JPH11290957A - Grooving method of pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable grooving with high dimensional precision by applying plastic deformation inward in a part of a pipe without using a mandrel. SOLUTION: While the outer circumferential side of a large diameter part 12 in the middle of a stepped pipe with a small diameter formed on both sides is held by a first preliminary die 36, a first small width groove 40 is machined by means of a first small width projection 38 installed on the inner circumferential face of the first preliminary die 36; then, through similar machining by a second preliminary die 44 or a normal die 50, the groove width is gradually expanded to form a key lock groove 20 having a target set-width. Since the outer circumference of the large diameter part 12 is held by each die 36, 44, 50, the large diameter part 12 is prevented from being crushed in the radial direction at the time of machining, with the groove width gradually expanding; consequently, a gap is hard to be caused between each die 44, 50 and the corner part 48b, 20b on both sides of the groove opening, as well as between each die and the internal angle part 48a, 20a on both sides of the groove bottom, enabling the corner part to be sharpened, so that a high dimensional precision can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a groove forming method for forming a groove by plastically deforming a part of a cylindrical pipe inward.

[0002]

2. Description of the Related Art As a steering main shaft of an automobile, a small-diameter portion is formed by plastically deforming one end of a cylindrical pipe, and a part of a large-diameter portion is plastically deformed inward, thereby forming a straight line for key lock. A structure in which a groove is formed is proposed in Japanese Patent Application Laid-Open No. 5-200634.
The linear groove for the key lock inserts a core having a concave portion corresponding to the groove into the inside of the large-diameter portion, and inserts a die with a projection corresponding to the groove on the inner peripheral surface outside the large-diameter portion. It is formed by fitting and moving in the axial direction. Further, after the linear groove for key lock is processed in this manner, the end of the large diameter portion is drawn to a small diameter.

[0003]

However, in such a conventional processing method, it is necessary to perform the plastic processing for reducing the diameter of both ends of the pipe before and after the groove processing step, which is not always efficient. Further, since the groove processing is performed using the core metal, the groove processing cannot be performed on the large diameter portion of the pipe having the small diameter portions on both sides in the axial direction with the large diameter portion interposed therebetween.

The present invention has been made in view of the above circumstances, and an object thereof is to form a groove with high dimensional accuracy by plastically deforming a part of a pipe inward without using a cored bar. To be able to do it.

[0005]

In order to achieve the above object, a first aspect of the present invention is to plastically deform a part of a cylindrical pipe inward to form a groove having a predetermined set width dimension in an axial direction. The groove forming method to be formed, wherein (a) an inner diameter is substantially the same as the outer diameter of the pipe or smaller by a predetermined dimension, and a small-width protrusion having a width smaller than the set width corresponding to the groove has an inner periphery. A spare die provided on the surface is fitted on the outer peripheral side of the pipe and relatively moved in the axial direction, and a part of the pipe is plastically deformed inward by the small-width projection, and the width is larger than the set width. A narrow groove processing step of forming a small groove having a small dimension; and (b) a width dimension substantially equal to or smaller than the inner diameter dimension of the spare die by a predetermined dimension, and substantially equal to the set width dimension corresponding to the groove. The regular dice with regular projections on the inner peripheral surface A regular groove processing step of fitting the outer peripheral side of the pipe after the groove processing step and relatively moving the pipe in the axial direction, and enlarging the groove width of the small groove by a regular protrusion thereof to a set width dimension. Features.

According to a second aspect of the present invention, in the method for forming a groove of a pipe according to the first aspect, the pipe integrally has a small diameter portion on both sides in the axial direction with the large diameter portion interposed therebetween. A groove having a bottom diameter equal to or larger than the outer diameter of the small diameter portion is formed.

According to a third invention, in the pipe groove machining method according to the first invention or the second invention, an inner diameter of the regular die is smaller than an inner diameter of the spare die by a predetermined dimension.
The regular groove forming step is characterized in that the groove width of the small groove is increased to the set width dimension while reducing the diameter of the pipe after the small groove processing step.

