JP2013166173A - Method of manufacturing ball screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a ball screw which can manufacture the ball screw further inexpensively.SOLUTION: In manufacturing a ball screw 1, part of an inner peripheral surface having a cylindrical planar shape of a blank 21 having approximately the same shape as a nut 5 is recessed by plastic forming, so as to form a recessed groove 22 and a thread groove 5a which form a ball circulation path 11. A die 30 which includes one projection 31 having an approximately rectangular parallelepiped shape is inserted into the blank 21 and the projection 31 of the die 30 is brought into contact with the inner peripheral surface of the blank 21. By strongly pressing the die 30 against the inner peripheral surface of the blank 21, plastic forming is performed, so as to form a recess 33 on the inner peripheral surface of the blank 21. The operation to form the recess 33 is performed a plurality of times so that each recess 33 is continued linearly, to form the thread groove 5a.

Description

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

  The ball screw is a spiral ball rolling path formed by a screw shaft having a helical thread groove on the outer peripheral surface, a nut having a screw groove facing the screw groove of the screw shaft on the inner peripheral surface, and both screw grooves. And a plurality of balls that are movably loaded therein. Then, when the nut and the screw shaft that are screwed to the screw shaft through the ball are relatively rotated, the screw shaft and the nut are relatively moved in the axial direction through the rolling of the ball. .

  Such a ball screw is provided with a ball circulation path that forms an endless ball path by communicating the start point and end point of the ball rolling path. That is, the ball moves around the screw shaft while moving in the ball rolling path and reaches the end point of the ball rolling path. The ball is scooped up from one end of the ball circulation path and passes through the ball circulation path. The ball is returned to the starting point of the ball rolling path from the other end of the circulation path. Thus, since the ball rolling in the ball rolling path is infinitely circulated by the ball circulation path, the screw shaft and the nut can continuously move relative to each other.

  As a ball circulation type using a ball circulation path, a tube type, a top type, etc. are generally used. However, in recent years, there has been a strong demand for reducing the manufacturing cost of a ball screw. A ball circulation system in which a part of the inner peripheral surface of the groove is recessed to form a groove and this groove is used as a ball circulation path has been studied. As a method of manufacturing a ball screw nut of such a ball circulation type, there is a method in which a part of the inner peripheral surface of the nut is recessed by forging using a die or the like to form the groove (for example, (See Patent Document 1).

JP 2008-281063 A

However, since the demand for reducing the cost of ball screws has become more and more severe, further reduction in manufacturing cost has been demanded.
Accordingly, it is an object of the present invention to provide a ball screw manufacturing method capable of solving the above-described problems of the prior art and manufacturing a ball screw at a lower cost.

  In order to solve the above problems, an aspect of the present invention has the following configuration. That is, a ball screw manufacturing method according to an aspect of the present invention includes a screw shaft having a helical thread groove on an outer peripheral surface, and a nut having a screw groove facing the screw groove of the screw shaft on an inner peripheral surface; A plurality of balls slidably loaded in a spiral ball rolling path formed by the both screw grooves, and a ball circulation path for circulating the ball from the end point of the ball rolling path to the start point, A method of manufacturing a ball screw in which the ball circulation path is configured by a concave groove formed on an inner peripheral surface of the nut, wherein a part of the inner peripheral surface of the nut is recessed by plastic working, and A screw groove and the concave groove are formed.

In this ball screw manufacturing method, the operation of forming a recess in the inner peripheral surface of the nut by plastic processing by pressing a convex portion of the processing tool against the inner peripheral surface of the nut is performed a plurality of times. It is preferable to form the thread groove by continuously forming a plurality of the depressions formed by performing a plurality of times.
The machining tool has a plurality of the convex portions, forms the plurality of depressions by one operation, and forms the screw groove by performing the operation to form the plurality of depressions a plurality of times. Alternatively, the processing tool has one convex portion, and forms one recess by one operation, and performs the operation to form one recess a plurality of times. The thread groove may be formed.

Further, in the above ball screw manufacturing method, the rotating member of the processing tool is pressed against the inner peripheral surface of the nut, and the processing tool is moved while rotating the rotating member to continuously perform plastic working. Then, it is preferable that a part of the inner peripheral surface of the nut is recessed in a linear shape to form the thread groove.
The rotating member may be a disk-shaped member, and the peripheral edge of the disk-shaped member may be pressed against the inner peripheral surface of the nut. Alternatively, the rotating member may be a spherical member, and the spherical member may be the inner peripheral surface of the nut. You may press on the surface.

  According to the ball screw manufacturing method of the present invention, a part of the inner peripheral surface of the nut is recessed by plastic working to form a screw groove and a ball circulation path, so that the ball screw can be manufactured at low cost. it can.

