“Advanced blades, with higher corrosion resistance, can be applied to older engines and can replace or substitute new brazing technologies for older brazing processes,” he says. “In fact, we have developed a special high- temperature brazing process for hot-section components.”
To prepare for the first GEnx shop visits, GE Aviation is expending considerable effort on repairs. The GEnx-2B engine went into service in 2011 on the Boeing 747-8 and the -1B, entered service on the Boeing 787 last year. Those engines, he says, will start making their initial shop visits in 2015, with turbine blade recoating and repair, as well as static and rotating seals servicing. In tandem, GE, which spends $45-50 million annually on developing unique repairs—more than 1,300 this year (compared with 600 four years ago)—is focusing heavily on compressor blisk repairs, says Bill Dwyer, chief marketing officer for GE Aviation's service business.
“There is a lot of incentive to develop advanced repairs on compressor blisks, which are located on the forward end of the high-pressure compressor,” Dwyer notes. “The technology to repair an entire blisk unit is based on a more advanced welding process introduced by GE over the past year specifically for that purpose. This, in fact, was developed in anticipation of the first shop visits of the GEnx engine family.” Blisks are located in the GEnx compressor Stages 1, 2 and 5.
The incorporation of blisks has proliferated in turbine engine design due to the aerodynamic and weight-saving benefits they provide, says Dwyer.
But GE also is applying its new, improved welding technologies to older engines, with the introduction during the past 18 months of a 3C airfoil restoration process specifically for the CFM56-5B and -7B.
“It was a more sophisticated repair that was designed for application to the complex airfoil shape of the high- pressure compressor blades, and the complex design geometry of the high-pressure compressors in those engines. The benefit is that more parts can be repaired and fewer need to be scrapped,” Dwyer explains.
He further reports that GE has introduced advanced wear-resistant coatings for the high-pressure compressor blades on the CFM56-5B and -7B, providing a longer on-wing time, and scrap-rate reduction. “The technology uses a proprietary material composition, which has very robust wear resistance,” Dwyer says. “While it is available to all operators of these engines, it is being specifically marketed to airlines operating in very harsh environments, such as the Middle East and China.” The company is studying the application of the coatings to other engines.
The use of powdered-metal applications to hot-section rotating seals and other rotating parts is another recently introduced repair technology at GE. As Dwyer explains, it gives the component the capability to operate at very high temperatures. “Powdered-metal technology has excellent resistance to 'creep', the term which describes the deformation, or loss of shape—and ultimately failure—of the metal part at high temperatures,” he says.
Another key area being targeted to reduce maintenance costs involves what Dwyer calls “lean burn combustion.”