9
1
Shielding gas
2
Arc
3
TIG filler rod
4
Weld pool
5
Collet
6
Tungsten Electrode
7
Workpiece
1
2
3
4
5
6
7
Schematic of the TIG welding process
DC Electrode Negative (DCEN)
In this mode the tungsten electrode is the
negative pole in the welding circuit, the
workpiece being the positive pole.
DC Electrode Positive (DCEP)
In this mode the tungsten electrode is the
positive pole in the welding circuit, the
workpiece being the negative pole.
Alternating Current (AC)
In this mode the polarity of the tungsten
electrode and the workpiece alternate between
negative and positive at the frequency of the
applied welding current.
Application
The TIG process is very versatile and may be
used to weld any metal or alloy system over
a wide range of thicknesses, but is usually
restricted to 10mm and under for economic
reasons. It is particularly suited to welding
sheet materials and for the root run in pipe
butt welds.
DCEN is the most common mode of operation
and is widely used for welding all carbon,
alloy and stainless steels, as well as nickel
and titanium alloys. Copper alloys, with the
exception of those containing aluminium in
significant amounts, can also be welded with
this polarity.
DCEP is used for aluminium alloys when
welding, with pure helium as the shielding gas,
since this polarity has a strong cathodic cleaning
effect capable of removing the tenacious
aluminium oxide film from the surface. It may
also be used for TIG welding magnesium alloys.
AC polarity is used most commonly when
welding aluminium and its alloys with pure
argon or argon-helium mixtures to take
advantage of the combination of the cyclic
heating and cleaning action. It is also suitable
for welding magnesium alloys and aluminium
bronze.
Applications
• High quality fabrications in stainless steel
• Aluminium, copper and nickel alloys
• Welding reactive and refractory metals such
as titanium, tantalum and zirconium
The process is used extensively in the
nuclear and aerospace industries and in the
construction and maintenance of chemical and
cryogenic process plant and pipework. It is also
used for fabrication of tube heat-exchangers in
petrochemical and power-generation plant, and
for brewing and food-processing vessels.
TIG Welding Equipment
The equipment used for TIG welding consists of:
• Power source
• Welding torch
• Tungsten electrode
• Leads and connectors
• Gas supply system
