JP2005083549A - Ball screw nut and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive ball screw nut superior in its durability and having a ball rolling groove of comparatively high accuracy, and to provide a method of easily manufacturing the ball screw nut. <P>SOLUTION: This method of manufacturing the ball screw nut having the ball rolling groove for rolling the ball on its inner-diameter face, comprises a process P1 for drilling the specific inner-diameter face at a center of a material, a process P2 for finishing an outer-diameter face and the inner-diameter face of the material by a tool, a process P3 for inserting a tapping tool to the inner-diameter face and cutting the ball rolling groove, and a heat treatment process P4 for carburizing quenching the ball rolling groove. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a ball screw nut having a spiral ball rolling groove on which a large number of balls roll and a method for manufacturing the same.

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

  Conventionally, in this ball screw nut, a ball rolling groove is generally formed on the inner periphery by cutting and grinding. That is, a drill hole is used to make a pilot hole, and a spiral ball rolling groove is cut on the peripheral surface of the pilot hole with a cutting tool. Next, after performing a heat treatment such as carburizing and quenching, the outer diameter portion is ground with a cylindrical grinder or the like, and finally the surface of the ball rolling groove cut with a grindstone is ground.

  However, in the conventional ball screw nut in which a ball rolling groove is formed by cutting and grinding, when grinding a ball screw nut having a small inner diameter, the grindstone cannot be inserted into the pilot hole, There were cases where processing was not possible. Also, even if the lead screw is not a ball screw nut with a small inner diameter, the lead angle is large, so that the amount of the grindstone inserted into the lower hole is limited, and grinding may not be possible. Naturally, the grinding process is disadvantageous in terms of cost because it takes time and man-hours to adjust nut centering and the like.

  As a solution to these problems, a ball screw nut as shown in FIG. 7 is known. The ball screw nut 50 has a substantially cylindrical shape, and has a flange 50a at one end thereof for coupling to a conveying machine or the like. A ball rolling groove 50c on which a ball (not shown) rolls is formed on the inner peripheral surface of the ball screw nut 50, and a flat portion 50b is formed on the outer diameter surface. A member such as a return pipe that connects one end and the other end of the ball rolling groove 50c is coupled to the flat surface portion 50b. The ball rolling groove 50c is formed into a Gothic arch groove or the like that combines two arcs having a radius of curvature slightly larger than the radius of the ball by rolling.

The ball screw nut 50 is manufactured by a process as shown in FIG. First, the outer periphery of the cylindrical material 51 is cut using a cutting tool 52, a flange 51a is formed on the material 51 (S1), and a pilot hole 51b is formed on the material 51 using a drill 53 (S2). Next, using the boring tool 54, the lower hole 51b is spread to a normal size (S3), and then the raw material 51 is rotated at a low speed of 100 to 200 rpm, and the rolling tap 55 is inserted into the lower hole 51b. The ball rolling groove 51c is rolled on the inner diameter surface of 51 (S4). In this way, the surface of the ball rolling groove 51c is burnished. Next, the end mill 56 is used to groove the return portion 51 d for circulating the ball through the material 51. Then, the outer diameter of the material 51 is cut using the cutting tool 52 to finish the outer diameter (S5). Finally, the rolling tap 55 is again passed through the ball rolling groove 51c of the material 51, and the ball rolling groove 51c is deburred.

Thus, since the ball rolling groove 51c is formed on the inner diameter surface of the material 51 in the rolling process (S4), there is no need for a grinding process for grinding the ball rolling groove using a conventional grindstone, Even with a small-diameter ball screw nut, the ball rolling groove 51c can be easily machined. For this reason, since the processing cost of the ball rolling groove 51c can be reduced and the number of processing steps can be reduced, the lead time can be shortened.
JP 2000-88072 A

  Incidentally, not only the fields of machine tools and semiconductor manufacturing equipment that require precise positioning, smooth operation, and quietness recently, but also the thrust of transfer machines and press machines that do not require much positioning accuracy. There is a tendency to increase the speed of the use for the purpose of controlling the noise and the vibration. In such a conventional ball screw nut 50, unlike the rolling process of the screw shaft, the cold plastic working for the ball rolling groove 50c on the inner diameter surface has a processing problem. That is, since the plastic flow in the axial direction of the hollow nut body can hardly be expected, a large stress is generated in the rolling tap 55 inserted into the inner diameter, and the rolling tap 55 is often damaged.

