Welding Torch

DESCRIPTION WELDING TORCH TECHNICAL FIELD The present invention relates to a welding torch having a forced power feeder mechanism which is for example used for consumable electrode gas shield arc welding. BACKGROUND ART A collet type forced power feeder structure is known as a forced power feeder mechanism (Patent document 1). This is a structure such that the power feeder is cylindrical and its inner diameter is nearly equal to the outer diameter of the welding wire (hereinafter called wire), and the cylindrical feeder is divided into a plurality of sections on a plane including the central axis or provided with a slit formed by slitting, and the inner diameter surface of the cylindrical feeder is pressed against the wire by an activating means. The configuration and action of a welding torch having a collet type forced power feeder structure disclosed in Patent document 1 is briefly described in the following. The cylindrical chip is formed with a through-hole as a passage for the wire that is a consumable electrode at the axial center thereof, and provided with conical projections at either end, and its end portion is at least halved by slitting. The cylindrical chip is disposed between the chip holder having a conical depression and a conical depression at the front end of the torch body detachable from the torch body base. The pressure means is formed by a spring support member disposed at the rear end of the torch body, of which the axial position can be freely set by a screw or the like, and a spring member disposed between the spring support member and the chip holder. The chip holder is pressed against the cylindrical chip by the pressure means, and a power feed member is connected to the torch body. In the above configuration, the pressure generated by the pressure means is applied to both ends of the cylindrical chip and changed in direction to the centripetal direction due to the conical slopes at both ends, and thereby, the wire is always held by the conical chip. Accordingly, even in case the conical chip becomes worn, the wire is axially held and free from change of the wire position. Also, power feed to the wire is reliably executed at a constant position and it is possible to obtain an excellent welding result. However, a conventional welding torch having a collet type forced power feeder structure as described above is actually hardly prevalent because of the following problems. Particularly, as a welding torch used for robot welding, in order to cope with complicated jigs and work, a so-called curved torch with the torch body partially curved and improved in accessibility to the work or jig is widely employed. However, the method mentioned in Patent document 1 cannot be directly used for a curved torch. And, when it is intended to use the method for a curved torch, a first idea is such that the pressure means is disposed not at the rear portion of the torch body but at the front end side beyond the curved portion of the torch body. However, the structure becomes complicated at the front end, and also, as pointed out in Patent document 1, the spring member that is a pressure means may deteriorate due to the influence of arc heat generated during the welding. Also, in the case of the conventional welding torch described above, the inner diameter surface of the cylindrical chip gradually wears, and therefore, there is provided a through-hole nearly equal to the wire diameter in the initial condition, but in this case, the wire cannot be smoothly set through because it is caught at the rear end side of the cylindrical chip that is the wire insertion side. Further, in the case of the conventional welding torch described above, when the cylindrical chip is divided into a plurality of sections by slitting, the inner diameter is displaced in the narrowing direction even in case of no pressure applied by the pressure means. Consequently, the wire cannot be set through, and it is necessary to completely remove the cylindrical chip or the chip body end portion holding the cylindrical chip before setting the wire. After that, the plurality of divided cylindrical chips must be individually abutted on the wire and must be set on the front end of the chip body while keeping them in a state of being held, resulting in considerable worsening of the workability. On the other hand, when the cylindrical chip is halved instead of dividing into a plurality of portions, the pressure given by the pressure means is required to be high enough to be able to deform the cylindrical chip itself in accordance with wear of the cylindrical chip. Accordingly, in the initial condition of less wear, it is configured in that the axial position of the spring support member can be freely set by a screw or the like so that the pressure can be adjusted in accordance with wear of the cylindrical chip. However, it is very difficult to adjust the pressure in accordance with wear of the cylindrical chip that cannot be checked from outside, and it is almost impossible to make reliable adjustments at all times during the production. Patent document 1: Unexamined Japanese Patent Publication H2-27074 DISCLOSURE OF THE INVENTION In order to solve the above problem, the welding torch of the present invention comprises a cylindrical feeder collet formed with a slit in the front end portion for feeding power to a welding wire internally set through; a collet case for storing the feeder collet therein, having an abutment on which the front end of the feeder collet is abutted; a flexible inner tube for leading the welding wire to the feeder collet; a torch body with the inner tube inserted therein and the collet case detachably disposed at the front end thereof; and a pressure mechanism for pressurizing the feeder collet toward the end of the welding wire, wherein there is provided a taper surface on at least any one of the front end of the feeder collet and the abutment of the collet case. Thus, the feeder collet can be pressurized in the welding wire feeding direction by using the pressure means via the inner tube having flexibility (bending property), and thereby, the welding wire can be reliably held by the feeder collet. Accordingly, even in the case of a so-called curved torch of which the torch body of the welding torch is at least partially curved, it is possible to realize a forced feeder mechanism. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic sectional view showing a welding torch in the preferred embodiment 1 of the present invention. Fig. 2 is an enlarged sectional view showing a collet case in the preferred embodiment 1 of the present invention. Fig. 3 is an enlarged sectional view showing an essential portion of a torch body in the preferred embodiment 1 of the present invention. Fig. 4A is a top view of a feeder collet in the preferred embodiment 1 of the present invention. Fig. 4B is a front view of a feeder collet in the preferred embodiment 1 of the present invention. Fig. 4C is a bottom view of a feeder collet in the preferred embodiment 1 of the present invention. Fig. 5 is an enlarged sectional view showing an essential portion of a torch body in the preferred embodiment 2 of the present invention. Fig. 6 is an enlarged sectional view showing a collet case in the preferred embodiment 2 of the present invention. DESCRIPTION OF THE REFERENCE NUMERALS AND SIGNS 1 Torch cable 1a Torch body connection 1b, 3c Wire guide storing section 2 Conduit tube 3 Torch body 3a Torch cable connection 3b Collet case connection 4, 12 Inner tube 4a, 12a Wire guide connection 4b, 12b Conduit tube storing section 4c Coiled portion 5 Spring 6 Feeder collet 6a Taper surface 6b Slit portion 6c Feeding section 6d Wire insertion opening 7 Collet case 7a Insulative guide

