Ball screw device and method for manufacturing screw shaft

Abstract

To provide a method for manufacturing a screw shaft in which a recess part for housing a piece is not formed.SOLUTION: A method for manufacturing a screw shaft comprises a groove surface forming step of cutting a raw material with a helical cutter to form an annular groove surface. An outer peripheral surface of a raw material is formed into a cylindrical shape with a first center line of the raw material as a center. The helical cutter has a cutting blade that protrudes from the outer peripheral surface of the shaft and cuts the outer peripheral surface of the material with its cutting edge. In the groove surface forming step, the relative positions of the helical cutter and the raw material are changed so that the helical cutter moves circumferentially along the outer peripheral surface of the raw material, to form an annular groove surface on the outer peripheral surface. Further, the helical cutter is gradually moved relative to the raw material in one axial direction parallel to the first center line to form an outer peripheral raceway surface. The helical cutter is gradually moved relative to the raw material in the other axial direction to form a circulation groove surface.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a method for manufacturing a screw shaft of a ball screw device. [Background technology]

[0002] The ball screw device of the following patent document includes a nut, a screw shaft penetrating the nut, a plurality of balls arranged between the nut and the screw shaft, and a circulation part. An inner peripheral raceway surface is formed on the inner peripheral surface of the nut. An outer peripheral raceway surface facing the inner peripheral raceway surface is formed on the outer peripheral surface of the screw shaft. A spiral track is formed between the inner peripheral raceway surface and the outer peripheral raceway surface. The plurality of balls are arranged on the track and move in a spiral direction along the track. The circulation part is a device that returns balls that have moved from one end of the track to the other end of the track to one end of the track. The circulation part of the following patent document is a top that returns the balls by one lead. The top is attached to a recess formed on the outer peripheral surface of the screw shaft. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-175406 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, if the machining precision of the recess is low, the circulation groove surface provided on the top and the outer circumferential raceway surface of the screw shaft will not coincide, which will result in the balls not moving smoothly and the operability of the ball screw device being reduced.

[0005] The present disclosure has been made in consideration of the above, and aims to provide a manufacturing method for a screw shaft of a ball screw device that does not form a recess for accommodating a top. [Means for solving the problem]

[0006] In order to achieve the above object, a manufacturing method of a screw shaft of a ball screw device according to one embodiment of the present disclosure includes a groove surface forming step of cutting an outer circumferential surface of a material of the screw shaft with a helical cutter to form an annular groove surface on the outer circumferential surface. The outer circumferential surface of the material is formed cylindrically with a first center line of the material as a center. The annular groove surface has an outer circumferential raceway surface and a circulating groove surface. The helical cutter has a rotatable shaft and cutting blades that protrude from the outer circumferential surface of the shaft, are arranged in a circumferential direction on the outer circumferential surface of the shaft, and cut the outer circumferential surface of the material with their cutting edges. The groove surface forming step changes the relative positions of the helical cutter and the material so that the helical cutter moves in the circumferential direction along the outer circumferential surface of the material to form the annular groove surface on the outer circumferential surface of the material. Furthermore, when the helical cutter moves circumferentially along the outer peripheral surface of the workpiece, the relative positions of the helical cutter and the workpiece are changed so that the helical cutter gradually moves in one axial direction parallel to the first center line relative to the workpiece, thereby forming the outer peripheral orbital surface, and the relative positions of the helical cutter and the workpiece are changed so that the helical cutter gradually moves in the other axial direction relative to the workpiece, thereby forming the circulating groove surface.

[0007] According to the present disclosure, a circulating groove surface is formed on the screw shaft, which prevents the circulating groove surface of the top from matching with the outer circumferential raceway surface of the screw shaft, preventing the balls from moving smoothly.

[0008] In addition, in the manufacturing method of the screw shaft of the ball screw device, when the outer circumferential raceway surface is formed in the groove surface forming process, the angle at which the cutting blade contacts the material may be maintained, and the outer circumferential raceway surface may be formed to have the same shape as the cutting edge of the cutting blade.

[0009] In the method for manufacturing the screw shaft of the ball screw device, the width of the cutting blade gradually increases from the cutting edge toward the shaft. When the circulation groove surface is formed in the groove surface forming step, the cutting blade is cut deeper than the outer circumferential raceway surface while maintaining an angle at which the cutting blade contacts the material.

[0010] According to this configuration, the circulating groove surface is wider than the outer circumferential raceway surface.

