Method for manufacturing ball screw nuts

Abstract

This invention provides a method for manufacturing ball screw nuts that enables the formation of circulation grooves in the nuts with higher precision compared to conventional technologies. [Solution] A method for manufacturing a ball screw nut having a spiral groove on which a plurality of rolling elements roll, and a circulation groove 18 that returns the rolling elements from one end to the other of the spiral groove, comprising a circulation groove forming step and a spiral groove forming step. In the circulation groove forming step, a convex portion 42 corresponding to the concave portion of the circulation groove 18 is formed, and the outer diameter of the blank 9 is reduced relative to a first mold 40 located radially inside the blank 9 of the nut, thereby forming the circulation groove 18 on the inner circumferential surface 12 of the blank 9. In the circulation groove forming step, the outer circumferential surface 13 of the blank 9 is pressed against the inner circumferential surface 12 of the blank 9 by moving a second mold 50 located radially outside the blank 9 radially inside without moving it axially, thereby pressing the inner circumferential surface 12 of the blank 9 against the first mold 40.

Description

Technical Field

[0005] ,

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

Background Art

[0002] Conventionally, in a ball screw having a nut, a screw shaft, and a plurality of rolling elements, as one of the circuit structures for circulating the plurality of rolling elements, a return path (return orbit) provided on the inner peripheral surface of the nut separately from the groove for the main path (main orbit). A structure having a circulation groove is known. In such a ball screw, various methods for directly forming a circulation groove on the inner peripheral surface of the nut have been proposed.

[0003] For example, Patent Document 1 discloses a method for manufacturing a nut for a ball screw having a spiral groove (ball rolling path) in which a plurality of balls roll and a circulation groove (ball circulation path) for returning and circulating the balls from the end point to the start point of the spiral groove. This method for manufacturing a nut includes a punch having a convex portion corresponding to the circulation groove and a drawing die for reducing the outer diameter of the blank by squeezing the outer peripheral surface of the nut blank. According to the technique described in Patent Document 1, it is said that a circulation groove can be formed on the inner peripheral surface of the nut by reducing the diameter of the blank with the drawing die and pressing it against the punch.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Therefore, in the prior art described in Patent Document 1, there was a problem in that the circulation groove formed in the nut was formed with high precision in the method for manufacturing a ball screw nut in which a circulation groove is integrally formed in the nut.

[0007] Therefore, the present invention aims to provide a method for manufacturing a ball screw nut that can form circulation grooves in the nut with higher precision compared to the conventional technology. [Means for solving the problem]

[0008] To solve the above problems, this invention proposes the following means. A method for manufacturing a ball screw nut according to a first aspect of the present invention is a method for manufacturing a ball screw nut having a helical groove on which a plurality of rolling elements roll, and a circulation groove that returns the rolling elements from one end to the other end of the helical groove, comprising: a circulation groove forming step in which the circulation groove is formed on the inner circumferential surface of the nut by reducing the outer diameter of the blank with respect to a first mold which has a convex portion corresponding to the concave portion of the circulation groove and is located inside the blank of the nut; and a helical groove forming step in which the helical groove is formed on the inner circumferential surface by a removal process, wherein in the circulation groove forming step, the circulation groove is formed by pressing the outer circumferential surface of the blank by moving a second mold which is located on the radially outer side of the blank inward without moving it in the axial direction, thereby pressing the blank against the first mold. [Effects of the Invention]

[0009] The present invention provides a method for manufacturing ball screw nuts that allows for the formation of circulation grooves in the nuts with higher precision compared to the conventional method. [Brief explanation of the drawing]

