JP4993705B2 - Ball screw and thread groove machining method thereof - Google Patents

Description

  The present invention relates to a ball screw used in an actuator of an automobile or the like, in which a spiral thread groove on which a large number of balls roll is formed, and a method for machining the thread groove.

  A ball screw has a ball screw shaft composed of a ball screw shaft having a spiral thread groove formed on the outer periphery, a ball screw nut having a spiral thread groove formed in a cylindrical surface, and both opposing screw grooves. It is a mechanical element that is composed of a large number of balls that are rotatably accommodated in the road, and converts the rotation of the ball screw shaft or ball screw nut into translational motion in the axial direction.

  2. Description of the Related Art Conventionally, in a ball screw used in an actuator for an automobile, the thread groove of the ball screw shaft or nut is subjected to a process of turning the thread groove on a raw material, a quenching process, and a process of grinding the thread groove. Has been processed. In the turning process, a tool (total type bite) having the same shape as the thread groove is used.

  However, when turning with a full-length tool, the cutting resistance against the tool is large and the rigidity is insufficient, and the tool vibration, so-called chattering, is likely to occur. As a result, the machining accuracy deteriorates, and it is necessary to leave a large machining allowance, which takes time for the grinding process. In order to solve these problems, the present applicant has already proposed a method of processing a thread groove of a ball screw that can easily cope with a change in the shape of the thread groove and can reduce the total processing time.

As shown in FIG. 7, the thread groove machining method is a method of machining the thread groove 52 in the screw shaft 51, and includes a step of turning the thread groove 52 to a workpiece W made of raw material, and the turned workpiece. A step of quenching W and a step of grinding the thread groove 52 of the workpiece W after quenching. First, as shown in FIG. 2A, the thread groove 52 is turned in the raw bar work W. (A) shows the state where the workpiece W is gripped by the spindle chuck 53 of the lathe, and (b) shows an enlarged cross section of the thread groove 52 at the stage where the turning has proceeded. The turning in this case is performed by so-called point cutting. That is, using a general-purpose tool 54 in which the nose R of the cutting edge 54a is smaller than the radius of curvature of the screw groove 52, the general-purpose tool 54 is moved a plurality of times by the effective length of the screw groove 52, and each movement path P1, The entire thread groove 52 is turned by sequentially shifting P2 to Pn in the arc direction of the cross-sectional shape of the thread groove 52. After the turning of the screw groove 52 is completed, the workpiece W is quenched in the heating furnace 55 (FIG. 7B), and the quenched workpiece W is ground by the grindstone 56 to complete the screw shaft 51 (FIG. 7C )).
JP-A-6-249317

  According to such a conventional processing method, since point cutting is performed with a small cutting tool 54, the shape of the thread groove 52 can be easily changed by simply changing the path of the cutting tool 54, and the cutting resistance with respect to the cutting tool 54 is reduced, resulting in chattering. It has the feature that it can be turned with high accuracy without any problems. However, it is possible to reduce the cost to some extent as compared with the turning process using the total-type tool, but it is necessary to control the shape by forming the grindstone 56 every time the grinding process is performed. Since this grinding process occupies a large weight with respect to the machining cost of the entire machining process of the thread groove 52, there is a limit to further reducing the machining cost.

  In addition, in the case of a ball screw used for an actuator of an automobile or the like, since it is required to be compact, a piece type ball screw in which the circulating member does not protrude from the outer diameter of the nut and the outer diameter of the nut can be reduced is generally used. Often used. In this piece-type ball screw, since the ball circulates in a substantially S-shaped groove formed on the inner diameter of the piece member while colliding with the screw groove shoulder portion of the screw shaft, the ball passes smoothly. It is necessary to improve the operability of the ball screw by forming the shoulder of the thread groove into an arc shape. In this case, it is considered that a thread groove is formed by point cutting and the groove shoulder portion is processed by using an R-shaped cutting tool separately. .

  The present invention solves these conventional problems, provides a smooth thread groove shoulder, improves the operability of the ball screw, and provides a ball screw and a method for machining the thread groove with a short machining time and low cost. For the purpose.

