JP7176349B2 - Linear motion device and its manufacturing method - Google Patents

Description

The present invention relates to a linear motion device such as a ball screw device and a linear guide device, and a manufacturing method thereof.

Linear motion devices such as ball screws and linear guide devices are used in machine tools and transport devices, but there is a strong demand for smoother operation, quietness, high speed, and improved durability. is required.

In response to these demands, the raceway surfaces of the screw shaft and nut of the ball screw device, and the raceway surfaces of the guide rail and slider of the linear guide device are hardened or smoothed to improve wear resistance. are being improved. For example, Patent Literature 1 describes shot peening treatment. The shot peening process is a process in which fine beads of about several tens of μm made of a hard material are sprayed onto the machined surface at high speed to increase the hardness of the machined surface due to the collision of the beads. In addition, the effect of smoothing the surface is also obtained by the shot peening treatment. In Patent Document 1, SiC beads or steel balls with a particle size of 40 to 60 μm are used to subject the raceway surface to shot peening to form a hardened layer and reduce the surface roughness Ra to 1.0 μm or less.

As a technique for increasing the hardness of the surface of the raceway surface, Patent Document 2 discloses forming a hardened layer of TiN, TiC, TiAlN, DLC, or the like by vapor deposition, plating, or thermal spraying, or performing a shot peening treatment, followed by the above-described is described to form a cured layer of

JP-A-2005-90570 JP 2005-114076 A

In the manufacturing process of the linear motion device, cutting and grinding are performed when forming the raceway surface. However, on the raceway surface after cutting or grinding, streaky traces are formed along a certain direction. These streak-like traces do not have sufficient ability to retain lubricant, causing seizure, damage to the surface of the ball, and damage such as peeling, which reduces durability. It is the cause. As described above, Patent Literature 1 and Patent Literature 2 also aim to improve durability, but although they indicate that the surface hardness of the raceway surface is increased or smoothed, there are no machining marks. No attention is paid to solving the deterioration of the durability derived therefrom.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to solve the problem of reduced durability due to traces of grinding or cutting on the raceway surface.

As a result of intensive studies to solve the above problems, we found that the streak-like processing marks caused by cutting and grinding have low lubricant retention performance, and simply increasing the smoothness of the surface will increase the lubricant retention performance. I found out that I can't. Then, they found that it is effective to eliminate streak-like working marks and to form minute unevenness on the raceway surface to provide the function as an oil reservoir.

That is, the present invention relates to the following linear motion device and its manufacturing method.
(1) a guide shaft extending in the axial direction and having a raceway surface on the outer peripheral surface;
a moving body having a track surface facing the track surface of the guide shaft inside and reciprocating along the guide shaft;
A linear motion device comprising a ball that rolls in a space defined by the raceway surface of the guide shaft and the raceway surface of the moving body,
At least one of the raceway surface of the guide shaft and the raceway surface of the moving body has 200 to 500 irregularities per 1 mm ² with an opening diameter of 10 to 30 μm and a depth of 1 to 3 μm. Device.
(2) The linear motion device according to (1) above, wherein Str of the raceway surface is 0.2 or more.
(3) a guide shaft extending in the axial direction and having a raceway surface on the outer peripheral surface;
a moving body having a track surface facing the track surface of the guide shaft inside and reciprocating along the guide shaft;
In a method for manufacturing a linear motion device comprising a ball that rolls in a space formed by the raceway surface of the guide shaft and the raceway surface of the moving body,
At least one of the raceway surface of the guide shaft and the raceway surface of the moving body is ground or cut after the quenching process, and then the surface of the raceway surface is blasted to have an opening diameter of 10 to 30 μm, A method for manufacturing a linear motion device, characterized by forming 200 to 500 unevennesses with a depth of 1 to 3 μm per 1 mm ² .
(4) The straight line according to (3) above, wherein the blasting is shot peening, and the shot material is caused to collide with the raceway surface at an angle orthogonal to a tangent line of the cross-sectional shape of the raceway surface. A method for manufacturing a moving device.
(5) The method of manufacturing a linear motion device according to (3) or (4) above, wherein the surface of the raceway surface has a Str of 0.2 or more.

According to the present invention, blasting such as shot peening is applied to streak-like machining marks formed by cutting or grinding when forming the raceway surface of the guide shaft or moving body. As a result, streak-like machining marks are eliminated, and specific unevenness is formed at a specific density. As the lubricant accumulates in the unevenness, the lubricant holding capacity is enhanced, and the durability of the linear motion device is greatly improved.