[0010] [Figure 1] A schematic cross-sectional view showing a ball screw according to an embodiment. [Figure 2] A flowchart showing the process for manufacturing a ball screw nut according to the embodiment. [Figure 3] A cross-sectional view showing an overview of the circulation groove formation process in the manufacturing method of nuts. [Figure 4] A cross-sectional view showing an overview of the circulation groove formation process in the manufacturing method of nuts. [Figure 5] A perspective view illustrating the outline of the circulation groove formation process in the manufacturing method of nuts. [Figure 6] A cross-sectional view showing an overview of the mold removal process in the manufacturing of nuts. [Figure 7] A cross-sectional view along the line VII-VII in Figure 4. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described with reference to the drawings. In one embodiment, the ball screw 10 is incorporated into various mechanical devices such as electric brake systems and automatic manual transmissions (AMTs) of vehicles, and positioning devices of machine tools, 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 systems are applicable, such as EMB (Electro-Mechanical Brake) which applies braking force via a ball screw driven by a motor, and EHB (Electro-Hydraulic Brake) which controls the hydraulic pressure of a hydraulic brake via a ball screw driven by a motor. The ball screw 10 can also be applied to mechanical devices other than those mentioned above.

[0012] In the following description, unless otherwise specified, axial, radial, and circumferential directions refer to the direction along the central axis C of the ball screw 10 (nut 1), the radial direction of the ball screw 10 (nut 1), and the direction around the central axis C of the ball screw 10 (nut 1), respectively.

[0013] (Ball screw) Figure 1 is a schematic cross-sectional view showing a ball screw 10 according to an embodiment. The ball screw 10 is a device that converts rotational motion into linear motion. As shown in Figure 1, the ball screw 10 comprises a screw shaft 2, a nut 1 (the ball screw nut 1 of the claim), and a plurality of rolling elements 3 arranged between the screw shaft 2 and the nut 1.

[0014] The screw shaft 2 comprises a shaft body 20 and a helical screw groove (outer helical groove 21) provided on the outer circumferential surface of the shaft body 20. In one example, at least a portion of the screw shaft 2 is made of metal. The outer helical groove 21 is formed by machining or plastic deformation (e.g., rolling) on ​​the outer circumferential surface of the shaft body 20. Grinding can be additionally performed in the formation of the outer helical groove 21. The cross-sectional shape of the outer helical groove 21 is, for example, a Gothic arch or a circular arc containing two arcs.

[0015] The nut 1 comprises a cylindrical nut body 11 and a helical screw groove (inner helical groove 15 (helical groove of the claim)) provided on the inner circumferential surface 12 of the nut body 11. A screw shaft 2 is inserted and positioned inside the nut 1. In one example, at least a part of the nut 1 is made of metal. The inner helical groove 15 is formed by machining or plastic deformation on the inner circumferential surface 12 of the nut body 11. Grinding can be additionally performed in the formation of the inner helical groove 15. The cross-sectional shape of the inner helical groove 15 corresponds to the shape of the outer helical groove 21 of the screw shaft 2, and is, for example, a Gothic arch or a circular arc.

[0016] A plurality of rolling elements 3 are arranged between the screw shaft 2 and the nut 1. The rolling elements 3 are, for example, balls. In one example, the plurality of rolling elements 3 are made of metal (such as steel) or ceramics. In a state where the screw shaft 2 and the nut 1 are combined, an outer peripheral spiral groove 21 formed on the screw shaft 2 and an inner peripheral spiral groove 15 formed on the nut 1 are arranged opposite to each other, thereby forming a spiral rolling path 25. The rolling elements 3 move in this rolling path 25 as the relative rotation between the screw shaft 2 and the nut 1 occurs.

