JP2002283195A - Method for manufacturing ball screw shaft - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for a ball screw shaft capable of largely reducing a manufacturing cost without deteriorating machining quality, and capable of sufficiently enhancing the abrasion resistance of a ball screw groove. SOLUTION: A spiral roughly machined screw groove S0 is formed on the outer peripheral surface Ws of a cylindrical raw material W0 by infeed rolling by leaving a grinding margin Wk, and thereafter, the ball screw groove S1 is formed by grinding the roughly machined screw groove S0 of the cylindrical raw material W0. Before entering grinding after the infeed rolling, surface hardening is applied to a raw material outer peripheral surface Ws part for forming the roughly machined screw groove S0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art A ball screw shaft is widely used as a component of a ball screw mechanism in a feeder of precision equipment. Here, the ball screw mechanism includes a ball screw shaft having a helical ball screw groove (male screw groove) formed on an outer peripheral surface, and a bearing having a female screw groove formed on an inner wall surface surrounding the outer peripheral surface of the ball screw shaft. And a plurality of ball bearings interposed between the male and female screw grooves facing each other and rolling, and when the ball screw shaft rotates, the bearing member adjusts the screw according to the rotation amount. It is displaced in the axial direction of the shaft.

The above-mentioned ball screw shaft is often formed with a ball screw groove by grinding so that precise feeding can be performed.

FIG. 6 shows an outline of a ball screw groove grinding method.

In FIG. 6, W0 is a cylindrical material,
It is made of steel. Reference numerals 51, 53, and 55 denote end support members, grinding wheels, and the like, which are components of the screw grinder 50.
Work spindle. When the work spindle 55 is driven, the cylindrical material W0 is moved to the left end support member 5 in the figure.
Rotate through 1. Further, the grinding wheel 53 has a chevron 54 having an arc-shaped cross section on the outer peripheral surface thereof, and is rotatably driven by driving means (not shown). The grinding wheel 53 includes a single grinding wheel and a plurality of grinding wheels.

The screw grinder 50 is provided with, in addition to the above-mentioned components, a feeder capable of relatively moving the cylindrical raw material W0 and the grinding wheel 53 at a set feed speed, a dresser, and the like.

When the ball screw groove is ground by the screw grinder 50, the cylindrical raw material W0 and the grinding wheel 53 are relatively moved at a set feed speed while being rotated in a predetermined direction, and the grinding wheel is rotated. The angle portion 54 of 53 is moved toward the cylindrical material W0 by a predetermined cutting amount,
The outer peripheral surface of the cylindrical material W0 is spirally ground at a predetermined depth.

[0008] By repeating this grinding operation several tens of times, a helical ball screw groove S1 having an arc-shaped cross section is formed on the outer peripheral surface of the cylindrical material W0. That is,
The ball screw shaft W is manufactured.

Before the grinding process, the outer peripheral surface of the material W0 is generally carburized and quenched to perform a surface hardening treatment. Thereby, it is said that the outer peripheral surface of the cylindrical material W0 is hardened and is easily ground, and the wear resistance of the ball screw groove S1 formed on the outer peripheral surface is increased.

During the above-mentioned grinding step, the shape and clogging of the grinding wheel 53 are corrected by using a dresser (not shown) if necessary.

[0011]

In the manufacture of the above-described ball screw shaft W, there is a strong demand for reducing the manufacturing cost without lowering the processing quality.

In order to meet such demands, it is necessary to shorten the manufacturing time and to extend the life of the grinding wheel 53 and the like. However, if the number of grinding operations is reduced by increasing the depth of the grinding wheel 53 per one cut into the cylindrical material W0 as a measure for shortening the manufacturing time or the like, an excessive load is applied to the grinding wheel 53 and the life is reduced. As a result, it is necessary to frequently correct the deformation and clogging of the grinding wheel 53, and the production time may be prolonged.

Although the outer peripheral surface of the cylindrical raw material W0 is subjected to a surface hardening treatment before grinding, a part of the outer peripheral surface is spirally removed by grinding to form a ball screw groove S1, so that the ball screw groove S1 is formed. The hardness of the surface portion of the screw groove S1 is not uniform, but decreases toward the bottom. for that reason,
It is difficult to sufficiently increase the wear resistance of the ball screw groove S1.

In order to enhance the wear resistance of the ball screw groove S1, for example, it is conceivable to form a thick carburized and quenched layer on the outer peripheral surface of the material W0. However, in this case, the bending of the material W0 after quenching becomes large, and it takes a lot of trouble to correct the bending. In addition, the toughness of the material W0 is reduced, and the smaller the diameter of the material W0, the more easily the material W0 is broken.