[0011] In addition, in the manufacturing method of the screw shaft of the ball screw device, when the circulation groove surface is formed in the groove surface forming step, the relative positions of the helical cutter and the material are changed so as to change the angle at which the cutting blade contacts the material, thereby forming the circulation groove surface wider than the width of the cutting blade. Alternatively, in the manufacturing method of the screw shaft of the ball screw device, when the circulation groove surface is formed in the groove surface forming step, the relative positions of the helical cutter and the material are changed so as to move the position of the cutting blade relative to the material in the axial direction, thereby forming the circulation groove surface wider than the width of the cutting blade.

[0012] According to the above configuration, the time and effort required for replacing the helical cutter with one having a wider cutting blade can be eliminated, and the productivity of the screw shaft is improved.

[0013] In the method for manufacturing the screw shaft of the ball screw device, the circulating groove surface is wider than the outer circumferential raceway surface. A junction where a start point and an end point of the cutting portion in the groove surface forming step join together is on the circulating groove surface.

[0014] According to the manufacturing method of the present disclosure, a step may be formed at the junction. According to the above-mentioned configuration, a step may be formed on the circulation groove surface. On the other hand, the circulation groove surface is wide, and a gap is generated between the circulation groove surface and the ball. Therefore, even if a step is formed on the circulation groove surface, the movement of the ball is unlikely to be hindered.

[0015] In the method for manufacturing the screw shaft of a ball screw device, the cutting edge of the cutting blade may be in a Gothic arc shape.

[0016] The method for manufacturing the screw shaft of the ball screw device further includes a heat treatment step of heat treating the material after the groove surface forming step.

[0017] When a screw shaft having a recess is heat-treated, cracks (so-called "quench cracks") may occur at the edge of the opening of the recess. On the other hand, according to the present disclosure, the screw shaft does not have a recess. Therefore, quench cracks can be avoided. Furthermore, the heat treatment provides the screw shaft with the desired hardness and toughness.

[0018] The method for manufacturing the screw shaft of the ball screw device further includes, after the heat treatment step, a grinding step of grinding the outer circumferential raceway surface.

[0019] According to the above-described configuration, the movement of the balls becomes smoother, and the operability of the ball screw device is improved. Effect of the Invention

[0020] According to the present disclosure, a screw shaft that does not require a recess can be manufactured. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a cross-sectional view of a ball screw device according to an embodiment. [Diagram 2] FIG. 2 is a view of the screw shaft of the embodiment as viewed from the outer periphery side. [Diagram 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Diagram 5] FIG. 5 is a flow diagram showing a method for manufacturing the screw shaft according to the embodiment. [Figure 6] FIG. 6 is a diagram showing a state in which a material is attached to a machining center in a preparation step according to the embodiment. [Figure 7] FIG. 7 is a side view of the helical cutter according to the embodiment. [Figure 8] FIG. 8 is an enlarged view of a cutting blade according to an embodiment. [Figure 9] FIG. 9 is a diagram showing how an annular groove surface (outer peripheral raceway surface) is formed on the outer peripheral surface of a material in an embodiment. [Figure 10]FIG. 10 is a diagram showing how an annular groove surface (circulation groove surface) is formed on the outer circumferential surface of a material in an embodiment. [Figure 11] FIG. 11 is a diagram showing a state in which an outer circumferential raceway surface is formed on the outer circumferential surface of a material in the embodiment. [Figure 12] FIG. 12 is a diagram showing a state in which a circulating groove surface is formed on the outer peripheral surface of a material in an embodiment. [Figure 13] FIG. 13 is an enlarged view showing a state in which a circulating groove surface is being formed in a groove surface forming step according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the following modes for carrying out the invention (hereinafter, referred to as embodiments). Furthermore, the components in the following embodiments include those that a person skilled in the art can easily imagine, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the components disclosed in the following embodiments can be appropriately combined.

[0023] Fig. 1 is a cross-sectional view of a ball screw device of an embodiment. Fig. 2 is a view of the screw shaft of the embodiment as viewed from the outer periphery side. Fig. 3 is a cross-sectional view taken along line III-III in Fig. 2. Fig. 4 is a cross-sectional view taken along line IV-IV in Fig. 2. Before describing a manufacturing method for the screw shaft of the embodiment, a ball screw device 100 including a screw shaft 1 will be briefly described.

[0024] As shown in Fig. 1, a ball screw device 100 of the embodiment includes a nut 101, a screw shaft 1 arranged inside the nut 101, and a plurality of balls 110 (not shown in Fig. 1, see Figs. 3 and 4). The nut 101 is formed in a cylindrical shape centered on a center line O1 of the screw shaft 1. An inner peripheral surface 102 of the nut 101 is formed with a spiral inner peripheral raceway surface 103. The inner peripheral raceway surface 103 extends continuously from one end of the inner peripheral surface 102 to the other end.

