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AC TIG Welding - AC Wave Balance Control
AC (alternating current) enables us to TIG weld non ferrous alloys like Aluminum, Magnesium and Aluminum
Alloys. These materials have an insulating surface oxide layer that melts at a higher temperature than the base
metal making it dicult to weld the base metal if the oxides are not removed. AC welding current is ideal because
the nature of the AC wave form assists in breaking the surface oxide layer.
AC (alternating current) has a current cycle that ows from + (direct) polarity to - (reverse) polarity.
The reversing of the polarity breaks the surface oxide while the direct polarity melts the base material.
reverse polarity
straight polarity
There are inherent problems that come with AC TIG arc rectication, arc stutter, arc wandering and arc
stoppage. These problems typically occur during the transition between + and - cycles.
The current is less (30%) during the half of the cycle when the electrode is positive and there is a resist-
ance of the electron ow during this half cycle (rectication). The lack of current ow during this half cycle
makes the AC arc unstable.
To overcome this lack of ow during one half of the cycle, a high-frequency (HF) voltage is generated and
fed into the welding circuit. The HF maintains the arc stability during the half cycle when the electrode is
High-frequency voltage ows continually in the welding circuit and keeps the shielding arc in the welding
area in an ionized state. When the arc is ionized the arc is maintained during the half of the cycle when the
electrode is positive. However while the arc is maintained less current ows during this half of the AC cycle,
producing an unbalanced wave.
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