the first embodiment is configured as a curved double-layered pipe (see FIG. 1). The double-layered pipe refers to a tubular member with a double-tube structure including an outer pipe and an inner pipe that are arranged so as to overlap with a gap. The workpiece 1 is configured of a metal such as iron, and includes an outer pipe 10 and an inner pipe 13. The outer pipe 10 and the inner pipe 13 have a cross section (hereinafter simply referred to as a cross section) perpendicular to the extension direction that is approximately circular, and the diameter of the cross section of the outer pipe 10 is larger than the diameter of the cross section of the inner pipe 13. In addition, a gap is provided between the inner pipe 13 and the outer pipe 10, surrounding the inner pipe 13.

[0020] The workpiece 1 is formed as follows. That is, a rectangular plate is curved to butt the opposing edges together, and these edges are welded to form two tubular members extending linearly. Each tubular member corresponds to an outer tube 10 and an inner tube 13, and a weld bead extending linearly in the extension direction from the first end to the second end is formed on the outer tube 10 and the inner tube 13. Then, the outer tube 10 and the inner tube 13 are overlapped and joined so that the cross section is concentric, and the center is curved to form the workpiece 1.

[0021] A flat portion 12A having a flat shape is generated on the outer peripheral side of the central curved portion 12 of the outer tube 10 formed by bending the workpiece 1. The gap between the outer tube 10 and the inner tube 13 is narrower in the flat portion 12A than in other portions. For this reason, in the first embodiment, the outer tube 10 of the workpiece 1 is expanded by hydroforming using a die described later, widening the gap, thereby manufacturing the two-layered tube 2 shown in Fig. 2. The two-layered tube 2 has the same configuration as the workpiece 1, except for the flat portion 12A.

[0022] The outer tube 10 has a substantially constant cross-sectional diameter, and is formed with a curved portion 12 in the center, and the curved portion 12 is formed with the flat portion 12A described above. The inner tube 13 is curved in the center and includes a main body portion 14 , an expanded diameter portion 15 , and a connecting portion 16 .

[0023] The connecting portion 16 is a cylindrical portion adjacent to the first end 13A of the inner tube 13, and has a larger cross-sectional diameter than the main body portion 14. The connecting portion 16 also has a plurality of joint portions 17 and a plurality of communication portions 18 aligned in the circumferential direction. The joint portions 17 protrude outward beyond the communication portions 18, and the joint portions 17 and the communication portions 18 are arranged alternately.

[0024] Moreover, the first end 13A of the inner pipe 13 is located inside the first end 10A of the outer pipe 10, and the connecting portion 16 is provided near the first end 10A of the outer pipe 10. Each joint portion 17 is welded to the outer pipe 10, and a gap is formed between the outer pipe 10 and each communication portion 18.

[0025] The main body 14 is a cylindrical portion extending from the second end 13B of the inner tube 13 toward the connecting portion 16, and an expanded diameter portion 15 is provided between the main body 14 and the connecting portion 16. The expanded diameter portion 15 has a cross-sectional diameter that expands toward the first end 13A.

[0026] Furthermore, the second end 13B of the inner pipe 13 is located inside the second end 10B of the outer pipe 10, and the outer peripheral surfaces of the main body portion 14 and the expanded diameter portion 15 are spaced apart from the inner peripheral surface of the outer pipe 10. In other words, a space surrounding the main body portion 14 and the expanded diameter portion 15 is formed between the main body portion 14 and the expanded diameter portion 15 and the outer pipe 10, and the space communicates with the outside via gaps between the outer pipe 10 and each communicating portion 18. The second end 13B of the inner pipe 13 may protrude outward beyond the second end 10B of the outer pipe 10.

[0027] In the first embodiment, as an example, the weld beads 11 of the outer pipe 10 extend at a substantially constant interval from the axis 1A, and are disposed so as to be furthest from the horizontal plane when the workpiece 1 is disposed so that the axis 1A is along the horizontal plane. Note that the axis 1A is a line passing through the approximate centers of the cross sections of the outer pipe 10 and the inner pipe 13. Of course, this is not limiting, and the position of the weld beads 11 of the outer pipe 10 can be determined as appropriate.

