Method for manufacturing hollow shaft member

Abstract

To provide a method for manufacturing a hollow shaft member, which needs no retrofitting of a flange part to a shank and is high in freedom of material selection.SOLUTION: A hollow workpiece 1c is an integrated article. A shank 2c and a flange part 3c are integrally connected. A molding hole 503 has a flange part guide part 504, a shank guide part 505, and a squeezed part 506. In a method for manufacturing a hollow shaft member 1d, a tapered part 211d is molded in a shank 2d of the hollow shaft member 1d by pushing the hollow workpiece 1c into the molding hole 503. The manufacturing method has a squeezing step. In the squeezing step, when the hollow workpiece 1c is pushed into the molding hole 503 through forging, the flange part 3c is guided by the flange part guide part 504 to stabilize a posture of the hollow workpiece 1c, squeezing is executed in an opening 40c of a hollow part 4c at the squeezed part 506, and the tapered part 211d is molded in the shank 2d.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to a method for manufacturing a flanged hollow shaft member. [Background technology]

[0002] A hollow shaft member with a flange is manufactured by, for example, shrinking a hollow pipe material by drawing (see, for example, Patent Document 1), and then joining a flange portion to the pipe material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-151755 Summary of the Invention [Problem to be solved by the invention]

[0004] However, this manufacturing method requires joining, or later attaching, a flange portion to a pipe material. This requires a large number of steps and makes the process complicated. Furthermore, the shaft portion must be made of pipe material. This limits the freedom of material selection. Therefore, the manufacturing method of a hollow shaft member disclosed herein aims to eliminate the need to later attach a flange portion to the shaft portion and increase the freedom of material selection. [Means for solving the problem]

[0005] (1) In order to solve the above-mentioned problems, the present disclosure provides a method for manufacturing a hollow shaft member, which includes forcing a hollow workpiece, the hollow workpiece including a shaft portion, a flange portion protruding radially outward from the shaft portion, and a hollow portion opening at one axial end of the shaft portion, into a forming hole of a die to form a tapered portion in the shaft portion, wherein the hollow workpiece is a single piece, and the shaft portion and the flange portion are integrally connected, and the direction in which the hollow workpiece is pushed into the forming hole in the axial direction of the shaft portion is referred to as the pushing direction, the front side of the pushing direction at the one axial end side is referred to as the front side, and the rear side of the pushing direction is referred to as the rear side. The forming hole has a flange guide portion, a shaft guide portion that is arranged on the front side of the flange guide portion and has an inner diameter smaller than that of the flange guide portion, and a narrowing portion that is arranged on the front side of the shaft guide portion and has an inner diameter that narrows from the rear side to the front side, and is characterized in that when the hollow workpiece is forced into the forming hole by forging, the flange guide portion is used to guide the flange portion to stabilize the posture of the hollow workpiece, while the narrowing process is performed on the opening of the hollow portion using the narrowing portion, and the tapered portion is formed on the shaft portion.

[0006] The hollow shaft member disclosed herein is a hollow shaft member with a flange. According to this configuration, the hollow workpiece is a single piece, and the shaft portion and the flange portion are integrally connected. Therefore, there is no need to later attach a flange portion to the shaft portion of the hollow workpiece. This reduces the number of manufacturing steps. Furthermore, the process can be simplified. According to this configuration, the material for the shaft portion can be selected from hollow pipe material, solid bulk material, etc. This allows for a high degree of freedom in material selection.

[0007] The forming hole of this configuration is equipped with a flange guide portion. Therefore, when the hollow workpiece is pushed into the forming hole, the flange guide portion guides the flange portion, thereby stabilizing the posture of the hollow workpiece. Therefore, the hollow workpiece can be aligned with the forming hole.

[0008] (1-1) In the above configuration (1), it is preferable that the hollow workpiece is manufactured from a solid bulk material. According to this configuration, the hollow shaft member can be manufactured from a solid bulk material, which is cheaper than a hollow pipe material. Therefore, the manufacturing cost can be reduced compared to when the hollow shaft member is manufactured from a pipe material.

[0009] (1-2) In any of the above configurations, the necking process is preferably performed by cold forging. With this configuration, the necking process can be performed on the opening of the hollow portion to form a tapered portion on the shaft portion without intentionally heating the hollow workpiece.

[0010] (1-3) In any of the above configurations, it is preferable that the flange guide continuously guides the flange while the tapered portion is being formed on the shaft. With this configuration, the posture of the hollow workpiece can be continuously stabilized while the tapered portion is being formed.

[0011] (1-4) In any of the above configurations, it is preferable that the narrowing portion has a plurality of hole-side tapered portions whose inner diameter decreases from the rear side to the front side, and that the plurality of hole-side tapered portions be arranged at predetermined intervals in the axial direction. According to this configuration, in the narrowing step, a tapered portion can be formed on the shaft portion by the hole-side tapered portions of the narrowing portion. Also, the plurality of tapered portions can be arranged intermittently on the shaft portion.

[0012] (1-5) In any of the above configurations, it is preferable that the hollow shaft member is an intermediate product of a rotor shaft of a motor. According to this configuration, when manufacturing the rotor shaft, it is not necessary to later attach a flange portion to the shaft portion of the hollow workpiece. This reduces the number of steps required to manufacture the rotor shaft. In addition, the process can be simplified.

