Manufacturing method for nut for ball screw, and ball screw

Abstract

To provide a manufacturing method for a nut for a ball screw that can restrain plastic working from affecting a subsequent process.SOLUTION: A screw groove (34) corresponding to a main path (50) in which a plurality of balls roll is formed in an inner wall surface (32) of a nut body. A return groove (35) corresponding to a return path (60) with respect to the main path (50) is formed in the inner wall surface (32) by plastic working. Before the formation of the return groove (35), a concave part (70) is formed in a partial region in the inner wall surface (32) by cutting. The concave part (70) is set wider than the formation region of the return groove (35) in each of a circumferential direction and an axial direction.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a nut for a ball screw, and to a ball screw. [Background technology]

[0002] A ball screw includes a nut, a screw shaft, and a plurality of balls (rolling elements) disposed between the nut and the screw shaft. One known circuit structure for circulating the plurality of balls is one that includes a groove for a return path (return raceway) formed on the inner wall surface of the nut body, separate from a groove for a main path (main raceway) (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-281063 Summary of the Invention [Problem to be solved by the invention]

[0004] When the groove for the return path is formed in the nut body by plastic working, part of the nut body may be deformed during the plastic working, which may affect subsequent processes.

[0005] One object of the present invention is to provide a method for manufacturing a nut for a ball screw that can suppress the effects of plastic processing on subsequent processes. Another object of the present invention is to provide a method for manufacturing a nut for a ball screw that is advantageous for making the nut body compact. Yet another object of the present invention is to provide a method for manufacturing a nut for a ball screw, a nut for a ball screw, and a ball screw that are advantageous for reducing costs. [Means for solving the problem]

[0006] A method for manufacturing a nut for a ball screw according to one aspect of the present invention includes: a thread groove forming step of forming a thread groove corresponding to a main path along which a plurality of balls roll on an inner wall surface of a nut body; a return groove forming step of forming a return groove corresponding to a return path relative to the main path on the inner wall surface by plastic processing; and a recess forming step of forming a recess in a partial region of the inner wall surface by cutting processing prior to the return groove forming step, the recess being set so as to be wider than the formation region of the return groove in both the circumferential and axial directions. [Effects of the Invention]

[0007] According to one aspect of the present invention, a method for manufacturing a ball screw nut is provided that can suppress the effects of plastic processing on subsequent processes. The method for manufacturing a ball screw nut is also provided, which is advantageous for making the nut body compact. Furthermore, the method for manufacturing a ball screw nut, the ball screw nut, and the ball screw are also provided, which are advantageous for reducing costs. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a ball screw according to an embodiment. [Figure 2] FIG. 4 is a diagram schematically showing an inner wall surface of a nut body. [Figure 3] FIG. 10 is a flowchart showing an example of a method for manufacturing a nut for a ball screw. [Figure 4] 1A and 1B are diagrams showing a part of a manufacturing process of a nut, in which part (a) is a schematic perspective view and part (b) is a schematic cross-sectional view. [Figure 5] 1A and 1B are diagrams showing a part of a manufacturing process of a nut, in which part (a) is a schematic perspective view and part (b) is a schematic cross-sectional view. [Figure 6] 1 is a diagram schematically showing an example of plastic working (forging) using a die and a cam mechanism. [Figure 7] FIG. 4 is a schematic enlarged cross-sectional view showing an inner wall surface on which a return groove and a recess are formed. [Figure 8]1A and 1B are diagrams showing a part of a manufacturing process of a nut, in which part (a) is a schematic perspective view and part (b) is a schematic cross-sectional view. [Figure 9] 1A and 1B are diagrams showing a part of a manufacturing process of a nut, in which part (a) is a schematic perspective view and part (b) is a schematic cross-sectional view. [Figure 10] 10A and 10B are schematic cross-sectional views showing a modified example of the method for manufacturing a nut for a ball screw. [Figure 11] FIG. 10 is a schematic cross-sectional view showing another modified example of the method for manufacturing a nut for a ball screw. [Figure 12] FIG. 10 is a schematic cross-sectional view showing another modified example of the method for manufacturing a nut for a ball screw. [Figure 13] FIG. 10 is a schematic perspective view showing another modified example of the method for manufacturing a nut for a ball screw. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of the present invention will be described with reference to the drawings. In one embodiment, a ball screw is incorporated into various mechanical devices, such as an electric brake device for a vehicle, an automatic manual transmission (AMT), or a positioning device for a machine tool, and is used to convert the rotational motion of a drive source, such as an electric motor, into linear motion to operate a driven part (operating part). Various types of electric brake devices are applicable, such as an electro-mechanical brake (EMB) that applies braking force via a ball screw driven by a motor, and an electro-hydraulic brake (EHB) that controls the hydraulic pressure of a hydraulic brake via a ball screw driven by a motor. The ball screw can also be applied to mechanical devices other than those mentioned above.

