Method for manufacturing nut for ball screw and method for thinning and drawing

Abstract

A method for manufacturing a nut (5) for a ball screw provided with: a screw shaft (3) in which a spiral ball rolling groove (3a) is formed on the outer peripheral surface; a nut (5) having a spiral ball rolling groove (5a) formed on the inner peripheral surface thereof so as to face the ball rolling groove (3a) of the screw shaft (3); and a plurality of balls (9) disposed in a ball rolling path (7) formed by two ball rolling grooves (3a, 5a), the nut (5) having a ball circulation groove (20) for returning the balls (9) from an end point to a starting point of the ball rolling path (7) on an inner circumferential surface, characterized in that: in a ball circulation groove forming step for forming the ball circulation groove (20), the ball circulation groove (20) is formed in the ball rolling path (7); a ball circulation groove (20) and a phase reference (S) are simultaneously formed on a blank (M) of a nut (5) by plastic working, and a ball rolling groove forming step for forming a ball rolling groove (5a) is performed using the phase reference (S).

Description

Technical Field

[0001] The invention relates to a method for manufacturing a nut for a ball screw and a method for thinning and drawing a nut. Background Art

[0002] The ball screw has: a nut having a spiral groove formed on the inner circumference; a screw shaft having a spiral groove formed on the outer circumference; balls arranged in a track formed by the spiral grooves of the nut and the screw shaft; and a ball return path that returns the balls from the end of the track to the starting point. The ball screw is a device in which the nut moves relative to the screw shaft as the balls roll in the track. Such a ball screw is not only used for positioning devices of general industrial machinery, but also for electric actuators mounted on vehicles such as automobiles, two-wheeled vehicles, and ships.

[0003] The ball return path of the ball screw has a circulation tube method, a cover plate method, etc. In the case of the cover plate method, a cover plate having a recessed portion constituting the ball return path is embedded in the through hole of the nut. In contrast, if the recessed portion (ball circulation groove) constituting the ball return path is directly formed on the inner circumferential surface of the nut, the assembly work and cost can be reduced, and the reliability of the ball circulation can also be expected to be improved.

[0004] Patent document 1 describes a method for manufacturing a nut for a ball screw, wherein the nut for a ball screw has a ball rolling groove and a ball circulation groove formed on the inner circumference, wherein the ball rolling groove forms a track for ball circulation together with the spiral groove of the screw shaft, and the ball circulation groove returns the ball from the end point of the track to the starting point. The method for manufacturing a nut for a ball screw is characterized in that it has the following steps: a blank forming step, in which a cylindrical blank is formed from a raw material for a nut; a circulation groove forming step, in which a ball circulation groove is formed on the inner circumference of the blank; and a rolling groove forming step, in which a ball rolling groove is formed on the inner circumference of the blank, a processing reference is formed in a step earlier than the rolling groove forming step, and the processing reference has a phase reference, an axial reference, and a radial reference formed in the blank forming step, and the above processing reference is used in both the circulation groove forming step and the rolling groove forming step.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent No. 6015444 Summary of the invention

[0008] Problems to be solved by the invention

[0009] However, as proposed in Patent Document 1, when the phase reference formed in the blank forming process is used in both the circulation groove forming process and the rolling groove forming process, it is necessary to fit the components on the groove (circulation groove, rolling groove) forming device side with the phase reference formed in the blank forming process to determine the position. However, it was found that a minimum gap is required to fit the components on the groove forming device side with the phase reference, and the gap causes phase deviation in each of the circulation groove forming process and the rolling groove forming process, which becomes a problem.

[0010] In view of the above problems, an object of the present invention is to provide a high-precision method for manufacturing and thinning a nut for a ball screw that can form a ball circulation groove with high precision and prevent positional deviation between the ball rolling groove and the ball circulation groove.

[0011] Means for solving problems

[0012] The present inventors have conducted various studies and verifications to achieve the above-mentioned object, and as a result, have found out the following technical matters, thereby completing the present invention.

[0013] (1) A manufacturing method includes, in a circulation groove forming step, a step of simultaneously forming a ball circulation groove and a phase reference with a small phase shift with the ball circulation groove.

[0014] (2) A manufacturing method for performing a rolling groove forming step in a subsequent step using a phase reference having a small phase deviation from a ball circulation groove.

[0015] (3) A thinning and drawing method, wherein the inner die is set to a high-rigidity split structure that can reduce the diameter, and in the circulation groove forming process, the outer peripheral surface of the nut blank is thinned and drawn using a drawing die to transfer the ball circulation groove to the molding surface of the inner die to form it.

