Finishing grinding tool, method for grinding female screw member, and female screw member

Abstract

To provide a finish grinding tool which can improve productivity of a female screw member, and can ensure good property of a female screw member.SOLUTION: A finish grinding tool 3 comprises a thread part 5 in which a thread is spirally formed on an outer peripheral surface, and groove parts which are formed so as to extend in an axial direction at a plurality of locations in a circumferential direction of the outer peripheral surface. The screw part has at least a taper part 7 in which an outer diameter of the thread becomes larger as approaching a rear side in the axial direction, a flank angle of the thread is not provided in the whole area in the axial direction, and abrasive grains are fixed over the entire axial length of the thread.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a female screw member having a female screw portion formed with a thread spirally on an inner peripheral surface, a finishing grinding tool for performing finishing grinding on the female screw member, and a grinding method for the female screw member.

Background Art

[0002] A feed screw device includes a screw shaft having a male screw portion on an outer peripheral surface and a nut having a female screw portion that engages with the male screw portion on an inner peripheral surface. When the feed screw device is used, the screw shaft and the nut are relatively displaced in the axial direction by relatively rotating the screw shaft and the nut.

[0003] The female screw portion of the nut is formed by performing cutting on an inner peripheral surface with a tool called a tap. FIGS. 7 and 8 show a tap described in Japanese Utility Model Laid-Open No. 63-140323 (Patent Document 1). The tap 100 includes a screw portion 102 formed with a thread 101 spirally on an outer peripheral surface, and groove portions 103 formed so as to extend in the axial direction at a plurality of locations in the circumferential direction on the outer peripheral surface (in the illustrated example, four equally spaced locations in the circumferential direction).

[0004] The screw portion 102 is disposed at an end portion on the front side in the axial direction (the left side in FIG. 7), and has a biting portion 104 in which the outer diameter of the thread 101 (the diameter of the circumscribed circle of the thread 101 centered on the central axis O of the tap 100) increases toward the rear side in the axial direction (the right side in FIG. 7), and a full thread portion 105 disposed on the rear side in the axial direction of the biting portion 104 and having a constant outer diameter of the thread 101 over the axial direction.

[0005] Note that the front side in the axial direction is the front side in the insertion direction of the tap 100 into the nut when forming the female screw portion on the inner peripheral surface of the nut, which is the left side in FIG. 7, and the rear side in the axial direction is the rear side in the insertion direction into the nut, which is the right side in FIG. 7.

[0006] The tap 100 has lands 106 between adjacent groove portions 103 in the circumferential direction. In each of the lands 106, a scooping surface 107 is provided on the circumferentially front side surface of the thread 101, and a cutting edge 108 is provided at the circumferentially front end of the peak of the thread 101 (the connection portion between the scooping surface 107 and the outer peripheral surface of the thread 101). Further, in each of the lands 106, a relief angle (secondary relief) is provided on the thread 101. In other words, the relief angle (secondary angle) θ of the thread 101 is made larger than 0°. That is, the distance d between the central axis O of the tap 100 and the peak of the thread 101 becomes shorter as it goes toward the circumferentially rear side from the cutting edge 108.

[0007] Note that the illustrated example shows a tap 100 for forming a right-handed thread. The circumferentially front side means the front side in the rotation direction when the tap 100 is inserted into the nut while relatively rotating the tap 100 with respect to the nut to form an internal thread portion on the inner peripheral surface of the nut, which is the counterclockwise front side in FIG. 8, and the circumferentially rear side means the rear side in the rotation direction when the tap 100 is inserted into the nut while relatively rotating the tap 100 with respect to the nut, which is the counterclockwise rear side in FIG. 8.

[0008] Furthermore, the tap 100 is provided with an abrasive layer on the surface of the thread 101 in the complete thread portion 105 of the threaded portion 102. That is, abrasive grains are fixed to the surface of the thread 101 in the complete thread portion 105.

[0009] When forming an internal thread portion on the inner peripheral surface of the nut with the tap 100, the tap 100 is inserted radially inward of the nut while rotating it in the counterclockwise direction in FIG. 8 with the biting portion 104 at the front. Thereby, the inner peripheral surface of the nut is cut by the cutting edge 108 in the biting portion 104, and further, an internal thread portion is formed by grinding with the abrasive layer provided on the surface of the thread 101 in the complete thread portion 105. Note that the cutting chips and grinding chips generated by the machining are discharged through the groove portion 103.

[0010] According to the tap 100, cutting for forming a thread (thread groove) on the inner peripheral surface of the nut and grinding for improving the surface roughness can be performed within the same process, and the manufacturing cost of the nut can be reduced.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0012] The tap 100 described in Japanese Utility Model Laid-Open No. 63-140323 has room for improvement in terms of improving the productivity of the nut. That is, in the tap 100 described in Japanese Utility Model Laid-Open No. 63-140323, a relief angle is provided for the thread 101 at each of the lands 106. Therefore, when forming a female thread portion on the inner peripheral surface of the nut, among the grinding wheel layers provided on the surface of the thread 101 in the complete thread portion 105, the portion that contacts the flank surface of the thread constituting the female thread portion is limited to the portion covering the front end surface in the circumferential direction of the thread 101 at each of the lands 106. For this reason, the abrasive grains fixed to the front end surface in the circumferential direction of the thread 101 are likely to fall off, and the grinding performance of the tap 100 is likely to deteriorate. When the grinding performance of the tap 100 deteriorates, maintenance such as replacing the tap 100 becomes necessary, increasing the cost and working time.

