JP2012180539A - Method for manufacturing nut for ball screw, and nut for ball screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a nut for a ball screw, which can further reduces the cost and labor hours while minimizing thermal deformation by heat treatment for surface hardening, and a nut for a ball screw manufactured by the method.SOLUTION: An inner circumferential surface 11 of a nut material 10 having a rolling groove 16 formed on the inner circumferential surface 11 and one or more circulation grooves 15 formed on the inner circumferential surface 11 to return a ball disposed between the rolling groove 16 and a rolling groove formed on the outer circumferential surface of a screw shaft from the end point of a raceway to the start point thereof is high-frequency heated, while an outer circumferential surface 12 thereof is cooled.

Description

  The present invention relates to a method of manufacturing a nut constituting a ball screw and a ball screw nut manufactured by the manufacturing method.

A ball screw has a raceway formed by a nut having a rolling groove formed on the inner peripheral surface, a screw shaft having a rolling groove formed on the outer peripheral surface, and the nut rolling groove and the screw shaft rolling groove. A device that includes a ball disposed between 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 by rolling the ball in the track. .
When the surface of such a ball screw nut is hardened by carburizing and quenching, the machining allowance when grinding the rolling groove of the nut increases as the strain increases due to heat treatment. As a result, there was a problem that the processing efficiency was lowered.

Therefore, in order to solve such a problem, Patent Document 1 discloses a method for forming a hardened layer that improves processing efficiency.
In Patent Document 1, the entire nut is heated from the outer diameter side to a predetermined temperature with a low frequency coil, and then the nut inner diameter is heated with a high frequency coil disposed on the nut inner diameter side, thereby forming a uniform hardened layer along the rolling groove. Is disclosed.

JP 2003-183735 A

However, in the method described in Patent Document 1, since the entire nut is heated from the outer diameter side to a predetermined temperature and then heated by the high frequency coil from the inner diameter side, the switching of the coil, the equipment for that, etc., cost and labor However, there is room for improvement.
Therefore, the present invention has been made paying attention to the above-mentioned problems, and its purpose is to minimize the thermal deformation due to heat treatment for surface hardening, and to further reduce the cost and labor. A manufacturing method and a nut of a ball screw manufactured by the manufacturing method.

A ball screw nut manufacturing method according to claim 1 of the present invention for solving the above-described problems includes a nut having a rolling groove formed on an inner peripheral surface and a screw shaft having a rolling groove formed on an outer peripheral surface. And a ball disposed between the raceway formed by the rolling groove of the nut and the rolling groove of the screw shaft, and at least one circulation groove for returning the ball from the end point of the raceway to the start point A method of manufacturing a nut of a ball screw formed on an inner peripheral surface of a nut,
The surface to be cured of the nut is heated by high frequency, and the surface opposite to the surface to be cured is cooled, and then the surface to be cured of the nut and the surface on the opposite side are cooled.

According to the first aspect of the present invention, since the through hole penetrating the inner peripheral surface and the outer peripheral surface of the nut is not formed in the nut, the central axis of the coil for high frequency heat treatment and the central axis of the nut Can be uniformly heated.
Further, since the through hole is not formed in the nut, the nut can be uniformly cooled even when the nut is cooled, and as a result, thermal deformation of the nut can be minimized.

Furthermore, since the heating and cooling of the nut is not time-consuming, it is possible to make a quick transition from the heating process to the cooling process. As a result, it is easy to control the quenching depth, and the hardness of each part of the nut is optimized. Can be a value.
The ball screw nut manufacturing method according to claim 2 of the present invention for solving the above-mentioned problem is the ball screw nut manufacturing method according to claim 1, wherein the coil has a shape along the rolling groove. It is characterized by being.

According to the second aspect of the present invention, an effective hardened layer that is uniform in the depth direction can be formed over substantially the entire rolling groove.
A ball screw nut according to a third aspect of the present invention for solving the above problems includes a nut having a rolling groove formed on an inner peripheral surface, a screw shaft having a rolling groove formed on an outer peripheral surface, and a nut. A ball disposed between the raceway formed by the rolling groove of the screw shaft and the rolling groove of the screw shaft, and at least one circulation groove for returning the ball from the end point of the raceway to the starting point is provided in the nut. A ball screw nut formed on the circumferential surface,
The nut is manufactured by the ball screw nut manufacturing method according to claim 1 or 2.

