Method for manufacturing a hollow shaft member and hollow member

Abstract

The objective is to provide a method for manufacturing a hollow shaft member that is resistant to distortion of the shaft portion, and to provide a hollow shaft member. [Solution] In the method for manufacturing a hollow shaft member, a tapered portion 211d is formed on the shaft portion 2c of a hollow workpiece 1c having a shaft portion 2c, a flange portion 3c, and a hollow portion 4c, using a mouth-drawing mold 5. The mouth-drawing mold 5 has a first mold 50 and a second mold 51. The first mold 50 has a first housing hole 501 and a first support portion 502. The second mold 51 has a mouth-drawing portion 511. The shaft portion 2c has a housing portion 20c and a protruding portion 21c. In the mouth-drawing step of the method for manufacturing a hollow shaft member, the housing portion 20c is housed in the first housing hole 501, and with the flange portion 3c supported by the first support portion 502 from the front, the protruding portion 21c is pressed from the rear with the mouth-drawing portion 511, and a mouth-drawing process is performed on the opening 40c of the hollow portion 4c, forming a tapered portion 211d on the protruding portion 21c.

Description

Technical Field

[0005] ,

[0001] The present disclosure relates to a method for manufacturing a hollow shaft member with a flange and a hollow member.

Background Art

[0002] Patent Document 1 discloses a method for manufacturing a gear member by cold forging. In the case of this manufacturing method, first, a hollow portion is recessed in a workpiece by backward extrusion. The workpiece after the backward extrusion has a bottomed cylindrical shape that opens to the rear side. Specifically, the workpiece includes a bottom wall portion and a cylindrical shaft portion extending rearward from the bottom wall portion. The hollow portion is partitioned inside the shaft portion in the radial direction. Next, the opening of the hollow portion of the workpiece after the backward extrusion is constricted by necking. By the necking, the rear end (the end on the opening side) of the shaft portion is reduced in diameter and deformed. That is, a tapered portion is formed on the shaft portion. In contrast, the front end (the end on the bottom wall portion side) of the shaft portion is increased in diameter and deformed. Thus, in the case of the manufacturing method of this document, the shaft portion of the workpiece is deformed by necking to constrict the opening of the hollow portion.

[0003] Patent Document 2 discloses a method for manufacturing a piston for a disc brake by cold forging. In the third step of this manufacturing method, cold forging is performed to apply necking to the end portion on the opening side of a cup-shaped component at a predetermined inclination angle.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the manufacturing method of Patent Document 1, the forming load tends to concentrate on the thin-walled, cylindrical shaft portion during the neck drawing process. As a result, the shaft portion is prone to radial distortion. Consequently, the rotational balance of the shaft portion tends to decrease. Furthermore, in order to suppress the distortion of the shaft portion, the drawing angle (the angle of inclination of the neck drawing portion with respect to the radial direction of the shaft portion) must be increased. Consequently, the length of the workpiece in the front-to-back direction (shaft length) becomes longer. The same applies to the manufacturing method of Patent Document 2. Therefore, the present disclosure aims to provide a method for manufacturing a hollow shaft member in which the shaft portion is less prone to radial distortion and the shaft length can be shortened. The present disclosure also aims to provide a hollow member with high strength and rigidity and a small number of parts. [Means for solving the problem]

[0006] (1) To solve the above problems, the present disclosure provides a method for manufacturing a hollow shaft member, comprising a shaft portion, a flange portion projecting radially outward from the shaft portion, and hollow portions opening at one or both axial ends of the shaft portion, wherein a tapered portion is formed on the shaft portion of the hollow workpiece using a mouth-drawing mold, with the axial end being the rear side and the opposite side of the rear side being the front side, the mouth-drawing mold having a first mold and a second mold accessible from the rear side to the first mold, the first mold having a first housing hole and a first support positioned outside and at the rear of the first housing hole and supporting the flange portion from the front side The second mold has a cylindrical constricted portion whose inner diameter decreases from the front to the rear, and the shaft portion has a receiving portion which is located in front of the flange portion and is housed in the first receiving hole, and a protruding portion which is located behind the flange portion and protrudes to the rear from the first receiving hole, and the mold is characterized in that, with the receiving portion housed in the first receiving hole and the flange portion supported from the front by the first support portion, or supported after the start of molding, the protruding portion is pressed from the rear by the constricted portion to perform a constricting process on the opening of the hollow portion and form the tapered portion on the protruding portion.

[0007] In the mouth-drawing process, the flange portion of the hollow workpiece is supported by the first support portion of the first mold (e.g., fixed mold), or supported after the start of forming, and the opening of the hollow workpiece is drawn using the mouth-drawing portion of the second mold (e.g., movable mold). This allows the forming load to be distributed between the shaft portion and the flange portion. Therefore, distortion of the shaft portion can be suppressed compared to the case where the first mold does not support the flange portion. Furthermore, if the hollow shaft member is a rotating member (e.g., a rotor shaft or an intermediate product thereof), a decrease in rotational balance can be suppressed.

[0008] Furthermore, because the molding load can be distributed, distortion of the shaft can be suppressed even if the constriction angle (the angle of inclination of the constricted opening relative to the radial direction of the shaft) is reduced, compared to a case where the first mold does not support the flange portion. As a result, the axial length of the hollow shaft member can be shortened. In addition, the weight of the hollow shaft member can be reduced.

[0009] (1-1) In the configuration of (1) above, it is preferable that the hollow workpiece be a single unit and that the shaft portion and the flange portion are integrally connected. With this configuration, there is no need to add the flange portion to the shaft portion of the hollow workpiece afterwards. Therefore, the manufacturing man-hours can be reduced. In addition, the process can be simplified.

[0010] (1-2) In any of the above configurations, it is preferable that the mouth-drawing process be performed by cold forging. With this configuration, a mouth-drawing process can be applied to the opening of the hollow portion and a tapered portion can be formed on the protruding portion without intentionally heating the hollow workpiece.

[0011] (2) In any of the above configurations, it is preferable to have a configuration in which the angle of inclination of the tapered portion with respect to the radial direction is 30° or more. With this configuration, it is possible to suppress the outward bulging of the protruding portion in the radial direction during molding, compared to the case in which the tapered angle is less than 30°. As a result, it is possible to suppress the occurrence of a missing material on the inner circumferential surface of the tapered portion. In addition, it is possible to suppress the occurrence of an excess material on the outer circumferential surface of the tapered portion.

[0012] Furthermore, if a predetermined subsequent process (for example, the crushing process described later) is performed after this process (of course, the subsequent process does not have to be performed), it is possible to prevent the excess material generated by the molding die for the mouth-filling process in this process from being caught in the molding die for that process (for example, the crushing molding die described later) in the subsequent process.

[0013] (2-1) In the configuration of (2) above, it is preferable to have a tapered angle of 35° or more. With this configuration, compared to the case where the tapered angle is less than 35°, it is possible to further suppress the occurrence of a missing material on the inner surface of the tapered portion. Furthermore, it is possible to further suppress the occurrence of an excess material on the outer surface of the tapered portion.

[0014] (3) In any of the above configurations, it is preferable to use a crushing mold comprising: a third mold having a third housing hole and a third support portion positioned outside and rear of the third housing hole and supporting the flange portion from the front; and a fourth mold having a cylindrical pressing portion and a punch positioned radially inward of the pressing portion, and being accessible from the rear to the third mold, and to perform a crushing process after the neck-drawing process, in which the housing portion is housed in the third housing hole and the flange portion is supported from the front by the third support portion, or is supported after the start of molding, the punch is inserted from the rear into the opening after the neck-drawing process, and the tapered portion is pressed from the rear with the pressing portion to crush the tapered portion and form a crushed portion on the tapered portion.

[0015] In the crushing process, with the flange portion of the hollow workpiece supported by the third support portion of the third mold, or supported after the start of forming, the punch of the fourth mold is inserted into the opening after the neck drawing of the hollow workpiece, and the tapered portion is crushed using the pressing portion of the fourth mold.

[0016] Therefore, the molding load can be distributed between the shaft and the flange. Consequently, distortion of the shaft can be suppressed compared to a case where the third mold does not support the flange. Furthermore, if the hollow shaft member is a rotating member, a decrease in rotational balance can be suppressed.

[0017] Furthermore, because the molding load can be distributed, the crushing angle (the angle of inclination of the pressing portion relative to the radial direction) can be reduced (including the case where the crushing angle is 0° (i.e., a planar shape that expands radially)). As a result, the axial length of the hollow shaft member can be further shortened. In addition, the weight of the hollow shaft member can be reduced.

[0018] Furthermore, in the aforementioned processes of mouth drawing, radial forging, and metal spinning, the hollow workpiece is formed from the radially outer side. As a result, the area between the unprocessed portion and the drawn portion becomes tapered, making it difficult to adjust the wall thickness of the tapered portion. Therefore, when a bearing press-fit portion is created in the drawn portion during post-processing (of course, this configuration does not limit the presence or absence of a bearing press-fit portion), a bearing contact surface (a surface that extends in a direction perpendicular to the extending direction of the bearing press-fit portion (for example, the radial direction)) must be created in the tapered portion, requiring the removal of a large amount of excess material (hereinafter referred to as "scrap" as appropriate). In addition, the wall thickness on the inside of the contact surface becomes thinner, and depending on the degree of thinning, this may result in insufficient strength, so it is necessary to design the product with this in mind to avoid problems.

[0019] In this configuration, when the tapered portion is pressed by the pressing portion from the rear, the tapered portion is supported by the punch from the radially inward side. Therefore, it is possible to suppress the flow of the tapered portion's material radially inward. Consequently, the material of the tapered portion can be preferentially allowed to flow forward. Thus, the thickness of the crushed portion can be increased.

[0020] (3-1) In the configuration of (3) above, it is preferable to have a configuration in which the angle of inclination of the narrowed mouth portion with respect to the radial direction is the narrowing angle, and the angle of inclination of the pressing portion with respect to the radial direction is the crushing angle, and the crushing angle is less than the narrowing angle. With this configuration, the tapered portion can be crushed (the material flows to the front side) more reliably than when the crushing angle is greater than or equal to the narrowing angle.

[0021] (3-2) In the configuration of (3) or (3-1) above, it is preferable that the crushing process be carried out by cold forging. With this configuration, the tapered portion can be crushed and a crushed portion formed in the tapered portion without intentionally heating the hollow workpiece.

[0022] (4) In any of the configurations described in (3) to (3-2) above, it is preferable to have a configuration in which the angle of inclination of the constricted mouth portion with respect to the radial direction is the constriction angle, and the angle of inclination of the pressing portion with respect to the radial direction is the crushing angle, the constriction angle is greater than the crushing angle, and the angle difference between the constriction angle and the crushing angle is within the range of greater than 0° and less than or equal to 25°.

[0023] In the mouth-drawing process, the tapered section is formed by plastically deforming (distorting) the material of the protruding part of the shaft. As a result, the hardness of the tapered section is high. In contrast, the housing part of the shaft is not easily plastically deformed. Therefore, the housing part has lower hardness than the tapered section.

