Most TIG welding is done with the machine on the DC negative setting. This means that the workpiece is positive and the tungsten electrode is negative. Because of this, about 70 percent of the heat generated by the arc is concentrated on the work rather than at the tungsten. A few metals, particularly aluminum, are welded with the machine in the AC setting. That will be explained later.
TIG welding is both easy to learn and difficult to master. The process itself is simple: Start an arc and aim it at the two pieces being joined together. Increase the heat (amperage) using the foot pedal until a small puddle of molten metal appears, and quickly dab the filler rod into the puddle. Once the filler material wicks into the base metal, move forward with the torch, repeating the process over and over until the joint is fused. It takes a lot of practice to get a weld that looks good, though. The tip of the electrode must stay between 11/416 and 11/48 inch above the puddle. At this distance, it's easy to accidentally touch the tip of the electrode with the filler rod or dip it into the weld puddle. When this happens (and it frequently will), the tungsten becomes contaminated and the arc becomes erratic. You must remove the electrode from the torch and grind the contamination off. Also, if you don't maintain a steady distance above the weld puddle with the torch, your "stack of dimes" weld bead will look more like a stack of dimes, pennies, and quarters. The bead will be uneven.
The great thing is that once you get the technique right, you can make anything. And anything you make, whether it is a rollcage, filler neck, or seat bracket, will look like a work of art. You will know that it is structurally sound, too. Because you have absolute control over the weld process, you are able to see the weld puddle forming on both pieces being joined while you're welding. And you'll see the filler material melt and flow into the joint, leaving no doubt that the weld is sound.
GMAW
As you've probably guessed, GMAW stands for gas metal arc welding. This process is commonly, though not always accurately, referred to as metal inert gas (MIG) welding. Not quite correct, because the shielding gas most frequently used in MIG welding has up to 20 percent carbon dioxide, a reactive gas, in it. So you may run across a smartass who will inform you that the more appropriate moniker is metal active gas (MAG) welding. Silence him by simply referring to it as wire-feed welding, a more general but always appropriate term.
GMA welding differs from GTA welding in several key ways. It operates in DC positive polarity-the electrode is positive, and the work is negative-and no welding rod is used. Instead, the filler material, or welding wire, is the positive electrode. It is wound on a spool inside the body of the welding machine and is fed through the power cable, exiting at the tip of the torch. With GMA welding, the operator does not have as much "real-time" control over the process as in GTA welding. Yes, changes can be made while welding, but to do so the operator may have to look away from the weld to fiddle with the controls, and that can be a risky endeavor. Starts and stops don't blend together in the weld bead with MIG welding as nicely as they do in TIG welding, so to get a smooth weld, it's best to have all the controls properly set ahead of time so you can run a continuous bead.