Stud welding tool
This invention relates to an improved tool for welding studs to workpieces. 
     A welding tool in accordance with the invention is particularly designed to end weld a small stud having a precisely formed tip to a workpiece in a downhand position, with the workpiece horizontal. The stud is held by a chuck assembly having a chuck leg and a chuck which holds the stud with the tip extending forwardly. An electrical coil magnetically holds the chuck leg in a fixed, retracted position after the operator manually retracts the chuck assembly. When the coil is deenergized, a plunge spring which is under compression plunges the chuck leg, chuck and stud back toward the workpiece. A high voltage is imposed between the stud and the workpiece prior to the stud contacting the workpiece by a capacitive power source. When the stud tip reaches the workpiece, the tip is vaporized and adjacent portions of the stud and workpiece melt with the stud becoming securely welded thereto. 
     The present invention provides an improved welding tool and specifically one which end welds small tipped studs in the manner described above. The welding tool includes an inexpensive and simplified means for removably connecting a chuck to a chuck leg which enables the chuck to be quickly replaced when necessary. The connection includes a ring located around a rear portion of the chuck which engages a beveled surface of an end of the chuck leg and in turn is engaged by a beveled surface of a nut which is threadedly connected to the chuck leg. As the nut is tightened, it forces the ring inwardly into engagement with the chuck. 
     The new welding tool also has a welding foot having positioning posts which abut the workpiece to position a spark shield around the end of the chuck and a stud held thereby. The spark shield can float or move to a limited extent toward and away from the tool body to assure that the end of the spark shield will be in the plane of the stud tip and against the workpiece when the weld is effected. 
     The welding foot is adjustably connected by a pair of supporting legs to the tool body and can be moved in and out to change the spacing of the welding foot and positioning posts from the tool body and change the length of the plunge stroke of the stud. A threaded rod and sleeve are connected between the welding foot and the tool body to select the position of the foot, the sleeve being calibrated to accurately position the foot. 
     The new tool also has means for adjusting the compression of the coil plunge spring which plunges the chuck leg, chuck, and stud back toward the workpiece. To accomplish this, the coil plunge spring is located around a rear portion of the chuck leg and has one end engaging a seating shoulder on the leg. A seating sleeve is located around the rear portion of the chuck leg but separate therefrom, with the sleeve engaging the opposite end of the coil spring. The sleeve can be moved toward and away from the seating shoulder of the chuck leg to adjust the compression on the spring. The movement of the sleeve is accomplished by a threaded member which is rotatably supported by the tool body but prevented from moving longitudinally. The threaded member has an internal thread which engages external threads on the sleeve to move the sleeve longitudinally when the member is turned. The member also has visual means for enabling an operator to determine the position of the sleeve and thus provide an indication of the degree of compression on the coil plunge spring. 
     It is, therefore, a principal object of the invention to provide an improved welding tool having the features discussed above. 
    
    
     Many other objects and advantages of the invention will be apparent from the following detailed description of a preferred embodiment thereof, reference being made to the accompanying drawings, in which: 
     FIG. 1 is a side view in elevation, with parts broken away and with parts in section, of a welding tool according to the invention; 
     FIG. 2 is a view in transverse cross section taken along the line 2--2 of FIG. 1; 
     FIG. 3 is a fragmentary front view in elevation of the welding tool of FIG. 1; 
     FIG. 4 is a fragmentary view in longitudinal cross section of a portion of the tool of FIG. 1, but showing components in a different position; 
     FIG. 5 is a fragmentary view in longitudinal cross section of a portion of the tool of FIG. 1, but showing components in a different position; 
     FIG. 6 is a view in transverse cross section taken along the line 6--6 of FIG. 5; 
     FIG. 7 is an enlarged, detailed view in longitudinal section of a small portion of the apparatus of FIG. 1; and 
     FIG. 8 is a view in transverse cross section taken along the line 8--8 of FIG. 1. 
    
    
     Referring to the drawings, a stud welding tool 10 embodying the invention is used to weld a tipped stud 12 having a specially and precisely formed tip 14 to a workpiece. The tool includes means for holding the stud in a position retracted from the workpiece, and means for plunging the stud toward and against the workpiece. Before the stud is plunged against the workpiece, a high voltage is imposed between the stud and the workpiece. When the stud approaches the workpiece, the tip 14 is vaporized and an arc is established between the stud and the workpiece which melts adjacent portions of the stud and the workpiece to weld the stud firmly thereto. 
     The tool 10 has an overall main body or housing 16 including a central portion 18 of suitable dielectric material and an integral pistol grip 20. The body 16 further includes a front metal frame 22 and a front wall 24 of dielectric material. The frame 22 holds the wall 24 in position and is affixed to the central body portion 18 by side fasteners 25 (FIG. 2). A separate rear end cap 26 closes off the rear of the central body portion 18. 
