JP2007111740A - Method for forming screw thread and screw thread in ball screw thread - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming a screw thread capable of producing a screw thread in a ball screw mechanism at a lower cost, and to provide a screw thread formed thereby. <P>SOLUTION: The outer diameter of a diameter-shrunk part 10a is gradually reduced as it goes to the outer direction of the axial direction, thus, as it goes to the edge part corresponding to the part Wa to be worked, the plastically deformed amount thereof reduces, and the formation of an excess metal part swollen out from the tip part thereof to the axial direction is suppressed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a screw shaft of a ball screw mechanism that is assembled in, for example, a general industrial machine or used in an automobile, and a screw shaft forming method for processing the same.

  In recent years, labor saving of vehicles and the like has progressed, and for example, a system has been developed in which a transmission, a parking brake, and the like of an automobile are performed not by hand but by the power of an electric motor. An electric actuator used for such an application may use a ball screw mechanism in order to convert the rotational motion transmitted from the electric motor into the axial motion with high efficiency.

Here, as the rolling process for manufacturing the screw shaft of the ball screw mechanism, a through rolling method and an in-feed rolling method are known. The through rolling method is a method in which when a roll die is pressed against a product to be rolled, the roll die is rolled with a slight angle difference between the lead angle of the roll die and the lead angle of the material to be rolled. When the roll die or the rolled material is rotated relatively, the roll die and the rolled material are rolled while moving relative to each other due to the difference in the lead angle. When relatively rotating, rolling can be performed automatically without forcibly moving in the axial direction (see Patent Document 1).
Japanese Patent Laid-Open No. 2001-300675 Japanese Patent Laid-Open No. 9-133195

  1 and 2 are diagrams showing through-rolling processing according to a comparative example. As shown in FIG. 1 (a), through-rolling processing is performed in such a manner that a cylindrical workpiece W having a processed portion Wa and supporting portions Wb, Wb is axially disposed between a pair of rotating rolling dies RD, RD. By letting it pass, a male thread groove CW is formed in the workpiece Wa of the cylindrical workpiece W. Accordingly, as shown in FIG. 1B, the male thread groove CW formed thereby has the same shape over the entire length. According to this through rolling process, as shown in FIG. 1 (c) showing an enlarged portion of the workpiece Wa, the end portion of the workpiece Wa is plastically deformed, thereby surplusing in the axial direction. Part Wc is generated. However, if the bearing BRG (dotted line) is provided on the support portion Wb adjacent to the workpiece Wa, there is a risk of interference with the surplus portion Wc. The part Wc is deleted. However, cutting and grinding of the surplus portion Wc formed between the support portion Wb is difficult to process, and a tool having a small diameter must be used, which may cause premature wear of the tool. Furthermore, if the allowance for the surplus portion Wc is large, there is a problem that it takes time and effort for post-processing.

  On the other hand, as shown in FIG. 2A, it is also conceivable to provide a chamfered portion Wd in advance at the end of the workpiece Wa of the cylindrical workpiece W. In such a case, when the cylindrical workpiece W is rolled through using the rolling dies RD and RD shown in FIG. 1, the chamfered portion Wd is formed, and therefore, as shown in FIG. 2B. Moreover, since the rolling dies RD and RD are not in contact with the end portion of the processed portion Wa and plastic deformation is not performed, the formation of the surplus portion is suppressed. However, there is a problem that pre-processing for forming the chamfered portion Wd is required. In addition, as shown in FIG. 2C, when the bearing BRG is provided on the support portion Wb, the area of the contact portion A between the end portion of the workpiece Wa and the inner ring of the bearing BRG is reduced, and the stress is increased. As a result, the end of the workpiece Wa or the inner ring of the bearing BRG may be deformed. On the other hand, if the outer diameter φS of the support portion Wb is reduced, the area of the contact portion A between the end portion of the workpiece Wa and the inner ring of the bearing BRG increases, but the strength of the support portion Wb decreases accordingly. There is a problem.

  On the other hand, as shown in Patent Document 2, by making the shape of the in-feed rolling die special, it is possible to form screw shafts with rounded ends at both ends, and thereby the amount of plastic deformation at the ends. It is possible to suppress the formation of excess meat. However, the die shown in Patent Document 2 is difficult to manufacture, and there is a problem that the cost of the screw shaft increases. In addition, it is conceivable to form the screw shaft of the ball screw mechanism by cutting or grinding, and according to such processing, it is optional to cut the both ends of the screw groove, so the plasticity of the end The amount of deformation can be suppressed to suppress the formation of surplus. However, there is a problem that cutting and grinding require time and production efficiency is poor.

