Patent GB-1445864-A (GB)
Title: Welding system comprising at least one arc welding apparatus  one resistance welding apparatus and a control device therefor
IPC: B23K9/10
Filed: 1973-09-19
Abstract: 1445864 Control circuits for welding apparatus ARO SA 19 Sept 1973 [20 Sept 1972] 43906/73 Heading H2H A control circuit for a welding system includes a switch with at least two positions, in a first position of which a timing circuit 26 enables arc welding apparatus (not shown) to perform a welding operation during a first adjustable time period, and in a second position of which the timing circuit enables a resistance welding apparatus (not shown) to perform a welding operation during a second adjustable time period. The switch comprises six ganged wafers 1a-1g and having six contacts Ia-VIa and a respective wiper contact 6a-6g. In the first position of the switch the primary of a transformer 8 is disconnected from the supply so that the control circuit is de-energized. When the switch is manually rotated to position II and a switch 4 is closed a relay 10 is energized via a bridge rectifier 17 to change over a contact 10a so that a motor 2 drives a welding wire for the arc welding operation. Relays 11, 14 are also energized closing contacts 11a, 14a to energize an electromagnetic valve 9 which supplies CO 2  gas to the nozzle of the welding apparatus. A welding transformer (not shown) is also energized. A capacitor 27 in the timing circuit 26 commences to charge and, at the end of the first time period determined by the setting of an adjustable resistor 29, triggers a unijunction transistor 30 which in turn fires a thyristor 31 to energize a relay 24. Contacts 24a, 24b change over to discharge the capacitor and deenergize the bridge 17. The motor 2 is therefore de-energized but the discharge current of a capacitor 20 holds the relay 11 energized to enable the nozzle to continue supplying gas for a short period of time. The switch 4 may be opened and then re-closed to enable a repeat of the spot weld. In position III of the switch, a capacitor 38 of a "repeat" circuit 34 is not short circuited but at the end of a predetermined time period triggers a unijunction transistor 37 which fires a thyristor 36 to commutate the thyristor 31 thereby de-energizing the relay 24 and returning the contacts 24a, 24b to their indicated positions. Thus a succession of spot welds may be automatically effected. In position IV of the switch both the circuits 26, 34 are de-energized and continuous arc welding is possible. On closing a switch 5 and rotating the control switch to position V, a contactor 25 is energized to supply a transformer (not shown) of the resistance welding apparatus. Also a resistor 33 is connected in parallel with the resistor 29 to define the second time period during which resistance welding takes place. In position VI of the control switch, a transistor 41 conducts until the voltage applied between points B, C from an induction coil connected to the resistance welding apparatus increases to a predetermined value, whereupon the blocking of the transistor enables the capacitor 27 to charge and the control circuit operates as in the case when the switch is in position V.