JP2008286353A - Koma-type ball screw and manufacturing method thereof - Google Patents

Abstract

[PROBLEMS] To reduce cost by reducing processing man-hours, and to prevent the occurrence of burrs when processing a piece window, to facilitate smooth circulation of the ball, and to improve the reliability of the piece type ball screw and its A manufacturing method is provided.
In a manufacturing method of a piece-type ball screw having a piece member 5 fitted with a piece window 6 having a circular cross section in a nut 3 and formed with a connecting groove 5a, the screw groove 3a of the nut 3 is cut. After finishing the above, the hole 6a is roughly machined by drilling the piece window 6, and the boring tool 10 inserted into the pilot hole 6a is rotated from the inner diameter side of the nut 3 toward the outer diameter side. Since the piece window 6 is finished to a predetermined size, it is possible to prevent burrs from occurring at the edge of the piece window 6 in the screw groove 3a. Accordingly, the burr removal process is not required, and it is possible to reduce the cost in combination with the abolition of the grinding process of the screw groove 3a and to smoothly circulate the balls.
[Selection] Figure 4

Description

  The present invention relates to a ball screw used in various machine tools such as an electric discharge machine or a tapping center, or an electric power steering or an actuator of an automobile, and more particularly, a piece type ball screw using a piece member as a ball circulation part and its It relates to a manufacturing method.

  The ball screw is composed of a screw shaft having a helical thread groove formed on the outer peripheral surface, a nut externally fitted to the screw shaft, and a spiral screw groove formed on the inner peripheral surface, and both opposing screw grooves. It is equipped with a large number of balls accommodated in the formed rolling path and a circulation mechanism having the rolling path as a circuit path, and is used as a motion conversion mechanism that linearly moves the screw shaft by rotating the nut, for example. ing.

  Generally, there are various types of ball screws having different ball circulation mechanisms, one of which is called a piece type. This piece-type ball screw has a threaded groove connection path, and a circulation piece member with a rolling path as a circulation path is attached to the nut. The structure is relatively simple and compact. There are advantages you can do.

  A typical example of such a piece-type ball screw is shown in FIG. This piece-type ball screw 50 includes a screw shaft 51 having a helical thread groove 51a formed on the outer peripheral surface thereof, and a nut that is fitted on the screw shaft 51 and has a helical screw groove 52a formed on the inner peripheral surface thereof. 52, a large number of balls 53 accommodated in a rolling path formed by the opposing screw grooves 51a and 52a, and a piece member 54 serving as a circulation member for the balls 53.

  The cylindrical nut 52 has a generally circular piece window 55 that penetrates the inner and outer peripheral surfaces and cuts out a part of the screw groove 52a. A circular piece member 54 is fitted. A connecting groove 54a is formed on the inner side of the piece member 54 to connect adjacent ones of the screw grooves 52a, and the ball 53 rolls between the connecting groove 54a and the substantially one part of the screw groove 52a. Constitutes the road. A large number of balls 53 interposed between the inner and outer screw grooves 51a and 52a in the rolling path roll along the screw grooves 51a and 52a, and are guided by the connecting grooves 54a of the piece member 54 to be screw shafts. After overcoming the 51 screw thread, it returns to the adjacent screw groove 52a and rolls along the screw grooves 51a, 52a again.

  The connecting groove 54 a of the piece member 54 is formed to be curved in a substantially S shape so as to smoothly connect the adjacent thread grooves 52 a and 52 a of the nut 52. The depth of the connecting groove 54a is set to such a depth that the ball 53 can exceed the thread of the screw groove 51a in the screw shaft 51 in the connecting groove 54a.

  Here, as shown in FIG. 7, the piece type ball screw 50 has arms 56 formed in a round bar shape with a substantially circular cross section on both sides of the piece member 54, and a predetermined groove groove 52 a of the nut 52 has a predetermined shape. Are engaged through a radial clearance. The arm 56 positions the piece member 54 in the axial direction with respect to the nut 52 and prevents the piece member 54 from coming out of the piece window 55 radially outward. Thus, since the piece member 54 is formed in a circular cross section, the number of processing steps of the piece window 55 can be reduced and the cost can be reduced, and the piece member 54 is accurately in the axial direction with respect to the nut 52. The positioning can be performed easily and easily, and the reliability can be improved.

