JP2010115669A - Welding torch and collet for welding torch - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a welding torch capable of avoiding any positional deviation or eccentricity of a long electrode. <P>SOLUTION: The welding torch comprises a long electrode 12, a collet part 14 for holding the electrode, a collet body 20 with the collet part 14 being inserted therein and a torch head 24, a torch body 32 in which the torch head 24 is inserted and positioned and a shield gas feeding passage 36 is formed between the torch head 24 and itself, a torch nozzle 30 for ejecting shield gas between the collet body 20 and itself, and a torch cap 44 for regulating the electrode 12 in an advancible/retractable manner at a fore end of the torch nozzle 30. The collet part 14 has a first collet 16 and a second collet 18. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  In the present invention, when the welding electrode is ground or replaced in automatic welding, the welding electrode can be accurately positioned in a direction perpendicular to the axis thereof, or the protruding length of the tip can be easily adjusted. The present invention relates to a welding torch and a collet for welding torch.

  In a welding torch used in TIG (Tungsten Inert Gas) welding, plasma welding, or the like, a collet chuck is used to position and hold a welding electrode. The electrode is fitted into the collet chuck, and the collet chuck is guided to be inserted into the collet body. The collet chuck is used for positioning the electrode and adjusting its protruding length.

  Patent Document 1 discloses a technical idea in which tapered surfaces are provided at the front end portion and the rear end portion of the collet chuck.

  In the prior art of Patent Document 1, a tapered surface is provided at the tip of the collet chuck, and only this tapered surface is guided to the collet body. For this reason, the collet chuck is easily decentered in a direction perpendicular to the axial direction of the collet body, and there is a disadvantage that accurate positioning of the electrode tip cannot be ensured.

JP 59-163084 A

  Even when the collet chuck is used as described above, when replacing the electrode of the torch or when attaching and detaching the electrode to polish the tip, the axial position of the electrode is displaced, or the degree of protrusion of the electrode tip is long or short. May occur. When such misalignment occurs, there may be variations in the gap (gap) between the workpiece and the electrode when performing delicate welding using an automatic welding machine or welding to a narrow point. is there. As a result, there are disadvantages such as poor contact and poor weld quality such as welding to a part different from the desired weld point, and failure to obtain weld quality. Moreover, if there is a shift in the length of the welding tip as described above, there is a concern of misfire. Therefore, when the electrode is replaced or polished to sharpen the tip, it is important to position the electrode accurately. In particular, in high-precision arc welding such as micro TIG welding, a high-precision centering operation is required in which the error of the electrode position must be within the range of (+ −) 0.05 mm.

  The present invention has been made to solve the various problems described above, and in a welding torch, it becomes possible to sufficiently increase the positioning accuracy of the electrode when replacing the electrode. An object of the present invention is to provide a welding torch which can be positioned easily and in a short time, and as a result, a product excellent in welding quality can be obtained.

  The invention specified in claim 1 of the present invention includes a long electrode, a collet portion for inserting and holding the electrode, a collet body and a torch head into which the collet portion is inserted, and the torch head being inserted. A torch body positioned, and the collet portion has a first collet and a second collet, and the first collet is in contact with a tapered surface formed on the inner side of the collet body. And the second collet has a tail-end tapered surface that abuts against a tapered surface of a collet support provided inside the torch head.

  In the present specification, the distal end portion or the distal end side indicates an end portion located in the distal end direction of the welding torch or an end portion facing the distal end direction. On the other hand, the tail end portion or the tail end side indicates an end portion located at the rear of the welding torch or an end facing the rear.

  According to the invention specified in claim 1, the tapered surface of the first collet holding the electrode is in contact with the tapered surface of the collet body, and the tapered surface of the tail end of the second collet is in contact with the tapered surface of the collet support. Touch. That is, the tapered surfaces come into contact with each other at both end portions of the collet portion, and the axial position is determined at two locations in the axial direction (electrode extending direction). As a result, the electrodes can be easily positioned and fixed, and centering can be easily performed.

  The invention specified in claim 2 of the present application is the welding torch according to claim 1, wherein a relief portion having a diameter larger than the diameter of the electrode is provided inside each of the first collet and the second collet. And the tail end portion of the first collet and the tip end portion of the second collet are integrally formed with each other.

