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	Double Operator AC TIG welding of an aluminium vessel.

TIG Welding

Tungsten inert gas (TIG) welding is a high quality low deposition rate welding process. It uses an arc struck between a nonconsumable tungsten electrode and the work to fuse the base material and thereby form a welded joint.

The TIG welding process may be used on thin sheet material without the addition of a filler metal (autogenous TIG welding). Alternatively, when working on thicker sheet or when joining dissimilar materials, a separate wire filler metal is added into the arc region where it is melted and directed by the welder into the molten weld pool.

The weld pool, the hot tungsten electrode and the melting filler wire are protected from atmosphere by a shield of inert or slightly reducing gas. Argon is often used although productivity and quality benefits can be gained by using mixtures of argon and helium or argon and hydrogen (see the table of recommended Gemini™ gases).

Operation

TIG welding is suitable for manual, mechanised and automatic (orbital) operation.

In manual welding, the operator points the tungsten electrode in the direction of welding and uses the arc to melt the base material along the joint, ahead of the molten weld pool. The filler metal is generally added at the leading edge of the advancing weld pool.

Welding current

Both Direct Current (DC) and Alternating Current (AC) may be used when TIG welding, the choice depending upon the type of material to be welded.

Electrode diameter to current
dia.mm	maximum operating current (A)
	thoriated DC	zirconiated AC
1.2	70	40
1.6	145	55
2.4	240	90
3.2	380	150
4.0	440	210
4.8	500	275
Taken from British Standards BS3019: Part 1

DC (electrode negative) is used for the following materials:

• carbon steel
• copper
• stainless steels
• nickel alloys
• titanium
• zirconium

AC is used for the following materials:

• aluminium and its alloys
• magnesium
• aluminium bronze

Non-consumable electrodes

Pure tungsten electrodes may be used for TIG welding. Special tungsten electrode materials with controlled additions of metallic oxides are, however, generally preferred because they allow easier arc starting and provide enhanced arc stability.

Thoriated tungsten electrodes, containing generally 2% thorium oxide, are commonly used for DC welding of steels. Zirconated tungsten electrodes, containing 2% zirconium oxide, are recommended for the AC welding of aluminium and its alloys.

The diameter of the non-consumable TIG electrode is chosen to suit the welding current. Below the minimum current, for a given electrode, the arc becomes unstable and cannot be maintained. Above the maximum current, the electrode may become overheated, erode quickly and even melt.

Ozone reduction

Research carried out by Air Products' European Technology Group has shown that, when welding stainless steels, the Astec™ and Hytec™ ranges of Gemini™ gases produce significantly lower levels of harmful ozone than traditional shielding gases.

 

Autogenous TIG welding of stainless steel.

Gemini™ gases for TIG welding

Argon may be used for all of the commonly welded materials. However, the Astec range of gases gives enhanced welding speeds and deeper penetration in a range of applications when compared to argon. The Hytec gas mixtures provide improved weld profile, welding speed, penetration and surface finish when compared to argon for the welding of austenitic stainless steels, cupro-nickel and nickel alloys.

 

 

Recommended Gemini gases for TIG welding
carbon steels	austenitic stainless steels	ferritic/ martensitic stainless steels	duplex/ super duplex stainless steels	aluminium & alloys	magnesium & alloys	copper & alloys	cupro- nickel	nickel & alloys	titanium & alloys
argon	Hytec 2 Astec 30 argon	Astec 30 argon	Duplex 1 Duplex 2	Astec 75 Astec 30 argon	argon Astec 75	Astec 75 Astec 30 argon	Hytec 2 Astec 30	argon Astec 75 Astec 50	HP argon Astec 75
The selection of optimum Gemini gas for your application depends upon a number of features including material thickness, welding position etc.

 

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TIG Welding

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