The whats, whys, and whens of GTAW

Exclusive to thefabricator.com The whats, whys, and whens of GTAW By Jack Fulcer, Contributing Writer November 6, 2007 More difficult to learn than some welding processes, gas tungsten arc welding (GTAW) can be used to weld a greater range of materials than most other processes. This article explains GTAW, examines its advantages and disadvantages, describes appropriate and inappropriate applications, and discusses how important cleanliness is in GTAW If you are among those who want to learn about welding just for fun, or if you are considering a new career, knowledge is always the key to success. Well, that and a little practice! Gas tungsten arc welding (GTAW) is among the more difficult welding processes to learn, and just like shielded metal arc welding (SMAW) or gas metal arc welding (GMAW), it has distinct advantages and disadvantages (see Figure 1). GTAW is suitable for certain applications and totally inappropriate for others. To master GTAW, it is important to know these details before you begin. GTAW Advantages GTAW Disadvantages Clean, high-quality welds Lower deposition rates Welds a wide range of metals Requires high level of operator skill No spatter or slag, sparks, or smoke Higher level of UV rays Allows for welding in all positions Requires good eye and hand coordination to achieve quality weld Figure 1 What Is GTAW? The GTAW process uses a nonconsumable electrode—tungsten—to create an arc and transfer heat (or, the current) to the base metal that is being welded. At the same time, an inert gas, usually argon or an argon/helium mixture, shields the weld puddle from the atmosphere and protects the weld from contamination. Unlike SMAW or GMAW, GTAW does not require a consumable filler metal for every application; however, when one is used, it is slowly fed into the weld pool by the hand opposite that holding the torch. GTAW filler metals, often called rods or cut-lengths, are available in diameters ranging from 1/16 in. to ¼ in. They also are available in multiple compositions or specifications to meet the chemical and mechanical properties of the base material being welded (see Figure 2). Base Material Common GTAW Filler Metals Carbon Steel ER70S-6 or ER70S-3 Aluminum ER4043 or ER5356 Stainless Steel ER308, ER309, or ER316 Chrome-Molybdenum ER80S-D2 or ER70S-2 Titanium ERti-5ELI Figure 2 Why Use GTAW? Considering what GTAW is, the next logical question seems to be: Why use it? First, it can be used to weld more materials than any other welding process, even exotic and heavier-alloyed metals. Among those materials you can successfully use GTAW for (with practice!) are stainless steel, aluminum, chrome-moly, nickel, and titanium. Of course, you also can weld plain old carbon steel with GTAW. Next, GTAW produces very clean and high-quality welds, making it a good choice for applications in which aesthetics count or X-ray-quality welds are required. It also works well on thin materials, even those measured by gauge as opposed to inches. For example, you can weld material down to 30 gauge with GTAW, which makes it a good process for computer housings, electronic components, and tubing. This is because the process allows for a more direct, or concentrated, arc and produces a narrow heat-affected zone (HAZ) on the base material. HAZ comprises the area surrounding the weld, which has not melted but has been altered by the heat. By minimizing the HAZ, GTAW helps prevent distortion, particularly on thin materials. Overall, the lower heat generated by the GTAW process also minimizes the chances of burn-through on thin materials. As a rule, GTAW does not produce sparks, spatter, or fumes, making it a relatively clean process. It can be, and often is, completed in the comfort of an air-conditioned room, although proper ventilation is always critical. An important note: If the material being welded is dirty, then the previous rule may not apply. For that reason, one of the oldest and most important adages about GTAW is clean and clean some more! The base material you are welding should be cleaned either with a brush, cloth, or an appropriate chemical compound to achieve the full GTAW advantage. If you are not certain of the best cleaning method for the material you are welding, check with your local welding distributor. Finally, another reason GTAW is often used is that it does not require a lot of postweld cleaning. For example, you will not have to chip slag or grind spatter after welding. Note, however, that you may have to, or simply want to, grind a gas tungsten arc weld for aesthetic reasons. Appropriate Applications All of this said, GTAW sounds great, right? Well, it is—but only under the right circumstances. Good applications (especially for material less than ½ in. thick) include: ·  Automotive work, including roll cages, frames, and exhausts ·  HVAC applications, including ductwork ·  Petrochemical and pipe applications ·  Metal artwork and ornamental applications ·  Maintenance and repair, including machine components and tools Not the Fastest If you have thicker materials (about ½ in. or thicker) that can be welded using GMAW or SMAW, you may want to consider these processes instead of GTAW, because they generally are faster. That is a drawback of GTAW: It is a slow process. For example, whereas the travel speed (the rate at which you weld) during GMAW is determined by the rate at which the welding wire is being fed through the gun and the amperage at which you are welding (among other factors), generally GTAW is only as fast as you are, or, more accurately, as fast as you can feed the filler rod into the weld puddle. The GTAW process requires much practice and skill to master, and even more of both to do it quickly and precisely. Also, GTAW deposition rates are lower than SMAW's or GMAW's. Deposition rate is the amount of filler metal that is deposited in a given amount of time. As an example, the average deposition rate for a GMAW application using a solid welding wire is 8 to 9 lbs. per hour, but GTAW deposits only 2 to 3 lbs. per hour. In short, GTAW probably won't be your first choice to weld thick materials quickly. It also should not be your first choice for material that is rusty or has mill scale on it, as GTAW filler rods do not have the added deoxidizers that allow many SMAW electrodes and GMAW welding wires to produce successful welds under these conditions. GTAW has its place, just like the other welding processes. It is neither superior to SMAW or GMAW, nor is it inferior. Rather, it is more suitable for certain metals, material thicknesses, and environments. If you are at all confused about when or how to use the GTAW process, or if you are ready to take your skill to the next level, contact your local welding distributor or welding equipment manufacturer for pointers. Often these groups have technical support teams whose advice can be invaluable. And don't forget the importance of just a bit of practice too!

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