[0017] On the inner peripheral surface 12 of the nut 1, in addition to the inner peripheral spiral groove 15, a plurality (four in this embodiment) of circulation grooves 18 are formed. The circulation grooves 18 are integrally formed on the inner peripheral surface 12 of the nut 1 by a manufacturing method to be described in detail later. The circulation grooves 18 connect one end and the other end of the spiral rolling path 25 formed by the nut 1 and the screw shaft 2, constituting an infinite circulation circuit. And when a plurality of rolling elements 3 are filled in this infinite circulation circuit, the rolling elements 3 infinitely circulate in the infinite circulation circuit. When viewed from the radially inner side of the nut 1, the circulation grooves 18 are formed, for example, in a curved S shape. The circulation grooves 18 are formed in a U-shaped cross section corresponding to the spherical surface of the rolling elements 3 in a cross-sectional view perpendicular to the traveling direction of the rolling elements 3. The maximum depth of the circulation grooves 18 is set to be larger than the maximum depth of the inner peripheral spiral groove 15. For example, the depth of the circulation grooves 18 is set such that the rolling elements 3 can overcome the thread of the screw shaft 2 in a state where the screw shaft 2 and the nut 1 are combined.

[0018] The rolling elements 3 rotate around the screw shaft 2 while moving in the rolling path 25 and reach one end (the end point) of the rolling path 25, where they are guided into the circulation groove 18 from one end of the circulation groove 18. The rolling elements 3 guided by the circulation groove 18 are pushed by the subsequent rolling elements 3 and move to the other end of the circulation groove 18. And the rolling elements 3 are configured to return from the other end of the circulation groove 18 to the other end (the starting point) of the rolling path 25. The starting point and the end point of the rolling path 25 are interchanged according to the relative rotation direction between the screw shaft 2 and the nut 1. Thus, as the relative rotation between the screw shaft 2 and the nut 1 occurs, the rolling elements 3 can continuously circulate in a circulation path (circulation circuit) including the rolling path 25 and the circulation groove 18.

[0019] (Manufacturing Method of Nut for Ball Screw) Next, an example of the manufacturing method of the nut 1 for the ball screw 10 described above will be described with reference to FIGS. 2 to 7. FIG. 2 is a flowchart showing the flow of the manufacturing method of the nut 1 for the ball screw according to the embodiment. As shown in FIG. 2, the manufacturing method of the nut 1 includes a circulation groove forming step ST01, a removal step ST02, and a spiral groove forming step ST03. The circulation groove forming step ST01 includes a diameter reduction step ST12 and a mold removal step ST13.

[0020] FIGS. 3 and 4 are cross-sectional views showing the outline of the circulation groove forming step ST01 in the manufacturing method of the nut 1. FIGS. 3 and 4 show the outline of the diameter reduction step ST12 in the circulation groove forming step ST01. FIG. 5 is a perspective view showing the outline of the circulation groove forming step ST01 in the manufacturing method of the nut 1. FIG. 6 is a cross-sectional view showing the outline of the mold removal step ST13 in the manufacturing method of the nut 1. FIG. 7 is a cross-sectional view taken along line VII-VII of FIG. 4. As shown in FIG. 3, first, a blank 9 of the nut 1 processed into a cylindrical shape (the nut body 11 in a state before the inner circumferential rolling groove and the circulation groove 18 are formed) is prepared. Note that the above-mentioned nut body 11 and the blank 9 are substantially the same part, but for the convenience of explanation, in the following description, the one before the circulation groove 18 is formed on the inner circumferential surface 12 is referred to as the blank 9, and the one after the circulation groove 18 is formed may be referred to as the nut body 11.

[0021] Next, the diameter reduction step ST12 is performed. In the diameter reduction step ST12, the blank 9 is arranged with respect to a predetermined mold device. As shown in FIGS. 3 and 5, in the present embodiment, the mold device used in the circulation groove forming step ST01 (diameter reduction step ST12) includes a first mold 40 arranged inside the blank 9 in the radial direction, a second mold 50 and a cam slider 60 (the third mold in the claims) arranged outside the blank 9 in the radial direction.