An object of the present invention is to provide a method of manufacturing a ball screw shaft capable of achieving a significant reduction in manufacturing cost without lowering processing quality. Another object of the present invention is to provide a method of manufacturing a ball screw shaft which is hardly broken even with a small diameter and can sufficiently enhance the wear resistance of the ball screw groove.

[0016]

According to a first aspect of the present invention, in order to achieve the above object, a spiral rough machining screw groove is formed on an outer peripheral surface of a cylindrical material while leaving a grinding allowance. Then, the rough screw groove of the cylindrical material is ground to form a ball screw groove.

In the case of this invention, since the rough thread groove is formed by in-feed rolling prior to the formation of the ball screw groove on the outer peripheral surface of the cylindrical material, the portion to be ground is greatly reduced. . For this reason, the number of grinding operations by operating a grinding wheel or the like is greatly reduced. In addition, since the load on the grinding wheel is greatly reduced, the number of times of correcting the deformation and clogging of the grinding wheel is drastically reduced, and the life of the grinding wheel is extended. Further, the life of other moving parts and the like is extended by reducing the number of grinding operations.

Since the rough thread groove is formed by in-feed rolling, the dimensional accuracy is good irrespective of whether the cylindrical material is thick or thin, and does not hinder the subsequent grinding. Further, the formation of the rough thread groove by in-feed rolling is completed in a short time.

Therefore, the manufacturing time can be shortened and the life of the grinding wheel or the like can be prolonged. As a result, the manufacturing cost can be greatly reduced.

Further, by reducing the above-mentioned grinding allowance as much as possible, the effect of forming the rough thread groove by rolling (that is, since the peripheral structure of the groove becomes a dense flow line without being cut, the static And both impact strength and fatigue strength are high.). Therefore, it is possible to provide a ball screw shaft superior in strength to a conventional ball screw shaft manufactured only by grinding.

A second aspect of the present invention is a method of manufacturing a ball screw shaft for performing a surface hardening process on an outer peripheral surface portion of a material on which a rough thread groove is formed before the grinding process after the in-feed rolling. is there.

In the case of this invention, a ball screw groove is formed by grinding the rough processing screw groove formed on the outer peripheral surface of the cylindrical material by a grinding allowance, so that the amount of shaving the surface hardened layer is smaller than that of the conventional example. It is much less than in comparison. For example, the bottom of the ball screw groove is also formed by slightly grinding. for that reason,
The hardness of the surface portion of the ball screw groove is uniform and high. Further, since there is no problem even if the above-mentioned surface hardened layer (such as a carburized and quenched layer) is formed considerably thinner than in the conventional example, the bending after quenching is small and the bending can be corrected more easily and in a shorter time than in the conventional case. Further, the toughness of the material does not decrease, and the material is hard to break even if it has a small diameter.

As a result, the same operation and effect as those of the first aspect of the invention can be obtained, and the ball screw groove is hardly broken even with a small diameter, and the wear resistance of the ball screw groove can be sufficiently improved.

[0024]

Embodiments of the present invention will be described below with reference to the drawings.

The method of manufacturing a ball screw shaft according to the present invention
A spiral rough processing screw groove S0 is formed on the outer peripheral surface Ws of the cylindrical material W0 by infeed rolling leaving a grinding allowance (Wk), and then the rough processing screw groove S0 of the cylindrical material W0 is ground. To form a ball screw groove S1.

Hereinafter, as an example, the screw outer diameter (= 10 m
m), pitch (= 2mm), screw length (= 300mm)
A method of manufacturing the ball screw shaft W having the ball screw groove S1 will be described.

First, an outer peripheral surface of a predetermined steel material (for example, chromium molybdenum steel (SCM415)) is turned to obtain a cylindrical material W having an outer diameter of 9.46 mm and a length of 360 mm.
Set to 0.

Next, as shown in FIG.
To the thread rolling machine 10 [in-feed rolling die (11, 1
2) etc.]. Here, the in-feed rolling dies (11, 12) have, for example, an outer shape of one.
89.2 mm, and the width (length in the axial direction) is 300 mm. On the outer periphery of the rolling dies (11, 12),
In order to form a rough machining screw groove S0 on the outer peripheral surface Ws of the cylindrical material W0, the angled portions (11a, 12a) having a triangular cross section are formed.
a) is provided in a predetermined number.

This in-feed rolling die (11, 1)
As shown in FIG. 2, a rough processing screw groove S0 having a helical shape and a triangular cross section is formed on the outer peripheral surface Ws of the cylindrical material W0 by using the method 2). The rough processing thread groove S0 has an outer diameter D1 of 10.3.
mm, root diameter D2 is 8.28 mm, tooth perpendicular pitch p2 is 1.9955 mm, thread angle θ is 55 °, and peak height H1 is 1.01 mm. The formation of the rough processing thread groove S0 by in-feed rolling has good dimensional accuracy even if the cylindrical material W0 has a small diameter, and the processing is completed in a short time. By the way, if the rough processing thread groove S0 is formed by cutting, it takes too much time and cost. Further, when the cylindrical material W0 has a small diameter, the rough machining screw groove S0 cannot be formed with high accuracy.