A fourth invention is a groove forming method for forming a groove having a predetermined width in the axial direction by plastically deforming a part of a cylindrical pipe inward, wherein the groove has a predetermined size from an outer diameter of the pipe. A die having a smaller inner diameter, and a protrusion having a width dimension substantially equal to the width dimension corresponding to the groove is provided on the inner peripheral surface, and is fitted to the outer peripheral side of the pipe and relatively moved in the axial direction. The groove is formed by plastically deforming a part of the pipe inwardly by the protrusion while reducing the diameter of the pipe.

[0009]

According to the first aspect of the present invention, in the method of forming a groove for a pipe, a small-width groove having a small width is provided by a small-width projection provided on an inner peripheral surface of the spare die while holding an outer peripheral side of the pipe with a preliminary die. After processing the same, while maintaining the outer peripheral side of the pipe with the regular die, the groove width of the small width groove is enlarged by the regular protrusion provided on the inner peripheral surface of the regular die to form the groove of the set width dimension. Therefore, grooves can be formed with high dimensional accuracy without using a cored bar. That is, since the outer circumference of the pipe is held by the die, the pipe is not liable to be crushed in the radial direction due to engagement with the small-width protrusion or the regular protrusion, and the groove width is increased after processing the small-width groove. In comparison with the case where the groove depth is gradually increased with the groove width of the set width dimension, not only the inner corners on both sides of the groove bottom, but also between the corners on both sides of the groove opening and the die. Therefore, high dimensional accuracy can be obtained such that a gap is hardly generated and a corner portion thereof can be sharpened.

Further, since the groove can be machined with high dimensional accuracy without using a metal core, the groove can be machined in the large diameter portion of the pipe having the small diameter portion on both sides of the large diameter portion as in the second invention. Thus, the degree of freedom in a series of processing designs is improved, for example, a groove can be formed in an intermediate large-diameter portion after forming a small-diameter portion on both sides of a pipe in advance.

In the second invention, since a cored bar cannot be used, by applying the present invention, a groove can be machined in a large diameter portion with high dimensional accuracy. In particular, since the large-diameter portion has small-diameter portions on both sides, the rigidity is higher than that of a pipe having open ends, and grooves can be machined with higher dimensional accuracy.

In the third invention, the inner diameter of the regular die is smaller than the inner diameter of the spare die.
To reduce the diameter of the pipe after the narrow groove processing step and increase the groove width of the small groove to the set width dimension, even if there is no core metal due to the reaction force against the diameter reduction, the gap between the die and the pipe further increases It is hard to occur, and the groove can be formed with higher dimensional accuracy corresponding to the regular projection.

According to a fourth aspect of the present invention, a groove is formed by plastically deforming a part of the pipe inward by a projection while reducing the diameter of the pipe using a dice having an inner diameter smaller than the outer diameter of the pipe by a predetermined dimension. In the same manner as in the third invention, even if there is no core metal due to the reaction force against the diameter reduction, a gap is hardly formed between the die and the pipe, so that the groove can be formed with high dimensional accuracy corresponding to the projection. Accordingly, a groove having a target width can be formed only by one-stage plastic working, and when a groove is machined in a plurality of steps such as the small-width groove forming step and the regular groove forming step, each plastic groove is formed. By applying the present invention to the processing step, a groove can be formed with higher dimensional accuracy.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Here, the narrow groove processing step may be a single plastic processing using a single spare die.
The width dimension of the narrow groove may be gradually increased by performing the plastic working a plurality of times using a plurality of spare dies having different width dimensions of the narrow protrusion. A single spare die is provided with a small-width protrusion in which the width dimension changes stepwise or continuously in the axial direction, and the spare die is relatively moved in the axial direction.
In the process, a small width groove having a relatively large width can be plastically worked. The regular groove processing step can be performed in a separate step using a regular die configured separately from the spare die.However, a regular protrusion is provided after the small-width protrusion to integrate the spare die and the regular die, Subsequent to the narrow groove processing step, a regular groove processing step may be performed in one step.

