Method for forming hollow member having flange part

Abstract

To integrally form a flange part on the outer peripheral surface of an intermediate part of a hollow stock by side extrusion while reducing the occurrence of folding-in.SOLUTION: In a first step, a hollow stock is set in a die hole. In a second step, a mandrel is inserted into the hollow stock to expand the inner and outer diameters of the base end of the hollow stock. Then, in a third step, a hollow member having a flange part on the outer peripheral surface of an intermediate part is formed by executing side extrusion for plastically supplying a material of the hollow stock into an annular cavity opened on the inner peripheral surface of the die hole by pressing the hollow stock in an axial direction by a sleeve. A hollow member including a solid part from a hollow stock of a bottomed cylindrical part having a solid part which is a solid columnar part to a tip and having a flange part can be formed at the tip.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for forming a hollow member having a flange portion. [Background technology]

[0002] In this technical field, a lateral extrusion technique is known in which a hollow or solid rod-shaped material is compressed in the axial direction inside a die hole, and the material that makes up the rod-shaped material is caused to flow into a cavity that opens to the inner peripheral surface of the die hole, thereby integrally forming a bulge (flange portion) on the outer peripheral surface of the middle part of the rod-shaped material.

[0003] For example, Patent Document 1 (Japanese Patent No. 5157957) discloses a technique for integrally forming multiple protrusions (flanges) extending radially from the outer periphery of a hollow or solid shaft. In this conventional technique, as shown in Figure 11, a hollow blank 00 is inserted into a shaft-forming cavity 31, a pressure punch 24 is inserted into the blank 00 to round it (slightly expand the inner diameter), and a ring punch 23 presses the rear end of the blank 00 to further push it into the shaft-forming cavity 31. A counter ejection punch 25 receives the front end of the blank 00 and compresses it in the axial direction. This guides some of the material that makes up the blank 00 into a protrusion-forming cavity 32 that opens onto the inner periphery of the shaft-forming cavity 31. As a result, as shown in Figure 12, an outer ring member (shaft-shaped member with protrusions) 10 having a hollow shaft portion 11 and a plurality of protrusions 12 extending radially outward from the outer peripheral surface of the shaft portion 11 is integrally formed by cold side extrusion. This conventional technology is a general technology in which the material (wall) that makes up the blank is forced to flow into the cavity by axial pressing to form a flange portion.

[0004] However, in the above-described conventional construction method, as illustrated in FIG. 13(a), the material of the blank 00 on both sides of the cavity 32 in the axial direction changes direction from the axial direction to the radially outward direction and flows into the cavity 32. At this time, as illustrated in FIG. 13(b), the material of the blank 00 is pulled toward the inner side of the cavity 32 (the radially outward side) at the change of direction, resulting in a common problem known as "folding" (see the area surrounded by the thick dashed line). The presence of this "folding" may cause mechanical defects due to stress concentration when the blank 00 is used in a product (especially a rotating part requiring high strength, such as a shaft). Therefore, it is preferable that the blank 00 does not have a fold in a product having a flange portion.

[0005] The present applicant has already proposed a technique for integrally forming a flange portion on a cylindrical body without causing creases in Patent Document 2 (JP 2023-92420 A). In this technique, as shown in FIG. 14 , for example, a mandrel 40 is inserted into an annular blank 20 fixed inside an outer mold by sandwiching a flange portion element 22 between a first outer mold 31 and a second outer mold 32 constituting the outer mold, and plastic working, including ironing, is performed on the annular blank 20. This results in a cylindrical body 10, which is a cylindrical member having a cylindrical portion 11, a flange portion 12 formed at the end of the cylindrical portion, and an annular protrusion 13 protruding from the inner peripheral edge of the flange toward the opposite side of the cylindrical portion, and whose inner peripheral surface is formed to be flush with one another. However, this technique does not involve lateral extrusion to integrally form a flange portion on the outer peripheral surface of a hollow blank (i.e., midway through the hollow tube). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5157957 [Patent Document 2] Japanese Patent Application Publication No. 2023-92420 Summary of the Invention [Problem to be solved by the invention]

[0007] As mentioned above, there is a need in the art for a technique for integrally forming a flange portion on the outer peripheral surface of the middle portion of a hollow material by lateral extrusion while reducing the occurrence of folding. [Means for solving the problem]

[0008] Therefore, as a result of extensive research, the inventors have found that the above-mentioned problems can be solved by performing lateral extrusion, in which a hollow blank is set in a die hole, a mandrel is inserted into the hollow blank to expand the inner and outer diameters of the base end of the hollow blank, and then the hollow blank is pressed axially with a sleeve to cause the material constituting the hollow blank to plastically flow into an annular cavity opening on the inner surface of the die hole.

[0009] Specifically, the method for forming a hollow member having a flange portion according to the present invention (hereinafter sometimes referred to as the "method of the present invention") is a method for forming a hollow member having a flange portion using an extrusion molding device equipped with a mandrel, a sleeve, a die, and a drive mechanism. The mandrel is a columnar core metal having a predetermined shape. The sleeve is a cylindrical member arranged coaxially with the mandrel. The die has a die hole, which is a hole having a predetermined shape. The drive mechanism drives the mandrel, sleeve, and die to move closer to each other in the axial direction.

[0010] The method of the present invention uses an extrusion molding apparatus as described above to insert a mandrel into a hollow blank and press the hollow blank with a sleeve to force the hollow blank into the die hole, thereby integrally forming a flange portion by lateral extrusion at a predetermined position between both axial ends of the hollow blank.

[0011] The hollow material is a cylindrical member having a first outer diameter which is a predetermined outer diameter, a first inner diameter which is a predetermined inner diameter, and a first thickness which is a predetermined wall thickness.

[0012] The hollow member includes an expanded diameter portion, a flange portion, an expanded inner diameter portion, an unmachined portion, and a reduced inner diameter portion. The expanded diameter portion is a cylindrical portion formed at the base end, which is upstream in the pressing direction, which is the direction in which the sleeve presses the hollow material, and has a second outer diameter larger than the first outer diameter, a second inner diameter larger than the first inner diameter, and a predetermined second thickness. The flange portion is formed adjacent to the distal end, which is downstream in the pressing direction, of the expanded diameter portion, and has a third outer diameter larger than the second outer diameter, a third inner diameter equal to the second inner diameter, and a third thickness larger than the second thickness. The expanded inner diameter portion is formed adjacent to the distal end of the flange portion and has a fourth outer diameter equal to the first outer diameter, a fourth inner diameter equal to the second inner diameter, and a fourth thickness smaller than the first thickness. The unprocessed portion is a portion that remains as the hollow blank at the tip end, and is a cylindrical portion that has a first outer diameter, a first inner diameter, and a first wall thickness, similar to the hollow blank. The reduced inner diameter portion is a portion that is formed between the enlarged inner diameter portion and the unprocessed portion, and whose inner diameter decreases from the fourth inner diameter to the first inner diameter as it approaches the unprocessed portion from the enlarged inner diameter portion side.