[0013] Moreover, in the method of using the tap 100 described in Japanese Utility Model Publication No. 63-140323, the cutting process for forming a thread on the inner peripheral surface of the nut and the grinding process for improving the surface roughness are performed in the same process (so-called one chuck). That is, the inner peripheral surface of the nut is cut by the cutting edge 108 at the biting portion 104 to form a thread on the inner peripheral surface of the nut. When cutting the inner peripheral surface of the nut with the cutting edge 108, among the cutting edges 108, the side edge on the front side in the axial direction bites into the inner peripheral surface of the nut more easily than the side edge on the rear side in the axial direction. If the side edge on the front side in the axial direction of the cutting edge 108 bites excessively into the inner peripheral surface of the nut, due to the reaction, the cutting edge 108 elastically deforms so as to be pushed back to the rear side in the axial direction. When such elastic deformation repeatedly occurs and the tap 100 vibrates, there is a possibility that the abrasive grains fixed to the surface of the thread 101 in the complete thread portion 105 are likely to fall off. Moreover, when the tap 100 vibrates and the biting and retracting of the cutting edge 108 with respect to the flank surface of the female thread portion are repeated, problems such as the occurrence of warping (periodic height difference) on the flank surface of the thread constituting the female thread portion or the inability to sufficiently ensure the accuracy of the female thread portion may occur.

[0014] In view of the above circumstances, an object of the present invention is to realize a female thread member capable of ensuring good properties of the female thread portion, a finishing grinding tool capable of improving the productivity of the female thread member, and a method of grinding the female thread member using the finishing grinding tool.

Means for Solving the Problems

[0015] The finishing grinding tool of the present invention is a thread portion formed by spirally forming a thread on the outer peripheral surface, and groove portions formed so as to extend in the axial direction at a plurality of locations in the circumferential direction of the outer peripheral surface. It is provided with.

[0016] The thread portion has at least a tapered portion in which the outer diameter of the thread (the diameter of the circumscribed circle of the thread centered on the central axis of the finishing grinding tool) increases as it goes toward the rear side in the axial direction, and a relief angle (secondary relief) is not provided on the flank surface of the thread over the entire axial range.

[0017] In the finishing grinding tool of the present invention, abrasive grains are fixed over the entire axial length of the thread portion.

[0018] In the finishing grinding tool of the present invention, the effective diameter in the tapered portion can be increased as it goes toward the rear side in the axial direction.

[0019] In the finishing grinding tool of the present invention, the thread portion can be arranged adjacent to the rear side in the axial direction of the tapered portion and can have a main grinding portion in which the outer diameter of the thread does not change over the axial direction.

[0020] The finishing grinding tool of the present invention can have lands between the groove portions, and each of the lands can have a rake face on the circumferential side surface of the thread. In this case, the rake angle of the rake face can be set to 0°. Alternatively, in each of the lands, the rake faces provided on the side surfaces on both circumferential sides of the thread can be symmetric with respect to the circumferential direction, and the rake angle of the rake face can be -10° or more and 10° or less.

[0021] The finishing grinding tool of the present invention can be provided with a guide portion that is arranged on the front side in the axial direction of the thread portion and has a constant outer diameter with respect to the axial direction.

[0022] The thread portion can be arranged on the rear side in the axial direction of the tapered portion and can have a back tapered portion in which the outer diameter of the thread decreases as it goes toward the rear side in the axial direction.

[0023] The finishing grinding tool of the present invention can be provided with a small-diameter cylindrical portion that is arranged on the rear side in the axial direction of the back tapered portion and has a constant outer diameter with respect to the axial direction.

[0024] The grinding method of the female screw member of the present invention is a method of performing finish grinding on the female screw portion formed on the inner peripheral surface of the female screw member using a finish grinding tool of the present invention, which is a finish grinding tool provided with a back taper portion.

[0025] In the grinding method of the female screw member of the present invention, while relatively rotating the finish grinding tool and the female screw member, the finish grinding tool is inserted into the inner side in the radial direction of the female screw member from the front side in the axial direction until the back taper portion is located on the inner side in the radial direction of the female screw member. Then, while relatively rotating the finish grinding tool and the female screw member in the reverse direction, the finish grinding tool is pulled out from the inner side in the radial direction of the female screw member to perform finish grinding on the female screw portion.

[0026] The female screw member of the present invention includes a female screw portion formed by spirally forming threads on the inner peripheral surface. The female screw portion has grinding streaks along the forming direction of the thread on the flank surface of the thread.

Effect of the Invention

[0027] According to the female screw member of the present invention, good properties of the female screw portion can be ensured. Further, according to the finish grinding tool and the grinding method of the female screw member of the present invention, the productivity of the female screw member of the present invention can be improved.

Brief Description of the Drawings

[0028]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0029] [First Example of Embodiment] The first example of the embodiment of the present invention will be described with reference to Figs. 1 to 4(B)(b). In this example, a finish grinding is performed on the female thread portion 2 provided on the inner peripheral surface of the nut 1, which is a female thread member constituting a sliding feed screw device, by the finish grinding tool of the present invention.

[0030] The finish grinding tool 3 of this example includes a thread portion 5 formed with a thread 4 spirally on the outer peripheral surface, and groove portions 6 formed to extend in the axial direction at a plurality of circumferential positions on the outer peripheral surface.

[0031] The thread portion 5 has a tapered portion 7, a main grinding portion 8, and a back tapered portion 9.