[0028] [2. Mold configuration] The die 3 used for hydroforming the work 1 comprises a pair of first and second members 3A, 3B (see Figs. 3 to 5). During hydroforming, these members are arranged overlapping each other with the first member 3A located on the lower side and the second member 3B located on the upper side. However, this is not limiting, and the positions of the first and second members 3A, 3B during hydroforming can be appropriately determined. Furthermore, the die 3 may be composed of one member, or three or more members.

[0029] The first and second members 3A, 3B each include a groove portion 30, first and second ends 32, 33, an abutment surface , a side surface 35, and a bottom surface . The abutment surface 34 , side surface 35 and bottom surface 36 are the outer surfaces of each member, with the bottom surface 36 located opposite the abutment surface 34 and the side surface 35 extending from the outer edge of the abutment surface 34 to the outer edge of the bottom surface 36 .

[0030] The groove portion 30 is a groove-shaped portion formed in the contact surface 34, and the workpiece 1 is placed therein during hydroforming. The cross section of the groove portion 30 is substantially semicircular. The first and second ends 32, 33 are recessed portions formed in the contact surface 34 and are connected to the first and second ends of the groove portion 30, respectively.

[0031] During hydroforming, the first and second members 3A, 3B are arranged so that the abutment surfaces 34 of each member abut and the side surfaces 35 of each member are flush with each other. At this time, the grooves 30 of each member are arranged to overlap, and a curved cylindrical space (hereinafter, molding space) is formed by these grooves 30. The molding space has the same shape as the two-layer pipe 2. More specifically, the molding surface 31 of the grooves 30 of each member has the same shape as the outer circumferential surface of the outer pipe 10 of the two-layer pipe 2.

[0032] At this time, the first and second ends 32, 33 of the members are also arranged so as to overlap each other. The overlapping first end 32 forms a space that opens to the side surface 35, and a blocking member 5, which will be described later, is arranged in this space. Similarly, the overlapping second end 33 also forms a space that opens to the side surface 35, and a sealing punch 6 is arranged in this space.

[0033] [3. Configuration of the pressing mechanism] The first member 3A is provided with a pressing mechanism 4 that presses the weld bead 11 of the outer pipe 10 of the workpiece 1 (see Figs. 3, 5 to 7). On the other hand, the second member 3B is not provided with a pressing mechanism 4. However, this is not limited to the above, and the pressing mechanism 4 may be provided only on the second member 3B, or the pressing mechanism 4 may be provided on each of the first and second members 3A and 3B.

[0034] Specifically, a storage portion 37, which is a groove-shaped portion extending along the extension direction, is provided at the bottom of the groove portion 30. The storage portion 37 extends from the vicinity of the first end portion 32 of the groove portion 30 to the vicinity of the second end portion 33.

[0035] Furthermore, a plurality of cylindrical through holes 38 reaching the bottom surface 36 of the first member 3A are provided at the bottom of the storage section 37. The through holes 38 are aligned at approximately regular intervals along the extension direction of the storage section 37.

[0036] The pressing mechanism 4 includes a pressing portion 40, a plurality of pillar portions 41, and a biasing portion . The pressing portion 40 is a long and thin portion made of an elastic material such as rubber, and comes into contact with the weld bead 11 of the outer pipe 10. The pressing portion 40 is disposed in the housing portion 37. Note that the pressing portion 40 may be made of a material that does not have elasticity.

[0037] Each pillar portion 41 is a columnar portion disposed in the through hole 38. A joining portion that is joined to the bottom portion of the pressing portion 40 is provided at the upper end of the pillar portion 41. The biasing portion 42 biases the pressing portion 40 so that the pressing portion 40 presses the weld bead 11 of the outer pipe 10 (in other words, so that the pressing portion 40 is displaced upward). As an example, the biasing portion 42 is configured as a plurality of coil springs provided corresponding to each column portion 41, and is arranged so as to surround the outer circumferential surface of the column portion 41. The upper end of each coil spring is joined to the joint portion at the upper end of the column portion 41, and the lower end is joined to the bottom of the accommodation portion 37.

