JP2015024471A - Processing tool and processing method for nut for ball screw - Google Patents

Abstract

[PROBLEMS] To form a rolling groove on the inner peripheral surface of a nut by helical machining, it is necessary to incline either the rotating shaft of the cutting tool or the nut by the lead angle, and the device is complicated and expensive. There was a problem. With the rotation axis of the cutting tool held parallel to the central axis of the nut, the inner peripheral surface of the nut is moved spirally while rotating the cutting tool around the rotation axis, and the cutting edge of the cutting tool is moved. A ball screw nut processing method, wherein an envelope in a plane perpendicular to the rolling groove of a locus drawn by an arbitrary point is substantially equal to a normal sectional shape of the rolling groove in a plane perpendicular to the rolling groove . [Selection] Figure 1

Description

  The present invention relates to a ball screw mechanism used in general industrial machines or used in automobiles, ships, and the like.

  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 a rotary motion transmitted from the electric motor into a linear motion with high efficiency.

  Usually, the ball screw mechanism is composed of a screw shaft, a nut, and a ball that rolls in a rolling groove formed between them, and the ball moves in the rolling groove when the screw shaft and the nut rotate relative to each other. Therefore, the rotational motion is converted into linear motion with very little friction. The nut is provided with a circulation mechanism that returns the ball to the starting point of the rolling groove. The types of circulation mechanism can be broadly classified. There is a circulation groove integrated type that is integrally formed on the inner peripheral surface. Among them, the circulation groove integrated type is low in cost because it does not require a separate part, and since there is no possibility that the separate part will be damaged or dropped, it has become popular in recent years.

  As a method of forming a ball rolling groove on the inner peripheral surface of the nut, cutting or grinding is usually used. The rolling groove is cut by rotating the nut around the central axis and moving the cutting tool in the axial direction of the nut in synchronism with the rotation (rotation) or by rotating the nut. There is a method of forming a rolling groove (helical machining) by a cutting tool moving spirally on the inner peripheral surface of a nut (Patent Document 1).

  Since the rolling groove and the circulation groove are integrated in the circulation groove integrated nut (see FIG. 2), it is necessary to stop the machining in a part of the circumferential direction in forming the rolling groove. In the processing, the rolling groove is formed without interruption from one axial end surface to the other end surface of the nut, so that a nut integrated with a circulation groove cannot be manufactured. Therefore, the latter helical machining is generally used for the production of the circulation groove integrated nut.

Japanese Patent Application No. 2010-175802

  However, in order to form a rolling groove on the inner peripheral surface of the nut by helical machining, it is necessary to incline either the rotating shaft of the cutting tool or the nut by the lead angle of the rolling groove, making the device complicated and expensive. There was a problem of becoming. In addition, a nut having a small inner diameter has a small room for inclining the rotation axis of the cutting tool, so that the lead angle that can be processed is limited. Furthermore, if a complete tool that can process the raceway surface, relief part, and chamfered part (see Fig. 3) constituting the rolling groove with one cutting tool is used, there is no need to change the tool for each part. Although the time can be shortened, in the case of using a general tool in conventional helical machining, it is necessary to incline either the cutting tool or the nut by the lead angle as described above.

  The present invention has been made in view of such problems, and its purpose is to cut each part by using a cutting tool having a special shape while keeping the rotation axis of the cutting tool and the central axis of the nut parallel to each other. An object of the present invention is to provide a ball screw nut processing method capable of forming a raceway surface, a relief portion, and a chamfered portion without exchanging a tool.

The object of the present invention is achieved by the following configurations.
(1) A screw shaft having a spiral rolling groove formed on the outer peripheral surface, and a nut formed with a rolling groove facing the rolling groove of the screw shaft on the inner peripheral surface, In processing a rolling groove of a ball screw nut in which the nut of a ball screw device in which the rolling groove and the rolling groove of the nut are screwed together via a plurality of balls is processed with a single cutting tool. In a state where the rotation axis of the cutting tool and the central axis of the nut are held in parallel, while rotating the cutting tool around the rotation axis, spirally once along the inner peripheral surface of the nut or When moved multiple times, the envelope in the plane perpendicular to the rolling groove of the locus drawn by any one point of the cutting edge of the cutting tool is a normal cross section of the rolling groove in the plane perpendicular to the rolling groove A method of processing a nut for a ball screw, characterized by being substantially equal to a shape.
(2) a screw shaft having a spiral rolling groove formed on the outer peripheral surface, and a nut having a rolling groove opposed to the rolling groove of the screw shaft on the inner peripheral surface; In processing a rolling groove of a ball screw nut in which the nut of a ball screw device in which the rolling groove and the rolling groove of the nut are screwed together via a plurality of balls is processed with a single cutting tool. The cutting tool is rotated around the rotation axis in a state where the rotation axis of the cutting tool and the central axis of the nut are held in parallel, and is moved spirally along the inner peripheral surface of the nut. Sometimes, the envelope in the plane perpendicular to the rolling groove of the locus drawn by any one point of the cutting edge of the cutting tool is substantially equal to the normal cross-sectional shape of the rolling groove in the plane perpendicular to the rolling groove. A ball screw nut cutting tool characterized by
(3) The ball screw nut cutting tool according to (2), wherein the envelope includes a raceway surface of the rolling groove, a relief portion, and a chamfered portion.

