31
BASIC MIG OPERATION
current to recover and rise to the established weld-
ing current to melt the wire after the wire contacts
the puddle and the current falls. This process is
happening many times a second so it isn
’
t visible to
the naked eye. But the overall effect is visible as the
wire burn off height is changed and a change in the
wetness of the puddle and how easily the molten
metal flows in toward the toes of the weld as it
melts off. If the unit has sufficient arc force, the edg-
es of the weld will easily wick into the puddle with
little or no spatter with little or no manipulation of
the torch required. The pitch of the arc will be me-
dium. With too much inductance the puddle may be
uncontrollable and the arc will have a throaty, raspy
sound. Too little inductance and the puddle will be
narrow and possibly have a high ridge in the center.
The pitch will be very high and the puddle will seem
sluggish and less fluid.
All MIGs have a preset inductance or arc force that is
inherent in the machine
’
s design. But few MIGs
have the adjustable Arc force. Arc force is part of
the personality of a MIG welder. It
’
s one reason that
some people prefer the arc of one brand over the
other as people develop personal preferences in arc
performance. With that in mind, having an adjusta-
ble arc force serves several functions:
1)
The arc force allows the user to dial the machine
to a performance level that the user is accus-
tomed to. This helps if multiple users are pre-
sent and improves the operator
’
s performance
with the welder.
2)
The arc force can help improve control and
weldability in out
-
of
-
position welds (weld posi-
tions other than flat) without having to change
other parameters.
3)
Different shielding gases require different levels
of inductance for optimum performance. The
arc force improves performance with different
gas mixes by being able to adjust the arc to ren-
der the best and smoothest possible arc for the
shielding gas being used. This is especially help-
ful when pure CO2 is used.
4)
The arc force can improve weldability of thinner
metals without having to step down a size in
wire. Whil
-
e ultimately there are limits to what
any given wire can weld on the lower end of it
’
s
range, it does help improve the low amp weld-
ing characteristics of the wire diameter.
For the best possible experience welding with the
PowerMTS welder, adjust the arc force after the
wire speed and voltage have been tuned. This will
keep the user from constantly having to hunt for the
best balance of the other two adjustments. Usually
once a particular arc force setting is selected that is
suitable to the user, it will work well throughout the
range of adjustments and will rarely require read-
justment once set to the operator
’
s satisfaction.
However, this is not to say that readjusting the arc
force from time to time is not beneficial. When the
operator must weld out
-
of
-
position, readjusting the
arc force control can help reduce clogging of the
nozzle and even make the puddle more controllable.
Avoid the temptation of setting the control at the
mid
-
point or even full left or full right without per-
forming a few test welds first. Few users will find
these settings to their liking. Turning the arc force to
the minimum setting does not turn the feature off.
A good starting point is somewhere between 6 and 8
with mixed gas. This will usually produce a desira-
ble arc with for most people and will produce mini-
mal spatter. Fine tune the adjustment from there
increasing in half increments to find the best perfor-
mance.
Burn Back Control.
After the trigger is released on the welder, it
’
s natu-
ral for a small extra amount of wire to coast out of
the gun. This small amount of extra wire may stick
fast in the weld as the molten puddle begins to cool.
This will require the operator to break it loose and
spend time trimming the wire. Even if the wire does
not stick in the puddle, it will often be left sticking
too far out from the contact tip for a proper restart.
Trimming is usually required with a pair of MIG pliers
or wire cutter before restarting the arc. With burn
back control, however, the arc can be kept energized
long enough to continue supplying power to the
wire long enough to burn the wire back to the de-
sired length after the wire stops feeding. The timer
control located under the cover sets the length of
time the that the arc remains on after the trigger is
released.
If the burn back control is set too long it can cause
the wire to burn back into the tip itself and welding
of the wire to the tip. Begin with setting the unit for
a little less than a quarter second. If the burn back
Basic Theory and Function
Section 3
