SURFACE POROSITY. Surface porosity usu-
ally results from atmospheric contamination. It can be
caused by a clogged nozzle, shielding gas set too low or
too high, or welding in a windy area. To avoid surface
porosity, you should keep the nozzle clean of spatter, use
the correct gas pressure, and use a protective wind shield
when welding in a windy area.
CRATER POROSITY. Crater porosity usually
results from pulling the torch and gas shield away before
the crater has solidified. To correct this problem, you
should reduce the travel speed at the end of the joint.
You also may try reducing the tip-to-work distance.
COLD LAP. Cold laps often result when the arc
does not melt the base metal sufficiently. When cold lap
occurs, the molten puddle flows into an unwelded base
metal. Often this results when the puddle is allowed to
become too large. To correct this problem, you should
keep the arc at the leading edge of the puddle. Also,
reduce the size of the puddle by increasing the travel
speed or reducing the wire-feed speed. You also may use
a slight whip motion.
LACK OF PENETRATION. Lack of penetra-
tion usually results from too little heat input in the weld
zone. If the heat input is too low, increase the wire-feed
speed to get a higher amperage. Also, you may try
reducing the wire stick-out.
BURN-THROUGH. Burn-through (too much
penetration) is caused by having too much heat input in
the weld zone. You can correct this problem by reducing
the wire-feed speed, which, in turn lowers the welding
amperage. Also you can increase the travel speed. Burn-
through can also result from having an excessive
amount of root opening. To correct this problem, you
increase the wire stick-out and oscillate the torch
WHISKERS. Whiskers are short pieces of elec-
trode wire sticking through the root side of the weld
joint. This is caused by pushing the wire past the leading
edge of the weld puddle. To prevent this problem, you
should cut off the ball on the end of the wire with side
cutters before pulling the trigger. Also, reduce the travel
speed and, if necessary, use a whipping motion.
GMA WELDING COMMON METALS
You can use the welding equipment and techniques
for gas metal-arc welding to join all types of metals;
however, as we discussed in the GTAWprocess, each of
the metals requires a unique welding method. In this
section, we discuss some of the welding methods asso-
ciated with a few of the more commonly welded metals.
The majority of welding by all methods is done on
carbon steels. When you are using GMA to weld carbon
steels, both the spray-arc and short-arc methods may be
applied. For spray-arc welding, a mixture of 5-percent
oxygen with argon is recommended. As we mentioned
earlier, this mixture provides a more stable arc. Also you
may use a mixture of argon and CO2 or straight CO2.
Straight CO2 is often used for high-speed production
welding; however, with CO2 the arc is not a true spray
arc. For short-arc welding, a 25-percent CO2 and 75-per-
cent argon mixture is preferred.
For GMA welding of thin materials (0.035 inch to
1/8 inch), no edge preparation is needed and a root
opening of 1/16 of an inch or less is recommended. For
production of adequate welds on thicker material, some
beveling is normally required. When welding plates 1/4
of an inch or greater in thickness, you should prepare a
single or double-V groove with 50- to 60-degree in-
The joint design for aluminum is similar to that of
steel; however, aluminum requires a narrower joint
spacing and lower welding current setting.
The short-arc welding method is normally used for
out-of-position welding or when welding thin materials
because short-arc produces a cooler arc than the spray
type arc. When welding thinner material (up to 1 inch in
thickness), you should use pure argon.
The spray-arc welding method is recommended for
welding thicker materials. With spray arc, more heat is
produced to melt the wire and base metal. When you are
welding thicker material (between 1 and 2 inches) a
mixture of 90-percent argon and 10-percent helium is
recommended. The helium provides more heat input and
the argon provides good cleaning action.
DCRP with a 1- or 2-percent oxygen with argon
mixture is recommended for most stainless steel weld-
ing. In general, you weld stainless steel with the spray-
arc welding method and a pushing technique. When
welding stainless steel up to 1/1 6 of an inch in thickness,
you should use a copper backup strip. For welding thin
materials in the overhead or vertical positions, the short-
arc method produces better results.