It is the photograph which image|photographed the raceway surface (comparative example 1) of the screw shaft before shot peening. FIG. 2 is a polar coordinate graph showing the directionality of three-dimensional surface roughness of the same raceway surface as in FIG. 1. FIG. 4 is a photograph of the raceway surface of the screw shaft after shot peening (Example 1). FIG. 4 is a polar coordinate graph showing the directionality of the three-dimensional surface roughness of the same track surface as in FIG. 3. FIG. FIG. 4 is a schematic diagram for explaining the injection mode of shot material onto a raceway surface; 10 is a graph showing the results of [Test 2]. 10 is a graph showing the results of [Test 3]. 10 is a graph showing the results of [Test 4]. 10 is a graph showing the results of [Test 5].

The present invention will now be described in detail with reference to the drawings.

(linear motion device)
In the present invention, the linear motion device is not limited, and can be applied to ball screw devices and linear guide devices in general. Therefore, specific illustrations of these devices are omitted in this specification. In the present invention, the surface properties of the raceway surfaces of the screw shaft and nut of the ball screw device, and the raceway surfaces of the guide rail and slider of the linear guide device are defined as follows.

There are no restrictions on the cross-sectional shape of the raceway surface, but in the case of a ball screw, for example, if the cross-sectional shape is a Gothic arch, it will be easier to adjust the clearance, and the nut will be able to be turned lightly due to point contact with the balls. Since then, it is widely spread. Also in the present invention, the cross-sectional shape of the raceway surface is preferably a Gothic arch.

On the surface of the raceway surface, a large number of fine streak-like irregularities are formed as traces of machining or grinding. FIG. 1 is an example, and is a photograph of a raceway surface of a nut of Comparative Example 1, which will be described later. When the same surface is observed with a three-dimensional surface roughness measuring machine, the polar coordinate graph shown in FIG. 2 is obtained. angular spectrum) appears. The polar graph and angular spectrum are specified in ISO 25178. In such streaky working marks, the valleys are aligned in one direction, and the lubricant holding capacity is low.

Therefore, in the present invention, after cutting or grinding, the raceway surface is subjected to a blasting treatment to eliminate streaks and to form a large number of fine irregularities. An example of the machined surface after blasting is shown in FIG. 3, which is a photograph showing the raceway surface of the nut of Example 1, which will be described later. As shown in the figure, it can be seen that the streak-like traces have disappeared and fine unevenness has been formed. This is the result that the apex of the streak-like machining marks was crushed by the impact of the shot material. Similarly, when the polar coordinate graph is obtained, as shown in FIG. 4, the angular spectrum is dispersed in almost all directions. there is Also, it can be said that the peak height of the angular spectrum does not become particularly high only at a specific angle, and unevenness is uniformly distributed in almost all directions.

In the present invention, if the distribution of unevenness is such that 200 to 500 fine unevennesses with an opening diameter of 10 to 30 μm and a depth of 1 to 3 μm are present at a density of 200 to 500 per 1 mm ² It is possible to obtain a linear motion device having a sufficiently high holding capacity and excellent durability. In particular, it is preferable that there are 300 to 400/mm ² irregularities with an opening diameter of 15 to 25 μm and a depth of 1.5 to 2.5 μm.

In the following description, a surface having unevenness (processing traces) along a certain direction as shown in FIGS. A surface on which unevenness is distributed toward the surface is called an “isotropic surface”.

A surface texture spectral ratio (Str) defined in ISO 25178 is known as an index representing an anisotropic surface and an isotropic surface. This Str ranges from 0 to 1, and the closer to 1, the higher the "isotropy".

In the present invention, Str is preferably 0.2 or more, more preferably 0.5 or more, and particularly preferably 0.7 or more. If Str is less than 0.2, the isotropy of the unevenness is insufficient, and the ability of the unevenness to retain the lubricant is insufficient, so that the effect of improving durability may not be sufficiently obtained.

In addition, as a result of the collision of the shot material by blasting, the compressive residual stress on the surface of the raceway surface increases. In order to form unevenness so as to increase Str as described above, it is preferable that the surface compressive residual stress is 500 MPa or more. More preferably, the surface compressive residual stress is 800 MPa or more.

In addition to having a high Str, it is preferable that the surface of the raceway surface is smooth. The smoother the surface, the less damage to the ball. Specifically, the average surface roughness Ra of the raceway surface is preferably 0.4 μm or less, and more preferably 0.3 μm or less.

In terms of durability, the harder the raceway surface is, the better. The hardness in the region (outermost surface portion) from the surface to a depth of 2 μm is preferably HV700 to 900, more preferably HV750 to 800. .