[0032] The tapered portion 7 is provided at the axially front side portion of the threaded portion 5 (the left side portion in FIGS. 1 and 3), and the outer diameter (nominal diameter) of the thread 4 increases toward the axially rear side (the right side in FIGS. 1 and 3). In this example, in the tapered portion 7, the height of the thread 4 increases toward the axially rear side (the difference between the outer diameter and the root diameter increases). That is, the height of the thread 4 at the axially rear side end of the tapered portion 7 is the same as the height of the thread 4 in the main grinding portion 8. On the other hand, at the axially front side end of the tapered portion 7, the thread 4 is interrupted. In the illustrated example, the axially front side end of the tapered portion 7 is constituted by a flat surface portion orthogonal to the central axis of the finishing grinding tool 3. However, when implementing the present invention, the axially front side end of the tapered portion may be configured to include an interrupted portion along the direction of the lead angle.

[0033] The main grinding portion 8 is provided at the axially intermediate portion of the threaded portion 5, and the outer diameter of the thread 4 does not change axially. In other words, in the main grinding portion 8, the height of the thread 4 is constant axially.

[0034] The back tapered portion 9 is provided at the axially rear side portion of the threaded portion 5, and the outer diameter of the thread 4 decreases toward the axially rear side. In this example, in the back tapered portion 9, the height of the thread 4 decreases toward the axially rear side (the difference between the outer diameter and the root diameter decreases). That is, the height of the thread 4 at the axially front side end of the back tapered portion 9 is the same as the height of the thread 4 in the main grinding portion 8. On the other hand, at the axially rear side end of the back tapered portion 9, the thread 4 is interrupted. In the illustrated example, the axially rear side end of the back tapered portion 9 is constituted by a flat surface portion orthogonal to the central axis of the finishing grinding tool 3. However, when implementing the present invention, the axially rear side end of the back tapered portion may be configured to include an interrupted portion along the direction of the lead angle.

[0035] The axial dimensions (lengths) of the taper portion 7, main grinding portion 8, and back taper portion 9 are appropriately determined according to the workpiece, that is, the female screw member, and the processing device (grinding machine). When the nut 1 constituting the sliding feed screw device is the processing object as in this example, it can be regulated, for example, as follows.

[0036] Axial dimension L of main grinding part 8 8 is the axial dimension L of nut 1 1 0.5 times or more and 2.0 times or less (0.5L 1 ≦L 8 ≦2L 1 The axial dimension L of the main grinding portion 8 can be set as follows: 8 is the axial dimension L of nut 1 1 Shorter than 0.5 times (L 8 <0.5L 1 ), there is a possibility that the flank surface of the female thread portion 2 of the nut 1 cannot be sufficiently ground. 8 is the axial dimension L of nut 1 1 It was made longer than 2.0 times (L 8 >2L 1 ), the effect of improving the surface roughness of the flank surface of the female thread portion 2 cannot be further obtained. However, the axial dimension L 8 The axial dimension L of nut 1 1 It can also be longer than 2.0 times (L 8 >2L 1 ).

[0037] Axial dimension L of tapered portion 7 7 is the axial dimension L of the main grinding part 8 8 1.0 to 3.0 times (L 8 ≦L 7 ≦3L 8 ), preferably 1.5 times or more and 2.5 times or less (1.5L 8 ≦L 7 ≦2.5L 8 The axial dimension L of the tapered portion 7 can be set as follows: 7 The axial dimension L of the main grinding part 8 8 Shorter than (L 7 <L 8) And, as will be described later, at the initial stage of the process of finish grinding the female thread portion 2 of the nut 1 using the finish grinding tool 3, the torque required to rotate the finish grinding tool 3 may increase unnecessarily. The axial dimension L of the tapered portion 7 7 is more than three times the axial dimension L of the main grinding portion 8 8 (L 7 > 3L 8 ) and the axial dimension of the finish grinding tool 3 may increase unnecessarily.

[0038] The axial dimension L of the back taper portion 9 9 is set to be not less than 0.5 times and not more than 1.5 times the axial dimension L of the main grinding portion 8 (0.5L 8 ≦ L 8 ≦ 1.5L 9 8 ). The axial dimension L of the back taper portion 9 9 If it is shorter than 0.5 times the axial dimension L of the main grinding portion 8 8 (L 9 <0.5L 8 9 ), as will be described later, when pulling out the finish grinding tool 3 from the inner side in the radial direction of the nut 1, the torque required to rotate the finish grinding tool 3 may increase unnecessarily. The axial dimension L of the back taper portion 9 9 If it is longer than 1.5 times the axial dimension L of the main grinding portion 8 8 (L 9 > 1.5L 8 ), the axial dimension of the finish grinding tool 3 may increase unnecessarily. Incidentally, when the axial dimension L of the main grinding portion 8 8 is 3.0 times or more the axial dimension L of the nut 1 1 , the back taper portion 9 can be omitted.

[0039] The thread portion 5 includes a thread 4 having a flank surface (tooth surface) and a crest (tip surface), and a bottom valley existing between the threads 4 in the axial direction. In this example, a relief angle (secondary relief) is not provided on the flank surface of the thread 4 over the entire axial range of the thread portion 5, that is, the relief angle (secondary angle) θ is set to 0°. Therefore, as shown in FIG. 2, the crest of the thread 4 in the main grinding portion 8 is located on the same circumference centered on the central axis O in a cross section orthogonal to the central axis O of the finishing grinding tool 3.

