JP2005074509A - Thread mandrel of ball screw and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thread mandrel of a ball screw having higher accuracy and being inexpensive, which is not affected by shear droop of an end caused by rolling, and does not require machining to remove the shear droop, and its manufacturing method. <P>SOLUTION: In the manufacturing method of the thread mandrel of the ball screw, a round bar material 1 is interposed between roll dies 2a, 2b on which helical convex threads 3a, 3b are formed, and the mandrel is rolled through thread grooves that continues helically on an outer peripheral face of that rolling portion 1a, wherein parallel portions 4a, 4b in which outside diameters of the convex threads 3a, 3b and outside diameters of helical flat portions 8a, 8b of which diameters are smaller than the above are constantly formed on surfaces of the roll dies 2a, 2b in a predetermined range of length, and bevel leads 5a, 5b and relief parts 6a, 6b having angles of inclination θ1, θ2 are formed at both sides of the parallel portions 4a, 4b. A small diametrical stepped portion 1b is formed in advance at an end of the round bar material 1, and an outside diameter of the small diametrical stepped portion 1b is set to be smaller than a distance between the convex threads 3a, 3b obtained when the roll dies 2a, 2b most approach. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a screw shaft of a ball screw used for a feed shaft of an automobile actuator and a method for manufacturing the same.

  A method of manufacturing a screw shaft of a ball screw by rolling is generally employed. Above all, the method of thread rolling using a pair of roll dies is cheaper and more productive than ground products because it only requires a single thread groove, and is expected to be applied in a wide range of fields in place of ground products. Has been. This thread rolling is a convex part formed by continuously inserting a material round bar as a material of a screw shaft between a pair of roll dies arranged at a desired interval and rotating, and spirally on the surface of the roll dies. Thus, a thread groove is formed on the outer peripheral surface of the material round bar.

  When manufacturing a screw shaft of a ball screw by thread rolling, when a material round bar is inserted between roll dies, a thread groove is formed from the end of the material round bar. At this time, a screw formed by rolling As the groove becomes deeper, the amount of plastic deformation caused by the roll die increases, so that the rolling resistance (working resistance) generated between the roll die and the material round bar increases.

  As described above, when the amount of plastic deformation increases and the processing resistance increases, a sudden load fluctuation occurs in the rolling device at the start of processing, and the force that holds the material round bar against the processing resistance generated at the processing start end. However, the friction force between the roll die and the material round bar cannot be sufficiently obtained, and the accuracy and roundness of the thread groove are deteriorated.

  As a solution to these problems, a method for manufacturing a screw shaft of a ball screw as shown in FIGS. 8 to 10 is known. In this manufacturing method, the processing start end portion 52 of the material round bar 51 shown in FIG. 8 is arranged between a pair of opposed roll dies 53a and 53b so as to overlap the entire constant diameter portions 54a and 54b of these dies. ing. Spiral convex portions 55a and 55b are formed on the surfaces of the roll dies 53a and 53b, respectively, and the tips of the convex portions 55a and 55b located at the constant diameter portions 54a and 54b are on the outer peripheral surface of the material round bar 51. In contact.

  From this state, as shown in FIG. 9, while pressing the roll dies 53a and 53b toward the central axis S of the material round bar 51 in the directions of arrows P and Q, the roll dies 53a and 53b are moved to the arrows U and V, respectively. Rolling is started in the direction of. Thereby, the material round bar 51 moves in the direction of the arrow T along the central axis S while relatively rotating in the direction of the arrow W between the roll dies 53a and 53b. Then, as shown in FIG. 10, a helical thread groove 56 is continuously formed on the outer peripheral surface 51 a of the material round bar 51.

  Also, the portions of both sides 56a and 56b along the thread groove 56 are raised by the recessed portion due to the formation of the thread groove 56, and the outer diameter is increased by the spiral flat portions 57a and 57b of the roll dies 53a and 53b. Is evenly arranged. The incomplete thread formed on the processing start end 52 by rolling while pressing the roll dies 53a and 53b at the start of processing is rolled from the processing start end 52 to the end of the processing end. Remove after doing.

  The threaded shaft of the ball screw thus rolled is arranged so that the machining start end 52 of the material round bar 51 overlaps the entire constant diameter portions 54a and 54b of the roll dies 53a and 53b, and rolling is started. Therefore, the plurality of convex portions 55 a and 55 b come into contact with the material round bar 51. Therefore, since equal force is applied to the material round bar 51 from the respective convex portions 55a and 55b, the material round bar 51 is not eccentric.

