Although Metal Inert Gas (MIG) and Tungsten Inert Gas (TIG) are both shielded arc fusion welding applications, the two processes differ quite substantially.

Essentially, MIG welds are created with a consumable wire electrode, while TIG welds require a non-consumable tungsten electrode to produce the weld.

MIG welding is a semi-automatic or automatic arc welding process, in which a continuous consumable wire electrode and a shielding gas (usually an inert gas such as argon) are fed through a welding gun. The arc burns between the consumable electrode being fed through the torch and the item being welded.

As in MIG welding, the TIG weld area is protected against atmospheric contamination by a shielding gas fed through the torch to shield the electrode and molten weld pool. This process generally requires a filler metal that is added to the weld pool separately. A constant current welding power supply produces energy which is conducted across the arc through a column of highly ionised gas and metal vapours, commonly known as plasma.

MIG and TIG arc welding can both be automated. While MIG is faster and more cost effective, TIG is a more complicated and costly process that does not lend itself to high throughput, but achieves high quality, precision welding, for example, for the pharmaceutical and food and beverage industries.

Orbital TIG welding is a specialised area of welding whereby the arc is rotated mechanically through 360° around a static work piece in a continuous process that creates a very smooth weld. This eliminates weld irregularities inside a pipe, for example, where bacteria could thrive.

Both MIG and TIG welding are suitable for all kinds of fusion weldable metals. The most commonly welded metal is mild steel, followed by other metals like high alloy steel or aluminium, as well as other, more exotic metals such as titanium and copper.

MIG welding offers a far higher level of productivity, but quality is not as good as TIG, with a somewhat higher risk of flaws. MIG is generally used where high throughput is required, for example, automotive production, shipyards and pipelines, as well as with materials for construction and earth moving equipment, quarrying equipment and forklift trucks.

Welding power sources for both MIG and TIG welding depend on the exact application for which they are needed. For the welding process in general, a transformer and rectifier are needed, producing a high current suitable for welding – sometimes as high as 400-500 Amps.

The required shielding gases depend on the material to be welded. When welding mild steel carbon dioxide (CO2) mixed with argon, or CO2 mixed with oxygen in argon predominate. Depending on the volumes required, welding gases are supplied in cylinders, multi-cylinder pallets, mini or micro bulk format, or via liquid gas storage tanks.

A recent innovation in MIG welding technology is controlled short arc welding. This welding technology is based on an intentional, systematic discontinuing of the arc, producing a ‘hot-cold’ sequence, particularly useful for joining thin materials in any position, but also thicker materials in the vertical and overhead position, for filling large gaps and where minimum distortion of the work piece is a requirement.

Other benefits include higher quality welded joints, freedom from spatter – a general problem in short arc welding- the ability to weld light-gauge sheet as thin as 0.5 mm and to join steel to aluminium and galvanised sheets.

The future of welding appears to include more purpose-built processes. As with controlled short arc welding for thin material, new processes for welding thick material are being developed and implemented. Welding challenges such as the demand for higher welding speeds, joining with fewer passes and welding of thicker materials are being answered by so-called high performance processes.

These processes include modifications of the MIG process such as tandem welding, or even combining other types of welding to create hybrid processes like plasma-MIG or laser-MIG welding.

With thanks...
gasworld would like to express its thanks to Linde Gases for contributing this month’s equipment profile.