Figure 8-28.Correct wire stick-out.
0.045-inch or 1/16-inch diameter wires. For thicker
metals, larger diameter electrodes may be required.
As you learned earlier, the position of welding is a
factor that must be considered. For instance, when you
are welding in the vertical or overhead positions, you
normally use smaller diameter electrodes.
Special attention must be given to ensure the wire
is clean. Unsound welds result from the use of wire that
is contaminated by oil, grease, dust, or shop fumes. You
can obtain the best welding results with wire that has
just been taken out of its carton. Wire should be stored
in a hot locker or in a warm dry area, and should be kept
covered. If welding is stopped for a long period of time,
you should remove the wire and place it in its original
carton to prevent contamination.
WIRE STICK-OUT. In gas metal-arc welding,
wire stick-out refers to the distance the wire extends
from the nozzle of the gun (fig. 8-28). The correct
amount of wire stick-out is important because it influ-
ences the welding current of the power source. Since the
power source is self-regulating, the current output is
automatically decreased when the wire stick-out in-
creases. Conversely, when the stick-out decreases, the
power source is forced to furnish more current. Too little
stickout causes the wire to fuse to the nozzle tip, which
decreases the tip life.
For most GMA welding, the wire stickout should
measure from 3/8 to 3/4 of an inch. For smaller (micro)
wires, the stick-out should be between 1/4 and 3/8 of an
WIRE-FEED SPEED. As we stated earlier, you
can adjust the wire-feed drive motor to vary the
wire-feed speed. This adjustment is limited to a definite
range, depending on the welding current used. (See table
8-6). The wire-feed speed is measured in inches per
minute (ipm). For a specific amperage setting, a high
wire-feed speed results in a short arc, whereas a low
speed produces a long arc. You use higher speeds for
overhead welding than with flat-position welding.
Personal Protective Equipment
As with any other welding process, SAFETY is
extremely important. A welding hood like the one used
in shielded metal-arc welding should be used for gas
metal-arc welding. The correct shade of lens depends on
the intensity of the arc. Chapter 3 provides a chart of
recommended lens shades based on the current setting
of the machine. Eye fatigue indicates you should use a
different shade of lens or there is leakage around the
protective filter glass.
In addition to the welding hood, protective clothing,
such as gloves and an apron, should be worn. Bare skin
should never be exposed to the rays of the welding arc
because it could result in painful burns.
TYPES OF GMA WELDING
When using the GMA welding process, metal is
transferred by one of three methods: spray transfer,
globular transfer, or short-circuiting transfer. The type
of metal transfer depends on the arc voltage, current
setting, electrode wire size, and shielding gas.
Spray-arc transfer is a high-current range method
that produces a rapid disposition of weld metal. This
type of transfer is effective for welding heavy-gauge
metals because it produces deep weld penetration. The
use of argon or a mixture of argon and oxygen are
necessary for spray transfer. Argon produces a pinching
effect on the molten tip of the electrode, permitting only
small droplets to form and transfer during the welding
process. Spray transfer is useful when welding alumi-
num; however, it is not practical for welding light-gauge
Globular transfer occurs when the welding current
is low. Because of the low current, only a few drops are