[0010] In the following description, unless otherwise specified, the axial direction, radial direction, and circumferential direction refer to the direction along the central axis of the ball screw (nut), the radial direction of the ball screw (nut), and the direction around the central axis of the ball screw (nut), respectively.

[0011] 1 is a schematic cross-sectional view of a ball screw 10. The ball screw 10 includes a screw shaft 11, a nut 12, and a plurality of balls (rolling elements) 13 arranged between the screw shaft 11 and the nut 12.

[0012] The screw shaft 11 has a shaft body 21 and a spiral thread groove (spiral outer peripheral rolling groove) 22 provided on the outer peripheral surface of the shaft body 21. In one example, at least a portion of the screw shaft 11 is made of metal. The thread groove 22 of the screw shaft 11 is formed by performing cutting and / or plastic processing (such as rolling) on ​​the outer peripheral surface of the shaft body. In forming the thread groove 22, grinding can be additionally performed. The thread groove shape (groove bottom shape) of the screw shaft 11 is, for example, a Gothic arch groove or a circular arc groove. The number of threads in the thread groove 22 is set to one, two, or more. In other examples, various forms are applicable to the screw shaft 11.

[0013] The nut 12 has a cylindrical nut body 31 and a helical thread groove (helical inner circumferential rolling groove) 34 provided on an inner wall surface (inner peripheral surface, inner wall, inner side of the peripheral wall) 32 of the nut body 31. The screw shaft 11 is inserted into the nut 12. In one example, at least a portion of the nut 12 is made of metal. The thread groove 34 of the nut 12 is formed by performing cutting and / or plastic processing on the inner wall surface 32 of the nut body 31. In forming the thread groove 34, grinding can be additionally performed. The thread groove shape (groove bottom shape) of the nut 12 corresponds to the groove shape of the screw shaft 11, and is, for example, a gothic arch groove or a circular arc groove. The number of threads of the thread groove 34 of the nut 12 corresponds to the number of threads of the screw groove 22 of the screw shaft 11 and is set to one start, two start, or more. In other examples, various shapes are applicable to the nut 12.

[0014] A plurality of balls 13 are arranged between the screw shaft 11 and the nut 12. In FIG. 1, two balls 13 are indicated by two-dot chain lines. In reality, the ball screw 10 includes a large number of balls 13. In one example, the plurality of balls 13 are made of metal (such as steel) or ceramics. As the screw shaft 11 and the nut 12 rotate relative to each other, the plurality of balls 13 roll within a main path 50. The main path (main raceway, rolling path, spiral path) 50 is a space formed based on the opposing arrangement of the screw groove 22 of the screw shaft 11 and the screw groove 34 of the nut 12.

[0015] In this embodiment, the ball 13 returns from the end point of the main path 50 to the start point via a return path (return raceway, sub-raceway) 60 provided in the nut 12. The nut 12 has a return groove (S-groove, S-shaped groove, S-shaped recess) 35 corresponding to the return path 60. The return groove 35 is provided on the inner wall surface 32 of the nut body 31. The maximum depth of the return groove 35 is set to be larger than the maximum depth of the screw groove 34. For example, the depth of the return groove 35 is set to a degree that allows the ball 13 to ride over the threads of the screw shaft 11 when the screw shaft 11 and the nut 12 are assembled together.

