This Time It's Personal
Welding training at Delta's TechOps Center raises the bar
By Mike Sammons
When it comes to welding, Delta Air Lines Technical Operations Center (TOC) at Atlanta's Hartsfield International Airport performs plenty, with more than 500 welding operators located there. It maintains and repairs a full range of aircraft, engines, and components including landing gear, accessories, and ground support equipment. TOC's welding training and certification program actually exceeds industry standards (AMS 1595 for aircraft welds, soon to be replaced by AWS D17.1, and AWS D1.1 for structural welds).
"We don't disregard defects on the ends of the joint even though AMS 1595 allows us to discard the last half inch. The reason is that some of our parts have ends," says Jody Collier, SCWI (Senior Certified Welding Inspector) and Delta's program manager, welding training. "Another criterion where we are stricter than the AMS standard is that we require at least one tie-in in the middle area of the joint that will be X-rayed. Stops and starts are more likely to have defects like crater cracking. Because repair welding of aircraft parts often necessitates sequence welding and stopping often in order to control heat input, we require our welding operators to demonstrate the ability to stop and start without creating defects."
TIG welding at TOC is far more difficult than almost any other maintenance application. Typical parts include a magnesium transfer case that costs $47,000, a 3-inch diameter, .020-inch wall titanium air duct that costs $800 per foot, and the .012-inch 157 stainless-steel skin of an exhaust sleeve on a Boeing 767 engine.
When welding on material this sensitive, operators should not be limited by the capabilities of their equipment. Unfortunately, some TOC machines were 30 to 35 years old; one machine had a serial number of 73 and another was built in 1962. Basic TIG power sources inherently last a long time, and Delta's clean operating environment further extended their life. However, just because a machine can still strike an arc doesn't mean that it should remain in use.
"We had a TIG machine from the 1980s. It had a terrible bottom end on it, about 20 or 30 amp, which doesn't lend itself to aircraft welding very well," says Robert Trudelle, TOC welding training instructor. "For example, the .012-inch exhaust sleeve is welded at 15 to 18 amps. We need something that can weld thin metals."
In addition to limitations on thin ferrous metals, older machines do not perform as well on nonferrous metals because they do not feature modern squarewave technology or incorporate advanced arc starting features (see sidebar story on page 24). Thus, at the same time TOC began intensifying its training program, it recognized the need to modernize its fleet of AC/DC TIG power sources.
TIG welding has always been an art, but the TOC training program adds science.
Collier says that, "The structure and consistency of our training program improve welding results. Before we had too many performance highs and lows. Delta's continuous improvement team assessed the operator's skill level and our training program. As a result, they determined we needed to fund and support a world-class training program that would produce operators whose skills surpass any industry standard."
Prepared by the Hobart Institute of Welding Technology, Troy, Ohio, the TOC training program for GTAW (TIG welding) covers all the materials encountered in aircraft maintenance and repair: carbon steel, nickel-based steels, cobalt-based alloys, titanium, aluminum, and magnesium, plus the relevant alloys of these metals. A hefty training manual covers every aspect of the TIG process, TIG equipment, and welding terms and symbols. Each metal type has a chapter devoted to it, enabling the operator to learn about that alloy's welding characteristics (including an alloy data sheet), pre-weld preparations, and welding instructions. Practical exercises, such as a square groove butt joint on .020-inch titanium (Group 7: 6AL4V) or a fillet weld T-joint on .063-inch 6061-T6 aluminum, test for real-world skills.
To prevent burn through when welding thin metal, Miller Electric™s Syncrowave 250 DX and 350 LX AC/DC TIG welders now have improved low-end DC TIG arc starting capabilities. While Miller...