In the linear motion device of the present invention, as long as the raceway surface satisfies the above uneven distribution, surface compressive residual stress, surface average roughness, and surface hardness, other components are not limited. It is preferable that the balls that come into contact with the surface also have similar irregularities. By eliminating machining marks on the surface of the ball and forming irregularities, the ball can retain more lubricant, and the durability of the linear motion device is further improved.

Incidentally, as in Patent Documents 1 and 2, the raceway surface is conventionally subjected to blasting treatment. However, in Patent Document 1, shot peening treatment is performed before and after heat treatment, and is aimed at removing scale by heat treatment and improving surface roughness, and forming unevenness like the present invention. is not. In the examples, it is described that the shot peening treatment is performed with steel balls having a particle size of 40 to 60 μm under a shot pressure of 0.5 MPa and a treatment time of 60 seconds. In contrast, the processing conditions are not so high as to form unevenness on the raceway surface.

Although shot peening is also performed in Patent Document 2, there is no description of the density of irregularities or Str.

(Production method)
The present invention also relates to a method for manufacturing the above linear motion device. The processes up to blasting can follow conventional methods. For example, materials made of high-carbon steel are processed into the shapes of screw shafts, nuts, guide rails and sliders, heat treated, and then cut and ground. to form the raceway surface, and then perform blasting. By this blasting, the shot material collides with the raceway surface at high speed, crushing the apex of streak-like processing traces by cutting or grinding to form fine unevenness.

Therefore, the treatment conditions for the blasting treatment are not limited as long as they can form the irregularities defined above and have surface properties such as roughness, hardness, compressive residual stress, etc. An example is as follows. be.

Shot blasting, sand blasting, shot peening, and the like are typical examples of blasting treatment, and shot peening treatment is preferable because it is efficient. Particles (shot material) made of ceramic such as steel or SiC can be used as the shot material. In addition, the shot material is preferably as small as possible. Shot material having a particle size of 30 to 60 μm is preferable, and shot material having a particle size of 40 to 50 μm is more preferable. The smaller the shot material, the finer the irregularities formed. The shape of the shot material can be various shapes other than the spherical shape. A higher injection speed of the shot material is advantageous, and the shot pressure is preferably 0.3 to 0.5 MPa or more, more preferably 0.35 to 0.45 MPa.

As for the injection angle of the shot material onto the raceway surface, it is preferable that the shot material collide perpendicularly to the tangential line of the cross section of the raceway surface. 5 is a cross-sectional view of the gothic arch-shaped raceway surface 1, the injection nozzle 10 is arranged so that the line A passing through the center of the injection port of the injection nozzle 10 and the tangent line L of the raceway surface 1 are orthogonal to each other. It is preferable to inject the shot material while swinging obliquely upward or obliquely downward on the same cross section. As a result, the shot material collides perpendicularly with the raceway surface, and unevenness can be efficiently formed.
In addition, since the raceway surface is a spiral groove, in order to uniformly blast the raceway surface, the shot target (screw shaft or nut) is rotated, and the injection nozzle is moved in the axial direction in synchronization with the rotation of the shot target. It is preferable to perform blasting while moving.
Furthermore, in FIG. 5, one arc of the Gothic arch-shaped raceway surface 1 is blasted, but a plurality of jet nozzles may be used to simultaneously blast both arcs of the raceway surface. As a result, the raceway surface can be efficiently blasted.

The present invention will be further described with reference to examples and comparative examples below.

[Test 1]
(Comparative example 1)
A high-carbon steel was machined into the shape of a screw shaft for a ball screw device, heat-treated, and then ground to form a raceway surface with a cross section in the shape of a gothic arch in a helical shape. Then, when this raceway surface was observed with an electron microscope, as shown in FIG. Further, when a polar coordinate graph was obtained for the same observation surface using a three-dimensional surface roughness measuring machine, a single angular spectrum was observed near 90°, as shown in FIG. When Str was determined, it was 0.03.

The average surface roughness Ra of the raceway surface was 0.2 μm, the hardness of the outermost surface was HV685, and the surface compressive residual stress was 174 MPa.

(Example 1)
The screw shaft produced in Comparative Example 1 was subjected to shot peening treatment using steel balls having an average diameter of 50 μm. The shot pressure was 0.3 MPa, and the shot material was injected so as to be perpendicular to the tangential line of the raceway surface as shown in FIG. When the raceway surface after the shot peening treatment was observed with an electron microscope, as shown in FIG. The unevenness had an opening diameter of 10 to 30 μm and a depth of 1.8 to 2.8 μm, and there were 450 of them per 1 mm ² . Further, when a polar coordinate graph was obtained for the same observation surface using a three-dimensional surface roughness measuring machine, as shown in FIG. 4, a uniform angular spectrum was observed in almost all directions. When Str was determined, it was 0.83.

