JP2009195930A - Infeed form rolling die and screw shaft of ball screw mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an infeed form rolling die with which working of a screw shaft in which the balls are prevented from falling off is easily performed and the screw shaft of a ball screw mechanism which is formed with the die. <P>SOLUTION: The balls 3 can pass through smoothly because the cross-sectional shape of a passage of a male screw groove 1a is lager than the cross-sectional shape of the ball 3, but the cross-sectional shape of the passage of a dummy male screw groove 1a' is smaller than the cross-sectional shape of the ball 3 and the ball 3 is stopped to pass through by the fact that the portions showed by double cross hatching are hit. That is, the balls 3 are prevented from falling off by providing the dummy male screw groove 1a'. <P>COPYRIGHT: (C)2009,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 an infeed rolling die 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

  By the way, the through rolling process forms a male screw groove on the outer periphery of the cylindrical workpiece by passing the cylindrical workpiece in the axial direction between a pair of rotating rolling dies, and thus is formed thereby. The male thread groove is continuous over the entire length. Therefore, when a ball screw mechanism is configured by assembling a screw shaft having such a male screw groove to a nut having a female screw groove, the balls arranged between the two screw grooves may fall off from both ends of the screw groove. Is inconvenient to handle. Therefore, in order to prevent the balls from falling off, a stopper or the like is provided in the thread groove, or the thread groove is deformed after rolling, but there is a problem that the number of parts and man-hours are increased.

  On the other hand, the in-feed rolling process is a process in which a pair of rotating rolling dies are moved closer to both sides of a cylindrical workpiece. Infeed rolling will be described. Fig.1 (a) is a figure which shows a general in-feed rolling die and a workpiece | work. FIG.1 (b) is a figure which shows the state at the time of rolling. FIG.1 (c) is sectional drawing of the axial direction which expands and shows the surface of this infeed rolling die.

  The pair of rolling dies RD have the same lead and the screw convex portion SP on the surface thereof, and therefore the same chevron shape repeats at the same pitch A in the cross section shown in FIG. ing. Further, as shown in FIG. 1 (a), the outer diameter φD of the male screw groove forming portion CW1 of the cylindrical workpiece CW is larger than the outer diameter φd of the male screw groove forming portions CW2 at both ends thereof. The total length b of the part CW1 is shorter than the total length B of the rolling die RD.

  As shown in FIG. 1 (b), when a pair of rolling dies RD are approached while rotating in the same direction while a cylindrical workpiece CW is interposed therebetween, a screw protrusion formed on the surface of the rolling dies RD. The part SP is pressed against the male thread groove forming part CW1 of the cylindrical workpiece CW, and a male thread groove can be formed on the surface thereof by rolling. At this time, the cylindrical workpiece CW does not move relative to the rolling die RD in the axial direction.

  Here, since the full length b of the male screw groove forming portion CW1 of the cylindrical work CW is shorter than the full length B of the rolling die RD, the male screw groove of the cylindrical work CW is formed by the screw convex portion SP of the rolling die RD. The male thread groove of the same lead is formed over the entire length of the forming portion CW1, and it is necessary to provide some measure for preventing the ball from dropping out, as in the above-described through rolling process.

  On the other hand, it is also conceivable to make the total length b of the cylindrical workpiece CW shorter than the total length B of the rolling die RD. Fig.2 (a) is a figure which shows another example of an in-feed rolling die and a workpiece | work. FIG. 2B is a diagram showing a state during the rolling process, but the rolling die is shown in cross section.

  In this example, since the total length b of the male thread groove forming portion CW1 of the cylindrical workpiece CW is longer than the total length B of the rolling die RD, the male screw of the cylindrical workpiece CW is formed by the screw projection SP of the rolling die RD. Except for both ends of the groove forming portion CW1, male screw grooves are formed. However, regions where the male screw grooves having the axial length a are not formed are formed at both ends of the male screw groove forming portion CW1. Therefore, since the ball of the ball screw mechanism cannot move outward in the axial direction from the region where the male screw groove is not formed, any measures for preventing the ball from falling off are unnecessary. However, according to such a rolling process, the stress applied to the screw shaft becomes non-uniform, and the screw shaft is bent, or the effective diameter of the male screw groove of the screw shaft is non-uniform (taper). It is not preferable because it may occur.

