JP5621634B2 - Nut for ball screw and manufacturing method thereof - Google Patents

Description

  The present invention relates to a method for manufacturing a nut constituting a ball screw.

The ball screw is disposed between a nut having a spiral groove formed on the inner peripheral surface, a screw shaft having a spiral groove formed on the outer peripheral surface, and a raceway formed by the spiral groove of the nut and the spiral groove of the screw shaft. And a ball return path for returning the ball from the end point of the track to the start point, and the nut moves relative to the screw shaft as the ball rolls in the track.
Such a ball screw is used not only for a general industrial machine positioning device but also for an electric actuator mounted on a vehicle such as an automobile, a two-wheeled vehicle or a ship.

  The ball return path of the ball screw includes a circulation tube system, a top system, and the like. In the case of the top system, a top formed with a recess that forms the ball return path is fitted in the through hole of the nut. On the other hand, Patent Document 1 (Japanese Patent Laid-Open No. 2003-307263) describes a ball screw in which a concave portion (ball circulation groove) forming a ball return path is directly formed on the inner peripheral surface of a nut. .

  Specifically, the nut member of the ball screw does not have a split surface in the circumferential direction, and is integrally formed by cutting or forging, and a female spiral groove (ball rolling groove) is formed on the inner peripheral surface of the nut member. It is described that a long S-shaped circulation path (ball circulation groove) having a deeper part (projecting radially outward) is formed and both ends of the female spiral groove are smoothly connected. However, it does not describe how the female spiral groove and the circulation path are specifically formed.

Patent Document 2 (Japanese Patent Application Laid-Open No. 2000-297854) has a recess (return groove), a spiral groove (inner thread groove), and a protruding portion on the outer peripheral surface (portion forming an outer diameter surface) forming a ball return path. It has been proposed to integrally form the nut with a sintered alloy.
In Patent Document 3 (Japanese Patent Laid-Open No. 2005-321059), a ball circulation path including a spiral load ball rolling groove and a ball circulation groove connecting one end and the other end of the ball circulation path includes an inner peripheral surface of a nut. The “screw device” formed in the above is described. As a method for forming the ball circulation path, it is described that the ball circulation path can be manufactured by an inner diameter grooving technique called “inner cam”.
Patent Document 4 (Japanese Patent Application Laid-Open No. 2008-281063) describes a method in which a ball circulation groove is directly formed on the inner peripheral surface of a nut material by plastic working. In this method, as shown in FIG. 5, a die having a cylindrical processing head 30 having S-shaped convex portions 37 and 38 corresponding to the shape of the ball circulation groove is used.

  Then, the nut material 1 is placed sideways on the base 200 (so that the axial direction is along the horizontal direction), the processing head 30 is placed inside the nut material 1 with the convex portions 37 and 38 facing upward, and the base end With the part 30a and the tip part 30b fixed, the upper member 20 of the mold is lowered by applying a pressing pressure. Thereby, the convex parts 37 and 38 are pressed against the inner peripheral surface 11 of the nut material 1 to plastically deform the inner peripheral surface 11 of the nut material 1.

JP 2003-307263 A JP 2000-297854 A Japanese Patent Laying-Open No. 2005-321059 JP 2008-281063 A

  A method of forming such a ball circulation groove by plastically deforming a nut material, which is different from the method of Patent Document 4, in which a cylindrical nut material is arranged so that the axial direction is along the vertical direction. In a state in which the outer peripheral surface and one end surface in the axial direction are constrained, the punch inserted in the nut material is moved radially outward of the nut material and pressed against the inner peripheral surface of the nut material. The forging method used) can be considered.

In this method, a concave bending force (ball circulation groove) corresponding to the protrusion shape of the punch is formed by denting the inner peripheral surface of the nut material with the pressing force of the punch, so that a strong bending stress acts on the punch. Further, the shape accuracy of the ball circulation groove is lowered due to the flow of the material existing in the recessed portion. In particular, when a plurality of ball circulation grooves are formed at a time, the shape accuracy and the positional accuracy in the axial direction and the circumferential direction are low, and variations in the shape of each ball circulation groove are likely to occur.
An object of the present invention is to form a ball circulation groove on the inner peripheral surface of a nut material by a forging method using a punch, and the material flow of the nut material can be suppressed and the bending stress acting on the punch can be reduced. Is to provide a method.

In order to solve the above-mentioned problems, the present invention manufactures a ball screw nut which comprises a ball screw together with a screw shaft and a ball, and has a ball circulation groove on the inner peripheral surface for returning the ball from the end point of the rolling track to the start point. A material deficient portion that is a through-hole penetrating in the radial direction of the nut material at a position where the ball circulation groove is formed in the axial direction of the cylindrical nut material, In a state where the outer peripheral surface and one end surface in the axial direction are constrained, by moving the punch inserted in the nut material to the outside in the radial direction of the nut material, while letting the material of the nut material escape to the material defect portion, The ball circulation groove is formed.

