MIG and TIG Welding - Merging Metal

Times change. It wasn't that long ago that if you owned a set of oxy-acetylene gas bottles for welding and cutting you would be considered to have a pretty well-equipped home shop. Maybe you progressed to a stick welder, and most likely moved on from that to a basic MIG welder. I know that's the progression I followed, having possessed a MIG welder at home for the past 20 years now.

However, in recent years the cost of TIG welders has come down significantly, to the point where we expect to see a TIG in any rod shop we visit, and they've made a significant in-road into home shops too. But if you're in the market for a new welder, which is best for you? That depends on a number of variables, probably the most important being what it will be used for. However, let's take a brief look at the differences between MIG and TIG first. We shan't mention gas welding or stick welding here, as they're pretty much"old school" now, though you should know most TIG welders can also operate as stick welders if desired.

MIG (Metal Inert Gas) welding, or wire feed welding, employs a consumable electrode in the form of the filler wire which is fed from the machine through the torch. Depressing the trigger will feed the wire, and as this touches the workpiece it strikes an electric arc, generating heat. Unfortunately MIG welding causes spatter because of this, which can cause damage to nearby objects and can be a fire risk. Another problem with MIG, especially for novices, is that while a perfect looking weld can be produced on top of the workpiece, there is a danger that it hasn't penetrated the metal at all, whereas with the TIG process, the metal is melted before the filler rod is added, ensuring penetration.

While MIG welding is useful when tackling body panels, and doesn't require such exacting tolerances between panels, the weld is harder than in TIG welding, and leaves a higher weld, meaning heat is generated when grinding a MIG weld back (which often isn't required at all with TIG) and the hard weld makes it tougher to work with a hammer and dolly to eliminate any warpage.

Developed originally for the aircraft industry some 60 years ago, TIG (Tungsten Inert Gas) or GTAW (gas tungsten arc welding) as it's also known, uses a non-consumable electrode to strike an electric arc, which produces heat. Similar to oxy-acetylene welding, a filler rod can be used, though it's not always required. The tungsten electrode and the filler rod are protected from the atmosphere by a shield of inert gas, usually Argon, to prevent oxidation of the weld and metal workpiece. The relatively slow speed of TIG means the porosity that can occur with MIG welding is eliminated, while it also produces a smaller heat-affected zone than MIG, reducing the amount of distortion in the metal being worked, as well as reducing stress and the chances of cracking.

TIG welding produces no spatter either, unlike MIG can sometimes do, and the torch is smaller and therefore easier to hold and work with. Unlike MIG, the operator can adjust the heat input whilst welding by using the foot-operated amperage control pedal. However, the work surface has to be extremely clean for TIG welding, especially when welding aluminum, and it is a relatively slow process. If the electrode touches the work it becomes contaminated and must be cleaned immediately, which can be frustrating while you learn to TIG weld, as you'll spend more time removing and cleaning the electrode than actually welding until you get the hang of it! The power source is constant current, either AC, DC, or combination of both (AC/DC), with the type of metal being welded determining which type is used. DC (direct current) is usually used for welding stainless steel and mild and low alloy steels, while AC (alternating current) is used for welding aluminum. TIG welds are smaller, neater and of higher quality than MIG welds, and are what we have come to expect when we see high quality, precision fabrication and chassis work.