Abstract:
A stud welding apparatus comprises a feeder to receive a plurality of studs and feed the stud one by one with the stud being fed in advance of a weld portion thereof from an outlet of the feeder; and a welding gun to receive the stud as fed from the feeder through a feeding pipe to hold the stud and to weld the stud to a workpiece. The outlet of the feeder is provided with a shuttle loader wherein a hollow shuttle is loaded to a rod body of the stud to extend the length of a short stud, so that the shuttle loaded stud is lengthened as a whole to prevent the shuttle loaded stud from tumbling in the feeding pipe and/or a stud path in the welding gun.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a stud welding apparatus for welding rod-shaped studs having a welding part to a workpiece in one end and more particularly to a stud welding apparatus comprising a feeder for accommodating a plurality of rod-shaped studs and feeding one stud at a time, with the welding part head first from an outlet thereof, and a welding gun to which is connected a feeder pipe extending from the outlet of the feeder to receive a stud fed from the feeder, holding that stud at its tip with the welding part and welding the welding part to a workpiece. 
     BACKGROUND OF THE INVENTION 
     In Japanese Application No. H7-171683, one example of a stud welding apparatus is described comprising a feeder for accommodating a plurality of rod-shaped studs having a welding part at one end and feeding one stud at a time, with the welding part head first, from an outlet thereof and a welding gun to which is connected a feeder pipe extending from the outlet of the feeder to receive a stud fed from the feeder, holding that stud at its tip with the welding part head first, and welding the welding part to a workpiece. This stud welding apparatus is provided with two escapes in the feeder, that is, with a stud queuing device so that stud feeding is speeded up. 
     In the stud welding apparatus cited in Japanese Application No. H7-171683 and in other conventional stud welding apparatuses, when feeding studs, it is necessary that the studs be at least of a predetermined length so they will not tumble in the feeder pipe or in the stud path of the welding gun. When the studs are short and tumble in the feeder pipe or welding gun stud path, the operation of sending studs in a suitable posture is hindered, and there is a danger of jamming inside the feeder pipe or welding gun stud path. 
     Therefore, an object of the present invention is to provide a stud welding apparatus by which, even when the studs are short enough to tumble inside the feeder pipe or welding gun stud path, studs can be sent in a suitable posture, and the danger of jamming inside the feeder pipe or welding gun stud path is eliminated. 
     SUMMARY OF THE INVENTION 
     In order to achieve the object stated above, based on the present invention, a stud welding apparatus is provided that comprises a feeder for accommodating a plurality of rod-shaped studs having a welding part at one end and feeding one stud at a time, with the welding part head first from an outlet thereof, and a welding gun to which is connected a feeder pipe extending from the outlet of the feeder to receive a stud fed from the feeder, holding that stud at its tip with the welding part head first and welding the welding part to a workpiece; wherein a shuttle mounting device is provided at the outlet portion of the feeder for mounting a hollow shuttle to the rod-shaped shank of the stud, which hollow shuttle receives the rod-shaped shank of the stud so as lengthen it; the overall length of the stud to which the shuttle has been mounted is then rendered a prescribed length so the stud will not tumble in the feeder pipe or in a stud path in the welding gun. 
     As described above, even when the studs are short enough to tumble inside the feeder pipe or in the welding gun stud path, the shuttle lengthens the studs overall so that they will not tumble in the feeder pipe or welding gun stud path. Studs can therefore be sent in a suitable posture in the feeder pipe and welding gun stud path, and the danger of jamming inside the feeder pipe or welding gun stud path can be eliminated. Furthermore, even if the studs are of various lengths and different shapes, when mounted in the shuttle, they can be made to have the same outer diameter and the same length, which facilitates making welding apparatuses more universal making it possible to handle studs of various lengths and different sizes with the same welding apparatus. In addition, it is also possible to provide a plurality of mounting devices so that even if the studs are of a different shapes for each mounting device, if they are mounted in a shuttle having the same outer diameter and length, the same welding gun can be used to select studs of different shape, either sequentially or randomly, and weld therewith. 