  The present invention has been made in view of the problems of the prior art, and provides a screw shaft forming method capable of manufacturing a screw shaft of a ball screw mechanism at a lower cost and a screw shaft formed by each. Objective.

The screw shaft forming method of the present invention is a screw shaft forming method for forming a male screw groove of a screw shaft of a ball screw mechanism.
An infeed rolling die having a shape in which the outer diameter of the threaded portion forming the male screw groove is uniform over the entire length, and the outer diameter of at least one of the axial end portions is reduced toward the outside. Rolling is performed by relative movement in the direction perpendicular to the axis with respect to the material.

  According to the screw shaft forming method of the present invention, the outer diameter of the threaded portion forming the male screw groove is uniform over the entire length, and the diameter is reduced as the outer diameter at least one of the end portions in the axial direction goes outward. Since the in-feed rolling die having the above shape is rolled by moving relative to the material in the direction perpendicular to the axis, the threaded portion of the in-feed rolling die has a uniform outer diameter, Can form a uniform male screw groove, and the outer diameter of at least one of the end portions in the axial direction is reduced toward the outside, so that the workpiece is processed without chamfering the material in advance. The excess meat of the part can be suppressed.

  Furthermore, it is preferable to roll the in-feed rolling die in such a manner that the axial end portion thereof corresponds to the axial end portion of the processed portion of the material.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 3 is a cross-sectional view showing an example of a ball screw mechanism using a screw shaft formed from the in-feed rolling die according to the present embodiment.

  A cylindrical nut 2 is arranged so as to surround the screw shaft 1 connected to a rotation shaft of a motor (not shown) and having a male screw groove 1a. The nut 2 is supported so as to be rotatable only with respect to a housing (not shown), and has a female screw groove 2a on the inner peripheral surface. A plurality of balls 3 are arranged so as to be able to roll in a spiral rolling path formed between the opposing screw grooves 1a, 2a. The nut 2 is provided with a tube 4 for returning the ball 3 from one end of the rolling path to the other end. The screw shaft 1, the nut 2, and the ball 3 constitute a ball screw mechanism.

  The operation of the ball screw mechanism will be described. When the screw shaft 1 is rotationally driven by a motor (not shown), the ball 3 rolls on the rolling path and circulates from one end of the rolling path to the other end via the tube 4. The rotational motion is efficiently converted into the axial motion of the nut 2.

  Next, the processing mode of the screw shaft will be described. FIG. 4 is a view showing the in-feed rolling die 10. As shown in FIG. 4, the in-feed rolling die 10 of the present embodiment has a substantially cylindrical shape having a length B in the axial direction, and at the right end thereof, gradually decreases as the outer diameter goes outward. A reduced diameter portion 10a is formed. That is, the outer shape of the reduced diameter portion 10a is tapered with a taper angle θ. The length of the reduced diameter portion 10a is preferably about 1/6 to 1/5 of the entire length B of the in-feed rolling die 10. On the outer periphery of the in-feed rolling die 10, a threaded portion 10b having the same lead as the male screw groove 1a and having a corresponding cross-sectional shape is formed over the entire periphery.

  FIG. 5 is a diagram illustrating a process of rolling the workpiece W using the infeed rolling die 10 of the present embodiment, but only a half of each of the pair of infeed rolling dies 10 is illustrated. Yes. 6A is a side view of the screw shaft 1 formed by the in-feed rolling die 10, and FIG. 6B is an enlarged view of an arrow VIB portion of the screw shaft in FIG. 6A. FIG. The workpiece W has a central processed portion Wa having an outer diameter φD and support portions Wb at both ends having an outer diameter φd (D> d), and a chamfer is formed on the processed portion Wa. Absent.

  First, as shown to Fig.5 (a), the workpiece | work W is set between a pair of in-feed rolling dies 10,10. At this time, it is desirable that the end portion of the reduced diameter portion 10a coincides with the end portion of the workpiece Wa. Further, it is desirable that the end portion (left end) where the reduced diameter portion 10a is not formed protrudes about 5 mm, for example, outward in the axial direction from the end portion of the processed portion Wa.

  Further, as shown in FIG. 5B, when the in-feed rolling dies 10 rotating in the same direction are brought close to each other in the direction perpendicular to the axis, the cutting of the surface of the rotating workpiece W starts. On the other hand, the workpiece Wa of the workpiece W can be processed by the outer periphery of the in-feed rolling die 10 without relatively moving in the axial direction. At this time, the external thread groove 1a is formed on the outer periphery of the processed part Wa by the threaded part 10b. When the male thread 1a having a predetermined dimension is formed, the infeed rolling dies 10 and 10 are separated from the work W, thereby completing the rolling process as shown in FIG.

