Grinding device for ball screw shaft

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical Field of Invention]

The present invention relates to a method for grinding a ball screw shaft that grinds an outer diameter and a groove in one step, and a ball screw shaft that has been ground by this processing method.

【0002】

[Conventional technology]

Centerless grinding is conventionally known as a technique for grinding a cylindrical workpiece. In centerless grinding, for example, as shown in FIG. 6A, the workpiece 100 is placed between the grinding wheel 101 and the adjusting wheel 102 without using a center or a chuck to perform grinding. That is, the workpiece 100 is supported at three points by the grinding wheel 101, the adjusting wheel 102, and the blade 103, is given rotation and axial feed by the adjusting wheel 102, and is ground by the grinding wheel 101.

【0003】

There are various types of workpieces, from the simple cylindrical workpiece 104 as shown in FIG. 6 (b) to the complex stepped cylindrical workpiece 105 as shown in FIG. 6 (c). It is used for grinding shaped workpieces, and it is being considered to be used for machining the tightening screw shaft 106 as shown in Fig. 6 (d).

【0004】

However, even if this centerless grinding is simply applied to the machining of a ball screw shaft, in the case of the tightening screw shaft 106, the tightening performance is not affected as long as the effective diameter of the screw thread is obtained. In the case of a ball screw shaft, since precise feed is performed, high accuracy is required not only for the effective diameter but also for the cylindricity of the effective diameter and the lead accuracy of the thread groove. That is, in the case of the tightening screw shaft 106, even if the effective diameter varies or there is a lead error, a predetermined surface pressure can be obtained for each screw thread by the axial force acting on the screw shaft at the time of tightening, but the ball screw. When precision feed such as a shaft is performed, the cylindricity of the effective diameter and the lead accuracy of the thread groove directly affect the feed accuracy.

【0005】

In addition, in the case of conventional centerless grinding of a screw shaft for fastening, since the outer circumference of the material is also ground at the same time as grinding the screw groove, accurate axial feed cannot be performed, and the screw groove must be precisely machined. I can't. Therefore, in the case of a ball screw shaft that requires precision machining, it is common to center the ball screw shaft at the shaft end of the material and perform screw grinding.

【0006】

On the other hand, in Japanese Patent Application No. 8-121141, the applicant spirally formed a ball screw groove on the outer diameter cylindrical surface of the material whose outer diameter was formed into a cylindrical shape with reference to the outer diameter cylindrical surface. By grinding, we proposed a grinding method that can process a ball screw shaft with sufficiently high cylindricity of effective diameter and lead accuracy of thread groove.

【0007】

[Problems to be Solved by the Invention]

In the processing method proposed above, as shown in exaggeratedly shown in FIG. 7 (a), in order to gradually increase the grinding margin, the shape of the grinding wheel 121 is changed to a small diameter on the axial material inlet side and a cross-sectional circle toward the outlet side. The structure is such that the diameter gradually increases in an arc shape.

【0008】

That is, when viewed from the direction of arrow A shown in FIG. 7 (a), the contact surface of the grinding wheel is as shown in FIG. 7 (b), and a, b, c, d, e in this figure. The cross-sectional view of is as shown in (c). In FIG. 7 (c), the arrow indicates the direction in which the grinding resistance acts. Grinding resistance acts in the direction of the normal at each point in the groove.

【0009】

When all of these grinding resistance vectors are added and decomposed into the grinding resistance X in the adjustment grindstone 122 direction and the grinding resistance Y in the opposite direction of the material feed direction, X becomes smaller than Y as shown in FIG. 7 (d). Therefore, in a state where only the tip of the material is ground at the entrance of the grinding wheel, the rotational force and thrust obtained by pressing the material against the adjusting wheel are accurate against the grinding resistance in the direction opposite to the material feeding direction. It is not big enough to send the material.

【0010】

Therefore, as shown in FIG. 8, an upper presser foot 128 that presses the material 110a against the adjusting grindstone 122 is separately provided to assist the feeding of the material.

