Unlike MIG welding, the process in which TIG (tungsten inert gas) welding is performed involves numerous variables, from the cleanliness or purity of the welding source to the cleanliness and purity of the welding material, as well as multi-dexterity of the person doing the welding. But once you’ve mastered the physical aspect and become familiar with all the equipment and material parameters, you realize why TIG welding is just as much an art as it is a mechanical process as you admire the beautiful beads you’re now able to lay down. And while many relate TIG welding with aluminum applications (something we’ll cover next month), it’s just as applicable with mild steel.

Our Miller Diversion 180 AC/DC TIG welder is a single-phase, inverter-based, air-cooled machine, which in layman’s (aka hobbyist) terms means, among other things, it has the ability to weld up to 3/16-inch material, takes up very little space, and best of all, is simple to operate. And it’s that last part that goes a long way toward expediting the learning process for beginners. This month we’re going to focus on welding mild steel, so let’s start by getting familiarized with the material first.

Mild Steel

Low carbon steels, commonly referred to as mild steels, are readily welded by the TIG process, also known as GTAW (gas tungsten arc welding). These groups of steels are available in many different alloys and types. The familiar structural shapes, plates, and hot-rolled sheetmetal are usually comprised of what is termed “semi-killed” steel (steel has been partially deoxidized during manufacturing). The steel, however, still contains some oxygen, and this oxygen can cause problems when welding. These problems will appear in the form of bubbles in the weld pool, and possibly in the finished weld bead. Killed steel has had more oxygen removed in its manufacture, and presents less of a problem when welding.

Consumables And Non-Consumables

A filler wire containing sufficient silicon and manganese, added as deoxidizers, is necessary. Lower grade filler rods used for oxyacetylene welding of many hot rolled products are not suitable for making high-quality TIG welds. Direct current (DC) electrode negative is recommended with high-frequency arc starts, and 2 percent Ceriated tungsten (EWCe-2; orange banded) with a point or taper on the electrode should be used.

Technique Basics

Tungsten extension is the distance the electrode extends out beyond the gas cup of the torch. Electrode extension may vary from flush with the gas cup to no more than the inside diameter of the gas cup. The longer the extension the more likely it will accidentally contact the weld pool, the filler rod being fed in by the welder, or even touch the side of a tight joint. A general rule would be to start with an extension of one electrode diameter. Joints that make the root of the weld hard to reach will require additional extension.

The torch and filler rod must be moved progressively and smoothly so the weld pool, the hot filler rod end, and the solidifying weld are not exposed to air that will contaminate the weld metal area or heat-affected zone. Generally, a large shielding gas envelope will prevent exposure to air. The filler rod is usually held at about a 15-degree angle to the surface of the work and slowly fed into the molten pool. Or it can be dipped in and withdrawn from the weld pool in a repetitive manner to control the amount of filler rod added. During welding, the hot end of the filler rod must not be removed from the protection of the inert gas shield. When the arc is turned off, the post-flow of shielding gas will not only shield the solidifying weld pool but the electrode and the hot end of the filler rod as well.