According to the third aspect of the present invention, it is possible to provide a ball screw nut that keeps thermal deformation due to heat treatment for surface hardening to a minimum and further reduces costs and labor.
The ball screw nut according to claim 4 of the present invention for solving the above-mentioned problem is the ball screw nut according to claim 3, wherein the surface hardness of the inner peripheral surface is HRC 58 to 62, and the effective hardened layer. The hardness is Hv550 or higher, the depth of the effective hardened layer is 0.4 mm or higher, and the core has a hardness of HRC40 or lower.

  According to the invention which concerns on Claim 4, while ensuring a rolling fatigue life, there exists an effect of improving toughness and suppressing the deformation | transformation by heat processing.

  According to the present invention, there is provided a ball screw nut manufacturing method that keeps thermal deformation due to heat treatment for surface hardening to a minimum and further reduces costs and labor, and a ball screw nut manufactured by the manufacturing method. can do.

It is a figure explaining one Embodiment of the manufacturing method of the nut of a ball screw concerning the present invention. The top view (a) which shows the fitting state of the cam slider and cam driver which comprise the metal mold | die used by one Embodiment of the manufacturing method of the nut of the ball screw concerning this invention, The perspective view (b) which shows a cam slider, It is a perspective view (c) which shows a cam driver. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure explaining one Embodiment of the manufacturing method of the nut of the ball screw which concerns on this invention, (a) is a perspective view which shows the state of the cutting process of a nut raw material, (b) is (a). It is the figure which looked at the nut raw material and cutting tool which are shown to the arrow VB direction. It is a figure explaining one Embodiment of the manufacturing method of the nut of the ball screw concerning the present invention, (a) is an axial direction sectional view after cutting processing of a nut material, and (b) is cutting of a nut material. It is a perspective view after processing. It is a figure explaining the hardening process in one Embodiment of the manufacturing method of the nut of a ball screw concerning the present invention. It is the graph which compared the relationship between the depth and the hardness from the surface of each circulation groove of the nut of the ball screw concerning the present invention, and the conventional ball screw nut.

  DESCRIPTION OF EMBODIMENTS Hereinafter, a ball screw manufacturing method according to the present invention and an embodiment of a ball screw nut manufactured by the manufacturing method will be described with reference to the drawings. FIG. 1 is a view for explaining an embodiment of a ball screw nut manufacturing method according to the present invention. FIG. 2 is a plan view (a) showing a fitting state of a cam slider and a cam driver constituting a mold used in an embodiment of a ball screw nut manufacturing method according to the present invention, and a perspective view showing the cam slider. FIG. 2B is a perspective view showing the cam driver.

<Mold>
As shown in FIG. 1, the mold 50 used in the present embodiment includes a material holder 20 having a recess 21 that holds the nut material 10, and a cam slider 30 and a cam driver 40 disposed inside the nut material 10. ing.

<Cam slider>
2A and 2B, the cam slider 30 is a substantially semi-cylindrical member having a plane 32 parallel to the outer peripheral surface 31 and the axial direction, and the diameter of the circle forming the outer peripheral surface 31 is as follows. The diameter is slightly smaller than the diameter of the circle 11 a forming the inner peripheral surface 11 of the nut material 10. On the flat surface 32 of the cam slider 30, a slope 33 extending in the axial direction is formed at the central portion in the radial direction. The inclined surface 33 corresponds to a plane connecting the bottom line 34 a of the recess 34 at one end (upper end) in the axial direction and the line 32 d forming the lower end of the plane 32. An S-shaped convex portion 35 corresponding to the S-shaped concave portion 15 that forms the ball return path is formed on the outer peripheral surface 31 of the cam slider 30.

