cleaning materials and backing strap, if they are
used.
T h e ac transformer with superimposed
high-frequency current, a GTA welding torch
e q u i p p e d with 3/16-inch diameter tungsten
electrode, argon gas, and necessary accessories are
the items of equipment needed.
The procedure is to bevel the abutting edge of
plates, as shown in figure 10-38. Clean all areas,
including the backing strap, if one is used. Brush
surfaces with a stainless-steel wire brush to remove
oxide film, and between passes if contamination is
apparent.
Figure 10-38.--Joint design flat-position single-pass butt
welds in aluminum sheet.
Regulate argon gas flow at 35 cubic feet per
hour, and select a welding current of 250 to 320
as shown in figure 10-38 without jigs. Position the
amperes.
plate and backup strap with all units supported and
level. Then tack weld.
Tack weld the assembly in the flat position, and
In welding practice, remember that good GTA
then arrange units as shown in figure 10-39. Use a
suitable jig to hold parts steady.
welding is dependent upon this definite
procedure-form the molten pool in the parent
Rules for quality welding in the flat position
sheet. Then feed the filler rod intermittently to the
must be followed for out-of-position GTA welding.
leading edge of the pool as the torch is being moved
Cleanliness, good joint fit-up, preheat, sufficient
forward. DO NOT feed the filler rod into the arc.
shielding gas, and correct welding current are
You should practice making single-pass butt welds
important. In addition, you will find it advisable not
until they are satisfactory. Workmanship must pass
to use high welding current or to deposit large weld
visual inspection standards.
Direct the arc so that there is no
beads.
overheating at any one area that produces sagging
Horizontal-Position Multipass Fillet
or undercutting. The filler metal addition, bead
and Butt Welds
size, and sequence have to be placed so that there
is complete fusion between passes.
This exercise will help you learn
horizontal-position welding. Use 1/2" by 6" by 12"
The welding of a fillet joint and a butt joint in
EC aluminum plate and 3/16-inch diameter 1100
a horizontal position is shown in figure 10-40, views
alloy filler rod, or any recommended parent
plate-filler alloy combination. You will also need
Figure 10-39.--Jolt design and weld pass sequence
Figure 10-40.--Welding a fillet and butt joint in the
horizontal-position multipass fillet and butt welds.
horizontal position.
10-35