[0024] In the pressing process, the thickness of the already high-hardness tapered portion is further plastically deformed to form the pressed portion. Therefore, the vicinity of the front end (near the root) of the inner peripheral surface of the tapered portion is likely to fold radially outward (into the thickness of the hollow workpiece). Also, due to the forming load, the vicinity of the rear end of the low-hardness housed portion is likely to bulge radially inward.

[0025] Here, the inner peripheral surface of the shaft portion of the hollow shaft member after the pressing process has a constant-diameter section that includes the inner peripheral surface of the housed portion and extends in the front-rear direction, and a diameter-reducing section that includes the inner peripheral surface of the pressed portion and reduces in diameter from the front side to the rear side.

[0026] As described above, when the vicinity of the front end of the inner peripheral surface of the tapered portion folds radially outward and the vicinity of the rear end of the housed portion bulges radially inward, a groove (forming defect) is likely to be formed near the boundary between the constant-diameter section and the diameter-reducing section of the hollow shaft member after the pressing process. In addition, after the forming load is removed, due to springback, the groove opens, and cracks are likely to propagate from the groove bottom.

[0027] In this regard, according to this configuration, the angle difference (= drawing angle - pressing angle) is set to be included in the range of more than 0° and 25° or less. Therefore, the tapered portion can be reliably pressed as compared with the case where the angle difference is 0° or negative. Also, the formation of the above-described groove can be suppressed as compared with the case where the angle difference exceeds 25°.

[0028] (5) In any of the configurations of (3) to (4) above, it is preferable that the third accommodation hole has a hole bottom surface at the front end, and in a state before the pressing process is performed on the tapered portion, when the housed portion is accommodated in the third accommodation hole and the flange portion is supported by the third support portion from the front side, the housed portion is not in contact with the hole bottom surface.

[0029] In this configuration, the hollow workpiece is suspended behind the bottom surface of the third housing hole. Therefore, during the crushing process, the material of the housing can flow forward using the space between the hollow workpiece and the bottom surface of the hole. This material flow allows the forming load to be relieved. Consequently, stress concentration near the front end of the inner circumferential surface of the tapered portion can be mitigated. As a result, the formation of the aforementioned groove can be suppressed.

[0030] (6) In the configuration of (5) above, it is preferable that the axial width of the gap between the front end of the receiving portion and the bottom surface of the hole be 2 mm or more. With this configuration, the flow space of the material in the receiving portion during crushing can be increased compared to the case where the axial width of the gap is less than 2 mm. As a result, the forming load can be relieved more reliably compared to the case where the axial width is less than 2 mm. As a result, the formation of the grooves mentioned above can be suppressed more reliably.

[0031] (7) In order to solve the above problems, the hollow member of the present disclosure is an integral hollow member comprising a shaft portion, a flange portion projecting radially outward from the shaft portion, and hollow portions opening at one or both axial ends of the shaft portion, wherein the axial end is the rear side and the opposite side of the rear side is the front side, the shaft portion has a housing portion located in front of the flange portion and a protruding portion located behind the flange portion, the protruding portion has a crushed portion that decreases in diameter from the front to the rear side, the inner circumferential surface of the shaft portion has a section of the same diameter extending in the front-rear direction including the inner circumferential surface of the housing portion and a section of reduced diameter that decreases in diameter from the front to the rear including the inner circumferential surface of the crushed portion, and the boundary between the section of the same diameter and the section of reduced diameter is preferably located in front of the front end of the flange portion.

[0032] In this configuration, the boundary between the same-diameter section and the reduced-diameter section is located further forward than the front end of the flange section. As a result, the thickness of the crushed section is increased. Therefore, the strength and rigidity of the hollow member can be improved. As an example, the hollow member of this configuration can be manufactured by the manufacturing method of the configurations described in (5)-(6) above.

[0033] (8) In order to solve the above problems, the hollow member of the present disclosure is an integral hollow member comprising a shaft portion, a flange portion projecting radially outward from the shaft portion, and hollow portions opening at one or both axial ends of the shaft portion, wherein the axial end is the rear side and the opposite side of the rear side is the front side, the shaft portion has a housing portion located in front of the flange portion and a protruding portion located behind the flange portion, the protruding portion has a crushed portion that decreases in diameter from the front to the rear side, the inner circumferential surface of the shaft portion has a same-diameter section extending in the front-rear direction including the inner circumferential surface of the housing portion and a reduced-diameter section that decreases in diameter from the front to the rear side including the inner circumferential surface of the crushed portion, the inclination angle of the crushed portion with respect to the radial direction is greater than 5°, and the same-diameter section and the reduced-diameter section are connected in a smooth manner.

[0034] In this configuration, the inclination angle of the crushed portion with respect to the radial direction is set to more than 5°. Furthermore, the same-diameter section and the reduced-diameter section are connected in a smooth manner. In other words, no molding defects such as grooves or cracks are formed near the boundary between the same-diameter section and the reduced-diameter section. Therefore, the strength and rigidity of the hollow member can be improved. As an example, the hollow member of this configuration can be manufactured by the manufacturing method of the configurations (2) and (4) above. That is, by setting the throttling angle to 30° or more in the configuration of (2) above, and setting the angle difference (= throttling angle - crushing angle) in the configuration of (4) above to be within the range of more than 0° and less than or equal to 25° above, the inclination angle of the crushed portion with respect to the radial direction can be set to more than 5°. A combination of this configuration and the configuration of (7) above may also be used.

[0035] (9) In order to solve the above problems, the hollow member of the present disclosure comprises a protruding end having an opening that opens to one end in the axial direction, a shaft portion having a hollow portion continuous with the protruding end, and a flange portion projecting radially outward from the shaft portion, wherein the shaft portion and the flange portion are a single, integral hollow member made of the same material, the shaft portion has a tapered portion continuous with the protruding end and the hollow portion, the tapered portion corresponds to the position where the flange portion is provided in the axial direction, and the inner diameter gradually decreases from the hollow portion toward the protruding end.

[0036] The shaft and flange are a single, integrated hollow member made from the same material. The shaft and flange are seamlessly connected. Therefore, compared to a hollow member that is a composite (a composite of a shaft and flange that are independent of each other), the strength (e.g., tensile strength, compressive strength, shear strength) and rigidity (e.g., torsional rigidity, bending rigidity) of the hollow member can be improved. In addition, the number of parts can be reduced compared to a hollow member that is a composite.

[0037] (10) In the configuration of (9) above, it is preferable to have a configuration in which the axial end is the rear side and the opposite side of the rear side is the front side, and the rear end of the tapered portion is located further rear than the front end of the flange portion.

[0038] This configuration includes "a configuration in which only the rear end of the tapered portion is located further back than the front end of the flange portion" and "a configuration in which both the rear and front ends of the tapered portion (i.e., the entire tapered portion) are located further back than the front end of the flange portion."

[0039] (11) In the configuration of (9) above, it is preferable that at least a portion of the tapered portion has a thicker wall than the protruding end and the flange portion. This configuration makes it possible to improve the strength and rigidity of the tapered portion. [Effects of the Invention]

[0040] The manufacturing method for hollow shaft members according to the present disclosure makes it possible to suppress radial distortion of the shaft portion. Furthermore, the manufacturing method for hollow shaft members according to the present disclosure makes it possible to shorten the axial length of the hollow shaft member. In addition, the hollow member according to the present disclosure makes it possible to improve strength and rigidity and reduce the number of parts. [Brief explanation of the drawing]

[0041] [Figure 1] Figures 1(A) to 1(F) are vertical cross-sectional views of the workpiece in the first to sixth steps of the first embodiment of the rotor shaft manufacturing method (an example of a manufacturing method for a hollow shaft member of the present disclosure). [Figure 2] Figure 2 is a cross-sectional view of the molding die used for mouth shaping during the initial stage of the mouth shaping process in the manufacturing method of a hollow shaft member. [Figure 3] Figure 3 is a vertical cross-sectional view of the molding die for neck filling at the end of the process. [Figure 4] Figure 4 is a vertical cross-sectional view of the crushing mold used in the initial crushing step of the manufacturing method for hollow shaft members. [Figure 5] Figure 5 is a vertical cross-sectional view of the crushing mold at the end of the process. [Figure 6] Figure 6 is a cross-sectional view in the vertical direction of the molding die for the mouth-drawing process at the initial stage of the mouth-drawing process in the manufacturing method of the hollow shaft member according to the second embodiment. [Figure 7] Figure 7 is a vertical cross-sectional view of the molding die for neck filling at the end of the process. [Figure 8] Figure 8 is a cross-sectional view of the crushing mold in the vertical direction during the initial crushing process of the manufacturing method for hollow shaft members. [Figure 9] Figure 9 is a cross-sectional view of the crushing mold in the vertical direction at the end of the process. [Figure 10] Figure 10 is a contour plot showing the analysis results (first stage) of Example 1. [Figure 11] Figure 11 is a contour plot showing the analysis results (second stage) of Example 1. [Figure 12]Figure 12 is a contour plot showing the analysis results (third stage) of Example 1. [Figure 13] Figure 13 is a contour plot showing the analysis results (fourth stage) of Example 1. [Figure 14] Figure 14 is a contour plot showing the analysis results (fifth stage) of Example 1. [Figure 15] Figure 15 is a contour plot showing the analysis results (first stage) of Example 2. [Figure 16] Figure 16 is a contour plot showing the analysis results (second stage) of Example 2. [Figure 17] Figure 17 is a contour plot showing the analysis results (third stage) of Example 2. [Figure 18] Figure 18 is a contour plot showing the analysis results (fourth stage) of Example 2. [Figure 19] Figure 19 is a contour plot showing the analysis results (fifth stage) of Example 2. [Figure 20] Figure 20 is a contour plot showing the analysis results (first stage) of Example 3. [Figure 21] Figure 21 is a contour plot showing the analysis results (second stage) of Example 3. [Figure 22] Figure 22 is a contour plot showing the analysis results (third stage) of Example 3. [Figure 23] Figure 23 is a contour plot showing the analysis results (fourth stage) of Example 3. [Figure 24] Figure 24 is a contour plot showing the analysis results (fifth stage) of Example 3. [Figure 25] Figure 25 is a contour plot showing the analysis results (first stage) of Example 4. [Figure 26] Figure 26 is a contour plot (partially enlarged view) showing the analysis results (first stage) of Example 4. [Figure 27] Figure 27 is a contour plot (partially enlarged view) showing the analysis results (second stage) of Example 4. [Figure 28] Figure 28 is a contour plot (partially enlarged view) showing the analysis results (third stage) of Example 4. [Figure 29] Figure 29 is a contour plot showing the analysis results (first stage) for Example 5. [Figure 30] Figure 30 is a contour plot (partially enlarged view) showing the analysis results (first stage) of Example 5. [Figure 31] Figure 31 is a contour plot (partially enlarged view) showing the analysis results (second stage) of Example 5. [Figure 32] Figure 32 is a contour plot (partially enlarged view) showing the analysis results (third stage) of Example 5. [Figure 33] Figure 33 is a contour plot showing the analysis results (first stage) of Example 6. [Figure 34] Figure 34 is a contour plot (partially enlarged view) showing the analysis results (first stage) of Example 6. [Figure 35] Figure 35 is a contour plot (partially enlarged view) showing the analysis results (second stage) of Example 6. [Figure 36] Figure 36 is a contour plot showing the analysis results (third stage) of Example 6. [Figure 37] Figure 37 is a contour plot (partially enlarged view) showing the analysis results (third stage) of Example 6. [Modes for carrying out the invention]

[0042] The following describes a method for manufacturing a hollow shaft member and embodiments of the hollow member according to the present disclosure.