[0016] FIG. 2 is a schematic diagram showing the inner wall surface 32 of the nut body 31. FIG. 2(a) shows an example in which the lead is relatively small, and FIG. 2(b) shows an example in which the lead is relatively large. As shown in FIG. 2, multiple circuits are formed on the inner wall surface 32 of the nut body 31, and each circuit includes a main path 50 formed based on the thread groove 34 and a return path 60 formed based on the return groove 35. In each circuit, the return path 60 spatially connects one end (first end 51) of the main path 50 to the other end (second end 52). In each circuit, the first end 61 of the return path 60 is connected to the first end 51 of the main path 50, and the second end 62 of the return path 60 is connected to the second end 52 of the main path 50.

[0017] As the screw shaft and the nut rotate relative to each other, balls move along the axes (orbital axes, extension axes) of the main path 50 and the return path 60. In one example, the ball moves from the first end (starting point) 51 of the main path 50 to the second end (ending point) 52. The ball that moves to the second end 52 of the main path 50 is guided to the return path 60. The ball positioned on the return path 60 is pushed by the following ball and moves from the second end 62 to the first end 61 of the return path 60. In other words, a ball that enters the return path 60 from the second end 52 of the main path 50 returns to the first end 51 of the main path 50 via the return path 60. The starting point and ending point of the main path 50 are reversed depending on the direction of relative rotation between the shaft and the nut. In the reverse direction of relative rotation, the ball moves from the second end (starting point) 52 to the first end (ending point) 51 of the main path 50. The ball that has moved to the first end 51 of the main path 50 is guided to the return path 60 and moves from the first end 61 to the second end 62 of the return path 60. That is, the ball that has entered the return path 60 from the first end 51 of the main path 50 returns to the second end 52 of the main path 50 via the return path 60. In this way, in the ball screw, the balls can continuously circulate through a circulation path (circulation circuit) that includes the main path 50 and the return path 60 as the shaft and the nut rotate relative to each other.

[0018] In this embodiment, as will be described later, during the manufacturing process of the nut 12, before the process of forming the return grooves 35 using plastic processing, recesses (recessed regions) 70 are formed in the inner wall surface 32 using cutting (shown by two-dot chain lines in FIG. 2 ). The recesses 70 are formed in a partial region 38 that includes the formation region of the return grooves 35 on the inner wall surface 32. That is, the formation region of the return grooves 35 is within the range of the recesses 70 (partial region 38). The recesses 70 are larger in both the circumferential and axial directions than the formation region of the return grooves 35. In one example, multiple return grooves 35 are formed in the inner wall surface 32. The multiple return grooves 35 are arranged shifted from one another in the circumferential direction, or the multiple return grooves 35 are arranged in the same phase in the circumferential direction. In the example of FIG. 2 , the multiple return grooves 35 are arranged so that their centers are spaced at a predetermined pitch in the axial direction. Alternatively, the multiple return grooves 35 are arranged so that their centers are equally spaced in the circumferential direction. In another example, the multiple return grooves 35 are formed in the inner wall surface 32 of the nut body 31 in a form different from that described above. The number of return grooves 35 formed on the inner wall surface 32 can be set arbitrarily. The number of return grooves 35 can be set to 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 or more. In one example, the recess 70 is provided extending circumferentially around the entire circumference of the inner wall surface 32. For example, the recess 70 has a stepped shape (edge, wall surface) along the circumferential direction. Alternatively, the recess 70 is provided extending circumferentially around a portion of the circumference of the inner wall surface 32. For example, the recess 70 has a stepped shape (edge, wall surface) along the circumferential direction and a stepped shape (edge, wall surface) along the axial direction. In another example, the recess 70 is formed on the inner wall surface 32 of the nut body 31 in a form different from that described above.