  Further, the arm 56 of the piece member 54 is formed in an arc shape along the screw groove 52a of the nut 52, and the radius of curvature R ′ of the arc along the width center of the arm 56 is the radius of curvature of the groove center of the screw groove 52a. A position where the arm 56 and the inner surface of the screw groove 52a are brought into contact with each other with no load is defined as the tip of the arm 56.

In this type of structure for preventing the piece member 54 from falling off, the arm 56 receives a pulling load applied to the connecting groove 54 a of the piece member 54. The removal load in this case is due to centrifugal force due to the revolution of the ball 53, or due to radial component force when the ball 53 rides on the inner surface of the thread groove 52a of the nut 52 from the connection groove 54a of the piece member 54. Can be mentioned. When such a falling load is received, the arm 56 is deformed to cause a poor circulation of the ball 53 or to reduce the reliability of the piece member 54 from dropping from the nut 52. When a load is applied to the piece member 54 from the loaded state, the arm 56 is elastically deformed so that the entire arm 56 comes into contact with the inner surface of the thread groove 52a of the nut 52, and the contact area between the two increases. Become. Therefore, excessive plastic deformation of the arm 56 is prevented, and the rigidity against the pulling force of the piece member 54 can be improved, and poor circulation of the ball 53 due to deformation of the arm 56 can be suppressed.
JP 2006-189124 A

  Such a conventional piece-type ball screw 50 prevents and positions the piece member 54 by the arm 56 of the piece member 54, thereby obtaining high-precision and high-strength performance, and against the removal force of the piece member 54. The rigidity is improved, and the circulation failure of the ball 53 due to the deformation of the arm 56 can be suppressed. Here, the thread groove 52a of the nut 52 is formed by grinding and finishing after roughing by cutting. In the conventional ball screw 50 of this type, the piece window 55 is formed on the outer diameter side by ball end milling or drilling after cutting the thread groove 52a so that the cutting process of the thread groove 52a is not interrupted. And penetrating toward the inner diameter side. At this time, burr is generated at the edge of the piece window 55 in the screw groove 52a due to the machining of the piece window 55, but since the screw groove 52a is ground as post-processing, the circulation failure of the ball 53 does not occur.

  On the other hand, this type of ball screw 50 is widely used as an electric actuator for automobiles. However, in the piece type ball screw 50 used for such an application, in order to reduce the number of processing steps and reduce the cost, Recently, there is a tendency to abolish grinding and finish the thread groove 52a only by cutting. In this case, the burr | flash which generate | occur | produces at the time of the process of the piece window 55 becomes a problem. Therefore, in order to prevent the defective circulation of the balls 53 due to the generated burrs, it is necessary to remove the burrs after the processing of the piece window 55. However, this deburring process is a manual operation and is not only complicated and time-consuming, but also works so as not to induce vibrations and noise of the balls 53 due to the occurrence of a step at the connecting portion between the connecting groove 54a and the screw groove 52a. Required skill. With this, the effect of eliminating the grinding process was halved, and there was a limit to cost reduction.

  The present invention has been made in view of such circumstances, reducing the number of processing steps and reducing the cost, and preventing the occurrence of burrs during the processing of the piece window, thereby achieving smooth ball circulation. An object of the present invention is to provide a piece type ball screw with improved reliability and a method for manufacturing the same.

  In order to achieve such an object, the invention according to claim 1 of the present invention includes a screw shaft having a spiral thread groove formed on the outer peripheral surface thereof, and is externally fitted to the screw shaft and spirally formed on the inner peripheral surface. A nut formed with a screw groove, a plurality of balls accommodated in a rolling path formed by the opposing screw grooves, and a piece window drilled in a body portion of the nut, And a piece member formed with a connecting groove for connecting between adjacent screw grooves of the nut. The piece window is formed in a circular cross section, and the piece corresponding to the piece window The member is formed in a circular cross section, and the piece window is formed of a finished surface formed to a predetermined size by boring.