It is sectional drawing of a ball screw. It is principal part sectional drawing of a nut. It is an expanded sectional view of a ball circulation way. It is a figure explaining 1st embodiment of the manufacturing method of the ball screw which concerns on this invention. It is sectional drawing of the nut explaining 1st embodiment of the manufacturing method of the ball screw which concerns on this invention. It is sectional drawing explaining 2nd embodiment of the manufacturing method of the ball screw which concerns on this invention. It is a figure explaining the 1st groove processing process of the method of a second embodiment. It is a figure explaining the 2nd groove processing process of the method of a second embodiment. It is sectional drawing of the processing tool explaining the modification of the method of 2nd embodiment. It is a figure explaining 3rd embodiment of the manufacturing method of the ball screw which concerns on this invention.

An embodiment of a ball screw manufacturing method according to the present invention will be described in detail with reference to the drawings.
[First embodiment]
FIG. 1 is a cross-sectional view (a cross-sectional view cut along a plane along the axial direction) of a ball screw according to an embodiment of the present invention.
As shown in FIG. 1, the ball screw 1 has a screw shaft 3 having a helical screw groove 3a on the outer peripheral surface and a helical screw groove 5a facing the screw groove 3a of the screw shaft 3 on the inner peripheral surface. A plurality of balls 9 movably loaded in a spiral ball rolling path 7 formed by the nut 5 and both screw grooves 3a, 5a, and the balls 9 are circulated back from the end point of the ball rolling path 7 to the starting point. And a ball circulation path 11 to be moved.

That is, the ball 9 moves around the screw shaft 3 while moving in the ball rolling path 7 to reach the end point of the ball rolling path 7, where it is scooped up from one end portion of the ball circulation path 11 to be ball circulation path. 11, the ball circulation path 11 is returned to the starting point of the ball rolling path 7 from the other end of the ball circulation path 11.
The material of the screw shaft 3, the nut 5, and the ball 9 is not particularly limited, and general materials can be used, and examples thereof include metals (steel etc.), ceramics, and resins.
When such a ball screw 1 is rotated relative to a nut 5 and a screw shaft 3 that are screwed to the screw shaft 3 via a ball 9, the screw shaft 3 and the nut 5 are moved via the rolling of the ball 9. And move relative to each other in the axial direction. An endless ball path is formed by the ball rolling path 7 and the ball circulation path 11, and the ball 9 circulates infinitely in the ball path. Therefore, the screw shaft 3 and the nut 5 are continued. Relative movement.

Here, the thread groove 5a formed in the inner peripheral surface of the nut 5 will be described in detail. The thread groove 5 a of the nut 5 is formed integrally with the inner peripheral surface of the nut 5. Specifically, a spiral groove formed by recessing a part of the cylindrical inner peripheral surface of the nut 5 by plastic working such as forging is referred to as a thread groove 5a.
Next, the ball circulation path 11 will be described in detail with reference to FIGS. The ball circulation path 11 is integrally formed on the inner peripheral surface of the nut 5. More specifically, the groove 22 formed by recessing a part of the cylindrical inner peripheral surface of the nut 5 by plastic working such as forging is used as the ball circulation path 11 (cut along a plane orthogonal to the axial direction). 2 is a partial sectional view of the nut 5). Therefore, unlike the case of a ball circulation type such as a tube type or a piece type, another member constituting the ball circulation path 11 is not attached.

  In addition, the ball circulation path 11 (concave groove 22) has a linear shape at both ends that are connected to the ball rolling path 7 (screw groove 5a), and an intermediate portion located between the both ends is curved. It has become a shape. Both ends of the intermediate portion and the both end portions are smoothly connected, and the overall shape of the ball circulation path 11 (concave groove 22) when the inner peripheral surface is viewed from the center of the nut 5 is substantially S-shaped. ing. However, this is only an example, and the overall shape of the ball circulation path 11 is not limited to a substantially S shape.

  Since such a ball circulation path 11 is provided, as shown in FIG. 3, the ball 9 that moves around the screw shaft 3 while moving in the ball rolling path 7 and reaches the end point of the ball rolling path 7 is Then, it enters into one end of the ball circulation path 11 and is lifted up to the ball circulation path 11 (intermediate part) from the vicinity of the boundary between the end and the intermediate part and into the inside of the nut 5 (radially outward). Sink. Then, after passing through the intermediate portion of the ball circulation path 11 and over the land portion 3b of the screw shaft 3 (the thread of the screw groove 3a), it reaches the other end of the ball circulation path 11 and from there the ball rolling path 7 Returned to the starting point.

