TIG Welding Shielding Gas
With the TIG welding process, shielding gases are required to protect the welding area from gases in the atmosphere including oxygen and nitrogen, which can create fusion defects, porosity, and embrittlement in the metal to be welded, if they come in contact with the welding metal, electrode or arc. The shielding gas also transfers heat from the tungsten electrode to the metal, and helps start and maintain a stable arc.
The selection of a TIG welding shielding gas depends on a number of factors, including the type of metal to be welded, joint design, and desired final weld bead appearance. Argon is the shielding gas most often used for TIG welding, because it helps prevent weld defects due to a varying arc length. When used with alternating current, the use of argon results in a high quality weld with good appearance.
Helium is sometimes used as a TIG welding shielding gas to increase weld penetration, welding speed, and to weld metals with higher heat conductivity, such as copper and aluminum. A significant disadvantage when using Helium as a shielding gas is the difficulty of striking an arc with helium gas, and the decreased weld quality associated with a varying arc length.
Argon-helium mixtures are also sometimes used as a TIG welding shielding gas, because the combined gases can increase control of the heat input while maintaining the benefits of using pure argon as a shielding gas. Argon-helium shielding gas mixtures are often made with about a 75% or higher concentration of helium and the balance argon. These mixtures increase speed and quality when TIG welding aluminum with Alternating Current(AC), and also make it easier to strike an arc.
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