[0019] In one example, the shape of at least a portion of the recess 70 and / or the bank 75 ( FIG. 7 ), which will be described later, ultimately remains on the inner wall surface (circumferential wall) 32 of the nut body 31 (finished product or semi-finished product) as a trace of the recess 70 and / or the bank 75. For example, as a trace of the recess 70, a protrusion shape and / or a step shape corresponding to at least a portion of the contour of the bank 75 remains on the inner wall surface 32. Alternatively, as a trace of the bank 75, a protrusion shape and / or a step shape corresponding to at least a portion of the contour of the bank 75 remains inside the trace of the recess 70 on the inner wall surface 32. In another example, the recess 70 and / or the bank 75 are substantially entirely removed from the nut body 31 by subsequent processing. Here, the plastic processing for forming the return groove 35 causes internal changes (such as changes in the internal metal structure and changes in metal flow) in the peripheral wall of the nut body 31. Such internal changes due to plastic processing vary depending on the thickness (radial thickness) of the peripheral wall. Furthermore, the change inside the peripheral wall also differs between (a) a case where a groove is formed by plastic processing in an area where a recess has been formed by cutting processing, and (b) a case where a groove is formed by plastic processing in an area where a recess has been formed by plastic processing. In one example, even when the entire shape of recess 70 is finally removed from nut body 31, traces (structural traces) of recess 70 can be confirmed based on a texture analysis and / or a structural analysis of nut body 31.

[0020] Next, an example of a manufacturing method for a ball screw nut will be described with reference to Figures 3 to 9. In one example, the manufacturing method includes a recess forming step of forming recesses 70 by cutting a partial region of the inner wall surface 32 of the nut body 31, a return groove forming step of forming return grooves 35 on the inner wall surface 32 by plastic processing, a thread groove forming step of forming thread grooves 34 on the inner wall surface 32, and an inner wall surface cutting step of cutting the entire inner wall surface 32 of the nut body 31. First, the nut body 31 is prepared, which has been machined into a predetermined shape.

[0021] Next, as shown in Fig. 4, recesses 70 are formed in the inner wall surface 32 of the nut body 31 by cutting (recess forming step). The formation of the recesses 70 is carried out prior to the formation of the return grooves 35. The recesses 70 are formed in a partial region (partial region 38) of the inner wall surface 32 of the nut body 31.

[0022] In this embodiment, the nut body 31 has a first portion 81 and a second portion 82 that are aligned in the axial direction. The first portion 81 has a flange 80 that extends in the radial direction. In the nut body 31, the radial thickness of the first portion 81 is greater than that of the second portion 82. The recess 70 is formed on the inner wall surface 32 of the first portion 81 in the axial direction of the nut body 31, but is not formed on the inner wall surface 32 of the second portion 82.

[0023] The recess 70 (partial region 38) is set to be wider in both the circumferential direction and the axial direction than the formation region of the return groove 35 (FIG. 5) that will be formed later. In one example, when the axial width of the recess 70 is W1 and the axial width of the formation region of the return groove 35 is W2, W1 / W2 is greater than 1.00 and is equal to or less than 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, or 1.35. In other examples, ratios other than those mentioned above can be set. The above numerical values ​​are merely examples and are not limiting.

[0024] Next, as shown in Fig. 5, the return groove 35 is formed in the inner wall surface 32 of the nut body 31 by plastic processing such as forging (return groove forming process). In one example, the plastic processing (forging) is performed using a die and a cam mechanism. In another example, the plastic processing is performed by another method.

[0025] FIG. 6 schematically shows an example of plastic working (forging) using a die and a cam mechanism. As shown in FIG. 6(a), in the cam mechanism 100, the nut body 31 is held by a holder 105. The die 110 has an outer diameter corresponding to the inner diameter of the nut body 31. The die 110 is inserted axially into the nut body 31, and the die 110 is set relative to the nut body 31. A punch 112 is attached to the die 110 so as to be movable in a direction perpendicular to the axial direction of the die 110. The die 110 has a hole 111 extending axially, and the shape of the hole 111 corresponds to the outer diameter shape of the mandrel 114. The die 110 may have an integral structure or a divided structure.