  Since the rolling groove is machined with the rotation axis of the cutting tool and the central axis of the nut being parallel, the apparatus can be simplified and the apparatus cost can be reduced as compared with conventional helical machining. In addition, since the raceway surface, relief part, and chamfered part that make up the rolling groove can be machined with a single cutting tool, there is no need to replace the cutting tool during machining, reducing machining time and tool costs. can do.

It is a schematic diagram which shows the aspect of implementation of this invention. It is a perspective view containing the cross section of a circulation groove | channel integrated nut. It is sectional drawing of a rolling groove. It is a schematic diagram which shows the processing form of a blank. It is a schematic diagram which shows the processing form of a 1st intermediate material. It is a schematic diagram which shows the processing form of a rolling groove. It is a schematic diagram which shows the cross-sectional shape of a blade edge | tip. (A) is a figure which shows the cross section orthogonal to the rotating shaft of the nut in cutting. (B) is a schematic diagram which shows the process in which the envelope of the locus | trajectory of several blade edges forms a rolling groove. It is a schematic diagram which shows the process in which the envelope of the locus | trajectory of a some blade edge | tip forms the rolling groove containing a track surface, a relief part, and a chamfering part. It is a schematic diagram which shows a mode that a rolling groove is formed by multiple times of cutting.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  In the present invention, the inner periphery of the nut 1 is rotated while the cutting tool 20 is rotated about the rotation axis Ck while the rotation axis Ck of the cutting tool 20 is held in parallel with the central axis Cw of the nut 1 as shown in FIG. When moved spirally along the surface 4, the envelope in the plane perpendicular to the rolling groove 8 of the locus drawn by an arbitrary point of the cutting edge 21 of the cutting tool 20 is rolled in the plane perpendicular to the rolling groove 8. The shape and diameter of the cutting edge 21 of the cutting tool 20 are set so as to be approximately equal to the regular cross-sectional shape of the moving groove 8.

  Hereinafter, the processing of the nut 1 will be described separately for each process. First, a cylindrical body (blank 10) having a flange 11 at one end in the axial direction is produced from a steel nut material with normal accuracy. Next, as shown in FIG. 4, the chuck 30 holds the end face 12 opposite to the flange 11 of the blank 10 and a half on the end face 12 side in the axial direction of the outer peripheral face, and the inner peripheral face of the blank 10. 4 and the end surface 11a and the outer peripheral surface 11b of the flange 11 are continuously cut or ground (without removing the blank 10 from the chuck 30). Thereby, the coaxial degree of the inner peripheral surface 4 of the blank 10 and the outer peripheral surface 11b of the flange 11 can be made small (for example, 0.01 mm or less). Further, the perpendicularity of the end surface 11a of the flange 11 with respect to the inner peripheral surface 4 of the blank 10 can be reduced. As the material of the nut 1, carbon steel, stainless steel, bearing steel, or the like can be used.

  As a next step, the circulation groove 3 is formed by plastic working on the inner peripheral surface 4 of the blank 10 with the end surface 11a of the flange 11 as an axial reference and the outer peripheral surface 11b of the flange 11 as a radial reference. 100. For example, the circulation groove is formed by the method shown in FIG. In the method of FIG. 5, a die having a machining head 6 having an outer peripheral surface 6 a corresponding to the inner peripheral surface 4 of the blank 10 and a holding member 5 that holds the blank 10 is used. An S-shaped convex portion 61 corresponding to the shape of the circulation groove 3 is formed on the outer peripheral surface 6 a of the processing head 6. When the machining head 6 is pressed toward the inner peripheral surface 4 of the blank 10 fixed by the holding member 5, the convex portion 61 plastically deforms a part of the inner peripheral surface 4 to form the circulation groove 3.

  Further, as shown in FIG. 6, the rolling groove 8 is formed on the inner peripheral surface 4 of the first intermediate material 100 by helical machining with the end surface 11 a of the flange 11 as an axial reference and the outer peripheral surface 11 b of the flange 11 as a radial reference. Form. That is, the holding member 9 of the first intermediate material 100 is a three-claw chuck including, for example, three claws 9a to 9c arranged at a position divided into three equal parts in the circumferential direction, and all the claws 9a to 9c are provided with flanges. 11 is formed with a seating surface 92 for receiving the end surface 11a and an inner peripheral surface 93 for receiving the outer peripheral surface 11b of the flange 11. The seating surface 92 of the holding member 9 is an axial reference setting surface, and the inner peripheral surface 93 is a radial reference setting surface.

