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TIG welding techniques
Best practice TIG welding techniques
Gas
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
root.
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
structures.
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 applications
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 being welded.
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
problem.
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 cause warpage.
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.
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