<Cam driver>
As shown in FIG. 2C, the cam driver 40 is a long plate-like member, and one side surface 41 is an inclined surface having the same inclination as the inclined surface 33 of the cam slider 30. The other side surface 42 is a circumferential surface along a circle 11 a that forms the inner circumferential surface 11 of the nut material 10. The axial dimension of the cam driver 40 is longer than the axial dimension of the cam slider 30. The cam driver 40 is slightly thinner than the thickness corresponding to the opening width of the recess 34 of the cam slider 30 (the dimension between both side surfaces of the slope 33).
The inclined surface 31 of the cam slider 30 and the inclined side surface 41 of the cam driver 40 constitute a cam mechanism of the mold 50.

<Method for producing ball screw nut>
The ball screw nut manufacturing method according to the present invention includes a circulation groove forming step of forming a circulation groove on the inner peripheral surface 11 of the nut material 10 and rolling to the inner peripheral surface 11 based on the position of the formed circulation groove. A rolling groove forming step of forming a groove.
[Nut material]
Here, the material of the nut material 10 is preferably S53C or SAE4150.
[Circulating groove forming process]
Using the mold 50, an S-shaped recess 15 that forms a ball return path (circulation groove) is formed on the inner peripheral surface 11 of the nut material 10 by the following method.

First, the nut material 10 is disposed in the recess 21 of the material holder 20, the cam slider 30 is placed inside the nut material 10, the recess 34 side is up, and the S-shaped protrusion 35 is formed on the inner peripheral surface 11 of the nut material 10. Insert to face. Next, the cam driver 40 is inserted between the cam slider 30 and the nut material 10. At that time, a portion on the side surface 41 side of the cam driver 40 is fitted into the recess 34 of the cam slider 30 so that the inclined surface 33 of the cam slider 30 and the inclined side surface 41 of the cam driver 40 are brought into contact with each other. FIG. 1A shows this state.

  Next, an S-shaped recess 15 that forms a ball return path is formed on the inner peripheral surface 11 of the nut blank 10 by forging. Specifically, when a press pressure is applied and the cam driver 40 is pushed from above, a force is transmitted from the inclined side surface 41 of the cam driver 40 to the inclined surface 33 of the cam slider 30. Accordingly, the downward force of the cam driver 40 is converted into a force that moves the cam slider 30 outward in the radial direction, and the S-shaped convex portion 35 formed on the cam slider 30 presses the inner peripheral surface 11 of the nut material 10. Plastic processing. FIG. 1B shows this state.

As a result, an S-shaped recess 15 that forms a ball return path is formed on the inner peripheral surface 11 of the nut blank 10.
Therefore, according to the method of this embodiment, even when a nut having a long axial dimension and a small inner diameter is manufactured, the S-shaped recess 15 can be formed without causing damage to the cam driver 4.

  In the case of forming two S-shaped concave portions on the inner peripheral surface 11 of the nut material 10, after forming one S-shaped concave portion 15 by the above-described method, the cam driver 40 is pulled out, and then the cam slider 30 is moved. The above method is performed by inserting the cam driver 40 again by placing a pedestal or the like on the bottom so as to change the position of the convex portion 35 or by using a cam slider having a different position of the convex portion 35. This is repeated when three or more S-shaped concave portions 15 are formed.

[Rolling groove forming process]
Next, the rolling groove 16 is formed on the inner peripheral surface 11 of the nut material 10 in which the circulation groove 15 is formed. FIG. 3 is a view for explaining an embodiment of a ball screw nut manufacturing method according to the present invention, (a) is a perspective view showing a cutting state of a nut material, (b) It is the figure which looked at the nut raw material and cutting tool which are shown to (a) in the arrow VB direction. FIG. 4 is a view for explaining an embodiment of a ball screw nut manufacturing method according to the present invention. FIG. 4 (a) is an axial sectional view after cutting a nut material, and FIG. These are the perspective views after the cutting process of a nut raw material.