[0040] Also, abrasive grains are fixed over the entire axial length of the thread portion 5. Specifically, in this example, over the entire axial range from the front end portion in the axial direction to the rear end portion in the axial direction of the thread portion 5, the entire surface of the thread portion 5, that is, the flank surface and the crest of the thread 4, and the entire bottom valley, abrasive grains are fixed. That is, the entire axial range of the surface of the thread portion 5 is used as a grinding surface for grinding the female thread portion 2 of the nut 1. As the abrasive grains, for example, diamond, cubic boron nitride (CBN), boron carbide (B 4 C), silica (SiO 2 ), tungsten carbide (WC), alumina (Al 2 O 3 ) and other high-hardness abrasive grains can be used. Also, as a method of fixing the abrasive grains to the surface of the thread portion 5, for example, electroplating, resin, a metal bond obtained by mixing metal powder and abrasive grains and sintering them, etc. can be adopted. Alternatively, the metal material constituting the thread portion 5 and the abrasive grains can be bonded by a binder such as vitrified.

[0041] The groove portion 6 is formed so as to extend in the axial direction at a plurality of circumferential positions on the outer peripheral surface of the finish grinding tool 3. In this example, the groove portion 6 is formed in parallel with the axial direction at four equally spaced circumferential positions in the axial range from the front end portion in the axial direction of the outer peripheral surface of the finish grinding tool 3 to the axial intermediate portion of the small-diameter cylindrical portion 10 described later. That is, the groove portion 6 is formed so as to cross the thread portion 5 in the axial direction. Note that the groove portion 6 can also be formed so as to extend in a direction orthogonal to the lead angle at the portion of the thread flank 4 where the groove portion 6 crosses. However, when the outer diameter of the thread portion 5 is small (about 10 mm or less in outer diameter), the groove portion 6 is preferably formed parallel to the axial direction. Also, the number of the groove portions 6 can be three or less or five or more. Note that FIGS. 1 and 3 show the groove portion 6 omitted.

[0042] Also, in this example, by regulating the circumferential width W 6 and the radial depth D 6 of the groove portion 6, the total volume of the four groove portions 6 is made smaller than the total volume of the thread flank 4. Specifically, the circumferential width W 6 of the groove portion 6 is set to be 1 / 50 or more and 1 / 2 or less of the sum (W 6 +W 11 ) of the circumferential width W 6 of the groove portion 6 and the circumferential width W 11 of the land 11 existing between the circumferentially adjacent groove portions 6 ((W 6 +W 11 ) / 50≦W 6 ≦(W 6 +W 11 ), preferably 1 / 10 or more and 1 / 8 or less ((W 6 +W 11 ) / 10≦W 6 ≦(W 6 +W 11 ), and the radial depth D 6 of the groove portion 6 is set to be 1.1 times or more and 2.5 times or less of the height H 4 of the thread flank 4 (1.1H 4 ≦D 6 ≦2.5H 4 ), preferably 1.3 times or more and 1.7 times or less (1.3H 4 ≦D 6 ≦1.7H 4) is adopted. However, the total volume of the groove portion 6 is preferably 1.5 times or more of the total volume of the abrasive grains fixed to the surface of the threaded portion 5.

[0043] Further, the finish grinding tool 3 has a rake face 14 on the side surfaces on both circumferential sides of the thread 4 in each of the lands 11, and the rake angle φ of the rake face 14 is set to 0°. In other words, no rake angle φ is provided on the rake face 14. For this reason, in this example, the inner surfaces on both circumferential sides of the groove portion 6 are constituted by flat surfaces parallel to each other.

[0044] The finish grinding tool 3 of this example further includes a guide portion 12, a small-diameter cylindrical portion 10, and a shank portion 13.

[0045] The guide portion 12 is disposed on the front side in the axial direction of the threaded portion 5 (the front side in the axial direction of the tapered portion 7), and the outer diameter does not change in the axial direction. That is, the portion of the outer peripheral surface of the guide portion 12 that deviates from the groove portion 6 in the circumferential direction exists on the same cylindrical surface.

[0046] In this example, the axial dimension L of the guide portion 12 12 is set to be equal to or greater than the inner diameter d of the nut 1 1 . Further, the outer diameter of the guide portion 12 is made substantially the same as the inner diameter d of the nut 1 1 , that is, the diameter of the inscribed circle of the thread 2a constituting the female threaded portion 2, so that the guide portion 12 can be fitted into the nut 1 with a small clearance fit. Specifically, the outer diameter of the guide portion 12 is made smaller than the inner diameter d of the nut 1 1 and is made as large as possible within the range where the outer peripheral surface of the guide portion 12 does not interfere with the crest of the thread 2a when the guide portion 12 is inserted into and removed from the nut 1.

[0047] The small-diameter cylindrical portion 10 is disposed on the rear side in the axial direction of the back tapered portion 9, and the outer diameter does not change in the axial direction. That is, the portion of the outer peripheral surface of the small-diameter cylindrical portion 10 that deviates from the groove portion 6 in the circumferential direction exists on the same cylindrical surface. The outer diameter of the small-diameter cylindrical portion 10 is made substantially the same as the root diameter of the threaded portion 5.

[0048] The shank portion 13 is provided at the axially rear end of the finish grinding tool 3 and has a circular cross-sectional shape. The shank portion 13 is a part for supporting the finish grinding tool 3 on a grinding machine. That is, the grinding machine supports the finish grinding tool 3 by gripping the shank portion 13 with a chuck.