[0013] The mandrel includes a small outer diameter portion, a large outer diameter portion, and an increasing outer diameter portion. The small outer diameter portion is a cylindrical portion formed at the distal end and having a fifth outer diameter corresponding to the first inner diameter. The large outer diameter portion is a cylindrical portion formed at the proximal end and having a sixth outer diameter corresponding to the second inner diameter. The increasing outer diameter portion is formed between the small outer diameter portion and the large outer diameter portion and has an outer diameter that increases from the fifth outer diameter to the sixth outer diameter as it approaches the large outer diameter portion.

[0014] The sleeve includes a pressing portion that is a cylindrical portion formed at the tip end and has a seventh outer diameter equal to the second outer diameter, a fifth inner diameter equal to the second inner diameter, and a fifth wall thickness equal to the second wall thickness.

[0015] The die hole includes a large inner diameter portion, a small inner diameter portion, and a flange-forming portion. The large inner diameter portion is formed on the base end side and has a sixth inner diameter that is an inner diameter corresponding to the second outer diameter. The small inner diameter portion is formed on the tip end side and has a seventh inner diameter that is an inner diameter corresponding to the first outer diameter. The flange-forming portion is formed between the large inner diameter portion and the small inner diameter portion and has an eighth outer diameter that is an outer diameter larger than the sixth inner diameter.

[0016] The method of the present invention comprises the following first to third steps. In the first step, a hollow blank is inserted into the small inner diameter portion of the die hole, and the tip end of the hollow blank is abutted against a stopper provided at the tip end of the die hole to fix the hollow blank in a predetermined position inside the die hole, and the small outer diameter portion of the mandrel is inserted into the internal space of the hollow blank from the base end side of the hollow blank.

[0017] In the second step, the mandrel is further inserted into the internal space of the hollow material and the large outer diameter portion of the mandrel is forced into the internal space of the hollow material, thereby expanding the inner diameter of the base end portion, which is the portion including the base end side end of the hollow material, from the first inner diameter to the second inner diameter, and expanding the outer diameter of the base end portion of the hollow material from the first outer diameter to the second outer diameter.

[0018] In the third step, during a predetermined period after the first time point, the base end of the hollow blank is pressed toward the tip end by the pressing portion of the sleeve, thereby performing lateral extrusion to plastically flow part of the material constituting the hollow blank toward the cavity, which is the space between the inner peripheral surface of the flange-forming portion of the die hole and the outer peripheral surface of the hollow blank. The first time point is the time in the second step when the tip end of the large outer diameter portion of the mandrel reaches the tip end of the flange-forming portion of the die hole. [Effects of the Invention]

[0019] As described above, in the method of the present invention, a hollow blank is placed in a die hole in step 1, a mandrel is inserted into the hollow blank to expand the inner and outer diameters of the base end of the hollow blank in step 2, and then a sleeve is used to press the hollow blank in the axial direction in step 3, causing the material constituting the hollow blank to plastically flow into the annular cavity opening on the inner peripheral surface of the die hole. As a result, the method of the present invention makes it possible to integrally form a flange on the outer peripheral surface of the middle part of the hollow blank while reducing the occurrence of folding.

[0020] Other objects, other features and attendant advantages of the present invention will be readily apparent from the following description of the embodiments of the present invention which will be given with reference to the drawings. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 2 is a schematic side view showing an example of the configuration of a hollow material used in a method (first method) for forming a hollow material having a flange portion according to the first embodiment of the present invention, and a hollow material having a flange portion molded from the hollow material. [Figure 2] FIG. 2 is a schematic cross-sectional view showing an example of the configuration of a mandrel, a sleeve, and a die used in the first method. [Figure 3] 1 is a flowchart illustrating the flow of first to third steps executed in a first method. [Figure 4] 1 is a schematic cross-sectional view showing an example of the change in shape of the hollow material as processing progresses from the first step to the third step in the first method, and the change in the positional relationship between the mandrel, sleeve, and die and the hollow material and hollow member. [Figure 5] Schematic cross-sectional views showing an example of the shape of the hollow material and hollow member at the end of the first step performed in the first method and at the time of performing the third step, and the positional relationship between the mandrel, sleeve, and die and the hollow material and hollow member. [Figure 6] 5A and 5B are schematic cross-sectional views for explaining that the occurrence of folding is reduced in a hollow member having a flange portion formed by the first method. [Figure 7] FIG. 1 is a schematic cross-sectional view showing an example of the configuration of a die, mandrel, and sleeve, in which the tip end of the die hole is blocked by a stopper without a stopper hole, used in the first method. [Figure 8] This is a schematic cross-sectional view showing an example of the change in shape of the hollow material and the change in the positional relationship between the mandrel, sleeve, and die and the hollow material and hollow member as processing progresses from the first step to the third step in the first method using a die whose tip end of the die hole is blocked by a stopper as illustrated in Figure 7, as well as a mandrel and sleeve. [Figure 9] FIG. 2 is a schematic side view showing an example of the configuration of a hollow material used in a method (second method) for forming a hollow material having a flange portion according to a second embodiment of the present invention, and a hollow material having a flange portion molded from the hollow material. [Figure 10] 10 is a schematic cross-sectional view showing an example of the change in shape of the hollow material as processing progresses from the first step to the third step in the second method, and the change in the positional relationship between the mandrel, sleeve, and die and the hollow material and hollow member. [Figure 11] 1 is a schematic cross-sectional view illustrating a method for forming an outer ring member having a hollow shaft portion and a plurality of protrusions extending radially outward from the outer peripheral surface of the shaft portion, according to the prior art disclosed in Patent Document 1. [Figure 12] 1 is a schematic diagram illustrating the configuration of an outer ring member having a hollow shaft portion formed by the conventional technology disclosed in Patent Document 1 and a plurality of protrusions extending radially outward from the outer peripheral surface of the shaft portion. [Figure 13] 1A and 1B are schematic diagrams illustrating how "folding" occurs, which is a common problem in the method of forming a hollow member having a flange portion according to the prior art. [Figure 14] FIG. 1 is a schematic cross-sectional view illustrating the molding of a cylindrical body having a cylindrical portion, a flange portion formed at the end of the cylindrical portion, and an annular protrusion protruding from the inner peripheral edge of the flange portion toward the opposite side of the cylindrical portion, using the conventional technology disclosed in Patent Document 2. DETAILED DESCRIPTION OF THE INVENTION

[0022] First Embodiment A method for forming a hollow member having a flange portion according to a first embodiment of the present invention (hereinafter, sometimes referred to as "first method") will be described below with reference to the drawings.