Examples of a method for forming the material defect portion in the nut material include turning, cutting, forging, and the like.
According to the method of the present invention, the material deficiency is formed by forming the ball circulation groove in the nut material in which the material deficiency portion is formed while allowing the material to escape to the material deficiency portion by a forging process using a punch. Compared with the case where the ball circulation groove is formed by a forging method using a punch on a nut material in which no portion is formed, the amount of material flow is reduced and the bending stress acting on the punch can be reduced.

Before SL material defects, after formation of the ball circulation groove, it is preferably formed to have a state without the ball circulation groove and the communication. Therefore, the material that has been released before the SL when forming the ball circulation groove, so that the radially inner side of the through hole forming the material defect is closed, sets the size of the through hole.

  According to the method of the present invention, in the method of forming a ball circulation groove on the inner peripheral surface of the axial direction end portion of the nut material by a forging method using a punch, the bending stress acting on the punch is suppressed while the material flow is suppressed. Therefore, the shape accuracy and position accuracy of the ball circulation groove are improved, and the life of the punch is improved.

It is a figure explaining the method of 1st Embodiment. It is a figure explaining the method of forming one ball circulation groove with the forging method using the punch employ | adopted by the method of 1st Embodiment. It is a figure explaining the method of forming a some ball | bowl circulation groove | channel at once with the forging method using the punch employ | adopted with the method of 1st Embodiment. It is a figure explaining the method of 2nd Embodiment. It is a figure explaining the method of patent document 4. FIG.

Embodiments of the present invention will be described below.
[First Embodiment]
In this embodiment, as shown in FIG. 1, the operation of forming a ball circulation groove 15 having a circular cross section and an S-shaped ball movement direction on the inner surface of a cylindrical nut material 1 is performed in two steps. .
First, a through hole (material defect portion) 13 extending in the radial direction is formed by cutting at a position where the ball circulation groove 15 is formed in the axial direction of the nut material 1. The through hole 13 is formed along the S-shaped ball moving direction of the ball circulation groove 15. Next, the ball circulation groove 15 is formed at a position where the through hole 13 is formed in the inner peripheral surface 11 of the nut material 1 by the method shown in FIG.
The mold used in the method shown in FIG. 2 includes an outer peripheral restraint die 2 that restrains the outer peripheral surface of the cylindrical nut material 1, a lower die 3 that restrains the lower end surface of the nut material 1, and an upper end surface of the nut material 1. A cylindrical presser member 4 to be mounted.

A cylindrical cam case 5 inserted into the nut material 1, a cam driver 6 inserted into the center hole 51 of the cam case 5, and a punch (cam slider) disposed in a through hole 52 along the radial direction of the cam case 5. 7
The cam case 5 is inserted in the nut material 1 with the through hole 52 formed on the upper side. On the punch 7, a protrusion 71 corresponding to the S-shaped ball circulation groove 15 is formed. The punch 7 has the same slope 72 as the slope 61 of the cam driver 6. These slopes 61 and 72 constitute a cam mechanism.

  By using this mold, the lower end surface (one axial end surface) of the nut blank 1 and the lower end surface of the cam case 5 are restrained by the lower mold 3. In this state, by pushing the cam driver 6, the punch 7 moves outward in the radial direction of the nut material 1, and the protrusion 71 of the punch 7 is pushed into the inner peripheral surface 11 of the nut material 1. As a result, the material of the nut material 1 pushed by the punch 7 is released to the through hole 13, the ball circulation groove 15 is formed on the inner peripheral surface 11, and the radially inner side of the through hole 13 is blocked. Thus, the ball circulation groove 15 is not communicated.

Therefore, as compared with the case where the ball circulation groove 15 is formed without providing the through hole 13 in the nut material 1, the amount of material flow is reduced and the bending stress acting on the punch 7 can be reduced. As a result, the shape accuracy of the ball circulation groove 15 and the positional accuracy in the axial direction and the circumferential direction are improved, and the life of the punch 7 is improved.
In the case where a plurality of ball circulation grooves are formed on the inner peripheral surface 11 of the nut material 1 at a time, a punch is used by, for example, the method shown in FIG. 3 after providing through holes 13 at a plurality of corresponding positions. Perform forging process.

  The mold used in the method shown in FIG. 3 includes an outer peripheral restraint die 2 that restrains the outer peripheral surface of the cylindrical nut material 1, a lower die 3 that restrains the lower end surface of the nut material 1, and an upper end surface of the nut material 1. A cylindrical presser member 4 to be mounted. Also, a cylindrical cam case 5A to be inserted into the nut material 1, a cam driver 6A to be inserted into the center hole 51 of the cam case 5A, and punches disposed in the through holes 52 and 53 along the radial direction of the cam case 5A ( Cam slider) 7A, 7B.