  Then, as shown in FIG. 6, the first intermediate material 100 is held by the holding member 9. At that time, the first intermediate material 100 is positioned in the radial direction by contact between the outer peripheral surface 11b of the flange 11 and the inner peripheral surfaces 93 of the first to third claws 9a to 9c. Further, the first intermediate material 100 is axially positioned by the contact between the end surface 11a of the flange 11 and the seating surfaces 92 of the first to third claws 9a to 9c. In this state, the cutting tool 20 is inserted into the space inside the first intermediate material 100 and is arranged at a position (cutting start point) where the axial position of the cutting edge is near one end of the circulation groove 3.

  Next, while rotating the cutting tool 20 about the rotation axis Ck, the cutting tool 20 is moved by a fixed amount radially outward to start cutting. The amount of movement in the radial direction corresponds to a “cut amount” in general cutting, and this amount is determined according to the material of the nut 1 and the processing capability of the cutting tool 20. Next, the cutting tool 20 is moved spirally along the inner peripheral surface 4 of the nut 1 while keeping the cutting depth constant. When the cutting edge 21 reaches the other end of the circulation groove 3, the cutting tool 20 is moved radially inward. Thereby, the spiral rolling groove 8 is formed so that both ends thereof are connected to the circulation groove 3. At this time, the pitch of the spiral ωw (the amount of axial movement per circumference) is equal to the lead of the rolling groove 8 to be formed.

  The nut cutting according to the present invention is characterized in that the rotation axis Ck of the cutting tool 20 is parallel to the central axis Cw of the nut 1, so that the blade edge 21 is inclined at the rolling groove 8 by the lead angle. Move across. Therefore, the cross-sectional shape of the cutting edge 21 is a shape obtained by compressing the basic shape in the axial direction so that the rolling groove 8 and the cutting tool 20 do not interfere in the lead direction, with the axial cross section of the rolling groove 8 as shown in FIG. The diameter is such that the rolling groove 8 and the cutting tool 20 do not interfere with each other. Further, the envelope in the plane perpendicular to the rolling groove 8 of the locus drawn by any one point of the cutting edge 21 by one or a plurality of times of cutting is the regularity of the rolling groove 8 in the plane perpendicular to the rolling groove 8. The shape of the cutting tool 20 is set so as to be substantially equal to the cross-sectional shape.

  Next, the process in which the rolling groove 8 is formed by cutting according to the present invention will be described in detail. FIG. 8A shows a cross section perpendicular to the central axis Cw of the nut 1 during cutting, and FIG. 8B shows a trajectory through which the cutting edge 21 of the cutting tool 20 passes through the AA cross section of the nut 1. . When the X axis, the Y axis, and θ are set as shown in FIG. 8A, the position of the cutting tool 20 involved in forming the rolling groove 8 at the position θ = 0 is from φ1 to φ2. If the position of the cutting tool 20 at an arbitrary time in the range of φ1 to φ2 is, for example, θ1 to θ4, the vicinity of the tip of the cutting tool 20 is closest to the inner diameter of the rolling groove 8 at the position of θ = 0 at the position of θ1. Involved in the formation of regions. When the rolling groove 8 of the nut 1 is a right-hand thread, the cutting tool 20 at θ1 is above the XY plane, and the cutting edge 21 of the cutting tool 20 at this time is as shown in FIG. It passes above the center line in the final shape of the rolling groove 8 and near the center of the nut 1.

  The locus of the blade edge 21 at θ2 is closer to the center line of the rolling groove 8 at the position θ = 0 than at θ1, and moves to the outside in the radial direction of the nut 1. When the cutting tool 20 comes to a position of θ = 0, the locus of the cutting edge 21 has an axial position that matches the final shape of the rolling groove 8, and a radial position at the tip of the locus matches the final shape of the rolling groove 8. . After passing through the position of θ = 0, the locus of the blade edge 21 moves downward from the center line in the final shape of the rolling groove 8 and moves radially inward of the nut 1 as it moves to θ3 and θ4. Thus, in the process of moving the cutting tool 20 in the range of φ1 to φ2, the locus of the blade edge 21 at an arbitrary position forms a part of the cross-sectional shape of the rolling groove 8 at the position of θ = 0. As a result, the rolling groove 8 has a regular cross-sectional shape.

  Further, the present invention is characterized in that the raceway surface 81, the relief portion 82, and the chamfered portion 83 are formed by one cutting tool in the formation of the rolling groove 8. Specifically, as shown in FIG. 9, the envelope formed by the movement range of the cutting edge 21 is substantially equal to the normal cross-sectional shape of the rolling groove 8 including the raceway surface 81, the relief portion 82, and the chamfered portion 83. Thus, the cross-sectional shape and diameter of the cutting tool 20 are set.