  According to the specified invention specified in the second aspect, in the collet portion having a tapered portion on both sides of the tip portion and the tail end portion, the relief portion is formed inside the collet portion. As a result, a long electrode can be easily inserted into the collet part, and the collet part and the electrode are in contact with each other at the tip part and the tail part, so that the electrode can be reliably fed through the collet part. Can do.

  Next, in the welding torch according to the present invention, the tail end portion of the first collet and the tip end portion of the second collet may be fitted by press fitting or may be joined by brazing. In any configuration, the first collet and the second collet can be integrally formed without shifting their axes. As a result, the collet portion is firmly held by the tip tapered surface and the tail end tapered surface, so that no eccentricity occurs in the direction perpendicular to the axial direction of the electrode.

  The invention specified in claim 5 of the present application is the welding torch according to any one of claims 1 to 4, wherein the tip end portion of the first collet and the tail end portion of the second collet are respectively in the axial direction. It is characterized in that slits extending and arranged at equal intervals around the axis are formed.

  According to the invention specified in claim 5, since the slit is formed in the first collet and the second collet constituting the collet portion, the tip end portion of the first collet and the tail end portion of the second collet The portion where the slit is formed is bent, and the electrode can be securely held. In addition, since the slits are arranged at equal intervals around the axis, it is possible to hold the slits at the tip or tail end with an equal force from the outer periphery of the electrode. As a result, it is possible to prevent the electrode core from being displaced.

  In the welding torch according to the present invention having such a slit, it is more desirable that the slits are disposed at an interval of 90 degrees.

  According to the present invention, the tapered surface of the first collet and the tapered surface of the collet body are engaged, and the tail end tapered surface of the second collet and the tapered surface of the collet receiver are engaged, whereby the long electrode is formed. There is obtained an effect that the position of the electrode tip can be easily positioned under the action of the torch cap without being decentered in the direction orthogonal to the axial direction and being displaced.

  The welding torch according to the present invention will be described in detail below with reference to the accompanying drawings, with the TIG welding torch as a preferred embodiment.

  FIG. 1 is a longitudinal sectional view along the axial direction of a TIG welding torch 10 (hereinafter referred to as a welding torch 10) according to the present invention, and FIG. 2 is an exploded perspective view thereof.

  The welding torch 10 has a collet portion 14 for holding and fixing a long electrode 12 made of, for example, tungsten. FIG. 3 shows a longitudinal sectional view of the collet portion 14. The collet portion 14 includes a first collet 16 and a second collet 18. The first collet 16 and the second collet 18 can be formed using, for example, copper or an alloy containing copper. As shown in FIG. 3, each of the first collet 16 and the second collet 18 is hollow, and a tapered surface 16a is formed at the tip of the first collet 16, and the tip is It is divided into four by slits 16b that are displaced by 90 degrees.

  The inside of the distal end portion of the first collet 16 is substantially the same as the diameter of the electrode 12, and a contact portion 16 e is formed as a portion that contacts the outer periphery of the electrode 12. When the contact portion 16 e comes into contact with the electrode 12, a current is supplied to the electrode 12 through the collet portion 14. That is, the contact part 16e functions as a power feeding part.

  The inner peripheral portion 16c on the tail end side of the contact portion 16e is formed to have a sufficiently large diameter as compared with the diameter of the electrode 12. For this reason, in a state where the electrode 12 is inserted through the first collet 16, the electrode 12 and the inner peripheral portion 16c do not come into contact with each other, and as a result, an escape portion 16f is defined. In the present embodiment, a step is formed at the boundary between the contact portion 16e and the inner peripheral portion 16c, and the diameter of the inner peripheral portion 16c is equal throughout the entire area. In addition, the said inner peripheral part 16c is good also as a taper shape formed so that it might become diameter direction toward a tail end part side. An annular recess 16 d is formed on the inner end surface of the tail end of the first collet 16.

  The second collet 18 has an annular convex portion 18a that fits into the annular concave portion 16d at the tip thereof. An inner peripheral portion 18b from the tip portion to the tail end portion of the annular convex portion 18a is formed to have a diameter sufficiently larger than the diameter of the electrode 12, and functions as a relief portion 18f. A contact portion 18 e having the same diameter as that of the electrode 12 is formed at the tail end portion of the second collet 18. The contact portion 18 e functions as a power feeding portion that supplies current to the electrode 12 by contacting the electrode 12.

