GB1489773A - Resistance welding apparatus affording operator protectio - Google Patents

Abstract

1489773 Welding by pressure BRITISH LEYLAND UK Ltd 24 Sept 1975 [26 Sept 1974] 41988/74 Heading B3R [Also in Division G3] Resistance welding apparatus features a power-driven movable electrode E1 and a stationary electrode E2, the former being advanced towards the electrode E2 initially by a first non-welding force, i.e. a force low enough to be resisted by an operator's hand, and then by a second, higher, welding force, the switch from the first to second forces occurring when a low voltage induced in the secondary windings of a welding transformer T is short-circuited by the electrodes E1, E2 through the workpiece (not shown). In operation, the electrode E2 is advanced in the first non-welding mode, by a pneumatic piston actuator P, when two valves AV2, AV3 are energized (dotted lines, Fig. 2). Since the piston of the actuator has a greater effective area in chamber P2 than in chamber P1, the piston is moved downwardly, governed also by the relation between two pressure regulators RR1, RR2, such that the descent may be arrested by an inadvertently placed non- conducting obstruction. When the electrode E1 contacts the workpiece a Detection Device (Fig. 1) detects the short-circuit of the low voltage induced in the secondary winding, by a Low Voltage Source (Fig. 1), so triggering the energization of valve AV1 through a Welding Controller) and, immediately following, the deenergization of the valves AV2, AV3. Compressed air is then supplied at its full pressure to the chamber P2, resulting in a large welding force between the electrodes E1, E2. The welding current is switched on simultaneously by the Detection Device triggering the Welding Controller, which subsequently operates to close a Weld-time Control Switch to connect a 400 V. power supply to the primary winding of the transformer T. The operation can be repeated continually if an initiation switch in the Detection Device is kept closed. If the compressed air supply fails, the electrode E1 will descend under its own weight, retarded by the air trapped in the chamber P1 being relieved through the regulator RR1. An electronic circuit (Fig. 3, not shown) of the Detection Device is disclosed.