(a) Welding Torch, Tungsten electrode and filler metal.
(b) Welding power source, high frequency unit, DC suppressor unit and cables.
(c) Inert gas cylinder, pressure regulator and flow meter.
(d) Cooling water supply.
(e) Water and gas solenoid valves.
Welding torch which may be air or water cooled, energises the tungsten electrode held in a collet and feed shielding gas to the weld puddle. When welding above 150 Amps, generally a water-cooled torch is preferred.
The electrode material may be tungsten, or tungsten alloy, i.e., thoriated tungsten or zirconiated tungsten. Alloy-tungsten electrodes possess higher current carrying capacity, high resistance to contamination and produce a steadier arc, as compared to pure tungsten electrodes.
When welding copper in nitrogen atmosphere, alloy-tungsten electrodes are preferred because nitrogen attacks liquid (pure) tungsten; but, for the welding of aluminium under argon shielding pure tungsten electrode is more suitable. In figure below shows the electrode geometry for AC and DC welding.
A filler rod is generally used when welding thicker pieces with edges prepared. Preferably the filler rod should possess the similar chemical composition and be of the diameter same as the thickness of the work piece to be welded. Filler metals up to 4.5 mm diameter in the form of Straight lengths or coils are available for TIG welding of different metals and alloys.
Both DC and AC welding machines with good current control can be used for TIG welding. DC is preferred for welding of stainless steel, nickel, copper and copper alloys whereas DCRP or AC is used for welding magnesium, aluminium and their alloys. Reverse polarity of current removes oxide film on aluminium and magnesium.
When using AC a high frequency unit is employed to keep the arc ignited and stabilized. A DC suppressor unit is incorporated in the elec trical circuit to balance the current wave. A DC suppressor unit reduces the effect of DC component of current which comes into operation due to the fact that arc voltage is more when electrode is positive than when it is negative.
In the absence of a DC suppressor unit, arc may blow and behave critically and the transformer may become saturated, over-heated and derated.
Inert gases ordinarily used in TIG welding are:
(i) Argon (ii) Helium
(iii) Argon-helium mixtures (iv) Argon-oxygen mixtures
(v) Argon-hydrogen mixtures
Pressure regulator and flowmeter are used respectively to step down the inert gas pressure from cylinder pressure (approx. 140 kg/cm2) to working pressure (1–1.5 kg/cm2) and to feed the same at a definite flow rate (4-12 Ipm) to the welding torch.
For welding mild steel, aluminium and its alloys, copper, nickel and their alloys and stainless steel, generally argon, helium or a mixture of argon and helium can be used. Argon is preferred for welding bronzes and argon or helium can be employed for the welding of titanium and magnesium.
Gas and water solenoid valves if incorporated in the system, control the respective flow, i.e., they start the gas and water flow before the arc ignites and stop the same after the welding is over, tungsten electrode has cooled and weld metal has solidified.
Base Metal Welded:
(i) Carbon and alloy steels, (ii) Stainless steels
(iii) Heal resisting alloys, (iv) Refractory metals,
(V) Aluminium alloys, (vi) Copper alloys,
(vii) Magnesium alloys, (viii) Nickel alloys, etc.
TIG welding is well adapted to welding thicknesses up to 6 mm.
Joint Design :
- Butt, Lap, Comer, Edge and T-joint-are all used in TIG welding.
- A square groove butt joint is used for smaller thicknesses.
- A single V groove butt joint is required for base metal thicknesses between 4.8 and 9.6 mm. The included angle of V groove is 60° and root face 3.2 to 6.4 mm.
- A double V groove butt joint is generally used on base metals thicker than 12.5 mm.
- A corner joint is used for fabricating boxlike structures.
- An edge joint does not usually require the addition of filler metal
References : A Textbook of Welding Technology by o. P. Khanna