GB1266010A - - Google Patents

Abstract

1,266,010. Spot welding systems. INSTITUT ELEKTROSVARKI IMENI E. O. PATONA. 10 Sept., 1969, No. 44712/69. Heading H2H. A spot welding machine wherein a capacitor is charged and then discharged into a welding transformer to effect a weld is controlled so that the capacitor is discharged twice in succession, the first discharge being effective to form the contact surfaces of the weld and the second discharge effecting the weld. A spot welding apparatus comprises a welding transformer 7 which is energized by the discharge of a capacitor 3 under the control of a thyristor 6. To start a weld a push button is operated which closes contacts 27 and opens contacts 27<SP>1</SP>. Opening of contacts 27<SP>1</SP> biases bi-directional device 1 into conduction thereby to charge the capacitor 3. The increasing voltage across the capacitor 3 appears across potentiometers 9, 10 to charge capacitors 11, 12. The voltage across capacitor 11 eventually causes a breakdown device 22 to conduct so as to produce a pulse in a transformer 15 which triggers the thyristor 6 to discharge the capacitor 3 through the welding transformer 7 in a pulse having an amplitude determined by the setting of potentiometer 9 and the value of the capacitor 11. Capacitor 11 does not recharge since device 22 is maintained conductive by a bias source 26 so that at the end of the pulse the capacitor 3 re-charges until the capacitor 12 charges from the potentiometer 10 to break down device 23 whereupon a pulse appears at transformer 16 again triggering thyristor 6 to discharge the capacitor 3 through the welding transformer 7, the pulse amplitude of the second pulse being determined by the setting of potentiometer 10 and which is higher than that of the first pulse. Simultaneously the pulse in the transformer 16 breaks down a device 29 to render the bidirectional device 1 non-conducting to end charging of the capacitor 3. The first pulse through the welding transformer 7 prepares the surfaces to be welded and the second pulse effects the welding operation.