©
COPYRIGHT 1998 THE ESAB GROUP, INC. LESSON
II 2.3
GAS TUNGSTEN ARC WELDING
Gas Tungsten Arc Welding*
is a welding process performed using the heat of an arc
established between a nonconsumable
tungsten electrode and the work piece. See Figure 5.
The electrode, the arc, and the area
surrounding the molten weld puddle are protected from the
atmosphere by an inert gas shield. The electrode is not consumed in the
weld puddle as in shielded
metal arc welding. If a filler metal is necessary,
it is added to the leading the
molten puddle as shown in 2.3.0.1
Gas tungsten arc welding
produces exceptionally clean welds
no slag is produced, the chance
inclusions in the weld metal is
and the finished weld requires
virtually no cleaning. Argon
and Helium, the primary
shielding gases employed,
are inert gases. Inert gases
do not chemically combine
with other elements and
therefore, are used to exclude
the reactive gases, such as oxygen
and nitrogen,
from forming compounds that could be
detrimental to the weld metal. 2.3.0.2
Gas tungsten arc welding may be used
for welding almost all metals — mild steel, low
alloys, stainless steel, copper and copper alloys, aluminum and aluminum alloys,
nickel and nickel
alloys, magnesium and magnesium alloys, titanium, and others. This process
is most extensively
used for welding aluminum and stainless steel alloys where weld integrity is of
the utmost importance. Another
use is for the root pass (initial pass) in pipe welding, which
requires a weld of the highest quality.
Full penetration without an excessively high inside bead
is important in the root pass, and
due to the ease of current control of this process, it lends
itself to control of back-bead size.
For high quality welds, it is usually necessary to provide an
inert shielding gas inside the pipe
to prevent oxidation of the inside weld bead. *
Gas Tungsten Arc Welding (GTAW) is
the current terminology approved by the American Welding Society,
formerly known as "TIG" (Tungsten Inert
Gas) welding. FIGURE
5 TRAVEL
DIRECTION TORCH
SHIELDING GAS
NOZZLE INERT
GAS SHIELD
WORK PIECE TUNGSTEN
ELECTRODE ARC
FILLER METAL
GAS TUNGSTEN ARC WELDING
