Nuts & Bolts Wear long sleeves, hand protection, and eye protection

Building Basics Torch should be 15 to 20 degrees off perpendicular

Use ER80S-D2, ER70S-2, or ER70S-6 filler rod for aviation applicaltions

2-percent-thoriated tungsten probe should stick out 1/8 inch from cup Tungsten tip is placed 1/8 inch from base metal 4130 steel tubing

Arc de Triumph

LEEANN ABRAMS

Hold the filler rod at a 90 degree angle from the torch

THINK WELDING, AND THE The rig delivers its charge image of a torch streaming a and a stream of gas to an long jet of burning gas like a airbrush-shaped torch. The space shuttle booster rocket nubby cover on the torch probably comes to mind. has a large opening, the gas Tungsten Inert Gas—TIG—welding is a That method—oxyacetycup, with a needle of tunglene welding—is one way to sten poking out. The cover versatile technique for aviation applications bond metal to metal, but it’s also directs a stream of not the only one airplane argon through the gas cup, GREG LASLO builders use. explains Art Papineau, a Welding, in its most general ment setting, or gas ratios to fuss welding instructor for Lincoln terms, involves the joining of two with. Electric. pieces of metal—say pieces of steel The “inert gas” in TIG is typically By learning the basics of TIG tubing for a fuselage frame—by welding, torch preparation, and argon or helium—argon is most heating the two pieces, melting metal-specific tricks for 4130 steel common for the metals and thickthem slightly, and adding a filler tubing and non-structural alu- nesses found in homebuilding, material to strengthen the bond minum, aircraft builders can quickly Papineau says. It creates an environwhen it cools. The torch, whether put the technique to use on their ment for the arc to form, and it it’s an oxyacetylene, TIG, or stick projects. With very little make- “seals” the area around the weld, system, provides the heat to make ready, the TIG torch is ready to grab creating an oxygen- and nitrogenthat bond occur. free environment. That reduces the and go. Tungsten Inert Gas-welding, chance of contamination from more popularly known as TIG weld- Materials oxides and nitrides; contaminated ing, is relatively easy to learn, excep- A TIG rig looks something like a areas are usually the first to weaken tionally fast, and versatile enough to portable generator with a gas cylin- and crack. use on a wide range of materials, der attached. In essence, that’s what Welding with a TIG rig is a lot like including chromoly steel, stainless it is. TIG welding uses an intense driving a manual transmission car. steel, aluminum, magnesium, zinc, electrical charge to create the heat One hand holds the torch, the other and even copper. An electrically necessary to bond materials—up to holds the filler, and one foot operoperated device, it’s also safer to 7,000 degrees. However, it allows ates the rheostat pedal. store in your home workshop than you to adjust the output to match tanks of flammable gas, and you the type and thickness of metal Preparing to Weld The torch is “ignited” with a twohave no tip selection, torch adjust- you’re working with. 86

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Get Into the Loop! step process. First the tungsten tip is placed about 1/8 inch from the base metal—the stuff you’re welding together. Press the foot pedal to activate the current. The torch’s tungsten probe flashes to life with a “zap” and a bright blue arc. Press the foot pedal for more power, and let up to ease off. Arm yourself with a welding shield that has a No. 9 to No. 13 visor, says Lincoln instructor Joe Kolasa. Because of the intensity of the arc, normal welding goggles won’t prevent eye damage. With inadequate protection, you’ll flash burn your eyes—an extremely painful burn that feels like you’ve got sand in your eyes, Kolasa says. The torch can be held any way that’s comfortable. Papineau recommends holding on to the base of the Tshaped torch—it’s far enough away from the arc to keep your hand cool. Even with heavy leather gloves, a couple thousand degrees can still toast your fingers. Measure closely. A tight fit of the metal pieces you’re welding means less distortion in the overall product. Smooth any cut edges, and remove loose particles from the trim. Clean the trimmed surfaces with a hydrocarbon solvent, such as acetone or alcohol. Make sure the filler is clean, too. The current you’ll use is determined by the size of your power source, the kind of joint desired, the type of base material and its thickness, and the welding position. You’ll want to use the highest possible current that’s practical. One rule of thumb is 1 amp per .001 inch of metal. The tip of the torch’s tungsten probe should be 15 or 20 degrees off perpendicular, pointing in the direction you’re moving the torch, says Papineau. Keep it within 1/8 and 1/16 of an inch from the material, but don’t touch it to the material. It’ll stick and contaminate the tip and the weld. Move your head if you need to see better, not the torch. That way, you’re less likely to change the distance between the tungsten and the base metal. The TIG motion is similar to oxyacetylene welding whether you’re bonding chromoly steel or aluminum, Papineau says. Heat the base metal until it forms a 1/4or 3/8-inch pool of molten material. Hold the filler rod in your other hand at a 90-degree angle from the torch. Stick the filler material into the pool until about 1/4 inch of it melts, then nudge the torch slightly forward. Repeat that “move, dab, move, dab” motion until the weld is finished. The space between the rings in the suture will be about 1/8 inch on a good weld.