[0013] (2) In any of the above configurations, the state before the shaft portion is pushed into the narrowing portion is defined as an unpressed state, and it is preferable that in the unpressed state, a gap of 1.0 mm or more and 2.5 mm or less is secured between the shaft portion and the shaft portion guide portion.

[0014] In the necking process, the shaft is compressed in the front-to-rear direction (axial direction) by the pushing load and the reaction force. This compression force makes it easier for the shaft to expand radially outward. As a result, the portion of the shaft that has not yet entered the internal space of the shaft guide (hereinafter referred to as the "shank guide unentered portion") is less likely to enter the internal space of the shaft guide. Furthermore, the portion of the shaft that has already entered the internal space of the shaft guide (hereinafter referred to as the "shank guide entered portion") is more likely to be pressed against the shaft guide.

[0015] In this regard, with this configuration, a gap is secured between the shaft and the shaft guide in an unpressed state. This gap can absorb the amount of expansion of the shaft. This makes it easier for the portion of the shaft guide that has not yet entered to enter the internal space of the shaft guide. Also, the portion of the shaft guide that has entered is less likely to be pressed against the shaft guide.

[0016] In the unpressed state, the gap is set to 1.0 mm or more. Therefore, compared to when the gap is less than 1.0 mm, the portion that has not yet entered the shank guide portion is more likely to enter the internal space of the shank guide portion. Also, the portion that has entered the shank guide portion is less likely to be pressed into contact with the shank guide portion. Also, in the unpressed state, the gap is set to 2.5 mm or less. Therefore, compared to when the gap exceeds 2.5 mm, the gap is more likely to be filled by the expanded portion of the shank after the narrowing process is completed. Therefore, the outer diameter of the shank portion can be stabilized.

[0017] (3) In any of the above configurations, it is preferable that the constriction angle, which is the inclination angle of the constricted nozzle with respect to the pushing direction, is less than 20°. If the constriction angle is large, the pushing load is more likely to act in the diameter reduction direction and less likely to act in the pushing direction. This makes it difficult for the hollow workpiece to advance in the pushing direction. In this regard, according to this configuration, the constriction angle is set to less than 20°. This makes it easier for the hollow workpiece to advance in the pushing direction compared to when the constriction angle is 20° or more.

[0018] (4) In any of the above configurations, it is preferable that the inner diameter of the hollow portion before the narrowing process is the pre-molding inner diameter, and the minimum outer diameter of the tapered portion after the narrowing process is the post-molding outer diameter, and that the pre-molding inner diameter is smaller than the post-molding outer diameter.

[0019] When the "inner diameter before forming ≧ outer diameter after forming", the amount of drawing increases. As the amount of drawing increases, it becomes more difficult for the hollow workpiece to move in the pushing direction. In this regard, with this configuration, the "inner diameter before forming < outer diameter after forming" is set. Therefore, compared to when the "inner diameter before forming ≧ outer diameter after forming", it becomes easier for the hollow workpiece to move in the pushing direction. Therefore, the overall length of the tapered section in the pushing direction can be increased. [Effects of the Invention]

[0020] According to the manufacturing method of the hollow shaft member of the present disclosure, it is not necessary to later attach a flange portion to the shaft portion, and the degree of freedom in material selection can be increased. [Brief explanation of the drawings]

[0021] [Figure 1] 1(A) to 1(E) are vertical cross-sectional views of a workpiece in each step of a method for manufacturing a rotor shaft. [Figure 2] FIG. 2 is a vertical cross-sectional view of a forging die at the beginning of a necking step in the manufacturing method of a hollow shaft member. [Figure 3] FIG. 3 is a vertical cross-sectional view of the forging die at the end of the process. [Figure 4]FIG. 4 is a contour diagram showing the analysis results (first stage) of Example 1. [Figure 5] FIG. 5 is a contour diagram showing the analysis results (second stage) of Example 1. [Figure 6] FIG. 6 is a contour diagram showing the analysis results (third stage) of Example 1. [Figure 7] FIG. 7 is a contour diagram showing the analysis results (first stage) of Example 2. [Figure 8] FIG. 8 is a contour diagram showing the analysis results (second stage) of Example 2. [Figure 9] FIG. 9 is a contour diagram showing the analysis results (third stage) of Example 2. [Figure 10] FIG. 10 is a contour diagram showing the analysis results (first stage) of Example 3. [Figure 11] FIG. 11 is a contour diagram showing the analysis results (second stage) of Example 3. [Figure 12] FIG. 12 is a contour diagram showing the analysis results (third stage) of Example 3. [Figure 13] FIG. 13 is a contour diagram showing the analysis results (first stage) of Example 4. [Figure 14] FIG. 14 is a contour diagram showing the analysis results (second stage) of Example 4. [Figure 15] FIG. 15 is a contour diagram showing the analysis results (third stage) of Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, an embodiment of a method for manufacturing a hollow shaft member according to the present disclosure will be described.

[0023] [Position of the manufacturing method of the hollow shaft member according to the present embodiment relative to the manufacturing method of the rotor shaft] First, the positioning of the manufacturing method of the hollow shaft member of this embodiment relative to the manufacturing method of the rotor shaft will be described. Figures 1(A) to 1(E) show vertical cross-sectional views (axial cross-sectional views) of a workpiece in each step of the manufacturing method of the rotor shaft.