     A chuck assembly 28, comprising a chuck leg 30 and a chuck 32, holds the stud 12 in front of the tool 10 during a welding operation. In this instance, the front end of the chuck 32 is surrounded by a permanent spark shield 34 carried by a welding foot 36. The welding foot is adjustably supported by two supporting legs 38 which are adjustably held in the body 16 and specifically in the metal frame 22. The permanent spark shield 34 lasts for a multiplicity of welds before it needs replacement, although a ceramic ferrule can be employed for some applications, if desired. 
     Referring particularly to FIG. 7, the connection between the chuck 32 and the chuck leg 30 will be discussed. The chuck leg 30 has a recess 40 including a forward end portion 42 which receives a rear cylindrical end portion 44 of the chuck 32. The portion 42 of the leg 30 has a bevel 46 extending inwardly and away from the recess and the outer surface of the chuck leg 30 has a threaded portion 48 at the forward end. A nut 50 has a central opening 52 and a larger opening at the other end having internal threads 54 which are threadedly engaged with the threaded portion 48 of the leg 30. The nut 50 also has a bevel 56 adjacent the central opening 52 with the bevel facing inwardly and toward the chuck leg 30. A connecting ring 58 has an inner diameter just slightly larger than the end portion 44 of the chuck 32 and fits over the end when it extends through the opening 52 of the nut 50 and into the shoulder portion 42 of the recess 40. When the nut 50 is tightened on the leg 30, with the ring 58 in place, the beveled surfaces 46 and 56 engage the edge portions of the arcuate outer contour of the ring 58 and force it into engagement with the outer surface of the end portion 44 of the chuck 32. This firmly holds the chuck in place relative to the chuck leg. With this arrangement, the chuck 32 can be quickly connected or disconnected from the chuck leg 30. Further, the chuck 32 can be initially longitudinally positioned as desired within limits relative to the chuck leg 30 and yet is securely held at all times. 
     A plastic sleeve 60 is located within the chuck leg recess 40 and backs up the chuck 32, the sleeve having an internal threaded passage 62. A threaded rod 64 is threadedly engaged in the sleeve 60 and extends into a central passage 66 in the chuck 32 to back up the end of the stud 12 when held by jaws 68 (FIG. 1) of the chuck 32. 
     The welding foot 36 includes a body 70 of conducting material, e.g., aluminum, of predetermined thickness having an opening 72 therein which receives the spark shield 34 and specifically a cylindrical portion 74 thereof. The spark shield has a shoulder or flange portion 76 of a size larger than that of the opening 72 to limit the extent to which the spark shield can move toward the body 16. The spark shield also has removable means in the form of a resilient ring 78 located in a groove 80 of the spark shield. The ring extends beyond the periphery of the cylindrical portion 74 and limits movement of the spark shield 34 away from the body 16. However, the spark shield 34 can float toward and away from the body 16 relative to the foot 36 to assure that an outer annular end 82 of the shield will be against the workpiece during a welding cycle. The floating spark shield also eliminates the need for tight tolerances on the shield and on three positioning posts or feet 84, which tolerances are otherwise required to make certain both the shield and posts are in exactly the same plane. 
     The positions of the stud 12 and the spark shield 34 are determined by the positioning posts 84 which are threadedly engaged in the foot 36 and extend forwardly therefrom equal distances. The stud 12, in its outermost position, preferably extends slightly through the plane of the positioning posts 84 to assure that the stud 12 will plunge back against the workpiece during the welding operation. In the forwardmost position of the spark shield 34, the forward annular edge 82 likewise extends slightly beyond the plane of the posts 84 to assure that the spark shield will be in contact with the workpiece when the positioning posts 84 are in engagement therewith. 
     The distance between the welding foot 36 and the tool body 16 is maintained by setscrews 86 (FIG. 4) which engage flats 88 on the legs 38 when within passages 90 of the frame 22. The foot 36 can be adjusted simply by loosening the setscrews and sliding the legs 38 in and out relative to the passages 90. In order to accurately position the foot 36, a threaded rod 92 is threadably engaged in a threaded passage 94 in the frame 22 and extends forwardly thereof. A forward end of the threaded rod 92 is received in a threaded passage 96 of a threaded sleeve 98 having a forward end abutting the rear surface of the body 70 of the foot 36. To adjust the position of the foot 36, the set-screws 86 are loosened and the legs moved in or out to position the rear surface of the foot 36 against the forward end of the sleeve 98. As shown in FIG. 8, the sleeve has a hexagonal outer surface forming flats 100. When the sleeve is turned to the next flat, the foot accordingly is positioned in or out an accurate, predetermined amount dependent upon the pitch of the threaded rod 92, e.g., 0.005 inch. Suitable indicia can be placed on the sleeve for this purpose. 