In order to achieve such an object, the invention according to claim 1 of the present invention corresponds to a screw shaft in which a spiral thread groove is formed on the outer periphery, and is extrapolated to the screw shaft and corresponds to the screw groove on the inner periphery. A cylindrical nut having a spiral thread groove formed thereon, a large number of balls accommodated in a freely rolling manner between the both thread grooves, and a body of the nut, and the thread groove is provided on an inner periphery. In the ball screw provided with the piece member formed with the arc-shaped connection groove for connection, at least the screw groove in the screw shaft among the screw grooves is smaller than the groove curvature radius of the screw groove, and the groove curvature It is formed by point cutting with a general-purpose tool set close to the radius, and the shoulder portion of the thread groove is formed in an arc shape having a predetermined radius of curvature, and the shoulder portion is continuously cut from the thread groove. It is formed by processing.

In this way, in the piece-type ball screw, at least the screw groove on the screw shaft of the screw groove is smaller than the groove curvature radius of the screw groove, and by point cutting with a general-purpose tool set close to the groove curvature radius. Since the shoulder portion of the screw groove is formed in an arc shape having a predetermined radius of curvature, and the shoulder portion is formed by cutting continuously from the screw groove, the screw groove and the shoulder portion are formed. The ball can smoothly pass through the connecting groove of the piece member to improve the operability of the ball screw and provide a ball screw with a short processing time and low cost. it can.

In addition, the method invention according to claim 2 of the present invention is a ball screw thread groove machining method including a step of turning a thread groove on a workpiece made of raw material and a step of quenching the turned workpiece. wherein in a turning process, the cutting edge of the nose radius rather smaller than the groove radius of curvature of the thread groove, using a general purpose bytes set closer to the groove radius of curvature, the effective length of the this function byte the screw groove The entire thread groove is turned by moving it multiple times and sequentially shifting the movement path of each turn in the arc direction of the cross-sectional shape of the thread groove. The shoulder portion of the thread groove is continuously turned in an arc shape having a predetermined radius of curvature.

In this way, using a general-purpose tool set so that the nose radius of the cutting edge is smaller than the groove curvature radius of the thread groove and is set close to the groove curvature radius, the general-purpose tool is moved multiple times by the effective length of the thread groove. Thus, the entire thread groove is formed by point cutting by sequentially shifting the movement path of each turn in the arc direction of the cross-sectional shape of the thread groove, and the screw is threaded by the same general-purpose tool as the thread groove. Since the shoulder portion of the groove is continuously turned in an arc shape having a predetermined radius of curvature, the accuracy and durability of the ball screw can be secured, and the screw groove and shoulder portion can be cut by one-point point cutting. The forming process can be completed, and the conventional grinding process or turning process after heat treatment can be eliminated.

  According to a third aspect of the present invention, the shoulder portion is moved on the extension of the nose radius by shifting the movement path along the center locus of the nose radius of the cutting edge of the general-purpose tool. If the center of curvature is formed, the joint between the thread groove and the shoulder can be formed smoothly.

Further, as in the invention described in claim 4 , if at least the thread groove and the shoulder are finished by shot peening after the quenching step, the scale adhered to the thread groove and the shoulder The surface grain boundary oxide layer can be removed, and the durability of the ball screw can be improved.

The ball screw according to the present invention has a screw shaft in which a spiral thread groove is formed on the outer periphery, and a cylindrical shape in which a spiral thread groove corresponding to the screw groove is formed on the inner periphery and is extrapolated to the screw shaft. A plurality of balls that are rotatably accommodated between the two screw grooves, and an arc-shaped connecting groove that is attached to the trunk of the nut and connects the screw groove to the inner periphery. In the ball screw provided with a piece member, at least the screw groove in the screw shaft of the screw groove is smaller than the groove curvature radius of the screw groove, and point cutting is performed with a general-purpose tool set close to the groove curvature radius. And the shoulder portion of the thread groove is formed in an arc shape having a predetermined radius of curvature, and the shoulder portion is formed by cutting continuously from the thread groove. Smooth connection with the part Rukoto can, thereby improving the operability of the ball screw ball coupling groove passes through smoothly the bridge member, the processing time can be provided a short low-cost ball screw.