  In the present embodiment, a step is formed at the boundary between the contact portion 18e and the inner peripheral portion 18b, and the diameter of the inner peripheral portion 18b is equal throughout the entire area. The inner peripheral portion 18b may have a tapered shape that gradually decreases in diameter.

  Similarly to the first collet 16, a slit 18c that is displaced by 90 degrees is formed at the tail end of the second collet 18, and a tapered surface 18d is formed on the outer surface of the tail end. Accordingly, the first collet 16 and the second collet 18 constitute the collet portion 14 as a whole by fitting the annular convex portion 18a of the second collet 18 into the annular concave portion 16d of the first collet 16.

  The collet portion 14 configured as described above is inserted into the collet body 20. As can be easily understood from FIGS. 1, 2 and 4, the collet body 20 has a hollow shape with a through hole 20a formed therein, and has a tapered surface 16a of the first collet on the tip side. And a tapered surface 20b having the same inclination angle. The through-hole 20a whose diameter is enlarged by the tapered surface 20b is provided with the shield gas ejection holes 20c being displaced 90 degrees at a portion where the tapered surface 20b terminates. When the collet portion 14 is inserted as easily understood from FIG. 1, the expanded through hole 20a is between the outer peripheral portion of the collet portion 14 and the inner wall 20d forming the through hole 20a. A shield gas passage 22 is formed. In the middle of the collet body 20, a bulging portion 20f having a tapered surface 20e is formed, and a male screw 20g is formed on the tail end side of the collet body 20. In FIGS. 1 and 2, reference numeral 20 h indicates a tapered surface formed on the outer periphery on the tip side of the collet body 20.

  The torch head 24 is engaged with the collet body 20 configured as described above. The tip portion of the torch head 24 forms a cylindrical portion 24b in which a female screw 24a to be engaged with the male screw 20g of the collet body 20 is formed, and the tail end portion of the cylindrical portion 24b is reduced in diameter by 90 degrees. An offset hole 24c is formed. A long and thick cylindrical portion 24d extends from the reduced diameter portion where the hole 24c is formed. A male screw 24e is formed at the tail end portion of the cylindrical portion 24d (see FIG. 1), and the diameter of the male screw 24e is expanded from a terminal portion to form a torch cap receiving portion 24f described later. The through-hole 24g formed inside the cylindrical portion 24d is formed with a hole 24h having a diameter increased on the tail end side and partly provided with a male screw, and the tail end of the hole 24h further includes The hole 24i is formed by expanding the diameter.

  In the cylindrical portion 24d of the torch head 24 configured as described above, a collet receiver 26 is fitted at the tip portion thereof. The tip of the collet receiver 26 is formed with a tapered surface 26a having the same angle as the tapered surface 18d of the tail end of the second collet 18, and further, an annular recess 26b is formed on the tail end side. . Regarding the collet receiver 26, reference numeral 26 c indicates a through hole formed in the collet receiver 26.

  In the present embodiment, a collet body gripping body 28 is fitted on the collet portion 14. A male screw 28a is formed at the tip of the collet body gripping body 28, and the terminal portion thereof is formed in a cylindrical shape and is continuous with the flange portion 28b. The flange portion 28b is reduced in diameter in two steps on the tail end side to form an end portion 28c. A through hole is formed along the axial center of the collet body gripping body 28, and a tapered surface 28d having the same inclination angle as the tapered surface 20e of the collet body 20 is formed at a portion corresponding to the flange portion 28b. Is formed. Therefore, when the collet body gripping body 28 is fitted to the collet body 20, the tapered surface 20e of the collet body 20 and the tapered surface 28d of the collet body gripping body 28 are tightly joined.

  Next, the torch nozzle 30 is screwed into the male screw 28a. The torch nozzle 30 is formed with a shield gas ejection portion 30a having a reduced diameter at the tip and a tapered surface 30b having an enlarged diameter in the middle thereof, and a female screw 30c that is screwed into the male screw 28a of the collet body gripping body 28 is formed. It consists of a tail end 30d. A tapered surface 30b formed on the way from the shield gas ejection part 30a to the tail end part 30d is an inner inclined surface having substantially the same inclination angle as the tapered surface 20h of the collet body 20.