[0043] <First Embodiment> [Positioning of the manufacturing method for the hollow shaft member of this embodiment relative to the manufacturing method for the rotor shaft] First, the position of the manufacturing method for the hollow shaft member of this embodiment in relation to the manufacturing method for the rotor shaft will be explained. Figures 1(A) to 1(F) show the vertical cross-sectional views (axial cross-sectional views) of the workpiece in the first to sixth stages of the manufacturing method for the rotor shaft of this embodiment.

[0044] Furthermore, among the parts of workpieces 1a to 1e and rotor shaft 1f, parts whose numerical part of the symbol (numerical part, letter part) is common correspond to each other. For example, workpiece 1a in Figure 1(A) and workpiece 1b in Figure 1(B) correspond to each other. The vertical direction corresponds to the "axial direction" of this disclosure, the lower side corresponds to the "front side" of this disclosure, and the upper side corresponds to the "rear side" of this disclosure.

[0045] The manufacturing method of the rotor shaft progresses from Figure 1(A) to Figure 1(F). Workpiece 1a shown in Figure 1(A) is a solid bulk material cut from a bar made of S35C (JIS G 4051). Workpiece 1b shown in Figure 1(B) is workpiece 1a that has been hot forged. Workpiece 1c shown in Figure 1(C) is workpiece 1b with the inner circumferential surface of the hollow portion 4b of workpiece 1b machined to remove scale and improve dimensional accuracy. Workpiece 1d shown in Figure 1(D) is workpiece 1c that has been drawn at the mouth. Workpiece 1e shown in Figure 1(E) is workpiece 1d that has been crushed.

[0046] Figure 1(F) shows the rotor shaft (rotating component) 1f. In other words, the rotor shaft 1f is the finished product, and the workpieces 1a to 1e are intermediate products (items in the middle of the manufacturing process).

[0047] The manufacturing method for the hollow shaft member in this embodiment involves the mouth-drawing process shown in Figure 1(D) and the crushing process shown in Figure 1(E). The mouth-drawing process shown in Figure 1(D) performs a mouth-drawing process on the workpiece 1c shown in Figure 1(C). The crushing process shown in Figure 1(E) performs a crushing process on the workpiece 1d shown in Figure 1(D).

[0048] Workpiece 1c (workpiece before the mouth-filling process) shown in Figure 1(C) is included in the concept of "hollow workpiece" in this disclosure. Workpiece 1e (workpiece after the crushing process) shown in Figure 1(E) is included in the concept of "hollow shaft member" (hollow shaft member with flange) in this disclosure.

[0049] [Work structure] Next, we will explain the configuration of workpiece 1c (workpiece before the neck-sealing process), workpiece 1d (workpiece after the neck-sealing process and before the crushing process), and workpiece 1e (workpiece after the crushing process).

[0050] The workpiece 1c (workpiece before the neck drawing process) is a single piece comprising a shaft portion 2c, a flange portion 3c, and a hollow portion 4c. The shaft portion 2c extends in the vertical direction. The shaft portion 2c comprises a receiving portion 20c and a protruding portion 21c. The receiving portion 20c extends in the vertical direction and has a bottomed cylindrical shape that opens upwards. The protruding portion 21c has a cylindrical shape that extends in the vertical direction. The protruding portion 21c is connected to the upper side of the receiving portion 20c. The flange portion 3c has an annular shape. The flange portion 3c protrudes radially outward from the outer circumferential surface of the shaft portion 2c. The shaft portion 2c and the flange portion 3c are integrally connected. The receiving portion 20c is located in front of the flange portion 3c. The protruding portion 21c is located behind the flange portion 3c. The opening 40c of the hollow portion 4c is formed on the upper end surface (one end surface in the axial direction) of the shaft portion 2c. The hollow portion 4c extends in the vertical direction.

[0051] Workpiece 1d (workpiece after the neck-drawing process and before the crushing process) and workpiece 1c (workpiece before the neck-drawing process) have the same shape in the portions below the flange portions 3d and 3c. The protruding portion 21d of workpiece 1d is formed by the neck-drawing process to have a tapered portion 211d and a tip portion 213d. The tapered portion 211d has a tapered shape (tapered cylindrical shape) in which the inner and outer diameters decrease from the bottom to the top. The tip portion 213d is connected to the upper side of the tapered portion 211d. The tip portion 213d has a short-axis cylindrical shape that extends in the vertical direction.

[0052] Workpiece 1e (workpiece after the crushing process) and workpiece 1d (workpiece after the neck drawing process but before the crushing process) have the same shape in the portion below the flanges 3e and 3d. A crushed portion 212e is formed on the protruding portion 21e of workpiece 1e by the crushing process. The upper surface of the crushed portion 212e is annular and has a planar shape that expands horizontally (radially).

[0053] [Rotor shaft configuration] Next, the configuration of the rotor shaft 1f will be briefly explained. The shaft portion 2f of the rotor shaft 1f shown in Figure 1(F) includes a rotor press-fit portion 20f and a bearing press-fit portion 21f. The rotor press-fit portion 20f corresponds to the housing portion 20e in Figure 1(E). The bearing press-fit portion 21f corresponds to the protruding portion 21e in Figure 1(E).

[0054] The rotor press-fit portion 20f is press-fitted radially into the annular rotor (not shown). The bearing press-fit portion 21f is press-fitted radially into the annular bearing (not shown). Coolant (oil, coolant, etc.) flows through the hollow portion 4f via the opening 40f.

[0055] [Configuration of the molding die for mouth-shaping] Next, the configuration of the molding die used in the mouth-shaping process of the manufacturing method for the hollow shaft member of this embodiment will be described. Figure 2 shows a vertical cross-sectional view of the molding die in the initial stage of the mouth-shaping process. Figure 3 shows a vertical cross-sectional view of the molding die in the final stage of the same process.

[0056] As shown in Figures 2 and 3, the molding die 5 for spouting comprises a lower die (fixed die) 50 and an upper die (movable die) 51. The lower die 50 is included in the concept of the "first die" of this disclosure. The upper die 51 is included in the concept of the "second die" of this disclosure.

[0057] The lower mold 50 is made of metal and comprises a die 500, a first housing hole 501, and a first support portion 502. The first housing hole 501 is provided in the die 500. The first housing hole 501 extends in the vertical direction. The housing portion 20c of the workpiece 1c is housed in the first housing hole 501. The outer circumferential surface of the housing portion 20c is in full contact with the inner circumferential surface of the first housing hole 501.

[0058] The first support portion 502 is positioned at the opening edge of the first housing hole 501 (outside and above the hole of the first housing hole 501). The first support portion 502 is annular and planar in shape. The first support portion 502 supports the flange portion 3c from below.

[0059] The upper mold 51 is positioned above the lower mold 50. The upper mold 51 is movable in the vertical direction. The upper mold 51 can approach and separate from the lower mold 50 from above. The upper mold 51 is made of metal and comprises a cylindrical holder 510 and a constricted mouth section 511. The constricted mouth section 511 is positioned radially inward of the holder 510. The constricted mouth section 511 has a cylindrical shape that extends in the vertical direction. On the inner circumferential surface of the lower end opening edge of the constricted mouth section 511, there is a tapered annular constricted mouth surface 511a that decreases in diameter from the bottom to the top. The constriction angle (angle of inclination of the constricted mouth surface 511a with respect to the horizontal direction (radial direction)) θ1 is set to 35° or more. On the lower end surface of the constricted mouth section 511, there is an annular flat pressing surface (pressing surface) 511b. The flat pressing surface 511b is connected to the lower end of the constricted mouth surface 511a. The flat pressing surface 511b is annular and has a planar shape that extends horizontally.

[0060] [Configuration of the molding die for crushing] Next, the configuration of the crushing mold used in the crushing process of the manufacturing method for the hollow shaft member of this embodiment will be described. Figure 4 shows a vertical cross-sectional view of the crushing mold at the initial stage of the crushing process. Figure 5 shows a vertical cross-sectional view of the crushing mold at the final stage of the same process.

[0061] As shown in Figures 4 and 5, the crushing mold 6 comprises a lower mold (fixed mold) 60 and an upper mold (movable mold) 61. The lower mold 60 is included in the concept of the "third mold" of this disclosure. The upper mold 61 is included in the concept of the "fourth mold" of this disclosure.

[0062] The lower die 60 is made of metal and comprises a die 600, a third housing hole 601, and a third support portion 602. The third housing hole 601 is provided in the die 600. The third housing hole 601 extends in the vertical direction. The housing portion 20d of the workpiece 1d is housed in the third housing hole 601. The outer circumferential surface of the housing portion 20d is in full contact with the inner circumferential surface of the third housing hole 601.

[0063] The third support portion 602 is positioned on the opening edge of the third housing hole 601 (outside and above the hole of the third housing hole 601). The third support portion 602 is annular and planar in shape. The third support portion 602 supports the flange portion 3d from below. The lower surface of the flange portion 3d is in full contact with the third support portion 602.

[0064] The upper die 61 is positioned above the lower die 60. The upper die 61 is movable in the vertical direction. The upper die 61 can move towards and away from the lower die 60 from above. The upper die 61 is made of metal and comprises a cylindrical holder 610, a pressing portion 611, and a punch 612. The pressing portion 611 is positioned radially inward of the holder 610. The pressing portion 611 has a cylindrical shape that extends in the vertical direction. On the inner circumferential surface of the lower end opening edge of the pressing portion 611, there is a tapered annular narrowing surface 611a that narrows in diameter from the bottom to the top. Here, the narrowing angle (angle of inclination of the narrowing surface 611a with respect to the horizontal direction) θ2 of the narrowing surface 611a is greater than the narrowing angle θ1 of the narrowing surface 511a shown in Figure 2. On the lower end surface of the pressing portion 611, there is an annular flat pressing surface (crushing surface) 611b. The flat pressing surface 611b is connected to the lower end of the cinched mouth surface 611a. The flat pressing surface 611b is annular and has a planar shape that extends horizontally. The crushing angle of the flat pressing surface 611b (the inclination angle of the flat pressing surface 611b with respect to the horizontal direction) is 0°.

[0065] [Method for manufacturing the hollow shaft member of this embodiment] Next, the method for manufacturing the hollow shaft member of this embodiment will be described. The method for manufacturing the hollow shaft member of this embodiment includes a mouth-drawing step and a crushing step.

[0066] (Sealing process) In this process, as shown in Figures 1(C), 1(D), and 2-3, a neck-drawing process is performed on the workpiece 1c shown in Figure 1(C) to produce the workpiece 1d shown in Figure 1(D).

[0067] Specifically, first, as shown in Figure 2, the workpiece 1c is set in the first housing hole 501 of the lower mold 50. Hereafter, the state shown in Figure 2 (the state in which the workpiece 1c is set in the first housing hole 501 and the upper mold 51 is not pressed against the workpiece 1c) will be referred to as the "pre-filling process set state".