[0016] As a technical means to achieve the above-mentioned purpose, the first invention is a method for manufacturing a nut for a ball screw, the ball screw having: a screw shaft having a spiral ball rolling groove formed on the outer circumference; a nut having a spiral ball rolling groove formed on the inner circumference opposite to the ball rolling groove of the screw shaft; and a plurality of balls, the plurality of balls being arranged in a ball rolling path formed by the two ball rolling grooves, the nut having a ball circulation groove on the inner circumference for returning the balls from the end point to the starting point of the ball rolling path, characterized in that in the circulation groove forming process of forming the ball circulation groove, the ball circulation groove and a phase reference are simultaneously formed on the blank of the nut by plastic working, and the rolling groove forming process of forming the ball rolling groove is performed using the phase reference. According to the above-mentioned structure, the positional deviation of the ball rolling groove and the ball circulation groove can be prevented, thereby realizing a high-precision method for manufacturing a nut for a ball screw.

[0017] In particular, by making the plastic working for simultaneously forming the ball circulation groove and the phase reference in the above-mentioned circulation groove forming process a thinning and drawing process, the ball circulation groove can be formed with high precision, and the phase deviation between the ball circulation groove and the phase reference can be suppressed.

[0018] The second invention is a method for thinning and drawing a nut for a ball screw, the ball screw comprising: a screw shaft having a spiral ball rolling groove formed on the outer peripheral surface; a nut having a spiral ball rolling groove formed on the inner peripheral surface and opposite to the ball rolling groove of the screw shaft; and a plurality of balls, which are arranged in a ball rolling path formed by the two ball rolling grooves, the nut having a ball circulation groove on the inner peripheral surface for returning the balls from the end point of the ball rolling path to the starting point, characterized in that the mold used for the thinning and drawing processing includes :A split forming punch, which is formed with a convex portion corresponding to the concave portion of the ball circulation groove; a punch base, which limits the position of the split forming punch and bears the load acting on the split forming punch; a drawing die, which reduces the outer diameter of the blank by thinning and drawing the outer peripheral surface of the blank of the nut; and a punch holder, which bears the axial load acting on the blank when the outer peripheral surface of the blank is thinned and drawn, and limits the position of the split forming punch, and reduces the diameter of the blank by the drawing die, thereby forming the ball circulation groove. According to the above structure, the ball circulation groove can be formed with high precision. In addition, when the ball circulation groove and the phase reference are formed simultaneously in the circulation groove forming process, the phase offset between the ball circulation groove and the phase reference can be suppressed, thereby realizing a high-precision thinning and drawing method for nuts for ball screws. In addition, since the inner mold is set as a high-rigidity split type structure that can reduce the diameter, it is not only possible to form the ball circulation groove with high precision, but also advantageous in terms of mold life.

[0019] The punch holder has a molding surface corresponding to the phase reference when processing the ball rolling groove, and the ball circulation groove and the phase reference can be formed simultaneously by reducing the diameter of the blank through the drawing die, thereby promoting the suppression of the phase deviation between the ball circulation groove and the phase reference.

[0020] The die used for the ironing process described above further includes an upper surface restraining die, and the upper surface of the blank is restrained by the upper surface restraining die, thereby suppressing deformation in the axial direction.

[0021] Effects of the Invention

[0022] According to the method for manufacturing a ball screw nut of the first invention, it is possible to prevent the positional deviation of the ball rolling groove and the ball circulation groove, thereby realizing a method for manufacturing a ball screw nut with high precision.

[0023] According to the thinning and drawing processing of the nut for ball screw of the second invention, the ball circulation groove can be formed with high precision. In addition, when the ball circulation groove and the phase reference are formed simultaneously in the circulation groove forming process, the phase deviation between the ball circulation groove and the phase reference can be suppressed, thereby realizing a high-precision thinning and drawing processing method for the nut for ball screw. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a partial longitudinal sectional view of a ball screw used as a target by a method for manufacturing a ball screw nut according to an embodiment of the first invention and a method for ironing a ball screw nut according to an embodiment of the second invention.

[0025] Figure 2 yes Figure 1 Cross-sectional view of the main parts of the nut.

[0026] Figure 3 yes Figure 1 An enlarged longitudinal section view of the ball circulation circuit.

[0027] Figure 4 This is a longitudinal sectional view schematically showing a circulation groove forming step in a method for manufacturing a ball screw nut according to an embodiment of the first invention.

[0028] Figure 5 This is a longitudinal sectional view schematically showing a circulation groove forming step in the method for manufacturing a ball screw nut according to the present embodiment.

[0029] Fig. 6A The method for manufacturing a nut for a ball screw according to the present embodiment is shown, wherein a raw material for a nut having a ball circulation groove and a phase reference is formed. Fig. 6A These are a top view and a longitudinal cross-sectional view of the raw material for the nut after turning.