It is desirable that the projection width of the small width projection of the spare die is substantially the same as the groove depth of the groove to be formed. It may be made deeper. The regular projection of the regular die is provided with substantially the same dimension as the groove depth of the groove to be formed. The regular protrusion of the regular die is
It is desirable to set in consideration of the springback of the pipe. In addition, the small-width projection and the regular projection, or the bite-side end of the projection of the fourth invention, which bites into the pipe, may be provided with a bite portion having a gradually reduced width or protrusion. desirable.

According to the present invention, when a groove is formed in a large-diameter portion of a pipe integrally having a small-diameter portion on both sides in the axial direction with a large-diameter portion interposed therebetween as in the second invention, that is, a metal core may be used. It is preferably applied when it is not possible, but it can also be applied to groove processing where a cored bar can be used, such as when a groove is formed in a pipe having a constant diameter. It is desirable to provide a tapered part whose diameter dimension changes smoothly between the large diameter part and the small diameter part of the pipe of the second invention. When the first invention is carried out, if a spare die or a regular die having an inner diameter substantially the same as the outer diameter of the pipe is used, a core metal can be used together as necessary.

In the third invention, the inner diameter of the regular die is made smaller than the inner diameter of the spare die, and the groove width of the narrow groove is increased while reducing the diameter of the pipe. The narrow groove may be formed with high dimensional accuracy while reducing the diameter of the pipe by using a spare die having an inner diameter smaller than the outer diameter of the pipe. This is the fourth
It is also one embodiment of the invention.

The cross-sectional shape of the cylindrical pipe is desirably a perfect annular shape (true circle), but the present invention can be applied to a somewhat deformed cylindrical shape such as an ellipse. The groove to be formed in the pipe is, for example, a straight groove parallel to the axis of the pipe, but is relatively rotated around the axis while relatively moving the pipe and the die in the axial direction. The twisted groove can be plastically worked.

Further, the present invention is suitably applied to a method of manufacturing a steering main shaft of an automobile.
A step of preparing a cylindrical pipe having a constant wall thickness and diameter, and (b) reducing a predetermined range of the pipe by plastic working, and integrally forming a small diameter portion on both axial sides with a large diameter portion therebetween. And (c) a width of the key lock groove having an inner diameter substantially equal to or smaller by a predetermined dimension than the outer diameter of the large diameter portion of the stepped pipe. A spare die provided on the inner peripheral surface corresponding to the key lock groove with a smaller width dimension smaller than that of the key lock groove is fitted on the outer peripheral side of the large diameter portion and relatively moved in the axial direction. A small width groove forming step of forming a small width groove having a width smaller than the width of the key lock groove by plastically deforming a part of the large diameter portion inward by the small width projection; The inner diameter of the die is approximately the same as or smaller than the inner diameter of the die by a predetermined size. A regular die having a regular protrusion with a new width dimension provided on the inner peripheral surface corresponding to the key lock groove is fitted on the outer peripheral side of the pipe after the narrow groove processing step and relatively moved in the axial direction. And a regular groove processing step of enlarging the groove width of the small-width groove by the regular protrusion to obtain a target width dimension.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1A shows a front view of the steering main shaft 10, and FIG.
-B shows a sectional view. In the figure, the steering main shaft 10 has a hollow cylindrical shape, and has a pair of small diameter portions 14 and 15 on both sides in the axial direction with a large diameter portion 12 at a central portion therebetween. Large diameter part 12 and small diameter part 1
4 and 15 are provided with tapered portions 16 and 17 whose diameters change smoothly. A large diameter portion 12 has a pair of linear key lock grooves 20 linearly parallel to the axis. Is provided. The key lock groove 20 corresponds to a groove having a predetermined set width according to the first aspect, and the groove bottom diameter is slightly larger than the outer diameter of the small diameter portions 14 and 15. Serrations 18 and 19 are provided at the distal ends of the small diameter portions 14 and 15, respectively. The total length L of the steering shaft 10 of this embodiment is 400 mm.
The outer diameter of the large diameter portion 12 is 28.0 mm, and the small diameter portions 14 and 1
5 has an outer diameter of 19.0 mm, the width dimension (set width dimension) W of the key lock groove 20 is 9.0 mm, and the groove depth (from the groove bottom at the groove center to the extended arc surface of the outer peripheral surface of the large diameter portion 12). Is D 3.3 mm.