[0023] The first method is a method of forming a hollow member having a flange portion using an extrusion molding device equipped with a mandrel, a sleeve, a die, and a drive mechanism. The mandrel is a columnar core having a predetermined shape. The sleeve is a cylindrical member arranged coaxially with the mandrel. A die hole, which is a hole having a predetermined shape, is formed in the die. The drive mechanism drives the mandrel, sleeve, and die so as to approach each other in the axial direction.

[0024] The first method uses an extrusion molding device such as that described above, inserts a mandrel into a hollow blank, and presses the hollow blank with a sleeve to force it into the die hole, thereby integrally forming a flange portion by lateral extrusion at a predetermined position between both axial ends of the hollow blank.

[0025] 1(a) and 1(b) are schematic side views showing an example of the configuration of a hollow material used in the first method and a hollow member having a flange portion formed from the hollow material, respectively. As shown in FIG. 1(a), the hollow material 111 is a cylindrical member having a first outer diameter DO1, which is a predetermined outer diameter, a first inner diameter DI1, which is a predetermined inner diameter, and a first thickness T1, which is a predetermined wall thickness.

[0026] 1(b), the hollow member 121 includes an expanded diameter portion PEDOI, a flange portion PF, an expanded inner diameter portion PEDI, an unprocessed portion PUF, and a reduced inner diameter portion PTDI. The expanded diameter portion PEDOI is a cylindrical portion formed at the end of the base end, which is upstream in the pressing direction (the direction from top to bottom in FIG. 1) in which the hollow blank 111 is pressed by a sleeve (not shown), and having a second outer diameter DO2 (DO2>DO1) that is larger than the first outer diameter DO1, a second inner diameter DI2 (DI2>DI1) that is larger than the first inner diameter DI1, and a predetermined second thickness T2.

[0027] The flange portion PF is a flange-shaped portion formed adjacent to the tip side, which is downstream in the pressing direction of the expanded diameter portion PEDOI, and has a third outer diameter DO3 (DO3>DO2) larger than the second outer diameter DO2, a third inner diameter DI3 (DI3=DI2) equal to the second inner diameter DI2, and a third thickness T3 (T3>T2) larger than the second thickness T2.

[0028] As mentioned above, the flange portion PF is formed in the third step by performing lateral extrusion, in which the base end of the hollow blank is pressed toward the tip end with a sleeve, causing a portion of the material constituting the hollow blank to plastically flow toward the cavity, which is the space between the inner circumferential surface of the flange-forming portion of the die hole and the outer circumferential surface of the hollow blank. During this process, the plastically flowing material does not necessarily fill the cavity. Therefore, the outer circumferential surface of the flange portion PF in a cross section taken along a plane including the central axis of the hollow member 121 may not be linear, but may instead be convexly curved radially outward, as shown in FIG. 1(b). In such a case, as shown in FIG. 1(b), the third outer diameter DO3 of the flange portion PF refers to the maximum outer diameter of the flange portion PF, and the third thickness T3 of the flange portion PF refers to the maximum thickness of the flange portion PF.

[0029] The inner diameter enlarged portion PEDI is a cylindrical portion formed adjacent to the tip side of the flange portion PF and having a fourth outer diameter DO4 (DO4 = DO1) equal to the first outer diameter DO1, a fourth inner diameter DI4 (DI4 = DI2) equal to the second inner diameter DI2, and a fourth wall thickness T4 (T4 < T1) smaller than the first wall thickness T1.

[0030] The unprocessed portion PUF is a portion that remains as the hollow material 111 at the end on the tip side, and like the hollow material 111, is a cylindrical portion having the first outer diameter DO1, the first inner diameter DI1, and the first wall thickness T1. The inner diameter decreasing portion PTDI is a portion formed between the inner diameter enlarged portion PSI and the unprocessed portion PUF and having an inner diameter that decreases from the fourth inner diameter DI4 to the first inner diameter DI1 as it approaches from the side of the inner diameter enlarged portion PEDI to the side of the unprocessed portion PUF.

[0031] FIG. 2 is a schematic cross-sectional view showing an example of the configuration of a mandrel, a sleeve, and a die used in the first method. As illustrated in FIG. 2, the mandrel 131 includes a small outer diameter portion PSDO, a large outer diameter portion PLDO, and an outer diameter enlarged portion PTDO. The small outer diameter portion PSDO is a cylindrical portion formed at the end on the tip side and having a fifth outer diameter DO5 that is the outer diameter corresponding to the first inner diameter DI1. The large outer diameter portion PLDO is a cylindrical portion formed on the base end side and having a sixth outer diameter DO6 that is the outer diameter corresponding to the second inner diameter DI2. The outer diameter enlarged portion PTDO is a portion formed between the small outer diameter portion PSDO and the large outer diameter portion PLDO and having an outer diameter that increases from the fifth outer diameter DO5 to the sixth outer diameter DO6 as it approaches from the side of the small outer diameter portion PSDO to the side of the large outer diameter portion PLDO. In FIG. 2, only the small outer diameter portion PSDO, the large outer diameter portion PLDO, and the outer diameter enlarged portion PTDO, which are the main portions of the mandrel 131, are depicted, but the mandrel 131 may include portions other than these main portions, such as a mechanism for connecting a drive mechanism (not shown) to the base end side of the mandrel 131.

[0032] The sleeve 141 includes a pressing portion PP, which is a cylindrical portion formed at the end on the distal side and has a seventh outer diameter DO7 (DO7=DO2) equal to the second outer diameter DO2, a fifth inner diameter DI5 (DI5=DI2) equal to the second inner diameter DI2, and a fifth thickness T5 (T5=T2) equal to the second thickness T2. Note that while only the pressing portion PP, which is a main portion of the sleeve 141, is depicted in Fig. 2, the sleeve 141 may also include portions other than the pressing portion PP, such as a mechanism for connecting a drive mechanism (not shown) to the proximal end side of the sleeve 141.