[0022] In the diameter reduction step ST12, first, the first mold 40 and the second mold 50 are respectively arranged inside and outside the blank 9 in the radial direction. The first mold 40 includes a plurality of divided punches 41, a punch base 44, and a punch holding member 45. The number of divided punches 41 is the same as the number of circulation grooves 18 formed in the nut 1 (four in this embodiment), and they are positioned corresponding to each circulation groove 18. Each divided punch 41 has a protrusion 42 that corresponds to the recess of each circulation groove 18. The circulation grooves 18 are formed when this protrusion 42 is pressed against the inner circumferential surface 12 of the blank 9 and its shape is transferred. Therefore, the position of the protrusion 42 differs for each divided punch 41. The punch base 44 is provided radially inward from the plurality of divided punches 41. The punch base 44 restricts the position of each divided punch 41 and receives the load acting on the divided punches 41. The punch holding member 45 is positioned to contact the upper end surface of the divided punches 41. In the diameter reduction process ST12, an upward load is generated on the divided punches 41, so the punch holding member 45 suppresses the upward movement of the divided punches 41. The punch-holding member 45 is, for example, a hydraulic cushion. However, the configuration of the punch-holding member 45 is not limited to a hydraulic cushion.

[0023] The second mold 50 has a plurality of segmented dies 51. In this embodiment, the number of segmented dies 51 is the same as the number of circulation grooves 18 formed in the nut 1 (four in this embodiment), and they are arranged on the outer circumference of the blank 9 at positions corresponding to each circulation groove 18. Furthermore, on the inner surface of each segmented die 51, a relief portion 55 is formed at a position corresponding to each circulation groove 18 formed in the blank 9, which is recessed radially outward. Therefore, the position of the relief portion 55 differs for each segmented die 51. Each segmented die 51 is arranged so that its inner surface contacts the outer surface 13 of the blank 9. The relief portion 55 may be formed in a shape equivalent to the circulation groove 18 (for example, S-shaped).

[0024] As shown in Figure 3, the blank 9 is positioned axially by being held axially between a holder 81 and a pressing part 80, which are part of the mold apparatus. The holder 81 is located at one end of the blank 9 in the axial direction (the lower end in Figure 3) and supports the blank 9. The pressing part 80 is located at the other end of the blank 9 in the axial direction (the upper end in Figure 3). The pressing part 80 restricts the axial movement of the blank 9 by pressing the blank 9 downward in the axial direction. The pressing part 80 may be formed including an elastic member such as rubber or a spring. For example, the pressing part 80 may have a rigid body portion that contacts the end face of the blank 9 and an elastic member (such as a spring) that presses this rigid body portion toward the blank 9. In this case, the pressing part 80 may be configured to press the blank 9 axially by the elastic force of the elastic member. Alternatively, the pressing part 80 may press the blank 9 axially by using a hydraulic mechanism instead of an elastic member. In this case, a hydraulic cushion or the like may be used to cause the pressing part 80 to perform an action that simulates elastic force.

[0025] With the first mold 40, the second mold 50, the holder 81, and the retaining part 80 positioned in predetermined locations relative to the blank 9, the cam slider 60 is then extrapolated onto the second mold 50 from one axial side (the upper side in Figure 3). The cam slider 60 is formed in a cylindrical shape. The cam slider 60 is externally fitted into the second mold 50 from the axial direction. The inner circumference of the cam slider 60 has a planar tapered surface 60a, the inner diameter of which increases towards the insertion direction into the second mold 50. The outer circumference of the split die 51 also has a tapered surface 51a having the same inclination angle as the tapered surface 60a of the cam slider 60. In this embodiment, the tapered surface 60a of the cam slider 60 and the tapered surface 51a of the split die 51 form a cam mechanism 7. By externally fitting the cam slider 60 into the second mold 50 from the axial direction using the cam mechanism 7, the second mold 50 can be moved radially inward (see also the arrow in Figure 3). The tapered surface 60a of the cam slider 60 may be formed as a conical tapered surface. In this case, the tapered surface 51a of the corresponding divided die 51 may also be formed as a conical tapered surface.