[0038] Each column portion 41 is disposed in the through hole 38 so as to be displaceable up and down along the through hole 38. When the work 1 is not disposed in the groove portion 30, each coil spring of the urging portion 42 expands, and each column portion 41 protrudes from the through hole 38. Therefore, the pressing portion 40 protrudes from the accommodation portion 37 (in other words, from the molding surface 31). When the pressing portion 40 is pressed downward (in other words, toward the molding surface 31), each coil spring of the urging portion 42 contracts, and the pressing portion 40 is displaced downward. The pressing portion 40 can be displaced downward at least to a position where its upper surface is flush with the molding surface 31. Then, each column portion 41 is urged upward by the elastic force of each contracted coil spring, and the pressing portion 40 is pressed upward by each column portion 41.

[0039] [4. Configuration of the blocking member] The closing member 5 is disposed in the space formed by the first ends 32 of the first and second members 3A and 3B that are arranged one on top of the other during hydroforming, and closes the opening of the work 1 (see FIGS. 3 to 5 and 8). The closing member 5 includes a main body 50, an insertion portion 51, and an injection port 52.

[0040] The main body portion 50 is a disk-shaped portion. The insertion part 51 is a disk-shaped part that protrudes from the center of the circular outer surface of the main body part 50. The insertion part 51 is inserted into the opening of the first end 10A of the outer tube 10 during hydroforming to seal the opening. At this time, the insertion part 51 is separated from the first end 13A of the inner tube 13.

[0041] The injection port 52 is a hole penetrating the main body 50 and the insertion portion 51, and during hydroforming, liquid is injected into the inside of the workpiece 1 through the injection port 52. The injection port 52 passes through approximately the center of the circular outer surfaces of the main body 50 and the insertion portion 51.

[0042] [5. Configuration of seal punch] The seal punch 6 is disposed in the space formed by the second ends 33 of the first and second members 3A, 3B arranged one on top of the other during hydroforming, and closes the opening of the workpiece 1 (see Figs. 3 to 5 and 9). The seal punch 6 includes a main body portion 60 and an insertion portion 61. The seal punch 6 may be provided with an injection port for injecting liquid into the workpiece 1 during hydroforming.

[0043] The main body portion 60 is a cylindrical portion. The insertion portion 61 is a columnar portion protruding from the center of the circular end face of the main body portion 60. The insertion portion 61 is inserted into the opening of the second end 10B of the outer tube 10 during hydroforming to seal the opening. The insertion portion 61 has an outer peripheral portion 62 and a central portion 63.

[0044] The outer circumferential portion 62 is a wall-like portion provided along the outer circumferential surface of the insertion portion 61, and is inserted into the space between the outer tube 10 and the inner tube 13 when the insertion portion 61 is inserted into the opening of the outer tube 10. The central portion 63 is a columnar portion provided inside the outer circumferential portion 62, and is inserted into the opening of the second end 13B of the inner tube 13 when the insertion portion 61 is inserted into the opening of the outer tube .

[0045] When the insertion portion 61 is inserted into the opening of the outer tube 10, the portion near the second end 13B of the inner tube 13 is clamped between the outer peripheral portion 62 and the central portion 63, thereby fixing the second end 13B of the inner tube 13.

[0046] [6. About workpiece forming] As described above, the flat portion 12A is present on the outer peripheral side of the curved portion 12 in the outer tube 10 of the workpiece 1 (see FIG. 1). In order to eliminate the flat portion 12A and widen the gap between the outer tube 10 and the inner tube 13, the outer tube 10 is expanded by hydroforming using a die 3.

[0047] That is, the workpiece 1 is placed in the above-mentioned forming space surrounded by the forming surfaces 31 of the grooves 30 of the first and second members 3A and 3B arranged so as to overlap (see Figs. 3 and 4). Specifically, for example, the workpiece 1 is first placed in the grooves 30 of the first member 3A located on the lower side. At this time, the weld bead 11, which is a weak portion in the outer pipe 10, abuts against the pressing portion 40 of the pressing mechanism 4 provided at the bottom of the grooves 30 of the first member 3A. Then, the second member 3B is placed above the first member 3A so that the grooves 30 overlap each other.

