HOT WIRE-TIG

TUNGSTEN INERT GAS WELDING

•It is an arc welding process wherein coalescence is produced by heating the job with an electric arc struck between a tungsten electrode and the job. •A shielding gas is used to avoid atmospheric contamination of the molten weld pool.•This welding process can be done with or without using a filler material.

Line Diagram Of TIG

Hot Wire TIG In hot wire welding, filler wire is resistance heated until

close to the melting point and added to the weld puddle behind the tungsten.

This prevents the wire from chilling the weld pool and allows the filler metal to flow out across the weld puddle resulting in a smooth, attractive weld bead.

Since nearly all of the full energy of the welding arc is available for penetration or to generate the weld pool and fusion, a two to three times faster travel speed is realized.

More wire can be deposited and fill rates are increased with the added benefit of weld quality as good as or in some cases better than with cold wire GTAW 

Wire Entry

o The location of wire entry into the weld pool is critical.

o For hot wire GTA welding, wire entry is normally at the rear of the puddle with the wire deposited in the depression behind the arc at the rise of the weld pool.

o This permits faster travel speed than with cold wire GTAW where wire entry is at the leading edge of the puddle.

o Hot wire travel speeds of 8-9 IPM (203-228 mm/min) are typical compared to about 4 IPM (101 mm/min) for cold wire GTAW.

Significance of Shield Gas• Gas coverage Shielding with inert gas is

particularly important for hot wire GTAW applications because the larger weld pool and length of solidifying/cooling weld passes demand greater gas coverage.

• Effective design of gas cups is essential for hot wire GTAW.

• Lamellar gas coverage is critical. There must be adequate screening in the torch and the gas lens must seal snugly around the tungsten.

What is Trailing shield? The use of trailing shields to provide gas coverage to

the entire weld zone is highly recommended for hot wire GTA welding, especially for cladding operations and at the top of the groove.

This helps the solidifying and cooling of the weld and is critical for higher currents and welding speeds to minimize the formation of oxides and the potential for porosity.

In addition, a protected weld pool will have a lower surface tension and low viscosity that will wet and tie-in better.

The extent of coverage required depends on the material being welded and the temperature.

Effects Of Shielding Gas on Weld Puddle

The shield gas type and composition has been found to have a major effect on the shape of the weld bead.

Gas mixtures can be adjusted to suit particular applications. The bead shape produced with helium shielding is flat with

good wetting and is ideal for cladding and overlays. Argon produces a more rounded profile and deeper

penetration which is suitable for groove welding, while the addition of small amounts of hydrogen can be used to increase penetration.

Argon/helium mixes are generally preferred for hot wire welding in grooves, and have been used in cladding and buttering.

Hydrogen mixtures should not be used in applications where hydrogen-induced cracking could occur.

Advantages

It is an automated process with high levels of productivity

Able to make high quality welds on nearly all weldable metals and alloys.

No need to remove slag. No spatter. No need to change electrodes. Higher deposition rate

High welding speed. Welding is possible in all positions.

Disadvantages

Higher welding skills are required (for manual welding).

It is very expensive compared to other arc welding processes.

Applications

This process is used in joint welding and overlay welding(ex: Pipeline Construction)

Ship Building Off shore engineering power station

construction. It is also used to make root-run in

important element structures.

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