TIG Welding - Tig'ing For Pros

When it comes to Saturday night race shops, a MIG welder is about as common as a front door. When it comes to TIG welders, it's a different story. Although they can be quite useful and capable of attacking jobs not possible with a MIG, many racers leave this tool to the professional welder.

What is it? TIG stands for Tungsten Inert Gas, and the process is actually quite similar to MIG welding (which stands for Metal Inert Gas). A good TIG welder consists of a torch with a tungsten electrode connected to the power source, a supply of inert shielding gas, a power controller (usually a foot pedal), and a filler metal that is applied to the weld. Using the foot pedal to control the amperage to the torch, the welder uses an arc from the torch to the metal to be welded. Once the metal is hot enough to create a small puddle of molten metal, the welder touches the filler metal to the area to create a stronger weld. Just like in MIG welding, the inert gas is blown from the torch to keep the welding area free of contaminants.

TIG differs from MIG welding in that the current is not routed through the filler metal. Instead, the arc goes through a piece of nonconsumable tungsten to the material to be welded. The filler metal is held in the welder's other hand and added manually. Because it is added by hand and not through an automatic feeder, the welds are normally more precise, smaller in size, and usually cleaner. Because the torch is a precise instrument used only for creating a heat-generating arc between itself and the metal, it produces a very small arc, or "hot spot," which makes it ideal for welding high-heat conductivity materials (like aluminum). The drawback to this method is that it can be quite slower. Also, the TIG method is not good for "bridging" gaps when two pieces of metal do not fit perfectly. This, of course, may not be a bad thing if you suspect your rollcage fabricator is using fat welds to cover up his poor measurements.

"T" is for Tungsten Tungsten is used as the electrode in the welding torch because of its incredibly high melting point. This means that even when pushing a very hot arc through the electrode, it will not melt into the weld puddle. You should, however, make sure to never touch the tip of the electrode to the metal you are welding, as this will introduce contaminants into both the weld and the electrode.

The tungsten electrodes are available in a variety of sizes, lengths, and blends. Size, or diameter of the tungsten rod, should be chosen based on the thickness of the material you are welding. In general, the thicker the material, the larger the electrode you need to use. As a guideline, Andy Weyenberg, Miller Electric's racing specialist, recommends always using an electrode that is smaller in diameter than the thickness of the material you are welding to avoid burning through the piece. In racing, 11/416- and 11/48-inch-diameter tungsten electrodes are the most popular sizes.

Although tungsten is the major material in the electrodes, there are several blends available that are tailored to specific needs. Pure tungsten electrodes have a green identifying band and are most commonly used for welding aluminum. Tungsten mixed with blends of thorium is most commonly used when welding steel because it works well with a direct current (DC). Weyen- berg cautions that thorium is mildly radioactive. Tungsten/thorium blends are marked with either a red or yellow band. Although the radioactivity levels are low, he recommends switching to a cerium (orange) or lanthanum (black or blue) blend as neither is radioactive. Cerium blends work well with either alternating currents (AC) or DC and make a good all-purpose electrode if you are welding a lot of different materials. Lanthanum blends increase the electrode's current carrying capacity, which makes it suitable for materials like stainless steel with a high melting point.