In addition, as a measure against this breakage, when trying to set a small plastic deformation allowance, if the accuracy of the rough screw is not sufficient, not only the surface accuracy of the ball rolling groove can be expected, but also a stable quality due to residual machining. Problems remain in terms of maintenance. For this reason, there is no manufacturing method for simply forming a relatively high-precision ball rolling groove like a ball screw shaft, so the cost of a ball screw nut is high, but the ball rolling groove is formed by grinding. Currently, there are products available.

An object of the present invention is to solve such conventional problems, and to provide a ball screw nut having a ball rolling groove having excellent durability, low cost and relatively high accuracy, and a manufacturing method for simply forming the ball screw nut. To do.

  In order to achieve the object, the invention according to claim 1 of the present invention is a ball screw nut in which a ball rolling groove on which a ball rolls is formed on an inner diameter surface, wherein the ball rolling groove is formed by tapping. The configuration formed by the cutting surface was adopted.

  Thus, since the ball rolling groove is formed by a cutting surface by tapping, a ball screw nut having a ball rolling groove with relatively high accuracy at low cost can be provided.

  In the invention described in claim 2, since the ball rolling groove is formed in a Gothic arch shape, the contact point with the ball can be set stably, and smooth rolling of the ball is achieved. be able to.

  In the invention according to claim 3, since the surface roughness of the ball rolling groove is regulated to Ra 1.2 μm or less, it is possible to suppress the generation of noise and vibration even at high speed rotation.

  Moreover, since the hardened layer is formed in the range of 54-64HRC in the surface of the said ball rolling groove, the invention of Claim 4 improves rolling fatigue life, and has sufficient durability. .

  According to a fifth aspect of the present invention, there is provided a method for manufacturing a ball screw nut in which a ball rolling groove on which a ball rolls is formed on an inner diameter surface, wherein a predetermined inner diameter surface is drilled at the center of the material. A step of opening by machining, a step of inserting a tapping tool into the inner diameter surface to cut the ball rolling groove, and a heat treatment step of quenching the surface of the ball rolling groove.

  By adopting such a manufacturing method, it is possible to easily form a ball screw nut having a ball rolling groove with relatively high accuracy at low cost, and to provide a ball screw nut having sufficient durability. Can be provided.

  Further, the invention according to claim 6 detects the phase of the ball screw nut and the tapping tool, and the ball rolling groove is cut while being controlled by NC based on the information. Cutting can be performed efficiently through a single pass, and high-precision grooving can be performed at low cost.

  In the invention according to claim 7, since the cylindrical portion guided by the inner diameter surface is formed at the tip portion of the tapping tool, the tapping tool can be easily centered, and the cutting is performed with high accuracy. be able to.

The ball screw nut according to the present invention is a ball screw nut in which a ball rolling groove on which a ball rolls is formed on an inner diameter surface, and the ball rolling groove is formed by a cutting surface by tapping processing. It is possible to provide a ball screw nut having a ball rolling groove that is excellent in cost and is relatively low in cost.

  The ball screw nut manufacturing method according to the present invention is a ball screw nut manufacturing method in which a ball rolling groove on which a ball rolls is formed on an inner diameter surface, and a predetermined inner diameter surface is drilled at the center of the material. Since it includes a step of opening, a step of cutting a ball rolling groove by inserting a tapping tool into the inner diameter surface, and a heat treatment step of quenching the surface of the ball rolling groove, the cost is relatively low and relatively accurate. A ball screw nut having a high ball rolling groove can be easily formed, and a ball screw nut having sufficient durability can be provided.