[0030] Figure 6B The method for manufacturing a nut for a ball screw according to the present embodiment is shown, wherein a raw material for a nut having a ball circulation groove and a phase reference is formed. Figure 6B These are a top view and a longitudinal cross-sectional view of the nut material after the circulation groove forming process.

[0031] Fig. 7A This is a longitudinal sectional view schematically showing a rolling groove forming step in the method for manufacturing a ball screw nut according to the present embodiment.

[0032] Figure 7B It is a plan view showing an outline of a rolling groove forming step in the method for manufacturing a ball screw nut according to the present embodiment.

[0033] Fig. 8A It is a top view showing a split forming punch in a die in a method for ironing a ball screw nut according to an embodiment of the second invention.

[0034] Figure 8B This is a side view showing a split forming punch in a die in a method for ironing a ball screw nut according to an embodiment of the second invention.

[0035] Figure 8C This is a cross-sectional view showing a split forming punch in a die in a method for ironing a ball screw nut according to an embodiment of the second invention.

[0036] Fig. 9A The details of the split forming punch of FIG8 are shown. Fig. 9A yes Fig. 8A An enlarged view of part D of FIG.

[0037] Fig. 9B The details of the split forming punch of FIG8 are shown. Fig. 9B yes Fig. 8A Cross-sectional view of line EE.

[0038] Fig. 9C The details of the split forming punch of FIG8 are shown. Fig. 9C is along Figure 8B Figure viewed from the F direction.

[0039] Fig.10 It is a plan view showing a modified example of the split forming punch.

[0040] Fig.11A The punch base in the die in the ironing and drawing method of the ball screw nut according to the present embodiment is shown. Fig.11A yes Fig. 11B Right side view.

[0041] Fig. 11B The punch base in the die in the ironing and drawing method of the ball screw nut according to the present embodiment is shown. Fig. 11B It is a top view.

[0042] Fig. 11C The punch base in the die in the ironing and drawing method of the ball screw nut according to the present embodiment is shown. Fig. 11C yes Fig. 11B Left side view.

[0043] Fig.11D The punch base in the die in the ironing and drawing method of the ball screw nut according to the present embodiment is shown. Fig.11D yes Fig.11E Cross-sectional view of the HH line.

[0044] Fig.11E The punch base in the die in the ironing and drawing method of the ball screw nut according to the present embodiment is shown. Fig.11E yes Fig. 11B Longitudinal section view of the GG line.

[0045] Fig. 12A It is a plan view showing a punch holder in a die in the ironing method of the ball screw nut according to the present embodiment.

[0046] Fig. 12B This is a longitudinal sectional view showing a punch holder in a die in the ironing method of a ball screw nut according to the present embodiment.

[0047] Fig. 12C The punch holder in the die in the ironing and drawing method of the ball screw nut according to the present embodiment is shown. Fig. 12C yes Fig. 12A Cross-sectional view of line II.

[0048] Fig.13A The ironing process step in the ironing method for a ball screw nut according to the present embodiment is shown. Fig.13A It is a figure which shows the state which set the blank.

[0049] Fig. 13B The ironing step in the ironing method of the ball screw nut according to the present embodiment is shown. Fig. 13B This is a diagram showing a state immediately before ironing.

[0050] Fig. 13C The ironing process step in the ironing method for a ball screw nut according to the present embodiment is shown. Fig. 13C This is a diagram showing the ironing process start state.

[0051] Fig.13D The ironing process step in the ironing method for a ball screw nut according to the present embodiment is shown. Fig.13D It is a figure which shows the state at which the ironing process is completed.

[0052] Fig.13E The ironing process step in the ironing method for a ball screw nut according to the present embodiment is shown. Fig.13E It is a figure which shows the state which separated the raw material for a nut from a forming punch.

[0053] Fig.13F The ironing process step in the ironing method for a ball screw nut according to the present embodiment is shown. Fig.13F It is a figure which shows the discharge state of the raw material for nuts. DETAILED DESCRIPTION

[0054] First, according to Figures 1 to 3 A ball screw that is the target of a method for manufacturing a ball screw nut according to an embodiment of the first invention and a method for ironing a ball screw nut according to an embodiment of the second invention will be described. Figure 1 This is a partial longitudinal section view of the ball screw. Figure 2 yes Figure 1 Cross-sectional view of the main part of the nut, Figure 3 This is an enlarged longitudinal section view of the ball circulation circuit. Figure 1 As shown, the ball screw 1 comprises: a screw shaft 3, which has a spiral thread groove (also called ball rolling groove) 3a formed on the outer circumference; a nut 5, which has a spiral thread groove (also called ball rolling groove) 5a formed on the inner circumference and is opposite to the thread groove 3a of the screw shaft 3; a plurality of balls 9, which are loaded in a spiral ball rolling path 7 formed by two thread grooves 3a and 5a in a manner that allows them to roll freely; and a ball circulation path 11, which allows the balls 9 to return from the end point of the ball rolling path 7 to the starting point and circulate.

