Tweco 200 ACDC Arcmaster(April2006) - Manual (Page 41)

ARCMASTER 200 AC/DC
April 13, 2006 7-1
SECTION 7:
BASIC TIG WELDING GUIDE
7.01 Explanation of “Fluttery Arc” when
AC TIG Welding on Aluminum
The following will assist in understanding the
phenomenon of Arc Flutter, also referred to as Arc
Rectification.
The basic thesis is that the fluttering is caused by lack of
oxide in the weld pool.
The oxide layer on the plate reduced the energy for
electron emission. Electron emission from the weld pool
(DC+) causes the oxide layers to be disrupted, the so-
called “cleaning action”. However once the cleaning action
has produced a mirror like surface on the weld pool, the
effect of the oxide layer is limited because the oxide layer
has dissipated. This makes electron emission from the
weld pool more difficult and increases the chance of arc
instability.
This idea is supported by the observation that once
fluttering starts it can be made to stop by working the arc
away from the mirror like weld pool to an area of oxide
coated material. As soon as this is done the arc settles
back to a stable condition. So while the arc is “consuming”
oxide coated plate the instability does not occur. But once
the arc is stationary, the pool becomes thoroughly
“cleaned” by election emission, the fluttering begins.
Tests conducted on various types of AC TIG power
sources, Fluttery Arc is not confined to one type of power
source or its' design, both conventional and inverter types
suffer from the same problem.
AC TIG on aluminum
1. The Problem: Arc appears unstable and pulses or flutters. ie. appears to rapidly change welding current .
Conditions that accentuate arc flutter: Conditions that minimizes arc flutter:
• Cold work piece • Preheat the work piece
• Very short arc length • Increase the arc length
• Weld pool crater about 0.39” to 0.47”
(10 to 12mm) diameter
• Introduce filler rod material to the weld
pool, which introduces oxides
• Arc field in one spot to produce
“mirror” clean weld pool
• Move the weld pool around to introduce
oxides to the weld pool
• Increased cleaning action
i.e. Prolonged oxide emission from a
stationary weld pool increases the
likelihood of arc flutter
• Decrease the cleaning action by turning
the WAVE BALANCE to below 50% or
move the weld pool around
• Accentuated when tungsten running
near its current capacity, i.e. Molten ball
on end
• Use a larger diameter tungsten electrode
Table 7-1: Reduction of Arc Flutter
2. Conclusion: Fluttery Arc in AC TIG is a physical phenomenon independent of machine design.