  On the other hand, as shown in Patent Document 2, by making the shape of the in-feed rolling die into a through-feed rolling die shape, it is possible to form screw shafts with rounded ends at both ends, thereby forming a ball Can be prevented from falling off. However, the die shown in Patent Document 2 was originally designed for through-feed rolling, and its manufacturing cost is not only expensive, but when applied to in-feed rolling, the outer diameter of the processed part is reduced. There is also a problem that it cannot be kept uniform. It is also conceivable to form the screw shaft of the ball screw mechanism by cutting or grinding, and according to such processing, it is optional to perform processing so as to round up both ends of the thread groove. 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 is an in-feed rolling die that can easily process a screw shaft that can prevent the ball from falling off, and a screw of a ball screw mechanism formed thereby. The purpose is to provide an axis.

The in-feed rolling die of the present invention is an in-feed rolling die that forms a male screw groove of a screw shaft of a ball screw mechanism by rolling a material.
It has a spiral processed part that forms and forms a male screw groove on the outer periphery of the material, and the processed part is provided with at least one part having a small cross section.

  According to the infeed rolling die of the present invention, it has a spiral processed portion for forming a male screw groove on the outer periphery of the material, and the processed portion is provided with at least one portion having a small cross section. As a result, when the screw shaft is manufactured, at least a portion where the passage cross section (which is a cross section perpendicular to the rolling direction of the ball) is reduced is formed in the male screw groove, and such a passage cross section is reduced. Is formed closer to the end portion, the ball is prevented from passing through a portion where the cross section of the passage becomes small when the screw shaft is assembled to the ball screw mechanism, thereby preventing the ball from falling off. it can. Therefore, “the part where the cross section of the machined part becomes smaller” means that the machined part is rolled into a groove shape where the ball cross section becomes so small that the ball cannot pass through when the male thread groove of the screw shaft is formed by the machined part. Refers to the part.

  The effective outer diameter of the processed portion is preferably equal over the entire length of the region to be processed of the material, but can be intentionally formed into a tapered shape, for example.

  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 and dummy male screw grooves 1a 'and 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. 4A is a diagram showing the in-feed rolling die 10, and FIG. 4B is an axial sectional view schematically showing an enlarged surface of the in-feed rolling die 10. FIG. 4C is a diagram illustrating a cross-sectional shape of the processing screw portion 12a, and FIG. 4D is a diagram illustrating a cross-sectional shape of the processing screw portions 11a and 13a.

  The in-feed rolling die 10 of the present embodiment is formed from three cylindrical portions 11 to 13. More specifically, as shown in FIG. 4, the central cylindrical portion 12 is the same lead as the male screw groove 1 a and has a corresponding cross-sectional processed screw portion 12 a on the outer periphery. On the other hand, the cylindrical portions 11 and 13 at both ends have processing screw portions 11a and 13a having the same lead as the dummy male screw groove 1a 'and a corresponding cross-sectional shape on the outer circumferences. Here, it is assumed that the male screw groove 1a and the dummy male screw groove 1a 'have the same lead. Further, the effective outer diameters of the machining screw portions 11a to 13a are equal.

  The processing screw portions 11a to 13a shown in cross section in FIG. 4B are continuous spiral processing portions and are arranged at the same pitch, but the cross-sectional shapes thereof are shown in FIGS. 4C and 4D. It is different as shown. More specifically, the cross-sectional shape of the processed screw portions 11a and 13a is smaller than the cross-sectional shape of the processed screw portion 12a by cutting both slopes as shown by double hatching. In addition, the cross-sectional shape of the processing screw parts 11a ′ and 13a ′ according to the first modification shown in FIG. 4E is further cut away so that both slopes are shown by double hatching, so that the processing screw parts 12a It is smaller than the cross-sectional shape. In addition, the cross-sectional shape of the machining screw portions 11a "and 13a" according to the second modification shown in Fig. 4 (f) is cut so that the top surface thereof is shown by double hatching, whereby the machining screw portion 12a It is smaller than the cross-sectional shape.