[0068] In the pre-filling set state, the housing portion 20c of the shaft portion 2c of the workpiece 1c is housed in the first housing hole 501. Here, the outer circumferential surface shape of the housing portion 20c of the shaft portion 2c of the workpiece 1c and the inner circumferential surface shape of the first housing hole 501 (the portion of the first housing hole 501 that is radially opposite to the housing portion 20c) are symmetrical with respect to each other. Therefore, the outer circumferential surface of the housing portion 20c is in full contact with the inner circumferential surface of the first housing hole 501.

[0069] In the pre-filling stage, the first support portion 502 supports the flange portion 3c of the workpiece 1c from below. The lower surface of the flange portion 3c is in full contact with the first support portion 502. The protruding portion 21c of the shaft portion 2c of the workpiece 1c protrudes upward from the first housing hole 501. The central axis (radial central axis) C1 of the annular filled surface 511a, the central axis (radial central axis) A1 of the cylindrical workpiece 1c, and the central axis (radial central axis) B1 of the circular first housing hole 501 coincide with each other.

[0070] Next, as shown in Figures 2 and 3, the upper die 51 is lowered, and the constricted surface 511a and flat pressing surface 511b of the constricted portion 511 are pressed against the protruding portion 21c and flange portion 3c from above. Due to the pressure of the constricted surface 511a, the protruding portion 21c is deformed to shrink inward in the radial direction. Through the constricted portion process, a tapered portion 211d and a protruding end portion 213d are formed on the protruding portion 21d. In this way, the protruding portion 21d is subjected to constricted portion processing. The taper angle of the outer circumferential surface of the tapered portion 211d (the inclination angle of the outer circumferential surface of the tapered portion 211d with respect to the horizontal direction) coincides with the constriction angle θ1.

[0071] Due to the pressure contact of the flat pressing surface 511b, the flange portion 3c (which may include the base portion of the flange portion 3c of the protruding portion 21c) is crushed from above and below by the first support portion 502 and the flat pressing surface 511b. The flange portion 3c expands in diameter outward. The upper surface of the flange portion 3d after the expansion deformation is annular and has a planar shape that expands horizontally.

[0072] Next, the upper die 51 is raised, separating the constricted surface 511a and the flat pressing surface 511b of the constricted section 511 from the protruding section 21d and the flange section 3d. In this way, the workpiece 1d is completed. In the subsequent discharge process after constricting, the workpiece 1d is discharged from the bottom to the top by a knockout pin (not shown).

[0073] (Crushing process) In this process, as shown in Figures 1(D), 1(E), and 4-5, a crushing process is performed to crush the workpiece 1d shown in Figure 1(D) to produce the workpiece 1e shown in Figure 1(E).

[0074] Specifically, first, as shown in Figure 4, the workpiece 1d is set in the third housing hole 601 of the lower mold 60. Hereafter, the state shown in Figure 4 (the state in which the workpiece 1d is set in the third housing hole 601 and the upper mold 61 is not pressed against the workpiece 1d) will be referred to as the "pre-crushing set state".

[0075] The pre-crushing set state is the same as the pre-sealing set state described above. Specifically, in the pre-crushing set state, the housing portion 20d of the shaft portion 2d of the workpiece 1d is housed in the third housing hole 601. The outer circumferential surface of the housing portion 20d is in full contact with the inner circumferential surface of the third housing hole 601.

[0076] In the pre-crushing set state, the third support portion 602 supports the flange portion 3d of the workpiece 1d from below. The lower surface of the flange portion 3d is in full contact with the third support portion 602. Also, the protruding portion 21d of the shaft portion 2d of the workpiece 1d protrudes upward from the third housing hole 601. Furthermore, the central axis (radial central axis) C1 of the annular flat pressing surface 611b, the central axis (radial central axis) A1 of the cylindrical workpiece 1d, and the central axis (radial central axis) B1 of the circular hole-shaped third housing hole 601 coincide with each other.

[0077] Next, as shown in Figures 4 and 5, the upper die 61 is lowered and the punch 612 is inserted into the hollow portion 4d through the opening 40d. At the same time, the narrowed mouth surface 611a and the flat pressing surface 611b of the pressing portion 611 are pressed against the projection 21d (tapered portion 211d, tip end 213d) from above. Due to the pressure of the narrowed mouth surface 611a, the projection 21d is deformed to shrink inward in the radial direction. A tapered portion 211e is formed on the projection 21e. The taper angle of the outer surface of the tapered portion 211e (the inclination angle of the outer surface of the tapered portion 211e with respect to the horizontal direction) coincides with the narrowing angle θ2.

[0078] As shown in Figure 5, the tapered portion 211e is supported by the punch 612 from the radially inner side. This prevents the material of the tapered portion 211e from flowing radially inward.

[0079] The protruding portion 21e (the lower part of the tapered portion 211d) is crushed from above by the pressure contact of the flat pressing surface 611b. A crushed portion 212e is formed on the protruding portion 21e. The upper surface of the crushed portion 212e is annular and has a planar shape that expands horizontally. The inclination angle of the upper surface of the crushed portion 212e with respect to the horizontal direction (=0°) coincides with the crushing angle of the flat pressing surface 611b.

[0080] Next, the upper die 61 is raised, and the punch 612 is removed from the hollow section 4e through the opening 40e. At the same time, the narrowed mouth surface 611a and the flat pressing surface 611b of the pressing section 611 are separated from the protruding section 21e. In this way, the workpiece 1e is completed. In the subsequent post-crushing discharge process, the workpiece 1e is discharged from the bottom to the top by a knockout pin (not shown). After discharge, the workpiece 1e is subjected to predetermined processing to complete the rotor shaft 1f shown in Figure 1(F).

[0081] [Effects and Effects] Next, the manufacturing method of the hollow shaft member of this embodiment and the effects of the hollow member will be described. As shown in Figures 2 and 3, in the mouth drawing process, with the flange portion 3c of the workpiece 1c supported by the first support portion 502 of the lower die 50, drawing is performed on the opening 40c of the workpiece 1c using the mouth drawing portion 511 of the upper die 51. Therefore, the forming load can be distributed between the shaft portion 2c and the flange portion 3c. Consequently, distortion of the shaft portion 2c can be suppressed compared to the case where the lower die 50 does not support the flange portion 3c. Thus, a decrease in the rotational balance of the workpieces 1d to 1e and consequently the rotor shaft 1f can be suppressed.

[0082] Furthermore, as described above, since the molding load can be distributed between the shaft portion 2c and the flange portion 3c, even if the drawing angle θ1 shown in Figure 2 is made smaller (and the drawing ratio (=D / d, where D is the diameter of the opening 40c before the drawing process and d is the diameter of the opening 40d after the drawing process) is made larger) compared to the case where the lower mold 50 does not support the flange portion 3c, distortion of the shaft portion 2c can be suppressed. As a result, the axial length of the workpieces 1d to 1e and consequently the rotor shaft 1f can be shortened. In addition, the workpieces 1d to 1e and consequently the rotor shaft 1f can be made lighter.

[0083] As shown in Figures 2 and 3, during the neck-reducing process, the outer circumferential surface of the receiving portion 20c is in full contact with the inner circumferential surface of the first receiving hole 501. Therefore, compared to the case where there is a gap between the outer circumferential surface of the receiving portion 20c and the inner circumferential surface of the first receiving hole 501, it is possible to suppress the radial outward bulging of the shaft portion 2c.

[0084] According to the crushing process (crushing mold 6) shown in Figures 4 and 5, the molding load can be distributed between the shaft portion 2d and the flange portion 3d, similar to the mouth-filling process (mouth-filling mold 5) described above. Therefore, distortion of the shaft portion 2d can be suppressed compared to the case where the lower mold 60 does not support the flange portion 3d.

[0085] As shown in Figures 4 and 5, during the crushing process, the outer circumferential surface of the receiving portion 20d is in full contact with the inner circumferential surface of the third receiving hole 601. Therefore, compared to the case where there is a gap between the outer circumferential surface of the receiving portion 20d and the inner circumferential surface of the third receiving hole 601, it is possible to suppress the radial outward bulging of the shaft portion 2d.

[0086] As shown in Figure 1(B), workpiece 1b is a single unit. The shaft portion 2b and flange portion 3b of workpiece 1b are integrally connected. The same applies to workpieces 1c to 1e. Therefore, there is no need to attach the flange portions 3b to 3e to the shaft portions 2b to 2e afterwards. Consequently, manufacturing man-hours can be reduced, and the process can be simplified.

[0087] As shown in Figure 1(A), workpiece 1a is a solid bulk material. According to the manufacturing method of the hollow shaft member of this embodiment, the material for workpiece 1c before the neck drawing process can be selected from solid bulk material, hollow pipe material, etc. Therefore, there is a high degree of freedom in material selection.

[0088] The drawing angle θ1 shown in Figure 2 is set to 30° or more. Therefore, compared to the case where the drawing angle θ1 is less than 30°, it is possible to suppress the radial outward bulging of the protrusion 21c during molding. Consequently, it is possible to suppress the occurrence of material loss on the upper end surface and inner circumferential surface of the protrusion 21d shown in Figure 3 (specifically, the upper end surface of the tip 213d and the inner circumferential surface of the tapered portion 211d). In addition, it is possible to suppress the occurrence of excess material on the outer circumferential surface of the tapered portion 211d. Furthermore, because the occurrence of excess material is suppressed, it is possible to suppress the excess material from being sandwiched between the lower mold 60 and the upper mold 61 of the crushing mold 6 in the crushing process (a process after the mouth drawing process) shown in Figures 4 and 5.

[0089] The diaphragm angle θ1 shown in Figure 2 is set to 35° or more. Therefore, compared to the case where the diaphragm angle θ1 is less than 35°, it is possible to further suppress the occurrence of material loss on the upper end surface and inner circumferential surface of the protruding portion 21d (specifically, the upper end surface of the protruding portion 213d and the inner circumferential surface of the tapered portion 211d) shown in Figure 3. Furthermore, it is possible to suppress the occurrence of excess material on the outer circumferential surface of the tapered portion 211d.

[0090] As shown in Figures 4 and 5, in the crushing process, with the flange portion 3d of the workpiece 1d supported by the third support portion 602 of the lower die 60, the punch 612 of the upper die 61 is inserted into the opening 40d of the workpiece 1d after the neck drawing process, and the tapered portion 211d is crushed using the pressing portion 611 of the upper die 61.

[0091] Therefore, the molding load can be distributed between the shaft portion 2d and the flange portion 3d. Consequently, distortion of the shaft portion 2d can be suppressed compared to the case where the lower mold 60 does not support the flange portion 3d. Thus, a decrease in the rotational balance of the workpieces 1d to 1e and consequently the rotor shaft 1f can be suppressed.

[0092] Furthermore, because the molding load can be distributed, distortion of the shaft portion 2d can be suppressed even with a smaller crushing angle compared to a case where the lower die 60 does not support the flange portion 3d. As a result, the axial length of the workpiece 1e and thus the rotor shaft 1f can be further shortened. In addition, the workpiece 1e and thus the rotor shaft 1f can be made lighter.

[0093] Furthermore, in the crushing step of the manufacturing method for the hollow shaft member of this embodiment, when the tapered portion 211d is pressed from above by the pressing portion 611, the tapered portion 211d is supported by the punch 612 from the radially inward side. Therefore, it is possible to suppress the bulging of the material of the tapered portion 211d radially inward. Consequently, the material of the tapered portion 211d can be preferentially made to flow downward. Thus, the thickness of the crushed portion 212e can be increased.