[0024] Note that among the various parts of the workpieces 1a to 1d and the rotor shaft 1e, parts with the same numerical portion of the symbols (numeric portion, letter portion) correspond to each other. For example, the workpiece 1a in FIG. 1(A) corresponds to the workpiece 1b in FIG. 1(B). The dotted lines of the workpieces shown in FIG. 1(C) and FIG. 1(E) indicate the outline of the workpiece in the immediately preceding process. For example, the dotted line of the workpiece 1e shown in FIG. 1(E) indicates the outline of the workpiece 1d in FIG. 1(D). The up-down direction corresponds to the "axial direction" and "push-in direction" in this disclosure, the lower side corresponds to the "front side of the push-in direction" in this disclosure, and the upper side corresponds to the "rear side of the push-in direction" in this disclosure.

[0025] The rotor shaft manufacturing method progresses from Figure 1(A) to Figure 1(E). Workpiece 1a shown in Figure 1(A) is a solid bulk material cut out from a bar made of S35C (JIS G 4051). Workpiece 1b shown in Figure 1(B) is workpiece 1a that has been processed by forging or the like. Workpiece 1c shown in Figure 1(C) is workpiece 1b in which the inner surface of hollow portion 4b has been machined. Workpiece 1d shown in Figure 1(D) is workpiece 1c that has been subjected to a necking process.

[0026] FIG. 1(E) shows rotor shaft 1e. That is, rotor shaft 1e is a finished product (product), and workpieces 1a to 1d are intermediate products (items at intermediate stages in the manufacturing process). Corresponding to the configurations of workpieces 1c and 1d described below, workpiece 1b shown in FIG. 1(B) has a shaft portion 2b (columnar portion 20b, cylindrical portion 21b), a flange portion 3b, and a hollow portion 4b. Similarly, rotor shaft 1e shown in FIG. 1(E) has a shaft portion 2e (columnar portion 20e, cylindrical portion 21e), a flange portion 3e, and a hollow portion 4e.

[0027] The manufacturing method of the hollow shaft member of this embodiment is responsible for the necking process shown in Figure 1(D). This manufacturing method applies necking processing to the workpiece 1c shown in Figure 1(C). The workpiece 1c shown in Figure 1(C) (the workpiece before necking processing) is included in the concept of a "hollow workpiece" in this disclosure. The workpiece 1d (the workpiece after necking processing) shown in Figure 1(D) is included in the concept of a "hollow shaft member" (hollow shaft member with a flange) in this disclosure.

[0028] [Work configuration] Next, the configurations of the workpiece 1c (the workpiece before the manufacturing method of the hollow shaft member of this embodiment is performed) and the workpiece 1d (the workpiece after the manufacturing method of the hollow shaft member of this embodiment is performed) will be described.

[0029] The workpiece 1c (workpiece before necking) is a single piece and includes 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 includes a columnar portion 20c and a tubular portion 21c. The columnar portion 20c is a solid columnar portion with a constant diameter (the outer diameter is constant throughout the entire length in the vertical direction). The tubular portion 21c is a hollow cylinder with a constant diameter (the outer and inner diameters are constant throughout the entire length in the vertical direction). The tubular portion 21c is connected to the lower side of the columnar portion 20c. The tubular portion 21c has a larger outer diameter than the columnar portion 20c. The flange portion 3c is annular. The flange portion 3c protrudes radially outward from the outer peripheral surface of the lower end of the columnar portion 20c. The columnar portion 20c and the flange portion 3c are connected integrally. The hollow portion 4c is defined radially inside the cylindrical portion 21c. An opening 40c of the hollow portion 4c is formed at the lower end (one axial end) of the cylindrical portion 21c.

[0030] The workpiece 1d (the workpiece after the necking process) and the workpiece 1c (the workpiece before the necking process) have the same shape except for the cylindrical portions 21d and 21c. A tapered portion 211d is formed in the cylindrical portion 21d of the workpiece 1d by the necking process (the manufacturing method of the hollow shaft member of this embodiment).

[0031] That is, the tubular portion 21d includes a cylindrical portion 210d and a tapered portion 211d. The cylindrical portion 210d has a cylindrical shape with the same diameter. The tapered portion 211d is continuous with the lower side of the cylindrical portion 210d. The tapered portion 211d has a tapered shape (tapered cylindrical shape) in which the inner diameter and outer diameter decrease from the top to the bottom.

[0032] [Rotor shaft configuration] Next, the configuration of the rotor shaft 1e will be briefly described. The columnar portion 20e of the rotor shaft 1e shown in FIG. 1(E) is press-fitted radially inside an annular bearing (not shown). The columnar portion 20e is the "bearing press-fit portion." The cylindrical portion 210e is press-fitted radially inside an annular rotor (not shown). The cylindrical portion 210e is the "rotor press-fit portion." The upper portion of the tapered portion 211e is press-fitted into the annular bearing (not shown), and the lower portion is press-fitted into a seal ring (not shown). The upper portion of the tapered portion 211e is the "bearing press-fit portion." A coolant (oil, cooling water, etc.) is supplied to and discharged from the hollow portion 4e via an opening 40e.

[0033] [Forging die configuration] Next, the configuration of the forging die used in the manufacturing method of the hollow shaft member of this embodiment will be described. As described above, the manufacturing method of the hollow shaft member of this embodiment involves the necking process shown in FIG. 1(D). This manufacturing method applies necking processing to the workpiece 1c shown in FIG. 1(C). FIG. 2 shows a vertical cross-sectional view of the forging die at the beginning of the necking process. FIG. 3 shows a vertical cross-sectional view of the forging die at the end of the necking process.