The average surface roughness Ra of the raceway surface was 0.18 μm, the hardness of the outermost surface was HV705, and the surface compressive residual stress was 950 MPa.

[Test 2]
A ball screw device was assembled using a screw shaft of Comparative Example 1 and a nut that had not undergone shot peening treatment. A ball screw device was assembled using the screw shaft of Example 1 and a shot-peened nut. Also, the balls were common to both ball screw devices. [Test Example 3], "Test Example 4", and [Test Example 5] described below also used two similar ball screw devices.
Then, for both ball screw devices, torque values were measured while changing the number of revolutions. The results are shown in FIG. 6, and it can be seen that the torque is reduced by using the screw shaft of Example 1 subjected to the shot peening treatment. It is presumed that the reason for this is that the lubricant accumulates in the fine irregularities formed by the shot peening treatment, and the lubricating performance is improved.

[Test 3]
Both ball screw devices similar to Test 2 were operated at a low rotational speed of 1 min ⁻¹ and the residual torque rate was measured after 100 reciprocations. The results are shown in FIG. 7. When the shot peened screw shaft of Example 1 was used, the initial torque remained even after 100 reciprocations (residual rate: 100%). On the other hand, when the screw shaft of Comparative Example 1, which was not shot peened, was used, the torque after 100 reciprocations decreased to 34% of the initial value. In this way, by adding the shot peening process, it is possible to suppress the decrease in the residual torque ratio.

[Test 4]
Kyodo Yushi's grease "LRL3" mixed with 1% by mass of silica sand as foreign matter was supplied to both ball screw devices similar to Test 2, and the residual torque rate was measured in the same manner as Test 3. The results are shown in FIG. 8. When the screw shaft of Example 1 subjected to shot peening treatment was used, the residual torque rate was approximately double that of the screw shaft of Comparative Example 1 which was not subjected to shot peening treatment. is shown. In this way, by adding the shot peening treatment, it is possible to improve the resistance to foreign matter.

[Test 5]
Both ball screw devices similar to Test 2 were subjected to a high load durability test. The test conditions are as follows.
・ Lubricant: Grease “YS2” manufactured by Ryube Co., Ltd.
・The maximum surface pressure of the screw shaft is 2.6 GPa, and the maximum surface pressure of the nut is 2.2 GPa. The results are shown in FIG. , the life is greatly extended as compared with the case of using the screw shaft of Comparative Example 1 which is not subjected to shot peening treatment. By adding shot peening treatment in this manner, durability can be greatly improved even when the ball screw device is used under a high load.

The effect of applying shot peening treatment to the screw shaft and the nut was verified above, but it is presumed that almost the same effect can be obtained when the shot peening treatment is applied only to the nut. Furthermore, when both the nut and the screw shaft are subjected to the shot peening treatment, it is presumed that the synergistic effect will be more effective.

1 raceway surface 10 injection nozzle A line passing through the center of the injection hole of the injection nozzle L tangent to the raceway surface

Claims (3)

a guide shaft extending in the axial direction and having a raceway surface on its outer peripheral surface;
a moving body having a track surface facing the track surface of the guide shaft inside and reciprocating along the guide shaft;
A linear motion device comprising a ball that rolls in a space defined by the raceway surface of the guide shaft and the raceway surface of the moving body,
At least one of the raceway surface of the guide shaft and the raceway surface of the moving body has 200 to 500 irregularities per 1 mm ² with an opening diameter of 10 to 30 μm and a depth of 1 to 3 μm ,
Str of the raceway surface is 0.5 or more,
A linear motion device characterized by: a guide shaft extending in the axial direction and having a raceway surface on its outer peripheral surface;
a moving body having a track surface facing the track surface of the guide shaft inside and reciprocating along the guide shaft;
In a method for manufacturing a linear motion device including a ball that rolls in a space formed by the raceway surface of the guide shaft and the raceway surface of the moving body,
At least one of the raceway surface of the guide shaft and the raceway surface of the moving body is ground or cut after the quenching process, and then the surface of the raceway surface is blasted to have an opening diameter of 10 to 30 μm, 200 to 500 irregularities with a depth of 1 to 3 μm are formed per 1 mm ² ,
Str of the raceway surface is set to 0.5 or more,
A method of manufacturing a linear motion device, characterized by: 3. The manufacture of a linear motion device according to claim 2 , wherein said blasting treatment is shot peening treatment, and the shot material is caused to collide with said raceway surface at an angle orthogonal to a tangent line of the cross-sectional shape of said raceway surface. Method.

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