【0011】

That is, 1. With the grinding wheel 121 and the adjusting wheel 122 separated by a certain distance, place the material 110a on the support member 123, and arrange the material 110a and the grinding wheel 121 so that they overlap by 3 to 5 chevron protrusions in the axial direction. To do. 2. The upper presser foot 128 is pressed against the material 110a, the material 110a is pressed against the adjusting grindstone 122, and the grinding wheel 121 is slowly transferred to the material 110a in a state where the rotational force and the thrust are surely transmitted (the state shown in FIG. 8). When the material 110a is brought closer to the material 110a and the grinding resistance in the direction of the adjusting grindstone of the grinding wheel 121 becomes large enough for the material 110a to obtain rotational force and thrust from the adjusting grindstone 122, the pressure welding of the upper presser foot 128 is released. Was doing the operation. (Transition from in-feed grinding to through-feed grinding) The present invention has been made to further improve the above situation, and an object of the present invention is to do not increase the grinding margin on the material inlet side of the grinding wheel and without using an upper presser or the like. By obtaining sufficient rotational force and thrust of the material from the adjusting grindstone, it is an object of the present invention to provide a ball screw shaft grinding method and a ball screw shaft grinding device only for through-feed grinding, and thus the productivity of the ball screw shaft. Is to improve.

【0012】

[Means for solving problems]

In order to achieve the above object, in the present invention, a plurality of chevron protrusions corresponding to the cross-sectional shape of the ball screw groove are provided on the outer periphery of the grinding wheel at a predetermined pitch, and the adjusting wheel is in contact with the outer diameter cylindrical surface of the material. Grinding the ball screw shaft to form a ball screw groove by partially spiraling the outer diameter cylindrical surface of the material with the chevron protrusion of the grinding wheel by feeding the material in the axial direction while supporting and rotating the material with the support plate. It is a processing apparatus, and is characterized in that the chevron projection on the inlet side of the grinding wheel is formed as low as the other chevron projections with the same width.

【0013】

The resistance to feed the tip of the material between the grinding wheel and the adjusting wheel is reduced, and the material can be smoothly inserted at the start of grinding.

【0014】

In particular, the chevron protrusion on the entrance side is characterized in that its height is lowered by flattening the top of the chevron protrusion having the same shape as other chevron protrusions.

【0015】

Therefore, in the grinding method configured as described above, since the top of the chevron protrusion on the inlet side is formed flat, the grinding resistance in the direction of the adjusting grindstone becomes large, and the rotational force and thrust obtained by the material from the adjusting grindstone are increased. , It is sufficiently larger than the grinding resistance against the material feed (grinding resistance in the direction opposite to the material feed direction).

【0016】

As a result, even when only the tip of the material is ground at the entrance of the grinding wheel, the material is accurately fed, and it is not necessary to use an upper presser or the like, and the grinding wheel and the adjusting wheel at the grinding position are not required. High-precision grinding can be started simply by feeding the tip of the material into the space in the axial direction. (Ball screw shaft grinding method only for through feed grinding) Further, the chevron protrusion is characterized in that the height gradually increases from the entrance side to the exit side.

【0017】

As a result, the grinding allowance gradually increases, and the grinding resistance is evenly distributed in the axial direction of the grinding wheel, so that the material can be pressed against the adjusting wheel in parallel with the axis, and accurate material feeding becomes possible. .. On the other hand, since a uniform load is applied to the grinding wheel itself in the axial direction, the dressing interval of each chevron protrusion is constant, and the rotating shaft of the grinding wheel is not damaged.

【0018】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will be described in detail, exemplary, with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative arrangements, etc. of the components described in this embodiment are not intended to limit the scope of the present invention to those. Absent.

【0019】

(Embodiment 1) FIG. 1 shows an example of a basic processing method and a processing apparatus of the ball screw shaft grinding method according to the first embodiment of the present invention.

【0020】

As shown in FIG. 1 (c), the ball screw shaft has a spiral ball screw groove 13 engraved on the outer diameter cylindrical surface 11 of the shaft body 1. The ball screw groove 12 is formed in an arc shape in cross section, and an outer diameter cylindrical surface 11 remains spirally between the ball screw grooves 12. Further, the shaft body 1 is hardened from the surface to a layer deeper than the depth of the ball screw groove 12.

