THE ARRIVAL OF

TIG WELDING BYRONMYERS With the introduction of smaller and affordable TIG machines designed for the homebuilder, you can weld your aircraft together like the "big boys."

INTRODUCTION -[ r ^

In the not so distant past, the price of a complete TIG welding machines was several thousand dollars, which made this welding process too expensive for the average homebuilder to afford. Fortunately, times have changed. Now a complete TIG welder designed for the homebuilder to weld aircraft metals can be purchased for less than $1600. More homebuilders are discovering the low cost and advantages of this FAA-approved process and as a result, TIG welding is rapidly gaining in popularity. Perhaps some of you know TIG welding as heli-arc welding. This was the original name for TIG welding years ago when helium shielding gas was used. In today's world, argon has replaced helium as the shielding gas of choice for the vast majority of TIG welding. For this reason, the heli-arc process today is more commonly called G.T.A.W. or TIG welding. G.T.A.W. stands for Gas Tungsten Arc Welding and is the proper terminology as recognized by the American Welding Society. TIG is the slang term for G.T.A.W and is the common term used in industry. TIG stands for Tungsten Inert Gas.

reason, it is impractical to use a wire machine for TIG welding. The power supply of choice should be an AC/DC machine. W h i l e most metals are TIG welded with DC, a l u m i n u m and magnesium are welded with AC. The TIG power supply should come equipped with built-in high frequency circuitry for arc starting and stabilization. A m a c h i n e rated for 175 amps maximum is sufficient for homebuilt aircraft. The TIG torch holds the tungsten electrode and delivers the shielding gas to the weld puddle. The tungsten is slid EQUIPMENT into a collet, which is surrounded by a collet body, which is firmly held by a TIG welding equipment consists of a backcap that screws into the torch. A power supply, TIG torch, electrode, ceramic gas-shield cup screws onto exshielding gas equipment, shielding gas, ternal threads of the collet body. filler metal, and optional current control. Shielding gas flows into the torch and The TIG process requires a con- out of the cup, protecting the electrode stant-current power supply so that and weld puddle. Torches up to a rating current remains relatively stable with of 150 amps may be air cooled, while changes in arc length, important for a those rated over 150 amps are generally hand-held process. A constant-current water cooled. An air cooled torch is machine's output reacts differently sufficient for use on homebuilt aircraft. than a wire machine's output, which Tungsten electrodes used for airhas a constant-voltage output. For this craft metals are commonly one of two

types — pure or thoriated. In general, for aluminum and magnesium, pure tungsten is recommended. For the other metals, thoriated tungsten works best. Tungsten is manufactured in diameters from .010 inch to 1/4 inch. The diameter recommended depends (continued on the next page) SPORT AVIATION 101

upon the thickness of the base metal and the amount of current desired to weld it. For homebuilt aircraft, a 1/16 inch diameter tungsten is a good all around size to choose. Tungsten is chosen for the electrode because it's extremely high melting point prohibits it from being consumed by the arc. As stated before, 100% pure argon is the preferred gas for the TIG welding of aircraft metals. This shielding gas is readily available from your nearest welding distributor. Also needed is a regulator, flow meter and gas hose to deliver the argon to the TIG torch. For some welded joint designs, a filler metal is used and is applied by hand after the weld puddle is established. Types of filler metal vary and depends upon the base metal being welded. For mild steel and chromoly tubing, an ER70S-2 filler metal is preferred. For aluminum, a 4043 or 5356 filler metal is commonly recommended. For other filler metal recommendations, consult your local welding distributorship. Filler metals are manufactured in diameters ranging from 1/16 inch to 1/4

inch. For homebuilt aircraft, a diameter of 1/16 inch works well. While TIG welding can be accomplished without any external current control, a foot or t h u m b control is highly recommended. While welding, subtle current changes are many times desirable and this is easily accomplished with a foot or thumb control.

is needed to switch from the welding of aluminum plate to the welding of chromoly tubing. 2. Extremely thin metals can easily be welded if the TIG machine used has a stable, low-end welding arc. For example, at the welding workshops at Oshkosh and Sun 'n Fun, demonstrations of welding aluminum foil are conducted using an under $1600 maADVANTAGES chine that has a low-end rating of 12 amps. Yet, with the same machine, aluThe advantages of TIG welding are minum up to 1/4 inch thick and even numerous, m a k i n g it the welding thicker steels are easily TIG welded. process of choice for the larger aircraft 3. The welding arc of a TIG mamanufacturers. Some of the advan- chine is extremely hot but very easily tages are listed below. controlled. For this reason, heat input 1. TIG welding can be used to eas- into a welded joint is very localized. ily join almost all aircraft metals, This allows for very little base metal including mild steel, stainless steel, distortion as compared with the gas chromoly steel, nickel, aluminum, tita- welding method. nium, magnesium and various alloys 4. TIG welded j o i n t s are of exof those. While welding-procedure tremely high quality. Clean and changes might be made when chang- beautiful beads, excellent penetration ing the various base metals, very little and high strength joints are all hallin the equipment itself needs to be marks of TIG welding. changed. For example, only a polarity 5. Most TIG machines are also stick change and a low cost tungsten change machines. Therefore, two welding processes are purchased for the price of one machine. TIG welding and stick welding can be easily used for other projects or repairs around the home or business. 6. Anybody with gas welding experience can learn TIG welding easily, as the two processes are applied in a similar fashion. Those with no gas welding experience have no trouble learning the basics, but as with anything else, a little practice makes for better welds.

CONCLUSION

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102 SEPTEMBER 1998

G.T.A.W. or TIG welding is a viable, high quality, FAA approved process that has been used for years in the manufacturing of military and commercial aircraft. The prices of TIG welding machines have fallen into the area of affordability for many homebuilders. With a TIG machine and a little knowledge and practice, welds equivalent to those of the "big boys" can easily be accomplished. For more information and to try your hand at TIG welding, stop by and see us at the welding workshops, forums, and sales booths at Oshkosh and Sun 'n Fun. (Ron Myers is a Technical Sales Representative for the Lincoln Electric Company, an EAA member and has for years been a welding workshop volunteer at the Oshkosh fly-in.)