When, where and why to use TIG welding

Mick Andrews, superintendent of the Murex Welding Process Centre, explains TIG welding and the advantages this process offers for specialist applications.

Of all the arc welding processes, TIG (tungsten inert gas) welding (also known as gas tungsten arc welding or GTAW) is capable of achieving the highest quality welds and is the most versatile in terms of what can be welded and the position of the welds.

Only SuperPulse Mig (metal inert gas) welding comes close, but TIG still comes out on top for weld integrity and versatility.

As in most industrial processes, however, quality comes at the expense of time.

TIG is generally slower than MIG or MMA (manual metal arc) welding but, where weld integrity is critical, production engineers are prepared to accept the additional process time.

In some cases, however, a welded joint will use TIG in conjunction with MIG welding.

For example, when joining pipes for offshore applications, TIG might be specified for the root weld then MIG for subsequent runs.

This gives the high integrity that is essential at the root, in conjunction with the speed and quality of MIG for the rest of the joint.

TIG welding is an extremely versatile process; it can be used with virtually any weldable metals, including dissimilar metals and thicknesses from 0.5mm upwards.

TIG welding machines are typically available in current ratings from 150A to 350A and are capable of operating at currents as low as 3A for a 150A machine.

In addition, TIG machines can be used for brazing and MMA welding, which helps to improve the return on an investment in TIG equipment.

The most commonly used gas for TIG welding is pure argon for all materials.

You would use argon/helium for thick aluminium and copper because added heat is required from the helium.

This is in contrast to MIG welding, where the correct gas or gas mixture has to be used for the material being welded.

However, TIG operatives do need to be aware that the correct tungsten electrode must be used, otherwise problems can be experienced with striking the arc and maintaining a stable arc.

TIG can be used either with or without a filler wire - in a similar way to oxyacetylene gas welding.

Murex, which has been involved with TIG welding almost since its commercialisation, offers an array of different filler wires to suit the variety of applications for which TIG is used.

Furthermore, for complex or unusual applications, Murex can undertake welding trials on behalf of customers to help optimise the welding parameters.

Support can also be provided to ensure that the customer's operatives are familiar with the equipment and process.

One of the advantages of TIG welding is that the weld not only possesses high integrity but it also has an aesthetic surface finish.

Consequently welds can often be left 'as is', with no need for grinding.

This is beneficial in terms of the time saved, plus it avoids any problems associated with grinding on site, such as noise and dust.

Depending on the model of TIG welder used, the operative can have control over many of the weld parameters so as to optimise the weld quality.

Modern inverter-based TIG power sources are lighter and more portable than traditional units, so on-site TIG welding is commonplace for both fabrication and modifications/repairs.

Typical applications for TIG welding include architectural stainless steel fabrications, such as balustrades.

More unusual applications include jewellery (even gold can be welded with TIG), dentistry (for chrome cobalt frameworks) and titanium (for specialist high-strength, low-weight applications).

For fine work and low-current applications, TIG is increasingly being used as a more versatile alternative to micro-plasma welding.

Skilled operatives can produce outstanding results with TIG welding, but automation can be used economically on straight runs and arcs to avoid any variability associated with operative skill levels or fatigue.

Anywhere that a tractor unit can be installed, TIG welding can be automated; specialised units are also available for making pipe joints.

In welding applications the most expensive element is usually the welding operative.

It is therefore a relatively simple matter to work out the savings that can accrue from automating a welding process and hence the payback period that can be expected when automating a TIG welding operation.

Of all the arc welding processes, TIG requires the highest level of skill.

This is largely because it is a two-handed process, with one hand required for the TIG torch and the other for the filler wire.

Even autogenous welding (without a filler wire) requires good skills.

If a fabricator is considering investing in TIG welding, there are numerous training providers available nationwide, who can either train an operative from scratch or retrain an operative who has used MMA, MIG or gas welding.

Interestingly, welders who have experience with gas welding often find it easiest to make the transition, as they are used to hand feeding a filler wire.

TIG welding is based on a very simple concept, in that an arc is struck between the tungsten electrode and the workpiece and a filler wire is fed into the weld pool.

However, the process is continually being developed.

For example, pulsed TIG has traditionally used pulses measured in seconds, whereas the latest micropulse technology produces pulses measured in milliseconds.

This enables TIG to be used on metals with a thickness of just a few tenths of a millimetre.

Other recent developments relate to the way the frequency of the arc can be adjusted, and balance control, which enables the operative to vary the positive/negative balance in AC TIG welding.

Generally speaking, TIG welding is suitable for niche applications in which weld integrity and aesthetics are more important than speed.

Having said that, TIG welding is also the most versatile welding process in terms of the materials that can be welded, the material thicknesses, the option to use a filler wire or not and the way it can be used for all-positional welding.

Murex offers a broad range of TIG welding machines, both DC only and DC/AC, plus a choice of control panels.

The range covers everything from lightweight, portable single-phase units to heavy-duty three-phase industrial machines rated up to 350A.

Murex can supply machines to suit almost any TIG application.

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