[0025] The screw shaft 1 is a cylindrical shaft tube centered on a center line O1. Other components (not shown) can be fitted to an inner peripheral surface 6 of the screw shaft 1. Note that the present disclosure may be a columnar (solid) screw shaft 1.

[0026] As shown in Fig. 2, four annular groove surfaces 3 are provided on the outer peripheral surface 2 of the screw shaft 1. The four annular groove surfaces 3 are arranged offset in a direction parallel to the center line O1. The annular groove surface 3 has an outer peripheral raceway surface 4 and a circulating groove surface 5. That is, in this embodiment, four outer peripheral raceway surfaces 4 and four circulating groove surfaces 5 (only three are shown in Fig. 2) are formed on the outer peripheral surface 2 of the screw shaft 1.

[0027] The outer circumferential raceway surface 4 is a spiral groove surface extending in the same direction as the inner circumferential raceway surface 103 (see FIG. 1). The outer circumferential raceway surface 4 extends approximately one revolution in the circumferential direction around the center line O1. A raceway is formed between the outer circumferential raceway surface 4 and the inner circumferential raceway surface 103, and balls 110 are arranged on this raceway. In this embodiment, since there are four outer circumferential raceway surfaces 4, the number of raceways (the number of circuits) is also four. However, in the present disclosure, the number of raceways (the number of circuits) may be one or more, and is not limited to four as exemplified in the embodiment.

[0028] The circulation groove surface 5 is an S-shaped groove surface. One end and the other end of the S-shaped direction along the circulation groove surface 5 form an inlet / outlet 5a that connects to one end or the other end of the outer circumferential track surface 4. As a result, the balls 110 that have moved from one end of the track to the other end move along the circulation groove surface 5 and circulate to one end of the track.

[0029] As shown in Fig. 3, the groove shape of the outer peripheral raceway surface 4 is a Gothic arc shape. As shown in Fig. 4, the groove shape of the circulating groove surface 5 is formed in a Gothic arc shape. In the present disclosure, the groove shapes of the outer peripheral raceway surface 4 and the circulating groove surface 5 are not limited to the examples shown in the embodiment.

[0030] As shown in Figures 3 and 4, the circulation groove surface 5 is formed deeper than the outer peripheral raceway surface 4. The groove width of the circulation groove surface 5 is greater than the groove width of the outer peripheral raceway surface 4. The depth of the circulation groove surface 5 gradually increases from the entrance 5a (see Figure 2) toward the center 5b. This allows the balls 110 moving along the circulation groove surface 5 to move without getting caught on the threads of the inner peripheral raceway surface 103. Next, a manufacturing method of the screw shaft 1 will be described.

[0031] Fig. 5 is a flow diagram showing a method for manufacturing the screw shaft of the embodiment. As shown in Fig. 5, the method for manufacturing the screw shaft 1 of the embodiment includes a preparation step S1, a groove surface forming step S2, a heat treatment step S3, and a grinding step S4.

[0032] The preparation step S1 is a step of preparing a material 10 for the screw shaft 1 and attaching the material 10 to a machining center 20 (see FIG. 6). As shown in FIG. 5, the material 10 is a cylindrical steel material centered on a first center line O10. A direction parallel to the first center line O10 is referred to as an axial direction. Note that the material of the present disclosure may be formed of a metal material other than steel, and is not particularly limited.

[0033] The outer peripheral surface 11 and the inner peripheral surface 12 of the material 10 have a circular cross-sectional shape. The material 10 also has a first end surface 13 facing one side in the axial direction and a second end surface 14 facing the other side in the axial direction. The inner peripheral surface 12 of the material 10 is already the same as the inner peripheral surface 6 of the screw shaft 1, so it is not particularly processed in this manufacturing method. However, in this disclosure, the inner peripheral surface 12 of the material 10 may be processed as appropriate. That is, the inner peripheral surface 12 of the material 10 may be processed before the start of the manufacturing method of the screw shaft (before the preparation step S1), or the inner peripheral surface 12 of the material 10 may be processed after the manufacturing method of the screw shaft is completed (after the grinding step S4). Alternatively, a process of processing the inner peripheral surface 12 of the material 10 may be inserted between each process of the manufacturing method of the screw shaft. That is, in this disclosure, there is no particular restriction on the presence or absence of processing of the inner peripheral surface 12 of the material 10, the processing method, and the order of processing.