[0055] The ball 9 moves in the ball rolling path 7 while rotating around the screw shaft 3 to reach the end of the ball rolling path 7, where it is scooped up from one end of the ball circulation path 11 and passes through the ball circulation path 11, and returns to the starting point of the ball rolling path 7 from the other end of the ball circulation path 11.

[0056] When the ball screw 1 causes the nut 5 threaded with the screw shaft 3 and the screw shaft 3 to rotate relative to each other via the balls 9, the screw shaft 3 and the nut 5 move relative to each other in the axial direction via the rolling of the balls 9. Moreover, an annular ball passage is formed by the ball rolling path 7 and the ball circulation path 11, and the balls 9 rolling in the ball rolling path 7 circulate infinitely in the annular ball passage, so that the screw shaft 3 and the nut 5 can continuously move relative to each other. The cross-sectional shape of the ball rolling path 7 can be an arc or a pointed arch. The materials of the screw shaft 3, the nut 5, and the balls 9 are not particularly limited, and general materials such as metals, steel, ceramics, etc. can be used.

[0057] Reference Figure 2 , Figure 3 The ball circulation path 11 is described. The ball circulation path 11 is integrally formed on the inner peripheral surface of the nut 5. A portion of the cylindrical inner peripheral surface of the nut 5 is recessed to form a ball circulation groove 20, and the ball circulation groove 20 is used as the ball circulation path 11. Therefore, unlike the case of a tube type, a cover plate type, or other ball circulation forms, other components constituting the ball circulation path are not installed.

[0058] like Figure 3 As shown, the ball 9 that has rolled to the end of the ball rolling path 7 is scooped up from one end of the ball circulation path 11 and sunk into the inside of the nut 5, that is, the radially outer side. Then, the ball 9 passes through the ball circulation path 11 and passes over the threaded portion 3b of the thread groove 3a of the screw shaft 3, and returns to the starting point of the ball rolling path 7 from the other end of the ball circulation path 11. The cross-sectional shape of the ball circulation path 11 can be an arc or a pointed arch.

[0059] Thus, the inner peripheral surface of the nut 5 is formed with a thread groove 5a for the balls 9 to roll and a ball circulation groove 20 for the balls 9 to circulate. The thread groove 5a is a ball rolling groove, and therefore is also referred to as a ball rolling groove 5a. The ball rolling groove and ball circulation groove in the claims are used in the above-mentioned meanings.

[0060] <Embodiment of the first invention>

[0061] Reference Figure 4 7 , a method for manufacturing a ball screw nut according to an embodiment of the first invention will be described. Figure 4 and Figure 5 6 is a longitudinal sectional view showing an overview of a circulation groove forming process in a method for manufacturing a nut for a ball screw according to an embodiment of the first invention, and FIG. 7 shows a raw material for a nut having a ball circulation groove and a phase reference formed thereon according to the method for manufacturing a nut for a ball screw according to the present embodiment. Figure 6B It is a top view and a longitudinal cross-sectional view of the raw material for the nut after the circulation groove forming process. Fig. 6A FIG. 7 is a top view and a longitudinal cross-sectional view of the raw material for nuts after turning. FIG. 8 is a schematic diagram of the rolling groove forming process. Fig. 7A is a longitudinal section view, Figure 7B It is a top view.

[0062] The circulation groove forming step in the method for manufacturing a ball screw nut of this embodiment shows an example in which the ironing and drawing process described later is applied. Figure 4 and Figure 5 As shown, the die used for thinning and drawing processing includes: a split forming punch 30, which is formed with a convex portion 30a corresponding to the concave portion of the ball circulation groove 20; a punch base 31, which limits the position of the split forming punch 30 and receives the load acting on the split forming punch 30; a drawing die 32, which reduces the outer diameter of the blank M by thinning and drawing the outer peripheral surface of the blank M of the nut 5; and a punch retainer 33, which receives the axial load acting on the blank M when the outer peripheral surface of the blank M is thinned and drawn, and limits the position of the split forming punch 30.