  The cross-sectional shape of the ball circulation path 11 (the cross-sectional shape when cut along a plane perpendicular to the longitudinal direction of the ball circulation path 11) may be an arc shape (single arc shape) or a gothic arc shape. Further, the cross-sectional shape of the screw grooves 3a and 5a (the cross-sectional shape when cut along a plane perpendicular to the longitudinal direction of the screw grooves 3a and 5a) may be arcuate (single arc) or gothic arc-shaped. . Further, the ball circulation path 11 and the ball rolling path 7 are smoothly connected. That is, the ball circulation path 11 and the ball rolling path 7 are arranged so that the locus of the contact point between the ball 9 and the inner surface of the concave groove 22 and the locus of the contact point between the ball 9 and the inner surface of the screw groove 5a are smoothly continuous. Is connected. As a result, the ball 9 circulates smoothly in the ball passage.

In the ball screw 1 of this embodiment, the screw groove 5a of the nut 5 and the concave groove 22 constituting the ball circulation path 11 are both concaved by plastic working on a part of the inner peripheral surface of the nut 5. Since it is formed, the manufacturing cost is low in addition to high productivity as compared with the conventional ball screw in which the thread groove 5a is formed by cutting.
The application of the ball screw 1 of this embodiment is not particularly limited, but can be suitably used for automobile parts, positioning devices, machines, and the like.

Next, an example of the manufacturing method of the ball screw 1 of this embodiment is demonstrated, referring FIG. FIG. 4 is a view for explaining the first embodiment of the ball screw manufacturing method according to the present invention, and is a perspective view in which a part of the blank is not shown.
First, a columnar steel material (not shown) was processed by plastic working such as cold forging to obtain a blank 21 having substantially the same shape (substantially cylindrical shape) as the nut 5 (rough forming step). At this time, a flange is also formed on the outer peripheral surface of the blank 21 by plastic working.

Next, part of the cylindrical inner peripheral surface of the blank 21 is recessed by plastic working such as cold forging to form a ball circulation path 11 that communicates the end point and the start point of the ball rolling path 7, for example, approximately S A letter-shaped concave groove 22 was formed (ball circulation path forming step).
Specific examples of the method for forming the concave groove 22 include the following. That is, a mold (not shown) having a convex portion corresponding to the concave groove 22 is inserted into, for example, a blank 21 accommodated in a cylindrical receiving die (not shown), and the blank 21 The concave portion 22 can be formed by bringing the convex portion of the mold into contact with the inner peripheral surface and pressing the mold strongly toward the inner peripheral surface of the blank 21 for plastic working (forging).

  For example, the concave groove 22 may be formed using a mold of a cam mechanism having a cam driver (not shown) and a cam slider (not shown) having a convex portion corresponding to the concave groove 22. Good. More specifically, a cam driver and a cam slider are inserted into the blank 21. At that time, the cam slider is disposed between the blank 21 and the cam driver, and the convex portion is disposed toward the inner peripheral surface of the blank 21. The cam slider and the cam driver arranged in the blank 21 are in contact with each other at an inclined surface extending in a substantially axial direction of the blank 21 (a direction slightly inclined from the axial direction of the blank 21). A cam mechanism is configured.

  Here, when the cam driver is moved along the axial direction of the blank 21, the cam slider is moved outward in the radial direction of the blank 21 by the cam mechanism (wedge action) constituted by both inclined surfaces. That is, a force is transmitted from the inclined surface of the cam driver to the inclined surface of the cam slider, and the axial force of the cam driver is converted into a force that moves the cam slider radially outward. As a result, the convex portion of the cam slider strongly presses the inner peripheral surface of the blank 21, so that the concave groove 22 is formed on the inner peripheral surface of the blank 21 by forging.

Next, a part of the inner peripheral surface of the blank 21 in which the concave groove 22 is formed is concaved by plastic working such as cold forging and connected to both extreme ends of the ball circulation path 11 (concave groove 22). Thus, the helical screw groove 5a was formed (screw groove forming step).
Specific examples of the method for forming the thread groove 5a include the following. That is, a die 30 (corresponding to a processing tool which is a constituent element of the present invention) having a linear shape corresponding to the shape of the screw groove 5a and having a shorter length than the screw groove 5a is inserted into the blank 21; The convex portion 31 of the mold 30 is brought into contact with the inner peripheral surface of the blank 21, and the metal mold 30 is strongly pressed toward the inner peripheral surface of the blank 21 to perform plastic working (forging). Then, a recess 33 having a shape corresponding to the shape of the convex portion 31 is formed on the inner peripheral surface of the blank 21.

  Since the shape of the convex portion 31 is a linear shape corresponding to the shape of the screw groove 5a and shorter than the screw groove 5a, the shape of the recess 33 when the inner peripheral surface is viewed from the center of the blank 21 is substantially rectangular. Yes. Moreover, the cross-sectional shape of the convex part 31 (the shape of the cross section when cut by a plane orthogonal to the longitudinal direction of the convex part 31) is the cross-sectional shape of the screw groove 5a (cut by a plane orthogonal to the longitudinal direction of the screw groove 5a). The shape corresponding to the shape of the cross section), that is, the shape of the arc (single arc shape) or the Gothic arc shape, the cross section of the recess 33 (when cut along a plane orthogonal to the longitudinal direction of the recess 33) The shape of the cross section) is also an arc shape (single arc shape) or a gothic arc shape.