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Welding Chromoly To TIG-weld steel you’ll need to pick a tungsten probe and prepare it for welding. Most welds can be done with a 2-percent-thoriated tungsten, Papineau says. The tungsten should stick out about 1/8 inch from the cup. In tight spaces on the aircraft frame, you may want to Sport Aviation

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For more information, visit SPORT AVIATION on the Web at www.eaa.org

Building Basics extend the tungsten further out of the tip, but keep it within a cup’s diameter. On a wheel dedicated to tungsten grind the tungsten to a point, with its length being about two or three times the diameter of the tungsten. Set the TIG machine to DC-negative current. The amperage you’ll use depends on the width of the tubing and the diameter of your tungsten. The welding rig’s owner’s manual will help you pick the right setting. You’ll also need to select the right filler. Many aviation welders use ER80S-D2, ER70S-2, or ER70S-6 rod material—regardless of whether they’re using gas or TIG rigs. For .035 tubing, use a .035- or .045-inch rod. Papineau suggests starting with sheets of scrap chromoly to learn proper technique. Start with thicker metals, then try thinner ones. When you’re happy with consistent results, you can move to tubing. Break tube welds into parts. Position the torch, make the first weld, and then release the foot pedal. Hold the torch over the weld for four or five seconds to give it a chance to set under a curtain of clean argon gas. Reposition the torch, and make your next weld. Again, hold the torch over the new weld for four or five seconds. Allow your steel welds to cool naturally.

Aluminum TIG-welding aluminum is slightly different than welding steel, and that difference makes it somewhat more difficult. Aluminum is a great conductor of heat. The heat in the filler and melted base spreads through the material in front of it. The base metal will get hot enough that it will need less current to form a pool. Constant current will make it warp, so gradually ease up on the foot pedal as you go. You’ll use only a fraction of your original current by the time you hit the end of the 88

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sheet. Ease off the pedal like you’re coasting downhill in a car. If you don’t, you’ll cut the sheet. “That’s the challenging thing about it,” Papineau says. To set up for aluminum welding, use a pure tungsten with a beaded head, which normally forms naturally. You’ll probably use filler material made of 5356 and 5183 alloys— but check with a professional to be sure. Aluminum, magnesium, and zinc are welded in AC, instead of

The TIG rig looks something like a portable generator with a gas cylinder attached. DC-negative. AC does double duty cleaning and bonding the metals together, leaving a strong weld. Done properly, a new TIG weld in aluminum will have a “polished” area right along the edges of the seam, where the oxides were burned away. If you don’t have that polished area, your weld pool may be bigger than the argon shroud under the gas cup. Less heat—by easing up on the rheostat or by moving faster—should solve the problem. You’ll also produce a “flat” seam and ripple the back side of your base material if your weld gets too hot. Conversely, if you’re not hot enough or you move too quickly, you’ll just melt the filler—essentially just soldering the materials together. Move along the weld as fast as it takes to make the 1/4-inch weld pool. After you cut power, hold the torch over the weld for two seconds to keep it clean, Papineau says. TIG-welding aluminum may take some getting used to. Practice by working with scrap metal, without filler, and get used to forming

weld pools. Then work up to building joints. Remember, it’s hard to make a bad TIG weld in aluminum so long as the base metal melts and the filler gets into the pool. Likewise, it’s going to be hard to make a pretty one.

Learning More TIG welding is a versatile alternative to oxyacetylene welding, but it may take some experience before you’re completely comfortable with the technique. EAA SportAir Workshops (www.sportair.com) teach TIG welding techniques at workshops in Griffin, Georgia, and clinics at EAA AirVenture Oshkosh. Check with your local junior college and vocational-technical school, too—most offer TIG welding classes, although their emphasis will not be on the thin-walled materials airplane builders use. Lincoln Electric also hosts weeklong beginning and advanced welding schools (www.lin colnelectric.com/knowledge/training/w eldschool/) focusing on motor sports applications. Both Lincoln Electric (www.lincol nelectric.com) and Miller Electric (www.millerwelds.com) offer online tutorials on using their TIG rigs. They also have online stores that sell training videos, CD-ROMs, and books. Lincoln also sells scrap metal packs of various thicknesses and a kit to weld an aluminum toy biplane for practice. Performance Welding, by Richard Finch, can be found on the SportAir website, and it is a good general-purpose reference. New welders may feel uncomfortable using TIG welding, especially if they’ve heard horror stories, but it’s worth a try. It’s not terribly difficult to learn, and with some practice, it’s faster, cleaner, and safer than gas welding. And while it’s pricey to get a TIG rig (about $1,300), welders who are happy with their results may find their confidence is worth the cost.