[0034] 2 and 3, the forging die 5 is made of metal and includes a lower die (fixed die) 50, an upper die (movable die) 51, and a knockout pin 53. The lower die 50 includes a die 500, a die holder 501, and a die holder 502.

[0035] An accommodation hole 501A is formed in the die holder 501. The accommodation hole 501A passes through the die holder 501 in the vertical direction. The die holder 502 is disposed below the die holder 501. An accommodation hole 502A is formed in the die holder 502. The accommodation hole 502A passes through the die holder 502 in the vertical direction.

[0036] The die 500 includes a first die 500A, a second die 500B, and a pin guide 500C. The first die 500A has a cylindrical shape. The first die 500A is accommodated in an accommodation hole 501A of a die holder 501. A first molding hole 503A is defined at the radial center of the first die 500A. The first molding hole 503A passes through the first die 500A in the vertical direction.

[0037] The inner circumferential surface of the first molding hole 503A is provided, from top to bottom, with a flange portion guide portion 504 and a shaft portion guide portion 505. The flange portion guide portion 504 has a constant diameter (the inner diameter is constant over the entire length in the vertical direction). The shaft portion guide portion 505 is connected to the lower side of the flange portion guide portion 504 via a step portion 509. The shaft portion guide portion 505 has a constant diameter. The inner diameter of the shaft portion guide portion 505 is smaller than that of the flange portion guide portion 504.

[0038] The second die 500B is inserted into the receiving hole 502A of the die holder 502. The second die 500B is disposed below the first die 500A. A second molding hole 503B is defined at the radial center of the second die 500B. The second molding hole 503B passes through the second die 500B in the up-down direction. The second molding hole 503B is connected to the lower side of the first molding hole 503A.

[0039] The inner circumferential surface of the second molding hole 503B is provided, from top to bottom, with a narrowed mouth portion 506 and a pin guide portion 507. The narrowed mouth portion 506 is connected to the lower side of the shaft guide portion 505. A hole-side tapered portion 506a is arranged on the entire surface of the narrowed mouth portion 506. The inner diameter of the hole-side tapered portion 506a gradually decreases from top to bottom. In other words, the hole-side tapered portion 506a has a tapered surface shape. The pin guide portion 507 is connected to the lower side of the narrowed mouth portion 506.

[0040] The molding hole 503 is provided, from top to bottom, with the above-mentioned first molding hole 503A and second molding hole 503B. The inner circumferential surface of the molding hole 503 is provided, from top to bottom, with a flange guide portion 504, a shaft guide portion 505, a narrowed mouth portion 506, and a pin guide portion 507. The flange guide portion 504, the shaft guide portion 505, the narrowed mouth portion 506, and the pin guide portion 507 are linearly connected in the vertical direction.

[0041] The pin guide 500C is disposed below the second die 500B. A pin insertion hole 508 is defined in the pin guide 500C. The pin insertion hole 508 passes through the pin guide 500C in the up-down direction. The pin insertion hole 508 is connected to the underside of the pin guide portion 507.

[0042] The knockout pin 53 is made of metal and is inserted into the pin insertion hole 508 and the second molding hole 503B (the internal space of the pin guide portion 507) from below. The knockout pin 53 is reciprocable in the up and down direction (one axial direction). The knockout pin 53 is able to advance and retreat from the below with respect to the molding hole 503.

[0043] The upper die 51 is equipped with a metal punch 510. The punch 510 extends in the vertical direction. The punch 510 is capable of reciprocating in the vertical direction (one axial direction). The punch 510 is capable of advancing and retreating from above relative to the molding hole 503 (first molding hole 503A). The punch 510 and the knockout pin 53 face each other in the vertical direction.

[0044] [Method for manufacturing hollow shaft member of this embodiment] Next, a 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 necking process. In the necking process, a necking process is performed on the workpiece 1c shown in Figure 1(C) to manufacture the workpiece 1d shown in Figure 1(D).

[0045] Specifically, first, as shown in Fig. 2, the workpiece 1c is set in the forming hole 503 of the lower die 50. In the set state, the lower end (opening 40c) of the cylindrical portion 21c of the shaft portion 2c of the workpiece 1c abuts from above against the upper end of the narrowed mouth portion 506 (more specifically, the portion below the upper end (inside the hole-side tapered portion 506a)). This set state is included in the concept of the "unpressed-fit state" of the present disclosure.

[0046] In the unpressed state, the outer peripheral surface of the flange portion 3c abuts against the flange portion guide portion 504 of the forming hole 503 over the entire circumference. In the unpressed state, when viewed from above (axially), the shaft portion 2c is disposed radially inward of the flange portion guide portion 504. A gap C1 is defined over the entire circumference between the outer peripheral surface of the shaft portion 2c and the flange portion guide portion 504. The radial width of the gap C1 is constant over the entire circumference. Furthermore, in the unpressed state, when viewed from above, the shaft portion 2c is disposed radially inward of the shaft portion guide portion 505. A gap C2 is defined over the entire circumference between the outer peripheral surface of the shaft portion 2c and the shaft portion guide portion 505. The radial width of the gap C2 is constant over the entire circumference.