[0094] As shown in Figure 1(F), a bearing press-fit portion 21f is positioned above the crushed portion 212f of the rotor shaft 1f. The upper surface of the crushed portion 212f functions as a contact surface that supports the bearing from below. In this respect, according to the manufacturing method of the hollow shaft member of this embodiment, the crushed portion 212e can be formed by forging, as shown in Figure 5. Therefore, the amount of scrap can be reduced compared to the case where the crushed portion 212f shown in Figure 1(F) is formed by cutting, for example from the workpiece 1d shown in Figure 1(D).

[0095] Furthermore, in the cases of the mouth-drawing process, radial forging, and metal spinning shown in Figures 2 and 3, the workpiece 1c is formed from the radially outer side. As a result, the area between the unprocessed portion and the drawn portion becomes tapered, making it difficult to adjust the wall thickness of the tapered portion. Therefore, referring to Figure 1(F), when a bearing press-fit portion 21f is created in the drawn portion by post-processing, a contact surface (the upper surface of the crushed portion 212f; a surface that extends in a direction perpendicular to the extending direction of the bearing press-fit portion 21f (radial direction, horizontal direction)) is created in the tapered portion, requiring the removal of a large amount of excess material. In addition, the wall thickness on the inside of the contact surface becomes thinner, and depending on the degree of thinning, this may result in insufficient strength.

[0096] In this regard, in the crushing process shown in Figures 4 and 5, when the tapered portion 211d is pressed from above by the pressing portion 611, the tapered portion 211d is supported by the punch 612 from the radially inward side. Therefore, it is possible to suppress the flow of the material of the tapered portion 211d radially inward. Consequently, the material of the tapered portion 211d can be made to flow downward. Thus, the thickness of the crushed portion 212e can be increased.

[0097] The crushing angle (=0°) of the flat pressing surface 611b shown in Figure 4 is less than the throttling angle θ1 of the mouth throttling surface 511a shown in Figure 2. Therefore, the tapered portion 211d can be crushed more reliably compared to the case where the crushing angle is greater than or equal to the throttling angle θ1. Consequently, as shown in Figure 5, the upper surface of the crushed portion 212e can be brought closer to the horizontal plane.

[0098] The mouth-drawing process shown in Figures 2 and 3 is performed by cold forging. Therefore, without intentionally heating the workpiece 1c, the mouth-drawing process can be applied to the opening 40c of the hollow portion 4c, and the tapered portion 211d can be formed on the shaft portion 2d.

[0099] The crushing process shown in Figures 4 and 5 is performed by cold forging. Therefore, the tapered portion 211d can be crushed and the crushed portion 212e formed on the tapered portion 211d without intentionally heating the workpiece 1d.

[0100] As shown in Figure 1(D), the inner diameter of the tapered portion 211d of workpiece 1d gradually decreases from the hollow portion 4d towards the opening 40d. As shown in Figure 1(E), the inner diameter of the crushed portion 212e of workpiece 1e gradually decreases from the hollow portion 4e towards the opening 40e. As shown in Figure 1(F), the inner diameter of the crushed portion 212f of workpiece (rotor shaft) 1f gradually decreases from the hollow portion 4f towards the opening 40f.

[0101] The tapered portion 211d, crushed portion 212e, and crushed portion 212f described above are all included in the concept of "tapered portion" of the "hollow member" in this disclosure. Workpieces 1d to 1f, that is, workpieces after the completion of the mouth-drawing process shown in Figures 2 to 3, are all included in the concept of "hollow member" in this disclosure.

[0102] In workpiece 1d, the shaft portion 2d and the flange portion 3d are seamlessly connected. Therefore, compared to the case where workpiece 1d is a composite (a composite of the shaft portion 2d and the flange portion 3d, which are independent of each other), the strength (e.g., tensile strength, compressive strength, shear strength) and rigidity (e.g., torsional rigidity, bending rigidity) of workpiece 1d can be improved. In addition, the number of parts can be reduced compared to the case where workpiece 1d is a composite. The same applies to workpieces 1e to 1f.

[0103] Regarding the tapered portion 211d of workpiece 1d, at least a portion of the tapered portion 211d has a thicker wall than the protruding end portion 213d having an opening 40d and the flange portion 3d of the shaft portion 2d. Therefore, the strength and rigidity of the tapered portion 211d can be improved. The same applies to the crushed portion 212e of workpiece 1e and the crushed portion 212f of workpiece 1f. The aforementioned protruding end portion 213d, projection portion 21e, and projection portion 21f are all included in the concept of a "protruding end portion" having an opening as described in this disclosure.

[0104] <Second Embodiment> The difference between this embodiment and the first embodiment is that the pressing portion of the upper die of the crushing mold has a crushing surface. The main differences will be explained here.

[0105] Figure 6 shows a vertical cross-sectional view of the molding die for the neck-filling process at the initial stage of the neck-filling process in the manufacturing method of the hollow shaft member of this embodiment. Figure 7 shows a vertical cross-sectional view of the molding die for the neck-filling process at the final stage of the same process. Note that parts corresponding to those in Figures 2 and 3 are indicated by the same reference numerals.

[0106] As shown in Figures 6 and 7, the first housing hole 501 of the lower mold 50 houses the housing portion 20c of the workpiece 1c. The first support portion 502 of the lower mold 50 supports the flange portion 3c from below. On the inner circumferential surface of the lower end opening edge of the cylindrical mouth constriction portion 511 of the upper mold 51, a tapered annular mouth constriction surface 511a is arranged, which decreases in diameter from the bottom to the top.

[0107] Figure 8 shows a vertical cross-sectional view of the crushing mold in the initial stage of the crushing process in the manufacturing method of the hollow shaft member of this embodiment. Figure 9 shows a vertical cross-sectional view of the crushing mold in the final stage of the same process. The same reference numerals are used for parts corresponding to those in Figures 4 and 5.

[0108] As shown in Figures 8 and 9, the internal space of the third housing hole 601 of the lower mold 60 is cylindrical in shape with the same diameter extending in the vertical direction. At the lower end of the third housing hole 601, there is a hole bottom surface 601a that expands in the horizontal direction. A pin insertion hole 601b is provided at the radial center of the hole bottom surface 601a. ​​The knockout pin 603 can enter the third housing hole 601 from below through the pin insertion hole 601b. The hole bottom surface 601a and the upper end surface of the knockout pin 603 are positioned substantially flush with each other.

[0109] As shown in Figure 8, a tapered annular crushing surface 611c is arranged on the inner circumferential surface of the lower end opening edge of the pressing portion 611, with the diameter decreasing from the bottom to the top. The constriction angle θ1 of the constriction surface 511a shown in Figure 6 is greater than the crushing angle (angle of inclination of the crushing surface 611c with respect to the horizontal (radial) direction) θ3 of the crushing surface 611c shown in Figure 8. The angular difference Δθ (=θ1-θ3) between the constriction angle θ1 and the crushing angle θ3 is within the range of greater than 0° and less than or equal to 25°. In other words, the relationship 0° < Δθ ≤ 25° holds true.

[0110] As shown in Figure 8, in the initial stage of the crushing process (before the tapered portion 211d is crushed, with the receiving portion 20d housed in the third receiving hole 601 and the flange portion 3d supported from below by the third support portion 602), the receiving portion 20d is not in contact with the bottom surface 601a of the hole. A space exists between the receiving portion 20d and the bottom surface 601a of the hole. Thus, the workpiece 1d is set in the lower die 60 with only the flange portion 3d supported from below (floating above the bottom surface 601a). A gap D is secured between the lower end (front end) 20da of the receiving portion 20d and the bottom surface 601a of the hole. The vertical width (axial width) of the gap D is set to 2 mm or more.

[0111] As shown in Figure 9, the workpiece 1e after crushing is a single hollow member (hollow shaft member) comprising a shaft portion 2e, a flange portion 3e projecting radially outward from the shaft portion 2e, and a hollow portion 4e opening at the upper end of the shaft portion 2e.

[0112] The shaft portion 2e has a receiving portion 20e positioned below the flange portion 3c and a protruding portion 21e positioned above the flange portion 3c. The protruding portion 21e has a crushed portion 212e that decreases in diameter from bottom to top. The inner circumferential surface of the receiving portion 20e extends in the vertical direction. The inner circumferential surface of the crushed portion 212e decreases in diameter from bottom to top.

[0113] The inner circumferential surface of the shaft portion 2e (the inner circumferential surface of the hollow portion 4e) has a same-diameter section 41e that extends vertically and includes the inner circumferential surface of the housing portion 20e, and a reduced-diameter section 42e that includes the inner circumferential surface of the crushed portion 212e and decreases in diameter from the bottom to the top. The boundary 43e (the starting point of the reduced-diameter section 42e) between the same-diameter section 41e and the reduced-diameter section 42e is located below (in front of) the lower end (front end) 30e of the flange portion 3e. More specifically, the area near the joint between the same-diameter section 41e and the reduced-diameter section 42e is curved. The boundary 43e is the lower end of this curved surface (the starting point of the reduction in diameter).

[0114] This embodiment and the first embodiment have similar effects and advantages in respect of parts that share a common structure. In the mouth-drawing process shown in Figures 6 and 7, the tapered portion 211d is formed by plastically deforming (distorting) the material of the protruding portion 21c of the shaft portion 2c. Therefore, the hardness of the tapered portion 211d after mouth-drawing is high. In contrast, the housing portion 20c of the shaft portion 2c is not easily plastically deformed. Therefore, the hardness of the housing portion 20d after mouth-drawing is lower than that of the tapered portion 211d.

[0115] In the crushing process shown in Figures 8 and 9, the crushed portion 212e is formed by further plastically deforming the already high-hardness tapered portion 211d. As a result, during the crushing process, the lower end (near the base) of the inner surface of the tapered portion 211d tends to fold radially outward (into the material of the workpiece 1d). Also, due to the forming load, the upper end of the low-hardness housing portion 20d tends to bulge radially inward (into the hollow portion 4d). Consequently, a groove (forming defect) that is recessed radially outward is likely to be formed near the boundary 43e of the workpiece 1e after the crushing process. In addition, after the forming load is removed, the groove opens due to springback, and cracks tend to propagate from the bottom of the groove.

[0116] In this regard, the diaphragm angle θ1 shown in Figure 6 is set to be larger than the crushing angle θ3 shown in Figure 8. Furthermore, the angular difference Δθ (=θ1-θ3) between the diaphragm angle θ1 and the crushing angle θ3 falls within the range of greater than 0° and less than or equal to 25°. In other words, the relationship 0° < Δθ ≤ 25° holds true. Therefore, the tapered portion 211d can be crushed more reliably compared to the case where the angular difference Δθ is 0° or negative. Also, the formation of the grooves mentioned above can be suppressed compared to the case where the angular difference Δθ exceeds 25°.