  Since the mold 30 has one protrusion 31, one depression 33 is formed by pressing the mold 30 described above once. Therefore, the thread groove 5a can be formed by performing the operation of forming the recess 33 a plurality of times so that each recess 33 is continuous in a line. The first depression 33A is formed so as to be continuous with one end of the concave groove 22, and the second depression 33B is formed so as to be continuous with the end of the first depression 33A, thereby extending the groove linearly. If the depressions 33 are sequentially formed so as to continue, and finally the depressions 33 are formed so as to be continuous with the other end of the groove 22, one completely closed circuit is formed by the grooves 22 and the screw grooves 5a. (See FIG. 5).

Of course, if the plurality of depressions 33 are finally continuously formed in a linear shape and the thread groove 5a is formed, the plurality of depressions 33 are not formed sequentially so as to extend the grooves in a linear shape, but randomly. They may be formed in any order.
In addition, the screw groove 5a may be formed after the concave groove 22 is formed, but conversely, the concave groove 22 may be formed after the screw groove 5a is formed.

Further, since the ball passage is constituted by one completely closed circuit, clogging is unlikely to occur in the circulating ball 9. One ball passage may be formed on the inner peripheral surface of the blank 21, or a plurality of the ball passages may be formed side by side in the axial direction.
Further, as shown in FIG. 4, the mold 30 for forming the recess 33 may be a cam mechanism mold having a cam driver (not shown) and a cam slider 35 having a convex portion 31. The cam slider 35 is a substantially rod-shaped member, and includes a convex portion 31 at one end and an inclined surface 37 at the other end. The cam slider 35 is arranged with the convex portion 31 facing the inner peripheral surface of the blank 21. On the other hand, the cam driver has an inclined surface facing the inclined surface 37 of the cam slider 35. The cam slider 35 and the cam driver are in contact with each other at an inclined surface extending in a substantially axial direction of the blank 21 (a direction slightly inclined from the axial direction of the blank 21), and both inclined surfaces constitute a cam mechanism of the mold 30. ing.

  Here, when the cam driver is moved along the axial direction of the blank 21, the cam slider 35 is moved outward in the radial direction of the blank 21 by the cam mechanism (wedge action) constituted by both inclined surfaces. That is, a force is transmitted from the inclined surface of the cam driver to the inclined surface 37 of the cam slider 35, and the axial force of the cam driver is converted into a force that moves the cam slider 35 radially outward. As a result, the convex portion 31 of the cam slider 35 strongly presses the inner peripheral surface of the blank 21, so that a recess 33 is formed on the inner peripheral surface of the blank 21 by forging.

  The mold 30 can be moved in the axial direction of the blank 21 while being rotated in the circumferential direction of the blank 21 by being driven by a driving device 39 via a screw or a ball screw. Examples of the drive device 39 include a servo motor, a rotary actuator, and a rotary hydraulic cylinder. By driving the drive device 39, the convex portion 31 of the mold 30 can be moved in the axial direction by the lead amount corresponding to the rotation angle while rotating the convex portion 31 of the mold 30 in the circumferential direction by the function of the screw or ball screw. Therefore, if the depressions 33 are sequentially formed while moving the convex portion 31 of the mold 30 as described above, the spiral thread groove 5a can be formed. However, the blank 30 may be moved without moving the mold 30.

  Finally, the nut 21 was obtained by subjecting the blank 21 to heat treatment such as carburizing, carbonitriding, quenching, tempering, induction hardening under desired conditions and further grinding the thread groove 5a or the like as desired. When the heat treatment is carburizing or carbonitriding, the material of the nut 5 is preferably chromium steel or chromium molybdenum steel (for example, SCM420, SCM415) having a carbon content of 0.10 to 0.25% by mass, In the case where the heat treatment is induction hardening, carbon steel having a carbon content of 0.4 to 0.6% by mass (for example, S53C, SAE4150) is preferable.

The ball screw 1 was manufactured by combining the nut 5 manufactured in this way, the screw shaft 3 and the ball 9 manufactured by a conventional method.
As described above, in the ball screw 1 manufactured in this way, the screw groove 5a of the nut 5 and the concave groove 22 constituting the ball circulation path 11 are both plastically machined on a part of the inner peripheral surface of the nut 5. Therefore, as compared with the conventional ball screw in which the thread groove 5a is formed by cutting, the productivity is low and the manufacturing cost is low.