  Next, the torch body 32 is engaged with the tail end side of the collet body gripping body 28. The torch body 32 is cylindrical, and an annular convex portion 32 a is formed at the tip of the torch body 32. The annular convex portion 32 a is engaged with the distal end portion of the flange portion 28 b of the collet body gripping body 28. A female screw 32 b is formed on the tail end side of the torch body 32, and the female screw 32 b is screwed with the male screw 24 e of the torch head 24. A hole 32c is formed on the tail end side of the torch body 32 so as to be orthogonal to the axial direction of the torch body 32, and a shield gas supply unit 34 is attached to the hole 32c. The shield gas supply unit 34 has a cylindrical shape with a step, and a passage 34a is formed along the axial direction thereof. An internal thread 34b is formed in communication with the passage 34a. A shield gas supply connector (not shown) is screwed into the female screw 34b.

  A passage 36 is formed between the torch head 24 and the inner peripheral wall of the torch body 32. A cylindrical handle 40 is fitted to the outer periphery of the torch body 32. Therefore, the handle 40 has a hollow shape with a circular cross section. A semi-oval cutout 40a is provided on the tail end side of the handle 40, and the cutout 40a receives the root side of the shield gas supply unit 34 when the handle 40 is fitted to the torch body 32. To fix. In this case, the distal end portion of the handle 40 is engaged with the nozzle packing 42. As can be easily understood from FIG. 2, the nozzle packing 42 engages with the stepped portion formed on the tail end side of the torch nozzle 30, and the inner peripheral surface of the annular projecting portion 42 a is the collet body gripping body. It engages with the tip side of 28. As already described, the tail end of the nozzle packing 42 engages with the tip of the torch body 32.

  On the other hand, when focusing on the tail end side of the welding torch 10, the torch cap 44 is inserted into the through hole 24g of the torch head 24 (see FIG. 1). A hollow insert member 44 a is provided at the tip of the torch cap 44, and the tip of the insert member 44 a is fitted into the annular recess 26 b of the collet receiver 26. The tail end side of the insert member 44a is connected to an enlarged diameter holding portion 44b, and a male screw 44c is formed on the distal end side of the holding portion 44b. The male screw 44c is screwed with a female screw in a hole 24h provided in the torch cap receiving portion 24f. A knob 44d is provided further on the tail end side of the holding part 44b, and a seal part 44e is formed between the knob 44d and the holding part 44b. Actually, the seal portion 44e includes an O-ring 44f press-fitted on the inner peripheral wall of the hole 24i of the torch head 24.

  The welding torch 10 according to the present embodiment is basically configured as described above. Next, the function and effect will be described.

  First, the case where the welding torch 10 is assembled will be described.

  The first collet 16 and the second collet 18 are joined to form the collet portion 14. Specifically, the annular convex portion 18 a of the second collet 18 is joined to the annular concave portion 16 d of the first collet 16. In the present embodiment, as a method of joining the first collet 16 and the second collet 18, a method of press-fitting the annular convex portion 18a into the annular concave portion 16d is adopted. If it carries out like this, the 1st collet 16 and the 2nd collet 18 can be joined with high precision, without a core shift. The first collet 16 and the second collet 18 may be joined by brazing.

  The electrode 12 is inserted through the collet portion 14. Specifically, the electrode 12 is inserted from the contact part 18 e of the second collet 18, is taken out from the contact part 16 e of the first collet 16, and penetrates the collet part 14. Since the contact portion 16e and the contact portion 18e are formed slightly larger than the outer diameter of the electrode 12, the electrode 12 can be easily inserted.

  In this state, the collet receiver 26 is then inserted from the tail end side of the electrode 12 so as to be fitted onto the electrode 12, and the tapered surface 26 a of the collet receiver 26 comes into contact with the tapered surface 18 d of the second collet 18. Next, the insert member 44 a constituting the torch cap 44 is inserted so as to be fitted from the tail end side of the electrode 12, and the distal end portion of the insert member 44 a reaches the annular recess 26 b of the collet receiver 26.

  In this case, the tail end portion of the electrode 12 may be a free end. FIG. 5 shows a longitudinal sectional view of the electrode 12, the collet portion 14, the collet receiver 26 and the torch cap 44 incorporated as described above.