[0049] The finish grinding tool 3 as described above is obtained, for example, by subjecting a cylindrical material made of metal to cutting or forging, and then performing heat treatment such as quenching, tempering, and cryogenic treatment as necessary to obtain an intermediate member, and then subjecting the intermediate member to grinding or the like to adjust the shape of the threaded portion 5, and further fixing abrasive grains to the surface of the threaded portion 5. In this example, the threaded portion 5 is formed by performing cutting or forging so that the effective diameter is constant over the axial direction of the portion where the threaded portion 5 is to be formed, performing heat treatment and grinding, and then performing grinding on the crest of each thread 4 of the portion where the tapered portion 7 and the back tapered portion 9 are to be formed to form the tapered portion 7 and the back tapered portion 9. Alternatively, before performing the grinding, cutting can be performed on the crest of each thread 4 of the portion where the tapered portion 7 and the back tapered portion 9 are to be formed. In any method, the root diameter of the threaded portion 5 is constant over the axial direction. However, as in the second example of the embodiment described later, the effective diameter of the threaded portion 5 in the tapered portion 7 and the back tapered portion 9 can also be changed with respect to the axial direction.

[0050] An example of a method for performing finish grinding on the female threaded portion 2 of the nut 1 using the finish grinding tool 3 of this example will be described with reference to FIG. 3.

[0051] The nut 1, which is the workpiece, is provided with an internal thread portion 2 having a thread 2a spirally formed on its inner peripheral surface. The nut 1 is obtained by subjecting the inner peripheral surface of a cylindrical workpiece to cutting or plastic working for forming the thread 2a to form the internal thread portion 2. As for the specific methods of cutting or roll forging for forming the thread 2a on the inner peripheral surface of the workpiece, various conventionally known methods can be adopted. In any case, at the stage before forming the internal thread portion 2 and performing finish grinding, as shown in Fig. 4(A), radial streaks are formed on the flank surface of the thread 2a constituting the internal thread portion 2, and the surface of the flank surface is rough (the surface roughness is large). Incidentally, when the thread 2a is formed by roll forging, the smaller the outer diameter of the thread 2a and the larger the lead angle, the faster the moving speed of the tool and the larger the undulation. Therefore, when the tool blade reciprocates to form the thread 2a, radial streaks are likely to be formed. On the other hand, when the outer diameter of the thread 2a is large and the lead angle is small, radial streaks are less likely to be formed. However, when the thread 2a is formed by cutting, since the cutting tool and the workpiece are deflected, undulation tends to remain on the flank surface of the thread 2a regardless of the outer diameter and lead angle of the thread 2a.

[0052] When performing finish grinding on the female thread portion 2 of the nut 1, first, the nut 1 is supported (floating support) by a fixed vise on the grinding machine so as to allow axial displacement and prevent rotation. Next, as shown by the solid line in FIG. 3, the guide portion 12 of the finish grinding tool 3 is inserted inside the nut 1 in the radial direction. Thereby, the axial alignment between the nut 1 and the finish grinding tool 3 is performed. Next, the finish grinding tool 3 is rotated in a predetermined direction (the direction of arrow α in FIG. 3 (clockwise)). Then, the finish grinding tool 3 is slightly displaced toward the front side in the axial direction, and the thread portion 5 of the finish grinding tool 3 and the female thread portion 2 of the nut 1 are slightly screwed together. Then, based on the screwing together of the thread portion 5 of the finish grinding tool 3 and the female thread portion 2 of the nut 1, while the nut 1 moves toward the rear side in the axial direction with respect to the thread portion 5, the surface of the female thread portion 2 is ground by the surface of the thread portion 5. Note that the grinding chips generated when grinding the surface of the female thread portion 2 are discharged to the outside through the groove portion 6. And, as shown by the two-dot chain line in FIG. 3, the position of the nut 1 with respect to the thread portion 5 is moved toward the rear side in the axial direction until the end portion on the front side in the axial direction of the nut 1 is located around the back taper portion 9 of the thread portion 5. When the nut 1 moves until it is located around the back taper portion 9, as a gap is generated between the female thread portion 2 of the nut 1 and the thread portion 5 of the finish grinding tool 3, the grinding chips existing between the female thread portion 2 and the thread portion 5 are easily discharged.

[0053] Thereafter, the finish grinding tool 3 is rotated in the direction opposite to the predetermined direction (the direction of arrow β in FIG. 3 (counterclockwise)). Then, based on the screwing together of the thread portion 5 and the female thread portion 2, while the nut 1 moves toward the front side in the axial direction with respect to the thread portion 5, the surface of the female thread portion 2 is ground by the surface of the thread portion 5. The grinding chips generated when grinding the surface of the female thread portion 2 are discharged to the outside through the groove portion 6. Thereafter, the finish grinding tool 3 is further rotated in the direction opposite to the predetermined direction to unscrew the thread portion 5 and the female thread portion 2, and the finish grinding tool 3 is pulled out from inside the nut 1 in the radial direction.

[0054] In the above manner, finish grinding is performed on the female thread portion 2 of the nut 1 using the finish grinding tool 3. The female thread portion 2 of the nut 1 thus obtained has grinding streaks along the forming direction of the thread crest 2a on the flank surface of the thread crest 2a, as shown in Fig. 4(B).

[0055] When performing finish grinding on the female thread portion 2 of the nut 1 using the finish grinding tool 3, the grinding of the surface of the female thread portion 2, particularly the grinding of the bottom of the female thread portion 2, is mainly performed by the main grinding portion 8 among the thread portions 5 of the finish grinding tool 3. Note that the finish grinding by the finish grinding tool 3 is not limited to the above method and can be changed as appropriate.

