Patent GB-692559-A (GB)
Title: Improvements in and relating to electric welding systems
IPC: B23K11/00
Filed: 1949-11-09
Abstract: 692,559. Welding by pressure. GRAHAM MANUFACTURING CORPORATION. Nov. 9, 1949 [March 12, 1949], No. 28729/49. Class 83 (iv). A stud is welded to a workpiece by means of a pneumatically-operated welding gun comprising a piston 16, Fig. 2, reciprocable in a cylinder 14 and having a piston rod 22 carrying a chuck 36 for holding the stud, and an electric power source such as a capacitor being connected between the gun and the workpiece, characterized in that air is admitted to the cylinder to move the piston until the stud contacts the workpiece to complete and to maintain an electric welding circuit and concomitantly to force the stud into contact with the workpiece and to maintain it so forced until welding is complete, and restoring controls are provided for returning the piston and concomitantly disconnecting the source after completion of the weld. The operating air is supplied above the piston 16 through a flexible hose 19, and restoring air is supplied beneath the piston through a hollow arm 11 and a conduit 28 connected by a ball and socket joint 29 providing an adjustable mounting for the gun. The piston 16 is of insulating material and has a larger surface exposed to the operating air so that it is moved downwardly. The piston rod 22 slides in an insulating bushing 24 and is screwed at its lower end into a member 41 to which is screwed the chuck body 36 and to which is connected an electric supply lead 53. The chuck body 36 has three jaws 38 formed by axial slots 39, and is surrounded by a sleeve 42 having a flange 52 against which bears an annular cup 51 within a recess in the member 41, to which compressed air may be supplied through a conduit 48 to move the sleeve 42 downwardly to clamp the jaws 38 around the stud. In an alternative construction the piston is of metal and the gun is attached by screws to the arm 11 with the interposition of an insulating gasket, and the annular cup 51 is replaced by a resilient diaphragm. Fig. 9 shows a welding system comprising two guns 10, 10<SP>1</SP> for welding studs w to a workpiece W. The welding operation is commenced by pressing hand-operated switches s7, s8 and opening simultaneously a foot-operated valve V3 to allow compressed air to pass to and expand a bellows B1 to close a switch s12, and complete a circuit from supply lines c, d through normally open contacts of the switches s7, s8 and a solenoid L2. Hand pressure on the switches s7, s8 also opens normally closed contacts thereof to de-energize a solenoid L1 for actuating a switch s6 in the charging circuit of two banks of condensers C1 to C5 and C6 to C10, so that the latter are disconnected from the supply lines c, d. The solenoid L2 operates a valve V4 to allow compressed air to pass through a pipe p9 to a piston device 71 to close a switch s1, thereby connecting one side of each of the two banks of condensers to the workpiece W. Before the switch s1 has closed the air pressure in the pipe p9 expands a bellows B2 sufficiently to open a safety switch s9 in series with the solenoid L1 to ensure its de-energization even if a current path is accidentally provided through the switches s7, s8. After closure of the switch s1 a bellows B3 is expanded sufficiently to operate a switch s11 to energize solenoids operating valves V1, V2, so that the latter open and allow compressed air to pass to the upper sides of the pistons in the guns 10, 10<SP>1</SP> to depress the studs w into contact with the workpiece W, thereby discharging the condensers C1 to C10 to provide a welding current. The workpiece W is secured to a table 13 by means of pneumatically operated clamps 63 supplied with comprsssed air, on opening of the valve V3, through a pipe p6 which also supplies compressed air for actuating the chucks 23, 23<SP>1</SP>. On completion of the weld the valve V3 is closed to release the studs w from the chucks. Also the bellows B1 collapse opening switch s12 so that the valve V4 is moved to vent the conduit p9 to atmosphere, thus collapsing the bellows B3 to open the switch s11 and close the valves VI, V2 so that the chucks 23, 231 are retracted by the compressed air which is supplied continuously through conduits p1, p2 to the lower surfaces of the pistons. The bellows B2 contract to close the switch s9 only after movement of the piston device 71 to open the switch s1 in the welding circuit to prevent short-circuiting of the supply lines lines c, d in the event that either of the guns 10 or 101 fails to retract. Specification 692,553 is referred to.