Also, the ball screw thread groove machining method according to the present invention is a ball screw thread groove machining method including a step of turning a screw groove on a workpiece made of raw material and a step of quenching the turned workpiece. in turning processes, the cutting edge of the nose radius rather smaller than the groove radius of curvature of the thread groove, using a general purpose bytes set closer to the groove radius of curvature, the generic byte valid only the length of the said screw groove By moving a plurality of times and sequentially shifting the movement path of each turn in the arc direction of the cross-sectional shape of the screw groove, the entire screw groove is turned and the screw is rotated by the same general-purpose tool as the screw groove. since the shoulder portion of the groove is turned continuously in an arc shape having a predetermined radius of curvature, it is possible to ensure the accuracy and durability of the ball screw, the screw groove and the shoulder by a point cutting one step Of molding can be completed, it is possible to eliminate the grinding or turning after a conventional heat treatment.

In the ball screw thread groove processing method including the step of turning a thread groove on a workpiece made of raw material and the step of quenching the turned workpiece, the nose radius of the cutting edge is the groove of the thread groove in the turning step. radius of curvature rather smaller than, using a general purpose bytes set closer to the groove radius of curvature, the generic byte is moved a plurality of times effective length of the said screw groove, each time the movement path of the thread groove By sequentially shifting the cross-sectional shape in the arc direction, the entire thread groove is turned, and the shoulder of the thread groove is continuously formed in an arc shape having a predetermined radius of curvature by the same general-purpose tool as the thread groove. is turned by, by shifting the moving path along the nose radius of the central trajectory of the cutting edge in the general-purpose byte, the center of curvature of the shoulder portion on the extension of the nose radius is formed in a state that the position There.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a longitudinal sectional view showing an embodiment of a ball screw according to the present invention, FIG. 2 is an explanatory view showing a thread groove machining state of the screw shaft according to the present invention, and FIG. 3 is a screw shaft according to the present invention. 4 is an enlarged sectional view of the thread groove showing the thread groove machining step, FIG. 4 is an enlarged view of the main part showing the thread groove of the screw shaft, and FIG. 5 is a conceptual diagram showing the cutting of the thread groove shoulder of FIG. 6 is an explanatory view showing a thread groove machining state of the nut according to the present invention.

  The ball screw 1 is made of medium carbon steel such as S55C or case-hardened steel such as SCM415, and is made of a screw shaft 2 having a spiral thread groove 2a formed on the outer periphery and a case-hardened steel such as SCM430. 2, a nut 3 in which a spiral ball screw groove 3 a corresponding to the screw groove 2 a is formed on the inner periphery, and a large number of balls 4 that are rotatably accommodated between the two screw grooves 2 a, 3 a And a piece member 5 which is attached to the body of the cylindrical nut 3 and has a connecting groove 5a for connecting the screw groove 3a. Then, a ball rolling path is constituted by the thread grooves 2a and 3a, and a large number of balls 4 can be infinitely circulated by the connecting groove 5a of the piece member 6.

  Here, the thread grooves 2 a and 3 a are formed in a Gothic arch groove in which two arcs having a radius of curvature slightly larger than the radius of the ball 4 are combined. Of course, the thread grooves 2a and 3a may have an arcuate shape in circular contact with the ball 4 other than the Gothic arch shape.

  FIG. 2 shows a machining state of the thread groove 2 a in the screw shaft 2. A raw material bar-shaped workpiece W (2) is gripped by a spindle chuck of a lathe (not shown), and is turned by a general-purpose tool 6 while being rotated in a predetermined direction. The cutting tool 6 is fixed to a holder 7 supported so as to be movable back and forth in the radial direction and movable in the axial direction. The turning in this case is performed by so-called point cutting. That is, a general-purpose cutting tool 6 having a nose radius R2 of the cutting edge 6a of the cutting tool 6 smaller than the groove curvature radius R1 of the thread groove 2a is used, and the cutting tool 6 is moved a plurality of times by the effective length of the thread groove 2a. The groove 2a is formed.