[0048] At this time, the first end 10A of the outer pipe 10 is located near the first end 32 of the first and second members 3A and 3B, and the second end 10B is located near the second end 33. Furthermore, at the flat portion 12A of the curved portion 12 of the outer pipe 10, the outer peripheral surface of the outer pipe 10 is separated from the molding surface 31, but at other portions, the outer peripheral surface of the outer pipe 10 abuts against the molding surface 31.

[0049] At this time, the weld bead 11 on the outer peripheral surface of the outer pipe 10 is pressed by the pressing unit 40 of the pressing mechanism 4. In the first embodiment, as an example, the pressing unit 40 extends from the end of the main body 14 of the inner pipe 13 on the first end 13A side to near the end face of the insertion unit 61 of the seal punch 6 inserted into the workpiece 1. Therefore, the portions of the weld bead 11 near both ends of the outer pipe 10 are not pressed by the pressing unit 40. Of course, this is not a limitation, and the range over which the weld bead 11 is pressed can be determined as appropriate.

[0050] Then, hydroforming is started in a state where the pressing part 40 presses the weld bead 11. That is, the insertion part 51 of the blocking member 5 is inserted into the opening of the first end 10A of the outer pipe 10, and the opening is sealed (see FIG. 8). Also, the insertion part 61 of the seal punch 6 is inserted into the opening of the second end 10B of the outer pipe 10, and the opening is sealed (see FIG. 9). At this time, the outer peripheral part 62 of the insertion part 61 is inserted into the gap between the outer pipe 10 and the inner pipe 13, and the central part 63 is inserted into the opening of the second end 13B of the inner pipe 13, and as a result, the second end 13B of the inner pipe 13 is fixed. Then, liquid is injected into the inside of the workpiece 1 through the injection port 52 of the blocking member 5, and hydroforming is started.

[0051] As a result, liquid fills the inside of the inner pipe 13 and the space between the inner pipe 13 and the outer pipe 10. The inner and outer circumferential surfaces of the inner pipe 13 are pressed by the liquid, so the shape of the inner pipe 13 is generally maintained even after hydroforming. On the other hand, the inner circumferential surface of the outer pipe 10 is pressed by the liquid. As described above, the outer circumferential surface of the outer pipe 10 is separated from the molding surface 31 at the flattened portion 12A, but the outer circumferential surface abuts against the molding surface 31 in other portions. As a result, the flattened portion 12A of the outer pipe 10 expands outward, while the shape of the other portions is maintained.

[0052] The hydroforming continues until the entire outer peripheral surface of the outer pipe 10 abuts against the forming surface 31, and when the hydroforming is completed, the two-layer pipe 2 (see FIG. 2) is formed. The pressing of the weld bead 11 of the outer pipe 10 by the pressing unit 40 also continues until the hydroforming is completed. Note that, during the hydroforming, pressing of both ends of the workpiece 1 along the axis 1A is not performed.

[0053] [Second embodiment] [7. Work configuration] The workpiece 7 of the second embodiment is configured as a curved tightly contacted double pipe (see FIG. 10). The tightly contacted double pipe means a tubular member having a double pipe structure including an outer pipe and an inner pipe arranged so as to overlap in a state of almost abutting each other. Note that almost abutting means a state in which the two parts are abutting each other or arranged with a small gap therebetween.

[0054] The workpiece 7 is made of a metal such as iron, and includes an outer pipe 70 and an inner pipe 80 that are in approximate contact with each other. The outer pipe 70 and the inner pipe 80 have an approximate circular cross section, and the diameter of the cross section of the outer pipe 70 is larger than the diameter of the cross section of the inner pipe 80. The workpiece 7 is formed in the same manner as the workpiece 1 of the first embodiment, and weld beads are formed on the outer pipe 70 and the inner pipe 80.