The in-feed rolling dies (11, 1)
The area of the cross section of the angled portion (11a, 12a) of 2) is enlarged so that the cross-sectional shape becomes an arc shape at the base end portion, so that the cylindrical material W0 is formed as shown in FIG. The rough processing thread groove S0 having a smaller grinding allowance (Wk) can be formed on the outer peripheral surface Ws.

Next, after the in-feed rolled material outer peripheral surface Ws portion is subjected to surface hardening treatment, as shown in FIG. 1A, the outer peripheral surface Ws is ground to have an outer diameter of 10 mm. Here, the surface hardening process is a process of hardening the surface of the material outer peripheral surface Ws portion, and includes carburizing, induction hardening, nitriding, carbonitriding, and the like. Surface hardening treatment (carburizing and quenching)
As a result, a hardened surface layer is formed on the rough machining screw groove S0 portion of the outer peripheral surface Ws of the cylindrical material W0.

In this embodiment, carburizing and quenching are performed. Thereby, the outer peripheral surface Ws of the cylindrical material W0
A carburized and quenched layer is formed on the surface portion of the rough-formed thread groove S0 formed in the step (a). The carburized and quenched layer is formed to be considerably thinner than the conventional example.

Thereafter, using a thread grinder 20 shown in FIGS. 4A and 4B, the rough machining thread groove S0 of the cylindrical material W0 is formed.
Is ground to form a ball screw groove S1.

The screw grinder 20 has a grinding wheel 21, an adjusting wheel 22 arranged opposite to the grinding wheel 21, and a pair of grinding wheels (21, 22) that are parallel to the rotation axis of the grinding wheel 21. A support plate 23 disposed to rotatably support the cylindrical material W0, and a guide plate provided before and after the support plate 23 along a feed direction of the cylindrical material W0 (the left-right direction in FIG. 4B). (Not shown), a grinding fluid ejection nozzle 25, a dresser for a grinding wheel, a dresser for an adjusting wheel (all not shown), and the like.

On the outer peripheral surface of the grinding wheel 21, a predetermined number of angled portions 21a having an arc-shaped cross section corresponding to the ball screw groove S1 are formed. The angled portion 21a is formed over the entire outer peripheral surface of the grinding wheel 21 and is aligned with the thread pitch p1 of the ball screw groove S1 in the width direction of the grinding wheel 21 (the left-right direction in FIG. 4B). A plurality are provided at different pitches.

When the ball screw groove S1 is ground on the outer peripheral surface Ws of the cylindrical material W0 by the screw grinder 20, the cylindrical material W0 and the grinding wheel 21 are set while being rotated in a predetermined direction. 4 (B) at the feed speed, and the angled portion 2 of the grinding wheel 21 is relatively moved.
1a is moved toward the cylindrical material W0 by a predetermined cutting amount, and the outer peripheral surface Ws of the cylindrical material W0 is spirally ground to a predetermined depth.

By repeating this grinding operation a predetermined number of times, the outer peripheral surface Ws of the cylindrical material W0 is placed on the outer peripheral surface Ws of FIG.
As shown in (C), a helical ball screw groove S1 having an arc-shaped cross section is formed. That is, the ball screw shaft W is manufactured.

During the above-mentioned grinding process, the shape and clogging of the grinding wheel 21 are corrected by using a dresser as necessary.

Here, as described above, the rough machining screw groove S0 is formed on the outer peripheral surface Ws of the cylindrical material W0 by infeed rolling before forming the ball screw groove S1. The number of parts to be ground has been greatly reduced. That is, only the portion Wk in FIG. 1B is ground. As shown in FIG. 5 (A), when the rough machining screw groove S0 shown in FIG. 5 (A) is formed on the outer peripheral surface Ws of the cylindrical material W0, grinding is performed in the same manner. Only the portion Wk in (B) is shown, and the portion to be further ground is reduced.

For this reason, the number of grinding operations by operating the grinding wheel 21 and the like is greatly reduced. In addition, since the load on the grinding wheel 21 is greatly reduced, the number of times of correcting the deformation and clogging of the grinding wheel 21 is drastically reduced, and the life of the grinding wheel 21 is extended. Further, the life of other moving parts and the like is extended by reducing the number of grinding operations.

