Coastal Marine Welding and CAD Fabrication

TIG Welding

What is Tungsten Inert Gas (TIG) welding?

TIG welding is also called GTAW (Gas Tungsten Arc Welding) and Heliarc® welding. Heliarc® was the trade name given to the process by Linde's when it was introduced decades ago. The arc is started with a tungsten electrode shielded by inert gas and filler rod is fed into the weld puddle separately. The gas shielding that is required to protect the molten metal from contamination and amperage are supplied during the TIG welding operation.

TIG welding is a slower process than MIG, but it produces a more precise weld and can be used at lower amperages for thinner metal and can even be used on exotic metals. TIG welding is a commonly used high quality welding process. TIG welding has become a popular choice of welding processes when high quality, precision welding is required. The TIG welding process requires more time to learn than MIG. It is similar in technique to gas welding.

Characteristics of the TIG welding process

TIG:

	Uses a non-consumable tungsten electrode during the welding process,
	Uses a number of shielding gases including helium (He), argon (Ar), and carbon dioxide (CO₂),
	May harden the welded materials,
	May reduce fatigue strength,
	Is easily applied to thin materials,
	May leave a poor appearance,
	May reduce corrosion resistance at the weld,
	May create cracks and porosity in the materials welded,
	Produces very high-quality, superior welds,
	Welds can be made with or without filler metal,
	Provides precise control of welding variables (i.e. heat),
	Welding yields low distortion,
	Leaves no slag or splatter.

In TIG welding, an arc is formed between a non-consumable tungsten electrode and the
metal being welded. Gas is fed through the torch to shield the electrode and molten weld
pool. If filler wire is used, it is added to the weld pool separately.

The TIG welding process utilizes a number of shielding gases including:

	argon
	argon + hydrogen
	argon/helium
	helium

Argon is superior for welding metals. It operates at a higher arc voltage, makes the arc start more easily, and is commonly used to weld mild steel, aluminum and titanium.
Helium is generally added to increase heat input (increase welding speed or weld penetration) and is used for high speed welding of mild steel and titanium. Helium offers a smaller heat affected zone and therefore, penetrates metals deeply. It also can increase the welding speed up to 40%. Helium is also commonly used to weld stainless steel and copper.

Hydrogen will result in cleaner looking welds and also increase heat input, however, hydrogen may promote porosity or hydrogen cracking.

The argon/helium combination gas is used for a hotter arc in welding aluminum and aluminum alloys. It is also used in automatic welding applications.

Even though TIG is a commonly used welding process, there are a number of limitations. These include:

	TIG requires greater welder dexterity than MIG or stick welding,
	TIG yields lower deposition rates,
	TIG is more costly for welding thick metal sections.