Next, the process of processing the thread groove 2a will be described with reference to FIGS.
FIG. 3A shows a rod-shaped raw material before turning, and the cutting edge 6a is fed in the axial direction of the workpiece W in the order of (b) to (d), and the schematic shape of the thread groove 2a is as follows. It is formed by the cutting edge 6 a of the cutting tool 6. Here, when the nose radius R2 of the cutting edge 6a is set close to the groove curvature radius R1 of the thread groove 2a, the approximate shape of the thread groove 2a is obtained without moving the cutting edge 6a in the axial direction. Time can be shortened.

  Then, as shown in FIG. 3E, point cutting is started when the turning of the thread groove 2a has progressed to some extent. As shown in (e) to (j), the cutting edge 6a is moved a plurality of times by the effective length of the thread groove 2a, and the thread path is sequentially shifted in the arc direction of the thread groove 2a. The entire shape of 2a is turned. In the present embodiment, even if the thread groove 2a has a Gothic arch shape, the nose radius R2 of the cutting edge 6a of the cutting tool 6 is set smaller than the groove curvature radius R1 of the thread groove 2a. Does not interfere with the thread groove 2a opposed to each other.

  Here, as shown in FIG. 4, the shoulder 8 of the thread groove 2a is formed in an arc shape having a predetermined radius of curvature r. And this shoulder part 8 is formed of the same general purpose tool as the point cutting of the thread groove 2a. That is, as in the point cutting of the thread groove 2a, as shown in FIG. 5, in the movement of the general-purpose tool a plurality of times, the movement path is shifted along the center locus L of the nose radius R2 of the cutting edge 6a, thereby The center of curvature O of the shoulder 8 is formed on the extension of R2.

  Thus, in the present embodiment, the nose radius R2 of the cutting edge 6a is made smaller than the groove curvature radius R1 of the thread groove 2a, and the thread groove 2a is formed by point cutting, and the shoulder portion 8 is formed by the thread groove. Since it is continuously formed by the same general-purpose tool as the point cutting of 2a, the forming process of the thread groove 2a and the shoulder portion 8 can be completed by the point cutting in one step, and the thread groove 2a and the shoulder portion 8 can be completed. The ball screw 1 can be formed smoothly, the circulation of the balls 4 is smooth, the operability is excellent, and the processing cost is reduced.

  Furthermore, in this embodiment, after the forming process of the thread groove 2a is completed by point cutting, a hardened layer in the range of 55 to 62HRC is formed on the surface by heat treatment. The heat treatment may be carburization quenching or quenching by high frequency induction heating, but it is preferable to use induction hardening that can suppress the grain boundary oxide layer on the surface layer and that can locally heat and set the hardened layer depth relatively easily. .

Further, finish processing (not shown) by shot peening is performed in order to remove scales and surface grain boundary oxide layers adhering to the screw grooves 2a and the like by heat treatment. In this shot peening, the particle size of the steel beads was 20 to 100 μm, the injection time was about 90 seconds, the injection pressure was 1 to 3 kg / cm ² , and the distance between the injection nozzle and the surface of the workpiece was about 140 mm.

  FIG. 6 shows a threaded state of the nut according to the present invention. In addition, the same code | symbol is attached | subjected to the components and site | part which have the same or the same function as the Example mentioned above, and the duplicate description is avoided.

  Here, in the same manner as the processing of the screw groove 2a in the screw shaft 2 described above, the general-purpose tool 6 (3) in which the raw material cylindrical workpiece W (3) is gripped by a spindle chuck of a lathe (not shown) and rotated in a predetermined direction. Is turned by. The cutting tool 6 is fixed to a holder 7 supported so as to be movable back and forth in the radial direction and movable in the axial direction. Turning in this case is also performed by point cutting. That is, using a general-purpose tool 6 in which the nose radius R2 of the cutting edge 6a of the tool 6 is smaller than the groove curvature radius R1 of the screw groove 3a, the tool 6 is moved a plurality of times by the effective length of the screw groove 3a, and each time The thread groove 3a is turned by sequentially shifting the movement path in the arc direction of the thread groove 3a.