[0034] Fig. 6 is a diagram showing a state in which a material is attached to a machining center in a preparation process of an embodiment. Fig. 7 is a side view of the helical cutter of the embodiment. Fig. 8 is an enlarged view of a cutting blade of the embodiment. As shown in Fig. 6, the machining center 20 includes a helical cutter 21, a drive device (not shown) that drives (rotates) the helical cutter 21, a lifting device (not shown) that supports the drive device (not shown), a posture changing device 30, and a table device (not shown) that moves the posture changing device 30. The lifting device (not shown), the posture changing device 30, and the table device (not shown) are devices for changing the relative positions of the helical cutter 21 and the material 10.

[0035] 7, the helical cutter 21 is a cutting tool having a cylindrical shaft 22 centered on a center line O22 and a plurality of cutting blades 23 provided at the tip of the shaft 22. The cutting blades 23 protrude from the outer circumferential surface of the shaft 22. The plurality of cutting blades 23 are disposed in the circumferential direction with respect to the outer circumferential surface of the shaft 22.

[0036] The imaginary line O23 shown in Fig. 8 is an imaginary straight line that is perpendicular to the center line O22 (see Fig. 7) and passes through the center of the cutting blade 23 in the width direction (parallel to the center line O22). The cutting blade 23 is formed symmetrically in the width direction with the imaginary line O23 as a boundary. The width W23 of the cutting blade 23 gradually increases from the cutting edge 23b toward the base 23a. The cutting edge 23b of the cutting blade 23 has a Gothic arc shape.

[0037] When a driving device (not shown) is driven, the helical cutter 21 rotates around the center line O22 of the shaft 22. Each of the multiple cutting blades 23 moves in the circumferential direction around the center line O22. As a result, the cutting edges 23b of the multiple cutting blades 23 scrape off the outer peripheral surface 11 of the material 10, and an annular groove surface 3 is formed on the outer peripheral surface 11 of the material 10.

[0038] 6, the lifting device (not shown) is a device that moves the helical cutter 21. The direction in which the helical cutter 21 can be moved by the lifting device (not shown) is the third direction Z. The third direction Z is a direction parallel to the center line O22. In this embodiment, the center line O22 extends in the vertical direction.

[0039] The table device (not shown) is a device that moves the posture changing device 30 in the first direction X and the second direction Y. The imaginary plane K20 shown in Fig. 6 is an imaginary plane perpendicular to the third direction Z. In other words, the imaginary plane K20 is a horizontal plane. The first direction X is a direction parallel to the imaginary plane K20. The second direction Y is a direction parallel to the imaginary plane K20 and perpendicular to the first direction X when viewed from the third direction Z.

[0040] The posture changing device 30 includes a base 31 placed on a table device (not shown), a rotating unit 32 supported by the base 31, a mounting base 33 supported by the rotating unit 32, a first drive unit (not shown) that rotates the rotating unit 32, and a second drive unit (not shown) that rotates the mounting base 33. The base 31 supports the rotating unit 32 so as to be rotatable about a center line O32. The rotating unit 32 supports the mounting base 33 so as to be rotatable about a center line O33.

[0041] The installation table 33 has a circular installation surface 34 centered on a center line O33. A chuck 35 for fixing the raw material 10 is provided on the installation surface 34. In this embodiment, the chuck 35 abuts against the inner peripheral surface 12 of the raw material 10 to fix the raw material 10. Note that in the present disclosure, the raw material 10 may be fixed by the chuck 35 abutting against the outer peripheral surface 11 of the raw material 10. In addition, when the screw shaft (raw material) is solid, the chuck 35 abuts against the outer peripheral surface 11 of the raw material 10 to fix the raw material 10.

[0042] When the raw material 10 is fixed to the chuck 35, the first center line O10 of the raw material 10 becomes coaxial with the center line O33. When the second driving unit is driven, the installation table 33 rotates about the center line O33. As a result, the raw material 10 also rotates about the center line O33, and the portion cut by the helical cutter 21 moves in the circumferential direction. In this embodiment, the raw material 10 is disposed such that the first end surface 13 (not shown in FIG. 6, see FIG. 5) faces the installation surface 34, and the second end surface 14 faces in the opposite direction.

[0043] A center line O32 of the rotating part 32 extends in the horizontal direction. Therefore, when a first driving part (not shown) is driven, the rotating part 32 rotates about the center line O32. As a result, the material 10 fixed to the installation table 33 tilts, and the attitude of the material 10 changes. Next, the groove surface forming process S2 will be described.