[0033] Furthermore, the mandrel 131 and the sleeve 141 may be configured to be driven independently by separate drive mechanisms (e.g., actuators, etc.). Alternatively, the mandrel 131 and the sleeve 141 may be configured to be driven integrally while their positional relationship is fixed. Furthermore, the mandrel 131 and the sleeve 141 may be configured as a single unit formed integrally. In addition, as will be described in detail later, the mandrel 131 and the sleeve 141 may be driven by a common drive mechanism, but the positional relationship between the mandrel 131 and the sleeve 141 may be configured to be variable, for example, by interposing a spring between the mandrel 131 and the drive mechanism. The configuration and drive method of the mandrel 131 and the sleeve 141 can be determined appropriately, for example, depending on the configuration of the hollow member having a flange portion to be formed by the first method (e.g., the axial lengths of the enlarged diameter portion PEDOI, the flange portion PF, and the enlarged inner diameter portion PEDI, and the size of the third outer diameter DO3, which is the outer diameter of the flange portion PF).

[0034] The die hole 151a formed in the die 151 includes a large inner diameter portion PLDI, a small inner diameter portion PSDI, and a flange forming portion PFF. The large inner diameter portion PLDI is a portion formed on the base end side and has a sixth inner diameter DI6 that is an inner diameter corresponding to the second outer diameter DO2. The small inner diameter portion PSDI is a portion formed on the tip end side and has a seventh inner diameter DI7 that is an inner diameter corresponding to the first outer diameter DI1. The flange forming portion PFF is a portion formed between the large inner diameter portion PLDI and the small inner diameter portion PSDI and has an eighth outer diameter DI8 (DI8>DI6) that is an outer diameter larger than the sixth inner diameter DI6.

[0035] The die 151 illustrated in FIG. 2 is depicted as if it were a single unit in which the large inner diameter portion PLDI, the small inner diameter portion PSDI, and the flange-forming portion PFF are integrally formed. However, the die 151 must be configured so that the hollow member 121 having the final flange portion can be removed from the die 151. Specific examples of such a die 151 include a die 151 configured so that it can be divided along a plane perpendicular to the axis AX and passing through the flange-forming portion PFF, and a die 151 configured so that it can be divided along a plane including the axis AX. However, the configuration of the die 151 is not limited to these, as long as the die hole 151a satisfies the above requirements and the hollow member 121 having the final flange portion can be removed from the die 151. Furthermore, the die 151 may be configured so that it can be divided into even smaller pieces than the above configuration. In the example shown in FIG. 2, a stopper hole 161a is formed in a stopper 161 provided at the end on the tip side of the die hole 151a, and the stopper hole 161a will be described later.

[0036] Fig. 3 is a flowchart illustrating the flow from step 1 to step 3 performed in the first method. Fig. 4 is a schematic cross-sectional view showing an example of the change in shape of the hollow material and the change in the positional relationship between the mandrel, sleeve, and die and the hollow material and hollow member as processing progresses from step 1 to step 3 in the first method. Fig. 5 is a schematic cross-sectional view showing an example of the shape of the hollow material and hollow member and the positional relationship between the mandrel, sleeve, and die and the hollow material and hollow member at the end of step 1 performed in the first method and during step 3. Fig. 5(b) is an enlarged view of the area surrounded by the thick dashed line in Fig. 5(a).

[0037] The first method includes the following first to third steps. 4(a) and 5(a) and 5(b), the hollow blank 111 is inserted into the small inner diameter portion PSDI of the die hole 151a, and the tip end of the hollow blank 111 is brought into contact with a stopper 161 provided at the tip end of the die hole 151a to fix the hollow blank 111 at a predetermined position inside the die hole 151a. In addition, in the first step, the small outer diameter portion PSDO of the mandrel 131 is inserted into the internal space of the hollow blank 111 from the base end side of the hollow blank 111.

[0038] 4(b), the mandrel 131 is further inserted into the internal space of the hollow material 111, and the large outer diameter portion PLDO of the mandrel 131 is pressed into the internal space of the hollow material 111 (see the black arrow). This causes the inner diameter of the base end portion, which is the portion including the end portion on the base end side of the hollow material 111, to expand from the first inner diameter DI1 to the second inner diameter DI2, and simultaneously causes the outer diameter of the base end portion of the hollow material 111 to expand from the first outer diameter DO1 to the second outer diameter DO2.

[0039] Next, in the third process executed in step S30, as illustrated on the right side of the axis AX in Fig. 4(c) and Fig. 5(a) and (b), the base end of the hollow blank 111 is pressed toward the tip end by the pressing portion PP of the sleeve 141 (see the outline arrow). This executes lateral extrusion, which plastically flows part of the material constituting the hollow blank 111 toward the cavity 151c (the area surrounded by the thick dashed line in Fig. 5(b)), which is the space between the inner peripheral surface of the flange forming portion PFF of the die hole 151a and the outer peripheral surface of the hollow blank 111.

[0040] By carrying out the third step, a portion of the material (wall) constituting the hollow material 111 is allowed to flow into the interior of the cavity 151c, thereby forming a hollow member 121 having a flange portion PF formed between the enlarged diameter portion PEDOI and the enlarged inner diameter portion PEDI, as illustrated in (b) of Figure 1.

[0041] 4 and 5, a stopper hole 161a, which is a hole for receiving the small outer diameter portion PSDO of the mandrel 131 in the stopper 161, is formed in the region of the stopper 161 that faces the small outer diameter portion PSDO of the mandrel 131 in the direction of the axis AX. Therefore, the tip end of the small outer diameter portion PSDO of the mandrel 131 can reach a position closer to the tip than the tip end of the hollow material 111 (i.e., closer to the tip than the base end of the stopper 161).

[0042] Furthermore, from the viewpoint of preventing unintended deformation of hollow blank 111 and improving processing accuracy during the process of forming a hollow member from a hollow blank by the first method, it is preferable that small outer diameter portion PSDO of mandrel 131 be fitted into stopper hole 161a to close the tip side of die hole 151a by the start of step 3 at the latest, thereby defining a space in which unmachined portion PUF remains at the tip portion, which is a portion including the tip-side end of hollow member 121. Therefore, stopper hole 161a has ninth inner diameter DI9, which is an inner diameter corresponding to fifth outer diameter DO5, which is the outer diameter of small outer diameter portion PSDO of mandrel 131. As described above, fifth outer diameter DO5, which is the outer diameter of small outer diameter portion PSDO of mandrel 131, corresponds to first inner diameter DI1, which is the inner diameter of hollow blank 111. Therefore, the ninth inner diameter DI9, which is the inner diameter of the stopper hole 161a, is equal to the first inner diameter DI1, which is the inner diameter of the hollow material 111 (DI9=DI1).

