Basic knowledge of Gas Tungsten Arc Welding (GTAW) for freshers in the field. This is one of the welding process that produces one of the highest quality of weld for high integrity structures...

1. By Ayuba Isaac

2. Introduction
 Gas Tungsten Arc Welding (GTAW)also
known as Tungsten Inert Gas welding
(TIG) is an electric arc welding process that
produces an arc between a non-
consumable electrode (tungsten which
does not melt due to its high melting point)
and the work piece to be welded. The weld
is shielded from the atmosphere by a
shielding gas that forms an envelope
around the weld area. However, a filler
metal is usually used in the process.

3. GTAW set-up
 Below is a simple diagram illustrating
the set-up of GTAW process...

4. Equipments use in gtaw
 Below are some of the tools used in GTAW process;
 Gas supply (cylinder)
 Electrical power source (AC/DC)
 Electrode holder, torch or gun
 Connection cables
 Hose (for gas supply)
 Tungsten electrode
 Coolant
 Filler rods
 NOTE: the above mentioned are not limited to the,
however other special could be used for specific
purposes...

5. Working principle
 An arc is established between the end of a
tungsten electrode and the parent metal at the
joint line. The electrode is not melted and the
welder keeps the arc gap constant. The
current is controlled by the power-supply unit.
 A filler metal, usually available in 1 m lengths
of wire, can be added to the leading edge of
the pool as required. The molten pool is
shielded by an inert gas which replaces the air
in the arc area.
 Argon and helium are the most commonly
used shielding gases.

6.  The process may use direct current
electrode positive, direct current
electrode negative or alternating
current. The chart above indicates the
operating characteristics of each of
these current types.
 DCEN or “straight polarity” is used for
welding most materials other than
aluminium. The electrode tip geometry
is generally a sharp point with a small
blunted end since most of heat
balance is on melting of the base
material.

7.  DCEP or “reverse polarity” is rarely
used since it results in low penetration.
Also the constant bombardment of the
tungsten electrode by electrons in the
DCEP mode degrades the electrode.
 Alternating current is used primarily to
weld aluminium, which has a tenacious
oxide surface layer. Although the
diagram above states that there is a
50% cycle from DCEN to DCEP, it is
possible through solid state electronics
to vary the amount of time at each
polarity and also the current at each
polarity.

8.  High-quality welds in metals such as
aluminium, stainless steels, nimonic
alloys and copper in chemical plants;
sheet work in aircraft engines and
structures; Mainly thin sheets.

9. Effects of Polarity

10. Advantages
 GTAW produces precise and clean, nearly spatter
free welds on almost all metals with superior quality
in comparison to the other arc welding processes. It
has found use in the aerospace, food processing,
and nuclear industries. It is particularly useful on
smaller sectioned parts and on reactive metals such
as titanium.
 It can be used with filler metal or without filler metal
(autogenous). This process allows the heat source
and filler metal additions to be controlled
independently.
 It is easily automated and can produce welds in all
positions, even with intricate geometries.

11.  Superior quality welds, generally free
from spatter, porosity, or other defects
 Precise control of arc and fusion
characteristics
 Weld almost all metals
 Used with or without filler wire
 Easily automated
 Used in all positions
 Intricate geometries weldable

12. Disadvantages
 Deposition rates are lower with GTAW than
any other arc welding process. In general,
the process is limited to thicknesses of 3/8-
inch or less since productivity makes the
process cost prohibitive. Tungsten
inclusions or contamination of the weld
pool may occur if the electrode touches the
weld pool or proper gas
 Higher operator skill Required
 Sensitive to drafts
 shielding is not maintained.

13.  Manual GTAW requires more dexterity
and welder coordination than with
manual GMAW or SMAW. As with the
other gas shielded processes, drafts
can blow away the shielding gas,
which limits the outdoor use of the
process.
 Less economical than consumable
electrode processes for sections
thicker than 3/8 inch
 Lowest deposition rate of all arc
processes
 Tungsten inclusions

14. Added notes;
 For TIG of carbon and stainless steels,
the selection of a filler material is
important to prevent excessive porosity.
Oxides on the filler material and
workpieces must be removed before
welding to prevent contamination, and
immediately prior to welding, alcohol or
acetone should be used to clean the
surface

15. Safety Precautions
 To prevent injury to personnel, extreme
caution should be exercised when using
any types of welding equipment. Injury
can result from fire, explosions, electric
shock, or harmful agents. Both the
general and specific safety precautions
listed below must be strictly observed by
workers who weld or cut metals.
 Do not permit unauthorized persons to
use welding or cutting equipment.

16.  Remove all flammable material, such as
cotton, oil, gasoline, etc., from the
vicinity of welding. Do not weld in a
building with wooden floors, unless the
floors are protected from hot metal by
means of fire resistant fabric, sand, or
other fireproof material. Be sure that hot
sparks or hot metal will not fall on the
operator or on any welding equipment
components.

17.  Mark all hot metal after welding operations
are completed. Soapstone is commonly
used for this purpose.
 Before welding or cutting, warn those in
close proximity who are not protected to
wear proper clothing or goggles.
 Remove any assembled parts from the
component being welded that may become
warped or otherwise damaged by the
welding process.


18.  Do not leave hot rejected electrode
stubs, steel scrap, or tools on the floor
or around the welding equipment.
Accidents and/or fires may occur.
 Keep a suitable fire extinguisher nearby
at all times. Ensure the fire extinguisher
is in operable condition.