TIG welding is becoming increasingly critical for transportation industries as vehicles that range from cars and trucks to aircraft are made lighter to reduce fuel consumption and save on ever-higher costs of fuel.

Cutting the weight out of cars, trucks and aircraft becomes possible by reducing the gauges of the wall sections for parts that are used to build them. In addition, aluminum and exotic alloys are being used more than ever to build vehicles.

John Luck, product manager for Miller Electric's TIG unit, said there are new applications for aluminum and exotic metal alloys and that Miller (www.millerwelds.com) sees many industries going to aluminum and other light-weight thin-walled parts that are perfect for TIG welding because of the preciseness of the arc.

“When the arc comes off the tungsten it's very precise and gives the ability to adjust the amps up or down. Because the process is slower than MIG, as far as the speed with which you can weld, you get better control of the arc — the penetration — and a better weldment. What provides you with the ability to weld thick and thin materials is the preciseness of the arc,” Luck said.

In comparing TIG with MIG, Luck said TIG is slower but much more precise.

“With MIG, it is more difficult to achieve perfection in smaller, more critical components because you have to be right on to control the heat,” he said.

Exotic materials, such as titanium and Inconel are high-temperature materials and can handle changing temperatures well.

Because of its ability to withstand high heat yet deliver the necessary performance, Inconel is used in automotive exhaust systems and in air conditioning/heating units and for complex industrial radiators, where heating and cooling cycles are regular and severe. In each of those applications, TIG welding is the preferred process.

Titanium is nearly 45 percent lighter than steel, and it's far more costly and nearly 60 percent heavier than aluminum, but it is more than three times stronger than either steel or aluminum so it lowers life cycle costs because of its long service life and reduced maintenance and repair costs, Luck said.

However, titanium is a finicky metal to weld, but TIG is the primary process used.

“Titanium is one of the more challenging materials to weld because it has an affinity to oxygen, so it needs to be shielded really well. Typically, welding titanium is done in a vacuum chamber or with special torches that use a lot of shielding gases over the part, and welding titanium requires a bit more knowledge and expertise.”

Best Practices for Welding Titanium

John Luck, product manager for Miller Electric's TIG unit, and Jack Fulcer, product and marketing manager for Weldcraft (www.weldcraft.com), have written a paper with tips for TIG-welding titanium.

Titanium is part of a family of reactive metals. It is so reactive that its affinity for oxygen allows it to react — at room temperatures — with oxygen to form titanium dioxide.

“This passive, impervious coating resists further interaction with the surrounding atmosphere, and gives titanium its famous corrosion resistance,” Luck and Fulcer said.

“The oxide layer must be removed prior to welding because it melts at a much higher temperature than the base metal and because the oxide could enter the molten weld pool, create discontinuities and reduce weld integrity. Interstitial absorption of these oxides embrittles the weldment and may render the part useless,” they said.

For that reason, all parts of the heat-affected zone in a weldment must be shielded from the atmosphere until the temperature drops below 800 deg. F.

However, Fulcer and Luck note that experts disagree on the exact temperature that the metal should reach before shielding is cut off. The recommendations range from 500 deg. F to 1,000 deg. F., and 800 degrees F. is recommended as a reasonable median unless procedures, standards or codes indicate otherwise.

“One of the most common mistakes when welding titanium is not verifying the many variables that contribute to good shielding gas coverage prior to striking the first arc.

“Make it a practice to always weld on a test piece before beginning each ‘real’ welding session. To ensure that gas purity meets your requirements, AWS recommends using analytical equipment to measure shielding gas purity prior to welding. Gas purity varies by application. Typical applications require that the shielding gas — typically argon — be not less than 99.995 percent pure with not more than 5 ppm to 20 ppm free oxygen and have a dew point better than - 50 deg. F to - 75 deg. F,” Luck and Fulcer said.

One of the critical things to remember about TIG welding titanium is that contamination also causes embrittlement, and embrittlement is the leading cause of weld failure. Contamination can come from oil on fingers, lubricants, cutting fluids, paints, dirt or other substances.

“When working with titanium, follow the three Cs of welding: clean, clean, clean! Keep a clean work area, one free from dust, debris and excess air movement that could interfere with the shielding gas. Clean the base metal and bag parts not immediately welded, clean the filler rod and wear nitrile gloves when handling the filler rod and parts,” Fulcer and Luck said.