Further, since the thread groove forming step is performed by plastic working (forging), the thread groove 5a of the nut 5 is strengthened by work hardening.
Further, when the screw groove 5a is formed by the plastic processing as described above, the surplus generated when the screw groove 5a is formed moves, and a protrusion protruding radially inward is generated around the screw groove 5a. There is. In other words, linear protrusions along the thread groove 5a may occur on both edges of the thread groove 5a on the inner peripheral surface of the nut 5. This protrusion makes it easier for the ball 9 to be held in the screw groove 5a, so that the depth of the screw groove 3a of the screw shaft 3 can be reduced. On the other hand, a recessed portion is formed in advance in a portion corresponding to a portion where the screw groove 5a is formed on the outer peripheral surface of the blank 21, and an escape portion into which surplus material generated when the screw groove 5a is formed by plastic working flows. If it is provided, the protrusions are unlikely to occur. In this case, there are advantages such that the torque of the ball screw 1 is reduced and the lubricating oil is easily retained.

  Furthermore, since the rough forming step, the ball circulation path forming step, and the thread groove forming step are performed by plastic working (forging), the manufacturing method of the ball screw 1 has high accuracy in addition to high material yield. Can be manufactured at low cost. Furthermore, since it is manufactured by plastic working (forging), the metal flow (forged streamline) of the steel material is hardly cut, and thus a high-strength nut 5 is obtained.

  The type of plastic working for forming the concave groove 22 and the screw groove 5a is not particularly limited, but forging is preferable, and cold forging is particularly preferable. Although hot forging can be used, cold forging can finish with higher accuracy than hot forging, so it is possible to obtain a sufficiently accurate nut 5 without post-processing. Can do. Therefore, the ball screw 1 can be manufactured at low cost. It is preferable that all of the plastic working in the rough forming step, the ball circulation path forming step, and the thread groove forming step be cold forging, but the plastic working in any one or two steps may be cold forging.

  In the ball circulation path forming step and the thread groove forming step, the circumferential position where the concave groove 22 and the depression 33 are formed needs to be precisely controlled, so that phase alignment is required in each step. As a method of phase alignment, a concave portion for phase alignment is provided on one end surface in the axial direction of the blank 21, and a convex portion that engages with the concave portion for phase alignment is provided in a receiving mold. There is a method of accommodating the blank 21 in the receiving mold while being engaged.

[Second Embodiment]
A second embodiment of the ball screw manufacturing method according to the present invention will be described with reference to FIGS. FIG. 6 is a cross-sectional view (a cross-sectional view cut along a plane along the axial direction) illustrating the manufacturing method of the second embodiment. Moreover, FIG. 7 is a figure explaining the 1st groove processing process of the manufacturing method of 2nd embodiment, and FIG. 8 is a figure explaining the 2nd groove processing process of the manufacturing method of 2nd embodiment. is there.
Since there are parts similar to those of the first embodiment in the configuration, operation, and effects of the ball screw manufacturing method of the second embodiment, description of the same parts is omitted, and only different parts are described. 6-8, the same code | symbol as FIGS. 1-5 is attached | subjected to the part which is the same as that of FIGS.

In the first embodiment, the mold 30 used in the thread groove forming step has one convex portion 31, but in the second embodiment, a plurality of molds 30 (see FIGS. 6 to 6). 8 has three or four convex portions 31.
First, a part of the inner peripheral surface of the blank 21 manufactured in the same manner as in the first embodiment is recessed by plastic working such as cold forging, and the ball circulation path 11 that communicates the end point and the start point of the ball rolling path 7. For example, a substantially S-shaped concave groove 22 and a part of the plurality of depressions 33 for forming the screw groove 5a are formed (first groove processing step).

  As shown in FIGS. 6 and 7, the mold 30 used in the first groove processing step has three convex portions 31 for forming the screw groove 5 a (depression 33) and the concave groove 22. It has one convex part 41 of the shape corresponding to the concave groove 22 for doing. The shape of the convex portion 31 is a linear shape corresponding to the shape of the thread groove 5a and is shorter than the thread groove 5a. Specifically, four cam sliders similar to those of the first embodiment are provided on a substantially cylindrical member, and one cam slider has a convex portion 41 having a shape corresponding to the concave groove 22, and the remaining 3 Each cam slider has a convex portion 31 having a shape corresponding to the shape of the thread groove 5a. These four cam sliders are equally arranged in the circumferential direction with a phase difference of 90 °. Further, the three cam sliders having the convex portions 31 have different axial positions.

  Therefore, when the cam driver is moved along the axial direction of the blank 21, the four cam sliders are moved outward in the radial direction of the blank 21 by the cam mechanism. As a result, the convex portion 31 and the convex portion 41 of the cam slider strongly press the inner peripheral surface of the blank 21, so that the concave groove 22 and the three recesses 33 are simultaneously formed on the inner peripheral surface of the blank 21 by forging. The Of course, the number of the convex portions 31 is not limited to three.