FIG. 2 is a view sequentially showing the steps of manufacturing the steering main shaft 10 over (a) to (c). In FIG. 2, in the step (a), the thickness t = 2.6 mm to 2.
A pipe 24 having a diameter of about 8 mm and a diameter φ of about 28.0 to 29.0 mm and a cross section of a substantially perfect circle is prepared. Pipe 24
For example, carbon steel tubes for machine structures (STKM15
C) or the like is used, and the product length L = 5 than 400 mm.
The sheet was cut short by about 10 mm and subjected to annealing and bonding to improve workability. In addition, when STKM15A is used as carbon steel pipe for machine structures, it is also possible to perform only bond processing.

Next, in the step (b), both ends of the pipe 24 are reduced by plastic working using the molds 30 and 31 shown in FIG. Then, a stepped pipe 26 integrally having a pair of small diameter portions 14 and 15 is formed. At this stage, the pipe 24 is extended in the axial direction to become a stepped pipe 26 slightly longer than the product length. In the molding dies 30 and 31 of FIG.
The inner diameters of the molding surfaces indicated by 4 are φ28 and φ28, respectively.
19, φ16, φ12, φ18, and these molds 30, 31 are fitted from both sides to both ends of the pipe 24, which is a processing material, and are swaged by cold pressing in the axial direction. To form the desired shape. Although the pipe 24 can be forged into the stepped pipe 26 using only the molds 30 and 31, a plurality of stages are used to perform swaging forging in a plurality of stages so that a stepped shape is obtained. Is also good. Note that hot forging may be performed as necessary, or another forging method such as reducing the diameter by pressing the pipe 24 from the outer peripheral side may be employed.

In the step (c) of FIG. 2, the stepped pipe 2
By forming a pair of linear key lock grooves 20 parallel to the axis of the pipe in the large-diameter portion 12 at the center of 6,
The steering main shaft 10 is manufactured. FIG. 4-
FIG. 6 shows a first preliminary die 36 and a second preliminary die 36 used in the step (c).
FIGS. 3A and 3B are diagrams showing a spare die 44 and a regular die 50, respectively. FIG. 3B is a cross-sectional view taken along line bb of FIG. 3A, and FIG. 3A is a front view seen from the left side of FIG.

A first spare die 36 shown in FIG. 4 is a cylindrical member having an inner diameter (28.0 mm) substantially equal to the outer diameter of the large diameter portion 12 of the stepped pipe 26, and is provided with the key lock groove. A pair of first small-width projections 38 having a width dimension of about 6.0 mm smaller than the set width dimension W of 9.0 = 20 mm and a projection dimension of about 3.3 mm substantially equal to the groove depth D are opposed to each other. It is provided on the inner peripheral surface, and the biting side of the pair of first small-width projections 38 is 15 ° with respect to the inner peripheral surface.
The first biting portions 42 inclined at an angle of the order are provided respectively. Also, the corners of the first small-width projection 38 and the first biting portion 42, that is, reference numerals 70, 71, 72, 7 in the drawing
Each of the concave and convex portions indicated by 3 has a radius of curvature R5,
R is added at R5, R2, and R3.

The second spare die 44 shown in FIG. 5 is a cylindrical member having an inner diameter of about 28.0 mm.
A width dimension of about 7.0 mm, which is smaller than the set width dimension W of 0 and larger than the width dimension of the first small width projection 38, and a projection dimension of about 3.3 mm substantially equal to the groove depth D of the key lock groove 20. It has substantially the same shape as the first spare die 36 except that a pair of second small-width protrusions 46 are provided on inner circumferential surfaces opposed to each other. 2
A biting portion 49 is provided. The width of the second biting portion 49 is substantially symmetrically and smoothly (linearly) narrowed from both sides toward the front side away from the second small width projection 46, and the first spare die 36 is formed at the front end. Is smaller than the width dimension (6.0 mm) of the first small-width projection 38 of FIG.
Also, the corners of the second small-width projection 46 and the second biting portion 49, that is, each of the concavo-convex portions indicated by reference numerals 74, 75, 76, and 77 in FIG. R is added at R3, R3, R1.5, and R2.