  As described above, a piece member that is fitted to a piece window formed in the trunk portion of the nut, has a rolling path as a circulation path, and a connection groove that connects between adjacent screw grooves of the nut is provided. Since the window is formed in a circular cross section, the piece member is formed in a circular cross section corresponding to this piece window, and the piece window is composed of a finished surface formed to a predetermined size by boring processing. Therefore, the piece member can be positioned and fixed with high accuracy.

  Preferably, as in the invention described in claim 2, if the thread groove of the nut is formed by cutting, the grinding process can be abolished, the number of processing steps can be reduced, and the cost can be reduced.

  Further, as in the invention described in claim 3, if the thread groove of the screw shaft is formed by rolling, the yield of the material can be improved and the cost can be further reduced.

  Further, as in the invention described in claim 4, if the piece member is formed of a sintered alloy made of carburized metal powder by MIM and hardened by carburizing and quenching, the degree of work is high and the shape is complicated. Even so, it can be easily and accurately formed into a desired shape and size, and the wear resistance can be improved.

  According to a fifth aspect of the present invention, there is provided a method invention according to claim 5, wherein a screw shaft having a spiral thread groove formed on the outer peripheral surface, and a screw thread screw fitted on the screw shaft and having a spiral thread groove on the inner peripheral surface. The formed nut, a plurality of balls accommodated in a rolling path formed by the opposing screw grooves, and a piece window drilled in the body of the nut are fitted into the rolling path. And a piece member formed with a connecting groove for connecting between adjacent screw grooves of the nut, the piece window is formed in a circular cross section, and the piece member is formed in a circular shape corresponding to the piece window In the manufacturing method of the piece type ball screw formed in the boring process, after the screw groove of the nut is finished by cutting, the pilot hole is rough processed by drilling and inserted into the prepared hole. When the tool is rotated, from the inner diameter side to the outer diameter side of the nut The bridge window is sent me is finishing to size.

  As described above, a piece member that is fitted to a piece window formed in the trunk portion of the nut, has a rolling path as a circulation path, and a connection groove that connects between adjacent screw grooves of the nut is provided. In the method of manufacturing a piece type ball screw in which a window is formed in a circular cross section and a piece member is formed in a circular cross section corresponding to the piece window, the piece window is drilled after the thread groove of the nut is finished by cutting. A rough hole is machined by machining, and the boring tool inserted in this pilot hole is sent from the inner diameter side of the nut toward the outer diameter side in a rotated state, and the piece window is finished to a predetermined size. Therefore, it is possible to prevent burrs from occurring at the edge of the piece window in the thread groove. This eliminates the need for deburring and reduces costs by reducing the number of processing steps, and also prevents the generation of vibration and noise from the ball passing through this part, thereby improving the reliability of the ball. A piece-type ball screw can be provided.

  According to a sixth aspect of the present invention, the boring tool is composed of a holder and a tip that is replaceably fixed to the tip of the holder, and a cutting edge is formed at the tip of the tip. If a corner is attached and this cutting edge angle is set in the range of 10 to 30 °, when the tip reaches the opening of the piece window, chips remain at the base of the tip and are difficult to fall off, It is discharged smoothly as small chips. Therefore, the chips are not extruded in a ring shape, the chip replacement frequency can be extended and the cost can be further reduced, the processing accuracy of the piece window can be improved, and the piece member can be accurately Can be positioned and fixed.

  The piece ball screw according to the present invention includes a screw shaft having a helical thread groove formed on the outer peripheral surface, a nut externally fitted to the screw shaft, and a spiral screw groove formed on the inner peripheral surface, The nut is fitted into a plurality of balls accommodated in a rolling path formed by the both screw grooves facing each other, and a piece window drilled in a body portion of the nut, and the rolling path serves as a circulation path, and the nut And a piece member formed with a connecting groove connecting between adjacent screw grooves, the piece window is formed in a circular cross section, and the piece member is formed in a circular cross section corresponding to the piece window, Since the piece window is composed of a finished surface formed to a predetermined size by boring, the piece window machining accuracy can be improved and the piece member can be positioned and fixed with high accuracy.