In addition, since the machining resistance between the roll dies 53a and 53b and the material round bar 51 is gradually changed, and a sudden load fluctuation does not occur in the rolling device, the material round bar 51 is fixed diameter portion 54a of the roll dies 53a and 53b. , 54b are firmly held by the convex portions 55a, 55b, and the accuracy and roundness of the thread groove 56 are not deteriorated.
JP 2003-33841 A

  In such a conventional method for manufacturing a screw shaft of a ball screw, a long material round bar 51 is cut after rolling and subjected to shaft end processing, whereby a plurality of screw shafts can be efficiently manufactured from one material round bar 51. However, depending on the product, the shorter the finished shaft length, the less likely it is to be affected by lead changes after heat treatment. Rolling round bars may be advantageous for mass production.

  However, in the case of rolling the short material as a single item by this conventional thread rolling method, at the start of rolling the material round bar 51 and at the end of rolling when the material round bar 51 comes out of the roll dies 53a, 53b. As shown in FIG. 11, a so-called sagging 58 in which the plastically deformed meat protrudes from the end face of the material round bar 51 occurs. In particular, when the shaft end processed portion is a component mounting portion 59 such as a bearing, machining is necessary to remove the sag 58 generated on the end face after rolling. Furthermore, when this rounded sag 58 is removed by post-processing of the end face, a sharp edge is generated in the same part, and chamfering of the end part is necessary for quality and safety. As the sag 58 is removed, the number of processing steps increases, which causes a cost increase.

The present invention solves such a conventional problem, and provides a highly accurate and low-cost ball screw thread shaft that is not affected by the sagging of the end portion caused by rolling and does not require sagging removal processing, and a manufacturing method thereof. The purpose is to do.

  In order to achieve such an object, the invention according to claim 1 of the present invention is such that a material round bar is inserted between a pair of roll dies in which spiral ridges are formed, and a rolling part in the material round bar is provided. In the screw shaft of the ball screw formed by rolling through a spiral groove threaded continuously on the outer peripheral surface, a small diameter portion is formed at the end of the material round bar, and the outer diameter of the small diameter portion is defined as the screw groove. The diameter was set smaller than the groove bottom diameter.

  In this way, by forming a small diameter portion at the end of the material round bar and setting the outer diameter of this small diameter portion to be smaller than the groove bottom diameter of the thread groove, the convex strip of the roll die is formed in the small diameter portion. There is no contact, and the sag rising on the end face of the thread groove by rolling does not swell to the end face. Therefore, the end face of the screw shaft is not affected by this sagging and no sagging removal process is required. In particular, in a screw shaft having a component mounting portion at the end of a material round bar, even if the end face is removed by post-processing, this rounded sag is removed and a sharp edge is generated in the same portion. This eliminates the need for sagging removal processing, and provides a low-cost ball screw threaded shaft.

  In addition, the small diameter portion may be a cylindrical small diameter step portion as in the invention described in claim 2, or may be a chamfered portion as in the invention described in claim 3.

  Moreover, the method invention of Claim 4 among this invention inserts a raw material round bar between a pair of roll dice in which the spiral protruding item | line was formed, and is on the outer peripheral surface of the rolling part in this raw material round bar. In the manufacturing method of the screw shaft of a ball screw that rolls through a thread groove that is continuous in a spiral shape, the outer diameter of the ridge and the outer diameter of the spiral flat portion having a smaller diameter are predetermined on the surface of the roll die. A parallel portion formed with a constant outer diameter over a length range, and a bite portion and a relief portion configured to have a predetermined inclination angle on both sides of the parallel portion; A small-diameter portion was formed in advance at the end, and the outer diameter of the small-diameter portion was set smaller than the distance between the ridges when the pair of roll dies approached most closely.

As a result, the threaded shaft of the rolled ball screw is arranged such that the small diameter end portion of the material round bar is disposed through the biting angle of the roll die, and the rolled portion is a plurality of convex strips of the parallel portion of the roll die. Since rolling starts upon contact, an equal force acts on the material round bar from the ridges, and the material round bar can be rolled without being eccentric.