[0026] As shown in FIG. 6(b), when the mandrill 114 is inserted axially into the hole 111 of the die 110, the punch 112, pressed by the tapered surface 115 of the mandrill 114, moves radially outward and is forced into the nut body 31. As a result, a return groove 35 of a predetermined shape is formed on the inner wall surface 32 of the nut body 31. As shown in FIG. 6(c), when the mandrill 114 retracts axially, the punch 112 moves radially inward and separates from the nut body 31. Thereafter, as shown in FIG. 6(d), the die 110 is moved axially and removed from the nut body 31.

[0027] Here, when the return groove 35 is formed by plastic processing, minute banks (protrusions, convex portions) that protrude radially inward may occur on the inner wall surface 32 of the nut body 31. Such banks are formed, for example, as a result of the flow of material inside the nut body 31 during plastic processing. The banks are formed around the return groove 35 so as to surround the return groove 35. In the example of plastic processing shown in FIG. 6, the bank is formed by the portion of the inner wall surface 32 surrounding the return groove 35 rising in the direction opposite to the pressing direction of the punch 112. If a bank occurs, problems such as difficulty in removing the mold 110 shown in FIG. 6 or damage to the mold 110 due to bending stress may occur.

[0028] In this embodiment, such a bank is likely to occur on the inner wall surface 32 in the first portion 81 where the radial thickness of the nut body 31 is relatively large as shown in Fig. 5. On the other hand, in the second portion 82 where the radial thickness of the nut body 31 is relatively small, a bank is relatively unlikely to occur on the inner wall surface 32 due to outward deformation of the outer surface (outer wall surface) of the nut body 31, for example.

[0029] In this embodiment, as shown in Fig. 5, a first return groove 35A is formed in the inner wall surface 32 of the first portion 81 in the axial direction of the nut body 31. A second return groove 35B is formed in the inner wall surface 32 of the second portion 82 in the axial direction of the nut body 31. A recess 70 is formed in advance in the inner wall surface 32 of the first portion 81. That is, in the first portion 81, the first return groove 35A is formed in the bottom surface of the recess 70. In the second portion 82, the second return groove 35B is formed in an area of ​​the inner wall surface 32 where the recess 70 is not formed.

[0030] In this embodiment, in the first portion 81 where a bank is likely to occur, a recess 70 is formed in advance in the region of the inner wall surface 32 where the return groove 35 is formed. Therefore, as shown in FIG. 7 , even if a bank 75 occurs on the inner wall surface 32, the bank 75 is located inside the recess 70. For example, the height of the bank 75 from the bottom surface of the recess 70 is smaller than the depth of the recess 70. By arranging the bank 75 in the internal space of the recess 70, the influence of the bank 75 on subsequent processes is prevented.

[0031] 8, the thread groove 34 is formed on the inner wall surface 32 of the nut body 31 (thread groove forming step). For example, one end of the return groove 35 is connected to a part of the thread groove 34, and the other end of the return groove 35 is connected to the other part of the thread groove 34.

[0032] Next, as shown in FIG. 9 , the entire inner wall surface 32 of the nut body 31 is cut (inner wall surface cutting process). For example, the cutting depth of the inner wall surface 32 is set to be equal to or greater than the depth of the recessed portion 70. The inner wall surface 32 is cut to have a specified inner diameter over the entire circumferential and axial directions. As a result, the inner wall surface 32b is formed with a specified shape and with ensured surface precision. For example, the cutting of the inner wall surface 32 removes at least a portion of the recessed portion 70 and / or the bank 75 ( FIG. 7 ). Alternatively, the cutting may not be performed, and at least a portion of the shape of the recessed portion 70 and / or the bank 75 may remain on the inner wall surface 32.

[0033] As described above, in this embodiment, by forming the recess 70 in advance on the inner wall surface 32 based on cutting processing, even if a part of the nut body 31 is deformed during subsequent plastic processing, it is possible to avoid affecting subsequent processes.

[0034] In this embodiment, the recess 70 is set to be wider in both the circumferential direction and the axial direction than the formation area of ​​the return groove 35. Therefore, deformation of the bank or the like that occurs around the recess 70 is reliably accommodated inside the recess 70.

