GTAW and Power Sources

GTAW Welding
GTAW
Also referred to as TIG Welding
Uses a shield gas, a non-consumable tungsten
electrode and a hand fed filler rod
Excellent for welding thin metals, pipeline
welding and exotic metals
Highly skilled labor needed for this process
Gas Tungsten-Arc
Welding
The gas tungsten-arc welding process, formerly known

as TIG (for tungsten inert gas) welding.
Equipment for gas tungsten-arc welding

operations. Source: American Welding
Society.
Comparison of Laser-Beam and

Tungsten-Arc Welding
Figure 27.16
Comparison of the
size of weld beads in
(a) electron-beam or
laser-beam welding
to that in (b)
conventional
(tungsten-arc)
welding. Source:
American Welding
Society, Welding
Handbook (8th ed.),
1991.
General Characteristics of
Fusion Welding Processes
TABLE27.1
Joiningprocess
Shieldedmetalarc
Operation
Manual
Submergedarc
Automatic
Gasmetalarc
Semiautomatic
orautomatic
Manualor
automatic
Semiautomatic
orautomatic
Manual
Gastungstenarc
Fluxcoredarc
Oxyfuel
Electronbeam,
Semiautomatic
Laserbeam
orautomatic
*1,highest;5,lowest.
Advantage
Portableand
flexible
High
deposition
Mostmetals
Mostmetals
High
deposition
Portableand
flexible
Mostmetals
Skilllevel
required
High
Welding
position
All
Current
type
ac,dc
Distortion
1to2
Lowto
medium
Lowto
high
Lowto
high
Lowto
high
High
Flatand
horizontal
All
ac,dc
1to2
Medium
dc
2to3
All
ac,dc
2to3
Mediumto
high
Medium
All
dc
1to3
Medium
All
2to4
Low
Medium
tohigh
All
3to5
High
Costof
equipment
Low
The GTAW (TIG) Process

Temperatures of up to 35,000 F/ 19,426 C.
The torch contributes only heat to the work piece.
Advantages
weld more kinds of metals and metal alloys
stainless steel, nickel alloys such as Monel and Inconel,
titanium, aluminum, magnesium, copper, brass, bronze, and
even gold.
dissimilar metals
Concentrated Arc
pin point control of heat input to the work piece resulting in a
narrow heat-affected zone.
advantage when welding metals with high heat conductivity
such as aluminum and copper.
No Slag- welders vision of the molten weld pool.
The finished weld will not have slag to remove between
passes.
No Sparks or Spatter
no transfer of metal across the arc.
no sparks produced if the material being welded is free of
contaminants.
GTAW Disadvantages
low filler metal deposition rate.
hand-eye coordination necessary
The arc brighter than those produced by SMAW and GMAW.
Polarity
Direct Current Electrode Negative (DCEN)
practically all metals.
approximately 70% of the heat will be concentrated into the
workpiece.
deep penetration
The electrode receives a smaller portion of the heat energy than
when using Alternating Current (AC) or Direct Current Electrode
Positive polarity (DCEP).
This accounts for the higher current carrying capacity of a
given size tungsten electrode with DCEN than with DCEP or AC.
Direct Current Electrode Positive (DCEP),

Approximately 70% of the heat will be concentrated at the
positive side of the arc.
electrode receives the greatest amount of heat and becomes very
hot, the electrode must be very large even when low amperages are
used, to prevent overheating and possible melting.
shallow penetration.
disadvantage - magnetic forces the arc will sometimes wander
from side to side when making a fillet weld when two pieces of
metal are at a close angle to one another.
DCEP
cleaning done continuously while the welding
oxide can be removed by the welding arc
positively charged gas ions strike the work piece with sufficient
force to break up and chip away the brittle aluminum oxide
Why GMAW uses mostly DCEP

stable arc, smooth metal transfer, relatively low spatter,
good weld bead characteristics and deep penetration for a
wide range of welding currents.
DCEN
The molten droplet size tends to increase and the droplet
transfer becomes irregular, thereby increasing large grain
spatter.
However, some specific wires with unique chemical
composition have been developed specifically for DCEN,
which offers excellent performance on galvanized sheets.
Attempts to use conventional AC have generally been
unsuccessful due to the instable arc in GMAW.
SMAW is the most versatile welding process in terms of polarity

The majority of covered electrodes use either AC or DCEP.
Some electrodes, specifically E6013 (RB-26), E6019 (B-17) and E7024(ZERODE43F) offer good performance with AC, DCEP or DCEN.
In contrast, high cellulose type electrodes such as E6010 (KOBE-6010), E7010-P1
(KOBE-7010S), and E8010-P1 (KOBE-8010S) for pipe welding are designed for
use with DCEP only for smoother droplet transfer.
Low carbon type Cr-Mo electrodes such as E7015-B2L (CMB-95) and E8015-B3L
(CMB-105) are also designed for use with DCEP only, for better performance.
Some specific electrodes such as LB-80UL for high strength steels and NB-1S for
low temperature steels are recommended to use AC only in order to guarantee
strict requirements for strength and impact toughness of weld metal in
fabrication.
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GTAW and Power Sources

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GTAW Welding

The gas tungsten-arc welding process, formerly known

Equipment for gas tungsten-arc welding

Comparison of Laser-Beam and

The GTAW (TIG) Process

Direct Current Electrode Positive (DCEP),

Why GMAW uses mostly DCEP

SMAW is the most versatile welding process in terms of polarity

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