Next, a part of the cylindrical inner peripheral surface of the blank 21 is made concave by plastic working such as cold forging, and the remainder is formed among the plurality of depressions 33 for forming the screw groove 5a, The thread groove 5a was formed by continuously connecting all the concave grooves 22 and the depressions 33 formed in the first groove processing step in a line (second groove processing step).
As shown in FIG. 8, the mold 30 used in the second groove processing step has four convex portions 31 for forming the thread groove 5 a (depression 33). The shape of the convex portion 31 is a linear shape corresponding to the shape of the thread groove 5a and is shorter than the thread groove 5a. More specifically, four cam sliders similar to those in the first embodiment are provided on a substantially cylindrical member, and each cam slider has a convex portion 31. These four cam sliders are arranged at equal intervals in the circumferential direction while having a phase difference of 90 °, and the positions in the axial direction are different.

Therefore, when the cam driver is moved along the axial direction of the blank 21, the four cam sliders are moved outward in the radial direction of the blank 21 by the cam mechanism. As a result, the convex portion 31 of the cam slider strongly presses the inner peripheral surface of the blank 21, so that four recesses 33 are simultaneously formed on the inner peripheral surface of the blank 21 by forging.
With the four depressions 33, the concave grooves 22 and the depressions 33 formed in the first groove processing step are all linearly continued to form the screw groove 5a. That is, the screw groove 5a is formed by continuously performing the operation of forming the three recesses 33 (first groove processing step) and the operation of forming the four recesses 33 (second groove processing step). A completely closed circuit similar to FIG. 5 was formed by the groove 22 and the thread groove 5a. Of course, the number of convex portions 31 provided on the mold 30 used in the second groove processing step is not limited to four. Moreover, in this embodiment, although all the depressions 33 were formed by two operations of a 1st groove processing process and a 2nd groove processing process, you may form by 3 or more operations.

  In the first grooving process and the second grooving process, the circumferential positions where the concave grooves 22 and the depressions 33 are formed need to be precisely controlled. Necessary. As a method of phase alignment, a concave portion for phase alignment is provided on one end surface in the axial direction of the blank 21, and a convex portion that engages with the concave portion for phase alignment is provided in a receiving mold. There is a method of accommodating the blank 21 in the receiving mold while being engaged.

  Further, the concave groove 22 may not be formed simultaneously with the depression 33 as described above, and may be formed separately from the depression 33 by the same method as in the first embodiment. In this case, the recesses 22 may be formed first and then all the recesses 33 may be formed to complete the circuit, or after all the recesses 33 are formed and finally the recesses 22 may be formed to The circuit may be completed. And since the metal mold | die 30 used at the 1st groove processing process cannot be used for formation of the hollow 33 since it has the convex part 41, for example, it is recessed from the metal mold | die 30 used at the 1st groove | channel processing process. All of the depressions 33 are formed by a plurality of operations using a mold that omits the cam slider having the convex portion 41 having a shape corresponding to the groove 22 and a mold similar to the mold 30 used in the second groove processing step. May be formed.

  Further, when the ball passage is formed with eight grooves (the concave groove 22 and the seven depressions 33) as in the above example, the circumferential lengths of these eight grooves (the circumference of the nut 5). The length in the direction along the direction) is preferably the same (the circumferential length corresponding to 1/8 of the entire circumference), but the circumferential length of the concave groove 22 is 1/8 of the entire circumference. It does not necessarily have a corresponding circumferential length. For example, when the circumferential length of the concave groove 22 is shorter than the circumferential length corresponding to 1/8 of the entire circumference, the shape of the convex portion 41 may be as follows.

  That is, since the thread groove 5 a needs to be continuous at both ends of the concave groove 22, the shape of the convex portion 41 has the same cross-sectional shape as the concave portion 33 at both ends of the short convex portion corresponding to the short concave groove 22. It is good to make it the shape which provided the convex part which forms a short hollow continuously. And the circumferential direction length which combined the short convex part of the shape corresponding to the short concave groove 22, and the convex part which forms the short hollow of both ends becomes the circumferential direction length equivalent to 1/8 of a perimeter. In addition, the length in the circumferential direction of the convex portion that forms the short dent may be set. Of course, instead of this, the circumferential length of the convex portion 41 is set according to the circumferential length of the concave groove 22, and the circumferential length of some or all of the convex portions 31 to correspond to this. May be changed.

Furthermore, since the two molds 30 used in the second embodiment are both slightly larger than the mold 30 used in the first embodiment, the method of the second embodiment has a relatively large diameter. The method of the first embodiment is suitable for manufacturing a ball screw having a relatively small diameter.
Furthermore, one ball path constituted by one completely closed circuit may be formed on the inner peripheral surface of the blank 21 or a plurality of ball paths may be formed side by side in the axial direction. When a plurality of ball paths are formed, the first grooving process and the second grooving process described above may be performed at different axial positions. Alternatively, if the mold 30 as shown in FIG. 9 is used, the convex portions 31 corresponding to the respective ball passages are provided at different axial positions, so that without performing the work of changing the axial position for processing, A plurality of ball paths can be formed simultaneously. FIG. 9 shows, as an example, a mold used when two ball paths are formed side by side in the axial direction. The method using the mold 30 shown in FIG. 9 is suitable for manufacturing a ball screw having a relatively large pitch between the ball passages.