[0117] Specifically, the taper angle of the outer surface of the tapered portion 211d shown in Figure 8 (the inclination angle of the outer surface of the tapered portion 211d with respect to the horizontal direction) coincides with the narrowing angle θ1 shown in Figure 6. Therefore, compared to the case where the angle difference Δθ exceeds 25°, setting the angle difference Δθ to 25° or less allows the crushing surface 611c to be laid flat along the outer surface of the tapered portion 211d. As shown in Figure 9, the crushing surface 611c can press over a wide area from the tapered portion 211d to the flange portion 3d. Therefore, the pressing load is more easily applied to the radially outer portion of the protruding portion 21d and the flange portion 3d. Consequently, it is possible to suppress the concentration of the pressing load near the lower end of the tapered portion 211d. Thus, the tapered portion 211d can be reliably crushed, and the formation of the grooves mentioned above can be suppressed.

[0118] As shown in Figure 8, at the beginning of the crushing process, the receiving portion 20d is not in contact with the bottom surface 601a of the hole. The workpiece 1d is floating above the bottom surface 601a of the third receiving hole 601. In contrast, as shown in Figure 9, at the end of the crushing process, the lower end 20da of the receiving portion 20d reaches the upper end surface of the knockout pin 603, i.e., the bottom surface 601a of the hole. In this way, during the crushing process, the material of the receiving portion 20d can flow downward by utilizing the space between the workpiece 1d and the bottom surface 601a of the hole. This material flow allows the forming load to be relieved. Therefore, stress concentration near the lower end of the inner circumferential surface of the tapered portion 211d can be alleviated. As a result, the formation of the aforementioned groove can be suppressed.

[0119] Here, if the material of the receiving portion 20d flows downward, it is conceivable that the area around the flange portion 3e after crushing, as shown in Figure 9, will become thinner (for example, the top surface will be concave). For this reason, the thickness of the tapered portion 211d of the workpiece 1d before crushing, as shown in Figure 8, is set to be thicker in advance.

[0120] As shown in Figure 8, the vertical width of the gap D between the lower end 20da of the receiving portion 20d and the bottom surface 601a of the hole is set to 2 mm or more. Therefore, compared to the case where the vertical width of the gap D is less than 2 mm, the flow space for the material in the receiving portion 20d during crushing can be increased. Consequently, the forming load can be relieved more reliably compared to the case where the vertical width is less than 2 mm. As a result, the formation of the grooves mentioned above can be suppressed more reliably.

[0121] As shown in Figure 9, the boundary 43e between the same-diameter section 41e and the reduced-diameter section 42e on the inner circumferential surface of the workpiece (hollow member, hollow shaft member) 1e after crushing is located below the lower end 30e of the flange section 3e. This allows for a thicker wall thickness in the crushed section 212e. In other words, a thick, firm crushed section 212e can be formed. Consequently, the strength and rigidity of the workpiece 1e can be improved. In particular, when the gap D is large (when the amount of material flowing downwards is large), the boundary 43e tends to be located lower.

[0122] The inclination angle of the crushed portion 212e with respect to the horizontal direction (radial direction) shown in Figure 9 (more specifically, the inclination angle of the outer surface of the crushed portion 212e) is the same as the crushing angle θ3 shown in Figure 8. The inclination angle of the crushed portion 212e is set to more than 5°. Furthermore, the same-diameter section 41e and the reduced-diameter section 42e are connected in a smooth (curved) manner. In other words, no molding defects such as grooves or cracks are formed near the boundary 43e between the same-diameter section 41e and the reduced-diameter section 42e. Therefore, the strength and rigidity of the workpiece 1e can be improved.

[0123] <Other> The method for manufacturing a hollow shaft member and embodiments of the hollow member have been described above. However, the embodiments are not particularly limited to the above forms. Various modified and improved forms can be implemented by those skilled in the art.

[0124] The tapering angle θ1 of the tapered surface 511a shown in Figure 2 is not particularly limited. The tapering angle θ1 may be single or multiple. For example, the tapered surface 511a may have a shape in which multiple tapered surfaces with different tapering angles θ1 are connected. In this case, the outer circumferential surface of the tapered portion 211d shown in Figure 3 (the surface to be formed by the tapered surface 511a) can be formed into a shape in which multiple tapered surfaces with different inclination angles (angles corresponding to the tapering angle θ1) are connected.

[0125] The shape of the constricted surface 511a is not particularly limited. It is acceptable as long as it is an annular shape that tapers from the bottom to the top. For example, in the vertical cross-section shown in Figure 2, the constricted surface 511a may be straight, curved inward in the radial direction, curved outward in the radial direction, or a shape that is an appropriate combination of these shapes. The same applies to the shape of the outer circumferential surface of the tapered portion 211d. The same also applies to the shape of the crushed surface 611c shown in Figure 8 and the shape of the outer circumferential surface of the crushed portion 212e shown in Figure 9.

[0126] The workpiece 1c shown in Figure 1(C) may be manufactured from workpiece 1a, i.e., solid bulk material, or from hollow pipe material. The neck-drawing process shown in Figures 2 and 3 may be carried out by cold forging, warm forging, or hot forging.

[0127] Workpiece 1b shown in Figure 1(B) may or may not be an intermediate part of the rotor shaft 1f shown in Figure 1(F). It may also be an intermediate part of a flanged hollow shaft member other than the rotor shaft 1f. The same applies to workpieces 1c to 1e shown in Figures 1(C) to 1(E). Workpiece 1d shown in Figure 1(D) may be a finished product. The same applies to workpiece 1e shown in Figure 1(E).

[0128] The crushing process shown in Figures 4 and 5 may or may not be performed after the neck-filling process shown in Figures 2 and 3. Alternatively, another process may be performed between the neck-filling and crushing processes. Or, a process other than the crushing process may be performed after the neck-filling process. In other words, there are no particular limitations on the presence or absence of a post-finishing process, or the type of post-finishing process. The crushing process shown in Figures 4 and 5 may be performed independently of the neck-filling process shown in Figures 2 and 3. Before the crushing process, it is sufficient to prepare the workpiece 1d shown in Figure 1(D) by various manufacturing methods (e.g., radial forging or spinning).

[0129] The throttling angle θ1 of the throttling surface 511a shown in Figure 2 is not particularly limited. The throttling angle θ1 of the throttling surface 511a may be less than 30° or 30° or more. The same applies to the crushing angle of the flat pressing surface 611b shown in Figure 4, the throttling angle θ2 of the throttling surface 611a, and the crushing angle θ3 of the crushing surface 611c shown in Figure 8.

[0130] The angular difference Δθ (=θ1-θ3) between the aperture angle θ1 shown in Figure 6 and the compression angle θ3 shown in Figure 8 may or may not fall within the range of greater than 0° and less than or equal to 25°. The angular difference Δθ may be 0° or less, or greater than 25°.

[0131] The presence or absence of a gap D between the lower end (front end) 20da of the receiving portion 20d and the bottom surface 601a of the hole, as shown in Figure 8, and its vertical width (axial width) are not particularly limited. The vertical width may be 2 mm or more, or less than 2 mm (including 0 mm). The inclination angle of the crushed portion 212e with respect to the horizontal direction (more specifically, the inclination angle of the outer circumferential surface of the crushed portion 212e with respect to the horizontal direction), as shown in Figure 9, is not particularly limited. This inclination angle may be greater than 5°, or 5° or less (including 0°).

[0132] The hollow portion 4b of the workpiece 1b shown in Figure 1(B) may open at both the upper and lower ends of the shaft portion 2b, or it may open only at the upper end. In other words, the hollow portion 4b only needs to open at at least the upper end of the shaft portion 2b. The same applies to the hollow portions 4c to 4e of the workpieces 1c to 1e shown in Figures 1(C) to 1(E). The same applies to the hollow portion 4f of the rotor shaft 1f shown in Figure 1(F). Coolant may be flowed into the hollow portion 4f. A radial through hole may be made between the inner circumferential surface of the bearing press-fit portion 21f that defines the hollow portion 4f and the outer circumferential surface of the bearing press-fit portion 21f. Coolant may be supplied to the bearing through this radial through hole.

[0133] In the mouth-filling process shown in Figures 2 and 3, the flange portion 3c of the workpiece 1c is supported by the first support portion 502 of the lower die 50, and the opening 40c of the workpiece 1c is filled. Here, the timing at which the flange portion 3c is supported by the first support portion 502 is not particularly limited. For example, at the initial stage of the process shown in Figure 2 (set state before the mouth-filling process), the flange portion 3c does not need to be in contact with the first support portion 502 (it does not need to be supported). In this case, after the process has started, the flange portion 3c may come into contact with the first support portion 502 and be supported by the first support portion 502. Thus, the flange portion 3c may be supported by the first support portion 502 after the start of molding. The same applies to the crushing process shown in Figures 4 and 5, and Figures 8 and 9.

[0134] The molding die for narrowing the neck and the molding die for crushing used in the manufacturing method of the hollow shaft member of this disclosure can each be used independently. The configuration of the molding die for narrowing the neck will be described below. According to the following configuration, the neck narrowing step of the manufacturing method of the hollow shaft member of this disclosure can be performed. Therefore, the same effects and advantages as the neck narrowing step can be enjoyed.

[0135] A molding die for forming a tapered portion on the shaft of a hollow workpiece comprising a shaft portion, a flange portion projecting radially outward from the shaft portion, and hollow portions opening at one or both axial ends of the shaft portion, wherein the die comprises a first die and a second die accessible from the rear of the first die, with the axial end being the rear side and the opposite side being the front side, the first die having a first housing hole and a first support portion positioned outside and at the rear of the first housing hole to support the flange portion from the front side, and the second die having an inner diameter that decreases from the front to the rear side. A molding die for forming a mouth, having a cylindrical mouth-reducing portion, wherein the shaft portion has a receiving portion positioned in front of the flange portion and housed in the first receiving hole, and a protruding portion positioned behind the flange portion and protruding rearward from the first receiving hole, wherein the receiving portion is housed in the first receiving hole, and the flange portion is supported from the front by the first support portion, or supported after the start of forming, the protruding portion is pressed from the rear by the mouth-reducing portion to perform a mouth-reducing process on the opening of the hollow portion, thereby forming the tapered portion on the protruding portion. The following describes the constituent requirements of the crushing mold. According to this configuration, the crushing process of the manufacturing method for the hollow shaft member of this disclosure can be performed. Therefore, the same effects as the crushing process can be enjoyed. However, the hollow workpiece (unprocessed workpiece) to be processed by the crushing mold may be a processed workpiece of the mouth-filling mold described above, or it may not be a processed workpiece of the mouth-filling mold.