[0056] In the grinding method of this example, the finish grinding for grinding the surface of the female thread portion 2 to improve the surface roughness is performed in a separate process (independently) from the process of forming the female thread portion 2 by performing cutting or forging on the inner peripheral surface of the nut 1. Therefore, in the grinding method of this example, like the case of using the tap 100 described in Japanese Utility Model Laid-Open No. 63-140323, when cutting with the cutting edge 108, the front side edge in the axial direction of the cutting edge 108 bites into the inner peripheral surface of the nut and the cutting edge 108 elastically deforms. to Based on this, problems such as the tap 100 vibrating do not occur. Therefore, according to the grinding method of this example, problems such as the abrasive grains fixed to the surface of the female thread portion 2 falling off are less likely to occur, the cost and working time required for the maintenance of the finish grinding tool 3 can be reduced, and the productivity of the nut 1 can be improved.

[0057] Further, since the finishing grinding tool 3 of this example does not cause problems such as the generation of vibrations associated with cutting by the cutting edge, the flank surface of the thread 4 constituting the threaded portion 5 can be stably brought into contact (sliding contact) with the flank surface of the thread 2a constituting the female threaded portion 2. Further, in this example, abrasive grains are fixed to the entire surface of the threaded portion 5, that is, the flank surface and the crest of the thread 4, and the entire bottom of the valley, in the entire axial range from the front end in the axial direction to the rear end in the axial direction of the threaded portion 5. Therefore, in the method of using the finishing grinding tool 3 of this example, during finishing grinding, it is possible to sufficiently ensure the contact amount (sliding contact length) between the portion of the surface of the threaded portion 5 to which the abrasive grains are fixed and the surface of the female threaded portion 2 of the nut 1, and it is easy to improve the surface roughness of the flank surface and the crest of the thread 2a constituting the female threaded portion 2, and it is easy to ensure good shape accuracy of the thread 2a.

[0058] In the method of using the finishing grinding tool 3 of this example, as shown in FIG. 4(B), grinding streaks are formed on the flank surface of the thread 2a constituting the female threaded portion 2 of the nut 1 after finishing grinding along the forming direction (helical direction) of the thread 2a. In short, the forming direction of the grinding streaks can be set to the sliding contact direction between the flank surface of the thread 2a constituting the female threaded portion 2 of the nut 1 and the flank surface of the thread constituting the male threaded portion of the screw shaft when a feed screw device is configured in combination with the nut 1 and the screw shaft. Also from this surface, the properties of the female threaded portion 2 of the nut 1 can be improved.

[0059] Further, in this example, the finishing grinding for grinding the surface of the female threaded portion 2 to improve the surface roughness is performed in a process separate from the process of forming the female threaded portion 2 by performing cutting or rolling on the inner peripheral surface of the nut 1. Therefore, the grinding chips generated by the finishing grinding with the finishing grinding tool 3 are not so many. For this reason, the total volume of the groove portion 6 can be made smaller than the total volume of the thread 4. That is, the circumferential width W 6 of the groove portion 6 can be kept small. In other words, the circumferential width W 11It can be ensured sufficiently. Also from this aspect, the contact amount of the surface of the thread portion 5 with respect to the surface of the female thread portion 2 of the nut 1 can be ensured, and it is easy to improve the surface roughness of the flank surface and the crest of the thread groove 2a constituting the female thread portion 2, and it is easy to ensure good shape accuracy of the thread groove 2a.

[0060] In the finishing grinding tool 3 of this example, in the entire axial range of the thread portion 5, a relief angle (secondary relief) is not provided on the flank surface of the thread groove 4 constituting the thread portion 5. For this reason, when performing finishing grinding on the female thread portion 2 of the nut 1, the entire circumferential range of the surface of the thread groove 4 can be brought into contact with the surface (flank surface and bottom valley) of the female thread portion 2. In short, according to the finishing grinding tool 3 of this example, problems such as the abrasive grains fixed to the end surface on the front side in the circumferential direction of the thread groove 101 falling off and the grinding performance of the tap 100 decreasing as in the conventional tap 100 (FIGS. 7 and 8) described in Japanese Utility Model Laid-Open No. 63-140323 are less likely to occur. Therefore, it is possible to suppress an increase in the cost and working time required for maintenance of the finishing grinding tool 3, and it is possible to improve the productivity of the nut 1.

[0061] Furthermore, in the finishing grinding tool 3 of this example, since a relief angle is not provided on the flank surface of the thread groove 4 in the entire axial range of the thread portion 5, the cross-sectional shape of the thread groove 4 is constant over the formation direction (helical direction) of the thread groove 4 in the main grinding portion 8 of the thread portion 5. For this reason, regardless of the rotation direction of the finishing grinding tool 3, the contact manner of the surface of the thread groove 4 in the main grinding portion 8 with respect to the surface of the female thread portion 2 can be made the same, and deterioration of the properties of the female thread portion 2 can be prevented.

[0062] Furthermore, in the finishing grinding tool 3 of this example, at each of the lands 11, the rake angle φ of the rake face 14 provided on the side surfaces on both circumferential sides of the thread 4 is set to 0°. Therefore, at each of the lands 11, the way the rake face 14 of the thread 4 contacts the surface of the female thread portion 2 can be made the same regardless of the rotation direction of the finishing grinding tool 3. From this aspect as well, deterioration of the properties of the female thread portion 2 can be prevented. Further, when performing finishing grinding on the female thread portion 2, the entire radial range of the rake face 14 (the side edges on both axial sides) can be brought into contact with the surface of the female thread portion 2 simultaneously. From this aspect as well, shedding of the abrasive grains fixed to the surface of the thread portion 5 can be prevented.