[0026] As shown in Figure 4, when the tapered surface 60a of the cam slider 60 and the tapered surface 51a of the split die 51 are in contact, and the cam slider 60 is further inserted axially toward the second mold 50, the split die 51 of the second mold 50 moves radially inward while deforming the blank 9. The second mold 50 presses against the outer circumferential surface 13 of the blank 9 by moving radially inward relative to the blank 9 without moving axially relative to the blank 9. This reduces the outer and inner diameter dimensions of the blank 9 (reduces its diameter). The reduced diameter blank 9 is pressed against the convex portion 42 of the split punch 41 of the first mold 40. As a result, a circulation groove 18 with a shape transferred from the shape of the convex portion 42 is formed on the inner circumferential surface 12 of the blank 9. In other words, in the diameter reduction process ST12, the outer diameter of the blank 9 is reduced relative to the first mold 40 which is positioned radially inward of the blank 9, thereby forming multiple circulation grooves 18 on the inner circumferential surface 12 of the blank 9. Furthermore, in the diameter reduction process ST12, it is possible to simultaneously form multiple circulation grooves 18 with a single plastic deformation, that is, a single movement of the second mold 50 radially inward. As a result of the formation of the circulation grooves 18, a portion of the flowing blank 9 material flows toward the relief portion 55 of the split die 51, forming a raised portion 33 that protrudes toward the outer circumference of the nut body 11. The raised portion 33 is removed by a removal process described later.

[0027] Next, the mold removal process ST13 is performed. In the mold removal process ST13, first, the cam slider 60 is moved to the opposite side from the second mold 50 to release the engagement of the cam mechanism 7. Then, the blank 9 is removed from the second mold 50 by moving the divided die 51 radially outward (moved in the opposite direction to the arrow in Figure 3). Next, as shown in Figure 6, the punch base 44 of the first mold 40 is pulled out axially to remove it from the blank 9. This allows the divided punch 41 to move radially inward, so the divided punch 41 is tilted toward the inner diameter to disengage the protrusion 42 from the circulation groove 18, and the divided punch 41 is also removed by pulling it out axially. Multiple divided punches 41 are removed in the same manner. As a result, the first mold 40 is removed from the inner circumference of the blank 9. When the mold removal process ST13 is completed, a blank 9 (nut body 11) is formed with multiple circulation grooves 18 formed on the inner circumferential surface 12.

[0028] Once the circulation groove formation process ST01 is completed, the removal process ST02 is then performed. In the removal process ST02, the inner circumferential surface 12 and outer circumferential surface 13 of the nut body 11 are subjected to removal processing. In this embodiment, the inner circumferential surface 12 and outer circumferential surface 13 of the nut body 11 are machined to remove irregularities such as raised portions 33 (see Figure 6) and stepped portions 38 (see Figure 7) that were created in the circulation groove formation process ST01 described above. Here, as shown in Figure 7, in the circulation groove formation process ST01 described above, the blank 9 is reduced in diameter with the divided die 51 and divided punch 41 in contact with the surface of the blank 9, so some of the blank 9 material that flows during the reduction in diameter tends to flow towards the boundary portion 36 between the divided parts. For this reason, a stepped portion 38 may be formed on the inner circumferential surface 12 and outer circumferential surface 13 of the nut body 11 after the reduction in diameter, at a position corresponding to the boundary portion 36. Although Figure 7 shows only one of the stepped portions 38 corresponding to the boundary portion 36 of the divided die 51, in reality, the same number of stepped portions 38 as the number of boundary portions 36 of the divided die 51 are formed on the outer circumference. Similarly, the same number of stepped portions 38 as the number of boundary portions of the divided punch 41 are formed on the inner circumferential surface 12 of the nut body 11. In the removal process ST02, these stepped portions 38 and raised portions 33 are removed by cutting or other processes. Note that removal processes other than cutting, such as polishing, may also be performed.