[Third embodiment]
A third embodiment of the ball screw manufacturing method according to the present invention will be described with reference to FIG. The configuration, operation, and effects of the ball screw manufacturing method according to the third embodiment also include parts similar to those of the first embodiment, and therefore description of the same parts is omitted, and only different parts are described. In FIG. 10, the same reference numerals as in FIGS. 1 to 5 are given to the same or corresponding parts as in FIGS.
In the first and second embodiments, the mold 30 used in the thread groove forming step has the convex portion 31, but in the third embodiment, the mold 30 is a disk-shaped roller 45 (this (Corresponding to a disk-shaped member which is a constituent of the invention).

More specifically, the mold 30 according to the third embodiment includes a roller 45, a support base 48 that supports the roller 45 so as to be rotatable about an inclination axis that is inclined by a lead angle with respect to the axis of the blank 21, and not shown. And a rotary lift 47 to which a support 48 is attached so as to be movable in the radial direction by a mechanism (for example, a cam slider mechanism).
First, the blank forming step and the ball circulation path forming step were performed in the same manner as in the first embodiment, and the blank 21 having the concave groove 22 was obtained. Next, a part of the inner peripheral surface of the blank 21 is recessed by plastic working such as cold forging using the mold 30 and is connected to both extreme ends of the ball circulation path 11 (concave groove 22). Thus, the helical screw groove 5a was formed (screw groove forming step).

  Specific examples of the method for forming the thread groove 5a include the following. That is, the mold 30 having the disk-shaped roller 45 is inserted into the blank 21, the support base 48 is moved radially outward, and the peripheral edge of the roller 45 is brought into contact with the inner peripheral surface of the blank 21. The metal mold 30 is strongly pressed toward the inner peripheral surface of 21 to perform plastic working (forging). Then, a recess having a shape corresponding to the shape of the peripheral edge of the roller 45 is formed on the inner peripheral surface of the blank 21.

Then, the mold 30 is moved while rotating the roller 45 around the central axis of the disk-shaped roller 45 while keeping the mold 30 strongly pressed toward the inner peripheral surface of the blank 21. Then, plastic working is continuously performed from the peripheral edge of the roller 45, and a part of the inner peripheral surface of the blank 21 is spirally recessed to form the thread groove 5a.
The mold 30 can be moved in the axial direction of the blank 21 while being rotated in the circumferential direction of the blank 21 by being driven by a driving device 39 via a screw or a ball screw. Examples of the drive device 39 include a servo motor, a rotary actuator, and a rotary hydraulic cylinder. Therefore, when the driving device 39 is driven, the die 30 can be moved in the axial direction by the lead amount corresponding to the rotation angle while rotating the mold 30 in the circumferential direction by the function of the screw or the ball screw. Therefore, if the roller 30 is rotated while the mold 30 is moved as described above and plastic deformation is performed, the spiral thread groove 5a can be formed. However, the blank 30 may be moved without moving the mold 30.

The cross-sectional shape of the peripheral part of the roller 45 (the cross-sectional shape when cut along a plane perpendicular to the circumferential direction of the roller 45) is the cross-sectional shape of the screw groove 5a (when cut along a plane perpendicular to the longitudinal direction of the screw groove 5a) Are substantially arcuate (single arc) or gothic arc so that the shape of the cross section is arcuate (single arc) or gothic arc.
In addition, although the thread groove 5a may be formed after forming the groove 22, the groove 22 may be formed after forming the thread groove 5a.

[Fourth embodiment]
A fourth embodiment of the ball screw manufacturing method according to the present invention will be described. Since the configuration, operation, effects, and the like of the ball screw manufacturing method of the fourth embodiment are substantially the same as those of the third embodiment, description of similar parts is omitted, and only different parts are described.
In the third embodiment, the mold 30 used in the thread groove forming step has the roller 45. However, in the fourth embodiment, the mold 30 is a ball (a spherical member which is a constituent element of the present invention). Corresponding to).
First, the blank forming step and the ball circulation path forming step were performed in the same manner as in the first embodiment, and the blank 21 having the concave groove 22 was obtained. Next, a part of the inner peripheral surface of the blank 21 is recessed by plastic working such as cold forging using a die 30 having a ball (not shown), and both ends of the ball circulation path 11 (concave groove 22). A spiral thread groove 5a was formed so as to be connected to the portion (thread groove forming step).

