Tungsten Inert Gas (TIG) or Gas Tungsten Arc (GTA) welding

TIG Welding

Tungsten Inert Gas (TIG) or Gas Tungsten Arc (GTA)
welding is the arc welding process in which arc is generated
between non consumable tungsten electrode and workpiece. The
tungsten electrode and the weld pool are shielded by an inert
gas normally argon and helium. Figures  show the
principle of tungsten inert gas welding process.

Fig. Principle of TIG Welding

The tungsten arc process is being employed widely for
the precision joining of critical components which require
controlled heat input. The small intense heat source provided
by the tungsten arc is ideally suited to the controlled
melting of the material. Since the electrode is not consumed
during the process, as with the MIG or MMA welding processes,
welding without filler material can be done without the need
for continual compromise between the heat input from the arc
and the melting of the filler metal. As the filler metal,
when required, can be added directly to the weld pool from a
separate wire feed system or manually, all aspects of the
process can be precisely and independently controlled i.e.
the degree of melting of the parent metal is determined by
the welding current with respect to the welding speed, whilst
the degree of weld bead reinforcement is determined by the
rate at which the filler wire is added to the weld

Fig. Schematic Diagram of TIG Welding

In TIG torch the electrode is extended beyond the
shielding gas nozzle. The arc is ignited by high voltage,
high frequency (HF) pulses, or by touching the electrode to
the workpiece and withdrawing to initiate the arc at a preset
level of current.

Selection of electrode composition and size is not
completely independent and must be considered in relation to
the operating mode and the current level. Electrodes for DC
welding are pure tungsten or tungsten with 1 or 2% thoria,
the thoria being added to improve electron emission which
facilitates easy arc ignition. In AC welding, where the
electrode must operate at a higher temperature, a pure
tungsten or tungsten-zirconia electrode is preferred as the
rate of tungsten loss is somewhat lesser than with thoriated
electrodes and the zirconia aids retention of the ‘balled’

Tungsten electrodes are commonly available from 0.5 mm
to 6.4 mm diameter and 150 – 200 mm length. The current
carrying capacity of each size of electrode depends on
whether it is connected to negative or positive terminal of
DC power source. AC is used only in case of welding of
aluminum and magnesium and their alloys.

he power source required to maintain the TIG arc has a
drooping or constant current characteristic which provides an
essentially constant current output when the arc length is
varied over several millimeters. Hence, the natural
variations in the arc length which occur in manual welding
have little effect on welding current. The capacity to limit
the current to the set value is equally crucial when the
electrode is short circuited to the workpiece, otherwise
excessively high current shall flow, damaging the electrode.
Open circuit voltage of power source ranges from 60 to 80

Argon or helium may be used successfully for most
applications, with the possible exception of the welding of
extremely thin material for which argon is essential. Argon
generally provides an arc which operates more smoothly and
quietly, is handled more easily and is less penetrating than
the arc obtained by the use of helium. For these reasons
argon is usually preferred for most applications, except
where the higher heat and penetration characteristic of
helium is required for welding metals of high heat
conductivity in larger thicknesses. Aluminum and copper are
metals of high heat conductivity and are examples of the type
of material for which helium is advantageous in welding
relatively thick sections.

Pure argon can be used for welding of structural
steels, low alloyed steels, stainless steels, aluminum,
copper, titanium and magnesium. Argon hydrogen mixture is
used for welding of some grades of stainless steels and
nickel alloys. Pure helium may be used for aluminum and
copper. Helium argon mixtures may be used for low alloy
steels, aluminum and copper.

TIG welding can be used in all positions. It is
normally used for root pass(es) during welding of thick pipes
but is widely being used for welding of thin walled pipes and
tubes. This process can be easily mechanised i.e. movement of
torch and feeding of filler wire, so it can be used for
precision welding in nuclear, aircraft, chemical, petroleum,
automobile and space craft industries. Aircraft frames and
its skin, rocket body and engine casing are few examples
where TIG welding is very popular.