  FIG. 5 is a diagram showing a process of rolling the workpiece 20 using the in-feed rolling die 10 of the present embodiment. Here, the cylindrical workpiece 20 which is the material of the screw shaft 1 has a male screw groove forming portion (processed region) 20a and male screw groove forming portions 20b and 20b on both sides thereof. The outer diameter φD of the portion 20a is larger than the outer diameter φd of the male thread groove formed portions 20b and 20b at both ends thereof. Furthermore, the full length b of the male thread groove forming portion 20 a is shorter than the full length B of the in-feed rolling die 10.

  First, as shown in FIG. 5A, the workpiece 20 is set between a pair of in-feed rolling dies 10. Further, as shown in FIG. 5B, the infeed rolling dies 10 rotating in the same direction are brought close to each other so that the male thread groove forming portion 20 a of the work 20 is replaced with the cylindrical portions 11 to 11 of the infeed rolling dies 10. 13 is processed. The workpiece 20 can be rotated together with the rotation of the in-feed rolling die 10, so that the entire circumference can be rolled.

  Further, the overall length b of the male thread groove forming portion 20a is shorter than the overall length B of the infeed rolling die 10, that is, the cylindrical portions 11 to 11 having the same effective outer diameter of the infeed rolling die 10 over the entire length of the workpiece 20. Since 13 is in contact, the generated stress becomes uniform, and the occurrence of bending of the workpiece 20 and non-uniformity (tapering) of the effective diameter can be suppressed.

  As a result of the above rolling process, as shown in FIG. 5C, the male screw groove 1 a is formed in the central region X of the male screw groove forming part 20 a of the workpiece 20 by the processing screw part 12 a of the infeed rolling die 10. In addition, dummy male screw grooves 1a ′ and 1a ′ are formed by the second cylindrical portions 11 and 13 in the end regions Y and Y of the male screw groove forming portion 20a. Finally, the screw shaft 1 is manufactured by separating the in-feed rolling dies 10 from each other. However, since post-processing is not necessary, the manufacturing cost can be kept low.

  FIG. 6A is a side view of the screw shaft 1 formed as described above, and FIG. 6B is an axial sectional view schematically showing an enlarged surface of the screw shaft 1. FIG. 6C shows the passage cross-sectional shape of the male screw groove 1a, and FIG. 6D shows the passage cross-sectional shape of the dummy male screw groove 1a ′.

  As apparent from FIGS. 6C and 6D, the cross-sectional shape of the male screw groove 1a rolled by the processing screw portion 12a is larger than the cross-sectional shape of the ball 3 indicated by the alternate long and short dash line. Can pass through. On the other hand, the passage cross-sectional shape of the dummy male screw groove 1a ′ rolled by the processed screw portions 11a and 13a is smaller than the cross-sectional shape of the ball 3 indicated by the alternate long and short dash line, and the ball 3 Is blocked from passing. In other words, the ball 3 can be prevented from falling off by providing the dummy male screw groove 1a '.

  Similarly, the passage cross-sectional shape of the dummy male screw groove 1a ″ formed by rolling with the processed screw portions 11a ′ and 13a ′ according to the first modification is the cross-sectional shape of the ball 3 as shown in FIG. The smaller, double-hatched portion hits to prevent the ball 3 from passing. Further, the dummy male screw groove 1a ′ ″ formed by rolling with the processed screw portions 11a ″ and 13a ″ according to the second modification. As shown in FIG. 6 (f), the passage cross-sectional shape is smaller than the cross-sectional shape of the ball 3, and the passage of the ball 3 is prevented by hitting a portion indicated by double hatching.

  FIG. 7 is a view showing an in-feed rolling die 10 ′ according to the second embodiment. In the in-feed rolling die 10 'of the present modification, the cylindrical portion 11 having the processed screw portion 11a is connected to only one side with respect to the cylindrical portion 12 having the processed screw portion 12a in the embodiment described above. Since the points are different, the same components are denoted by the same reference numerals and the description thereof is omitted.