[0055] In the second embodiment, the outer tube 70 of the workpiece 7 is expanded (in other words, enlarged in diameter) by hydroforming using the mold 3 of the first embodiment, and a gap is formed between the outer tube 70 and the inner tube 80, thereby producing a two-layer tube 9 (see Figure 11).

[0056] The outer tube 70 is curved in the center and includes a first end portion 72, a first enlarged diameter portion 73, an intermediate portion 74, a second end portion 75, and a second enlarged diameter portion 76 (see FIG. 10). The first and second end portions 72, 75 are cylindrical portions adjacent to the first and second ends 70A, 70B of the outer tube 70, respectively, and have a larger cross-sectional diameter than the intermediate portion 74.

[0057] The first expanded diameter portion 73 is located between the first end portion 72 and the intermediate portion 74, and the cross-sectional diameter increases toward the first end 70A. The second expanded diameter portion 76 is located between the second end portion 75 and the intermediate portion 74, and the cross-sectional diameter increases toward the second end 70B.

[0058] The intermediate portion 74 is a cylindrical portion located between the first enlarged diameter portion 73 and the second enlarged diameter portion 76, and has a curved center. The inner tube 80 is curved in the center and includes a first end portion 81, a first enlarged diameter portion 82, an intermediate portion 85, a second end portion 86, and a second reduced diameter portion 87 (see FIG. 10).

[0059] The first end portion 81 is a cylindrical portion adjacent to the first end 80A of the inner pipe 80, and has a larger cross-sectional diameter than the intermediate portion 85. The first end portion 81 also includes a plurality of joint portions 83 and a plurality of communication portions 84 similar to those provided in the connecting portion 16 of the inner pipe 80 in the first embodiment.

[0060] The first expanded diameter portion 82 is located between the first end portion 81 and the intermediate portion 85, and the cross-sectional diameter increases toward the first end 80A. The second end portion 86 is a cylindrical portion adjacent to the second end 80B of the inner tube 80, and has a smaller cross-sectional diameter than the intermediate portion 85.

[0061] The second reduced diameter portion 87 is located between the second end portion 86 and the intermediate portion 85, and has a cross-sectional diameter that decreases toward the second end 80B. The intermediate portion 85 is a cylindrical portion located between the first enlarged diameter portion 82 and the second reduced diameter portion 87, and has a curved center.

[0062] The first end 80A of the inner pipe 80 is located inside the first end 70A of the outer pipe 70, and the first end portion 81 of the inner pipe 80 is provided inside the first end portion 72 of the outer pipe 70. Also, each joint portion 83 is welded to the first end portion 72 of the outer pipe 70, and a gap is formed between the first end portion 72 and each communication portion 84.

[0063] Further, the second end 80B of the inner pipe 80 is located inside the second end 70B of the outer pipe 70, and the second end portion 86 of the inner pipe 80 is provided inside the second end portion 75 of the outer pipe 70. A gap is formed between the outer peripheral surface of the second end portion 86 and the second reduced diameter portion 87 of the inner pipe 80 and the inner peripheral surface of the second end portion 75 and the second expanded diameter portion 76 of the outer pipe 70.

[0064] Furthermore, the intermediate portion 85 of the inner pipe 80 is disposed inside the intermediate portion 74 of the outer pipe 70 , and the outer peripheral surface of the intermediate portion 85 of the inner pipe 80 approximately abuts against the inner peripheral surface of the intermediate portion 74 of the outer pipe 70 . Similarly to the first embodiment, the weld bead 71 of the outer pipe 70 is disposed so as to be farthest from the horizontal plane when the workpiece 1 is disposed so that the axis 7A is along the horizontal plane. Of course, this is not limiting, and the position of the weld bead 71 of the outer pipe 70 can be determined as appropriate.

[0065] [8. About workpiece forming] As described above, in the second embodiment, the outer tube 70 of the workpiece 7 is expanded by hydroforming using the mold 3 of the first embodiment, thereby forming a gap between the middle portion 74 of the outer tube 70 and the middle portion 85 of the inner tube 80, which are approximately abutting each other.

