TWI Frequently asked questions
The greater stability of thyristor and transistor controlled power sources allows very low current levels to be used i.e. for micro-TIG (GTA) welding. As the welding current can be as low as 1A, with an accuracy of ±0.5%, it haslargely replaced the micro-plasma process for micro-welding operations such as welding thin sheets, or even foils, and wires on to pins. The newer inverter, square wave AC, or switched DC, power sources are particularly attractive forwelding aluminium. By rapidly switching between the polarities, arc reignition is made easier so that the HF which is required for reigniting the arc can be reduced or even eliminated.
By using the maximum position of about 90% electrode negative polarity, it is possible to maintain a pointed electrode. When welding heavily oxidised aluminium, the balanced position (50% electrode positive and negative polarities)is preferred to increase the degree of cleaning. Some power sources have intelligent control systems which automatically adjust the electrode positive to negative polarity balance according to the amount of cleaning required.
Copyright by TWI, 1999