     In the stud welding apparatus described above, the welding gun welds a stud to the workpiece while holding the shuttle and then after welding that stud, moves away from the workpiece while holding the shuttle so that it separates from that welded stud, and the shuttle held by the welding gun is thereafter returned to the stud welding apparatus through a return pipe provided between the welding gun and the stud welding apparatus. In this way, the shuttle can be removed from the welding stud, and these used shuttles can be used again. The shuttle comprises a hollow rod-shaped body for receiving and holding the stud and is lengthened so that the stud will not tumble in the feeder pipe or the stud path in the welding gun. For that reason, even if the studs are so short as to be undesirable for feeding, they can be sent in a suitable posture to the welding gun. This shuttle has an entrance part contacted flush by the large-diameter welding part of a received stud and a terminating part closing off a hollow part for receiving the other end of such received stud. Also, a threaded member is provided in its terminating part and is of such length as can abut the other end of the received stud; the extension length from the terminating part can then be changed to match the length of the received stud. In this way, a stud received in a shuttle can be held without wobbling. In this case, the shuttle has a plurality of slits formed in the circumferential direction, extending in the longitudinal direction from the entrance part toward the terminating part, and the inner diameter of the stud-receiving hollow part of the shuttle is formed to be either equal to or slightly smaller than the outer diameter of the stud. By these slits, the portion of the shuttle from the entrance part to the terminating part is formed of a plurality of elastic pieces that extend in the longitudinal direction, and the rod-shaped shank of a stud received in the hollow part, due to these elastic pieces, can then be easily inserted, and the received stud will be held without wobbling. A stud queuing device is provided in the feeder, and the shuttle mounting device is provided between the stud queuing device and the outlet. In this way, when shuttles are mounted on the studs, the studs will be queued so mounting is easy and the used shuttles can easily be reused. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of a stud welding apparatus relating to one embodiment of the present invention, and also shows an initial stage I of the welding gun operation, a welding stage II, a pulling-up stage III and a shuttle return stage IV. 
         FIGS. 2A and 2B  are a right side elevation and front elevation of a stud. 
         FIGS. 3A and 3B  are a view of a shuttle as seen from the entrance part end and a vertical section thereof. 
         FIG. 4  is a vertical section of a shuttle wherein the shuttle shown in  FIG. 3  has been mounted to the stud shown in  FIG. 2 . 
         FIGS. 5A to 5D  are vertical sections of shuttles wherein the shuttle shown in  FIG. 3  has been mounted to various studs. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A stud welding apparatus  1  relating to one embodiment of the present invention shall now be described with reference to the drawings.  FIG. 1  shows the stud welding apparatus  1 , comprising a feeder  5  for accommodating a plurality of rod-shaped studs  3  having a welding part  2  at one end and feeding one stud  3  at a time, with the welding part  2  head first from an outlet portion  40  thereof, and a welding gun  9  to which is connected a feeder pipe  6  extending from the outlet portion  40  of the feeder  5  to receive a stud  3  fed from the feeder, holding that stud  3  at its tip with the welding part  2  head first and welding the welding part  2  thereof to a workpiece  7 . A stud queuing device  10  is provided at the outlet portion  40  of the feeder  5  for queuing the studs  3  fed one at a time from the outlet portion  40 , with the welding parts  2  of the studs  3  head first. The welding gun  9  also has a stud path  11  for receiving the studs  3  fed from the feeder pipe  6  and sending them to its tip. The welding gun  9 , furthermore, may be any stud welding gun, but in the embodiment shown, the gun is described as one for arc-welding studs, that is a gun that melts material being worked by generating an arc between the welding part  2  of a stud  3  held at the tip of the welding gun  9 , on the one hand, and the weld position on the workpiece  7 , on the other, and also one that is brought to abut the melted material by pressure so as to weld the studs  3  to the workpiece  7 . It may be another welding gun such as, for example, a welding gun for performing resistance welding. Also, although not shown in the drawings, a controller is provided in the stud welding apparatus  1  for effecting control so that the welding operations indicated by stages I to IV in  FIG. 1  are performed. First, the welding gun  9  is placed in an initial position in stage I in  FIG. 1 . Next, the welding gun  9  is moved to the welding operation position indicted at stage II in  FIG. 1 , and welding is performed. After this welding, the welding gun  9  is pulled up to a pulled-up position indicated at stage III in  FIG. 1 . And finally, the welding gun  9  finishes the welding at stage IV in  FIG. 1 . 