【0021】

As a method for processing such a ball screw shaft, in the present invention, as shown in FIGS. 1 (a) and 1 (b), the process of forming the material 10a before the outer shape processing and the process of forming the material 10a before the outer shape processing are roughly divided. It includes a step of forming an outer diameter cylindrical surface 11 and a spiral ball screw groove 12 by grinding.

【0022】

The molding of the material 10a consists of a step of preparing the round bar 10 as a raw material, a step of quenching the surface of the round bar 10 as a heat treatment, and a step of straightening the distortion of the round bar caused by the quenching. I have.

【0023】

Quenching is performed by, for example, high-frequency quenching in order to improve wear resistance, and a hard quenching layer is formed at least from the outer peripheral surface to a depth equal to or greater than the groove depth of the ball screw groove 12.

【0024】

In the straightening step, the warp or the like of the material 10a caused by the heat treatment is straightened.

【0025】

Next, the outer diameter cylindrical surface 11 and the ball screw groove 12 are machined by grinding.

【0026】

Grinding the ball screw groove is performed by a grinding machine as shown in FIG.

【0027】

The grinding device is a grinding wheel 21, an adjusting wheel 22 arranged side by side facing the grinding wheel 21, and a material 10a arranged between the grinding wheel 21 and the adjusting wheel 22 in parallel with the rotation axis of the grinding wheel 21. A blade 23 to support, a guide plate 24 provided in front of and behind the blade 23 along the feeding direction of the material 10a, a dresser 25 for forming a grinding wheel and a dresser 26 for forming an adjusting grindstone, and grinding that supplies a grinding fluid to a grinding part. It is configured to be equipped with a liquid ejection nozzle 27.

【0028】

As shown in FIG. 2C, the rotation axis of the adjusting grindstone 22 is tilted by a predetermined angle θ so that the front side of the material 10a in the feeding direction faces downward with respect to the axis parallel to the rotation axis of the grinding wheel 21. , The material 10a is rotated and fed in the axial direction by the rotation of the adjusting grindstone 22.

【0029】

The adjusting grindstone 22 is formed into a drum shape whose outer peripheral surface is formed by a rotating hyperboloid in order to make line contact with the material 10a in an inclined state.

【0030】

The widths of the grinding wheel 21 and the adjusting wheel 22 are appropriately selected according to the size of the material 10a and the grinding allowance.

【0031】

A chevron portion 21a having an arcuate cross section corresponding to the ball screw groove 12 is formed on the outer peripheral surface of the grinding wheel 21. The chevron portion 21a is formed all around the outer peripheral surface of the grinding wheel 21, and a plurality of chevron portions 21a are provided at a pitch matching the screw pitch of the ball screw groove 12 in the width direction of the grinding wheel 21.

【0032】

The material 10a rotates at a peripheral speed that is almost the same as the peripheral speed of the adjusting grindstone 22 due to the contact frictional force with the adjusting grindstone 22. Further, as described above, since the central axis of the adjusting grindstone 22 is tilted so that the front side in the feed direction of the material 10a faces downward, the material 10a is formed along the blade 23 arranged in the axial direction of the adjusting grindstone 22. It is sent in the axial direction at a speed corresponding to the axial component of the peripheral speed.

【0033】

In this way, the material 10a is positioned by the blade 23 and the adjusting grindstone 22, and the depth of cut of the chevron portion 21a is accurately determined with reference to the outer diameter cylindrical surface 11 of the material 10a, so that the effective diameter of the ball screw groove 12 is determined. The degree of cylindricity can be accurately manufactured with reference to the outer diameter cylindrical surface 11. Further, the lead accuracy of the ball screw groove 12 can be precisely machined by controlling the peripheral speed of the adjusting grindstone 22.

【0034】

Further, in order to accurately transfer the shape of the ball screw groove 12 by the chevron protrusion 21a of the grinding wheel 21, it is preferable to process the material 10a on the line connecting the centers of the grinding wheel 21 and the adjusting wheel 22. .. In this way, the ball screw groove can be accurately machined. In addition, with such an arrangement relationship, the material 10a can be pressed between the three contacts of the grinding wheel 21, the adjusting wheel 22, and the blade 23, and the position of the material 10a is stable and the ball screw groove is more accurately formed. Can be processed.