[0063] The drawing die 32 has a cylindrical inner circumferential surface 32a, and a tapered inner circumferential surface 32b is formed below the cylindrical inner circumferential surface 32a and expands toward the end surface of the drawing die 32. A molding surface 33a that forms a phase reference and a surface 33b that restricts the end surface of the nut raw material 5' are formed on the upper surface of the punch holder 33. An upper surface restraining die 34 is provided to be slidably fitted on the cylindrical inner circumferential surface 32a of the drawing die 32.

[0064] Details as described below Fig.13A As shown, the drawing die 32 and the upper surface restraining die 34 retreat upward, and the split forming punch 30 moves upward relative to the punch base 31. When the split forming punch 30 moves upward relative to the punch base 31, the split forming punch 30 becomes a reduced diameter state. In this state, the cylindrical blank M is externally embedded in the split forming punch 30 and is arranged on the punch holder 33. After that, the drawing die 32 and the upper surface restraining die 34 descend, the upper surface restraining die 34 abuts against the split forming punch 30, and the split forming punch 30 moves relative to the punch base 31 along the inclined surface of the punch base 31. The split forming punch 30 moves along the inclined surface of the punch base 31 and expands to a specified radial dimension. Figure 4 This state is shown (as described later). Fig. 13B correspond).

[0065] Then, if Figure 5 (As described later Fig.13DAs shown in the figure, when the drawing die 32 is lowered, the outer peripheral surface of the blank M is thinned and drawn by the tapered inner peripheral surface 32b of the drawing die 32, and the blank M is subjected to a drawing action inward in the radial direction and a flow action axially downward. The blank M is reduced in diameter by the drawing action, and the ball circulation groove 20 is transferred to the inner peripheral surface of the blank M by the convex portion 30a of the split forming punch 30. In addition, the flow action of the blank M in the axial direction is limited by the punch holder 33, but a concave forming surface 33a for forming a phase reference is formed on a part of the punch holder 33, and a part of the material subjected to the flow action axially downward flows toward the concave forming surface 33a, forming a convex portion S for phase reference for positioning in the phase direction in the rolling groove forming process. In this way, the ball circulation groove 20 and the phase reference S are formed at the same time.

[0066] The material whose flow in the axial direction is restricted by the punch holder 33 tends to flow to the gap between the punch holder 33 and the drawing die 32 and to the axial direction upward. When the material flows in the axial direction upward, the material pressed on the convex portion 30a of the split forming punch 30 is pulled by the material flow in the axial direction upward and separated from the upper surface of the convex portion 30a of the split forming punch 30, and the convex shape of the convex portion 30a of the split forming punch 30 is not correctly transferred. Therefore, by constraining the upper surface of the blank M with the upper surface constraining die 34, the material flow in the axial direction upward can be suppressed, and the convex shape of the convex portion 30a of the split forming punch 30 can be transferred to the inner peripheral surface of the blank M with high accuracy.

[0067] Details as described below Fig.13E As shown, when the drawing die 32 is raised, the nut raw material 5" formed with the ball circulation groove 20 rises together with the drawing die 32 while being embedded in the drawing die. In addition, the convex portion 30a of the split forming punch 30 is engaged with the ball circulation groove 20 of the nut raw material 5", and thus rises together with the nut raw material 5". When the split forming punch 30 rises, it rises along the inclined surfaces of the punch retainer 33 and the punch base 31, and thus moves radially inward relative to the nut raw material 5", and the convex portion 30a of the split forming punch 30 disengages from the ball circulation groove 20 of the nut raw material 5", so that the nut raw material 5" can be removed from the split forming punch 30.

[0068] A method for manufacturing a ball screw nut according to the present embodiment will be described with reference to FIG. 6 , in which a nut material having ball circulation grooves and a phase reference is formed. Figure 6B It is a top view and a longitudinal cross-sectional view of the nut raw material 5" after the circulation groove forming process (after the ironing and drawing process). Fig. 6A 1 and 2 are a plan view and a longitudinal sectional view of the nut blank 5' after turning. Figure 6BAfter the circulation groove forming process shown in the figure, the nut raw material 5" is turned to remove the excess material on the outer peripheral surface and one end to form Fig. 6A The nut raw material 5' is shown. The ball circulation groove 20 and the phase reference S are formed on the nut raw materials 5' and 5".

[0069] use Fig. 6A The phase reference S of the nut raw material 5' shown is used to form a ball rolling groove forming step in the subsequent step. The rolling groove forming step will be described with reference to FIG. Fig. 7A is a longitudinal sectional view showing an overview of the rolling groove forming process. Figure 7B It is a plan view showing an outline of the rolling groove forming step.