Therefore, the manufacturing time can be shortened and the life of the grinding wheel or the like can be prolonged. As a result, the manufacturing cost can be greatly reduced. For example, FIGS. 1 (A), (B),
When the manufacturing process shown in (C) is performed, it can be manufactured in half the time required to manufacture a conventional ball screw shaft. When the manufacturing steps shown in FIGS. 5A, 5B, and 5C are performed, the manufacturing can be performed in one-third of the time required to manufacture a conventional ball screw shaft. Also, when manufacturing one ball screw shaft W, the manufacturing time can be greatly reduced and the cost can be significantly reduced as compared with the conventional manufacturing method.

Further, by reducing the grinding allowance (Wk) as much as possible, the effect of forming the rough thread groove S0 by rolling (that is, a dense flow line without cutting the peripheral structure of the groove S0). Therefore, static strength, impact strength, fatigue strength, etc. are all high.). Therefore, it is possible to provide a ball screw shaft W that is superior in strength to a conventional ball screw shaft manufactured only by grinding.

Further, as described above, if the rough machining screw groove S0 formed on the outer peripheral surface Ws of the cylindrical material W0 is ground by a grinding allowance (Wk), the ball screw groove S1 is formed. The amount of shaving the layer (the carburized and quenched layer in this embodiment) is significantly reduced as compared with the conventional example. For example, the bottom of the ball screw groove S1 is also formed by slightly grinding. Therefore, the hardness of the surface portion of the ball screw groove S1 is uniform and high. As a result, the wear resistance of the ball screw groove S1 can be sufficiently increased.

Further, since the carburized and quenched layer is formed to be considerably thinner than the conventional example, there is little bending after quenching, and the bending can be corrected more easily and in a shorter time than in the conventional example. Further, the toughness of the material W0 does not decrease, and the material W0 (therefore, the ball screw shaft W) is hardly broken even if it has a small diameter.

The thread rolling machine and the thread grinding machine used for in-feed rolling are not limited to the thread rolling machine 10 and the thread grinding machine 20 described above.

[0046]

According to the first aspect of the present invention, a helical rough thread groove is formed on the outer peripheral surface of the cylindrical material by in-feed rolling except for a grinding allowance. Since the ball screw groove is formed by grinding the processing screw groove, the number of parts to be ground is greatly reduced, the number of grinding operations is significantly reduced, the load on the grinding wheel, etc. is reduced, and the grinding wheel is deformed and clogged The number of times to correct is drastically reduced. As a result, manufacturing costs can be significantly reduced. Further, by reducing the above-mentioned grinding allowance as much as possible, the effect of forming the rough thread groove by rolling (that is, since the peripheral structure of the groove becomes a dense flow line without being cut, static strength, impact Strength and fatigue strength are all high.). Therefore, it is possible to provide a ball screw shaft superior in strength to a conventional ball screw shaft manufactured only by grinding.

According to the second aspect of the invention, after the in-feed rolling and before the grinding, the outer peripheral surface portion of the material on which the rough thread groove is formed is subjected to the surface hardening treatment. The amount to be removed is significantly smaller than in the conventional example.
Therefore, the hardness of the surface portion of the ball screw groove is uniform and high. In addition, there is no problem even if the surface hardened layer (the carburized and quenched layer, etc.) is formed considerably thinner than the conventional example,
There is little bending after quenching, and bending can be corrected more easily and in a shorter time than before. Further, the toughness of the material does not decrease, and the material is hard to break even if it has a small diameter. As a result, the same effects as those of the first aspect of the invention can be obtained, and the ball screw groove is hardly broken even with a small diameter, and the wear resistance of the ball screw groove can be sufficiently increased.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention.

FIG. 2 is also a view for explaining a rough machining screw groove formed by in-feed rolling.

FIG. 3 is a view for explaining in-feed rolling.

FIG. 4 is a view for explaining a thread grinding process.

FIG. 5 is also a view for explaining a process until a ball machining screw groove is formed.

FIG. 6 is also a view for explaining a conventional method of manufacturing a ball screw shaft.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Thread rolling machine 11, 12 Rolling die 20 Thread grinding machine 21 Grinding wheel W Ball screw shaft W0 Cylindrical material S1 Ball screw groove S0 Rough screw groove

Claims (2)

[Claims] 1. A spiral rough processing screw groove is formed on an outer peripheral surface of a cylindrical material by infeed rolling, leaving a grinding allowance, and thereafter, the rough processing screw groove of the cylindrical material is ground to form a ball. A method for manufacturing a ball screw shaft formed with a screw groove. 2. The method of manufacturing a ball screw shaft according to claim 1, wherein after the in-feed rolling and before the grinding process is performed, a surface hardening process is performed on an outer peripheral surface portion of the material on which the rough screw groove is formed.