Everlast Powertig 255 EXT Operator's Manual page 24

Section 3
3. AC Wave Forms. The wave form control is a
useful feature for achieving a desired type of arc
performance in AC mode. There are 4 wave forms
to choose from. The standard, default wave form
is the advanced square wave. This wave form is
excellent for all types of welding, and offers quick
puddle wet-in, and good arc stability. The triangu-
lar wave form is useful in situations where a fast
freezing puddle is desired, particularly on thin alu-
minum. The soft square wave offers a buttery arc,
with a smooth feel similar to the feel of a standard
square wave transformer-based welder. The sine
wave form mimics older transformer welders. This
is the softest wave form, and offers less arc defini-
tion and control than other wave forms. This is
preferred by some older more experienced weld-
ers. When using various wave forms, only the Ad-
vanced Square wave offers a relatively high pulse
frequency, 250 Hz, in the standard pulse mode. All
other wave forms are limited to a maximum of 10
Hz. Advanced pulse mode limits the pulse fre-
quency to 10 Hz for other wave forms.
4. AC Frequency. The AC frequency only applies to
the AC mode. Standard transformer welders typi-
cally have a fixed frequency of 60 Hz which is es-
sentially the line input frequency supplied by the
power company. But with inverters, the capability
of AC frequency adjustment is practically limitless
due to the IGBT components that create its own
frequency. Frequency adjustment capability is use-
ful to help improve directional control of the arc,
and to focus the arc so that a narrower bead profile
can be achieved. Also, at higher frequencies, the
puddle agitation is greater which improve the
breakup of undesirable oxides. All wave forms can
be adjusted from 20-250 Hz
200 Hz
5. AC Balance. The AC output is formed by rapidly
alternating polarity between electrode negative
and electrode positive, creating something that
resembles a wave when viewed on an oscilloscope.
Normally, with standard transformer welders, both
standard sine wave and even square wave welders
60 Hz
24
Basic theory and function
have little or no way to change the ratio of EN to EP,
which results in welding with a molten ball at the tip
of the tungsten and a less stable arc. Electrode nega-
tive (EN) provides penetration in the TIG welding pro-
cess. Electrode positive (EP) creates a strong reverse
flow of electricity that breaks up the weld-resistant
oxidation that covers aluminum and magnesium com-
ponents. It also places a lot of heat on the tungsten.
In a "balanced" wave where both EP and EN are equal
in time length (50%), penetration is reduced and over-
cleaning results in wide etch lines running parallel to
the side of the weld. Not all welds conditions will be
alike so more cleaning is required at times than others.
Similarly, more penetration will be required at times
than others. Ordinarily, about 20-35% electrode posi-
tive is considered an ideal amount (65-75% electrode
negative). This means that more heat is put into the
work than on the tungsten and a sharper point can be
used. Cleaning is still sufficient at that level. Good re-
sults can be achieved with about 30% EP or less. The
cleaning action is still significant even at these levels.
Ideally, the cleaning action should be adjusted until a
small amount of frosting can be seen no more than
1/8" distance from the edge of the weld. If a piece of
metal is particularly heavily oxidized or dirty, more
cleaning action will be required. If too much cleaning
action is used, the tungsten will begin to ball and may
even start to burn away. If this much cleaning action is
truly needed, then switch to a larger sized tungsten
that can handle the increased heating level. Signs of
too little cleaning action while welding aluminum are
sooty, black or dull looking welds. A dedicated stain-
less brush and suitable aluminum cleaner such as ace-
tone should still be used before welding any type of
aluminum to help break up the heaviest oxide layer so
less EP is needed and better penetration can be
achieved. Even if the aluminum has a mirror like
shine, it is still oxidized.
Cleaning/Frosted Area of Aluminum
30% EP
Narrow bead/etching/sharp tungsten
50% EP
Wider bead/etching/rounded tungsten
65% EP
Wide bead/etching/balled tungsten