Although not shown, the width dimension is 8.0.
A third spare die having a third small-width protrusion having a protrusion dimension of about 3.3 mm and a dimension of about 3.3 mm is also prepared.

The regular die 50 shown in FIG.
It is a cylindrical member of about 8.0 mm.
Is about 9.0 mm, which is substantially equal to the set width dimension W, and 3.3 mm is substantially equal to the groove depth D of the key lock groove 20.
Except that a pair of regular projections 52 having a similar projection dimension are provided on opposing inner peripheral surfaces.
6 and the second spare die 44, and a regular biting portion 56 is provided on the biting side of the regular projection 52. The width of the regular biting portion 56 is narrowed symmetrically and smoothly (linearly) from both sides toward the front side away from the regular protrusion 52, and at the front end, the third small width of the third spare die is reduced. It is narrower than the width dimension (8.0 mm) of the projection. The regular projection 52 and the regular bite 5
6 at the corners, that is, the concave and convex portions indicated by reference numerals 78, 79, 80, and 81 in the figure, respectively, have curvature radii R3 and R3, respectively.
3, R is added at R0.7 to 0.8 and R0.5.

FIGS. 7A to 7C show first spare dies 36,
The grooves formed by sequentially expanding the width dimension of the stepped pipe 26 by the second preliminary die 44 and the regular die 50 are shown. In FIG. 7, in the first small groove processing step (a), the first spare die 36 is fitted to the outer peripheral side of the large-diameter portion 12 of the stepped pipe 26 from the first bite portion 42 side and axially. The key lock groove 2 is relatively moved, and the large-diameter portion 12 is plastically deformed inward by the first small-width protrusion 38.
The first small-width groove 40 having a width smaller than the set width W of 0 and having a groove depth substantially equal to the groove depth D is formed. Next, in the second narrow groove processing step (b), the same pre-extrusion processing as in (a) is performed using the second preliminary die 44, whereby the width dimension of the first small groove 40 is slightly expanded. The second small width groove 48 is formed. And the third not shown
The groove width of the second small-width groove 48 is further expanded by using a spare die. The width is further expanded and the desired set width W
The key lock groove 20 is formed. The key lock groove 20 formed in this way is Hv23 by work hardening.
The strength is improved to about 0 to 240, so that a sufficient function as a lock member can be achieved.

As described above, according to this embodiment, the outer peripheral side of the large diameter portion 12 of the stepped pipe 26 is provided on the inner peripheral surface of the first spare die 36 while being held by the first spare die 36. After processing the first small width groove 40 having a smaller width dimension than the key lock groove 20 by the first small width projection 38,
By performing similar processing with the second spare die 44, the third spare die (not shown), and the regular die 50,
Groove width is gradually increased, and key lock groove 2 with set width W
Since 0 is formed, the key lock groove 20 can be formed with high dimensional accuracy without using a cored bar. That is, the outer circumference of the large diameter portion 12 of the stepped pipe 26 is fixed to each of the dies 36, 44, 5
0, the first narrow protrusion 38 and the second
The large diameter portion 1 is formed by engagement with the small width projection 46 and the regular projection 52.
2 is not crushed in the radial direction, and the first narrow groove 4
Since the groove width is enlarged after machining 0, the inner corners 48a and 20a on both sides of the groove bottom are compared with the case where the groove depth is gradually increased with the groove width of the set width dimension W. Of course, the corners 48b, 20b on both sides of the groove opening and each die 4
A high dimensional accuracy is obtained, for example, it is difficult to form a gap between the first and fourth substrates 50 and 50, and the corners thereof can be sharpened.