[0047] Thus, in the unpress-fitted state, the flange portion 3c abuts against the entire circumference of the forming hole 503. Furthermore, gaps C1 and C2 are defined from top to bottom between the workpiece 1c and the forming hole 503. Furthermore, the central axis A1 of the workpiece 1c is aligned with the hole axis A2 of the forming hole 503.

[0048] Next, as shown in FIGS. 2 and 3, punch 510 of upper die 51 is inserted into forming hole 503 from above. Punch 510 is pressed from above against the upper end of columnar portion 20c of shaft 2c and the upper surface of flange 3c. Punch 510 presses flange 3c downward along flange guide 504 until it reaches step 509. Until flange 3c reaches step 509, the portion of shaft 2c below flange 3c (tubular portion 21c) moves downward within the internal space of shaft guide 505. Lower portion 211c of tubular portion 21c is pressed into narrowing portion 506. As shown in FIGS. 2 and 3, the hole-side tapered portion 506a of the necking portion 506 draws the opening 40c, and the lower portion 211c is reduced in diameter and deformed, thereby forming a tapered portion 211d in the cylindrical portion 21d. When the punch 510 reaches the bottom dead center of its stroke, the lower end (opening 40d) of the tapered portion 211d abuts against the knockout pin 53. Additionally, the lower surface of the flange portion 3c abuts against the stepped portion 509. In this manner, the workpiece 1d is completed. In the subsequent ejection process, the knockout pin 53 ejects the workpiece 1d from the bottom to the top. The ejected workpiece 1d is then subjected to a predetermined process, thereby completing the rotor shaft 1e shown in FIG. 1(E).

[0049] [Action and effect] Next, the effects of the manufacturing method of the hollow shaft member of this embodiment will be described. As shown in FIG. 2, the workpiece 1c is a single piece, and the shaft portion 2c and the flange portion 3c are integrally connected. Therefore, there is no need to later attach the flange portion 3c to the shaft portion 2c of the workpiece 1c. This makes it possible to reduce the number of manufacturing steps. In addition, the process can be simplified.

[0050] As shown in Figure 1(A), the workpiece 1a is a solid bulk material. According to the manufacturing method of the hollow shaft member of this embodiment, the material of the shaft portion 2c can be selected from a hollow pipe material, a solid bulk material, or the like. This allows for a high degree of freedom in material selection.

[0051] 2 and 3, the forming hole 503 is provided with a flange portion guide portion 504. Therefore, when the workpiece 1c is pressed into the forming hole 503, the flange portion 3c is guided by the flange portion guide portion 504, thereby stabilizing the posture of the workpiece 1c. In other words, the workpiece 1c can be aligned with respect to the forming hole 503. Therefore, a gap C2 can be secured between the shaft portion guide portion 505 and the workpiece 1c all around the circumference.

[0052] As shown in Figures 1(A) and 1(C), in the manufacturing method of the hollow shaft member of this embodiment, the workpiece 1c is manufactured from the workpiece 1a, i.e., solid bulk material. Therefore, the workpiece 1d (i.e., the rotor shaft 1e) can be manufactured from solid bulk material, which is cheaper than hollow pipe material. Therefore, the manufacturing cost can be reduced compared to when the workpiece 1d is manufactured from pipe material.

[0053] 2 and 3 is performed by cold forging, which allows the opening 40c of the hollow portion 4c to be narrowed and the tapered portion 211d to be formed in the shaft portion 2d without intentionally heating the workpiece 1c.

[0054] 2 and 3, while the tapered portion 211d is being formed, the flange portion guide portion 504 continuously guides the flange portions 3c and 3d. Therefore, while the tapered portion 211d is being formed, the postures of the workpieces 1c and 1d can be continuously stabilized.

[0055] As shown in Figures 1(D) and 1(E), the workpiece 1d is an intermediate product of the rotor shaft 1e of the motor. Therefore, when manufacturing the rotor shaft 1e, there is no need to later attach the flange portion 3d to the shaft portion 2d of the workpiece 1d. This reduces the number of steps required to manufacture the rotor shaft 1e. It also simplifies the manufacturing process.

[0056] In the necking process shown in FIGS. 2 and 3, the shaft portion 2c is compressed in the vertical direction (axial direction) due to the pressing load when the shaft portion 2c is pressed into the necking portion 506 and the reaction force of the pressing load. This compression force tends to cause the tubular portion 21c of the shaft portion 2c, in particular, to expand radially outward. As a result, the shaft portion guide portion unentered portion 2ca (the portion of the tubular portion 21c that has not yet entered the internal space of the shaft portion guide portion 505) shown in FIG. 2 of the tubular portion 21c is less likely to enter the internal space of the shaft portion guide portion 505. Furthermore, the shaft portion guide portion entering portion 2cb (the portion of the tubular portion 21c that has already entered the internal space of the shaft portion guide portion 505) shown in FIG. 2 is more likely to be pressed against the shaft portion guide portion 505.

[0057] In this regard, according to the necking process of this embodiment, as shown in FIG. 2, a gap C2 is secured between the tubular portion 21c and the shaft guide portion 505 in the unpressed state. The gap C2 can absorb the amount of expansion of the tubular portion 21c. This makes it easier for the shaft guide portion unentered portion 2ca to enter the internal space of the shaft guide portion 505. In addition, the shaft guide portion entering portion 2cb is less likely to be pressed against the shaft guide portion 505.

