AC balance adjusts the ratio of electrode negative to positive cycles. Too much cleaning action (more EP) can overheat the tungsten and destabilise the arc. Too little leaves oxide on the base metal, trapping gas. A starting point of 70-80% EN is common, but optimal balance depends on joint geometry and filler type.
Frequency influences arc stiffness and oxide break-up. Higher frequencies (100-200 Hz) narrow the arc cone, improving penetration in thin sections. Lower frequencies widen the arc, useful for cleaning wider areas on thick plates. Mismatch here can cause incomplete oxide removal and porosity.
Practical checks for a welding coordinator:
? Verify balance setting against the WPS before production.
? Monitor arc width during welding: a wandering arc often signals incorrect frequency.
? Inspect the weld surface: a grey, frosted appearance suggests excess cleaning action.
Porosity from AC settings is avoidable with proper setup. Auditors look for documented balance and frequency values in the WPS and actual machine readouts during qualification.
How do you verify AC parameters on site when the WPS does not specify them?