  In addition, the method of manufacturing the piece-type ball screw according to the present invention includes a screw shaft having a helical thread groove formed on the outer peripheral surface, and a screw thread that is externally fitted to the screw shaft and formed on the inner peripheral surface. And a plurality of balls accommodated in a rolling path formed by the opposing screw grooves, and a piece window formed in the body of the nut, and circulates around the rolling path. And a piece member formed with a connecting groove connecting between adjacent screw grooves of the nut, the piece window is formed in a circular shape in cross section, and the piece member is formed in a circular shape in cross section corresponding to the piece window In the manufacturing method of the formed piece-type ball screw, after the thread groove of the nut is finished by cutting, the boring window is rough-processed by drilling and the boring tool inserted into the prepared hole Is rotated from the inner diameter side to the outer diameter side of the nut. Since the bridge window is sent me is finishing to a predetermined size, it is possible to prevent the burrs at the edge of the bridge window in the thread groove. This eliminates the need for deburring and reduces costs by reducing the number of processing steps, and also prevents the generation of vibration and noise from the ball passing through this part, thereby improving the reliability of the ball. A piece-type ball screw can be provided.

  It is formed by a screw shaft having a helical thread groove formed on the outer peripheral surface, a nut externally fitted to the screw shaft and having a helical thread groove formed on the inner peripheral surface, and the opposing screw grooves. A plurality of balls accommodated in the rolling path and a coupling that is fitted to a piece window formed in the body of the nut and connects between adjacent screw grooves of the nut with the rolling path as a circular path. In the method of manufacturing a piece-type ball screw in which the piece window is formed in a circular cross section corresponding to the piece window, and the piece member is formed in a circular cross section corresponding to the piece window, After the screw groove is finished by cutting, the pilot hole is roughly drilled by drilling, and the boring tool inserted in the pilot hole is rotated from the inner diameter side to the outer diameter side of the nut. The piece window is finished to the specified size. It has been.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
1A is a plan view showing an embodiment of a piece-type ball screw according to the present invention, FIG. 1B is a longitudinal sectional view of FIG. 1A, and FIG. 2 is a longitudinal sectional view showing a single nut of FIG. FIGS. 3 (a) and 3 (b) are front views showing a tool for machining the piece window, and FIGS. 4 (a) to 4 (d) are explanatory views showing the process steps of the nut according to the present invention. FIGS. 5A and 5B are schematic views showing the processing state of the piece window.

  This piece-type ball screw 1 includes a screw shaft 2 having a helical thread groove 2a formed on the outer peripheral surface, and a nut externally fitted to the screw shaft 2 and having a helical screw groove 3a formed on the inner peripheral surface. 3, a large number of balls 4 that are rotatably accommodated in a rolling path formed by opposing screw grooves 2 a, 3 a, and a piece member 5 that serves as a circulation member for these balls 4.

  The cylindrical nut 3 has a circular cross-section window 6 that penetrates the inner and outer peripheral surfaces and cuts out a part of the screw groove 3a, and has a substantially circular cross section corresponding to the piece window 6. The piece member 5 is fitted. A connecting groove 5a is formed on the inner side of the piece member 5 so as to connect adjacent ones of the screw grooves 3a, and the ball 4 rolls between the connecting groove 5a and the substantially one part of the screw groove 3a. Constitutes the road. A large number of balls 4 interposed between the inner and outer screw grooves 2a and 3a in the rolling path roll along the screw grooves 2a and 3a, and are guided by the connecting groove 5a of the piece member 5 to be screw shafts. 2 over the thread 2 and return to the adjacent thread groove 3a, and roll along the thread grooves 2a and 3a again.

