After years of self taught point-n-shoot MIG welding around the home shop, I was finally offered the opportunity to get a bit of an actual welding education. A few weeks ago, Miller Electric Manufacturing invited me to a tech session at its Rancho Cucamonga, California, tech center and I immediately accepted, figuring I could use any help I could get when it came to welding. Plus, though I have been welding for a while, I'd really never given much thought to the science or history behind the process, so this chance to hang with the experts for the day would prove to be really interesting.
Well, I was right. I learned quite a bit about Miller equipment, the history and science behind electric welding, and a bunch of cool tips that I'm hoping will improve my barely passable welding skills. That said, let me thank the folks at Miller for sharing their expertise (and for not laughin' at me during the hands-on sessions) and allowing me to use material and images from their wealth of information on the subject so I could try to pass on a bit of what I learned.
What The Heck Is Gmaw?
Gas Metal Arc Welding is actually the general term for the welding process we hot rodders refer to as MIG (Metal Inert Gas) welding. It's the method of joining metal by heating it with an electric arc. The arc actually is between the metal workpiece and the consumable machine-fed wire electrode exiting the welder's gun and is shielded from contamination from the atmosphere by a shielding gas, usually a combination of Argon/CO2.
GMAW's beginning came in the late 1940s as a speedier alternative to GTAW (Gas Tungsten Arc Welding) or TIG welding as we know it. The MIG welders machine-fed filler wire was a much faster method than hand fed filler used in the TIG process. This was a bonus especially during the hectic manufacturing days and years of WWII. After the war, the extremely competitive peacetime economy gave rise to this new, more economical process that has become the most common form of welding in industry (and the home workshop) today.
GMAW For Garage Dwellers
Though there are actually three different types of GMAW (semiautomatic, machine, and automatic) welding, the method us guys know and love is of the semiautomatic variation in which the machine controls and supplies the electrical current, the supply of shielding gas to the arc area, and the feeding of the wire electrode, and we control the gun-or in my case attempt to control the gun.
As I understand it, the MIG process works like this: There's an electrical circuit from the welder through the electrode lead to the gun, then from the gun to the wire, and from the wire to the workpiece, and then back to the machine through the work lead (what I've always called the ground clamp). This is the vicious circle that allows us to join pieces of our hot rods together by both the heat generated by the weld arc and the added molten material supplied by the filler wire. In other words, the MIG welding process joins metal by heating them with an electric arc.
The arc is between a continuously fed consumable filler wire and the workpiece. Externally supplied gas or gas mixture (commonly Argon/CO2) provides shielding from the atmosphere. Common MIG welding is also referred to as short-circuit transfer welding. Metal is deposited only when the wire actually touches the work. No metal is transferred across the arc. Another method of MIG welding, spray transfer moves a stream of tiny molten droplets across the arc from the electrode to the weld puddle.