[0044] Fig. 9 is a diagram showing how an annular groove surface (outer peripheral raceway surface) is formed on the outer peripheral surface of a raw material in an embodiment. Fig. 10 is a diagram showing how an annular groove surface (circulation groove surface) is formed on the outer peripheral surface of a raw material in an embodiment. As shown in Figs. 9 and 10, the groove surface forming step S2 is a step of cutting the outer peripheral surface 11 of the raw material 10 with a helical cutter 21 to form an annular groove surface 3 on the outer peripheral surface 11 of the raw material 10. In this embodiment, the groove surface forming step S2 is performed four times to form four annular groove surfaces 3.

[0045] In the groove surface forming process S2, first, a driving device (not shown) is rotated to rotate the helical cutter 21. Next, a lifting device (not shown), a posture changing device 30, and a table device (not shown) are driven to bring the cutting edge 23b of the cutting blade 23 of the helical cutter 21 into contact with the outer peripheral surface 11 of the material 10. As a result, the outer peripheral surface 11 of the material 10 is cut.

[0046] 9 and 10, the lifting device (not shown), the attitude changing device 30, and the table device (not shown) are driven so that the helical cutter 21 moves in the circumferential direction along the outer peripheral surface 11 of the raw material 10. This causes the cutting area to extend in the circumferential direction. Note that in this embodiment, the helical cutter 21 moves in the clockwise direction around the raw material 10 when viewed from the direction facing the second end face 14 of the raw material 10 (see arrow A in FIGS. 6, 9, and 10).

[0047] The lifting device (not shown), the attitude changing device 30, and the table device (not shown) are driven so that the cutting point goes around the outer circumferential surface 11 of the material 10, in other words, so that the starting point of the cutting point and the end point of the groove surface are connected. As a result, an annular groove surface 3 is formed on the outer circumferential surface 11 of the material 10.

[0048] 9, when the helical cutter 21 moves in the circumferential direction along the outer peripheral surface 11 of the raw material 10, the lifting device (not shown), the attitude changing device 30, and the table device (not shown) are driven so that the helical cutter 21 gradually approaches one side of the axial direction (toward the first end face 13) of the raw material 10. In other words, as shown in FIG. 9, the raw material 10 is tilted so that the center line O22 and the first center line O10 intersect (so that the angle formed by the center line O22 and the first center line O10 is θ1) when viewed from a direction parallel to a virtual line P perpendicular to each of the center line O22 and the first center line O10. As a result, the cutting portion extends in the spiral direction, and the outer peripheral track surface 4 is formed.

[0049] 10, when the helical cutter 21 moves in the circumferential direction along the outer peripheral surface 11 of the blank 10, the lifting device (not shown), the attitude changing device 30, and the table device (not shown) are driven so that the helical cutter 21 gradually approaches the other axial side (towards the second end face 14) of the blank 10. In other words, as shown in FIG. 10, when viewed from a direction parallel to a virtual line P perpendicular to each of the center line O22 and the first center line O10, the blank 10 is tilted so that the first center line O10 is tilted in the direction indicated by the arrow Q about the virtual line P (so that the angle formed by the center line O22 and the first center line O10 is θ2). As a result, the cutting portion extends toward the second end face 14, and the circulation groove surface 5 is formed.

[0050] Therefore, according to the above process, the outer circumferential raceway surface 4 and the circulation groove surface 5 can be formed continuously. In the present disclosure, the order in which the outer circumferential raceway surface 4 and the circulation groove surface 5 are formed does not matter. In addition, when forming the annular groove surface 3, it is preferable that the junction where the start point and the end point of the cutting part join is on the circulation groove surface 5. According to the groove surface forming process S2, a step is likely to occur on the groove surface at the junction where the start point and the end point of the cutting part join, which may hinder the smooth rolling of the ball 110. The circulation groove surface 5 of this embodiment has a large groove width and has a gap with the ball 110. Therefore, even if a step is provided, the rolling of the ball 110 is unlikely to be hindered.

[0051] Fig. 11 is a diagram showing a state in which the outer circumferential raceway surface is formed on the outer circumferential surface of a material in the embodiment. In addition, in the groove surface forming step S2, as shown in Fig. 11, when the outer circumferential raceway surface 4 is formed, cutting is performed while maintaining (without changing) the angle at which the cutting edge 23b of the cutting blade 23 contacts the outer circumferential surface 11 of the material 10. As a result, the groove shape of the outer circumferential raceway surface 4 becomes a Gothic arc shape that is the same shape as the cutting edge 23b of the cutting blade 23.

