Type of operation: Usually manual, but can be mechanized.
Mode of Operation: An arc is maintained between the end of a tungsten electrode and the work. The electrode is not consumed and the current is controlled by the power source setting. The operator must control the arc length and also add filler metal if needed to obtain the correct weld: consequently, a high degree of skill is needed for best results. In this method, coalescence is produced by heating the job with an electric arc struck between a tungsten electrode and the job. A shielding gas (Argon, Helium & Nitrogen) is used to avoid atmospheric contamination of the molten weld pool. A filler wire is separately added. Striking the arc, a weld puddle is developed on the job. A filler wire is dipped in the weld pool During welding alternatively filler rod and tungsten electrode will withdraw and come closer to the weld pool. At the end of the job, the arc is broken by increasing arc length. Shielding gas is allowed to fall on the weld pool for a few seconds.
TIG WELDING sets are manufactured in a range of sizes, identified by current: also important is whether the output is DC only, DC / AC or AC only. AC is needed for most work on aluminum. In DC welding, the electrode usually has negative polarity which reduces the risk of overheating which may otherwise occur with electrode positive. The ionized gas or plasma stream can attain a temperature of several thousand degrees centigrade. The shielding gas supplied to the arc has two functions:
1. It generates the arc plasma.
2. It protects the electrode, weld pool and weld bead from undesirable oxidation.
Electrodes for DC welding are pure tungsten or tungsten with 1 or 2% thorium. Thorium is added to improve electron emission which facilitates arc ignition. In AC welding, where the electrode must operate at a higher temperature, a pure tungsten or tungsten-zirconia electrode is preferred.
Shielding gas: The shielding gas composition is selected according to the material being welded. The most common shielding gas is Argon. This can be used for welding a wide range of material including mild steel, stainless steel, and the reactive aluminum, titanium and magnesium. Effective shielding can be maintained by controlling the gas flow. Too low results in porosity. High flow results to turbulence
ADVANTAGES:
Flux is not required
No slag entrapment problem
Cleaning is not required during welding
Best suited for all position welding and low thick components.
DISADVANTAGES:
Brittle and hard tungsten may entrap in the weld pool.
Equipment is costly
APPLICATIONS:
Welding boiler tubes, atomic energy and air craft industries
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