[0035] In this embodiment, the return grooves 35 are formed even in the portion having a relatively large radial thickness. Therefore, the thread grooves 34 can be formed over a wide range in the axial direction of the nut body 31. This is advantageous for making the nut 12 more compact.

[0036] In one example, three return grooves 35 are formed on the inner wall surface 32 of the nut body 31. For example, the three return grooves 35 are arranged so that their center positions are at a predetermined pitch in the axial direction. Also, the three return grooves 35 are arranged so that their center positions are equally spaced in the circumferential direction. In another example, a plurality of return grooves 35 are formed on the inner wall surface 32 of the nut body 31 in a form different from the above. The number of return grooves 35 formed on the inner wall surface 32 can be set as desired. The number of return grooves 35 may be one or two, or may be four or more.

[0037] Fig. 10 is a schematic cross-sectional view showing a modified example of the manufacturing method of a ball screw nut. In the example of Fig. 10, a plurality of return grooves 35A, 35B are formed in the inner wall surface 32 of the nut body 31. A plurality of recesses 70A, 70B are formed in the plurality of return grooves 35A, 35B, respectively. That is, the manufacturing method of the nut 12 includes the steps of forming a return groove (first return groove) 35A in the inner wall surface 32 by plastic working, forming a return groove (second return groove) 35B in the inner wall surface 32 by plastic working, forming recesses 70A in a partial region of the inner wall surface 32 by cutting before forming the return groove 35A, and forming recesses 70B in a partial region of the inner wall surface 32 by cutting before forming the return groove 35B. In this example, the recessed portions 70 are provided to extend in the circumferential direction around the entire circumference of the inner wall surface 32, or the recessed portions 70 are provided to extend in the circumferential direction around a portion of the circumference of the inner wall surface 32. Also, in this example, the multiple return grooves 35A, 35B are arranged to be shifted from each other in the circumferential direction, or the multiple return grooves 35A, 35B are arranged in the same phase in the circumferential direction.

[0038] In the example of FIG. 10, the recesses 70A, 70B are formed before the plastic working for forming the return grooves 35A, 35B, respectively, thereby reliably preventing the effects of the plastic working from affecting subsequent processes.

[0039] FIG. 11 is a schematic cross-sectional view showing another modified example of the manufacturing method for a ball screw nut. In the example of FIG. 11, multiple return grooves 35A, 35B are formed in the inner wall surface 32 of the nut body 31. Furthermore, one recess 70 is formed for each of the multiple return grooves 35A, 35B. That is, the manufacturing method for the nut 12 includes the steps of forming a return groove (first return groove) 35A in the inner wall surface 32 by plastic processing, forming a return groove (second return groove) 35B in the inner wall surface 32 by plastic processing, and forming the recess 70 by cutting in a partial region of the inner wall surface 32 that includes both the region where the return groove 35A is formed and the region where the return groove 35B is formed, which is performed before the formation of the return groove 35A and the return groove 35B. In this example, the recess 70 is provided to extend circumferentially around the entire circumference of the inner wall surface 32, or the recess 70 is provided to extend circumferentially around a portion of the circumference of the inner wall surface 32. In this example, the plurality of return grooves 35A, 35B are arranged to be shifted from one another in the circumferential direction, or the plurality of return grooves 35A, 35B are arranged in the same phase in the circumferential direction.

[0040] 11, the shared recess 70 is formed before the plastic working for forming the multiple return grooves 35A, 35B, thereby reliably preventing the effects of the plastic working from extending to subsequent processes. Also, using one recess 70 for the multiple return grooves 35A, 35B is advantageous in terms of reducing costs.

[0041] 11, the entire region where the return groove 35A is formed may be located within the region where the recess 70 is formed, and only a portion of the region where the return groove 35B is formed may be located within the region where the recess 70 is formed. In other words, in a portion of the nut body 31 where the radial thickness is relatively small, a configuration may be applied in which a portion of the region where the return groove 35B is formed overlaps with the region where the recess 70 is formed, and the other portion does not overlap with the region where the recess 70 is formed.