  In a ball screw nut manufacturing method in which a ball rolling groove for rolling a ball is formed on an inner diameter surface, a step of drilling a predetermined inner diameter surface at the center of the material by drilling, and an outer diameter surface and an inner diameter surface of the material A step of finishing with a cutting tool, a step of inserting a tapping tool into the inner diameter surface to cut the ball rolling groove, and a heat treatment step of carburizing and quenching the ball rolling groove.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a longitudinal sectional view showing an embodiment of a ball screw nut according to the present invention.

  This ball screw nut 1 is made of case-hardened steel such as SCM415 or SCM420, and is externally fitted to the ball screw shaft 3 and corresponds to the spiral ball rolling groove 4 formed on the outer diameter surface 3a of the ball screw shaft 3. A spiral ball rolling groove 2 is formed in the inner diameter surface 1a by cutting with a tapping tool 9 described later. A ball rolling path is formed by these ball rolling grooves 2, 4, and a large number of balls 7 circulate infinitely by a piece member 6 in which a connecting groove 5 that connects the ball rolling grooves 2 of the ball screw nut 1 is formed. Can do. The ball circulation method is not limited to the piece type exemplified here, and may be a return tube type or an end cap type.

  In FIG. 2, the manufacturing process of the ball screw nut 1 in embodiment of this invention is shown. First, a predetermined inner diameter surface is formed with a drill or the like at the center of a cylindrical material (P1). The outer diameter surface and inner diameter surface of the material are finished with a cutting tool (P2). Next, as shown in FIG. 3, the ball screw nut 1 and the tapping tool 9 are mounted on the chuck 8 a and the tail stock (not shown) of the turning center 8, respectively, and then the inner surface 1 a of the ball screw nut 1 is tapped. The tool 9 is inserted, and the ball screw nut 1 and the tapping tool 9 are rotated to perform cutting while controlling the respective phases with NC control (P3). As a result, the ball rolling groove 2 can be efficiently cut by one pass, and high-precision grooving can be performed at low cost.

As shown in FIG. 4, the tapping tool 9 is formed with a cylindrical portion 9a at the tip so that centering is possible using the inner diameter surface 1a of the ball screw nut 1 as a guide. A cutting edge portion 9b having a gradually larger diameter is formed rearward from the cylindrical portion 9a, and a rectangular chuck portion 9d to be attached to the tailstock is formed at the rear end portion via the shank portion 9c. . As the cutting teeth 9b of the tapping tool 9 rotate, the ball rolling groove 2 is formed on the inner diameter surface 1a of the ball screw nut 1 by cutting. Here, the cutting edge portion 9b of the tapping tool 9 is formed in a Gothic arch groove that is a combination of two arcs having a radius of curvature slightly larger than the radius of the ball 7, and the desired groove shape can be efficiently achieved by a single threading process. Can be cut. Of course, the ball rolling groove 2 may have an arcuate shape in circular contact with the ball 7 other than the illustrated Gothic arch shape.

After the tapping process, a hardened layer is formed on the surface of the ball screw nut 1 in a range of 54 to 64 HRC by carburizing and quenching (P4). Here, although carburizing and quenching is exemplified as the heat treatment, the curing treatment is not limited to this, and tempering treatment or induction quenching, or using a high carbon chromium steel such as SUJ2 as a raw material, may be quenched. .

FIG. 5 is data showing the surface roughness of the ball rolling groove 2 in the ball screw nut 1 according to the present invention. As can be seen from this figure, although it does not reach the surface roughness of the groove surface by grinding, a good surface roughness of Ra 1.2 μm at the maximum and Ra 1.0 μm or less on the average can be obtained. Compared with surface roughness Ra of 1.5 to 2.0 μm, surface roughness is improved. Thereby, generation | occurrence | production of a noise, a vibration, etc. can be suppressed also in high speed rotation.