[0043] In the process of forming the flange portion by pressing the hollow blank in the axial direction as described above, the material (wall) constituting the hollow blank on both sides of the axial direction of the cavity changes direction from the axial direction to the radially outward direction and flows into the cavity. As described above with reference to Figure 13, in the conventional construction method, the wall of the hollow blank is pulled toward the back of the cavity (radially outward) at the change of direction, resulting in a common problem known as "folding." The presence of this "folding" may cause mechanical defects due to stress concentration when the hollow blank is used as a product (especially a rotating part requiring high strength, such as a shaft). Therefore, it is necessary to reduce the occurrence of folding in hollow members with flange portions formed therein.

[0044] On the other hand, in the first method, as described above, the hollow blank 111 is set in the die hole 151a in the first step, the mandrel 131 is inserted into the hollow blank 111 in the second step to expand the inner and outer diameters of the base end of the hollow blank 111, and then in the third step, the hollow blank 111 is pressed in the axial direction by the sleeve 141 to perform lateral extrusion, causing the material constituting the hollow blank 111 to plastically flow into the annular cavity 151c opening on the inner peripheral surface of the die hole 151a. As a result, according to the first method, it is possible to integrally form a flange portion PF on the outer peripheral surface of the middle part of the hollow blank 111 while reducing the occurrence of folding.

[0045] Fig. 6 is a schematic cross-sectional view illustrating the reduction in the occurrence of folding in a hollow member having a flange portion formed by the first method. The left side of axis AX in Fig. 6 is an enlarged view of the vicinity of the cavity at the time when the first step described above is completed. Upon completion of the first step, the tip end of hollow blank 111 inserted into the small inner diameter portion of die hole 151a abuts against stopper 161 (not shown), fixing hollow blank 111 at a predetermined position inside die hole 151a, and small outer diameter portion PSDO of mandrel 131 is inserted from the base end side of hollow blank 111.

[0046] 6 is a schematic cross-sectional view illustrating the third step being performed after the large outer diameter portion PLDO of the mandrel 131 is pressed into the hollow blank 111 in the second step, thereby expanding the inner and outer diameters of the base end of the hollow blank 111. As described above, in the third step, the base end of the hollow blank 111 is pressed toward the tip end by the pressing portion PP of the sleeve 141, thereby causing a plastic flow of part of the material constituting the hollow blank 111 toward the cavity 151c, which is the space between the inner circumferential surface of the flange forming portion PFF of the die hole 151a and the outer circumferential surface of the hollow blank 111. At this time, in the first method as well, the material constituting the hollow blank 111 is pulled toward the back of the cavity 151c (outward in the radial direction) as in the conventional processing method (see the black arrows).

[0047] However, in the first method, as described above, in the second step prior to the third step, the large outer diameter portion PLDO of the mandrel 131 is pressed into the hollow blank 111, thereby expanding the inner and outer diameters of the base end of the hollow blank 111. As a result, residual stress that attempts to return to the dimensions before the diameter expansion, which causes so-called "springback," is present in the base end of the hollow blank 111 (see the open arrow). In the first method, the force that attempts to pull the material that makes up the hollow blank 111 toward the back side of the cavity 151c (outside in the radial direction), is at least partially offset by the residual stress, which is thought to reduce the occurrence of the above-described "folding."

[0048] That is, in the first method, a hollow blank is set in a die bore in a first step, a mandrel is inserted into the hollow blank to expand the inner and outer diameters of the base end of the hollow blank in a second step, and then a sleeve pressing portion is used to press the hollow blank in the axial direction into an annular cavity opening on the inner peripheral surface of the die bore in a third step to perform lateral extrusion, thereby causing the material constituting the hollow blank to plastically flow into the annular cavity. As a result, according to the first method, a flange portion can be integrally formed on the outer peripheral surface of the middle portion of the hollow blank while reducing the occurrence of folding.

[0049] <Variation 1-1> 2, 4, and 5 referred to in the above description, a stopper hole 161a, which is a hole for receiving the small outer diameter portion PSDO of the mandrel 131 in the stopper 161, is formed in the region of the stopper 161 that faces the small outer diameter portion PSDO of the mandrel 131 in the direction of the axis AX. However, the stopper provided at the tip end of the die hole is not limited to a stopper having a stopper hole formed therein, and the tip end of the die hole may be blocked by a stopper without a stopper hole formed therein.

[0050] 7 is a schematic cross-sectional view showing an example of the configuration of a die, mandrel, and sleeve used in the first method, in which the tip end of the die hole is blocked by a stopper without a stopper hole. The stopper 162 shown in FIG. 7 does not have a stopper hole, and the tip end of the die hole 151a is blocked by the stopper 162. Therefore, in this case, the tip end of the small outer diameter portion PSDO of the mandrel 132 cannot reach further forward than the position where it abuts against the stopper 162.

[0051] As a result of the above, a space in which the unprocessed portion PUF remains is defined at the tip of the hollow member 121 by the tip of the small outer diameter portion PSDO of the mandrel 132 abutting against the stopper 162, rather than by the small outer diameter portion PSDO of the mandrel 131 fitting into the stopper hole and blocking the tip side of the die hole 151a as described above. Therefore, from the viewpoint of preventing unintended deformation of the hollow blank 111 and improving processing accuracy in the process of forming the hollow member from the hollow blank by the first method, it is preferable to perform the third step after the tip of the small outer diameter portion PSDO of the mandrel 132 abuts against the stopper 162.

[0052] As described above, the third step is a step in which the proximal end of the hollow material 111 is pressed toward the distal end by the pressing portion PP of the sleeve 141. However, at the start of the third step, the distal end of the small outer diameter portion PSDO of the mandrel 132 is already abutting against the stopper 162, so the mandrel 132 cannot be driven further toward the distal end. Therefore, in the third step, the mandrel 132 is not moved, and only the sleeve 141 is driven toward the distal end. In this case, as described above, the mandrel 132 and the sleeve 141 may be configured to be independently driven by separate drive mechanisms (e.g., actuators, etc.). Alternatively, the mandrel 132 and the sleeve 141 may be driven by a common drive mechanism, but the positional relationship between the mandrel 132 and the sleeve 141 may be configured to be changeable, for example, by interposing a spring between the mandrel 132 and the drive mechanism. The latter configuration will be described below.