  The connecting groove 5a of the piece member 5 is formed in a substantially S-shape so as to smoothly connect the adjacent screw grooves 3a and 3a of the nut 3. The depth of the connecting groove 5a is such that the ball 4 can exceed the thread of the screw groove 2a in the screw shaft 2 within the connecting groove 5a.

  The cross-sectional shape of each screw groove 2a, 3a of this piece type ball screw 1 may be a circular arc shape or a gothic arc shape, but here, the contact angle with the ball 4 is large and the axial clearance is large. Is formed in a Gothic arc shape that can be set small. Thereby, the rigidity with respect to an axial load becomes high and generation | occurrence | production of a vibration can be suppressed.

  The piece member 5 is made of a sintered alloy obtained by adjusting a metal powder into a plastic shape and molded by an injection molding machine. In this injection molding, first, metal powder and a binder made of plastic and wax are kneaded with a kneader, and the kneaded product is granulated into a pellet. The granulated pellets are supplied to a hopper of an injection molding machine, and are molded by so-called MIM (Metal Injection Molding) in which the pellets are pressed into a mold in a heated and melted state. A sintered alloy formed by such an MIM can be easily and accurately formed into a desired shape / dimension even if it has a high workability and a complicated shape.

  As the metal powder, materials that can be carburized and quenched later, for example, C (carbon) is 0.13 wt%, Ni (nickel) is 0.21 wt%, Cr (chromium) is 1.1 wt%, Cu (copper) Exemplifies SCM415 which is 0.04 wt%, Mn (manganese) is 0.76 wt%, Mo (molybdenum) is 0.19 wt%, Si (silicon) is 0.20 wt%, and the rest is Fe (iron). Can do. The piece member 5 is hardened by carburizing and quenching so that the surface hardness is in the range of 30 to 40 HRC, and is provided with wear resistance.

  As shown in FIG. 2, the nut 3 is provided with a plurality of piece windows 6 having a circular cross section into which the piece members 5 are fitted. Here, one piece is provided at each end, but in the present embodiment, after the thread groove 3a is finished by cutting, these piece windows 6 are roughened by drilling, and the piece windows 6 are formed. Finished by boring. On the other hand, the thread groove 2a of the screw shaft 2 is formed by rolling. Thereby, the yield of a raw material can be improved and cost reduction can be achieved further.

  As shown in FIGS. 3A and 3B, the boring window 6 is cut with tools 10 and 11 having chips 8 and 9 fixed to the tip of the holder 7 so as to be replaceable. The chips 8 and 9 are formed into a substantially triangular shape or a parallelogram shape. However, the present invention is not limited to this. For example, although not illustrated, the chips 8 and 9 may be formed into a rhombus shape. Chips 8 and 9 are made of high-speed steel, cemented carbide, or a cemented carbide base material brazed with a CBN (cubic boron nitride) sintered body as a cutting edge. ing.

Next, a method for processing the nut 3 will be described in detail with reference to FIG.
First, after the thread groove 3a is cut, the pilot hole 6a is rough processed by drilling the piece window 6, and the tool 10 is inserted into the pilot hole 6a as shown in FIG. Next, as shown in (b), the tool 10 is set so as to be offset in the axial direction in the pilot hole 6a and to have a predetermined cutting allowance. Then, as shown in (c) and (d), the tool 10 is fed from the inner diameter side toward the outer diameter side while rotating in a predetermined direction, and the piece window 6 is formed with a predetermined size.

  In the present embodiment, after the thread groove 3a is cut, the pilot hole 6a is subjected to rough machining by drilling, and the tool 10 inserted into the pilot hole 6a is directed from the inner diameter side toward the outer diameter side. Since the piece window 6 is formed in a circular cross section by cutting out a part of the screw groove 3a through the inner and outer peripheral surfaces, the burr is generated at the edge of the piece window 6 in the screw groove 3a. Can be prevented. This eliminates the need for deburring and reduces the number of processing steps by eliminating the grinding of the thread groove 3a, thereby reducing the cost and preventing vibration and noise of the ball 4 passing through this portion. Thus, the piece-type ball screw 1 can be provided in which the ball is smoothly circulated and the reliability is improved.