In addition, since the material round bar is firmly held by the multiple ridges located in the parallel part of the roll die without giving a sudden load fluctuation to the rolling device, the accuracy and roundness of the thread groove deteriorates. Can be prevented. Furthermore, the protruding line of the roll die does not come into contact with the small diameter portion, and the sag rising on the end surface of the thread groove by rolling does not swell to the end surface. Therefore, sagging removal processing is not required, and a highly accurate and low-cost ball screw thread shaft can be provided.

  Further, in the invention according to claim 5, since the component attachment portion is formed at the end portion of the material round bar and the small diameter portion is provided between the component attachment portion and the rolling portion, the end surface of the component attachment portion Even if it is removed by post-processing, the rounded sag is not removed and a sharp edge is not generated in the same part, and the sag removal processing is not required and the number of processing steps can be reduced. it can.

The screw shaft of the ball screw according to the present invention inserts a material round bar between a pair of roll dies formed with spiral ridges, and continues spirally on the outer peripheral surface of the rolling portion of the material round bar. In the screw shaft of a ball screw formed by rolling through a thread groove, a small diameter portion is formed at the end of the material round bar, and the outer diameter of the small diameter portion is set smaller than the groove bottom diameter of the thread groove. Therefore, the roll of the roll die does not come into contact with the small-diameter portion, and the sag rising on the end surface of the thread groove by rolling does not swell to the end surface. Therefore, the end face of the screw shaft is not affected by this sagging and no sagging removal process is required. In particular, in a screw shaft having a component mounting portion at the end of a material round bar, even if the end face is removed by post-processing, this rounded sag is removed and a sharp edge is generated in the same portion. This eliminates the need for sagging removal processing, and provides a low-cost ball screw threaded shaft.

  Further, in the method for manufacturing the screw shaft of the ball screw according to the present invention, a material round bar is inserted between a pair of roll dies formed with spiral ridges, and the rolling portion of the material round bar is inserted. In the method of manufacturing a screw shaft of a ball screw that is rolled through a thread groove that is spirally continuous on the outer peripheral surface, the outer diameter of the ridge and the outer diameter of the spiral flat portion having a smaller diameter are formed on the surface of the roll die. Has a parallel portion formed with a constant outer diameter over a predetermined length range, and a biting portion and a relief portion configured to have a predetermined inclination angle on both sides of the parallel portion, and the material A small-diameter portion was formed in advance at the end of the round bar, and the outer diameter of the small-diameter portion was set to be smaller than the distance between the ridges when the pair of roll dies were closest to each other. The screw shaft of the ball screw has a bite of the roll die at the small diameter end of the material round bar. Since the rolling part is arranged through the corner and the rolling part comes into contact with the plurality of protruding parts of the parallel part of the roll die and starts rolling, an equal force acts on the material round bar from the protruding part, The material round bar can be rolled without eccentricity.

In addition, since the material round bar is firmly held by the multiple ridges located in the parallel part of the roll die without giving a sudden load fluctuation to the rolling device, the accuracy and roundness of the thread groove deteriorates. Can be prevented. Furthermore, the convex line of the roll die does not come into contact with the small-diameter portion, and the sag rising on the end face of the thread groove by rolling does not swell to the end face. Therefore, sagging removal processing is not required, and a highly accurate and low-cost ball screw thread shaft can be provided.

  A ball screw screw is formed by inserting a material round bar between a pair of roll dies on which spiral ridges are formed, and rolling through a spiral groove continuously on the outer peripheral surface of the rolled part of the material round bar. In the shaft manufacturing method, the outer surface of the roll die is parallel to the outer diameter of the ridge and the outer diameter of the spiral flat portion having a smaller diameter so as to have a constant outer diameter over a predetermined length range. And a biting portion and a relief portion configured to have a predetermined inclination angle on both sides of the parallel portion, and forming a component mounting portion at an end portion of the material round bar. A cylindrical small-diameter step portion is provided between the rolling portions, and the outer diameter of the small-diameter step portion is smaller than the distance between the ridges when the pair of roll dies are closest to each other, and the component attachment portion The outer diameter was set larger than the outer diameter.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, a material round bar 1 serving as a screw shaft of a ball screw according to the present invention is disposed between a pair of opposed roll dies 2 a and 2 b. Helical ridges 3a and 3b are formed on the surfaces of the roll dies 2a and 2b, respectively. Parallel portions 4a and 4b in which the outer diameters of these ridges 3a and 3b and the outer diameter of the spiral flat portion having a smaller diameter are formed to have a constant outer diameter over a predetermined length range, and Biting parts 5a and 5b and relief parts 6a and 6b are formed on both sides of the parallel parts 4a and 4b.