  Here, cutting is performed using a cutting tool T as shown in FIG. The cutting tool T forms a blade Tb on the outer periphery of the rotation axis Ta. The cutting surface (surface facing in the circumferential direction) of the blade Tb matches the shape of the rolling groove 16. The rotation axis Ta rotates around its axis O (A in FIG. 3B), but independently revolves around the eccentric axis Q (B in FIG. 3B). As a mechanism for rotating and revolving the cutting tool T in this way, for example, a configuration in which the rotation shaft Ta is connected to a planetary gear of a planetary gear mechanism (not shown) is conceivable, but not limited thereto.

  When performing this cutting process, it is necessary to let the revolving trajectory of the rotating tool near the end surface of the nut material 10 escape from the center of the revolving track so that the rotating tool Tb does not contact the inner peripheral surface 11 of the nut material 10. . Further, as shown in FIG. 5, the rotational axis Ta of the cutting tool T is shifted radially outward at a predetermined axial position, and revolved while being sent in the axial direction at the pitch of the rolling grooves 16, at a higher speed. By rotating, the spiral rolling groove 16 of less than 360 degrees can be cut and formed on the inner peripheral surface of the nut material 10. At this time, by aligning the position and phase in the axial direction with the circulation groove 15, each circulation groove 15 can be formed to be connected to both ends of the rolling groove 16 as shown in FIG. 4. In the cutting tool T shown in FIG. 3, in order to form the two rolling grooves 16, the same nut material 10 is cut twice. However, two cutting tools Tb are formed on the rotation axis Ta. For example, it can be formed by a single cutting process.

[Quenching process]
Next, the nut material 10 is quenched. In this quenching process, as shown in FIG. 5, first, the coil 50 is inserted into the inner peripheral surface 11 of the nut material 10 so that the axis of the coil 50 and the axis of the nut material 10 are coaxial. Then, a high-frequency current (alternating current) is passed through the coil 50 to heat the inner peripheral surface 11 of the nut material 10. At this time, the outer peripheral surface 12 of the nut blank 10 is simultaneously cooled. This cooling process is performed, for example, by simultaneously injecting cooling water from the cooling nozzles for the inner peripheral surface and the outer peripheral surface, or by immersing the heated nut material 10 in the cooling liquid. As shown in FIG. 5, a jig or the like for preventing cooling water (cooling liquid) for cooling the outer peripheral surface from coming into contact with the inner peripheral surface is used. The shape of the coil 50 is preferably formed and arranged along the rolling groove 16. Thus, since the through-hole which penetrates the inner peripheral surface 11 and the outer peripheral surface 12 is not formed in the nut raw material 10, the inner peripheral surface 11 of the nut raw material 10 is heated uniformly.

  Next, the inner peripheral surface and the outer peripheral surface of the nut material 10 are cooled with cooling water. Even in this cooling process, the nut material 10 is not formed with a through-hole penetrating the inner peripheral surface 11 and the outer peripheral surface 12, so that cooling water flows into the through-hole as in the prior art, and The cooling rate in the vicinity of the hole does not increase, and the inner peripheral surface 11 of the nut blank 10 is uniformly cooled. Thereafter, the nut material 10 is tempered to obtain a ball screw nut in which the circulation grooves according to the present invention are integrated and the screw grooves are uniformly cured.

As described above, according to the present embodiment, since the through hole penetrating the inner peripheral surface and the outer peripheral surface of the nut is not formed in the nut, the central axis of the coil for high frequency heat treatment, and the nut By matching the central axis of the nut, the entire nut can be heated uniformly.
Further, since the through hole is not formed in the nut material 10, the nut can be uniformly cooled even when the nut is cooled, and as a result, thermal deformation of the nut can be minimized.

Moreover, since the surface of the inner peripheral surface 11 is subjected to high-frequency heat treatment while cooling the outer peripheral surface 12 of the nut material 10, it is possible to prevent the heating range of the inner peripheral surface 11 from being expanded, and to control the formation range of the effective hardened layer. It becomes easy to do.
Further, when the heating method of Patent Document 1 is applied to a piece type ball screw, it is necessary to form a piece hole after forming an effective hardened layer on the inner peripheral surface. Since no holes are formed and the rolling grooves and the circulation grooves are formed on the inner peripheral surface, heating and cooling of the nut material 10 does not take time. Therefore, a rapid transition from the heating process to the cooling process is possible, and as a result, the quenching depth can be easily controlled, and the hardness of each part of the nut can be set to an optimum value.