Further, since the key lock groove 20 can be machined with high dimensional accuracy without using a metal core as described above, both sides of the large-diameter portion 12 can be formed in the process of FIG. After the small diameter portions 14 and 15 are formed, the key lock groove 20 can be machined in the large diameter portion 12, and the degree of freedom in a series of machining designs is improved. Since the small-diameter portions 14 and 15 are provided on both sides of the large-diameter portion 12 via the tapered portions 16 and 17, the key lock has higher rigidity and higher dimensional accuracy than when both sides are open. Groove 20 can be formed.

While the embodiment of the present invention has been described in detail with reference to the drawings, the present invention can be applied to other embodiments.

For example, in the above-described embodiment, the first spare dice 36, the second spare dice 44, and the regular dice 5
The inner diameter of each of the pipes 0 is substantially the same as the outer diameter of the large-diameter portion 12, but the pipe 24 has a larger diameter than the large-diameter portion 12 of the steering main shaft 10, for example, φ29 to φ3.
In the swaging forging process shown in FIG. 2 (b), a large-diameter portion having a diameter larger than the large-diameter portion 12 is left in the middle, and a spare die and a regular die are shown in FIG. 2 (c). When processing the key lock groove 20 while gradually increasing the groove width using a die, the inner diameter of those dies is gradually reduced, and the outer diameter of the large diameter portion is gradually reduced,
You may make it the large diameter part 12 of the target outer diameter dimension.

FIG. 8 shows the key lock groove 20 as described above.
FIG. 4 is a view showing an example of a regular die 60 used when reducing the outer diameter of a large-diameter portion when machining a large-diameter portion. A large-diameter portion 70, a tapered portion 72, and a small-diameter portion 74 are provided on an inner peripheral surface thereof. In addition, the small diameter portion 74 is provided with a pair of regular projections 64 at symmetrical positions with respect to the axis, and the tapered portion 72 is provided with the regular biting portion 62 continuous with the regular projection 64. ing. The inner diameter of the small diameter portion 74 is the same as the desired large diameter portion 12.
The outer diameter of the large diameter portion 70 is 28.0 mm, the inner diameter of the large diameter portion 70 is slightly larger than the inner diameter of the spare dies used in the previous narrow groove processing, and after the narrow groove processing. When the stepped pipe is inserted from the left side in FIG. 8B, the regular biting portion 6 is reduced in the tapered portion 72 while reducing the large diameter portion to the target diameter (φ28).
2, the key width of the key lock groove 20 having the set width dimension W is formed. FIG. 8B is a sectional view taken along line bb of FIG.
(a) is a front view seen from the left side of (b).

If the groove width is increased while reducing the diameter in this manner, a gap is hardly generated between the regular die 60 and the stepped pipe even if there is no core metal due to the reaction force against the diameter reduction. The key lock groove 20 can be formed with high dimensional accuracy corresponding to the protrusion 64.

The processing by the regular die 60 corresponds to an embodiment of the invention described in claim 3, but is also an embodiment of the invention described in claim 4. Further, since the groove can be machined with such high dimensional accuracy, the large-diameter portion 7 of the regular die 60 can be formed without performing the small-width groove machining step depending on the conditions.
By making the diameter dimension of 0 larger than the outer diameter dimension of the large diameter portion before the groove processing, the key lock groove 20 of the target set width dimension W can be processed only by one-stage plastic processing. . In addition, the diameter reduction of the large diameter portion is extremely small and sufficient.
Although the axial elongation due to the diameter reduction is almost negligible, the length of the large diameter portion before the groove processing may be set in consideration of the axial elongation.

Although not specifically exemplified, the present invention can be implemented in various modified and improved forms based on the knowledge of those skilled in the art.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a steering main shaft provided with a key lock groove according to the method of the present invention, wherein (a) is a front view and (b) is a bb cross-sectional view of (a). .

2A and 2B are diagrams showing each manufacturing process of the steering main shaft of FIG. 1, wherein FIG. 2A is a pipe as a material, FIG. 2B is a stepped pipe formed by performing plastic working on the pipe,
(c) shows a steering main shaft in which a key lock groove is formed in a stepped pipe.