  Specific examples of the method for forming the thread groove 5a include the following. That is, the metal mold 30 having a ball is inserted into the blank 21, the ball is brought into contact with the inner peripheral surface of the blank 21, and the metal mold 30 is strongly pressed toward the inner peripheral surface of the blank 21. ) Then, a spherical recess corresponding to the shape of the ball is formed on the inner peripheral surface of the blank 21. Then, the inner peripheral surface of the blank 21 is continuously plastically processed by moving the die 30 while rotating the ball while keeping the state in which the die 30 is strongly pressed toward the inner peripheral surface of the blank 21. Is partially recessed to form a screw groove 5a.

  The mold 30 can be moved in the axial direction of the blank 21 while being rotated in the circumferential direction of the blank 21 by being driven by a driving device 39 via a screw or a ball screw. Therefore, when the driving device 39 is driven, the die 30 can be moved in the axial direction by the lead amount corresponding to the rotation angle while rotating the mold 30 in the circumferential direction by the function of the screw or the ball screw. Therefore, when the mold 30 is moved as described above and the ball is rotated to perform plastic deformation, the spiral thread groove 5a can be formed. However, the blank 30 may be moved without moving the mold 30.

Since the cross-sectional shape of the ball is an arc shape (single arc shape), the cross-sectional shape of the screw groove 5a (the cross-sectional shape when cut along a plane perpendicular to the longitudinal direction of the screw groove 5a) is an arc shape ( Single arc).
In addition, although the thread groove 5a may be formed after forming the groove 22, the groove 22 may be formed after forming the thread groove 5a.

  Moreover, the metal mold | die 30 which has a ball | bowl can also be diverted for a finishing process. That is, the ball 30 is inserted into the screw groove 5a formed by the method of the first or second embodiment, and the die 30 is rotated while the ball 30 is rotated while the die 30 is pressed toward the inner peripheral surface of the blank 21. , The finishing process for flattening the minute step formed at the boundary part between the concave groove 22 and the concave part 33 or the boundary part between the concave part 33 and the concave part 33, or the groove surface of the screw groove 5 a It is also possible to perform the entire finishing process.

  In addition, these 1st-4th embodiment showed an example of this invention, and this invention is not limited to said each embodiment. For example, in the ball screw 1 of each of the above embodiments, a nut circulation type ball screw in which the ball circulation path 11 for circulating the ball 9 from the end point of the ball rolling path 7 to the start point is formed in the nut 5 is illustrated. The invention can also be applied to a screw shaft circulation type ball screw in which a screw shaft corresponding to the ball circulation path 11 is formed.

DESCRIPTION OF SYMBOLS 1 Ball screw 3 Screw shaft 3a Screw groove 5 Nut 5a Screw groove 7 Ball rolling path 9 Ball 11 Ball circulation path 21 Blank 22 Concave groove 30 Die 31 Convex part 33 Concave part 41 Convex part 45 Roller

Claims (7)

  A screw shaft having a helical thread groove on the outer circumferential surface, a nut having a thread groove facing the screw groove of the screw shaft on the inner circumferential surface, and a spiral ball rolling path formed by the both screw grooves. A plurality of balls loaded in a freely movable manner, and a ball circulation path that circulates the balls from the end point of the ball rolling path to the start point, and circulates the ball by a groove formed on an inner peripheral surface of the nut. A method of manufacturing a ball screw having a path, wherein the screw groove and the groove are formed by recessing a part of an inner peripheral surface of the nut by plastic working. Manufacturing method.   It is formed by performing a plurality of operations to form a recess in the inner peripheral surface of the nut by plastic processing by pressing a convex portion of the processing tool against the inner peripheral surface of the nut, and performing the operation a plurality of times. The ball screw manufacturing method according to claim 1, wherein the screw groove is formed by linearly connecting a plurality of the recesses.   The machining tool has a plurality of the convex portions, forms a plurality of the recesses by one operation, and forms the screw groove by performing the operation to form the plurality of recesses a plurality of times. The method of manufacturing a ball screw according to claim 2.   The machining tool has one convex portion, and forms the one recess by one operation, and forms the screw groove by performing the operation to form one recess a plurality of times. The ball screw manufacturing method according to claim 2, wherein:   A part of the inner peripheral surface of the nut is continuously plastically processed by pressing the rotating member of the processing tool against the inner peripheral surface of the nut and moving the processing tool while rotating the rotating member. The ball screw manufacturing method according to claim 1, wherein the screw groove is formed in a concave shape in a linear shape.   The ball screw manufacturing method according to claim 5, wherein the rotating member is a disk-shaped member, and a peripheral portion of the disk-shaped member is pressed against an inner peripheral surface of the nut.   The ball screw manufacturing method according to claim 5, wherein the rotating member is a spherical member, and the spherical member is pressed against an inner peripheral surface of the nut.

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