Tungsten Arc Welding (GTAW) is referred to as TIG welding. TIG welding is a
commonly used high quality welding process. TIG welding has become a popular
choice of welding processes when high quality, precision welding is required. An
arc is formed between a tungsten electrode and the metal being welded. Gas is
fed through the torch to shield the electrode and molten weld pool. If filler
wire is used, it is added to the weld pool separately.
Good tig welding techniques require greater welder dexterity than MIG or
stick welding. It also has lower deposition rates, and is more costly for
welding thick sections.
TIG welding discontinuities
Incomplete Fusion - A weld discontinuity in which fusion did not
occur between weld metal and fusion faces or adjoining weld beads.
Undercut - A groove melted into the base metal adjacent to the weld
toe or weld root and left unfilled by weld metal.
Overlap - The protrusion of weld metal beyond the weld toe or weld
Underfill - A condition in which the weld face or root surface extends
below the adjacent surface of the base metal.
Incomplete Joint Penetration - A joint root condition in a groove
weld in which weld metal does not extend through the joint thickness
Partial joint penetration groove welds are commonly specified in lowly loaded
TIG Welding Techniques and Problems
Some TIG welding problems that can be corrected by good TIG welding
techniques include an erratic arc, excessive electrode consumption, oxidized
weld deposits, arc wandering, porosity, and difficult arc starting.
More TIG welding techniques: welding techniques for automotive
The TIG (Tungsten Inert Gas) welding process (also known as gas tungsten arc
welding, GTAW, or HELIARC, a trade name of Linde) generates heat from an
electric arc maintained between a non consumable tungsten electrode and the part
TIG may be used without the addition of a filler metal or a separate wire
filler metal can be added into the puddle when additional material is required,
much like the process in oxy-acetylene welding. The puddle, the tungsten
electrode and the filler rod are protected from atmosphere by a shield of inert
gas to prevent rapid oxidation of the weld and surrounding metal. Argon is the
most widely utilized gas.
Because the gas shield does not produce the slag that normally is created by
flux, the danger of slag inclusion in the weld metal is eliminated. Also, due to
the slow speed of the TIG process, gases and other impurities escape to the
surface of the puddle before solidification occurs, eliminating pockets called
"Porosity" common in weld processes that employ gas shielding but have greater
travel speeds than the TIG process. TIG also produces a welding heat is that is
confined between the weld and base metal at the point of fusion and produces a
narrow heat affected zone. This reduces stress, cracking and distortion in the
finished weld. Spatter is not produced by this process, leaving the weld and
surrounding metal clean. Because of the lack of spatter and flux smoke, the TIG
process allows the operator a clear view of the weld puddle.
The torch body in most cases is small enough that the operator can hold it
in the same manner as he would hold a pencil allowing easier manipulation. The
power source is constant current, either AC, DC, or combination AC/DC. Type of
metal determines which type is used. DC (direct current) is most normally used
for TIG welding of stainless steels and mild and low alloy steels. AC
(Alternating current) is used for TIG welding of aluminum. Surface oxidation is
automatically removed by the action of the arc each time the electrode becomes
positive, (60 times per. second). Because AC crosses over the zero volt point
120 times per second (once going positive and once going negative each cycle),
the arc shuts off 120 times per second. To keep the arc going when using AC, a
high frequency "arc stabilizer" is used. The high frequency also allows the
start of an arc in DC mode without having to "strike" an arc, thereby reducing
the possibility of tungsten contamination. If the electrode accidentally touches
the weld pool, it becomes contaminated and must be cleaned immediately to
prevent weld contamination. TIG technique requires an extremely clean surface to
weld successfully and is a fairly slow operation. On the plus side, TIG produces
high quality work and does not generate slag or spatter. The welder can adjust
the heat input while welding by using foot or hand amperage controls.
MIG (Metal Inert Gas), also referred to as wire feed welding, utilizes a
consumable arc. The process generates heat from an electric arc maintained
between a consumable wire feed electrode and the part being welded. This process
produces spatter making it difficult for the operator to see the weld and
causing damage to nearby surfaces and objects from the hot particles thrown off.
Flux cored "gasless" welders produce smoke from the flux, and pose a cleanup
Because of the higher welding speeds of the MIG process, the chance of
producing porosity is higher. A common mistake with novice welders utilizing the
MIG process is the possibility of producing a good looking weld with little
penetration. A MIG can produce an arc into the puddle, allowing one to create a
nice looking weld while the base metal underneath is not being properly melted.
This cannot be detected before failure without either destructive or
non-destructive testing. In the TIG process, the base metal is melted to produce
a puddle before any filler is introduced into the weld. This allows the operator
to see the penetration during the welding process.
Another drawback in MIG welding in restoration of automobiles is the
workability of the weld. The wire used in MIG cools harder than in TIG welding,
making it harder to hammer and dolly the weld afterwards. Because MIG welding
uses a constant fed wire to produce the arc, some buildup of material usually
occurs that has to be ground off. This also generates heat in the panel that can
With TIG welding, filler is only added when needed, and the thickness of the
filler can be changed by picking up a different size rod. These techniques
reduces post weld finishing. While TIG welding requires greater skill, the
results are far better than other welding methods. Welders of both types are
available from many sources, such as Eastwood, Daytona Mig, and Professional
sources such as Miller Electric.
These tig welding techniques are produced for informational purposes only.
More TIG Welding Techniques will be posted as we progress.