     Referring in more detail to the chuck leg 30, an operator&#39;s flange or disc 102 (FIGS. 1 and 4) is located on the threaded portion 48 of the leg 30 and can be engaged by the operator&#39;s fingers to retract the chuck assembly 28. A cylindrical portion 104 to the rear of the threaded portion 48 is slidably supported in a nylon bearing 106 which is mounted in the front wall 24. Between the bearing 106 and the flange 102 is a rubber bellows 108 for dirt protection. To the rear of the bearing 106, the cylindrical portion 104 of the leg 30 has an outwardly extending pin 110 (FIG. 2 also) which is received in a groove 112 of the wall 24 to prevent rotation of the leg and limit the maximum forward position of it. Below the pin 110, on the opposite side of the cylindrical portion 104, a welding cable 114 has a terminal ear 116 connected to the chuck leg 30 by a threaded fastener 118 affixing the ear 116 in a notch 120 of the leg. To the rear of the cylindrical portion 104 is a magnetic flange 122 extending outwardly well beyond the cylindrical portion 104. When the chuck assembly 28 is in a retracted position, as shown in FIG. 4, the flange 122 is held against an annular face 124 of an electrical coil 126 having suitable conductors 128 (FIG. 1) extending down into the handle. 
     To the rear of the flange 122, the chuck leg 30 has a rearwardly extending portion 130 (FIGS. 1 and 5) with a seating member of shoulder 132 located between the flange 122 and the rear portion 130. A coil plunge spring 134 has a forward end 136 engaging the seating member 132. A rear end 140 of the spring 134 engages a second seating member or sleeve 142. The sleeve 142 has a noncircular opening formed, in this instance, by a bushing 144 which is of a shape similar to the shape of the rear portion 130 of the chuck leg 30. Both the portion 130 and the bushing 144 are square, as shown in FIG. 6 to prevent the sleeve from turning relative to the rear portion. An outer threaded member 146 has internal threads 148 engagable with the outer threads 150 on the sleeve 142. The member also has a thick outer flange 152 which is rotatably held in an inner cavity 154 of the body portion 18 between a snap ring 155 on one side and a flat washer 156 and a wave washer 158 on the other side. The member 146 also has a rearwardly extending knob 160 with a knurled outer surface which can be turned by an operator to rotate the member 146 and thereby move the sleeve 142 in and out (compare FIGS. 1 and 5) to change the compression on the spring 134 and the plunge rate of the chuck assembly 28. The knob 160 has a slot 162 therein through which an operator can view the end of the sleeve 142 so as to determine the position of the sleeve 142 relative to the spring 134. To manipulate the threaded member 146, the cap 26 must be removed. The cap has a threaded shank 164 which is engaged in a bushing 166 in the knob 160. 
     In the operation of the tool 10, the setscrews 86 for the supporting legs 38 are loosened and the sleeve 98 adjusted relative to the rod 92 to position the foot 36. With the rear surface of the foot body 70 bearing against the end of the sleeve 98, the setscrews 86 are tightened to firmly position the foot 36 relative to the body 16 and thereby determine the length of the plunge stroke of the stud 12 and the chuck assembly 28. The rear limit of the stud stroke is always fixed, being with the flange 122 against the end 124 of the coil 126. With the floating spark shield 34, it is always assured that the outer end 82 will be against the workpiece when the positioning posts 84 are in position against the workpiece. 
     The operator can then pull back on the flange disc 102 to move the magnetic flange 122 against the coil where it is retained with the coil being energized. However, the flange 122 can be retracted otherwise, as by mechanical means or a solenoid. When a trigger 168 is pulled, power to the coil 126 is cut off and a high voltage potential from a capacitive power source is imposed through the cable 114 between the stud 12 and the workpiece when the positioning post 84 are in contact with the workpiece. A wire 170 (FIG. 2) is connected to the frame 22 and to the workpiece for this purpose. With the coil 126 off, the plunge spring 134 moves the chuck assembly 28 and the stud 12 toward the workpiece with the force of the plunge stroke determined by the amount of compression on the spring 134. The farther forward the sleeve 142, the greater is the compression of the spring 134 and the greater is the force of the plunge stroke. As the chuck assembly and the stud move forwardly, current will pass through the tip 14 as it contacts the workpiece. This vaporizes the tip 14 and causes an arc to exist for a short time between the stud and the workpiece, until the stud contacts the workpiece. The tip and adjacent portions of the stud and the workpiece become molten to provide a firm weld between the stud and the workpiece. 
     Various modifications of the above-described embodiment of the invention will be apparent to those skilled in the art and it is to be understood that such modifications can be made without departing from the scope of the invention, if they are within the spirit and the tenor of the accompanying claims.