Patent GB-692553-A (GB)
Title: Improvements in or relating to electric welding systems
IPC: B23K9/20
Filed: 1949-09-07
Abstract: 692,553. Welding by pressure. NEILL, H. J. (Graham Manufacturing Corporation). Sept. 7, 1949, No. 23178/49. Class 83 (iv). In a method of welding a workpiece having a comparatively large surface to a stud having a substantially reduced integral portion protruding from the end thereof, the shank proper is initially distanced by separate distancing means from the work, a potential difference is applied between the stud and work insufficient to form an arc across the gap between them, the stud is moved towards the surface at a speed that causes, before the shank proper reaches the surface, ionization of the gap by melting the reduced portion, and formation of an arc therein melting the shank end and the opposite region of the work surface, and the stud is forced into contact with the work to consolidate the melted metal whereby substantially all of the metal so consolidated is confined between the shank and the work surface. The reduced end of the stud may be pointed, wedge-shaped, or concave with a circular rim, or may consist of an integral wire portion. The welding may be effected by means of a welding gun comprising a chuck 250, Fig. 2, for the stud (not shown) and having a stem 245 carrying a percussion block 240, which, in the welding operation, receives a blow from a hammer 285 carried by a plunger 280 having latch springs 282 engaging an end 218 of a tube 219 in which the plunger 280 is slidable. The gun is operated by pressing a cap 212 on a tube 210 slidable over the plunger casing 215 against a spring 272, which is thereby compressed until an insulating block 222 held in the cap 212 engages and releases the latches 282 and the plunger 280 is forced by the spring 272 towards the block 240. Spring contacts 291 carried by the plunger 280 first engage the block 240 to apply a potential to the stud from a power supply connected to a contact 220 on the tube 219, the voltage being applied through the plunger 280, springs 291, block 240, and the chuck stem 245. Spacers 265 carried by the gun are held against the work surface to initially distance the stud. As soon as the stud contacts the work a current flows to melt the reduced end of the stud thusmomentarily interrupting the mechanical contact to form an arc fusing the adjacent parts of the work. Upon release of the cap 212 springs 271, 272 withdraw the plunger 280 until the latches 282 engage the sleeve 219 and a spring 270 thereupon withdraws the chuck 250 from the stud. Fig. 11 illustrates a circuit for operating the gun. On closing a switch s2 a solenoid M1 is engaged and closes a switch s1 to connect a terminal of a battery B to the contact 220 of the welding gun, the other battery terminal being connected to the work W. After the gun has been operated the switch s2 is again opened. In an alternative system the battery and relay are omitted, the current being supplied by discharge of a condenser charged from a direct current supply. In an alternative welding gun the circuit is not made and broken within the gun, the electric supply contact 220 being in permanent contact with the studholding chuck. An external switch S, Fig. 12, is then provided which is closed by a solenoid M2 when a condenser C has been charged to a predetermined value from supply mains c,d. The switch S is held closed by a latch l which is released when the gun is operated by the current surge through a solenoid M3. The switch s then opens and the condenser recharges in readiness for the next operation. Instead of providing the gun with spacers 265 the reduced protruding portion 502, Fig. 25, of the stud 501 may be provided with a head 521 of fairly brittle insulating material, e.g. plaster of Paris or clay with water glass as a binder, which disintegrates when the gun is actuated. The insulating material may also contain a flux, such as aluminium or iron powder or a mixture thereof, and an explosive such as black powder which develops an inert gas to protect the welding area. A material may be added which upon heating develops an inert gas. A stud having a number of projecting pins 512 may have applied thereto a single insulating head 525, Fig. 27, or individual heads 526, Fig. 28. Specification 663,186 is referred to.