[0058] In the unpressed state, the gap C2 (the radial width of the gap C2) is set to 1.0 mm or more. Therefore, compared to when the gap C2 is less than 1.0 mm, the shaft guide portion unentered portion 2ca is more likely to enter the internal space of the shaft guide portion 505. Also, the shaft guide portion entering portion 2cb is less likely to be pressed against the shaft guide portion 505. Furthermore, in the unpressed state, the gap C2 is set to 2.5 mm or less. Therefore, compared to when the gap C2 exceeds 2.5 mm, after the narrowing process is completed, the gap C2 is more likely to be filled by the expanded portion of the tubular portion 21c. Therefore, the outer diameter of the tubular portion 21c can be stabilized.

[0059] The narrowing angle θ1 shown in FIG. 2 is the inclination angle of the narrowed nozzle portion 506 (hole-side tapered portion 506a) relative to the axial direction (pushing direction) of the central axis A1 and hole axis A2. As the narrowing angle θ1 increases, the pushing load acts more easily in the diameter reduction direction and less easily in the pushing direction. This makes it difficult for the workpiece 1c to advance in the pushing direction. In this regard, in the narrowing process of this embodiment, the narrowing angle θ1 is set to less than 20°. This makes it easier for the workpiece 1c to advance in the pushing direction compared to when the narrowing angle θ1 is 20° or more.

[0060] The inner diameter of the hollow portion 4c before the narrowing process shown in Figure 2 (the inner diameter of the cylindrical portion 210d after the narrowing process shown in Figure 3) is set as the pre-molding inner diameter D1, and the minimum outer diameter of the tapered portion 211d after the narrowing process shown in Figure 3 (the outer diameter of the lower end of the tapered portion 211d) is set as the post-molding outer diameter D2, and the pre-molding inner diameter D1 is set to be smaller than the post-molding outer diameter D2.

[0061] When the "inner diameter before forming D1 ≧ outer diameter after forming D2", the amount of squeezing increases. As the amount of squeezing increases, it becomes more difficult for the workpiece 1c to move in the pushing direction. In this regard, in the necking process of this embodiment, the "inner diameter before forming D1 < outer diameter after forming D2" is set. Therefore, compared to when the "inner diameter before forming D1 ≧ outer diameter after forming D2", the workpiece 1c moves more easily in the pushing direction. Therefore, the overall length in the vertical direction of the tapered portion 211d shown in Figure 3 can be increased.

[0062] [others] The above describes an embodiment of the method for manufacturing a hollow shaft member according to the present disclosure. However, the embodiment is not particularly limited to the above embodiment. Various modifications and improvements that can be made by those skilled in the art are also possible.

[0063] As shown in Figures 2 and 3, the narrowed mouth portion 506 has a single hole-side tapered portion 506a. However, there is no particular limitation on the number of hole-side tapered portions 506a arranged in the narrowed mouth portion 506. There may be a single or multiple. For example, multiple hole-side tapered portions 506a may be arranged at predetermined intervals in the axial direction. In this way, multiple tapered portions 211d can be formed on the shaft portion 2d by each of the multiple hole-side tapered portions 506a. In other words, multiple tapered portions 211d can be arranged intermittently on the shaft portion 2d. The narrowing angle θ1 of the multiple hole-side tapered portions 506a may be the same or different. The same applies to the inclination angles of the multiple tapered portions 211d (angles corresponding to the narrowing angle θ1).

[0064] The workpiece 1c shown in FIG. 1(C) may be manufactured from the workpiece 1a, i.e., a solid bulk material, or from a hollow pipe material. The necking process shown in FIGS. 2 and 3 may be performed by cold forging, warm forging, or hot forging. The flange portion guide portion 504 may continuously guide the flange portions 3c and 3d while the tapered portion 211d is being formed on the shaft portions 2c and 2d. Alternatively, the flange portion guide portion 504 may intermittently or temporarily guide the flange portions 3c and 3d while the tapered portion 211d is being formed on the shaft portions 2c and 2d.

[0065] The workpiece 1d shown in Fig. 1(D) may or may not be an intermediate product of a rotor shaft 1e of a motor. It may also be an intermediate product of a flanged hollow shaft member other than the rotor shaft 1e. The workpiece 1d shown in Fig. 1 may also be a finished product.

[0066] In the non-press-fit state shown in FIG. 2, a gap C2 may or may not be provided between the cylindrical portion 21c and the shaft portion guide portion 505. If the gap C2 is provided, the radial width of the gap C2 may be uniform over the entire circumference or may be non-uniform. If the radial width of the gap C2 is uniform over the entire circumference, the radial width may be equal to or greater than 1.0 mm, or may be less than 1.0 mm. If the radial width of the gap C2 is uniform over the entire circumference, the radial width may be equal to or less than 2.5 mm, or may exceed 2.5 mm.

[0067] The angle of constriction θ1 shown in Figures 2 and 3 is not particularly limited. The angle of constriction θ1 may be less than 20° or may be equal to or greater than 20°. The relationship in magnitude between the pre-molding inner diameter D1 and the post-molding outer diameter D2 is not particularly limited. It may be "pre-molding inner diameter D1 ≧ post-molding outer diameter D2" or "pre-molding inner diameter D1 < post-molding outer diameter D2."

