7/20/2012 - ROBINS AIR FORCE BASE, Ga. -- A new aluminum alloy and forging are being used for bulkhead end fittings on C-5 aircraft during programmed depot maintenance at the Warner Robins Air Logistics Complex.
Not only have critical cracking issues on the end fittings been solved, but the new process saves time, money, man hours, and reduces wear and tear on tools.
The new process came about through the collaborative efforts of the Air Force Research Laboratory, C-5 System Program Office, 402nd Commodities Maintenance Group, 559th Aircraft Maintenance Squadron maintainers, Lockheed Martin and Alcoa Aluminum.
End fittings are large pieces of metal material that attach to the side and bottom frames of a C-5 floor structure. They're basically what hold together the lower and upper structures of the aircraft. The available material used in the past to make end fittings made the parts subject to cracking caused by stress corrosion.
Because of the random nature of stress corrosion cracking, it was not economical to acquire and stock forgings for the original parts, so end fittings were manufactured by machinists in the 402nd CMXG using plate stock.
It took nearly 80 hours of machine time for each end fitting. The stresses imparted to the fittings by the machining process also added to a reduction in service life.
Researchers at the AFRL - as part of the Durable C-5 Structural Improvements Program - used a more stress corrosion-resistant aluminum alloy, with the same strength as its predecessor but with better fatigue characteristics, to design two new forgings that could be used to manufacture more than 90 various fittings.
With the new forgings and aluminum material, the machine process is now cut in half, taking about 32 hours of machine time.
Several steps in the manufacturing process have also been cut, including a process known as heat treat and shot peen, resulting in time savings for work performed. And, less time spent inside machines means less wear and tear on expensive tools.
"The old material had a lot of stress in it when we received it," said Kyle Keene, 573rd Commodities Maintenance Squadron numerical control programmer. "We would have to machine it very carefully. Now, we stand a greater chance of not killing a part due to human error because there is less touch time."
The result is a higher quality product and a better process all the way down to the shop floor. Cost of machining the part from the new forging was cut in half, from $6,000 to $3,000.
There are 96 end fittings on a C-5. Included in that number are main frame end fittings, as well as intermediate ones which are located between each main fitting.
Work has been done more frequently at Robins on the older C-5A models, produced in the 1960s, sometimes repairing from four to six fittings on a single aircraft.
To date, one of the new end fittings was installed on a C-5C, a version of the C-5 that doesn't contain a troop compartment and hauls a larger payload.
A total of 12 were changed last fall on the C-5C, which at one time also happened to carry a boost launcher for the space shuttle, according to Wilbur Mathews, 559th AMXS work lead.
"The A and C models have been repaired for many years," he said. "Instead of just repairing end fittings on those, now we are completely changing them."