[0066] That is, similarly to the first embodiment, the workpiece 7 is placed in the molding space formed by the first and second members 3A and 3B (see FIG. 12). Specifically, for example, first, the workpiece 7 is placed in the groove portion 30 of the first member 3A located on the lower side. At this time, the weld bead 71 of the outer pipe 70 abuts against the pressing portion 40 of the pressing mechanism 4. Thereafter, the second member 3B is placed above the first member 3A so that the groove portions 30 overlap each other.

[0067] At this time, the outer circumferential surface of the outer tube 70 is separated from the molding surface 31 at the intermediate portion 74 and the first and second enlarged diameter portions 73, 76, but the outer circumferential surface abuts against the molding surface 31 in other portions. At this time, the weld bead 71 on the outer peripheral surface of the outer pipe 70 is pressed by the pressing portion 40 of the pressing mechanism 4. In the second embodiment, as an example, the pressing portion 40 extends from the end portion of the intermediate portion 74 of the outer pipe 70 on the first end 70A side to the end portion of the intermediate portion 74 on the second end 70B side. Therefore, the portions of the weld bead 71 near both ends of the outer pipe 70 are not pressed. Of course, this is not a limitation, and the range over which the weld bead 71 is pressed can be determined as appropriate.

[0068] Then, similarly to the first embodiment, hydroforming is started with the pressing portion 40 pressing the weld bead 71. That is, the opening of the first end 70A of the outer pipe 70 is sealed by the insertion portion 51 of the blocking member 5, and the opening of the second end 70B of the outer pipe 70 is sealed by the insertion portion 61 of the seal punch 6. Also, the second end 80B of the inner pipe 80 is fixed by the outer circumferential portion 62 and the central portion 63 of the insertion portion 61. Thereafter, liquid is injected into the workpiece 7 through the injection port 52 of the blocking member 5, and hydroforming is started.

[0069] As a result, the inside of the inner pipe 80 and the space between the inner pipe 80 and the outer pipe 70 are filled with liquid. Then, as in the first embodiment, the shape of the inner pipe 80 is generally maintained even when hydroforming is performed. Meanwhile, the inner circumferential surface of the outer pipe 70 is pressed by the liquid and expands. As a result, the middle section 74, the first enlarged diameter section 73, and the second enlarged diameter section 76 of the outer pipe 70 are separated from the inner pipe 80, and a gap surrounding the inner pipe 80 is generated between the inner circumferential surface of the outer pipe 70 and the outer circumferential surface of the inner pipe 80.

[0070] The hydroforming continues until the entire outer peripheral surface of the outer pipe 70 abuts against the forming surface 31, and when the hydroforming is completed, the two-layer pipe 9 is formed. The pressing of the weld bead 71 of the outer pipe 70 by the pressing unit 40 also continues until the hydroforming is completed. Note that, during the hydroforming, pressing of both ends of the workpiece 7 along the axis 1A is not performed.

[0071] [9. Effects] (1) According to the first and second embodiments, during hydroforming, the weld beads 11, 71 on the outer peripheral surface of the outer pipe 10, 70 are pressed by the pressing portion 40, suppressing elongation of the weld beads 11, 71. This makes it possible to suppress damage to the weld beads 11, 71 when the outer pipe 10, 70 is expanded.

[0072] (2) In addition, pressing portion 40 is made of an elastic material. Therefore, pressing portion 40 can effectively press weld beads 11, 71, and damage to weld beads 11, 71 can be further suppressed. (3) Furthermore, when both ends of the curved workpiece 1, 7 having a double pipe structure are pressed, there is a risk of the relative position between the outer pipe 10, 70 and the inner pipe 13, 80 changing. In contrast, according to the first and second embodiments, damage to the weld beads 11, 71 can be suppressed during hydroforming without pressing both ends of the workpiece 1, 7. Therefore, damage to the weld beads 11, 71 can be suppressed while suppressing changes in the relative position between the outer pipe 10, 70 and the inner pipe 13, 80.