[0052] FIG. 12 is a diagram showing a state in which a circulation groove surface is formed on the outer peripheral surface of a material in an embodiment. In the groove surface forming step S2, when the circulation groove surface 5 is formed, the circulation groove surface 5 is cut so as to be deeper than the outer peripheral raceway surface 4. Also, the circulation groove surface 5 is cut so as to be gradually deeper from the end of the S-shaped direction toward the center. Furthermore, when the circulation groove surface 5 is formed, cutting is performed while maintaining (without changing) the angle at which the cutting edge 23b of the cutting blade 23 contacts the outer peripheral surface 11 of the material 10. According to this, the groove shape of the circulation groove surface 5 becomes a gothic arc shape that is the same shape as the cutting blade 23. Also, the circulation groove surface 5 is wider than the outer peripheral raceway surface 4.

[0053] By performing the groove surface forming step S2 four times, four annular groove surfaces 3 are formed on the outer peripheral surface 11 of the material 10, as shown in Fig. 5. In this embodiment, in order to form the annular groove surfaces 3, the lifting device (not shown), the attitude changing device 30, and the table device (not shown) are driven so that the helical cutter 21 goes around the outer peripheral surface 11 of the material 10 once, but in the present disclosure, the helical cutter 21 may go around the outer peripheral surface 11 of the material 10 multiple times.

[0054] The heat treatment step S3 is a step of quenching and tempering the outer peripheral surface 52 of the material body 51. In the present disclosure, a carburizing treatment may be performed before quenching. This allows the screw shaft 1 to obtain the desired hardness and toughness. In the present disclosure, the heat treatment method is not particularly limited.

[0055] The grinding step S4 is a step of grinding the outer peripheral raceway surface 4 with a grindstone 80. This completes the manufacture of the screw shaft 1. Note that, in this embodiment, only the outer peripheral raceway surface 4 of the annular groove surface 3 is ground, but in the present disclosure, the circulating groove surface 5 may also be ground at the same time.

[0056] As described above, the manufacturing method of the screw shaft of this embodiment includes a groove surface forming step S2 in which the outer peripheral surface 11 of the raw material 10 of the screw shaft 1 is cut by the helical cutter 21 to form an annular groove surface 3 on the outer peripheral surface 11. The outer peripheral surface 11 of the raw material 10 is formed in a cylindrical shape centered on the first center line O10 of the raw material 10. The annular groove surface 3 has an outer peripheral raceway surface 4 and a circulating groove surface 5. The helical cutter 21 has a rotatable shaft 22 and cutting blades 23 that protrude from the outer peripheral surface of the shaft 22, are arranged in a circumferential direction on the outer peripheral surface of the shaft 22, and cut the outer peripheral surface 11 of the raw material 10 with the cutting edge 23b. In the groove surface forming step S2, the relative positions of the helical cutter 21 and the raw material 10 are changed so that the helical cutter 21 moves in the circumferential direction along the outer peripheral surface 11 of the raw material 10, thereby forming an annular groove surface 3 on the outer peripheral surface 11 of the raw material 10. Furthermore, as the helical cutter 21 moves in the circumferential direction along the outer peripheral surface 11 of the raw material 10, the relative positions of the helical cutter 21 and the raw material 10 are changed so that the helical cutter 21 gradually moves in one axial direction parallel to the first center line O10 relative to the raw material 10, thereby forming the outer peripheral raceway surface 4. In addition, the relative positions of the helical cutter 21 and the raw material 10 are changed so that the helical cutter 21 gradually moves in the other axial direction relative to the raw material 10, thereby forming the circulating groove surface 5.

[0057] According to the embodiment, the circulating groove surface 5 is formed on the screw shaft 1. This prevents the circulating groove surface 5 provided on the top from matching with the outer circumferential raceway surface 4 of the screw shaft 1, which would prevent the balls 110 from moving smoothly.

[0058] In addition, in the manufacturing method of the screw shaft of the embodiment, when forming the outer circumferential raceway surface 4 in the groove surface forming process S2, the angle at which the cutting blade 23 contacts the material 10 is maintained, and the outer circumferential raceway surface 4 is formed having the same shape as the cutting edge 23b of the cutting blade 23.

[0059] In the manufacturing method of the screw shaft of the embodiment, the width W of the cutting blade 23 gradually increases from the cutting edge 23b toward the shaft 22. When the circulation groove surface 5 is formed in the groove surface forming step S2, the cutting blade 23 is cut deeper than the outer circumferential raceway surface 4 while maintaining the angle at which the cutting blade 23 contacts the material 10.

[0060] According to this, the circulating groove surface 5 is wider than the outer circumferential raceway surface 4 .

[0061] In the manufacturing method of the screw shaft 1 of the embodiment, the cutting edge 23b of the cutting blade 23 has a Gothic arc shape.

[0062] Moreover, the manufacturing method of the screw shaft 1 of the embodiment includes a heat treatment step S3 in which the raw material 10 is heat-treated after the groove surface forming step S2.