  FIG. 5 is a schematic diagram showing the machining state of the piece window 6, but in this embodiment, the cutting edge angle θ is attached to the cutting edge portions of the chips 8 and 9. This cutting edge angle θ is set in a range of 10 to 30 °. As a result, when the chips 8 and 9 reach the opening of the piece window 6, that is, the outer diameter surface of the nut 3, chips remain on the bases of the chips 8 and 9 and do not easily fall off. It will be discharged smoothly. Therefore, the chips are not extruded in a ring shape, the replacement frequency of the chips 8 and 9 can be extended, the cost can be further reduced, and the processing accuracy of the piece window 6 can be improved. The member 5 can be positioned and fixed with high accuracy.

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

(A) is a top view which shows one Embodiment of the piece-type ball screw which concerns on this invention. (B) is a longitudinal cross-sectional view of (a). It is a longitudinal cross-sectional view which shows the nut single-piece | unit of FIG. (A), (b) is a front view which shows the tool for processing a piece window. (A)-(d) is explanatory drawing which shows the process process of the nut which concerns on this invention. (A), (b) is a schematic diagram which shows the processing state of a piece window. It is principal part sectional drawing which shows the conventional piece type ball screw. It is sectional drawing which shows the attachment state to the nut of a piece member same as the above.

Explanation of symbols

1 ······ Poma type ball screw 2 ·············· Screw shafts 2a, 3a Nut 4 ... Ball 5 ... Piece member 5a ... Connection groove 6 ... Piece Window 6a ····························· 7 Tool 50 ·················································································· ... 54 ... 54 pieces ... 54 ... Connection groove 55 ... ... piece window 56 ...・ ・ ・ ・ ・ Arm R ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Curve radius R ′ of screw groove center ・ ・ ・・ ・ ・ ・ ・ Curve radius θ of the arc along the width center of the arm ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Cutting edge angle

Claims (6)

A screw shaft having a helical thread groove formed on the outer peripheral surface;
A nut externally fitted to the screw shaft and having a spiral thread groove formed on the inner peripheral surface;
A plurality of balls accommodated in rolling paths formed by the opposing thread grooves;
A piece member that is fitted to a piece window formed in the trunk portion of the nut, has a rolling groove as a circulation route, and a connecting groove that connects between adjacent screw grooves of the nut; and
The piece window is formed in a circular section, and the piece member is formed in a circular section corresponding to the piece window,
A piece-type ball screw, wherein the piece window is formed of a finished surface formed to a predetermined size by boring.   The piece type ball screw according to claim 1, wherein the thread groove of the nut is formed by cutting.   The piece type ball screw according to claim 1 or 2, wherein the thread groove of the screw shaft is formed by rolling.   The piece type ball screw according to any one of claims 1 to 3, wherein the piece member is formed of a sintered alloy made of carburized metal powder by MIM and hardened by carburizing and quenching. A screw shaft having a helical thread groove formed on the outer peripheral surface;
A nut externally fitted to the screw shaft and having a spiral thread groove formed on the inner peripheral surface;
A plurality of balls accommodated in rolling paths formed by the opposing thread grooves;
A piece member that is fitted to a piece window formed in the trunk portion of the nut, has a rolling groove as a circulation route, and a connecting groove that connects between adjacent screw grooves of the nut; and
In the method of manufacturing a piece type ball screw in which the piece window is formed in a circular shape in cross section and the piece member is formed in a circular shape in cross section corresponding to the piece window,
After the thread groove of the nut has been finished by cutting, a rough hole is drilled in the piece window by drilling, and the boring tool inserted into the pilot hole is rotated from the inner diameter side of the nut. A method of manufacturing a piece-type ball screw, wherein the piece window is finished toward a predetermined size by being sent toward an outer diameter side.   The boring tool is composed of a holder and a tip that is interchangeably fixed to the tip of the holder, and a cutting edge angle is attached to the cutting edge of the tip, and the cutting edge angle is 10 to 30. The manufacturing method of the piece type ball screw according to claim 5, which is set in a range of °.

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