PRINCIPLES OF GAS TUNGSTEN ARC WELDING (GTAW)
Process
Description
Gas Tungsten Arc
Welding (GTAW), also known as tungsten inert gas (TIG) welding is a process
that produces an electric arc maintained between a nonconsumable tungsten electrode
and the part to be welded. The heat-affected zone, the molten metal, and the tungsten
electrode are all shielded from atmospheric contamination by a blanket of inert
gas fed through the GTAW torch. Inert gas (usually Argon) is inactive or
deficient in active chemical properties. The shielding gas serves to blanket the
weld and exclude the active properties in the surrounding air. Inert gases,
such as Argon and Helium, do not chemically react or combine with other gases.
They pose no odor and are transparent, permitting the the welder maximum
visibility of the arc. In some instances Hydrogen gas may be added to ehance
travel speeds.
The GTAW process can
produce temperatures of up to 35,000° F (19,426° C). The torch contributes heat only to the
workpiece. If filler metal is required to make the weld, it may be added
manually in the same manner as it is added in the oxyacetylene welding process,
or in other situations may be added using a cold wire feeder.
GTAW is used to weld steel,
stainless steel, nickel alloys such as MonelR and InconelR, titanium, aluminum, magnesium, copper, brass,
bronze, and even gold. GTAW can also weld dissimilar metals to one another such
as copper to brass and stainless steel to mild steel.
Advantages
of GTAW welding:
_ Concentrated
Arc - Permits pinpoint control of heat input to the workpiece resulting in an narrow
heat-affected zone.
_ No
Slag - No requirement for flux with this process; therefore no slag to obscure
the welder’s vision of the molten weld pool.
_ No
Sparks or Spatter - No transfer of metal across the arc. No molten globules of
spatter to contend with and no sparks produced if material being welded is free
of contaminants.
_ Little
Smoke or Fumes - Compared to other arc-welding processes like stick or flux
cored welding, few fumes are produced. However, the base metals being welded
may contain coatings or elements such as lead, zinc, copper, and nickel that
may produce hazardous fumes. Keep your head and helmet out of any fumes rising
off the workpiece. Be sure that proper ventilation is supplied, especially in a
confined space.
_ Welds
more metals and metal alloys than any other arc welding process.
_ Good
for welding thin material.
_ Good
for welding dissimilar metals together.
Disadvantages
of GTAW welding:
_ Slower
travel speeds than other processes.
_ Lower
filler metal deposition rates.
_ Hand-eye
coordination is a required skill.
_ Brighter
UV rays than other processes.
_ Equipment
costs can be higher than with other processes.
_ Concentrations
of shielding gas may build up and displace oxygen when welding in confined
areas − ventilate the area and/or use local forced
ventilation at the arc
to remove welding fumes and gases. If ventilation is poor, wear an approved
air-supplied respirator.
Selecting
A GTAW Power Source
Your choice of a TIG power source is driven by the type and thickness of
the material you will weld. This will determine whether you require a machine for
all weldable metals except Aluminum and Magnesium (DC) or one that is for all
weldable metals (AC/DC).
Items
to consider:
- Type of metal to be welded - (Aluminum, Steel, Stainless, etc.)
- Thickness of materials to be welded.
- Package solution that suits the welding application.
- Accessory components that add performance to the system.
- Physical Machine Size - Inverter/Transformer-Rectifier.
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