[0068] The columnar portion 20e of the rotor shaft 1e shown in FIG. 1(E) may be solid or hollow. For example, the columnar portion 20e may have an axial through-hole that penetrates the columnar portion 20e in the vertical direction and communicates with the hollow portion 4e. A coolant may flow through the axial through-hole and the hollow portion 4e. A radial through-hole may be provided at least either between the axial through-hole and the outer peripheral surface of the columnar portion 20e or between the hollow portion 4e and the tapered portion 211e. A coolant may be supplied to a bearing (not shown) through the radial through-hole.

[0069] There is no particular limitation on whether or not a core metal (not shown) is provided in the die 500 of the lower mold 50 of the forging die 5. For example, a core metal for forming the inner peripheral surface of the tapered portion 211d may be provided on the upper surface of the knockout pin 53 shown in Figures 2 and 3. This can improve the accuracy of the inner diameter of the tapered portion 211d. [Example]

[0070] A CAE (Computer Aided Engineering) analysis performed on the manufacturing method of the hollow shaft member of the present disclosure will be described below with reference to Figures 1 to 3. In the analysis, the following four levels (Examples 1 to 4) were set, and the manufacturing method of the hollow shaft member described above (narrowing process) was simulated.

[0071] [Regarding Examples 1 to 4] In each of Examples 1 to 4, a workpiece was used that was made of the same material and had the same structure as the workpiece 1c shown in Fig. 1(C). For the workpiece of Example 1, the radial width of the gap C2 shown in Figs. 2 and 3 was 1.0 mm (in the range of 1.0 mm to 2.5 mm), the aperture angle θ1 was 7° (in the range of less than 20°), the pre-forming inner diameter (diameter) D1 was φ29.5 mm, and the post-forming outer diameter (diameter) D2 was φ30.2 mm (pre-forming inner diameter D1 < post-forming outer diameter D2).

[0072] The only difference between the workpiece of Example 2 and the workpiece of Example 1 is the radial width of the gap C2. The radial width of the gap C2 of the workpiece of Example 2 is 0.3 mm (outside the range of 1.0 mm or more and 2.5 mm or less). The only difference between the workpiece of Example 3 and the workpiece of Example 1 is the aperture angle θ1. The aperture angle θ1 of the workpiece of Example 3 is 20° (outside the range of less than 20°).

[0073] The only difference between the workpiece of Example 4 and the workpiece of Example 1 is the relationship between the pre-forming inner diameter D1 and the post-forming outer diameter D2. The pre-forming inner diameter D1 of the workpiece of Example 4 is φ29.5 mm, and the post-forming outer diameter D2 is φ27.8 mm. In other words, in the case of the workpiece of Example 4, the relationship "pre-forming inner diameter D1 < post-forming outer diameter D2" does not hold.

[0074] [Analysis conditions] The analysis was performed using FORGE (Transvalor), a plastic processing simulation software. In the analysis, the stress distribution in the workpiece during the necking process was calculated. The forming speed (lowering speed of the punch 510) was set to 10 mm / s. The temperature of the entire workpiece and the forging die at the start of the necking process was set to 20°C. The coefficient of friction μ between the workpiece and the forging die was set to 0.05.

[0075] [About the analysis results] Example 1 Figures 4 to 6 show the analysis results (first to third stages) of Example 1 (Level 1) in contour diagrams. Similar to Figures 2 and 3, Figures 4 to 6 are vertical cross-sectional views. As shown in the bar at the left end of Figure 4, dark black areas are areas with low stress (compressive stress). Light black areas are areas with high stress. Stress increases from dark (black) to light (white).

[0076] As shown in Figure 4 (first stage, start of necking process) and Figure 2, in the non-press-fit state, the outer peripheral surface of the flange portion 3c abuts against the flange portion guide portion 504 of the forming hole 503 all around. In addition, gaps C1 and C2 are defined between the workpiece 1c and the forming hole 503. In addition, the central axis A1 of the workpiece 1c is aligned with the hole axis A2 of the forming hole 503.

[0077] As shown in Figure 5 (second stage, during necking), the third stage of Figure 6 (necking completed), and Figures 2 and 3, as the necking process progresses, the punch 510 pushes the flange portion 3c downward along the flange portion guide portion 504 until it reaches the step portion 509. The lower portion 211c of the tubular portion 21c is pushed into the necking portion 506. The hole-side tapered portion 506a of the necking portion 506 causes the lower portion 211c to undergo diameter reduction deformation. This diameter reduction deformation forms a tapered portion 211d in the tubular portion 21d.

[0078] As shown in Figures 4 to 6, 2, and 3, as the necking process progresses, stress is gradually applied to the workpiece 1c. Furthermore, higher stress is applied to the cylindrical portion 21c than to the columnar portion 20c. Furthermore, high stress is applied to the cylindrical portion 21c, particularly to the lower portion 211c (i.e., the tapered portion 211d). Thus, according to Example 1, although stress is applied to the workpiece 1c as the necking process progresses, the necking process can be performed on the workpiece 1c without any delay.

[0079] Example 2 Figures 7 to 9 show the analysis results (first to third stages) of Example 2 (Level 2) in contour diagrams. The diagrams can be read in the same way as Figures 4 to 6 above. As shown in Figures 7 to 9, as in Figures 4 to 6, stress is gradually applied to the workpiece as the necking process progresses.