【0035】

Next, the grinding wheel, which is a characteristic part of the present invention, will be described.

【0036】

FIG. 3 is an enlarged view of the inlet side end of the grinding wheel used in the ball screw shaft grinding apparatus according to the present embodiment. As shown in exaggeratedly shown in (a), the chevron 21a on the inlet side of the grinding wheel 22 has a shape like a cut-out top of the chevron 21a on the outlet side, and the top is formed flat and the grinding wheel The resistance to feed the tip of the material between the grinding wheel and the adjusting wheel is reduced so that the material can be inserted smoothly at the start of grinding.

【0037】

Fig. 3 (b) and (c) explain the cut state of the chevron protrusion in (a), and (b) is a conceptual diagram in which the chevron protrusion in the ground state is cut by the extension surface of the outer diameter cylindrical surface of the material. (c) is an explanatory view in which the cross-sectional shapes cut at the positions a to e in (b) are aligned along the center line of the chevron protrusion. Further, (d) is a comparison diagram of the grinding resistance vector related to the chevron projection.

【0038】

As shown by the arrow in (c), most of the grinding resistance is downward (toward the adjusting wheel). Then, the relationship between the grinding resistance X in the 22 direction of the adjusting grindstone and the grinding resistance Y in the opposite direction of the material feed direction is as shown in (d). Therefore, even when only the tip of the material is ground, the material is firmly pressed against the adjusting grindstone, and the rotational force and thrust obtained by the material from the adjusting grindstone are the grinding resistance against the material feed (grinding in the direction opposite to the material feed direction). It is sufficiently larger than the resistance).

【0039】

As a result, even when only the tip of the material is ground at the entrance of the grinding wheel, the material is accurately fed without slipping, and it is not necessary to use an upper presser or the like, and grinding is performed at the grinding position. High-precision grinding can be started simply by feeding the tip of the material between the grindstone and the adjusting grindstone in the axial direction.

【0040】

Further, by reducing the grinding margin on the inlet side of the grinding wheel 21 and gradually increasing it toward the outlet side, the grinding resistance is evenly distributed in the axial direction of the grinding wheel, so that the material is used as the adjusting wheel in parallel with the axis. It can be pressed, and accurate material feeding is possible. On the other hand, since a uniform load is applied to the grinding wheel itself in the axial direction, the dressing interval of each chevron protrusion is constant, and the rotating shaft of the grinding wheel is not damaged. The resistance to feed the tip of the material between the grinding wheel and the adjusting wheel is reduced so that the material can be smoothly inserted at the start of grinding.

【0041】

(Embodiment 2) FIG. 4 shows an enlarged view of the inlet side end of the grinding wheel used in the ball screw shaft grinding apparatus according to the second embodiment of the present invention.

【0042】

In the first embodiment, the top of the chevron protrusion 21a on the inlet side of the grinding wheel is formed into a flat surface parallel to the axis of the material, but in the present embodiment, it is minute with respect to the axis of the material 10a. It is formed on a flat surface that is inclined toward the angle exit side.

【0043】

As a result, the resistance to feed the tip of the material between the grinding wheel 21 and the adjusting wheel 22 is further reduced, and the material can be smoothly inserted at the start of grinding.

【0044】

Since other configurations and operations are the same as those in the first embodiment, the description thereof will be omitted.

【0045】

(Embodiment 3) FIG. 7 shows an enlarged view of the inlet side end of the grinding wheel used in the ball screw shaft grinding apparatus according to the third embodiment of the present invention.

【0046】

In the first embodiment described above, the top of the chevron protrusion 21a on the inlet side of the grinding wheel 21 is formed into a flat surface parallel to the axis of the material 10a, but in the present embodiment, the grinding wheel 21 has a width. Is the same and has a plurality of chevrons 21a formed so that the height gradually increases from the entrance side to the exit side.

【0047】

Since other configurations and operations are the same as those in the first embodiment, the description thereof will be omitted.

