OPERATION AND APPLICATION
ApplicationThe TIG process is very versatile and may be used to weld any metal or alloy system over a wide range of thicknesses, but is usually restricted to 10mm and under for economic reasons. It is particularly suited to welding sheet materials and for the root run in pipe butt welds.
DCEN is the most common mode of operation, and is widely used for welding all carbon, alloy and stainless steels, as well as nickel and titanium alloys. Copper alloys, with the exception of those containing aluminum in significant amounts, can also be welded with this polarity.
DCEP is used for aluminum alloys when welding with pure helium as the shielding gas, since this polarity has a strong cathodic cleaning effect capable of removing the tenacious aluminum
oxide film from the surface. It may also be used for TIG-welding magnesium alloys. AC polarity is used most commonly when welding aluminum and its alloys with pure argon or argon-helium mixtures to take advantage of the combination of the cyclic heating and cleaning action. It is also suitable for welding magnesium alloys and aluminum bronze. Hot-wire TIG is used predominantly for steel and nickel alloys where the electrical resistance of the wire can be used to increase productivity.
The main areas of application of the TIG process include:
OperationTIG welding suitable for both manual mechanised welding. In manual welding, the operator points the electrode in the direction of welding and uses the arc to melt the metal at the joint. If filler metal is required, if for example when making a fillet weld, it is added to the leading edge of the weld pool. The arc length is controlled by the operator and is usually between 2 and 5mm. The heat input to the arc depends on the current level chose by the operator and the travel speed is adjusted to match the time required to melt the joint.
Direct or alternating current power sources with constant current output characteristics are normally employed to supply the welding current. For DC operation, the tungsten may be connected to either output terminal but is most often connected to the negative pole. The output characteristics of the power source can have an effect on the quality of the welds produced. Shielding gas is directed into the arc area by the welding torch, and a gas lens within the torch distributes the shielding gas evenly over the weld area. In the torch, the welding current is transferred to the tungsten electrode from the copper conductor. The arc is then initiated by one of several methods between the tungsten and the work piece.
The purpose of the TIG Welding power source is to power the electric arc created between the base material and the tungsten electrode, through the output of current sufficient to keep the arc struck. Inside the power source there is usually a welding current adjustment device, of a mechanical (magnetic shunt) or electronic type (thyristor or inverter system).