[0053] 8 is a schematic cross-sectional view showing an example of the change in shape of the hollow blank and the change in the positional relationship between the mandrel, sleeve, and die and the hollow blank and hollow member as processing progresses from the first step to the third step in the first method using the die 151, whose distal end of the die hole 151a is blocked by the stopper 162 shown in FIG. 7, as well as the change in the positional relationship between the mandrel, sleeve, and die and the hollow blank and hollow member. In the example shown in FIG. 8, as described above, the mandrel 132 and sleeve 141 are driven by a common drive mechanism, but a spring is interposed between the mandrel 132 and the drive mechanism. As a result, even if the mandrel 132 and sleeve 141 are driven toward the distal end by the drive mechanism after the mandrel 132 abuts against the stopper 162, the contraction of the spring 171s allows only the sleeve 141 to move toward the distal end while the mandrel 132 is held in a position abutting against the stopper 162.

[0054] In the first process executed in step S10, as illustrated in Fig. 8(a), a hollow blank 111 is inserted into the small inner diameter portion PSDI of the die hole 151a, and the leading end of the hollow blank 111 is brought into contact with a stopper 162 provided at the leading end of the die hole 151a to fix the hollow blank 111 at a predetermined position inside the die hole 151a. In addition, in the first process, the small outer diameter portion PSDO of the mandrel 132 is inserted into the internal space of the hollow blank 111 from the base end side of the hollow blank 111. The process up to this point is basically the same as the example shown in Fig. 4(a).

[0055] Next, in the second process executed in step S20, as illustrated in FIG. 8(b), the mandrel 132 and sleeve 141 are driven toward the distal end by the upper base 171 of the drive mechanism (not shown), so that the mandrel 132 is further inserted into the internal space of the hollow material 111 and the large outer diameter portion PLDO of the mandrel 132 is pressed into the internal space of the hollow material 111 (see the black arrow). This causes the inner diameter of the proximal end portion, which includes the proximal end of the hollow material 111, to expand from a first inner diameter DI1 to a second inner diameter DI2. At the same time, in the second process, the outer diameter of the proximal end portion of the hollow material 111 is expanded from a first outer diameter DO1 to a second outer diameter DO2. The process up to this point is also basically the same as the example shown in FIG. 4(b).

[0056] Next, in step S30, the third process is performed. However, at the start of the third process, the tip of the small outer diameter portion PSDO of the mandrel 132 is already abutting against the stopper 162, so the mandrel 132 cannot be driven further toward the tip. However, in the example shown in FIG. 8 , as described above, the mandrel 132 and the sleeve 141 are driven by a common drive mechanism, but a spring 171s is interposed between the mandrel 132 and the upper base 171 of the drive mechanism (not shown). As a result, even if the mandrel 132 and the sleeve 141 are driven toward the tip by the upper base 171 of the drive mechanism after the mandrel 132 abuts against the stopper 162, the contraction of the spring 171s allows only the sleeve 141 to move toward the tip while the mandrel 132 is held in a position where it abuts against the stopper 162.

[0057] 8(c), the base end of the hollow blank 111 can be pressed toward the tip end by the pressing portion PP of the sleeve 141 (see the outline arrow) while the mandrel 132 is held in a position where it abuts against the stopper 162. This allows lateral extrusion to be performed, causing part of the material constituting the hollow blank 111 to plastically flow toward the cavity 151c, which is the space between the inner peripheral surface of the flange forming portion PFF of the die hole 151a and the outer peripheral surface of the hollow blank 111.

[0058] As described above, even when the tip end of the die hole 151a is blocked by a stopper 162 that does not have a stopper hole formed therein, by performing the third step, a portion of the material (wall) that constitutes the hollow blank 111 can be caused to flow into the cavity 151c, thereby forming a hollow member 121 in which a flange portion PF is formed between the enlarged diameter portion PEDOI and the enlarged inner diameter portion PEDI, as illustrated in (b) of Figure 1.

[0059] Second Embodiment A method for forming a hollow member having a flange portion according to a second embodiment of the present invention (hereinafter, sometimes referred to as the "second method") will be described below with reference to the drawings.

[0060] 1, 4, 5, and 8 referred to in the description of the first method above are cylindrical members with both ends open. However, as mentioned above, the hollow member is not particularly limited as long as it is a cylindrical member with a first outer diameter, a first inner diameter, and a first thickness. For example, the hollow member may be a cylindrical member with a bottom and a solid portion at the tip (including the end portion on the tip side) that is a solid columnar portion.

[0061] Therefore, the second method is the above-mentioned first method, in which the hollow material is a bottomed cylindrical member having a solid portion, which is a solid cylindrical part, at the tip, and the hollow member is a method for forming a hollow member having a flange portion that includes a solid portion at the tip of the unprocessed part.

[0062] 9A and 9B are schematic side views showing an example of the configuration of a hollow material used in the second method and a hollow member having a flange portion formed from the hollow material. As shown in (a) of Fig. 9, the hollow material 112 used in the second method is a bottomed cylindrical member having a configuration similar to the hollow material 111 shown in Fig. 1 in the description of the first method, except that it has a solid portion PS, which is a solid columnar portion, at its tip portion (the portion including the end portion on the tip side). According to the second method using such a hollow material 112, it is possible to form a hollow member 122 including a solid portion PS at the tip portion of an unprocessed portion PUF, as shown in (b) of Fig. 9.

[0063] Fig. 10 is a schematic cross-sectional view showing an example of the change in the shape of the hollow blank as processing progresses from step 1 to step 3 in the second method, and the change in the positional relationship between the mandrel, sleeve, and die and the hollow blank and hollow member. Fig. 10 is similar to Fig. 8 except that hollow member 122 is formed from hollow blank 112 shown in Fig. 9, and that a mandrel 133 is used that includes small outer diameter portion PSDO whose dimension (length) in the direction of axis AX is shorter than small outer diameter portion PSDO of mandrel 132 shown in Fig. 8, corresponding to the hollow blank 112 including solid portion PS at its tip.

