GB1162915A - Improvements relating to electrical resistance welding - Google Patents

Abstract

1,162,915. Welding by pressure. DIGITAL SENSORS Inc. 3 July, 1967, No. 30583/67. Heading B3R. [Also in Division H2] In electrical resistance welding the resistance between the welding electrodes is monitored while welding pressure is applied between the electrodes to the workpieces, the welding pressure is monitored to determine if it is or is not less than a predetermined value and welding current is passed only when the monitored resistance does not exceed a pre-determined value and the monitored pressure is not less than the pre-determined value. An A.C. voltage source 12 is connected across terminals 10, 11, the terminal 10 is connected via an on/off switch 14 to a terminal 8, and a checking circuit is connected across the terminals 8, 11. The checking circuit includes a transformer 9, one side of whose secondary 9B is connected to one welding electrode 4 and the other side through a normally closed relay 20A to the other electrode 5, and a cathode ray oscilloscope 1 having its vertical deflection terminals connected across the electrodes 4, 5. When the electrodes are open full secondary voltage occurs across them and the oscilloscope shows a full height vertical trace when the electrodes are pressed on to the workpieces a trace of smaller vertical height is shown, the optimum being a square trace. A satisfactory trace for the completed weld has a rectangular shape of width greater than height. A firing and welding circuit 25 has its output terminals connected to the electrodes 4, 5 and its input terminals in a series circuit including two normally open relay switches 15G, 16D, the relay coil 15 being energized when a manually operated switch 26 is closed and the relay coil 16 being energized when a switch 17 sensitive to the pressure exerted between the electrodes is closed at a preset pressure. The coil 16 is connected to the terminals 8, 11 via the switch 17 and a buzzer 28 is provided in parallel with the coil 16. The coil 15 is connected to terminal 11 and via switch 26 and normally open and normally closed respectively relay switches 15A, 16A to terminal 8. The relay coil 20 is connected to terminal 11 and via normally open relay switch 15D to terminal 8. In operation the workpieces are arranged between the electrodes and pressure applied until the buzzer sounds indicating closure of switch 17 which energizes coil 16 to open switch 16A and prevent energization of coil 15. If the oscilloscope display is appropriate the electrode pressure is removed, switch 17 opens and relay switch 16A closes, the switch 26 is closed to energize coil 15 to close switches 15A, 15D, 15G and switch 15A holds the relay coil 15 energized. The coil 20 is energized to open switch 20A and isolate the transformer 9. The preset pressure is applied by the electrodes causing switch 17 to close and then via contacts 15G and 16D an input is supplied to the circuit 25 which supplies a current to the electrodes. After welding the operator checks the condition of the weld by the oscilloscope trace.