ARC INITIATION
Touch Start
With the power supply energised and the shielding gas flowing through the cup, the torch is lowered toward the workpiece until the tungsten electrode makes contact with workpiece. Then torch is suddenly withdrawn a short distance to establish the arc. The benefits of this method of arc initiation is its simplicity of operation. The demerits of touch starting isthe tendency for the electrode to stick to the workpiece, causing electrode contamination and transfer of tungsten to the workpiece.
High Frequency Start
High frequency starting can be used with DC or AC power sources for both manual and automatic applications.Very High frequency generators usually have a spark gap oscillator that superimposes a high voltage AC output at radio frequencies in series with the welding circuit. The high voltage ionises the gas between the electrode and the work and the ionised gas will then conduct welding current that initiates the welding arc.