  Also in this embodiment, the nose radius R2 of the cutting edge 6a is made smaller than the groove curvature radius R1 of the thread groove 3a, and the thread groove 3a is formed by point cutting, and the shoulder portion 9 is a point of the thread groove 3a. Since it is formed continuously by the same general-purpose tool as the cutting, the forming process of the thread groove 3a and the shoulder 9 can be completed by one-point point cutting, and the connection between the thread groove 3a and the shoulder 9 can be completed. The part can be formed smoothly, and the circulation of the balls 4 becomes smoother.

  The embodiment of the present invention has been described above, but the present invention is not limited to such an embodiment, and is merely an example, and various modifications can be made without departing from the scope of the present invention. Of course, the scope of the present invention is indicated by the description of the scope of claims, and further, the equivalent meanings described in the scope of claims and all modifications within the scope of the scope of the present invention are included. Including.

  The ball screw according to the present invention can be applied to a ball screw used for an actuator of an automobile or the like.

It is a longitudinal section showing one embodiment of a ball screw concerning the present invention. It is explanatory drawing which shows the thread groove processing state of the screw shaft which concerns on this invention. (A)-(j) is an expanded sectional view of the thread groove which shows the thread groove processing process of the screw shaft concerning this invention. It is a principal part enlarged view which shows the thread groove of a screw shaft same as the above. It is a conceptual diagram which shows the cutting process of the thread groove shoulder part of FIG. It is explanatory drawing which shows the thread groove processing state of the nut which concerns on this invention. It is process explanatory drawing which shows the thread groove processing method of the conventional screw shaft.

Explanation of symbols

1 ... Ball screw 2 ... Screw shaft 2a, 3a ... Screw groove 3 ... ··· Nut 4 ························· 5・ ・ ・ ・ ・ General-purpose tool 6a ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Cutter 7 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Holder 8, 9 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Shoulder 51 ・ ・··················································································· Main spindle chuck 54 ······························· 55 The center locus O of the nose radius of the shoulder ... The center of curvature of the shoulder P1-Pn ... Root movement path R1 ...... Groove radius of curvature R2 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Nose radius r of cutting edge ・ ・ ・ ・ ・ Shoulder Radius of curvature W

Claims (4)

A screw shaft having a helical thread formed on the outer periphery;
A cylindrical nut that is extrapolated to the screw shaft and has a spiral thread groove corresponding to the thread groove on the inner periphery;
A large number of balls accommodated in a freely rollable manner between the screw grooves;
In a ball screw provided with a piece member mounted on the body of the nut and formed with an arc-shaped connecting groove for connecting the screw groove on the inner periphery,
At least the thread groove on the thread shaft of the thread groove is smaller than the groove curvature radius of the thread groove, and is formed by point cutting with a general-purpose tool set close to the groove curvature radius . A ball screw characterized in that a shoulder portion is formed in an arc shape having a predetermined radius of curvature, and the shoulder portion is continuously formed from the screw groove by cutting. A process of turning a thread groove on a workpiece made of raw material,
In a method of processing a thread groove of a ball screw including a step of quenching the turned workpiece,
Wherein in a turning process, the cutting edge of the nose radius rather smaller than the groove radius of curvature of the thread groove, using a general purpose bytes set closer to the groove radius of curvature, the effective length of the this function byte the screw groove The entire thread groove is turned by moving it multiple times and sequentially shifting the movement path of each turn in the arc direction of the cross-sectional shape of the thread groove. A thread groove machining method for a ball screw, wherein a shoulder portion of the thread groove is continuously turned in an arc shape having a predetermined radius of curvature.   The shoulder portion is formed in a state in which the center of curvature of the shoulder portion is positioned on an extension of the nose radius by shifting the movement path along the center locus of the nose radius of the cutting edge in the general-purpose tool. Item 3. A thread groove processing method for a ball screw according to Item 2. The ball screw thread groove processing method according to claim 2 or 3, wherein at least the thread groove and a shoulder are finished by shot peening after the quenching step .

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