[0029] Once the removal process ST02 is completed, the spiral groove forming process ST03 is performed. In the spiral groove forming process ST03, an inner spiral groove 15 is formed on the inner surface 12 of the nut body 11 by removal processes such as cutting. At this time, the inner spiral groove 15 is formed so that its inner shape is smaller than that of the circulation groove 18. The inner shape refers to the size of the cross-sectional shape of the groove (groove depth, cross-sectional area, etc.) in a cross section perpendicular to the direction of travel of the rolling elements 3 that roll in the circulation groove 18 or the inner spiral groove 15. In other words, the cross-sectional shape of the inner spiral groove 15 is smaller than that of the circulation groove 18. As a result, for example, one end of the circulation groove 18 is connected to a part of the inner spiral groove 15, and the other end of the circulation groove 18 is connected to another part of the inner spiral groove 15.

[0030] By going through the above steps, a nut 1 having an inner helical groove 15 and a circulation groove 18 on its inner circumferential surface 12 is formed. Although not explained in the above embodiment, for example, a rough forming step to obtain a blank 9 from the base material may be included before the circulation groove formation step ST01. Furthermore, an outer circumferential finishing step may be included in which gears, flanges, etc., are formed on the outer circumferential surface 13 of the nut body 11 by performing plastic deformation or removal processing on the outer circumferential surface 13 of the nut body 11. A chamfering step may be included separately to chamfer the boundary between the circulation groove 18 and the inner helical groove 15. After the helical groove formation step ST03 and the chamfering step, a heat treatment step such as carburizing, carbonitriding, quenching, or tempering may be included separately.

[0031] (Effect, Action) In the manufacturing method of the ball screw nut 1 of this embodiment, a circulation groove 18 is formed on the inner circumference of the nut 1 by reducing the diameter of the blank 9 of the nut 1 and pressing it against the first mold 40. Conventionally, another method for integrally forming the circulation groove 18 on the inner circumference 12 of the nut 1 is to move the first mold 40 radially outward and press it against the inner circumference 12 of the blank 9. However, this method requires the first mold 40 to be formed with high strength, which can make it difficult to apply to nuts 1 with particularly small inner diameters. In the manufacturing method of the ball screw nut 1 of this embodiment, the first mold 40 can be fixed, so the strength of the first mold 40 can be maintained at a high level compared to the manufacturing method in which the first mold 40 is expanded in diameter and pressed against the inner circumference 12 of the blank 9. Therefore, the mold life can be extended and the circulation groove 18 can be formed with high precision. In the circulation groove formation process ST01, the blank 9 is reduced in diameter by moving the second mold 50, which is positioned radially outside the blank 9, radially inward without moving it axially. This allows the circulation groove 18 to be formed while suppressing the axial flow of the blank 9 material. Therefore, compared to conventional techniques in which the blank 9 is reduced in diameter by axial drawing, this method suppresses deformation of the circulation groove 18 and a decrease in the positional accuracy of the circulation groove 18 caused by the axial flow of the blank 9 material. In addition, since no shear force is generated along the axial direction on the protrusion 42 of the first mold 40, deformation and damage to the protrusion 42 in the split punch 41 can be suppressed. Therefore, a decrease in the formation accuracy of the circulation groove 18 caused by deformation of the split punch 41 can be suppressed. Therefore, compared to conventional technology, it is possible to provide a method for manufacturing a ball screw nut 1 that can form a circulation groove 18 in the nut 1 with high precision. Furthermore, the manufacturing method for the ball screw nut 1 of this embodiment is advantageous in terms of mold life because no shear force is generated in the first mold 40.

[0032] The second mold 50 (multiple segmented dies 51) is moved radially inward by the cam mechanism 7. This allows for easy and highly accurate formation of the circulation groove 18.

[0033] In the circulation groove formation process ST01, multiple circulation grooves 18 are formed simultaneously by a single movement of the second mold 50. This improves the positional accuracy of the circulation grooves 18 even when multiple circulation grooves 18 are provided.

