Patent GB-550319-A (GB)
Title: Improvements relating to electric flash welding machines
IPC: B23K11/04
Filed: 1940-12-17
Abstract: 550,319. Electric welding. GORDON, S. H., MILLWOOD, W. H., and YOUNG, W. F. Dec. 17, 1940, No. 17794. [Class 83 (iv)] In an automatic resistance flash welding machine of the kind in which the work pieces are alternately brought together and separated during the preheating period, the stopping and reversal of the forward feed movement occurs as a result of the yielding of a resilient member interposed between the feed mechanism and the moving head, the yielding being a consequence of the mechanical resistance opposed by the meeting together of the work pieces. The feed movement may thus be effected by a desired means such as by screw and nut or cam mechanism. The movable head 10 may be operated by a shouldered rod 12 reciprocated by cams 38, 50 on a shaft 40 driven through worm gear by a reversible electric motor 44. The rod 12 drives the head through a spring 16 arranged between a shoulder 18 on the rod and a recess 14 in the head, the head being returned by a nut 26 on the end of the rod. When during the forward movement the cold work pieces come into contact the spring 18 is compressed and an adjustable stop 34 in the rod opens normally closed contacts 29 on the head so as to open the motor circuit to stop and then reverse the motor to separate the work pieces. Separation of the work pieces causes a drop in the circuit in the primary 62 of the welding transformer and the forward feed is reversed. When flashing occurs the resistance to forward movement ceases and an abrupt rise in the contour of the cam 38 brings about the butting movement to complete the weld. The motor is controlled by forward and rearward contactors 52, 54. To start the operation a hand switch 56 is closed which causes the welding contactor coil 58 to be energized through a circuit containing a cut out switch 60, and current is also supplied to the primary 62 of the welding transformer, but the relay 64 is not energized until the work pieces are engaged. At the same time the winding 66 of the contactor 52 is energized through a circuit containing contacts 68, 70, 56. The motor is thus rotated to drive the head 10 forwards and when the work pieces 72 meet the relay 64 is energized and the contacts 70 opened and 74 closed. The winding 66 is kept energized by a maintaining circuit through contacts 76 and 29. When the contacts 29 are opened the winding 66 is de-energized and the motor stops. A pair of contacts 78 mechanically connected to the contactor 52 through a lost motion device and provided with an adjustable dash pot 80 to cause delay in the closing of contacts 78 to allow heating of the work pieces, now close to complete a circuit through winding 82 to close the contactor 54 and reverse the motor. When the work pieces separate the relay 64 is de-energized to open the contacts 74 and close contacts 70 to resume the forward motion. The cycle of operations is repeated until flashing occurs when the motor continues in the forward direction. During butting of the work pieces the contacts 29 are opened but the winding 66 is maintained energized through a switch 86 closed by a triple cam 88 on the shaft 40. At the moment of butting the switch 60 is opened by the cam 88 to cut out the welding current, but the motor continues running until the switch 56 is opened by the cam 88. After removal of the work the switch 56 is again closed by hand to restart the motor in the forward direction. The reverse cam 50 then retracts the head 10 and the switch 56 is opened by the cam 88 to stop the machine with the parts in their initial position. The contacts 29 may be arranged to be normally open instead of closed or may be replaced by a normally open or closed fluid controlling valve operated as a result of relative motion between the rod 12 and head 10. The delay in the reversal of the motor may in such case be obtained by providing an adjustable gap between the stop on the rod 12 and the valve. Specification 539,660 is referred to.