548,453. Electric-welding. BRITISH FEDERAL WELDER & MACHINE CO., Ltd., and GALLE, A. G. March 8, 1941, Nos. 3181/41 and 3721/42. [Class 83 (iv)] In an automatic flash welding machine the relative movements between the work heads are controlled by a motor driven cam which is partially rotated to bring the parts into contact, the parts being subsequently preheated by parting and rebutting thereof whereupon at the termination of the preheating operation the rotation of the cam is continued to complete the weld. The head b<SP>1</SP> may be reciprocated at constantly increasing acceleration by a cam d driven by a reversible motor e through gearing f, When the parts come into contact and remain in contact until the short circuiting current produced is in the region of three or four times greater than a normal flashing current, a current relay embodied in the machine and arranged in a shunt in the welding transformer primary or secondary or fed from a current transformer in either of these circuits is closed for reversing the motor. The current falls on separation of the parts, the relay being thus opened again and the motor rotated in the forward direction again. When the parts, after a number of reciprocations, are preheated to a condition suitable for flash welding the flash over occurs when the parts again approach one another. In this case normal welding current flows and the relay is not at first operated, so that the cam moves further forward and the nose d<SP>1</SP> imparts a sudden movement to the head b<SP>1</SP> to upset the plastic metal and complete the weld. The excess current which eventuallyflows to close the relay at this stage may be used to actuate mechanism for indicating the number of welds, operate a flashguard, or close a circuit including a lamp or other visible or audible means for indicating that the weld has been completed. In another form the head b<SP>1</SP> is provided with a single acting piston pressed pneumatically against the cam d whereas the head b is reciprocated by a double acting pneumatically operated piston. The heads are first pressed outwards by fluid pressure and on manually closing the switch g a relay h is energized to start the motor, the shaft of which carries contact blades to operate relays and switches. When the motor starts a plugging relay i is closed thereby to energize the relay j so as to apply a high flashing voltage to the parts during their initial approach so as to flash trim the edges thereof. Motion of the motor shaft closes switch g<SP>1</SP> to keep the relay h energized independently of switch g. A recess in the cam comes opposite the head b<SP>1</SP> which is thus retracted. At this time the switch i opens to de-energize the relay and the switch g<SP>1</SP> opens to stop the motor. At this stage, however, the switch g<SP>2</SP> has been closed by a contact on the motor shaft and switch j<SP>1</SP> has been closed by de-energizing the relay j so that a relay k is energized so as to apply a low pre-heating voltage to the parts. A timing device is started when a pair of contacts k<SP>1</SP> are closed by relay k in a circuit containing a switch m<SP>1</SP> closed by energizing relay m at the initiation of the welding cycle. The timing contactor controls an air valve l so that compressed air is admitted through a reducing valve to the rear of the cylinder of head b to force the parts into contact. This movement opens a switch g<SP>3</SP> to de-energize relay m to open switch m<SP>1</SP>. When the desired preheating period has terminated the timing device opens the complementary contactor switch so that the air valve is operated to retract the head b. The switch g<SP>3</SP> thus closes again and the timing device is initiated again to repeat the preheating cycle. The head b may operate a ratchet counting mechanism to determine the number of preheats whereupon the counting device closes a switch g<SP>4</SP> to energize a relay o which opens a switch o<SP>1</SP> to deenergize relay k and reverse the head b and closes a switch o<SP>2</SP> to restart the motor. The switch i is thus closed again and relay is energized so as to apply again a high flashing voltage to the parts as the head bl approaches the head b. The portion d<SP>1</SP> of the cam thus completes the weld. During this stage of motion of the motor the switch g first closes, the switch g2 then opens to de-energize the relay k and the welding flash is terminated by a contact on the motor shaft opening a switch g<SP>5</SP> just prior to the upsetting operation. When the part d<SP>1</SP> of the cam passes the roller b<SP>2</SP> and the cam has turned through a complete revolution the switch g<SP>1</SP> opens again and the motor stops. According to the Provisional Specification the heads may be operated hydraulically.