We claim: 1. A welding torch comprising: a cylindrical feeder collet formed with a slit axially extending from a front end thereof for feeding power to a welding wire internally set through; a collet case for storing the feeder collet therein, having an abutment on which the front end of the feeder collet is abutted; a flexible inner tube for leading the welding wire to the feeder collet; a torch body with the inner tube inserted therein and the collet case detachably disposed at the front end thereof; and a pressure mechanism for pressurizing the feeder collet toward the end of the welding wire, wherein there is provided a taper surface on at least any one of the front end of the feeder collet and the abutment of the collet case. 2. The welding torch of claim 1, wherein the torch body is partially curved. 3. The welding torch of claim 1, wherein the inner tube is coil-formed with a wire material having a circular section spirally wound thereon. 4. The welding torch of claim 1, wherein the inner tube has lengthwise elasticity, and the pressure mechanism uses elasticity of the inner tube. 5. The welding torch of claim 1, wherein the pressure mechanism is formed of an elastic member disposed at the rear end of the inner tube. 6. The welding torch of claim 1, wherein the torch body includes a torch body connection disposed at the front end of a torch cable for feeding the welding wire and a torch cable connection detachably disposed at a rear end thereof; the inner tube includes a front end of a conduit tube for setting the torch cable through and a wire guide connection detachably disposed at the rear end thereof; and the pressure mechanism is formed of a spring member whose one end abuts the torch body connection and the other end abuts the wire guide connection. 7. The welding torch of claim 6, wherein the spring member is fixed on the wire guide connection. 8. The welding torch of claim 1, wherein the front end of the feeder collet is provided with a feeding section for feeding power to the welding wire, and the inner diameter of the feeding section is equal to the diameter of the welding wire, and the inner diameter of the rear end portion of the feeder collet is larger than the diameter of the welding wire. 9. The welding torch of claim 8, wherein the length of the slit portion is longer than the length of the feeding section. 10. The welding torch of claim 1, wherein the collet case has an insulative guide at the front end thereof which has a diameter larger than the diameter of the welding wire. 11. The welding torch of claim 2, wherein the inner tube is flexible and bends along a curved shape of the torch body.

It comprises cylindrical feeder collet (6) formed with a slit portion at a front end thereof for feeding power to a welding wire internally set through; collet case (7) for storing feeder collet (6) therein, having an abutment on which the end of feeder collet (6) is abutted; flexible inner tube (4) for leading the welding wire to feeder collet (6); torch body (3) with inner tube (4) inserted therein and collet case (7) detachably disposed at the front end thereof; and spring (5) for pressurizing feeder collet (6) toward the front end of the welding wire, wherein there is provided a taper surface on at least any one of the front end of feeder collet (6) and the abutment of collet case (7). Thus, it is structurally simple and applicable for a curved torch.