[0063] The heat treatment provides the desired hardness and toughness to the screw shaft 1. In addition, since no recesses are formed in the screw shaft 1 (material 10), there is no risk of quench cracks occurring at the edge of the opening of the recesses.

[0064] Moreover, the manufacturing method of the screw shaft 1 of the embodiment includes a grinding step S5 of grinding the outer circumferential raceway surface 4 after the heat treatment step S3.

[0065] This allows the balls 110 to move smoothly, improving the operability of the ball screw device 100.

[0066] Although the embodiment has been described above, the present disclosure is not limited to the examples described in the embodiment. For example, the manufacturing method of the screw shaft 1 of the present disclosure may not include the heat treatment step S3 and the grinding step S4. In addition, in the present embodiment, an example using the machining center 20 has been described, but the present disclosure may not use the machining center 20. In addition, in the present embodiment, the table device moves the posture conversion device 30 in a direction parallel to the virtual plane K20, but the present disclosure may be a table device that moves the lifting device in a direction parallel to the virtual plane K20. Alternatively, the present disclosure may be a table device that can move in each of the first direction X, the second direction Y, and the third direction Z by itself (without using the lifting device).

[0067] FIG. 13 is an enlarged view of the state in which the circulating groove surface is formed in the groove surface forming step according to the modified example. In the embodiment, when the circulating groove surface 5 is formed in the groove surface forming step S2, the angle at which the cutting edge 23b of the cutting blade 23 contacts the outer peripheral surface 11 of the material 10 is maintained, but the present disclosure is not limited thereto. For example, the lifting device (not shown), the attitude changing device 30, and the table device (not shown) may be driven so that the angle at which the cutting edge 23b of the cutting blade 23 contacts the outer peripheral surface 11 of the material 10 changes (see arrow B in FIG. 13). Alternatively, the lifting device (not shown), the attitude changing device 30, and the table device (not shown) may be driven so that the position of the cutting blade 23 moves in the axial direction (see arrow C in FIG. 13) while maintaining the angle at which the cutting edge 23b of the cutting blade 23 contacts the outer peripheral surface 11 of the material 10. In this way, the circulating groove surface 5 becomes wider than the cutting blade 23. This eliminates the need to replace the helical cutter with one having a wider cutting blade, improving productivity of the screw shaft.

[0068] The present disclosure may also be implemented in the following combinations: (1) A groove surface forming step of cutting an outer peripheral surface of a screw shaft material with a helical cutter to form an annular groove surface on the outer peripheral surface, The outer peripheral surface of the blank is formed into a cylindrical shape centered on a first center line of the blank, The annular groove surface has an outer circumferential raceway surface and a circulating groove surface, The helical cutter is A rotatable shaft; a cutting blade protruding from an outer circumferential surface of the shaft, arranged in a circumferential direction with respect to the outer circumferential surface of the shaft, and configured to cut the outer circumferential surface of the material with a cutting edge; having The groove surface forming step includes: changing a relative position between the helical cutter and the material so that the helical cutter moves in a circumferential direction along the outer circumferential surface of the material, thereby forming the annular groove surface on the outer circumferential surface of the material; Furthermore, when the helical cutter moves in a circumferential direction along the outer circumferential surface of the material, the relative positions of the helical cutter and the material are changed so that the helical cutter gradually moves in one axial direction parallel to the first center line with respect to the material, thereby forming the outer circumferential track surface, and the relative positions of the helical cutter and the material are changed so that the helical cutter gradually moves in the other axial direction with respect to the material, thereby forming the circulating groove surface. A method for manufacturing a screw shaft of a ball screw device. (2) When forming the outer circumferential raceway surface in the groove surface forming step, the angle at which the cutting blade contacts the material is maintained, and the outer circumferential raceway surface is formed to have the same shape as the cutting edge of the cutting blade. A method for manufacturing the screw shaft of the ball screw device described in (1). (3) The width of the cutting blade gradually increases from the cutting tip toward the shaft, When forming the circulating groove surface in the groove surface forming step, the cutting blade is cut deeper than the outer circumferential raceway surface while maintaining an angle at which the cutting blade contacts the material. A method for manufacturing a screw shaft of a ball screw device according to (1) or (2). (4) When forming the circulating groove surface in the groove surface forming step, the relative positions of the helical cutter and the material are changed so that the angle at which the cutting blade contacts the material is changed, and the circulating groove surface is formed to be wider than the width of the cutting blade. A method for manufacturing a screw shaft of a ball screw device according to (1) or (2). (5) When forming the circulating groove surface in the groove surface forming step, the relative positions of the helical cutter and the material are changed so that the position of the cutting blade with respect to the material is moved in the axial direction, thereby forming the circulating groove surface wider than the width of the cutting blade. A method for manufacturing a screw shaft of a ball screw device according to (1) or (2). (6) The circulation groove surface is wider than the outer circumferential raceway surface, The junction where the start point and the end point of the cutting portion of the groove surface forming process join together is on the circulation groove surface. A method for manufacturing a screw shaft of a ball screw device according to any one of (1) to (5). (7) The cutting edge of the cutting blade is in a Gothic arc shape. A method for manufacturing a screw shaft of a ball screw device according to any one of (1) to (6). (8) A heat treatment step of performing heat treatment on the material after the groove surface forming step is included. A method for manufacturing a screw shaft of a ball screw device according to any one of (1) to (7). (9) A grinding step of grinding the outer circumferential raceway surface is included after the heat treatment step. A method for manufacturing the screw shaft of the ball screw device described in (8). [Explanation of symbols]