【0048】

[Effect of the invention]

As described above, according to the present invention, the chevron protrusion on the inlet side of the grinding wheel is formed to have the same width as the other chevron protrusions and is formed as low as possible, so that the tip of the material is fed between the grinding wheel and the adjusting grindstone. The resistance is reduced, and the material can be inserted smoothly at the start of grinding. That is, the ball screw shaft grinding can be performed only by through-feed grinding, the setting at the start of grinding the material is not required, and continuous machining is possible, so that the productivity of the ball screw shaft is improved. It can be planned.

【0049】

In particular, the height of the chevron protrusion on the entrance side is lowered by flattening the top of the chevron protrusion that has the same shape as the other chevron protrusions, so that the grinding resistance in the direction of the adjusting grindstone increases, and the material is removed from the adjusting grindstone. The obtained rotational force and thrust are sufficiently larger than the grinding resistance with respect to the material feed (grinding resistance in the direction opposite to the material feed direction).

【0050】

As a result, the ball screw shaft grinding process of only through-feed grinding can be performed with higher accuracy.

【0051】

Further, the chevron protrusion is characterized in that the height gradually increases from the entrance side to the exit side.

【0052】

As a result, the grinding allowance gradually increases, and the grinding resistance is evenly distributed in the axial direction of the grinding wheel, so that the material can be pressed against the adjusting wheel in parallel with the axis, and accurate material feeding becomes possible. .. On the other hand, since a uniform load is applied to the grinding wheel itself in the axial direction, the dressing interval of each chevron protrusion is constant, and the rotating shaft of the grinding wheel is not damaged.

【0053】

As a result, the machining accuracy of the ball screw shaft is further improved, the quality of the ball screw shaft can be improved, and the life of the ball screw shaft grinding apparatus can be extended.

[Simple explanation of drawings]

[Figure 1]

FIG. 1 (a) is a process diagram of the processing method of the ball screw shaft of the present invention, FIG. 1 (b) is a schematic diagram of each processing process, and FIG. 1 (c) is a front view of the processed ball screw shaft.

[Figure 2]

FIG. 2 shows the basic configuration of the grinding apparatus used for machining the ball screw shaft according to the first embodiment of the present invention. FIG. 2A is a front view and FIG. 2B is a front view. The top view and the figure (c) are side views.

[Fig. 3]

FIG. 3A is an enlarged view showing the shape of the grinding wheel of the ball screw shaft grinding apparatus according to the first embodiment of the present invention. Fig. 3 (b) and (c) explain the cut state of the chevron protrusion in (a), and (b) is a conceptual diagram in which the chevron protrusion in the ground state is cut by the extension surface of the outer diameter cylindrical surface of the material. (c) is an explanatory view in which the cross-sectional shapes cut at the positions a to e in (b) are aligned along the center line of the chevron protrusion. Further, (d) is a comparison diagram of the grinding resistance vector related to the chevron projection.

[Fig. 4]

FIG. 4 is an enlarged view showing the shape of the grinding wheel of the ball screw shaft grinding apparatus according to the second embodiment of the present invention.

[Fig. 5]

FIG. 5 is an enlarged view showing the shape of the grinding wheel of the ball screw shaft grinding apparatus according to the third embodiment of the present invention.

[Fig. 6]

FIG. 6A is a diagram showing an example of conventional centerless grinding, and FIGS. 6B to 6D are diagrams showing an example of a workpiece processed by conventional centerless grinding.

[Fig. 7]

FIG. 7 (a) is an enlarged view showing the shape of the grinding wheel of the conventional ball screw shaft grinding machine. Fig. 7 (b) and (c) explain the cut state of the chevron protrusion in (a), and (b) is a conceptual diagram in which the chevron protrusion in the ground state is cut by the extension surface of the outer diameter cylindrical surface of the material. (c) is an explanatory view in which the cross-sectional shapes cut at the positions a to e in (b) are aligned along the center line of the chevron protrusion. Further, (d) is a comparison diagram of the grinding resistance vector related to the chevron projection.

[Fig. 8]

FIG. 8 is an explanatory view when grinding is started using the grinding wheel and the upper presser of FIG. 7.

[Explanation of symbols]

10a material 11 Outer diameter cylindrical surface 12 ball screw groove 21 Grinding wheel 21a chevron 22 Adjusting whetstone 23 Support stand 24 Information board 27 Nozzle for ejecting grinding fluid