[0136] A crushing mold for forming a crushed portion in the tapered portion of a hollow workpiece, comprising a shaft portion, a flange portion projecting radially outward from the shaft portion, a hollow portion opening at one or both axial ends of the shaft portion, and a cylindrical tapered portion positioned at one axial end of the shaft portion, wherein the mold comprises a third mold and a fourth mold accessible from the rear to the third mold, with the axial end being the rear side and the opposite side being the front side, the third mold having a third housing hole and a third support portion positioned outside and at the rear of the third housing hole and supporting the flange portion from the front, and the fourth mold having a cylindrical pressing portion and a portion radially inside the pressing portion A crushing mold having a punch to be positioned, the shaft portion having a receiving portion positioned in front of the flange portion and housed in the third receiving hole, and a protruding portion positioned behind the flange portion and protruding rearward from the third receiving hole, wherein the receiving portion is housed in the third receiving hole and the flange portion is supported from the front by the third support portion, or supported after the start of molding, the crushing process is performed by pressing the tapered portion from the rear with the pressing portion while inserting the punch into the opening of the hollow portion from the rear, thereby crushing the tapered portion and forming a crushed portion on the tapered portion. One embodiment of the hollow shaft member of the present disclosure may have the following configuration: "A hollow shaft member comprising a shaft portion, a flange portion projecting radially outward from the shaft portion, and a hollow portion opening at one axial end of the shaft portion, wherein the axial end is the rear side and the opposite side is the front side, the shaft portion and the flange portion are integrally connected, and the shaft portion has a tapered portion whose inner diameter gradually decreases from the front to the rear." In this configuration, the shaft and flange are integrally connected. Therefore, compared to cases where the hollow member is a composite (a composite of a shaft and flange that are independent of each other), the strength (e.g., tensile strength, compressive strength, shear strength) and rigidity (e.g., torsional rigidity, bending rigidity) of the hollow member can be improved. In addition, the number of parts can be reduced compared to cases where the hollow member is a composite.

[0137] In the above configuration, at least a portion of the tapered portion may have a thicker wall than the protruding end portion of the shaft portion that is located behind the tapered portion and defines the opening of the hollow portion. This configuration can improve the strength and rigidity of the tapered portion. Furthermore, in the above configuration, at least a portion of the tapered portion may have a thicker wall than the portion of the shaft portion that is located in front of the flange portion. This configuration can improve the strength and rigidity of the tapered portion. [Examples]

[0138] <Analysis 1> The following describes the CAE (Computer-Aided Engineering) analysis performed on the manufacturing method of the hollow shaft member disclosed herein, with reference to Figures 1 to 3. In the analysis, three levels (Examples 1 to 3) were set as shown below, and the above-mentioned manufacturing method of the hollow shaft member (mouth-drawing process) was simulated.

[0139] [Regarding Examples 1-3] In Examples 1 to 3, workpieces with the same material and configuration as workpiece 1c shown in Figure 1(C) were used in each example. The only difference between the workpieces in Examples 1 to 3 is the diaphragm angle θ1 shown in Figure 2. The diaphragm angle θ1 of the workpiece in Example 1 is 35°, the diaphragm angle θ1 of the workpiece in Example 2 is 30°, and the diaphragm angle θ1 of the workpiece in Example 3 is 25°.

[0140] [About the analysis conditions] The analysis was performed using FORGE (Transvalor), a plastic deformation simulation software. In the analysis, the stress distribution of the workpiece during the neck drawing process was calculated. The forming speed (lowering speed of the upper die 51) was set to 10 mm / s. The temperature of the entire workpiece and the forging die at the start of the neck drawing process was set to 20°C (cold forging). The friction coefficient μ between the workpiece and the forging die was set to 0.035.

[0141] [About the analysis results] (Example 1) Figures 10 to 14 show the analysis results (first to fifth stages) of Example 1 (Level 1) as contour plots. Figures 10 to 14 are vertical cross-sectional views, similar to Figures 2 and 3. In Figures 10 to 14, the molding die 5 for neck filling shown in Figures 2 and 3 is shown transparently (contour only). As shown by the bar on the left end of Figures 10 to 14, the darker black areas represent areas with low stress (compressive stress). The lighter black areas represent areas with high stress. Stress increases from dark (black) to light (white).

[0142] Figure 10 shows the workpiece before the neck-filling process. This workpiece corresponds to workpiece 1c (right half) shown in Figures 1(C) and 2. Figure 14 shows the workpiece after the neck-filling process. This workpiece corresponds to workpiece 1d (right half) shown in Figures 1(D) and 3.

[0143] As shown in Figures 2 and 10, in the first stage of the neck-drawing process, the receiving portion 20c of the workpiece 1c is housed in the first receiving hole 501. The outer circumferential surface of the receiving portion 20c is in full contact with the inner circumferential surface of the first receiving hole 501. The first support portion 502 supports the flange portion 3c from below. The first support portion 502 is in full contact with the lower surface of the flange portion 3c. The central axis A1 of the workpiece 1c is aligned with the central axis B1 of the first receiving hole 501.

[0144] As shown in Figures 2-3 and 11-14, as the neck-filling process progresses, the neck-filling portion 511 of the upper die 51 presses the opening 40c of the hollow portion 4c of the workpiece 1c from above. The neck-filling surface 511a of the neck-filling portion 511 causes the opening 40c of the hollow portion 4c to shrink in diameter. This shrinking deformation forms a tapered portion 211d and a protruding end portion 213d on the protruding portion 21d. As shown by the bar on the left end of Figures 11-14, the stress, or forming load, is continuously distributed during the neck-filling process. Therefore, distortion of the shaft portion 2c can be suppressed.

[0145] As shown in Figures 2-3 and 13, according to Example 1, as the mouth-drawing process progresses, the material of the protrusion 21d flows radially inward rather than radially outward. Therefore, the upper end surface and inner circumferential surface of the protrusion 21d can be formed on the workpiece 1d.

[0146] (Example 2) Figures 15 to 19 show the analysis results (first to fifth stages) of Example 2 (Level 2) in contour plots. The interpretation of the figures is the same as in Figures 10 to 14. As shown in Figures 2 to 3 and 16 to 19, as the neck-filling process progresses, the neck-filling portion 511 of the upper die 51 presses the opening 40c of the hollow portion 4c of the workpiece 1c from above. The neck-filling surface 511a of the neck-filling portion 511 causes the opening 40c of the hollow portion 4c to shrink in diameter. This shrinking deformation forms a tapered portion 211d and a protruding end portion 213d on the protruding portion 21d. As shown by the bar on the left end of Figures 16 to 19, the stress, i.e., the forming load, is continuously distributed during the neck-filling process. Therefore, distortion of the shaft portion 2c can be suppressed.

[0147] As shown in Figures 16 to 18, according to Example 2, as the mouth-drawing process progresses, the material of the protruding portion 21d flows radially inward rather than radially outward. Therefore, the protruding portion 21d (specifically, the tip portion 213d and the tapered portion 211d) can be formed on the workpiece 1d.

[0148] Comparing Figure 19 (Example 2) and Figure 14 (Example 1) (referencing Figure 4), Example 2 has a smaller taper angle (angle of inclination of the outer surface of the tapered portion 211d with respect to the horizontal direction) because the tapering angle θ1 is smaller than that of Example 1. Therefore, the axial length of the workpiece 1d can be shortened in Example 2 compared to Example 1.

[0149] Furthermore, the vertical length of the tip portion 213d is shorter in Example 2 than in Example 1. Therefore, it is more difficult to ensure sufficient wall thickness when manufacturing the bearing press-fit portion 21f in Example 2 than in Example 1. However, since the drawing angle θ1 of the workpiece in Example 2 is 30°, this does not have a significant impact, and it can be manufactured without problems if designed carefully.

[0150] (Example 3) Figures 20 to 24 show the analysis results (first to fifth stages) of Example 3 (Level 3) in contour plots. The interpretation of the figures is the same as that of Figures 10 to 14. As shown in Figures 2 to 3 and 21 to 24, as the neck-filling process progresses, the neck-filling portion 511 of the upper die 51 presses the opening 40c of the hollow portion 4c of the workpiece 1c from above. The neck-filling surface 511a of the neck-filling portion 511 causes the opening 40c of the hollow portion 4c to shrink in diameter. This shrinking deformation forms a tapered portion 211d and a protruding end portion 213d on the protruding portion 21d. As shown by the bar on the left end of Figures 21 to 24, the stress, i.e., the forming load, is continuously distributed during the neck-filling process. Therefore, distortion of the shaft portion 2c can be suppressed.

[0151] As shown in Figures 2-3 and 23, according to Example 3, as the narrowing process progresses, the material of the protruding portion 21d tends to flow more radially inward than radially outward. Therefore, a tapered portion 211d can be formed on the workpiece 1d. However, focusing on the radial inward flow of the material of the protruding portion 21d on the workpiece 1d, the order from highest to lowest flow rate is Example 1, Example 2, and Example 3. Therefore, comparing the vertical length of the tip 213d, the order from longest to shortest is Example 1, Example 2, and Example 3. In particular, since the vertical length of the tip 213d is short in Example 3, there is a greater risk of material loss when manufacturing the bearing press-fit portion 21f, making it more difficult to manufacture compared to Example 2. Therefore, when manufacturing the bearing press-fit portion 21f, it is preferable to set the narrowing angle θ1 to 30° or more.

[0152] Comparing Figure 24 (Example 3) and Figure 19 (Example 2) (referencing Figure 4), Example 3 has a smaller taper angle (angle of inclination of the outer surface of the tapered portion 211d relative to the horizontal direction) because the tapering angle θ1 is smaller than that of Example 2. Therefore, the axial length of the workpiece 1d can be shortened more in Example 3 than in Example 2. Thus, focusing on shortening the axial length of the workpiece 1d, the order from easiest to easiest to achieve is Example 3, Example 2, and Example 1.

[0153] From the above analysis, it can be seen that, focusing on the radial inward flow of the material of the protruding portion 21d of the workpiece 1d for Example 1 (throttling angle θ1 = 35°), Example 2 (throttling angle θ1 = 30°), and Example 3 (throttling angle θ1 = 25°), the order from highest to lowest flow rate is Example 1, Example 2, and Example 3. Furthermore, focusing on the shortening of the axial length of the workpiece 1d, the order from easiest to easiest shortening is Example 3, Example 2, and Example 1. In other words, it can be seen that an appropriate throttling angle θ1 should be set by considering the axial length of the workpiece 1d after molding, the thickness of the tapered portion 211d, and the axial length of the protruding portion 213d (and consequently, the axial length of the rotor shaft 1f shown in Figure 1(F), the thickness of the crushed portion 212f, and the axial length of the bearing press-fit portion 21f).

[0154] <Analysis 2> The CAE analysis performed on the manufacturing method of the hollow shaft member described herein will be explained below with reference to Figures 1 and 6-9. In the analysis, three levels (Examples 4-6) were set as shown below, and the above-mentioned manufacturing method of the hollow shaft member (mouth-drawing process, crushing process) was simulated.

[0155] [Regarding Examples 4-6] In Examples 4 to 6, workpieces with the same material and configuration as workpiece 1c shown in Figure 1(C) were used. The differences between the workpieces in Examples 4 to 6 are the shaping angle θ1 shown in Figure 6, the crushing angle θ3 shown in Figure 8, and the gap D.

[0156] In Example 4, the drawing angle θ1 of the workpiece is 45°, and the crushing angle θ3 is 15°. The gap D is 0. That is, the angle difference Δθ (=θ1-θ3) is 30°. In Example 5, the drawing angle θ1 of the workpiece is 45°, and the crushing angle θ3 is 25°. That is, the angle difference Δθ (=θ1-θ3) is 20°. The gap D is 0. In Example 6, the drawing angle θ1 of the workpiece is 45°, and the crushing angle θ3 is 15°. That is, the angle difference Δθ (=θ1-θ3) is 30° (same as Example 4). The vertical width (axial width) of the gap D is 3 mm. Thus, the angle difference Δθ is different between Example 4 and Example 5. The vertical width of the gap D is different between Example 4 and Example 6.