[0064] The second method illustrated in Fig. 10 also uses a die 151 and a sleeve 141 in which the tip end of the die hole 151a is blocked by the stopper 162 illustrated in Fig. 7, as in the first method illustrated in Fig. 8. Furthermore, although the mandrel 132 and the sleeve 141 are driven by a common drive mechanism (not shown), a spring is interposed between the mandrel 132 and the drive mechanism. As a result, even if the mandrel 133 and the sleeve 141 are driven toward the tip end by the drive mechanism after the tip end of the small outer diameter portion PSDO of the mandrel 133 abuts against the bottom surface inside the hollow material 112, the contraction of the spring 171s allows only the sleeve 141 to move toward the tip end while the mandrel 133 remains in a position abutting against the bottom surface inside the hollow material 112.

[0065] In the first process executed in step S10, as illustrated in Fig. 10(a), a hollow blank 112 is inserted into the small inner diameter portion PSDI of the die hole 151a, and the leading end of the hollow blank 112 is brought into contact with a stopper 162 provided at the leading end of the die hole 151a to fix the hollow blank 112 at a predetermined position inside the die hole 151a. In addition, in the first process, the small outer diameter portion PSDO of the mandrel 133 is inserted into the internal space of the hollow blank 112 from the base end side of the hollow blank 111. The process up to this point is basically the same as the examples shown in Figs. 4(a) and 8(a).

[0066] Next, in the second process executed in step S20, as illustrated in FIG. 10(b), the mandrel 133 and sleeve 141 are driven toward the distal end by the upper base 171 of the drive mechanism (not shown), so that the mandrel 133 is further inserted into the internal space of the hollow material 111 and the large outer diameter portion PLDO of the mandrel 133 is pressed into the internal space of the hollow material 112 (see the black arrow). This causes the inner diameter of the proximal end of the hollow material 112 to expand from the first inner diameter DI1 to the second inner diameter DI2. At the same time, in the second process, the outer diameter of the proximal end of the hollow material 112 is expanded from the first outer diameter DO1 to the second outer diameter DO2. The process up to this point is also basically the same as the examples shown in FIG. 4(b) and FIG. 8(b).

[0067] Next, in step S30, the third process is performed. However, at the start of the third process, the tip of the small outer diameter portion PSDO of the mandrel 133 is already in contact with the bottom surface inside the hollow material 112, so the mandrel 133 cannot be driven further toward the tip. However, in the example shown in FIG. 10 , as described above, although the mandrel 133 and the sleeve 141 are driven by a common drive mechanism, a spring 171s is interposed between the mandrel 133 and the upper base 171 of the drive mechanism (not shown). As a result, even if the mandrel 133 and the sleeve 141 are driven toward the tip by the upper base 171 of the drive mechanism after the mandrel 133 has come into contact with the bottom surface inside the hollow material 112, the contraction of the spring 171s allows only the sleeve 141 to move toward the tip while the mandrel 133 remains in contact with the bottom surface inside the hollow material 112.

[0068] 10(c), the mandrel 133 is held in a position where it abuts against the bottom surface inside the hollow blank 112, and the base end of the hollow blank 112 can be pressed toward the tip end by the pressing portion PP of the sleeve 141 (see the outline arrow). This allows for lateral extrusion to be performed, causing part of the material constituting the hollow blank 112 to plastically flow toward the cavity 151c, which is the space between the inner peripheral surface of the flange forming portion PFF of the die hole 151a and the outer peripheral surface of the hollow blank 112.

[0069] As described above, the second method uses a hollow material having a solid portion, which is a solid cylindrical portion, at the tip end. As a result, according to the second method, it is possible to form a bottomed hollow member 122 having a solid portion at the tip end and a flange portion PF formed between the enlarged diameter portion PEDOI and the enlarged inner diameter portion PEDI, as illustrated in Figure 9(b).

[0070] Third Embodiment A method for forming a hollow member having a flange portion according to a third embodiment of the present invention (hereinafter, sometimes referred to as the "third method") will be described below with reference to the drawings.

[0071] According to one finding obtained by the inventor, the occurrence of folding can be more reliably reduced by expanding the diameter of the base end of hollow material 111 or 112 in the second step so that the first thickness T1 of hollow material 111 or 112 and the second thickness T2 of the expanded diameter portion PEDOI of hollow member 121 or 122 are equal (T1 = T2). In other words, by expanding the diameter of the base end of the hollow material 111 or 112 in the second step so that the amount of expansion ΔDO (= DO2 - DO1) from the first outer diameter DO1, which is the outer diameter of the hollow material 111 or 112, to the second outer diameter DO2, which is the outer diameter of the expanded portion PEDOI of the hollow member 121 or 122, is equal to the amount of expansion ΔDI (= DI2 - DI1) from the first inner diameter DI1, which is the inner diameter of the hollow material 111 or 112, to the second inner diameter DI2, which is the inner diameter of the expanded portion PEDOI of the hollow member 121 or 122 (ΔDO = ΔDI), the occurrence of folding can be more reliably reduced.

[0072] Therefore, the third method is the first or second method described above, and is a method for forming a hollow member having a flange portion, in which the first thickness, which is the thickness of the hollow material, and the second thickness, which is the thickness of the expanded diameter portion of the hollow member, are equal.

[0073] According to the third method, as described above, the occurrence of folding can be more reliably reduced, and as a result, the risk of mechanical defects due to stress concentration can be more reliably reduced, particularly when the hollow member is used as a rotating part that requires high strength, such as a shaft.

[0074] Fourth Embodiment A method for forming a hollow member having a flange portion according to a fourth embodiment of the present invention (hereinafter, sometimes referred to as the "fourth method") will be described below with reference to the drawings.

[0075] According to another finding obtained by the inventor, when the expansion ratio RDO (= 100 × DO2 / DO1), defined as the percentage of the second outer diameter DO2, which is the outer diameter of the expansion portion PEDOI of the hollow member 121 or 122, to the first outer diameter DO1, which is the outer diameter of the hollow material 111 or 112, is 30% or less, a good balance can be achieved between reducing the occurrence of folding and forming the flange portion PF.

[0076] Therefore, the fourth method is a method for forming a hollow member having a flange portion, which is any of the first to third methods described above, in which the expansion ratio, defined as the percentage of the second outer diameter, which is the outer diameter of the expanded portion of the hollow member, to the first outer diameter, which is the outer diameter of the hollow material, is 30% or less.

[0077] As described above, the fourth method makes it possible to achieve a good balance between reducing the occurrence of creases and forming the flange portion PF. As a result, even when the hollow member is used as a rotating part that requires high strength, such as a shaft, it is possible to form a flange portion of a desired size and shape while more reliably reducing the risk of mechanical defects caused by stress concentration.

