32
BASIC MIG OPERATION
control is set correctly, it will leave about
1/4”
-
3/8”
wire sticking out beyond the contact tip. If a large
ball develops on the end of the wire, reduce the
burn back time so that it creates a balance between
ball size and stick
-
out. The short amount of post
flow that is built into the programming of the Power
i
-
MIG helps shield while the wire is burning back.
This helps control balling and prevents oxidation
during burn back. This is a unique feature that is not
found in many welders with burn back control. Burn-
back control without post flow can cause erratic
restarts due to the oxidized or over
-
balled wire tip.
Even with the burn back control properly adjusted,
due to operator error, an occasional quick trim of
the wire may be necessary for best arc starts. But
overall, when used in a production setting or in a
fabrication shop, the burn back control can save on
labor and aggravation.
Starting the Arc and Welding.
Starting the arc is a relatively simple process. Before
beginning, the wire should initially be trimmed to
between 1/4 to
3/8”.
Once the wire is trimmed, the
gun should be firmly grasped to prevent a phenome-
non often referred to as
“
machine gunning
”.
A light
grasp, especially at start, can cause the arc to stutter
as the wire pushes back on the gun, lengthening the
wire stick
-
out and creating an irregular start and
porous weld.
The end of the wire should be positioned just barely
above the metal when the trigger is pulled for the
cleanest start. This will position the end of the con-
tact tip about
1/2”
above the weld. The gun should
be in the vertical position, with no more than 5 de-
grees lean in either side to side direction. Holding
the wire too far off from the metal will result in
rough starting and too long of wire stick out.
Once the arc has been established, the gun can then
either be pushed or pulled in the direction of the
weld. In either case, the gun nozzle should be posi-
tioned directly over the weld without angling the
wire to one side or the other of the weld as already
mentioned. The gun should have no more than 15
degrees lean pointed into (push) or pointed away
from (pull) the direction of travel. In most cases a
push motion is desired. However, a lot of texts offer
conflicting information on whether to push or to pull
the gun. In reality, both are correct if used correctly
and with each having particular strength and weak-
ness. Either one done with too much gun angle will
result in undesirable results. Most open
-
minded
people who are well versed in MIG quickly develop
a sense of when to push and when to pull the gun.
Even for novices, a sense of when to push and pull
the gun comes quickly with a little practice. Pushing
can result in shallower penetration but the molten
puddle is easier to see and the arc sits easily on the
leading edge. It will usually leave a aesthetically
pleasing bead. However, be careful to prevent the
gun from leaning toward or away from the direction
of travel too much as spatter will increase and
shielding gas flow may become turbulent, creating
porosity in the weld. Pulling will result in deeper
penetration, but can result in a narrow bead without
much side fusion. It also can leave an undesirable
humped appearance if not done correctly or if travel
is too slow.
Whenever MIG welding with Aluminum,
whether with the standard MIG gun or the Spool
gun ALWAYS push the gun. If using Flux Core, a
dragging motion is almost always recommended.
Weaving (oscillating the torch from side to side in
one pattern or the other), particularly a MIG bead, is
a topic of controversy as much as whether to push
or pull the MIG gun. Stringer beads are often best
for novice welders. Stringers are simply straight
beads that move forward with little or no side to
side travel or oscillation. These will offer the sound-
est welds for a beginner. Stringer welds leave little
or no room for contaminates to enter the weld and
are the fastest to produce without creating an op-
1/4”
-
3/8”
(6mm–
9mm)
Basic Theory and Function
Section 3