[0042] FIG. 12 is a schematic cross-sectional view showing another modified example of the manufacturing method for a ball screw nut. In the example shown in FIG. 12, multiple return grooves 35A, 35B, and 35C are formed in the inner wall surface 32 of the nut body 31. Furthermore, multiple recesses 70A, 70B, and 70C are formed corresponding to the multiple return grooves 35A, 35B, and 35C, respectively. Furthermore, the nut body 31 has a uniform radial thickness throughout the entire axial direction. In this example, the recess 70 is provided to extend circumferentially around the entire circumference of the inner wall surface 32, or the recess 70 is provided to extend circumferentially around a portion of the circumference of the inner wall surface 32. In this example, the multiple return grooves 35A, 35B, and 35C are arranged shifted from one another in the circumferential direction, or the multiple return grooves 35A, 35B, and 35C are arranged in the same phase in the circumferential direction.

[0043] 12, similarly to the example of Fig. 9, the recesses 70A, 70B, and 70C are formed before the plastic processing for forming the return grooves 35A, 35B, and 35C, respectively, thereby reliably preventing the effects of the plastic processing from extending to subsequent processes. Also, stable processing is performed on the nut body 31 having a constant diameter and thickness.

[0044] Fig. 13 is a schematic cross-sectional view showing another modified example of the method for manufacturing a ball screw nut. In the example of Fig. 11, a return groove is formed in the inner wall surface 32 of the nut body 31. In addition, a recess 70 is formed in the return groove 35. The recess 70 is provided so as to extend in the circumferential direction on a part of the circumference of the inner wall surface 32.

[0045] 13, the recesses 70 are formed before the plastic working for forming the return grooves 35, thereby preventing the effects of the plastic working from affecting subsequent processes. In addition, the recesses 70 are formed only around the return grooves 35, which is advantageous in shortening the processing time and reducing costs.

[0046] The technical scope of the present invention is not limited to the scope of the embodiments. Various modifications or improvements can be made to the embodiments. Forms incorporating such modifications or improvements can also be included in the technical scope of the present invention. Furthermore, the present invention is not limited to the described embodiments, and any combination of these configurations may be used.

[0047] The present disclosure may be combined as follows: (1) In one embodiment, a method for manufacturing a nut for a ball screw includes: a thread groove forming step of forming a thread groove corresponding to a main path along which a plurality of balls roll on an inner wall surface of a nut body; a return groove forming step of forming a return groove corresponding to a return path relative to the main path on the inner wall surface by plastic processing; and a recess forming step of forming a recess in a partial region of the inner wall surface by cutting processing prior to the return groove forming step, the recess being set to be wider in both the circumferential and axial directions than the formation region of the return groove. (2) In the manufacturing method described in (1) above, the recess is provided so as to extend in the circumferential direction around the entire circumference of the inner wall surface. (3) In the manufacturing method described in (1) above, the recess is provided so as to extend in the circumferential direction on a part of the circumference of the inner wall surface. (4) In the manufacturing method described in any one of (1) to (3) above, the return groove forming step includes forming a plurality of return grooves, and the recess forming step includes forming a plurality of recesses in a plurality of partial regions including the region in which the plurality of return grooves are formed. (5) In the manufacturing method described in any one of (1) to (3) above, the return groove forming step includes forming a plurality of return grooves, and in the recess forming step, the partial region in which the recess is formed is set to include at least two of the plurality of return grooves. (6) In the manufacturing method described in any one of (1) to (3) above, the return groove forming step includes forming a plurality of return grooves, and in the recess forming step, the recesses are formed in some of the plurality of return grooves and not in others. (7) In the manufacturing method described in any one of (1) to (6) above, the nut body has a first portion and a second portion aligned in the axial direction, the radial thickness of the first portion of the nut body is greater than that of the second portion, and in the recess forming step, the recess is formed in the first portion but not in the second portion. (8) In the manufacturing method described in (7) above, the first portion includes a flange extending in the radial direction. (9) The manufacturing method according to any one of (1) to (8) above further comprises a step of cutting the inner wall surface on which the recess is provided. (10) In one embodiment, a ball screw includes a screw shaft, a nut manufactured using the manufacturing method described in any one of (1) to (9) above, and a plurality of balls arranged between the screw shaft and the nut. (11) In one embodiment, a ball screw includes a screw shaft, a nut, and a plurality of balls arranged between the nut and the screw shaft. The nut includes a screw groove formed on an inner wall surface of the nut and corresponding to a main path along which the plurality of balls roll, a return groove formed on the inner wall surface by plastic processing and corresponding to a return path relative to the main path, and a trace of a recess formed by cutting in a partial area of ​​the inner wall surface, the partial area being larger in both the circumferential and axial directions than an area where the return groove is formed. (12) The ball screw according to (11) above further comprises a bank trace on the inner wall surface that is generated when the return groove is formed by the plastic working. [Explanation of symbols]

