TIG welding - an overview

Exclusive to thefabricator.com TIG welding - an overview By Marty Rice, Contributing Writer October 11, 2005 Welding instructor Marty Rice explains the gas tungsten arc welding (GTAW) process, more commonly known as tungsten inert gas (TIG) welding. As I've said before, I like to begin my articles by relating a personal dumb but funny learning experience. Why do I do this, you might ask? Because I'm not afraid to admit I make mistakes; after all, I'm human. I've been taught by, worked for, and even been friends with a few people who think they are some kind of perfect. You know the type; it's their way or the highway. You could show them a better way, but they would still do it their way because they wouldn't dare admit that you could be right. Not me. Even though I've been in the welding field a long time, I still make a mistake now and then. And sometimes I don't see a solution to a problem, even when it's staring me in the face. I'm not afraid of learning something new either. If there's a better way of doing it, bring it on! I tell my new welding students that it's OK to make a mistake in our shop, because that's just what's going to happen when you're a "newbie." Newbie is a very affectionate term soldiers who had been there awhile called us new guys when we first arrived overseasâ€"that, or FNG, which I think must've meant "funny new guy." What's most important with my newbies is that they learn from their mistakes, and don't repeat them. A former student, Michael Salceda, now is an apprentice in the Ironworkers Union. He comes around and helps me when his work is rained out or slow. When Michael heard the story I'm about to relate, he just shook his head and said, "Mr. Rice, you should have had a pair of pliers or wire cutters in your truck." Yep, he was right; wire cutters would've saved me some pain and money. My son and I bought a bike to fix up from The Motorcycle Man in Dickinson, Texas, close to Galveston. We planned to pick it up and then eat some good seafood down on the coast. We found the shop and loaded the bike in my son's truck. I then pulled out the package of tie-down straps I had just boughtâ€"four tie-downs and each one had four wide, hard plastic bands around them. I popped the first band off with my pocket knife, but the next one was difficult to cut. I tried to pop it upward when it slipped and my pocket knife (did I mention I had just sharpened it?) stuck into the bone in my left inside forearm. Should have left it there, but my first reaction was to jerk it out. When I did, blood shot out of my arm like a garden hose, because I had hit an artery! (Also nicked a tendon and hit muscle, but no permanent damage, thank goodness.) I applied pressure with my hand, and Bill (the Motorcycle Man) wrapped my arm in a towel and whisked me to his car for a trip to the hospital. After I suppressed my urge to scream like a child, and once I realized I wasn't going to die, I thought about what a shame it was that I wouldn't get to eat some good seafood while I was in that part of Texas. (It's funny how my mind works in a crisis situation.) But thanks to the marvels of modern medicine, I was down on the coast eating fresh oysters and having a cool one just a couple of hours later. Besides having a bruise from my hand to my elbow, I was just fine. Most welders carry pocket knives. Be careful with them! I received a very painful reminder to use the right tool for the right job. Before I turn this whole article into my freak accident story, here's my synopsis of the tungsten inert gas (TIG) welding process and some of the tools it requires. Background Some older welders still refer to TIG as "heliarc," which is what the process originally was called. Heliarc was perfected around 1941 and was used to weld on magnesium, aluminum, and stainless. It was especially helpful in the war effort for welding on airplanes. Heliarc used pure helium as an inert (meaning it won't combine with other elements) shielding gas to protect the weld pool from the atmosphere. (Nitrogen, hydrogen, oxygen, carbon dioxide, and other elements cause weld defects if introduced to the weld pool.) Enter Argon After a while it was discovered that argon has some advantages over helium. Because argon is heavier than helium, less flow rate is needed. (We use about 20 to 25 cubic feet per hour (CFH) in our shop.) The lower flow rate requirement makes argon better for flat welding. Helium is good for overhead, because it is lighter and thus flows upward. Argon allows easier arc starting and a smoother, more stable arc than helium does. Actually, argon pretty much is the most widely used shielding gas nowadays. Since the heliarc process no longer used only helium, someone decided to rename it TIG for tungsten inert gas welding. Later the same guy who changed the "library" to the "learning resource center" must have decided TIG was too easy, so he named it gas tungsten arc welding (GTAW). But most everyone I know in the shop and field still call the process TIG. Nonconsumable Electrode TIG uses a tungsten electrode that is nonconsumable. In other words it does not burn up like an electrode in stick welding or the wire in metal inert gas (MIG) welding does. The tungsten acts as the torch: It generates heat, which melts the metal and/or filler metal. Thin metals can be joined by TIG welding without using filler metal. Joining thicker metals requires using an approximately 3-ft.-long filler rod of various diameters that is fed into the weld pool with one hand, while the torch is manipulated with the other. While MIG welding is relatively easy to learn, TIG isn't. It takes a lot more skill and know-how to make a good TIG weld. One of the best ways to learn TIG welding is to learn oxygen/acetylene welding or brazing first. Although oxyacetylene welding pretty much is obsolete as a major welding process, it is perfect for learning the premise of a good TIG bead. You have to hold the TIG torch at the right angle, keep the weld pool uniform, and add the correct amount of filler metal to produce a good bead. (And, of course, relax your hand, and watch the puddle!) A Process for All Metals If you watch "Orange County Choppers," "Monster Garage," or some of the other fabrication shows on TV, you probably have seen chromium molybdenum steel (chromoly) bike frames TIG welded, because TIG is good for all metals. I mainly teach TIG welding on mild steel first, followed by stainless steel, and then aluminum. It also is good for copper, magnesium, titanium, nickel, and a host of others. In the classroom we use a 3/32" tungsten electrode with direct current, electrode negative (DCEN) on small-gauge to 1/4-in. mild steel and stainless, then switch to alternating current (AC) on aluminum. (Remember, electricity always flows from negative to positive in DC and flows back and forth on a sine wave in AC.) I always used to use tungsten electrodes with 2 percent thorium until talking with someone who told me that thorium is radioactive and probably not a good substance to be touching and breathing. Avoid thoriated tungsten electrodes that can pose health and environmental risks at elevated exposure levels. Learning TIG For those interested in learning TIG welding, I strongly suggest that you check out a local welding school or college to find a course that offers good training in both theory and practice. Some schools will let you take specific classes to accommodate exactly what you want to learn. I know that Dewayne Roy at Mountain View College in Dallas tries to customize his classes to adults wanting to learn TIG or MIG. Perhaps you will find such a place where you live. A future article will discuss TIG welding machines. If you plan to purchase one, you can expect to lay out quite a few more bucks than you would for a MIG welding machine. Recommended TIG Welding Sites Short TIG page: http://www.weldingengineer.com/1tig.htm

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