  The biting portions 5a and 5b and the clearance portions 6a and 6b are respectively provided with predetermined biting angles θ1 and clearance angles θ2. Of these inclination angles θ1 and θ2, especially at the clearance angle θ2, if the angle is too small, an indentation is generated in the thread groove at the end of rolling, and if it is too large, the variation in the effective diameter of the thread groove 7 increases. It is known. According to the applicant's test, the clearance angle θ2 is preferably in the range of 0 ° 30 ′ or more and less than 2 °, although it varies slightly depending on the size, the number of leads, and the like.

On the other hand, a part mounting portion 1c to which a component such as a bearing is attached from the rolled portion 1a through a small diameter step portion 1b is formed in advance at the end portion of the material round bar 1. The outer diameter B of the small diameter step portion 1b is smaller than the distance A between the ridges 3a and 3b when the pair of roll dies 2a and 2b are closest to each other as shown in FIG. The diameter is set larger than the outer diameter C of the mounting portion 1c (A> B> C).

  From this state, as shown in FIG. 3, the roll dies 2 a and 2 b are pressed in the directions of arrows P and Q toward the central axis S of the material round bar 1, and the roll dies 2 a and 2 b are pressed by the arrows U and V, respectively. Rotate in the direction and start rolling. Thereby, the raw material round bar 1 is relatively rotated in the direction of the arrow W between the roll dies 2a and 2b, and the thread groove 7 is formed. At this time, since the feed dies 2a and 2b are provided with a slight feed angle, the material round bar 1 moves in the direction of the arrow T along the central axis S. Here, the feed angle refers to an intersection angle between the central axis S of the material round bar 1 and the rotation axes of the pair of roll dies 2a and 2b. And this thread groove 7 is helically transcribe | transferred by the outer peripheral surface of the rolling part 1a toward the protruding item | line 3b of the other roll die 2b from the protruding item | line 3a of one roll die 2a.

  As shown in FIG. 4, the material round bar 1 is further rotated by the roll dies 2 a and 2 b, so that a continuous spiral screw extending spirally is formed on the outer peripheral surface of the rolled portion 1 a of the material round bar 1. A groove 7 is formed. Further, the portions of both sides 7a and 7b along the thread groove 7 are formed by the thread groove 7, so that the material is plastically flowed up by the recessed portion, but the spiral flat portion 8a of the roll dies 2a and 2b. 8b, the outer diameter is uniformly formed.

The threaded shaft of the ball screw thus rolled has a small-diameter end portion of the material round bar 1 disposed through the biting angle θ1 of the roll dies 2a and 2b, and the rolled portion 1a is formed of the roll dies 2a and 2b. Since the rolling is started by contacting with the plurality of ridges 3a and 3b of the parallel parts 4a and 4b, an equal force acts on the material round bar 1 from the ridges 3a and 3b. It can be rolled without eccentricity.

Also, since the material round bar 1 is firmly held by the plurality of ridges 3a and 3b located on the parallel portions 4a and 4b of the roll dies 2a and 2b without giving a sudden load fluctuation to the rolling device, the thread groove 7 can be prevented from deteriorating in accuracy and roundness.

Further, in the present embodiment, a small-diameter end portion of the material round bar 1, that is, a cylindrical small-diameter step portion 1b is formed between the rolling portion 1a and the component mounting portion 1c, and an outer diameter B of the small-diameter step portion 1b is set. The distance between the ridges 3a and 3b when the roll dies 2a and 2b come closest to each other is set smaller than the distance A (groove bottom diameter of the screw groove 7) A and larger than the outer diameter C of the component mounting portion 1c. Therefore, as shown in FIGS. 5 and 6, the protrusion 3a (3b) of the roll die 2a (2b) does not come into contact with the small-diameter step portion 1b, and the sag 9 rising on the end surface of the screw groove 7 is formed. It does not bulge up to the component mounting portion 1c. Therefore, the component mounting portion 1c is not affected by the sag 9 and does not require the removal process of the sag 9, and can provide a screw shaft of a ball screw with high accuracy and low cost.

  FIG. 7 shows another embodiment of the material round bar according to the present invention. This embodiment is different from the above-described embodiment only in the shape of the end portion, and other parts that are the same are denoted by the same reference numerals and detailed description thereof is omitted.