[0073] (4) Furthermore, pressing portion 40 is biased by the elastic force of biasing portion 42 configured as a plurality of coil springs. Therefore, weld beads 11, 71 can be pressed effectively, and damage to weld beads 11, 71 can be further suppressed.

[0074] [10. Other embodiments] (1) In the above embodiment, during hydroforming, the weld beads 11, 71 of the outer pipes 10, 70 of the workpieces 1, 7 are pressed by the pressing portion 40. However, this is not limited to this, and a weak portion other than the weld bead in the outer pipes 10, 70 may be pressed.

[0075] (2) In the above embodiment, one pressing mechanism 4 is provided at the bottom of the groove portion 30 in the first member 3A of the die 3, and the pressing mechanism 4 is provided with one elongated pressing portion 40. However, the number and positions of the pressing mechanisms 4 and the number, positions and shapes of the pressing portions 40 in each pressing mechanism 4 can be determined appropriately depending on the weak portions of the workpiece.

[0076] (3) In the above embodiment, the workpieces 1 and 7 have a curved double-tube structure. However, for a tubular workpiece having a double-tube structure extending in a straight line, a workpiece composed of a single tube, or a workpiece having a multi-tube structure in which three or more tubes are arranged overlapping each other, hydroforming may be performed while pressing the fragile portion in the same manner as in the above embodiment.

[0077] Furthermore, when expanding a workpiece made of a single tube, the inner peripheral surface of the workpiece may be pressed by a method other than hydroforming. Specifically, for example, the inner peripheral surface of the workpiece may be pressed by a die arranged inside until the entire outer peripheral surface of the workpiece abuts against the molding surface 31 of the die 3, thereby expanding the workpiece. At this time, the weak portion of the workpiece may be pressed by the pressing unit 40 in the same manner as in the above embodiment from the start to the end of pressing the inner peripheral surface of the workpiece.

[0078] (4) Multiple functions possessed by one component in the above embodiments may be realized by multiple components, or one function possessed by one component may be realized by multiple components. Also, multiple functions possessed by multiple components may be realized by one component, or one function realized by multiple components may be realized by one component. Also, part of the configuration of the above embodiments may be omitted. Also, at least part of the configuration of the above embodiments may be added to or substituted for the configuration of another of the above embodiments. [Explanation of symbols]

[0079] 1...work, 10...outer tube, 11...weld bead, 12...curved portion, 12A...flat portion, 13...inner tube, 2...two-layer tube 2, 3...mold, 3A...first member, 3B...second member, 30...groove portion, 31...forming surface, 37...accommodation portion, 4...pressing mechanism, 40...pressing portion, 42...urging portion, 5...blocking member, 6...sealing punch, 7...work, 70...outer tube, 71...weld bead, 80...inner tube, 9...two-layer tube.

Claims

1. 1. A method for manufacturing a tubular member by expanding a tubular workpiece having a weakened portion, comprising: The workpiece is placed in a space surrounded by a molding surface of a die; While the pressing portion is pressing the fragile portion on the outer peripheral surface of the workpiece, pressing of the inner peripheral surface of the workpiece is started by hydroforming, and the workpiece is expanded while the pressing of the fragile portion and the pressing of the inner peripheral surface are continued until the outer peripheral surface of the workpiece abuts against the molding surface of the die; The workpiece is configured as a curved multi-tube in which a plurality of tubes are arranged to overlap each other, and has an outer tube which is an outermost tubular member, and at least one inner tube which is located inside the outer tube; the fragile portion is an elongated portion of the outer pipe where a weld bead is formed, and extends from one end to the other end so as to bend along the outer pipe, The outer peripheral surface and the inner peripheral surface of the workpiece are the outer peripheral surface and the inner peripheral surface of the outer tube, respectively; The pressing portion is an elongated portion provided so as to bend along the weakened portion. A method for manufacturing a tubular member.

2. A method for producing a tubular member according to claim 1, comprising the steps of: The pressing portion is made of an elastic material. A method for manufacturing a tubular member.

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