[0157] [About the analysis conditions] Similar to Analysis 1, the analysis was performed using FORGE. In the analysis, the effective strain distribution of the workpiece during the crushing process was calculated. The forming speed (lowering speed of the upper die 61) was set to 10 mm / s. The temperature of the entire workpiece and the forging die at the start of the crushing process was set to 20°C (cold forging). The coefficient of friction μ between the workpiece and the forging die was set to 0.035.

[0158] [About the analysis results] (Example 4) Figures 25 to 28 show the analysis results (first to third stages) of Example 4 (Level 4) as contour plots. Figures 25 to 28 are vertical cross-sectional views, similar to Figures 8 and 9. Figure 26 is an enlarged view of the upper part of Figure 25. The parts shown in Figures 27 and 28 correspond to the parts shown in Figure 26. In Figures 25 to 28, the crushing mold 6 shown in Figures 8 and 9 is shown transparently (outline only). As shown by the bar on the left end of Figure 25, the darker black areas are areas with small distortion (effective distortion). The lighter black areas are areas with large distortion. Distortion increases from dark (black) to light (white). Figure 25 shows the workpiece before crushing. This workpiece corresponds to workpiece 1d (right half) shown in Figures 1(D) and 8.

[0159] As shown in Figure 8, in the first stage of the crushing process, the receiving portion 20d of the workpiece 1d is housed in the third receiving hole 601. The third support portion 602 supports the flange portion 3d from below. The central axis A1 of the workpiece 1d is aligned with the central axis B1 of the third receiving hole 601.

[0160] As shown in Figures 8-9 and 25-28, as the crushing process progresses, the pressing portion 611 of the upper die 61 presses the upper surface of the tapered portion 211d and the upper surface of the flange portion 3d of the workpiece 1d from above. The punch 612 of the upper die 61 enters the hollow portion 4d. The crushing surface 611c of the pressing portion 611 deforms the tapered portion 211d downwards due to the angle difference Δθ (=30°). This deformation forms a crushed portion 212e on the protruding portion 21e. As shown in Figures 8-9 and 26-28, the crushing process causes significant distortion near the lower end of the inner circumferential surface of the tapered portion 211d. As a result, a groove that is recessed radially inward may be formed near the boundary 43e of the workpiece 1e after the crushing process.

[0161] (Example 5) Figures 29 to 32 show the analysis results (first to third stages) of Example 5 (Level 5) as contour plots. The interpretation of the figures is the same as in Figures 25 to 28.

[0162] As shown in Figures 8-9 and 29-32, similar to Example 4, as the crushing process progresses, the crushing surface 611c of the pressing portion 611 deforms the tapered portion 211d downwards by an angle difference Δθ (=20°). This deformation forms a crushed portion 212e on the protruding portion 21e. The angle difference θ (=20°) in Example 5 is smaller than the angle difference (=30°) in Example 4. Therefore, the crushing surface 611c can be laid flat so as to follow the outer circumferential surface of the tapered portion 211d. As shown in Figures 9 and 31-32, the crushing surface 611c can press over a wide area from the tapered portion 211d to the flange portion 3d. Therefore, the pressing load is more easily applied to the radially outer portion of the protruding portion 21d and the flange portion 3d. Consequently, it is possible to suppress the concentration of the pressing load near the lower end of the tapered portion 211d. Therefore, as shown in Figure 32, even after crushing, the area near the lower end of the inner circumferential surface of the tapered portion 211d does not distort significantly (it is less whitened than in Figure 28). As a result, the formation of grooves near the boundary 43e of the workpiece 1e after the crushing process can be suppressed.

[0163] (Example 6) Figures 33 to 37 show the analysis results (first to third stages) of Example 6 (Level 6) as contour plots. The interpretation of these figures is the same as for Figures 25 to 28. Figure 37 is an enlarged view of the upper portion of Figure 36.

[0164] As shown in Figures 8 and 33, in the initial stages of the crushing process, the receiving portion 20d is not in contact with the bottom surface 601a of the hole. The workpiece 1d is floating above the bottom surface 601a of the third receiving hole 601. Therefore, as shown in Figures 9 and 36, during the crushing process, the material of the receiving portion 20d can flow downward using the space between the workpiece 1d and the bottom surface 601a. ​​This material flow allows the forming load to be relieved. Consequently, as shown in Figures 9 and 37, stress concentration near the lower end of the inner circumferential surface of the tapered portion 211d can be mitigated (less whitening than in Figure 28). As a result, the formation of grooves near the boundary 43e of the workpiece 1e after the crushing process can be suppressed. [Explanation of symbols]

[0165] 1a~1b: Workpiece, 1c: Workpiece (hollow workpiece), 1d: Workpiece, 1e: Workpiece (hollow shaft member, hollow member), 1f: Rotor shaft, 2b~2f: Shaft portion, 20c~20e: Housing portion, 20da: Lower end (front end), 20f: Rotor press-fit portion, 21c~21e: Protruding portion, 21f: Bearing press-fit portion, 211d~211e: Tapered portion, 212e~212f: Crushed portion, 213d: Protruding end portion, 3b~3f: Flange portion, 30e: Lower end (front end), 4b~4f: Hollow portion, 40c~40f: Opening, 41e: Same diameter section, 42e: Reduced diameter section, 43e: Boundary, 5: Forming die for neck drawing, 50: Lower die (No. Type 1), 500: die, 501: first housing hole, 502: first support part, 51: upper die (Type 2), 510: holder, 511: mouth constriction part, 511a: mouth constriction surface, 511b: flat pressing surface, 6: crushing mold, 60: lower die (Type 3), 600: die, 601: third housing hole, 601a: hole bottom surface, 601b: pin insertion hole, 602: third support part, 603: knockout pin, 61: upper die (Type 4), 611c: crushing surface, 610: holder, 611: pressing part, 611a: mouth constriction surface, 611b: flat pressing surface, 612: punch, A1~C1: central axis, D: gap, θ1: constriction angle, θ2: constriction angle, θ3: crushing angle

Claims

1. A method for manufacturing a hollow shaft member, comprising forming a tapered portion on the shaft portion of a hollow workpiece having a shaft portion, a flange portion projecting radially outward from the shaft portion, and hollow portions opening at one or both axial ends of the shaft portion, using a molding die for neck drawing, With the aforementioned axial end facing the rear and the opposite side facing the front, The aforementioned molding die for narrowing the mouth comprises a first mold and a second mold that can be approached from the rear side relative to the first mold. The first type has a first housing hole and a first support portion positioned outside and behind the first housing hole, which supports the flange portion from the front. The second type has a cylindrical constricted mouth section whose inner diameter decreases from the front to the rear, The shaft portion has a receiving portion that is positioned in front of the flange portion and is housed in the first housing hole, and a protruding portion that is positioned behind the flange portion and protrudes rearward from the first housing hole. A method for manufacturing a hollow shaft member, characterized in that the receiving portion is housed in the first receiving hole, the flange portion is supported from the front by the first support portion, or is supported after the start of molding, the protruding portion is pressed from the rear by the mouth-reducing portion, the opening of the hollow portion is subjected to mouth-reducing processing, and the tapered portion is formed on the protruding portion.

2. The angle of inclination of the constricted portion with respect to the radial direction is defined as the constriction angle. The method for manufacturing a hollow shaft member according to claim 1, wherein the aforementioned diaphragm angle is 30° or more.

3. A third type having a third housing hole and a third support portion positioned outside and behind the third housing hole, which supports the flange portion from the front, A fourth type having a cylindrical pressing portion and a punch positioned radially inward of the pressing portion, and which can be approached from the rear of the third type, Using a crushing mold equipped with the following features, After the aforementioned mouth-closing process, A method for manufacturing a hollow shaft member according to claim 1, wherein the receiving portion is housed in the third receiving hole, the flange portion is supported from the front by the third support portion, or is supported after the start of molding, and the punch is inserted from the rear into the opening after the mouth drawing process, while pressing the tapered portion from the rear with the pressing portion to crush the tapered portion, thereby forming a crushed portion on the tapered portion.

4. A method for manufacturing a hollow shaft member according to claim 3, wherein the angle of inclination of the constricted opening portion with respect to the radial direction is defined as the constriction angle, and the angle of inclination of the pressing portion with respect to the radial direction is defined as the crushing angle, the constriction angle is greater than the crushing angle, and the angle difference between the constriction angle and the crushing angle is within the range of greater than 0° and less than or equal to 25°.

5. The third receiving hole has a hole bottom surface at its front end, The state before the crushing process is applied to the tapered portion, In a state where the receiving portion is housed in the third housing hole and the flange portion is supported by the third support portion from the front, The method for manufacturing a hollow shaft member according to claim 3, wherein the receiving portion is not in contact with the bottom surface of the hole.

6. The method for manufacturing a hollow shaft member according to claim 5, wherein the axial width of the gap between the front end of the housing portion and the bottom surface of the hole is 2 mm or more.

7. A hollow member comprising a shaft portion, a flange portion projecting radially outward from the shaft portion, and hollow portions opening at one or both axial ends of the shaft portion, With the aforementioned axial end facing the rear and the opposite side facing the front, The shaft portion has a housing portion located in front of the flange portion and a protruding portion located behind the flange portion. The aforementioned protruding portion has a flattened portion that decreases in diameter from the front to the rear. The inner circumferential surface of the shaft portion has a section of the same diameter extending in the front-rear direction including the inner circumferential surface of the receiving portion, and a section of reduced diameter that decreases in diameter from the front to the rear, including the inner circumferential surface of the crushing portion. The boundary between the same-diameter section and the reduced-diameter section is a hollow member positioned in front of the front end of the flange portion.

8. A hollow member comprising a shaft portion, a flange portion projecting radially outward from the shaft portion, and hollow portions opening at one or both axial ends of the shaft portion, With the aforementioned axial end facing the rear and the opposite side facing the front, The shaft portion has a housing portion located in front of the flange portion and a protruding portion located behind the flange portion. The aforementioned protruding portion has a flattened portion that decreases in diameter from the front to the rear. The inner circumferential surface of the shaft portion has a section of the same diameter extending in the front-rear direction including the inner circumferential surface of the receiving portion, and a section of reduced diameter that decreases in diameter from the front to the rear, including the inner circumferential surface of the crushing portion. The angle of inclination of the crushed portion with respect to the radial direction is greater than 5°, and the same-diameter section and the reduced-diameter section are connected in a smooth, hollow manner.

9. A protruding end having an opening that opens to one end in the axial direction, and a shaft portion having a hollow portion continuous with the protruding end, It comprises a flange portion that protrudes radially outward from the shaft portion, The shaft portion and the flange portion are a single, hollow member made of the same material. The shaft portion has a tapered portion that connects the tip end and the hollow portion. The tapered portion corresponds to the position where the flange portion is provided in the axial direction, and the hollow member has an inner diameter that gradually decreases from the hollow portion toward the tip.

10. With the aforementioned axial end facing the rear and the opposite side facing the front, The hollow member according to claim 9, wherein the rear end of the tapered portion is located further back than the front end of the flange portion.

11. The hollow member according to claim 9, wherein at least a portion of the tapered portion has a greater wall thickness than the protruding end portion and the flange portion.

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