[0063] On the other hand, in the conventional tap 100, at each of the lands 106, the rake angle φ (see FIG. 8) of the rake face 107 provided on the front circumferential surface of the thread 101 is made larger than 0°. Therefore, when the tap 100 is inserted into the nut while relatively rotating the tap 100 with respect to the nut in order to form a female thread portion on the inner circumferential surface of the nut, among the rake face 107 (the side edges on both axial sides), the radially outer portion contacts the surface of the female thread portion formed on the inner circumferential surface of the nut earlier than the radially inner portion. For this reason, there arise problems such that the abrasive grains fixed to the radially outer portion of the rake face 107 are likely to fall off, and the grinding performance by the tap 100 is likely to deteriorate.

[0064] In each of the lands 11, the scoop surfaces 14 provided on the both side surfaces in the circumferential direction of the thread 4 are symmetric with respect to the circumferential direction (symmetric with respect to the plane including the circumferential center position of the thread 4 and the central axis O of the finish grinding tool 3 in each of the lands 11). Specifically, in this example, in each of the lands 11, the scoop angle φ of the scoop surfaces 14 provided on the both side surfaces in the circumferential direction of the thread 4 is set to 0°. However, the scoop angle φ of the scoop surfaces 14 provided on the both side surfaces in the circumferential direction of the thread 4 can also be set in the range of -10° or more and 10° or less. In any case, by making the scoop surfaces 14 provided on the both side surfaces in the circumferential direction of the thread 4 symmetric with respect to the circumferential direction in each of the lands 11, in each of the lands 11, the way of hitting of the scoop surface 14 of the thread 4 against the surface of the female thread portion 2 can be made the same regardless of the rotation direction of the finish grinding tool 3.

[0065] Further, the finish grinding tool 3 of this example has a back taper portion 9 in the axially rear portion of the threaded portion 5, and the outer diameter of the thread 4 becomes smaller as it goes axially rearward. For this reason, it is possible to prevent the torque from becoming unduly large when starting to rotate the finish grinding tool 3 in the direction opposite to the predetermined direction in order to pull out the finish grinding tool 3 from the radially inner side of the nut 1, and the feed of the finish grinding tool 3 can be made smooth. Also from this aspect, the properties of the female thread portion 2 can be improved.

[0066] The finish grinding tool 3 of this example has a guide portion 12 at the axially front end portion. For this reason, by inserting the guide portion 12 into the radially inner side of the nut 1, it is possible to roughly align the nut 1 and the finish grinding tool 3 without screwing the female thread portion 2 of the nut 1 and the threaded portion 5 of the finish grinding tool 3. In short, the rough alignment work between the nut 1 and the finish grinding tool 3 can be facilitated and the work can be made efficient. Further, since the guide portion 12 and the taper portion 7 are connected by a stepped surface facing axially frontward, the threaded portion 5 can be easily started to be screwed with respect to the female thread portion 2 only by rotating the finish grinding tool 3 without particularly searching for the starting point of the threaded portion 5. Such an effect can be remarkably obtained when automating the grinding process of the nut 1 by the finish grinding tool 3.

[0067] Furthermore, in this example, the outer diameter of the guide portion 12 is made substantially the same as the inner diameter d of the nut 1 which is the workpiece. For this reason, it is possible to prevent the inclination of the central axis of the finish grinding tool 3 with respect to the central axis of the nut 1 at the initial stage of finish grinding, and it is possible to prevent the grinding position from shifting at the initial stage of finish grinding. Also from this aspect, it is easy to ensure good shape accuracy of the thread groove 2a constituting the female thread portion 2. 1

[0068] In this example, the method for grinding the female thread member of the present invention has been described for the case where it is applied to the method for grinding a nut constituting a sliding type feed screw device. However, the method for grinding the female thread member of the present invention is not limited to this, and for example, it can also be applied to the method for grinding a ball nut of a ball screw device. Further, a nut manufactured by applying the method for grinding the female thread member of the present invention can be used, for example, as a nut for an electric position adjusting device of a steering wheel provided with a telescopic mechanism for adjusting the front-rear position of the steering wheel and / or a tilt mechanism for adjusting the up-down position of the steering wheel.

[0069] Also, the shape of the thread groove constituting the female thread portion of the female thread member targeted by the present invention is not particularly limited, and for example, various conventionally known shapes such as a triangle, a trapezoid, and a concave arc shape can be adopted. Furthermore, the number of threads of the female thread portion of the female thread member is not particularly limited either.

[0070] When implementing the finish grinding tool of the present invention, the main grinding portion can also be omitted. In this case, a sufficient axial dimension of the tapered portion where the outer diameter of the thread groove increases toward the rear side in the axial direction is ensured. Thereby, even when the grinding allowance of the female thread portion of the workpiece is large, it is possible to suppress a sudden increase in the rotational torque of the finish grinding tool during finish grinding. In this case, the taper angle of the tapered portion (the inclination angle of the line connecting the tops of the thread grooves with respect to the central axis in a cross section with respect to a virtual plane including the central axis) can also be changed midway.

[0071] [Second Example of Embodiment] A second example of an embodiment of the present invention will be described with reference to FIG. 5. In the finishing grinding tool 3b of this example, in the tapered portion 7a, the effective diameter (the diameter passing through the point where the width of the thread 4 and the width of the thread groove are equal) increases toward the rear side in the axial direction.

[0072] Further, in the back tapered portion 9a, the effective diameter decreases toward the rear side in the axial direction.