  A part mounting part 1c to which parts such as a bearing are attached from the rolled part 1a via the chamfered part 1d is formed in advance at the end of the material round bar 10. The chamfered portion 1d is formed on a square surface in a range of 30 ° to 60 ° so that the ridges 3a and 3b do not interfere even when the pair of roll dies 2a and 2b come closest to each other.

As a result, the chamfered portion 1d becomes a guide portion when the material round bar 10 enters between roll dies (not shown), and the rolling portion 1a smoothly contacts the ridges of the roll die and starts rolling. The material round bar 10 can be rolled without being eccentric. Moreover, the convex line of the roll die does not contact the chamfered portion 1d and is not plastically processed, and the sag rising on the end surface of the screw groove does not bulge out to the component mounting portion 1c. Therefore, as in the above-described embodiment, the component mounting portion 1c is not affected by the sagging, and the sagging removal process is not necessary.

  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 screw shaft of the ball screw according to the present invention is not limited to a screw shaft having a component mounting portion such as a bearing at the end, but is a single product with a total length that allows for the total length of the finished product or the amount of change after heat treatment in advance, such as a short product. The present invention can also be applied to the case of rolling through.

It is explanatory drawing which shows the state before the process start in the manufacturing method of the screw shaft of the ball screw which concerns on this invention. It is a principal part enlarged view of FIG. 1 same as the above. It is explanatory drawing which shows the state by which the raw material round bar was rotated 1/4 from the state of FIG. 1 same as the above. FIG. 3 is an explanatory view showing a state in which rolling has advanced from the state of FIG. 2. It is principal part explanatory drawing which shows the state which the edge part of the raw material round bar contacted the roll die. It is a principal part enlarged view of FIG. It is a principal part enlarged view which shows other embodiment of the screw shaft of the ball screw which concerns on this invention. It is explanatory drawing which shows the state before the process start in the manufacturing method of the conventional screw shaft of a ball screw. It is explanatory drawing which shows the state by which the raw material round bar was rotated 1/4 from the state of FIG. FIG. 10 is an explanatory diagram showing a state in which rolling has further advanced from the state of FIG. 9. It is principal part explanatory drawing which shows the rolling state of the conventional raw material round bar which has a component attachment part in a shaft end process part.

Explanation of symbols

1, 10 ········ Material round bar 1a ···················································· ······ Roll dies 3a, 3b ... ridges 4a, 4b ... parallel parts 5a, 5b ... bite part 6a, 6b ························ 7 ····················································・ ・ Flat part 9 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Sag 51 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Material round bar 52 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Starting end 53a , 53b... Roll dies 54a and 54b... Constant diameter portions 55a and 55b... Convex portions 56. .... Both sides 57a, 57b of the screw groove Flat part 58 ·············· 59 ···················· Outside diameter C of the small diameter step part ········· Outside diameter S of the component mounting part ... θ1 ············································· 2

Claims (5)

A ball screw formed by rolling a material round bar between a pair of roll dies on which spiral ridges are formed, and passing through a spiral groove continuously on the outer peripheral surface of the rolled part of the material round bar. In the screw shaft of
A screw shaft of a ball screw, wherein a small diameter portion is formed at an end portion of the material round bar, and an outer diameter of the small diameter portion is set smaller than a groove bottom diameter of the screw groove.   The screw shaft of the ball screw according to claim 1, wherein the small diameter portion is a cylindrical small diameter step portion.   The screw shaft of the ball screw according to claim 1, wherein the small diameter portion is a chamfered portion.   A ball screw screw is formed by inserting a material round bar between a pair of roll dies on which spiral ridges are formed, and rolling through a spiral groove continuously on the outer peripheral surface of the rolled part of the material round bar. In the shaft manufacturing method, the outer surface of the roll die is parallel to the outer diameter of the ridge and the outer diameter of the spiral flat portion having a smaller diameter so as to have a constant outer diameter over a predetermined length range. And a bite portion and a relief portion configured to have a predetermined inclination angle on both sides of the parallel portion, and a small diameter portion is formed in advance at the end portion of the material round bar, and the outer diameter of the small diameter portion Is set to be smaller in diameter than the distance between the ridges when the pair of roll dies are closest to each other.   The manufacturing method of the screw shaft of the ball screw of Claim 4 which formed the component attachment part in the edge part of the said raw material round bar, and provided the said small diameter part between this component attachment part and the said rolling part.

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