  As described above, the electrode 12, the collet portion 14, the collet receiver 26, and the torch cap 44 are integrated, and the torch head 24 is mounted. That is, the integrated electrode 12, the collet part 14, the collet receiver 26, and the torch cap 44 are inserted into the torch cap receiving part 24f side. As a result, the first collet 16 side of the collet portion 14 is exposed to the outside from the cylindrical portion 24 b of the torch head 24. Next, the tail end portion on which the male screw 20g of the collet body 20 is formed is inserted from the first collet 16 side so as to be fitted. Therefore, when the male screw 20g is screwed with the female screw 24a of the torch head 24, the tapered surface 16a is brought into pressure contact with the tapered surface 20b of the collet body 20 and the tips of the wall portions forming the slit 16b are mutually connected. Bend inward to hold and position the electrode 12 securely. This combined state is shown in FIG. On the other hand, since the collet receiver 26 is mounted on the torch head 24 in advance, the tapered surface 26a of the collet receiver 26 engages with the tapered surface 18d of the second collet 18, and is held by the collet portion 14 and the collet portion 14. Positioning along the axial direction of the electrode 12 is achieved by the collet body 20 and the collet receiver 26. In this case, the wall forming the slit 18c of the second collet 18 bends inward and presses against the outer peripheral surface of the electrode 12 to hold the electrode 12 firmly, as in the first collet 16 side. .

  Next, the torch body 32 is engaged with the torch head 24. That is, the female screw 32 b of the torch body 32 is screwed into the male screw 24 e of the torch head 24. In this state, the nozzle packing 42 is fitted to the collet body 20, and the tail end portion of the nozzle packing 42 is engaged with the tip portion of the torch head 24. The nozzle packing 42 firmly fixes the collet body 20 and the cylindrical portion 24 b of the torch head 24.

  Next, the handle 40 may be inserted into the torch body 32 and the notch 40 a of the handle 40 may be engaged with the outer peripheral wall of one end of the shield gas supply unit 34. This prevents the torch body 32 from rotating about the axial direction. The nozzle packing 42 is fitted on the tip side of the collet body gripping body 28 so that the nozzle packing 42 engages with the tip of the handle 40. For this reason, the annular protrusion 42 a of the nozzle packing 42 abuts on the outer periphery of the tip of the collet body gripping body 28.

  Next, the torch nozzle 30 is screwed into the male screw 28 a formed at the tip of the collet body gripping body 28. That is, the female screw 30 c of the torch nozzle 30 is screwed into the male screw 28 a of the collet body gripping body 28. Thereby, the assembly of the welding torch 10 is completed.

  Next, if the knob 44d is rotated, the male screw 44c of the holding portion 44b is screwed with the female screw of the hole 24h formed in the torch cap receiving portion 24f, and the tapered surface 16a of the first collet 16 and the taper of the collet body 20 are engaged. The surface 20b is in pressure contact, and the tip of the insert member 44a presses the tapered surface 26a of the collet receiver 26 and the tapered surface 18d of the second collet 18, so that the electrode 12 is held by the contact portion 16e and the contact portion 18e. The As a result, the electrode 12 is positioned, and the direction orthogonal to the axial direction is firmly fixed by the first collet 16 and the second collet 18, so that the electrode 12 is not eccentric.

  When using as a welding torch after such a preparation stage, the handle 40 is gripped by a robot (not shown) and the shield gas is supplied from the shield gas supply unit 34. The shield gas passes from the passage 34 a through the passage 36, reaches the hole 24 c, and is ejected outward in the circumferential direction from the shield gas ejection hole 20 c of the collet body 20 through the shield gas passage 22. The jetted shield gas is jetted from the tip of the torch nozzle 30 so as to surround the tip of the electrode 12. At that time, if a predetermined current is supplied to the electrode 12 from a power source (not shown), the tip of the electrode 12 can be TIG welded to a workpiece (not shown).

  According to the present embodiment, the electrode 12 is fixed by the first collet 16 and the second collet 18 constituting the collet portion 14 in the longitudinal direction, and the first collet 16 is positioned by the collet body 20. The second collet 18 is positioned and fixed by a collet receiver 26 mounted inside the torch head 24.