[0070] In the release Fig. 7A , Figure 7B In the state of the chuck 50, the nut raw material 5' is arranged on the main spindle 51 of the lathe. Then, as Figure 7B As shown, the reference receiving portion 52 for positioning the phase reference S formed on the raw material 5' for the nut is locked to the phase reference S, and the chuck 50 is tightened. Since the reference receiving portion 52 on the side subjected to the force in the rotation direction of the spindle is locked (abutted) with the phase reference S, no phase shift caused by a gap occurs. The spindle is rotated, and the ball rolling groove 5a is turned on the inner circumference of the raw material 5' for the nut by the turning tool 53. The turning tool 53 is fed axially in synchronization with the rotation of the spindle to form the lead of the ball rolling groove 5a. Since the ball circulation groove 20 and the phase reference S are formed simultaneously in the rolling groove forming step of the aforementioned step, as shown in FIG. Fig. 7A As shown, the ball rolling groove 5a is accurately formed relative to the ball circulation groove 20, the end of the ball circulation groove 20 is not deviated from the end of the ball rolling groove 5a, and there is almost no step at the connection between the two, which is highly accurate. After turning, heat treatment is performed, and grinding finishing is performed using the phase reference S formed on the nut raw material 5'.

[0071] <Embodiment of the Second Invention>

[0072] Next, according to Figure 4 6 and 8 to 13 illustrate a method for thinning and drawing a ball screw nut according to an embodiment of the second invention. Figure 4The contents described in FIG. 6 are also the same in the thinning and drawing method of a nut for a ball screw according to an embodiment of the second invention, so all the above contents are applicable. Regarding the thinning and drawing method of a nut for a ball screw according to an embodiment of the second invention, the details of the mold and the thinning and drawing process are additionally described based on FIGS. 8 to 13.

[0073] FIG8 shows a split forming punch in a die in a method for ironing and drawing a nut for a ball screw according to an embodiment of the second invention, Fig. 8A It is a top view. Figure 8B is a side view, Figure 8C FIG. 9 shows the details of the split forming punch of FIG. 8 . Fig. 9A yes Fig. 8A The enlarged view of the D part, Fig. 9B yes Fig. 9A The cross-sectional view of the EE line, Fig. 9C is along Figure 8B Figure viewed from the F direction. Fig.10 FIG11 is a top view showing a modified example of a split forming punch. FIG12 shows a punch base in a die in a method for ironing and drawing a nut for a ball screw according to the present embodiment. Fig.11A yes Fig. 11B Right side view, Fig. 11B It is a top view. Fig. 11C yes Fig. 11B Left side view of Fig.11E yes Fig. 11B A longitudinal section of the GG line. Fig.11D yes Fig.11E FIG12 shows a punch holder in a die in a method for thinning and drawing a nut for a ball screw according to the present embodiment. Fig. 12A It is a top view. Fig. 12B is a longitudinal section view, Fig. 12C yes Fig. 12A Cross-sectional view of line II.

[0074] like Fig. 8A As shown, the split forming punch 30 in the thinning and drawing method of the ball screw nut of this embodiment is divided into two in a state where the convex portion 30a corresponding to the concave portion of the ball circulation groove 20 is formed on one split forming punch 30. Figure 8B and Figure 8C As shown, the split forming punch 30 has: a tapered outer peripheral surface 30b in an arc shape, which is Figure 4The tapered inner peripheral surface 33c of the punch holder 33 shown in the figure is slidably guided by the tapered inner peripheral surface 33c of the punch holder 33; and the V-shaped side surface 30c is slidably guided by the tapered guide surface 31a of the V-shaped punch base 31 (refer to FIG. 11). The tapered outer peripheral surface 30b of the split forming punch 30 is formed in an arc shape with a certain radius of curvature, so it can slide along the generatrix direction of the tapered inner peripheral surface 33c of the punch holder 33. In order to reduce the interference when the pair of split forming punches 30 are reduced in diameter and stabilize the abutting state, the axial area of ​​the split forming punch 30 on one side where the convex portion 30a is provided is formed parallel to the axial direction.

[0075] like Fig. 9A As shown, the convex portion 30a corresponding to the concave portion of the ball circulation groove 20 is formed in an S shape, and the center line C1 of both ends is formed to be smoothly connected to the center line C5 of the ball rolling groove 5a. Fig. 9B As shown in FIG. 1 , the cross-sectional shape of the EE line of the convex portion 30a is formed into an arc shape or a pointed arch shape. Fig. 9C As shown, when the F direction Figure 8B When the split forming punch 30 is viewed from the top, the circumferential shape of the protrusion 30a formed by protruding from the outer peripheral surface of the split forming punch 30 can be understood. The central part of the circumference of the protrusion 30a is transferred to the deeper part of the ball circulation groove 20, such as Figure 3 As shown, the balls 9 can pass over the threaded ridges 3 b of the screw shaft 3 .