[0073] According to the finishing grinding tool 3b of this example, at the initial stage when the threaded portion 5a of the finishing grinding tool 3b starts to be screwed into the female threaded portion 2 of the nut 1 (see FIGS. 3 and 4(B)), that is, in a state where the tapered portion 7a and the female threaded portion 2 are screwed together, a gap is formed between the female threaded portion 2 and the threaded portion 5a. For this reason, when performing finishing grinding with the finishing grinding tool 3b, the rotational torque of the finishing grinding tool 3b can be gradually increased. In other words, a rapid increase in the rotational torque of the finishing grinding tool 3b can be prevented. The configurations and operational effects of the other parts are the same as those in the first example of the embodiment.

[0074] [Third Example of Embodiment] A third example of an embodiment of the present invention will be described with reference to FIG. 6. In the finishing grinding tool 3a of this example, the groove portion 6a is formed in parallel with the axial direction at an odd number of positions (three positions at equal intervals in the circumferential direction in the illustrated example) on the outer peripheral surface of the finishing grinding tool 3a at equal intervals in the circumferential direction. According to this example, it is easier to ensure better shape accuracy of the thread 2a constituting the female threaded portion 2 of the nut 1 (see FIGS. 3 and 4(B)).

[0075] That is, when performing finishing grinding on the female threaded portion 2 of the nut 1 with the finishing grinding tool 3a, since there is no thread 4 in the portion (phase) where the groove portion 6a is located, the portions of the thread 4 located on both sides in the circumferential direction of the groove portion 6a bite into the female threaded portion 2 or, conversely, separate from the female threaded portion 2, and then elastically deform as they try to recover elastically. When such elastic deformation occurs, a so-called polygonal error is likely to occur, in which the shape of the thread 2a constituting the female threaded portion 2 becomes polygonal when viewed from the axial direction.

[0076] In this example, the number of the groove portions 6a is made odd so that no other groove portion 6a is located on the radially opposite side of one groove portion 6a, that is, so that the land 11 is located. Therefore, when the portions of the thread 4 located on both circumferential sides of the groove portion 6a tend to bite into the female thread portion 2 or, conversely, move away from the female thread portion 2, this movement (deformation) can be suppressed by the portion located on the radially opposite side of the groove portion 6a. For this reason, it is possible to make it difficult to generate a polygonal error, and it is easy to ensure good shape accuracy of the thread 2a constituting the female thread portion 2.

[0077] However, when the circumferential width of the groove portion is small, in other words, when the circumferential width of the land is sufficiently large, the number of the groove portions can also be made even. The configurations and the functions and effects of the other portions are the same as those in the first example of the embodiment.

Explanation of Signs

[0078] 1 Nut 2 Female thread portion 2a Thread 3, 3a, 3b Finishing grinding tool 4 Thread 5 Thread portion 6, 6a Groove portion 7, 7a Taper portion 8 Main grinding portion 9, 9a Back taper portion 10 Small-diameter cylindrical portion 11 Land 12 Guide portion 13 Shank portion 14 Scoop surface 100 Tap 101 Thread 102 Thread portion 103 Groove portion 104 Biting portion 105 Complete thread portion 106 Land 107 Scoop surface 108 Cutting edge

Claims

1. A threaded portion having a thread formed spirally on an outer peripheral surface, and groove portions formed so as to extend in the axial direction at a plurality of locations in the circumferential direction of the outer peripheral surface, comprising: the threaded portion has at least a tapered portion in which the outer diameter of the thread increases toward the rear side in the axial direction, and a relief angle is not provided on the flank surface of the thread over the entire axial range, abrasive grains are fixed over the entire axial length of the threaded portion, a finishing grinding tool.

2. The effective diameter in the tapered portion increases toward the rear side in the axial direction, The finishing grinding tool according to Claim 1.

3. The threaded portion is disposed adjacent to the rear side in the axial direction of the tapered portion and has a main grinding portion in which the outer diameter of the thread does not change over the axial direction, The finishing grinding tool according to Claim 1 or 2.

4. lands are provided between the groove portions, and on each of the lands, clearance faces are provided on both side faces in the circumferential direction of the thread, the clearance angle of the clearance face is 0°, The finishing grinding tool according to any one of Claims 1 to 3.

5. lands are provided between the groove portions, and on each of the lands, clearance faces are provided on both side faces in the circumferential direction of the thread, on each of the lands, the clearance faces provided on both side faces in the circumferential direction of the thread are symmetric with respect to the circumferential direction, and the clearance angle of the clearance face is -10° or more and 10° or less, The finishing grinding tool according to any one of Claims 1 to 3.

6. A guide portion is provided on the front side in the axial direction of the threaded portion and has an outer diameter that does not change with respect to the axial direction, The finishing grinding tool according to any one of Claims 1 to 5.

7. The threaded portion is disposed on the rear side in the axial direction of the tapered portion and has a back tapered portion in which the outer diameter of the thread decreases toward the rear side in the axial direction, The finishing grinding tool according to any one of Claims 1 to 6.

8. A small-diameter cylindrical portion is provided on the rear side in the axial direction of the back tapered portion and has an outer diameter that does not change with respect to the axial direction, The finishing grinding tool according to Claim 7.

9. A grinding method for a female threaded member, which comprises performing finishing grinding on a female thread portion formed on an inner peripheral surface of the female threaded member using the finishing grinding tool according to Claim 7 or 8, While relatively rotating the finishing grinding tool in a predetermined direction with respect to the female screw member, insert the finishing grinding tool radially inward of the female screw member from the front side in the axial direction until at least a part of the back taper portion is located radially inward of the female screw member, and then, while relatively rotating the finishing grinding tool in the direction opposite to the predetermined direction with respect to the female screw member, pull out the finishing grinding tool from radially inward of the female screw member to perform finishing grinding on the female screw portion. A method for grinding a female screw member.

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