  According to the present embodiment, since the outer diameter of the reduced diameter portion 10a gradually decreases as it goes outward in the axial direction, as shown in FIG. 6, as it goes toward the corresponding end portion of the workpiece Wa. The amount of plastic deformation is reduced, and the formation of the surplus portion protruding from the end portion in the axial direction is suppressed, so that interference with the bearing BRG can be avoided and the contact area between the two can be secured Reduction can be achieved. In addition, the threaded portion 10b of the reduced diameter portion 10a forms the incomplete threaded portion 1c at both ends of the processed portion Wa, where the difference from the outer diameter gradually decreases (that is, is rounded up). Since it can be used to prevent the screw shaft and nut from falling off, it is not necessary to separately provide a dropping-off prevention jig or the like, and labor and cost can be reduced. Further, the groove bottom diameter of the male screw groove 1a is uniform. Note that the outer diameter of the end portion of the workpiece Wa is larger than the outer diameter of the central portion, but no problem arises if it is smaller than the inner diameter of the nut 2.

  FIG. 7 is a view showing the in-feed rolling die 10 ′ according to the modification together with the workpiece W after processing. The in-feed rolling die 10 ′ of this modification example has the reduced diameter portions 10a and 10a formed at both ends with respect to the embodiment described above. Omitted. Similar to the above-described embodiment, a pair of similar in-feed rolling dies 10 ′ are provided with the workpiece W interposed therebetween, but only one of them is shown in the figure.

  In this modification, it is desirable that the end portions of the reduced diameter portions 10a and 10a be processed so as to coincide with the both ends of the processed portion Wa. In that case, the total length B of the in-feed rolling die 10 ′ is equal to the total length b of the workpiece Wa. As shown in FIG. 8, when processing is performed using the reduced diameter portions 10 a and 10 a, the plastic deformation amount decreases at both ends of the processed portion Wa toward the end portion, and from the end portion in the axial direction. The formation of the surplus part that protrudes is suppressed. In this modification, incomplete threaded portions 1c are formed at both ends of the workpiece Wa of the workpiece W. According to the present modification, by setting the appropriate total length B of the infeed rolling die 10 for the workpiece W, the balance at the time of infeed rolling can be balanced, so that the effective diameter taper generation and bending can be suppressed. There is.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate. For example, in an in-feed rolling die, the thread pitch of the machining thread portion in the first machining area X may be different from the thread pitch of the machining thread sections in the second machining areas Y and Y.

Fig.1 (a) is a figure which shows the infeed rolling die and workpiece | work shown as a comparative example. FIG.1 (b) is a side view of the workpiece W by which the rolling process was carried out. FIG.1 (c) is a figure which expands and shows the site | part shown by arrow IB of the workpiece | work W of FIG.1 (b). FIG. 2A is an enlarged view of the end portion of the workpiece Wa of another workpiece W. FIG. FIG. 2B is an enlarged view of the end of the workpiece Wa after the rolling process. FIG.2 (c) is a figure shown in the state which attached the bearing BRG to the support part Wb. It is sectional drawing which shows an example of the ball screw mechanism using the screw shaft formed from the infeed rolling die concerning this Embodiment. 1 is a view showing an in-feed rolling die 10. FIG. It is a figure which shows the process of rolling the workpiece | work W using the in-feed rolling die 10 of this Embodiment. 6A is a side view of the screw shaft 1 formed by the in-feed rolling die 10, and FIG. 6B is an enlarged view of an arrow VIB portion of the screw shaft in FIG. 6A. FIG. It is a figure which shows the in-feed rolling die 10 'concerning a modification with the workpiece | work W after a process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Screw shaft 1a Male thread groove 2 Nut 2a Female thread groove 3 Ball 4 Tube 10, 10 'In-feed rolling die 10a Reduced diameter part 10b Thread processing part W Work Wa Work part Wb Support part

Claims (3)

In the screw shaft forming method for forming the male screw groove of the screw shaft of the ball screw mechanism by rolling the material,
An infeed rolling die having a shape in which the outer diameter of the threaded portion forming the male screw groove is uniform over the entire length, and the outer diameter of at least one of the axial end portions is reduced toward the outside. A threaded shaft forming method, wherein rolling is performed by moving relative to a material in a direction perpendicular to the axis.   2. The screw shaft forming method according to claim 1, wherein rolling is performed in such a manner that an axial end portion of the infeed rolling die corresponds to an axial end portion of the processed portion of the material. A threaded shaft of a ball screw mechanism, which is rolled by the threaded shaft forming method according to claim 1 or 2.

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