[0076] Fig.10 A modification of the split forming punch 30 is shown. In this modification, a plurality of (two) convex portions 30a corresponding to the concave portions of the ball circulation groove 20 are formed. The number of convex portions 30a of the split forming punch 30 is an appropriate number according to the design specifications of the ball screw. The other structures of the split forming punch 30 are the same as those described in Figures 8 and 9, so repeated descriptions are omitted.

[0077] Next, if Fig. 11B As shown in FIG. 1 , the punch base 31 is a rod-shaped component composed of a tapered outer peripheral surface 31b on the left side (bottom side) of the figure and a straight small-diameter outer peripheral surface 31c. A V-shaped tapered guide surface 31a is formed on the tapered outer peripheral surface 31b and the straight small-diameter outer peripheral surface 31c. As described above, the V-shaped side surface 30c (see FIG. 1 ) of the split forming punch 30 is slidably guided on the V-shaped tapered guide surface 31a of the punch base 31. Figure 8B , Figure 8C ).like Fig.11A and Fig. 11C As shown, a pair of V-shaped tapered guide surfaces 31 a are formed to face each other in the radial direction of the punch base 31 .

[0078] As Fig. 11B The longitudinal section of the GG line Fig.11E As shown, the bottom 31d of the pair of V-shaped tapered guide surfaces 31a is inclined so that the radial distance becomes narrower toward the end side of the straight small-diameter outer peripheral surface 31c. As a result, the split forming punch 30 moves relative to the punch base 31 in the axial direction, so that the split forming punch can be reduced in diameter. Fig.11D Show Fig.11E The tapered outer peripheral surface 31b of the punch base 31 is fitted and fixed to the Fig. 12B The punch holder 33 shown has a tapered inner peripheral surface 33c.

[0079] like Fig. 12B As shown, the punch holder 33 is a conical cylindrical body. A conical inner peripheral surface 33c is formed on the inner periphery of the punch holder 33, and an end surface 33b for limiting the flow of the blank M in the axial direction and a phase reference S (see Figure 6B The concave molding surface 33a and the end surface 33b forming the phase reference S are as follows: Fig. 12A The cross-sectional view of line II Fig. 12C shown.

[0080] Finally, the ironing step of the ironing method for the ball screw nut according to the present embodiment will be described in detail with reference to FIG. 13 . Fig.13A Shows the state where the blank is set, Fig. 13B Shows the state just before the ironing and drawing process. Fig. 13C Shows the start of ironing and drawing. Fig.13D Shows the end state of ironing and drawing processing. Fig.13E The state of separating the forming punch from the raw material for the nut is shown. Fig.13F The discharge state of the raw material for nuts is shown.

[0081] like Fig.13A As shown in the figure, the drawing die 32 and the upper surface restraining die 34 retreat upward, and the split forming punch 30 moves upward relative to the punch base 31. When the split forming punch 30 moves upward relative to the punch base 31, the split forming punch 30 becomes a state of reduced diameter. In this state, the cylindrical blank M is externally fitted to the split forming punch 30 and is arranged on the punch holder 33.

[0082] Afterwards, if Fig. 13B As shown, the drawing die 32 and the upper surface restraining die 34 are lowered, the upper surface restraining die 34 abuts against the split forming punch 30, and the split forming punch 30 moves relative to the punch base 31 along the inclined surface of the punch base 31. The split forming punch 30 moves along the inclined surface of the punch base 31 and expands to a predetermined radial dimension. In this state, as shown in FIG. Fig. 13C As shown, the ironing and drawing process begins.

[0083] like Fig.13D As shown, when the drawing die 32 is lowered, the outer peripheral surface of the blank M is thinned and drawn by the tapered inner peripheral surface 32b of the drawing die 32, and the blank M is subjected to a drawing action inward in the radial direction and a flow action axially downward. The blank M is reduced in diameter due to the drawing action, and the ball circulation groove 20 is transferred to the inner peripheral surface of the blank M through the convex portion 30a of the split forming punch 30. In addition, the flow action of the blank M in the axial direction is limited by the punch retainer 33, but a concave forming surface 33a that forms a phase reference is formed on a portion of the punch retainer 33, and a portion of the material subjected to the flow action axially downward flows toward the concave forming surface 33a, forming a phase reference S for positioning in the phase direction in the rolling groove forming process (refer to Figure 6B ). In this way, the ball circulation groove 20 and the phase reference S are formed at the same time.

