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The most commonly used gas welding process is oxyacetylene
welding. It burns acetylene gas in a pure oxygen stream creating
a very high temperature. Hydrogen, propane, and natural gas
are also used in this process. The basic technique involves
melting the edges of a joint so they can be fused together.
A filler wire or rod may also be used to supply molten metal
to the interface, and may have flux coating to retard oxidation
by generating a gaseous shield around the weld area and dissolving
surface oxides. While gas welding is a relatively slow, manual
process requiring a skilled operator, it has the advantages
of being portable, versatile, and economical for low-quantity
work. The equipment consists of a welding torch, gas cylinders
and pressure regulation, and safety goggles and protective clothing.
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Gas
Metal-Arc Welding (GMAW), also called Metal Inert Gas (MIG)
welding, shields the weld zone with an external gas such as
argon, helium, carbon dioxide, or gas mixtures. Deoxidizers
present in the electrode can completely prevent oxidation in
the weld puddle, making multiple weld layers possible at the
joint. GMAW is a relatively simple, versatile, and economical
welding apparatus to use. This is due to the factor of 2 welding
productivity over SMAW processes. In addition, the temperatures
involved in GMAW are relatively low and are therefore suitable
for thin sheet and sections less than _ inch. GMAW may be easily
automated, and lends itself readily to robotic methods. It has
virtually replaced SMAW in present-day welding operations in
manufacturing plants.
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Gas
Tungsten-Arc Welding (GTAW), also known as Tungsten Inert
Gas or TIG welding, uses tungsten electrodes as one pole of
the arc to generate the heat required. The gas is usually argon,
helium, or a mixture of the two. A filler wire provides the
molten material if necessary. The GTAW process is especially
suited to thin materials producing welds of excellent quality
and surface finish. Filler wire is usually selected to be similar
in composition to the materials being welded. Atomic Hydrogen
Welding (AHW) is similar and uses an arc between two tungsten
or carbon electrodes in a shielding atmosphere of hydrogen.
Therefore, the work piece is not part of the electrical circuit.
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Brazing
and Braze Welding are joining processes where a filler metal
is placed at the joint and the temperature is raised to melt
the filler metal into the joint. The strength of the joint depends
upon the adhesion at the interface as well as the contact area
of the joint. Consequently, the surface should be clean and
free from rust, oil, and other contaminants. Filler metals melting
above 840íF are used in brazing, and those that melt below this
temperature are used in soldering. In braze welding, the filler
metal is deposited in the joint and fills it by capillary action.
The heat source is usually an oxy-acetylene torch. The filler
metal is selected to avoid embrittlement of the joint as well
as any galvanic corrosion. Fluxes are often used to prevent
oxidation, remove oxides, and reduce fuming. Brazing flux is
most often made of borax, boric acid, borates, fluorides, or
chlorides. Wetting agents may also be added to improve molten
metal capillary action. Furnaces may be used to braze whole
assemblies of complex parts (such as jet engine blades and shrouds)
and for diffusion brazing where the filler metal diffuses into
the workpiece. This has proven effective for stronger lap or
butt joints, and difficult operations. Dip brazing using molten
salt or metal baths is also utilized. Infrared heating employing
high-intensity quartz lamps is also used to braze thin parts.
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Arc
welding is a process utilizing the concentrated heat of
an electric arc to join metal by fusion of the parent metal
and the addition of metal to joint usually provided by a consumable
electrode. Either direct or alternating current may be used
for the arc, depending upon the material to be welded and the
electrode used.
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Shielded-Metal
Arc Welding (SMAW) is one of the oldest, simplest, and most
versatile arc welding processes. The arc is generated by touching
the tip of a coated electrode to the workpiece and withdrawing
it quickly to an appropriate distance to maintain the arc. The
heat generated melts a portion of the electrode tip, its coating,
and the base metal in the immediate area. The weld forms out
of the alloy of these materials as they solidify in the weld
area. Slag formed to protect the weld against forming oxides,
nitrides, and inclusions must be removed after each pass to
ensure a good weld. The SMAW process has the advantage of being
relatively simple, only requiring a power supply, power cables,
and electrode holder. It is commonly used in construction, shipbuilding,
and pipeline work, especially in remote locations.
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Plasma
Arc Welding (PAW) uses electrodes and ionized gases to generate
an extremely hot plasma jet aimed at the weld area. The higher
energy concentration is useful for deeper and narrower welds
and increased welding speed.
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Plasma
arc cutting can increase the speed and efficiency of both
sheet and plate metal cutting operations. Manufacturers of transportation
and agricultural equipment, heavy machinery, aircraft components,
air handling equipment, and many other products have discovered
its benefits. Plasma cutters are used in place of traditional
sawing, drilling, machining, punching, and cutting. The high-temperature
plasma arc cuts through a wide variety of metals at high speeds.
Although plasma arc cutting can cut most metals at thicknesses
of up to 4 to 6 inches, it provides the greatest economical
advantages, speed, and quality on carbon steels under 1 inch
thick, and on aluminum and stainless steels under 3 inches thick.
Plasma arc cutting has gained approval in both hand-held and
automated cutting operations. Some of the most impressive results
are achieved in automated systems. Advances in computer numerical
controls (CNC), robots, and other automation techniques have
offered manufacturers higher cutting speeds achieved through
plasma arc cutting.
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