Arc reignition characteristics when welding with sine-wave and square-wave power supplies

The power supply required for stabilising the welding arc must have a relatively high open-circuit voltage. When using a metal electrode and a sine wave alternative-current supply, the open-circuit voltage can be as high as 80 V. Recently developed square-wave power supplies offer the potential of reducing the open-circuit voltage to a safe-level because of the more rapid build up of current on current reversal. Two types of power sources are available, the squared sine wave AC and the switched DC power sources which produce rates of circuit current rise of typically 110 A/0.1 ms and 160 A/0.02 ms, respectively. Oscillograms of the current and voltage during the change of polarity were taken to show the characteristic reignition behaviour of metal electrodes when operated with sine wave, squared sine wave and square wave AC power supplies. Specific tests were carried out at low open-circuit voltages and it was demonstrated that the welding arc can be sustained at voltages as low as 62 V on a squared sine wave and 40 V on a square wave power supply.