     As shown in  FIG. 1 , a shuttle mounting device  14  is provided between the outlet  42  of the stud queuing device  10  provided on the outlet side of the feeder  5  and the intake of the feeder pipe  6  for mounting a shuttle  13  to the rod-shaped shank of a stud  3 , which shuttle is a hollow shuttle to receive the rod-shaped shank of the stud  3  so as to extend the length of the stud  3 . The shuttle mounting device  14  receives a queued stud  3  in a first section  15 , holds it in that state, then moves a shuttle  13  held in a prescribed orientation in a second section  17  toward that stud  3  and accommodates and holds the rod-shaped shank of that stud  3  in the hollow part of the shuttle  13 . The overall length of the stud  3  to which the shuttle  13  has been mounted is thus extended to a prescribed length so the stud will not tumble in the feeder pipe  6  or in the stud path  11  of the welding gun  9 . The manner in which the shuttle  13  is mounted to the stud  3  is not limited to that described above but may be some other method, and the structure may be any structure so long as the shuttle  13  can be mounted to a stud  3  queued and sent there in order to receive its rod-shaped shank. 
     Next, the stud  3 , equipped with the shuttle  13 , is sent through the feeder pipe  6  to the stud path  11  of the welding gun  9 . This manner of feeding may be a conventionally known one and may be performed by pressure transport using pressurized air or the like, for example. The stud  3  equipped with a shuttle  13  sent to the stud path  11  of the welding gun  9  is sent, as is, to the tip of the welding gun  9  and is held at the tip of the welding gun  9  with the welding part  2  head first. As explained earlier, the overall length of the stud  3  to which the shuttle  13  is mounted is extended to a prescribed length so the stud will not tumble in the feeder pipe  6  or in the stud path  11  of the welding gun  9 . By the shuttle  13 , short studs  3  can be lengthened and even in cases where a single stud  3  is short enough to tumble in the feeder pipe  6  or in the stud path  11  of the welding gun  9 , that stud  3  will then be sent through the feeder pipe  6  and through the stud path  11  of the welding gun  9  in a suitable posture, so the danger of jamming inside the feeder pipe  6  or stud path  11  can be eliminated. 
     In  FIG. 1 , the welding gun  9 , which is holding a stud  3  equipped with a shuttle  13  at its initial position in stage I, is positioned at a prescribed welding position on the workpiece  7 . As indicated by the arrow  18 , the welding gun  9  is moved so as to approach the workpiece  7  and is moved to the welding operation position of stage II. During the welding operation, an arc is generated between the workpiece  7  and the welding part  2  of the stud  3 ; that portion is melted, and, as indicated by the arrow  19  in stage II, the welding part  2  of the stud  3  equipped with the shuttle  13  held at the tip of the welding gun  9  is then pressed against the workpiece  7 , and the stud  3  is welded to the workpiece  7 . After the stud  3  has been welded to the workpiece  7 , the welding gun  9 , oriented in the direction of the arrow  21  as indicated in stage III, is pulled up so as to move away from the welded stud  3 . At that time, the welding gun  9  moves away from the workpiece  7  while still holding the shuttle  13  so that the latter separates from the welded stud  3 . Consequently, the shuttle  13  will then be held by itself by the welding gun  9 . 
     Then shuttle  13  held by the welding gun  9  is sent along a return path  22  of the welding gun  9  and through a return pipe  23  provided between [the welding gun  9  and] the shuttle mounting device  14  to a second section  17  of the shuttle mounting device  14 . In this way, the shuttle  13  is returned in the same attitude as the shuttle(s)  13  accommodated in the second section  17  and the returned shuttle  13  can therefore be reused as is. Furthermore, because the shuttle mounting device  14  is provided between the stud queuing device  10  and the outlet of the feeder, as described earlier, when mounting a shuttle  13  to a stud  3 , the stud  3  will already be in a queued condition, so mounting the shuttle  13  is easy, also facilitating handling used shuttles to be reused. 
     The stud  3  and shuttle  13  shall now be described with reference to  FIGS. 2 to 4 . The stud  3  is a commonly known item which, as shown in  FIGS. 2A and 2B , comprises a large-diameter welding part  2  of diameter d and a rod-shaped shank  25  of length L that is smaller in diameter than the welding part  2 . In the example shown, threads are formed in the rod-shaped shank  25 , and a bolt stud is provided therein. Alternatively, the stud may be some other commonly known rod-shaped stud. 
