Welding process | TIG - 141
This is a welding process in which the heat source is an electric arc between the workpiece and a non-fusible
(refractory) electrode within a protective atmosphere flowing from the torch nozzle.
The role of the gas is to protect the molten metal, the tungsten electrode (W) and the filler metal
(which is why it is left until the gas fades under the torch).
The nature of the gas (argon or helium) will also influence the energy of the arc,
the shape and depth of penetration (the voltages observed with helium are higher than with argon. This results in better penetration),
the surface appearance of the bead (better with helium).
Hydrogen (H) and nitrogen (N) can be used in a mixture with argon (Ar) or helium (He):
gas action in welding
the shielding gas will have an impact not only on the geometry of the bead
(better penetration because higher arc voltage with H) but also on the chemistry and metallurgical structure of the bead
(H being strongly reducing, it reduces traces of oxides on the beads / N favours the formation of austenitic structures).
The settings of the pre-gas and post-gas phases during TIG welding are important for oxidation and shrinkage defects.
The refractory electrode consists of tungsten (W) or tungsten alloy.
The choice is made according to the emissivity required in relation to the arc environment
(an environment that is too hot for an alloyed electrode may cause the electrode to disintegrate).
This electrode must be trimmed when it is too polluted, when it comes into contact with the molten metal
or the filler metal or when the tip is damaged (disintegrated due to the temperature).
This process can be used with or without filler metal (142). This process is rather slow with a
low deposition rate, the polarity is called direct (electrode at the negative pole of the generator).
The intensity is adjusted on a TIG station, the arc voltage being a function of the
torch height and the gas used. The torches can be air or water cooled and the nozzles adapted for the gas flow to generate a protective atmosphere.