FIG. 3 is a sectional view showing a molding die used in a step (b) of FIG. 2;

FIGS. 4A and 4B are diagrams showing a first spare die used in the step (c) of FIG. 2, wherein FIG. 4A is a front view and FIG. 4B is a bb cross-sectional view of FIG.

FIGS. 5A and 5B are views showing a second preliminary die used in the step (c) of FIG. 2, wherein FIG. 5A is a front view, and FIG. 5B is a bb cross-sectional view of FIG.

FIGS. 6A and 6B are diagrams showing a normal die used in the step (c) of FIG. 2, wherein FIG. 6A is a front view and FIG. 6B is a bb cross-sectional view of FIG.

7A and 7B are diagrams showing a cross-sectional shape of a groove formed by the dies of FIGS. 4 to 6, wherein FIG. 7A is a first narrow groove formed by a first spare die of FIG. 4, and FIG. The second narrow groove formed by the second spare die is shown in FIG. 6, and the key lock groove formed by the regular die shown in FIG. 6 is shown in FIG.

8A and 8B are diagrams showing a normal die according to another embodiment of the present invention, wherein FIG. 8A is a front view, and FIG. 8B is a sectional view taken along line bb of FIG. 8A.

[Explanation of symbols]

 12: Large diameter portion 14, 15: Small diameter portion 20: Key lock groove (groove) 26: Stepped pipe (Pipe) 36: First spare die (Spare die) 38: First small width projection (Small width projection) 40: 1st narrow groove (small groove) 44: 2nd spare die (spare die) 46: 2nd small width protrusion (small width protrusion) 48: 2nd small width groove (small width groove) 50: regular die 52: regular protrusion Part 60: regular die (die) 64: regular projection (projection) W: set width dimension

Claims (4)

[Claims] 1. A groove forming method for forming a groove having a predetermined set width dimension in an axial direction by plastically deforming a part of a cylindrical pipe inward, wherein the groove has a substantially same outer diameter as the pipe. A spare die having an inner diameter smaller than the predetermined width by a predetermined dimension and having a width smaller than the set width corresponding to the groove is fitted on the outer peripheral side of the pipe, Relative width in the direction, a small width groove processing step of forming a small width groove having a width smaller than the set width by plastically deforming a part of the pipe inward by the small width projection, and an inner diameter of the preliminary die. A normal die having an inner diameter dimension substantially the same as or smaller than the predetermined dimension by a predetermined dimension, and a regular projection having a width dimension substantially equal to the set width dimension corresponding to the groove is provided on the inner peripheral surface, after the narrow groove processing step. The pipe is fitted to the outer peripheral side of the pipe and relatively moved in the axial direction. Groove machining method of the pipe, characterized in that the enlarged groove width of the narrow grooves by projections and a regular groove processing step of the said set width. 2. The pipe has a small-diameter portion integrally formed on both sides in the axial direction with a large-diameter portion interposed therebetween, and a groove bottom diameter of the large-diameter portion is equal to or smaller than an outer diameter of the small-diameter portion. The method according to claim 1, wherein a large groove is formed. 3. An inner diameter dimension of the regular die is smaller than an inner diameter dimension of the spare die by a predetermined dimension, and the regular groove processing step includes reducing a diameter of a pipe after the small groove processing step while reducing a groove width of the small groove. 3. The method according to claim 1, wherein the set width dimension is enlarged by enlarging the set width dimension. 4. 4. A groove forming method for forming a groove having a predetermined width in an axial direction by plastically deforming a part of a cylindrical pipe inward, wherein an inner diameter smaller by a predetermined dimension than an outer diameter of the pipe is provided. By dimensions,
A die having a protrusion having a width substantially equal to the width corresponding to the groove is provided on the inner peripheral surface, fitted on the outer peripheral side of the pipe and relatively moved in the axial direction, and the pipe is reduced in diameter. And forming the groove by plastically deforming a part of the pipe inward by the protrusion.