[0048] 10 ball screws, 11 screw shaft, 12 nuts, 13 Balls (rolling elements), 21 shaft body, 22 thread groove, 31 Nut body, 32 interior wall surface, 34 thread groove, 35 return groove, 38 subregion, 50 main routes, 60 return routes, 70 recesses, 75 Bank.

Claims

1. a thread groove forming step of forming a thread groove corresponding to a main path along which a plurality of balls roll on an inner wall surface of the nut body; a return groove forming step of forming a return groove corresponding to a return path relative to the main path on the inner wall surface by plastic working; a recess forming step, which is performed before the return groove forming step, to form a recess in a partial region of the inner wall surface by cutting, and the recess is set to be wider than the formation region of the return groove in both the circumferential direction and the axial direction; A method for manufacturing a nut for a ball screw, comprising:

2. The recess is provided to extend in a circumferential direction around the entire circumference of the inner wall surface. The method for manufacturing the nut for a ball screw according to claim 1.

3. The recess is provided to extend in a circumferential direction on a part of the circumference of the inner wall surface. The method for manufacturing the nut for a ball screw according to claim 1.

4. the return groove forming step includes forming a plurality of return grooves; the recess forming step includes forming a plurality of recesses in a plurality of partial regions including regions in which the plurality of return grooves are to be formed, A method for manufacturing the nut for a ball screw according to any one of claims 1 to 3.

5. the return groove forming step includes forming a plurality of return grooves; In the recess forming step, the partial region in which the recess is formed is set to include at least two of the plurality of return grooves. A method for manufacturing the nut for a ball screw according to any one of claims 1 to 3.

6. the return groove forming step includes forming a plurality of return grooves; In the recess forming step, the recesses are formed in some of the plurality of return grooves and not in other of the plurality of return grooves. A method for manufacturing the nut for a ball screw according to any one of claims 1 to 3.

7. The nut body has a first portion and a second portion aligned in the axial direction, The radial thickness of the first portion of the nut body is larger than that of the second portion, In the recess forming step, the recess is formed in the first portion but not in the second portion. A method for manufacturing the nut for a ball screw according to any one of claims 1 to 3.

8. the first portion includes a radially extending flange; The method for manufacturing a nut for a ball screw according to claim 7.

9. The method further includes a step of cutting the inner wall surface on which the recess is provided. A method for manufacturing the nut for a ball screw according to any one of claims 1 to 3.

10. A screw shaft, A nut manufactured using the manufacturing method according to claim 1; a plurality of balls disposed between the screw shaft and the nut; A ball screw comprising:

11. A screw shaft, Nut and a plurality of balls disposed between the nut and the screw shaft; Equipped with The nut is a thread groove formed on an inner wall surface of the nut and corresponding to a main path along which the plurality of balls roll; a return groove formed on the inner wall surface by plastic working and corresponding to a return path relative to the main path; a trace of a recess formed by cutting in a partial region of the inner wall surface, the partial region being wider than a region in which the return groove is formed in both the circumferential direction and the axial direction; and Equipped with Ball screw.

12. The ball screw according to claim 11, further comprising a bank trace on the inner wall surface formed when the return groove was formed by the plastic working.

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