OVERHEAD WELDING. When GTA welding
in the overhead position, you should lower the welding
current by 5 to 10 percent of what normally is used for
flat welding. This reduced welding current enables you
to maintain better control of the welding puddle.
Conversely, you need a higher flow of shielding gas.
Hold the torch and the rod as you do for flat welding
(fig. 8-22). You should try to maintain a small weld
puddle to avoid the effects of gravity. Most inexperi-
enced welders find overhead welding awkward; there-
fore, try to get in as comfortable and relaxed a position
as possible when welding. This helps you to maintain
steady, even torch and filler rod manipulation.
GTA WELDING COMMON METALS
The actual welding technique for gas tungsten-arc
welding common metals is virtually the same; however,
each of the metals that we discuss has its own unique
welding characteristics. In this section we discuss some
of those characteristics. It is not the scope of this training
manual to provide you with an in depth study of the
welding procedures required to weld all types of metals.
This chapter is merely an introduction to gas shielded-
arc welding. For more information, refer to the manu-
facturers literature for the specific welding equipment
you use or any of the references listed in this book.
Steelworkers use the gas tungsten-arc welding pro-
cedure more for aluminum than for any other metal.
Aluminum is available in a variety of compositions.
Series 1000,3000, and 5000 aluminum alloys are con-
sidered nonheat-treatable and are easily weldable. The
heat-treatable alloys in the series 2000, 6000, and 7000
also can be welded; however, higher welding tempera-
tures and speed are needed.
You can weld aluminum in all positions, but better
welds are normally produced in the flat position. You
should also use copper backup blocks whenever
possible, especially on thin material. For best results use
ACHF current and argon for shielding gas.
In GTA welding of stainless steel, the welding tech-
niques used are similar to those used with aluminum.
The major differences are in the selection of the welding
current and the type of tungsten electrode used. To get
the best results in welding stainless steel, you should use
DCSP welding current; however, ACHF can be
The forehand welding technique should be used.
The amperage settings for GTA welding stainless
steel are higher than for aluminum. The amperage used
for different thicknesses of stainless should be accord-
ing to the recommended settings that you can find in the
manufacturers technical manual or the information
pamphlets provided with the equipment.
Copper and Its Alloys
Pure copper is easily welded; however, as with any
of the other metals we have discussed, it must be thor-
oughly cleaned before to welding. The GTA weldability
of each copper-alloy group depends largely upon the
alloying elements. Copper-silicon and copper-nickel
alloys are weldable using the GTA process. Copper-
zinc, copper-tin, and copper-lead alloys are difficult or
impossible to weld by the GTA process. Plates up to 1/4
of an inch thick are generally prepared with a square
edge. The forehand welding technique with DCSP is
recommended for materials thicker than 0.050 of an
inch. On lighter material, ACHF also can be used.
You can make sound welds using the GTA welding
process in three principal grades of cast iron: gray,
white, and malleable. Cast-iron parts must always be
preheated before to welding. Gray cast iron should be
preheated to a temperature ranging between 500°F to
1250°F. The required temperature depends on the size
and shape of the workpiece.
In either GTA or GMA welding, you should allow
the workpiece to cool slowly after welding. You can
accomplish this by covering the workpiece in a bed of
lime or ashes. This slow cooling prevents cracking and
The welding characteristics of magnesium are com-
parable to those of aluminum. Both have high-heat
conductivity, a low-melting point, high-thermal expan-
sion, and both oxidize rapidly. Both DCRP and ac pro-
vide excellent cleaning action to the weld metal. DCRP
can be used with helium gas to produce wide weld
deposits, high heat, and shallow penetration. ACHF with
helium, argon, or a mixture of the gases can be used to
join metals ranging from 0.20 to over 0.25 of an inch.
DCSP with helium produces deep penetration but no
Most satisfactory results on magnesium are ob-
tained by using the electrode in as nearly a vertical