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TUNGSTEN ARC GAS SHIELDED WELDING (TAGS & TIG) 1
TAGS (TUNGSTEN ARC GAS SHIELDED) welding, is more commonly referred to as the TIG or TUNGSTEN INERT GAS process. TIG is the term used for this process when an inert ARGON gas shield is used to protect the weld. The term HELISHIELD is sometimes used when welding with a HELIUM gas shield. All these various terms though, essentially describe the same basic welding process.
TIG is considered by most founders and fabricators to be the ideal welding process for joining wrought and cast designs formed in non-ferrous metals. Basic TIG hardware consists of a STEP DOWN ELECTRICAL TRANSFORMER, which in turn delivers either a direct (DC) current, or an alternating (high frequency AC) current to a welding torch that contains a non-consumable TUNGSTEN ELECTRODE. It is the tungsten electrode that directs the arc into the weld joint.
Arc welding equipment capable of producing higher electrical currents usually also has a facility to circulate water around the torch and power supply leads for cooling purposes. This allows continuous welding at the relatively high AMPERAGE values required to initiate and maintain a WELD POOL in heavy walled copper and aluminium alloy casts.
The WELDING TORCH is connected to the inert gas supply via an adjustable REGULATOR and supply hose. The rate of gas delivery to the torch typically set at between 7-14 litres per minute (lpm), this is controlled by a FLOW METER which is either attached to the cylinder regulator, or else built into the welding set’s main control panel. Shielding gases for TAGS welding are normally HIGH PURITY ARGON, or helium based mixes of variable composition – according to the exact alloy being welded. High purity argon is the usual choice in the art foundry workshop, though helium mixes are better for welding very heavy work – especially if cast in aluminium or high conductivity copper. The protective gas shield is directed over the weldpool by a CERAMIC SHROUD mounted at the front of the torch. The gas shield does not fuel the arc, instead it primarily prevents atmospheric contamination and oxidisation of the deposited weld, thus ensuring a strong, high quality FUSION JOINT.
The electric arc which forms the weld pool is directed into the joint from a sharpened tungsten electrode. This needle like electrode projects no more than 5mm (1/4”) past the aperture in the ceramic shroud. The tungsten electrode also contains a small percentage of either THORIUM OXIDE or ZIRCONIUM OXIDE. The diameter and exact composition of the electrode is determined by the level of the welding current being used and the type of the alloy being welded.
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