<Nut of ball screw>
The nut 1 of the ball screw manufactured as described above has a rolling groove 16 and a circulation groove 15 formed on the inner peripheral surface 11.
And the surface hardness of the inner peripheral surface 11 of this nut 1 is HRC58-62, the hardness of an effective hardening layer is Hv550 or more, the depth of an effective hardening layer is 0.4 mm or more, and a core part The hardness is HRC40 or less.
Here, the “effective hardened layer” refers to a layer up to the limit hardness (Hv550), and the “core” refers to the thickness center.

  As described above, when the nut material 10 is heated and cooled so that the surface hardness of the inner peripheral surface 11 of the nut 1 falls within the above range, the effective hardened layer depth is secured as shown in FIG. It can be seen that many layers that are not quenched can be formed. That is, it is possible to provide a ball screw nut manufacturing method that keeps thermal deformation due to heat treatment for surface hardening to a minimum and further reduces costs and labor, and a ball screw nut manufactured by the manufacturing method. .

(Other embodiments)
As another embodiment of the ball screw nut manufacturing method according to the present invention, the outer peripheral surface 12 of the nut material 10 is cured by high-frequency heat treatment in a state where the inner peripheral surface 11 of the nut material 10 is cooled, thereby forming an effective hardened layer. It may be formed. For example, when it is desired to form an effective hardened layer on the flange portion or the gear portion for rotating the nut 1 on the outer peripheral surface 12 of the nut 1, the coil 50 is arranged on the flange portion or gear portion, A high frequency current (alternating current) is passed to form an effective hardened layer. Thereby, since the through-hole which penetrates the inner peripheral surface 11 and the outer peripheral surface 12 of the nut raw material 10 is not formed in the nut raw material 10, the inner peripheral surface 11 and the outer peripheral surface 12 of the nut raw material 10 are hardened separately independently. it can.

  As mentioned above, although the manufacturing method of the nut of the ball screw which concerns on this invention, and embodiment of the nut of the ball screw manufactured by the manufacturing method were demonstrated, this invention is not limited to the said embodiment, this invention. Various modifications can be made without departing from the spirit of the present invention. For example, the ball screw nut manufacturing method according to the present invention and the ball screw nut manufactured by the manufacturing method can be applied to a ball screw nut adopting screw shaft circulation.

DESCRIPTION OF SYMBOLS 1 Ball screw nut 10 Nut material 11 Inner peripheral surface 12 Outer peripheral surface 15 Circulation groove 16 Rolling groove

Claims (4)

Arranged between a nut formed with a rolling groove on the inner peripheral surface, a screw shaft with a rolling groove formed on the outer peripheral surface, and a track formed by the rolling groove of the nut and the rolling groove of the screw shaft. And a ball screw nut manufacturing method in which one or more circulation grooves for returning the ball from the end point of the track to the start point are formed on the inner peripheral surface of the nut,
The surface of the object to be cured is heated by high frequency, the surface opposite to the surface of the object to be cured is cooled, and then the surface to be cured of the nut and the surface on the opposite side are cooled. Manufacturing method of screw nut.   The ball coil nut manufacturing method according to claim 1, wherein the coil has a shape along the rolling groove. Arranged between a nut formed with a rolling groove on the inner peripheral surface, a screw shaft with a rolling groove formed on the outer peripheral surface, and a track formed by the rolling groove of the nut and the rolling groove of the screw shaft. A ball screw nut formed on the inner peripheral surface of the nut, wherein one or more circulation grooves for returning the ball from the end point of the track to the start point are formed on the inner peripheral surface of the nut,
A nut of a ball screw, wherein the nut is manufactured by the ball screw nut manufacturing method according to claim 1 or 2.   The surface hardness of the inner peripheral surface is HRC58-62, the hardness of the effective hardened layer is Hv550 or higher, the depth of the effective hardened layer is 0.4 mm or higher, and the hardness of the core is HRC40 or lower. The ball screw nut according to claim 3, wherein the ball screw nut is provided.

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