[0069] 1 Screw shaft 2 Outer surface 3 Circular groove surface 4 Outer raceway surface 5 Circulation groove surface 10. Materials 11 Outer surface 13 First end surface 14 Second end face 20 Machining Center 21 Helical cutter 22 Shaft 23 Cutting blade 23b Cutting edge 30 Posture change device 100 Ball screw device 101 Nut 110 Ball 103 Inner raceway surface O10 1st center line

Claims

1. A groove surface forming step of cutting an outer peripheral surface of a screw shaft material with a helical cutter to form an annular groove surface on the outer peripheral surface, The outer peripheral surface of the blank is formed into a cylindrical shape centered on a first center line of the blank, The annular groove surface has an outer circumferential raceway surface and a circulating groove surface, The helical cutter is A rotatable shaft; a cutting blade protruding from an outer circumferential surface of the shaft, arranged in a circumferential direction with respect to the outer circumferential surface of the shaft, and configured to cut the outer circumferential surface of the material with a cutting edge; having The groove surface forming step includes: changing a relative position between the helical cutter and the material so that the helical cutter moves in a circumferential direction along the outer circumferential surface of the material, thereby forming the annular groove surface on the outer circumferential surface of the material; Furthermore, when the helical cutter moves in a circumferential direction along the outer circumferential surface of the material, the relative positions of the helical cutter and the material are changed so that the helical cutter gradually moves in one axial direction parallel to the first center line with respect to the material, thereby forming the outer circumferential track surface, and the relative positions of the helical cutter and the material are changed so that the helical cutter gradually moves in the other axial direction with respect to the material, thereby forming the circulating groove surface. A method for manufacturing a screw shaft of a ball screw device.

2. When forming the outer circumferential raceway surface in the groove surface forming step, the angle at which the cutting blade contacts the material is maintained, and the outer circumferential raceway surface is formed to have the same shape as the cutting edge of the cutting blade. A method for manufacturing the screw shaft of the ball screw device according to claim 1.

3. The width of the cutting blade gradually increases from the cutting tip toward the shaft, When forming the circulating groove surface in the groove surface forming step, the cutting blade is cut deeper than the outer circumferential raceway surface while maintaining an angle at which the cutting blade contacts the material. A method for manufacturing the screw shaft of the ball screw device according to claim 1 or 2.

4. When forming the circulating groove surface in the groove surface forming step, the relative positions of the helical cutter and the material are changed so that the angle at which the cutting blade contacts the material is changed, and the circulating groove surface is formed to be wider than the width of the cutting blade. A method for manufacturing the screw shaft of the ball screw device according to claim 1 or 2.

5. When forming the circulating groove surface in the groove surface forming step, the relative positions of the helical cutter and the material are changed so that the position of the cutting blade with respect to the material is moved in the axial direction, thereby forming the circulating groove surface wider than the width of the cutting blade. A method for manufacturing the screw shaft of the ball screw device according to claim 1 or 2.

6. The circulation groove surface is wider than the outer circumferential raceway surface, The junction where the start point and the end point of the cutting portion of the groove surface forming process join together is on the circulation groove surface. A method for manufacturing the screw shaft of the ball screw device according to claim 1 or 2.

7. The cutting edge of the cutting blade is in a Gothic arc shape. A method for manufacturing the screw shaft of the ball screw device according to claim 1 or 2.

8. A heat treatment step of performing heat treatment on the material after the groove surface forming step is included. A method for manufacturing the screw shaft of the ball screw device according to claim 1 or 2.

9. A grinding step of grinding the outer circumferential raceway surface is included after the heat treatment step. A method for manufacturing the screw shaft of a ball screw device according to claim 8.

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