  Further, the collet body 20 is positioned by a collet body gripping body 28 and the torch head 24 is positioned and fixed by a torch body 32. Accordingly, as a result, the electrode 12 is positioned by the various components aligned and fixed along the axial direction thereof, so that the eccentricity in the direction perpendicular to the axial direction of the electrode 12 is prevented and the torch is The length and positioning of the tip of the electrode 12 can be easily achieved by rotating the knob 44d of the cap 44. Accordingly, when the electrode 12 is worn out and replaced, or as a result of being worn out, the tip of the electrode 12 must be polished, so that the tip must be positioned easily and in a short time without requiring skill. Can carry out the work against. As a result, the work efficiency of welding is improved at once, and an effect that a product excellent in welding quality can be obtained is obtained.

  In addition, although the said embodiment demonstrated the torch for TIG welding, it cannot be overemphasized that it can be used also for another welding method, for example, plasma welding.

FIG. 1 is a longitudinal sectional view along the axial direction of a welding torch according to an embodiment of the present invention. FIG. 2 is an exploded perspective view of the welding torch shown in FIG. FIG. 3 is a longitudinal explanatory view of a state in which the first collet and the second collet constituting the welding torch shown in FIGS. 1 and 2 are integrated to hold an electrode. FIG. 4 is an enlarged longitudinal sectional view of the welding torch electrode, collet, collet body, nozzle packing, torch body, and torch head shown in FIGS. FIG. 5 is a partially longitudinal explanatory view of a state in which an electrode, a collet, a collet receiver, and a torch cap constituting a welding torch are combined. FIG. 6 is a partially longitudinal explanatory view of a state in which an electrode, a collet, a collet receiver, a torch cap, a collet body, and a torch head constituting a welding torch are combined.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Welding torch 12 ... Electrode 14 ... Collet part 16 ... 1st collet 18 ... 2nd collet 20 ... Collet body 24 ... Torch head 30 ... Torch nozzle 32 ... Torch body 34 ... Shield gas supply part 40 ... Handle 42 ... Nozzle packing 44 ... Torch cap

Claims (7)

A long electrode,
A collet for inserting and holding the electrode;
A collet body and a torch head into which the collet part is inserted;
A torch body through which the torch head is inserted and positioned;
Have
The collet portion has a first collet and a second collet, and the first collet has a tip tapered surface that comes into contact with a tapered surface formed inside the collet body,
2. The welding torch according to claim 1, wherein the second collet has a tail end tapered surface that abuts against a tapered surface of a collet support provided inside the torch head. The welding torch according to claim 1,
Provided inside each of the first collet and the second collet is a relief portion having a diameter larger than the diameter of the electrode,
A welding torch characterized in that a tail end portion of the first collet and a tip end portion of a second collet are integrally formed with each other. The welding torch according to claim 2,
The welding torch characterized in that the tail end portion of the first collet and the tip end portion of the second collet are fitted by press-fitting. The welding torch according to claim 2,
The welding torch characterized in that the tail end portion of the first collet and the tip end portion of the second collet are brazed together. In the welding torch according to any one of claims 1 to 4,
Welding characterized in that slits are formed in the tip end portion of the first collet and the tail end portion of the second collet, respectively, extending in the axial direction and arranged at equal intervals around the axis. For torch. The welding torch according to claim 5,
The welding torch according to claim 1, wherein the slits are arranged at intervals of 90 degrees. A collet for a welding torch that is disposed inside a welding torch body and holds a long electrode,
Having a first collet and a second collet formed hollow;
The first collet is
A tip tapered portion provided at the tip portion, a tip slit extending in the axial direction from the tip portion, a contact provided on the inner side of the tip portion and having a diameter substantially the same as the diameter of the electrode and contacting the electrode And a relief portion provided on the tail end side from the contact portion and formed to have a diameter larger than the diameter of the electrode,
The second collet is
A tail end tapered portion provided in the tail end portion, a tail end slit extending in the axial direction from the tail end portion, provided on the inner side of the tail end portion, and having a diameter substantially the same as the diameter of the electrode, A contact portion that comes into contact with the electrode, and a relief portion that is provided on the tip side from the contact portion and is formed with a diameter larger than the diameter of the electrode,
A collet for a welding torch, wherein a tail end portion of the first collet and a tip end portion of the second collet are coaxially engaged.

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