[0034] In the circulation groove formation process ST01, the circulation groove 18 is formed with the pressing portion 80 positioned at the end of the blank 9. The pressing portion 80 presses the blank 9 in the axial direction, restricting its movement in the axial direction. As a result, axial deformation and movement of the blank 9 are suppressed, and the circulation groove 18 can be formed with high precision.

[0035] On the inner circumferential surface of the second mold 50, a relief portion 55 is formed at a position corresponding to the recess (circulation groove 18), which is recessed radially outward. As a result, the blank 9 material extruded by the flow during the formation of the circulation groove 18 protrudes toward the relief portion 55 (see the raised portion 33 in Figure 4). This suppresses the axial flow of the blank 9 material and prevents the shape of the circulation groove 18 from collapsing. Therefore, the circulation groove 18 can be formed with high precision.

[0036] The manufacturing method for the ball screw nut 1 includes a removal step ST02 following a circulation groove forming step ST01. In the removal step ST02, a removal process (e.g., cutting) is performed on at least one of the inner circumferential surface 12 and the outer circumferential surface 13 of the nut 1. As a result, even when using divided first mold 40 and second mold 50, the stepped portion 38 etc. formed at the boundary portion 36 of the division of each mold on the nut 1 can be removed in the removal step ST02. Therefore, the surface of the nut 1 can be finished smoothly, improving the appearance quality.

[0037] It should be noted that the technical scope of the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention. For example, in the above embodiment, an example was described in which the inner circumferential surface 12 and the outer circumferential surface 13 of the nut body 11 are machined in the removal step ST02, but the invention is not limited to this. In the removal step ST02, removal may be performed on at least one of the inner circumferential surface 12 and the outer circumferential surface 13 of the nut body 11.

[0038] The number of split punches 41 is not limited to four. Depending on the number of circulation grooves 18 formed in the nut 1, the number of split punches 41 may be two, three, or five or more. Also, in the above embodiment, the same number of split punches 41 as the number of circulation grooves 18 formed in the nut 1 were used, but this is not limited to this. That is, the number of circulation grooves 18 formed in the nut 1 and the number of split punches 41 used may be different from each other. However, considering the removal of the mold, it is necessary to use at least two split punches 41. If the number of circulation grooves 18 and the number of split punches 41 are different, for example, multiple protrusions 42 may be provided on one split punch 41. Alternatively, the protrusions 42 of one circulation groove 18 may be formed across multiple split punches 41. Similarly, the number of segmented dies 51 may be 2, 3, or 5 or more.

[0039] In the embodiments described above, a method for manufacturing a ball screw nut having multiple circulation grooves 18 has been described, but the present invention may also be applied to the manufacture of a ball screw nut having only one circulation groove. In this case, for example, two split punches 41 may be prepared in the first mold 40, with one split punch having a protrusion 42 and the other split punch not having a protrusion. In other words, the first mold 40 may have a split punch 41 in which no protrusion 42 is formed.

[0040] A method other than the cam mechanism 7 may be used to move the second mold 50 radially inward. For example, a method using hydraulic pressure or air pressure, a method using a motor and ball screw, or a method using the elastic force of an elastic body may be used as a substitute for the cam mechanism 7. If the blank 9 is thin-walled, bulge forming (hydroforming) may be used.

