GB1109180A - Resistance welding - Google Patents

Abstract

1,109,180. Resistance welding. PRESSED STEEL FISHER Ltd. 7 Jan., 1966 [8 Oct., 1964], No. 41029/64. Heading H2H. [Also in Division B3] In a resistance spot welding circuit means dependent on expulsion of fused metal from the weld nugget are used to terminate the weld. In one arrangement a circuit detecting a sudden voltage drop across the welding electrodes terminates the weld. The electrode voltage is fed to a low pass filter and rectifier having a capacitor (not shown) across its output. The periodic charging of this capacitor drives two circuits each producing a series of square waves, one the converse of the other which together supply a continuous voltage to a gate element a. When expulsion occurs the reduction of voltage across the electrodes causes cessation of pulses from one circuit hence a "lock in " bi-stable circuit is triggered causing cessation of the welding current. An inrush protection circuit prevents operation of the gate element for the first two mains cycles. A pulse counting circuit also terminates the welding current after 32 cycles and gives a warning if expulsion does not occur within this period. This circuit also resets the welding circuit ready for another cycle. Expulsion may be alternatively detected by a strain gauge representing stress mounted on the electrode holding arms, or by a device sensitive to electrode movement. Current change may be also used as the terminating parameter.