     As shown in  FIGS. 3A and 3B , the shuttle  13  comprises a hollow rod-shaped body  41  for receiving and holding the stud  3 . In this embodiment, the welding gun  9  performs arc welding, so the shuttle  13  is formed of an electrically conducting material. In general, the shuttle will consist of an electrical conducting metal, but it may also be made of an electrical conducting plastic. The shuttle  13 , moreover, is lengthened so the stud will not tumble in the feeder pipe  6  or in the stud path  11  of the welding gun. Accordingly, even if the stud  3  is so short as to be unsuitable for feeding to the tip of the welding gun  9 , it can nevertheless be fed in a suitable posture to the tip of the welding gun  9 . This shuttle  13  has an entrance part  27  flushly contacted by the large-diameter welding part  2  of a stud  3  received into its hollow part  26  and a terminating part  29  for receiving the other end of the received stud  3  and closing off the hollow part  26 . A threaded member  30  is provided in the terminating part  29  and is of such length as to be able to abut the other end of the received stud  3  which can alter the extension length from the terminating part  29  to the hollow part  26  so as to match the length of the received stud  3 . In this way, a stud  3  received into the hollow part  26  of the shuttle  13  can be held so that it does not wobble. A lock nut  31  is provided in the threaded member  30  on the outside of the terminating part  29 , thus enabling fixing the lengthened threaded member  30  from the terminating part  29  to the hollow part  26 . Moreover, a plurality of slits  33  (six in the example shown) is formed in the shuttle  13  in the circumferential direction, extending in the longitudinal direction from the entrance part  27  toward the terminating part  29 . The inner diameter of the stud-receiving hollow part  26  of the stud  3 , moreover, is formed so as to be equal to or slightly smaller than the outer diameter of the stud  3 . The portion of the shuttle  13  from the entrance part  27  toward the terminating part  29  is formed by the slits  33  as a plurality of elastic pieces that extend in the longitudinal direction. The rod-shaped shank  25  of a stud  3  received into the hollow part  26  will then be held by these elastic pieces, so that insertion of the stud  3  is facilitated and, after insertion, frictional engagement is effected so that the received stud  3  does not wobble. The entrance part  27 , moreover, is formed in a bugle shape to facilitate receiving the rod-shaped shanks  25  of the studs  3 . 
       FIG. 4  shows how a short stud  3  has a shuttle  13  mounted to it so that its overall length  34  is extended. The overall length  34  is set at a length so the stud will not tumble in the feeder pipe  6  or in the stud path  11  of the welding gun. When the stud  3  and the shuttle  13  have been combined, the overall length  34  is set at a length so the stud will not tumble in the feeder pipe  6  or in the stud path  11  of the welding gun, but as shown in  FIG. 5 , there are also cases where the diameter of the welding part  2  of the stud  3  will fit deeply into the end of the bugle-shaped shuttle entrance part  27  so the overall length of the shuttle  13  may be set at a length so the stud will not tumble in the feeder pipe  6  or in the stud path  11  of the welding gun. 
       FIG. 5  shows examples wherein the shuttle  13  is mounted to various studs.  FIG. 5A  shows how the shuttle  13  is mounted to a short stud  3 A having a welding part  2 A of large diameter.  FIG. 5B  shows how the shuttle  13  is mounted to a slightly long stud  3 B and having a welding part  2 B of large diameter. Because the stud  3 B is long, the threaded member  30  does not extend to the hollow part of the shuttle  13 .  FIG. 5C  shows how the shuttle  13  is mounted to a short stud  3 C and having a welding part  2 C of small diameter.  FIG. 5D  shows how the shuttle  13  is mounted to a long stud  3 D but having a welding part  2 D of small diameter. As is evident from these diagrams, the overall length of a stud to which the shuttle  13  has been mounted is extended to a prescribed length  34  so the stud will not tumble in the feeder pipe  6  or in the stud path  11  of the welding gun  9 , and, furthermore, every one of the shuttle  13 -equipped studs, namely  3 A to  3 D, has a constant length  34 . In the embodiment shown, moreover, the threaded member  30  extends away from the terminating part  29  of the shuttle  13 , but this is no hindrance during feeding and also no hindrance in the feeding or holding in the welding gun  9 .