[0080] 6 and 9 (referring to FIGS. 2 and 3), stress is concentrated locally near the upper end of the cylindrical portion 210d (the base of the flange portion 3d) in Fig. 9. This shows that, since the radial width of the gap C2 in Example 2 is 0.3 mm (outside the range of 1.0 mm to 2.5 mm), it is more difficult for the shaft guide portion unentered portion 2ca shown in Fig. 2 to enter the gap C2 than in Example 1.

[0081] Example 3 Figures 10 to 12 show the analysis results (first to third stages) of Example 3 (Level 3) in contour diagrams. The diagrams can be read in the same way as Figures 4 to 6 above. As shown in Figures 10 to 12, as in Figures 4 to 6, stress is gradually applied to the workpiece as the necking process progresses.

[0082] 4 and 10 (referring to FIGS. 2 and 3), the angle of inclination (narrowing angle θ1) of the narrowed mouth portion 506 (hole-side tapered portion 506a) is larger in Example 3 (FIG. 10) than in Example 1 (FIG. 4). Accordingly, the vertical length of the narrowed mouth portion 506 (hole-side tapered portion 506a) is shorter in Example 3 than in Example 1.

[0083] Comparing Figures 5 and 11 (using Figures 2 and 3), it can be seen that, compared to Example 1 (Figure 5), Example 3 (Figure 11) has a larger narrowing angle θ1, resulting in higher overall stress during the narrowing process.

[0084] Example 4 Figures 13 to 15 show the analysis results (first to third stages) of Example 4 (Level 4) in contour diagrams. The diagrams can be read in the same way as Figures 4 to 6 above. As shown in Figures 13 to 15, as in Figures 4 to 6, stress is gradually applied to the workpiece as the necking process progresses.

[0085] As shown in Figures 6 and 15 (referring to Figures 2 and 3), in both Example 1 (Figure 6) and Example 4 (Figure 15), the stress is high in the upper part of the cylindrical portion 210d at the completion of the necking process. However, it can be seen that the section where high stress is distributed is wider in Example 4 (Figure 15) than in Example 1 (Figure 6).

[0086] From the above analysis, it was found that necking processing was possible in any of Examples 1 to 4 (Levels 1 to 4). Among Examples 1 to 4, it was found that Example 1 in particular was able to suppress both the stress applied to the entire workpiece and the stress applied locally to the workpiece. [Explanation of symbols]

[0087] 1a to 1b: workpiece, 1c: workpiece (hollow workpiece), 1d: workpiece (hollow shaft member), 1e: rotor shaft, 2c: shaft portion, 20c: columnar portion, 21c: cylindrical portion, 211c: lower portion, 21d: cylindrical portion, 210d: cylindrical portion, 211d: tapered portion, 3c: flange portion, 4c: hollow portion, 40c: opening, 5: forging die, 50: lower die, 500: die, 500A: first die, 500B: second die, 500C: pin guide, 501: die holder, 50 1A: accommodation hole, 502: die holder, 502A: accommodation hole, 503: molding hole, 503A: first molding hole, 503B: second molding hole, 504: flange guide portion, 505: shaft guide portion, 506: necking portion, 506a: hole side tapered portion, 507: pin guide portion, 508: pin insertion hole, 509: step portion, 51: upper die, 510: punch, 53: knockout pin, A1: center axis, A2: hole axis, C1: gap, C2: gap, D1: inner diameter before molding, D2: outer diameter after molding

Claims

1. A method for manufacturing a hollow shaft member, comprising: forcing a hollow workpiece having a shaft portion, a flange portion protruding radially outward from the shaft portion, and a hollow portion opening at one axial end of the shaft portion into a forming hole of a die, thereby forming a tapered portion in the shaft portion; The hollow workpiece is a one-piece body, and the shaft portion and the flange portion are integrally connected, The pushing direction of the hollow workpiece into the forming hole in the axial direction of the shaft portion is defined as the pushing direction, the front side of the axial end side in the pushing direction is defined as the front side, and the rear side of the pushing direction is defined as the rear side. the forming hole has a flange portion guide portion, a shaft portion guide portion that is disposed on the front side of the flange portion guide portion and has an inner diameter smaller than that of the flange portion guide portion, and a narrowing portion that is disposed on the front side of the shaft portion guide portion and has an inner diameter that decreases from the rear side to the front side, A method for manufacturing a hollow shaft member, characterized by including a necking process in which, when forging the hollow workpiece into the forming hole, the flange portion is guided by the flange portion guide portion to stabilize the posture of the hollow workpiece, while the necking portion performs necking processing on the opening of the hollow portion, thereby forming the tapered portion on the shaft portion.

2. The state before the shaft portion is pressed into the narrowed mouth portion is defined as an unpressed state, The method for manufacturing a hollow shaft member according to claim 1, wherein a gap of 1.0 mm or more and 2.5 mm or less is secured between the shaft portion and the shaft portion guide portion in the non-press-fit state.

3. The method for manufacturing a hollow shaft member according to claim 1, wherein a narrowing angle, which is an inclination angle of the narrowed portion with respect to the pushing direction, is less than 20°.

4. The inner diameter of the hollow portion before the narrowing process is defined as a pre-molding inner diameter, and the minimum outer diameter of the tapered portion after the narrowing process is defined as a post-molding outer diameter, The method for manufacturing a hollow shaft member according to claim 1 , wherein the inner diameter before molding is smaller than the outer diameter after molding.

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