Amperage and voltage are just as important in TIG welding as in any other type, though, as you might expect, they are used in slightly different ways. TIG welding is never carried out with the tungsten electrode in direct contact with the base metal; there is always at least some gap between the electrode and the substrate. Most of the heat is generated by the resistance of the air rather than that of the metal, which is part of the reason why TIG welding heat is concentrated in the joint and is less apt to warp nearby metal.
Starting a TIG welding arc
Starting the welding arc with a TIG welding machine varies by the exact type. High frequency (HF) starters are built into some of these implements, which allow you to start the welding arc with the tungsten electrode separated from the base metal by a narrow cushion of air. This lessens the chance of electrode contamination even further, but requires a fairly new, high-end machine to be present at all.
Other TIG welding machines oblige you to start the arc by striking it – the scratch method, as it is called, since it involves scratching the electrode over the metal’s surface almost like striking a match. Note that direct physical contact must be broken almost immediately so that the electrode will not become contaminated when the arc becomes active.
TIG welding amperage and voltage
The amperage of a TIG welding machine is manually adjusted using a control on the main body of the machine. Amperage controls the heat of the welding arc, and a higher amperage means deeper penetration. If you are welding thick pieces of metal together, then a higher amperage is obviously more useful, since a superficial weld will be weak compared to the thickness of the metal being joined.
If you are welding sheet metal or other thin, fine metallic objects, then a lower amperage is appropriate, so that you will not melt through the sheet or cause it to warp (which is still possible with TIG welding, even if it is less likely).
The typical TIG welding machine will be capable of being fitted with a foot pedal or a gun-mounted remote control to change the amperage while you are welding. This fitting is highly recommended for any TIG welder that is being used for complex welds, which may require different amperages on different parts of the joint.
Voltage, which is the other part of the electrical equation, controls the width of the weld, and is varied by moving the electrode closer to the metal, or farther away. A short arc produces high voltage, and a long arc produces low voltage. Remember that the electrode must be kept fairly close to the metal at all times, however, and “short” and “long” are relative terms in this case.