[0041] Furthermore, this disclosure may also be a combination of the following configurations. (1) A method for manufacturing a ball screw nut having a helical groove on which multiple rolling elements roll, and a circulation groove that returns the rolling elements from one end to the other end of the helical groove, A circulation groove forming step is performed by forming a convex portion corresponding to the concave portion of the circulation groove and reducing the outer diameter of the blank with respect to a first mold positioned radially inward of the blank of the nut, thereby forming the circulation groove on the inner circumferential surface of the nut, A helical groove forming step, in which the helical groove is formed on the inner circumferential surface by removal processing, Equipped with, In the circulation groove forming step, the circulation groove is formed by pressing the outer circumferential surface of the blank by moving the second mold, which is positioned radially outside the blank, radially inward without moving it axially, and pressing the inner circumferential surface of the blank against the first mold. A method for manufacturing ball screw nuts. (2) In the circulation groove forming step, the second mold is moved radially inward by a cam mechanism formed by the second mold and a third mold that is externally fitted to the second mold from the axial direction of the blank. (1) A method for manufacturing a ball screw nut as described in (1). (3) In the circulation groove formation step, multiple circulation grooves are formed simultaneously by a single movement of the second mold. A method for manufacturing a ball screw nut as described in (1) or (2). (4) In the circulation groove forming step, the circulation groove is formed with a pressing portion positioned at the axial end of the blank, which restricts the axial movement of the blank by pressing it from the axial direction. A method for manufacturing a ball screw nut as described in any one of (1) to (3). (5) The pressing portion includes an elastic member, and the elastic force of the elastic member presses the blank in the axial direction. (4) A method for manufacturing a ball screw nut as described in (4). (6) A relief portion is formed on the inner circumferential surface of the second mold at a position corresponding to the recess, which is recessed radially outward. A method for manufacturing a ball screw nut as described in any one of (1) to (5). (7) The process further includes a removal step, which is performed after the circulation groove forming step, on at least one of the inner circumferential surface and the outer circumferential surface of the nut. A method for manufacturing a ball screw nut as described in any one of (1) to (6). [Explanation of Symbols]

[0042] 1. Nut (for ball screw) 3 Rolling element 7 Cam mechanism 9 Blank 10 Ball screws 11 Nut body 12 Inner surface 13 Outer surface 15. Inner circumferential spiral groove (spiral groove) 18 Circulation groove 40 First Mold 42 Convex part 50 Second mold 55 Escape Club 60 Cam slider (third mold) 80 Pressing part ST01 Circulation groove formation process ST02 Removal process ST03 Spiral groove forming process

Claims

1. A method for manufacturing a ball screw nut having a helical groove on which multiple rolling elements roll, and a circulation groove that returns the rolling elements from one end to the other end of the helical groove, A circulation groove forming step is performed by forming a convex portion corresponding to the concave portion of the circulation groove and reducing the outer diameter of the blank with respect to a first mold positioned radially inward of the blank of the nut, thereby forming the circulation groove on the inner circumferential surface of the nut, A helical groove forming step, in which the helical groove is formed on the inner circumferential surface by removal processing, Equipped with, In the circulation groove forming step, the circulation groove is formed by pressing the outer circumferential surface of the blank by moving the second mold, which is positioned radially outside the blank, radially inward without moving it axially, and pressing the inner circumferential surface of the blank against the first mold. A method for manufacturing ball screw nuts.

2. In the circulation groove forming step, the second mold is moved radially inward by a cam mechanism formed by the second mold and a third mold that is externally fitted to the second mold from the axial direction of the blank. A method for manufacturing a ball screw nut according to claim 1.

3. In the circulation groove formation step, multiple circulation grooves are formed simultaneously by a single movement of the second mold. A method for manufacturing a ball screw nut according to claim 1.

4. In the circulation groove forming step, the circulation groove is formed with a pressing portion positioned at the axial end of the blank, which restricts the axial movement of the blank by pressing it from the axial direction. A method for manufacturing a ball screw nut according to claim 1.

5. The pressing portion includes an elastic member, and the elastic force of the elastic member presses the blank in the axial direction. A method for manufacturing a ball screw nut according to claim 4.

6. A relief portion is formed on the inner circumferential surface of the second mold at a position corresponding to the recess, which is recessed radially outward. A method for manufacturing a ball screw nut according to claim 1.

7. The process further includes a removal step, which is performed after the circulation groove forming step, on at least one of the inner circumferential surface and the outer circumferential surface of the nut. A method for manufacturing a ball screw nut according to any one of claims 1 to 6.

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