  FIG. 8 is a view showing a screw shaft 1 ′ formed by using the in-feed rolling die 10 ′ shown in FIG. 7. Since the screw shaft 1 'of the present modification is different from the above-described embodiment in that a dummy male screw groove 1a' is provided only on one side, the same components are described with the same reference numerals. Omitted.

  When the screw shaft 1 'according to this modification is incorporated in the ball screw mechanism shown in FIG. 1, the passage cross-sectional shape of the dummy male screw groove 1a' is smaller than the passage cross-sectional shape of the male screw groove 1a. Since the ball 3 cannot pass through the dummy male screw groove 1a ′ on one side, it is possible to prevent the ball 3 from dropping to one side.

  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, it suffices to provide a portion having a small cross-sectional shape at at least one location of the spiral processed portion. Further, the cross-sectional shape of the male screw groove 1a ′ in FIG. 6 does not need to be the same shape over the entire range of the male screw groove 1a ′. For example, the cross-sectional shape gradually changes toward the shaft end. May be.

Fig.1 (a) is a figure which shows a general in-feed rolling die and a workpiece | work. FIG.1 (b) is a figure which shows the state at the time of rolling. FIG.1 (c) is sectional drawing of the axial direction which expands and shows the surface of this infeed rolling die. Fig.2 (a) is a figure which shows another example of an in-feed rolling die and a workpiece | work. FIG.2 (b) is a figure which shows the state at the time of a rolling process. 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. FIG. 4A is a diagram showing the in-feed rolling die 10, and FIG. 4B is an axial sectional view schematically showing an enlarged surface of the in-feed rolling die 10. FIG. 4C is a diagram illustrating a cross-sectional shape of the processing screw portion 12a, and FIG. 4D is a diagram illustrating a cross-sectional shape of the processing screw portions 11a and 13a. FIG. 4E is a diagram showing a cross-sectional shape of the processed screw portions 11a and 13a according to the first modification. FIG. 4F is a diagram illustrating a cross-sectional shape of the processing screw portions 11a and 13a according to the second modification. It is a figure which shows the process of rolling the workpiece | work 20 using the in-feed rolling die 10 of this Embodiment. FIG. 6A is a side view of the screw shaft 1 formed as described above, and FIG. 6B is an axial sectional view schematically showing an enlarged surface of the screw shaft 1. FIG. 6C shows the passage cross-sectional shape of the male screw groove 1a, and FIG. 6D shows the passage cross-sectional shape of the dummy male screw groove 1a ′. FIG. 6E shows the cross-sectional shape of the passage of the dummy male thread 1a 'according to the first modification. FIG. 6F is a passage cross-sectional shape of the dummy male thread 1a 'according to the second modification. It is a figure which shows the in-feed rolling die 10 'concerning 2nd Embodiment. It is a figure which shows the screw shaft 1 'formed using the in-feed rolling die 10' shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1 'screw Shaft 1a Male thread groove 1a' Dummy male thread groove 2 Nut 2a Female thread groove 3 Ball 4 Tube 10, 10 'Infeed rolling die 11 Cylindrical part 11a Machining screw part 12 Cylindrical part 12a Machining screw part 13 Cylindrical part 13a Machining screw part 20 Work piece 20a Male thread groove forming part 20b Male thread groove forming part X First machining area Y Second machining area

Claims (3)

In the in-feed rolling die that forms the male screw groove of the screw shaft of the ball screw mechanism by rolling the material,
An in-feed rolling die having a spiral processed portion for forming a male screw groove on the outer periphery of the material, wherein the processed portion is provided with at least one portion having a reduced cross section.   2. The in-feed rolling die according to claim 1, wherein an effective outer diameter of the processed portion is equal over an entire length of a processed region of the material.   A threaded shaft of a ball screw mechanism, which is rolled by the in-feed rolling die according to claim 1 or 2.

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