  Further, the cutting of the rolling groove 8 is performed once or a plurality of times depending on the size of the rolling groove 8 and the material of the nut 1. When the rolling groove 8 is small, it can be formed by a single cutting process. However, when the material of the nut 1 is difficult to cut, or when the rolling groove 8 is relatively large, it is divided into a plurality of times. Need to be processed. In the case of performing the cutting process in a plurality of times, the diameter of the spiral ωw is increased for each cutting process, and the nut 1 is processed so that the radial cut becomes larger.

  FIG. 10 shows a state where the rolling groove 8 is formed by two cuttings as an example. FIG. 10A shows a cross section of one of the plurality of cutting edges 21 of the cutting tool 20, and FIG. 10B shows an envelope of a trajectory through which the plurality of cutting edges 21 pass as the cutting tool 20 rotates. Line C1 shows a state of forming an intermediate shape of the rolling groove 8 in the first cutting.

  Next, the cutting tool 20 is moved to the cutting start point, moved in a spiral shape with the cutting amount slightly increased from the first processing, and the second cutting is performed. The spiral ωw, which is the locus of the cutting tool at this time, has the same pitch and a larger diameter than the previous machining. FIG. 10C shows a state where the envelope C2 of the trajectory through which the plurality of cutting edges 21 pass forms the final shape of the rolling groove 8 in the process of the second cutting. In this way, when a plurality of cutting operations are completed, both ends of the rolling groove 8 having less than one lead are connected by the circulation groove 3 as shown in FIG.

  By performing the above-described machining, the rolling groove 8 is machined with the rotation axis Ck of the cutting tool 20 and the central axis Cw of the nut 1 in parallel, so the apparatus is simplified compared to conventional helical machining. And cost can be reduced. Further, since the raceway surface 81, the relief portion 82, and the chamfered portion 83 of the rolling groove 8 can be machined with a single cutting tool 20, there is no need to replace the cutting tool 20 during the machining, shortening the machining time and the tool. Cost reduction can be realized.

  The present invention can also be applied to a top type and a tube type nut. When machining a top nut, the position of a previously formed top insertion hole is measured and used as the cutting start point of the rolling groove 8. Further, when processing a tube-type nut, the position of a previously formed tube insertion hole may be measured and used as the cutting start point of the rolling groove 8. In addition, after the cutting process according to the present invention is performed, the rolling groove can be ground.

DESCRIPTION OF SYMBOLS 1 Nut 3 Circulation groove 4 Inner peripheral surface 5 Holding member 6 Processing head 61 Protruding part 8 Rolling groove 81 Track surface 82 Escape part 83 Chamfering part 9 Holding member 10 Blank 11 Flange 20 Cutting tool 21 Edge shape 100 1st middle Material Ck Rotating axis of cutting tool Cw Center axis of nut ωk Rotating direction of tool ωw Spiral

Claims (3)

  A screw shaft having a spiral rolling groove formed on the outer peripheral surface; and a nut having a rolling groove facing the rolling groove of the screw shaft on the inner peripheral surface, the rolling of the screw groove In the processing of the rolling groove of a ball screw nut in which the nut of a ball screw device in which the groove and the rolling groove of the nut are screwed together via a plurality of balls is processed by the cutting tool. When the cutting tool is rotated around the rotation axis while the rotation axis of the tool is held in parallel with the central axis of the nut, the tool is moved spirally along the inner peripheral surface of the nut. An envelope in a plane perpendicular to the rolling groove of a locus drawn by an arbitrary point on the cutting edge of the cutting tool is substantially equal to a normal cross-sectional shape of the rolling groove in a plane perpendicular to the rolling groove. A ball screw nut processing method.   A screw shaft having a spiral rolling groove formed on the outer peripheral surface; and a nut having a rolling groove facing the rolling groove of the screw shaft on the inner peripheral surface, the rolling of the screw groove In the processing of the rolling groove of a ball screw nut in which the nut of a ball screw device in which the groove and the rolling groove of the nut are screwed together via a plurality of balls is processed by the cutting tool. When the cutting tool is rotated around the rotation axis while the rotation axis of the tool and the central axis of the nut are held in parallel, and is moved spirally along the inner peripheral surface of the nut, An envelope in a plane perpendicular to the rolling groove of a locus drawn by an arbitrary point on the cutting edge of the cutting tool is substantially equal to a normal cross-sectional shape of the rolling groove in a plane perpendicular to the rolling groove. And a ball screw nut cutting tool. The ball screw nut cutting tool according to claim 2, wherein the envelope includes a raceway surface of the rolling groove, a relief portion, and a chamfered portion.

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