[0084] like Fig.13E As shown, when the drawing die 32 is raised, the nut raw material 5" formed with the ball circulation groove 20 is raised together with the drawing die 32 while being embedded in the drawing die 32. In addition, the convex portion 30a of the split forming punch 30 is engaged with the ball circulation groove 20 of the nut raw material 5", and thus rises together with the nut raw material 5". When the split forming punch 30 rises, it rises along the inclined surfaces of the punch retainer 33 and the punch base 31, and thus moves radially inward relative to the nut raw material 5". The convex portion 30a of the split forming punch 30 is disengaged from the ball circulation groove 20 of the nut raw material 5", and the nut raw material 5" can be removed from the split forming punch 30. Fig.13F As shown, the upper surface restraining die 34 descends, and the nut raw material 5" is discharged from the drawing die 32.

[0085] The rolling groove forming step shown in FIG. 7 described above can be performed using the phase reference S formed by the ironing method of the ball screw nut according to the present embodiment.

[0086] According to the ironing and drawing method of the ball screw nut of the present embodiment, the ball circulation groove can be formed with high precision. In addition, when the ball circulation groove and the phase reference are formed simultaneously by ironing and drawing, the phase shift between the ball circulation groove and the phase reference can be suppressed, and a high-precision ball screw nut can be realized. In addition, since the inner die composed of the split forming punch, the punch base, and the punch retaining frame is set as a high-rigidity split type structure capable of reducing the diameter, in addition to being able to form the ball circulation groove with high precision, it is also advantageous in terms of die life.

[0087] The present invention is not limited to the above-described embodiments, and can be implemented in various forms without departing from the spirit of the present invention. The scope of the present invention is indicated by the claims, and includes all modifications within the meaning and scope of the equivalents described in the claims.

[0088] Description of symbols

[0089] 1: ball screw; 3: screw shaft; 3a: thread groove, ball rolling groove; 5: nut for ball screw; 5': raw material for nut; 5": raw material for nut; 5a: thread groove, ball rolling groove; 7: ball rolling path; 9: ball; 11: ball circulation path; 20: ball circulation groove; 30: split forming punch; 30a: convex part; 31: punch base; 32: drawing die; 33: punch retainer; 33a: forming surface; 34: upper surface constraint die; M: blank; S: phase reference.

Claims

1. A method for manufacturing a nut for a ball screw, the ball screw comprising: A screw shaft having a spiral ball rolling groove formed on its outer peripheral surface; a nut having a spiral ball rolling groove formed on an inner peripheral surface thereof and facing the ball rolling groove of the screw shaft; and a plurality of balls, the plurality of balls being arranged in a ball rolling path formed by the two ball rolling grooves; The nut has a ball circulation groove on the inner peripheral surface for returning the ball from the end point to the starting point of the ball rolling path. It is characterized in that In the circulation groove forming step of forming the ball circulation groove, the ball circulation groove and the phase reference are simultaneously formed on the blank of the nut by plastic working. The rolling groove forming step of forming the ball rolling groove is performed using the phase reference.

2. The method for manufacturing a ball screw nut according to claim 1, It is characterized in that The plastic working for simultaneously forming the ball circulation groove and the phase reference in the circulation groove forming step is ironing and drawing.

3. A method for thinning and drawing a nut for a ball screw, the ball screw comprising: A screw shaft having a spiral ball rolling groove formed on its outer peripheral surface; a nut having a spiral ball rolling groove formed on an inner peripheral surface thereof and facing the ball rolling groove of the screw shaft; and a plurality of balls, the plurality of balls being arranged in a ball rolling path formed by the two ball rolling grooves; The nut has a ball circulation groove on the inner peripheral surface for returning the ball from the end point to the starting point of the ball rolling path. It is characterized in that The die used for the thinning and drawing process comprises: a split forming punch formed with a convex portion corresponding to the concave portion of the ball circulation groove; A punch base, which defines the position of the split forming punch and bears the load acting on the split forming punch; a drawing die for reducing the outer diameter of the blank by thinning and drawing the outer peripheral surface of the blank of the nut; and a punch holder that bears the axial load acting on the blank when the outer peripheral surface of the blank is thinned and deep drawn, and limits the position of the split forming punch, The ball circulation groove is formed by reducing the diameter of the blank by the drawing die.

4. The method for thinning and drawing a nut for a ball screw according to claim 3, It is characterized in that The punch holder has a molding surface corresponding to a phase reference when the ball rolling groove is machined, and the ball circulation groove and the phase reference are simultaneously formed by reducing the diameter of the blank by the drawing die.

5. The method for thinning and drawing a nut for a ball screw according to claim 3 or 4, It is characterized in that The die used for the ironing process further includes an upper surface constraining die, and the upper surface of the blank is constrained by the upper surface constraining die, thereby suppressing deformation in the axial direction.

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