You're only a little confused here. 1) TIG is an acronym for Tungsten Inert Gas. Also known as GTAW or Gas Tungsten Arc Welding. Tungsten is not a consumable. The consumable is a wire (whatever you are welding, stainless, aluminum, carbon, etc.) Welding GTA without a filler (consumable) is referred to as Autogenous welding. It depends entirely on what you are trying to accomplish whether or not you use filler metal. 2) MIG is an acronym for Metal Inert Gas welding, also known as GMAW or Gas Metal Arc Welding. And yes it is fed from a spool and by definition requires filler metal. Not to be confused with FCAW, better known as Flux Cored Arc Welding. Which is like MIG but has a flux in the hollow center of the wire. Some FCAW uses a gas shielding and some don't. Good luck.
Mike Sherman
Shermans Welding
The tungsten electrode used in TIG welding is very similar to the tungsten fillament in an incandescent light bulb. In the bulb, it carrys electrical current, heats up, and emits light. In a TIG torch, electrical current flows through the air/shielding gas between the tungsten and the work creating the arc that metals the base metal and the filler rod, if there is any. Tungsten is used because it has a very high melting point and good thermionic emission (it emits electrons easily when it gets hot).
The tungsten is considered nonconsumable. That is, it does not melt and is not intended to become part of the weld. Any part of it that does become a part of the weld is called an inclusion. This is an undesireable discontinuity in the weld metal. If an inclusion is large enough, or there are enough of them, the weld is considered rejectable. Of course, the weld would have to be subject to radiographic testing to detect them.
The term nonconsumable is somewhat misleading. The tungsten does get shorter over time. Everytime you contaminate it by dipping it into the molten weld pool you have to remove the contaminated portion and regrind it. You start off with a 7" tungsten electrode and sooner or later you have a 3" one. Beginners typically have a problem with this. Once you get the hang if it, though, a tungsten electrode can last a long time.
When welding thin metal with TIG, it may be possible to do the job without adding filler metal. You simply melt the two pieces together. When welding thicker material, some kind of groove will be required between the pieces to be joined and filler metal must be added. You hold the torch in one hand and feed filler metal in with the other hand.
MIG and TIG are different animals. TIG, at least as you will learn it in school, is a manual process. The filler metal typically comes in 3' lengths. And it is common to cut them in half to make them more manageable. The person doing the welding feeds the filler metal by hand. MIG is a semi-automatic process. The filler metal is fed in automatically. You press a trigger on a gun and it comes out at a preset rate. So, it makes sense it is on a spool.
TIG is typically used for critical applications when quality is imperative and productivity is not an issue. MIG is typically used when productivity is the important factor.
All this will start to become very clear as soon as your class starts.
Thanks again Malcolm. I think Im getting it. So say I buy a MIG. I make a jig for a regular steel rigid chopper. I can use the welder to peice together the steel tubes moving my body right along, w/out using a filler in my left hand? If Im making something out of sheetmetal, it would be pretty much the same thing, the spool feeding the welder with filler material no need for left hand? But, if you were to weld smething much bigger(a cracked engine block), a TIG welder, with some kind of filler to fill in the crack, or an airplane with alot of stress would be better? I usually see people working on bikes with TIG welders, I guess thats because they want to get finer smoother looking welds? I would rather buy a mig for cost reasons. It seems to me very hard to use a filler material, almost like soldering, and my hands shake from madications..Thanks for your help again malcolm
You've got the idea on how MIG works. Your other hand is essentially free to help steady your welding hand or body.
Thick metal can be welded just fine with MIG. You just need to make several passes. And the amount of stress isn't an issue. The most commonly used MIG wires have a nominal tensile strength of 70,000 psi. But one of them, ER70S-6, typically has a tensile strength of around 85,000 psi in the as welded condition. And there are filler metals available with even higher nominal tensile strength. What is important is a good weld, regardless of process used, and appropriate filler metal.
TIG rods are pretty much the equivalent of MIG wire. In fact, you can use MIG wire when doing TIG. I do it when I need something smaller than 1/16". That is the smallest TIG rod I normally have access to. But there is plenty of .035" MIG wire available.
One problem with MIG is that in short-circuit mode, which is what the typical home enthusiast runs, lack of fusion can be a problem. If your technique is good, no problem. If not, things can come apart at the most inopportune time. With some practice, and hopefully training or at least tutoring from someone who knows what they are doing, it shouldn't be a problem.
OTOH lack of fusion is seldom a problem with TIG. You are moving relatively slowly and can push the molten weld pool wherever you want. There is really no excuse for lack of fusion in a TIG weld.
MIG can be a problem on thin metal. It can be done. But it takes the correct technique and a good touch. Thin metal is not a big problem with TIG. You just turn down the current.
FWIW I have seen frames of NASCAR racers that were MIG welded. And you likely can become a decent MIG welder much faster than a decent TIG welder.
"You start off with a 7" tungsten electrode and sooner or later you have a 3" one." In almost every case a student will become an expert tungsten grinder long before he becomes proficient with the GTAW process!
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