[0078] For the purpose of explaining the present invention, several embodiments having specific configurations have been described above with reference to the accompanying drawings. However, the scope of the present invention should not be construed as being limited to these exemplary embodiments, and it goes without saying that appropriate modifications can be made within the scope of the claims and the matters described in the specification. [Explanation of symbols]

[0079] 111,112...Hollow material DO1…1st outer diameter DI1...First inner diameter T1...First thickness PS: solid part 121, 122...Hollow members PEDOI...Expanded diameter part DO2…2nd outer diameter DI2...Second inner diameter T2…Second wall thickness PF: Flange part DO3…3rd outer diameter DI3...Third inner diameter T3…Third wall thickness PEDI...Inner diameter expansion section DO4...Second outer diameter DI4...Second inner diameter T4…4th wall thickness PUF…unprocessed part PTDI…Reduced inner diameter part 131, 132, 133...Mandrel PSDO…Small outer diameter part DO5…5th outer diameter PLDO…Large outer diameter part DO6…6th outer diameter PTDO: Increased outer diameter section 141...Sleeve PP...Pressing part DO7…7th outer diameter DI5...5th inner diameter T5…5th wall thickness 151...Dice 151a...Die hole PLDI…Large inner diameter part DI6...6th inner diameter PSDI…Small inner diameter part DI7...7th inner diameter PFF: Flange forming part DI8...8th inner diameter 151c...cavity 161,162...Stopper 161a...Stopper hole DI9...9th inner diameter 171...Upper base (drive mechanism) 171s...Spring

Claims

1. 1. A method for forming a hollow member having a flange portion, the method comprising: using an extrusion molding device including a mandrel which is a columnar core metal having a predetermined shape; a sleeve which is a cylindrical member disposed coaxially with the mandrel; a die having a die hole which is a hole having a predetermined shape; and a drive mechanism which drives the mandrel, the sleeve, and the die to move closer to each other in the axial direction; inserting the mandrel into a hollow material; and pressing the hollow material with the sleeve to force the hollow material into the die hole, thereby integrally forming a flange portion by lateral extrusion at a predetermined position between both ends in the axial direction of the hollow material, the hollow material is a cylindrical member having a first outer diameter that is a predetermined outer diameter, a first inner diameter that is a predetermined inner diameter, and a first wall thickness that is a predetermined wall thickness, The hollow member includes an expanded diameter portion which is a cylindrical portion formed at an end portion on the base end side which is upstream in a pressing direction, which is a direction in which the hollow material is pressed by the sleeve, and which has a second outer diameter larger than the first outer diameter, a second inner diameter larger than the first inner diameter, and a second thickness which is a predetermined thickness; and a flange-like portion which is formed adjacent to a tip side which is downstream in the pressing direction of the expanded diameter portion, and which has a third outer diameter larger than the second outer diameter, a third inner diameter equal to the second inner diameter, and a third thickness larger than the second thickness. the hollow blank includes a flange portion; an enlarged inner diameter portion which is a cylindrical portion formed adjacent to the front end side of the flange portion and which has a fourth outer diameter equal to the first outer diameter, a fourth inner diameter equal to the second inner diameter, and a fourth thickness smaller than the first thickness; an unmachined portion which is a portion which remains as the hollow blank at an end on the front end side; and a reduced inner diameter portion which is formed between the enlarged inner diameter portion and the unmachined portion and whose inner diameter decreases from the fourth inner diameter to the first inner diameter as it approaches the unmachined portion from the enlarged inner diameter portion side, the mandrel includes: a small outer diameter portion that is a cylindrical portion formed at the end portion on the tip side and having a fifth outer diameter that is an outer diameter corresponding to the first inner diameter; a large outer diameter portion that is a cylindrical portion formed at the base end side and having a sixth outer diameter that is an outer diameter corresponding to the second inner diameter; and an increasing outer diameter portion that is formed between the small outer diameter portion and the large outer diameter portion and has an outer diameter that increases from the fifth outer diameter to the sixth outer diameter as it approaches the large outer diameter portion from the small outer diameter portion side, the sleeve includes a pressing portion that is a cylindrical portion formed at an end portion on the tip side and that has a seventh outer diameter equal to the second outer diameter, a fifth inner diameter equal to the second inner diameter, and a fifth wall thickness equal to the second wall thickness, the die hole includes: a large inner diameter portion formed on the base end side and having a sixth inner diameter corresponding to the second outer diameter; a small inner diameter portion formed on the tip end side and having a seventh inner diameter corresponding to the first outer diameter; and a flange-forming portion formed between the large inner diameter portion and the small inner diameter portion and having an eighth outer diameter larger than the sixth inner diameter; a first step of inserting the hollow blank into the small inner diameter portion of the die hole, abutting the tip end of the hollow blank against a stopper provided at the tip end of the die hole to fix the hollow blank at a predetermined position inside the die hole, and inserting the small outer diameter portion of the mandrel into the internal space of the hollow blank from the base end side of the hollow blank; a second step of further inserting the mandrel into the internal space of the hollow material and forcing the large outer diameter portion of the mandrel into the internal space of the hollow material, thereby expanding the inner diameter of a base end portion, which is a portion of the hollow material that includes an end portion on the base end side, from the first inner diameter to the second inner diameter and expanding the outer diameter of the base end portion of the hollow material from the first outer diameter to the second outer diameter; a third step of performing lateral extrusion by pressing the base end side end of the hollow blank toward the tip side with the pressing portion of the sleeve, thereby plastically flowing a part of the material constituting the hollow blank toward a cavity, which is a space between an inner peripheral surface of the flange-forming portion of the die hole and an outer peripheral surface of the hollow blank; Including, A method for forming a hollow member having a flange portion.

2. A method for forming a hollow member having a flange portion according to claim 1, comprising the steps of: the hollow material is a cylindrical member with a bottom having a solid portion at the tip end, the solid portion being a solid columnar portion, The hollow member includes the solid portion at the tip of the unprocessed portion. A method for forming a hollow member having a flange portion.

3. 3. A method for forming a hollow member having a flange portion according to claim 1 or 2, comprising: The first thickness and the second thickness are equal. A method for forming a hollow member having a flange portion.

4. 3. A method for forming a hollow member having a flange portion according to claim 1 or 2, comprising: an expansion ratio defined as a percentage of the second outer diameter to the first outer diameter of 30% or less; A method for forming a hollow member having a flange portion.

5. A method for forming a hollow member having a flange portion according to claim 3, comprising the steps of: an expansion ratio defined as a percentage of the second outer diameter to the first outer diameter of 30% or less; A method for forming a hollow member having a flange portion.

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