Next, the life test result of the ball screw incorporating the ball screw nut 1 according to the present invention is shown in FIG. Here, the specifications of the specimen are: shaft diameter: φ14.5, lead: 4 mm, ball diameter: φ2.778, circulation number: 1 turn, 4 rows, circulation method is piece type. Further, the test conditions are load application method; constant pressure preload by spring preload double nut, lubrication; oil VG68, rotation speed: 2000 rpm, stroke: 60 mm, and load load is 2648N.

  The notation of FIG. 6 is based on a ball screw having a ball rolling groove formed by grinding and is based on the basic dynamic load rating shown in the catalog as a reference, and the calculated L10 life time is 100. The test time until the end of the service life is graphed. As can be seen from this graph, the L10 ratio is more than twice as long as the ball screw (Comparative Examples 1 to 4) formed by the conventional rolling process, and is formed by cutting with the tapping tool 9. The ball screw nut 1 having the formed ball rolling groove 2 has sufficient durability.

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

  The ball screw nut according to the present invention can be applied to an automatic manual transmission, an electric brake, an electric power steering, an engine valve operating control actuator used for a vehicle such as an automobile, and also for width control of an electric shock absorber or a CVT pulley. It can also be applied to other actuators.

It is a longitudinal section showing one embodiment of a ball screw nut concerning the present invention. It is explanatory drawing which shows the manufacturing process of the ball screw nut which concerns on this invention. It is the schematic which shows the turning center for enforcing the manufacturing method of the ball screw nut which concerns on this invention. It is a top view which shows the tapping tool used for the process of the ball screw nut which concerns on this invention. It is the data which showed the surface roughness of the ball rolling groove in the ball screw nut concerning the present invention. It is a graph which shows the lifetime test result of the ball screw incorporating the ball screw nut which concerns on this invention. It is a longitudinal cross-sectional view which shows the conventional ball screw nut. It is process drawing which shows the manufacturing method of the conventional ball screw nut.

Explanation of symbols

1 ··············· Ball screw nut 1a ······· Inner diameter surface 2, 4 ······················· Ball rolling groove 3 ······· Ball screw shaft 3a ··· Outer diameter surface 5 ······· Connection groove 6 ······· Member 7 ... Ball 8 ... Turning Center 8a ... Chuck 9 ...・ ・ Tapping tool 9a ・ ・ ・ ・ ・ ・ Cylindrical part 9b ・ ・ ・ ・ ・ ・ Cutting tooth part 9c ・ ・ ・ ・ ・ ・ Shank part 9d ... Chuck part 50 ... Ball screw nuts 50a, 51a ... Flange 50b ... Plane parts 50c, 51c ... Ball rolling groove 51 51b ·························· 51d ·············································································· ···················································································· End mill

Claims (7)

  A ball screw nut in which a ball rolling groove on which a ball rolls is formed on an inner diameter surface, wherein the ball rolling groove is formed by a cutting surface by tapping.   The ball screw nut according to claim 1, wherein the ball rolling groove is formed in a Gothic arch shape.   The ball screw nut according to claim 1 or 2, wherein a surface roughness of the ball rolling groove is restricted to Ra 1.2 µm or less.   The ball screw nut according to any one of claims 1 to 3, wherein a hardened layer is formed on the surface of the ball rolling groove in a range of 54 to 64 HRC.   In the method of manufacturing a ball screw nut in which a ball rolling groove on which a ball rolls is formed on an inner diameter surface, a step of drilling a predetermined inner diameter surface at the center of the material, a tapping tool is inserted into the inner diameter surface, A method for manufacturing a ball screw nut, comprising: a step of cutting a ball rolling groove; and a heat treatment step of quenching the surface of the ball rolling groove.   The ball screw nut manufacturing method according to claim 5, wherein the phase of the ball screw nut and the tapping tool is detected, and the ball rolling groove is cut while performing NC control based on the detected information.   The manufacturing method of the ball screw nut of Claim 5 or 6 with which the cylindrical part guided by the said internal surface is formed in the front-end | tip part of the said tapping tool.

Images