Tinker unit designs new welding process for B-2

  • Published
  • By Ron Mullan
  • 72nd Air Base Wing Public Affairs
When the B-2 Systems Support Manager at Tinker AFB needed three spar caps refurbished for a spare right aft deck kit, he uncovered a larger problem.

The aft deck panels on the stealth bomber were not originally designed to be replaced, so there were only a couple of spare right aft deck kits produced. When premature cracking appeared on some of the aircraft the spares were quickly consumed.

The Air Force faced a major problem affecting the mission capable rate of the B-2 should another right aft deck panel need replacing. The Air Force couldn't purchase more spare kits because the original production line closed years ago. Start up costs to get another production line running would cost the government hundreds of millions of dollars.

The B-2 Systems Support Manager had plenty of questions that needed answers.

"There was a lot of concern about who should we go to, who can do it, are we going to be able to achieve what we need with this because it hasn't been done before," said Paul Koenig, a B-2 systems engineer with the 556th Aircraft Sustainment Squadron.

The B-2 Systems Support Manager turned to Tinker AFB's 76th Propulsion Maintenance Group for help.

"We had worked with the 76th PMXG on other projects and felt they could provide us with a quality product," Mr. Koenig said.

A 12-man team from 547th Propulsion Maintenance Squadron's Engine Repair Development Branch was formed to design the tooling needed and develop a process to refurbish the spar caps.

With no technical data or existing equipment to go by, the team had to start from scratch.

"We had to design a measurement fixture to hold the spar cap on a coordinate measurement machine," said Dustin Kyger, lead project engineer with the 547th PMSS. "In addition, we designed a holding fixture to do the welding and restrain it during the heat treatment process and designed an Argon gas heat treatment box."

The heat treatment box proved to be a challenge for the team.

"It was mostly trial and error," said Mr. Kyger. "We had to ensure even heat throughout the box. We kept burning out electrodes, so we'd tear it apart; try different electrodes until we found the right combination."

Another challenge for the team was developing a welding process to fill in the holes without warping the metal from the welding. The solution was to build a chiller system.

"Attaching chill blocks on either side of the welding site, ensured that heat would not be transferred to other areas causing warpage," Mr. Kyger said. "Because the heat build up was so great, the welders could not work on consecutive holes, but had to work back and forth from one end to the other."

The team began working on project in November 2006 and spent seven months developing the tools and processes before actually performing the work.

"We had all our tools built and our processes down last May," said Larry Whitley, lead engineering technician, 547th PMSS. "The actual welding took approximately nine weeks and we closed out the project in July."

The repair development cost for the refurbishment of the three spar caps was $160,000.

"We will be able to do future refurbishments a lot cheaper," said Mr. Kyger.

"The refurbished spar caps look like new, never drilled parts at this point," Mr. Koenig said. "The 76th PMXG has given us a spare that we can put into a box and, when needed, we can put it on a B-2 and fly it."