TIG Welding Machines

Most recently, the TIG welding process has been facing greater and greater competition from the ever-perfected MIG/MAG process and its related processes. These processes drastically increase productivity without concessions to quality. Despite its slower welding speed and lower deposition rate, the TIG process has been and still is for many applications the best guarantee for the highest quality results. Last but not least, innovations in the power source sector ensure a sustained future for TIG welding. The following comments are meant as a more detailed discussion of the basics.

Basic principle

The core of a TIG welding torch is a non-consumable, temperature-resistant tungsten electrode. The arc that proceeds from it heats and melts the material. As required, a filler wire is fed in manually or with a wire-feed unit. In many cases, a narrow gap needs no filler material at all when being welded. Ignition of the electrode normally takes place without the tungsten electrode touching the workpiece. This requires a high-voltage source that temporarily switches on during ignition. For the majority of metals, welding itself takes place using direct current. Aluminium, however, is welded using alternate current.

The nozzle for shielding gas is fitted around the tungsten electrode. The gas that flows out protects the heated material from chemical reactions with the surrounding air, thereby ensuring the required strength and durability of the weld metal. Inert gases such as argon, helium or their compounds are used as shielding gases. Even hydrogen is used occasionally. All these gases are inactive, which is what the specialist term “inert”, taken from the Greek, refers to. The term used to describe the process, “tungsten inert gas” (TIG) welding, comes from the type of shielding gas and the electrode material used.

The most-used shielding gas for TIG welding is argon. It optimises the ignition properties, as well as the stability of the arc, and helps obtain a better cleaning zone than helium. This in turn ensures an especially wide and deep fusion penetration, thanks to its thermal conductivity, which is nine times higher than that of argon. Used in conjunction with aluminium, pore formation is less pronounced. Furthermore, hydrogen is also sometimes used for austenitic steels, the percentage often only 2 to 5 %, the rest consisting of argon. The heat conductivity of hydrogen is even eleven times greater than argon, leading to a very deep fusion penetration and extremely effective outgassing.

When welding corrosion-resistant materials, for example stainless steels, the heated edges oxidise because of contact with oxygen in the air, which cannot always be completely avoided. The so-called annealing colours appear. These can be removed by rework, which restores corrosion resistance. It is preferable however to prevent the annealing colours from forming in the first place. This happens by using so-called forming gases. Forming gases keep the air away from the edges of the weld seam and in some cases even influence the root formation of the seam. Forming gases are primarily compounds of hydrogen and nitrogen, but argon is also used.

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