The punches 7A and 7B are formed with protrusions 71A and 71B corresponding to the shape of the ball circulation grooves 15 and 16 (the cross section is arcuate and the ball moving direction is S-shaped). The cam driver 6A has the same slope 61A as the slope 72A of the punch 7A and the same slope 61B as the slope 72B of the punch 7B. The slopes 61A and 72A have a smaller inclination angle than the slopes 61B and 72B. The slope 61A and the slope 72A, and the slope 61B and the slope 72B constitute a cam mechanism, respectively.
By using this die, the lower end surface (the other end surface in the axial direction) of the nut material 1 and the lower end surface of the cam case 5A are restrained by the lower die 3. In this state, by pushing the cam driver 6A, the punches 7A and 7B are moved radially outward of the nut material 1, and the protrusions 71A and 71B of the punches 7A and 7B are pushed into the inner peripheral surface 11 of the nut material 1. .

Thereby, the material of the nut material 1 pushed by the punches 7A and 7B is released to the respective through holes 13 to form the ball circulation grooves 15 and 16 on the inner peripheral surface 11, and the radial direction of the through holes 13 The inner side is blocked and the ball circulation grooves 15 and 16 are not communicated.
Therefore, compared to the case where the ball circulation grooves 15 and 16 are formed without providing the through holes 13 in the nut material 1, the amount of material flow is reduced and the bending stress acting on the punches 7A and 7B can be reduced. . As a result, the shape accuracy of the ball circulation grooves 15 and 16 and the positional accuracy in the axial direction and the circumferential direction are improved, and the lifetime of the punches 7A and 7B is improved.

[Second Embodiment]
In this embodiment, as shown in FIG. 4, the operation of forming a ball circulation groove 15 having a circular cross section and an S-shaped ball movement direction on the inner surface of a cylindrical nut material 1 is performed in two steps. .
First, a blind hole 14 that extends in the radial direction from the outer peripheral surface of the nut material 1 and does not reach the inner peripheral surface 11 is formed by turning at a position where the ball circulation groove 15 is formed in the axial direction of the nut material 1. This blind hole 14 is formed along the S-shaped ball moving direction of the ball circulation groove 15. Further, the bottom position of the blind hole 14 is set to the outside in the radial direction from the bottom position of the ball circulation groove 15.

Next, similarly to the first embodiment, the ball circulation groove 15 is formed at a position corresponding to the blind hole 14 of the inner peripheral surface 11 of the nut material 1 by the method using the mold of FIG. As a result, the material of the nut material 1 pushed by the punch 7 is released to the blind hole 14 to form the ball circulation groove 15 on the inner peripheral surface 11, and the ball circulation groove 15 and the blind hole 14 are not in communication with each other. Become.
Therefore, compared with the case where the ball circulation groove 15 is formed without providing the blind hole 14 in the nut material 1, the amount of material flow is reduced and the bending stress acting on the punch 7 can be reduced. As a result, the shape accuracy of the ball circulation groove 15 and the positional accuracy in the axial direction and the circumferential direction are improved, and the life of the punch 7 is improved.

In addition, when forming a plurality of ball circulation grooves on the inner peripheral surface 11 of the nut material 1 at a time, after forming the blind holes 14 at a plurality of corresponding positions, for example, by a method using the mold of FIG. Forging using the punches 7A and 7B is performed. As a result, the material of the nut material 1 pushed by the punches 7A and 7B is released to the blind holes 14, and the ball circulation grooves 15 and 16 are formed on the inner peripheral surface 11. The blind hole 14 is not in communication.
Therefore, compared with the case where the ball circulation grooves 15 and 16 are formed without providing the blind holes 14 in the nut material 1, the amount of material flow is reduced and the bending stress acting on the punches 7A and 7B can be reduced. . As a result, the shape accuracy of the ball circulation grooves 15 and 16 and the positional accuracy in the axial direction and the circumferential direction are improved, and the lifetime of the punches 7A and 7B is improved.

1 Nut material 11 Inner circumferential surface of nut material 13 Through hole (material missing part)
14 blind hole (material missing part)
15, 16 Ball circulation groove 2 Peripheral restraint type 3 Lower die 4 Holding member 5 Cam case 5A Cam case 51 Cam case center hole 52, 53 Cam case through hole 6 Cam driver 6A Cam driver 61, 61A, 61B Cam driver slope 7A, 7B Punch (cam slider)
71A, 71B Protrusion 72, 72A, 72B Slope of punch

Claims (2)

A method of manufacturing a ball screw nut having a ball circulation groove on an inner peripheral surface, which comprises a ball screw together with a screw shaft and a ball, and returns the ball from the end point of the rolling track to the start point,
After forming a material defect portion which is a through hole penetrating in the radial direction of the nut material at a position where the ball circulation groove is formed in the axial direction of the cylindrical nut material, the outer circumferential surface of the nut material is aligned with the axial direction. The ball circulation groove is formed while the punch material inserted in the nut material is moved radially outward of the nut material while the end face is constrained, while the material of the nut material is released to the material defect portion. A method for producing a nut for a ball screw. A ball screw nut manufactured by the method according to claim 1 .

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