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Next-Gen Jets Driving New Repair Technology Trends

With a rapid ramp-up to new platforms and new materials, MROs need to increase R&D and find new ways to make repairs.

With a new generation of commercial jets, seismic changes in repair technologies are occuring.

 “The aviation industry is entering a period of disruptive technology for the first time since the transition from analog to digital airplanes in the 1980s,” says Chris Doan, vice president of consulting firm Oliver Wyman. “New aircraft, built largely of composites and supermetal alloys, will be maintained differently than their predecessors.”

Along with new materials, these airplanes will generate a huge amount of component performance and health monitoring data, going from megabytes to terabytes. “We are entering the era of big data. The result will be a faster implementation of disruptive repair and data-management technology than previously seen,” adds Doan.

For the MRO industry, the implications are inescapable. By 2024, 20,000 new commercial aircraft will have been delivered. Of those, 9,000 will be replacements for currently operating jets, according to Oliver Wyman’s 2015 forecast and survey.

The survey also predicts that by 2020, 15-20% of the projected $83.2 billion MRO aftermarket spend for that year could be affected by new technology. It attributes this trend to the large amount of data generated by aircraft health monitoring and predictive maintenance systems as well as new repair technologies including additive manufacturing.

“The MROs will have to rethink the way they do business or risk losing as much as 20% of their market value. Those who think they will grow by leaving things as they are and doing nothing will be wrong,” Doan cautions.

“From what we are seeing with our partners, new research and development [R&D] is coming in leaps and bounds—mainly with engine shops, and composite airframe MROs,” says Josh Goring, business development director for AJW Technique in Montreal. He advises that as OEMs tighten their grip on new airframe and engine aftermarket support, third-party MROs need to increase their R&D budgets.

“If third-party MROs are going to retain their piece of the aftermarket support pie, more R&D will be needed for out-of-the-box thinking and reverse engineering, especially as the next-generation platforms require much higher proficiencies in avionic and electrical understanding,” he notes.

“Current repair technologies that are effective, but not cost-effective, will need additional R&D in order to make them cheaper and easier to implement,” says Scott Ingold, vice president-general manager of AAR Aircraft Component Services in New York. “There will continue to be major changes with surface and stress-fracture repair. In addition, a key area of focus will be advancements with non-destructive testing methods. These will help identify where the repair technology R&D should be focused.”

According to Doan, the MRO industry’s yearly R&D investment is typically about 10% of operating costs. Along with that, the MRO study determined that adopting new repair technologies has been slow. “The MRO industry is traditionally cautious, with innovations happening sporadically, at best. In fact, only about 13% of the MROs surveyed said they are comfortable with change and innovations,” says Doan.

But innovations in repair technologies are indeed taking place. In September, Spirit AeroSystems introduced a radical, out-of-autoclave repair process for composite propulsion system components.

“Generally, the repair techniques and materials used for the out-of-autoclave process apply to all propulsion family products that Spirit manufactures, but we have found that the [part with the] most imminent need for this technology is the thrust reverser inner wall,” says John Welch, the Wichita-based company’s chief scientist, global customer support and services. The repair, he reports, was granted FAA approval as an alternative method of compliance (AMOC) following 18 months of testing and data substantiation.

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“The goal was to develop a composite repair technology that will deliver the same capability for mission performance and restorative strength that would be achieved using an autoclave,” says Welch. “Also, the out-of-autoclave process benefits those customers who lack an autoclave, which is a very high- cost piece of equipment.” 

The new repair system can be performed in-house by Spirit AeroSystems or made available as a kit to approved MROs, says Welch. The kit can reduce the repair time to as little as two days, compared to 14 days with an autoclave. Welch attributes that time reduction, in part, to the fact that the repair process does not require complete disassembly of the thrust reverser’s inner wall structure—and that Spirit AeroSystems performs all pre-processing of the kit, including cutting, orientation and layup of each material layer.

At StandardAero Component Services, which spends 5-10% of its yearly operating expenses on R&D, the introduction of a relatively new cold spray method for dimensional restoration and corrosion repair of engine components is planned for early 2016. Tim Mathis, director of engineering for the Cincinnati-based component repair facility—specializing in GE, Pratt & Whitney, V2500 and Rolls-Royce engines—describes cold spray as a “super-high-pressure, low-temperature alternative” to thermal spray methods.

“Cold spray is essentially a solid-state coating process using a high-speed gas jet to accelerate powder particles at a supersonic speed on a substrate. The metal particles plastically deform and consolidate upon impact to fill in defects or build up discrepant dimensional features,” Mathis explains. “Based on testing, material properties are better using cold spray versus thermal spray.”

Mathis points out that cold-spray technology underwent an extensive evaluation process at StandardAero. The company determined it was particularly effective when applied to aluminum structures such as fan casings. “Steel and aluminum components are where you see a heavy degree of corrosion,” he notes. “We needed something that would enable the technician to target small, local areas of components with complex geometries, rather than having to spray large areas of the part, which has to be done with thermal sprayers—requiring removal of the excess spray medium.”

Interestingly, Mathis reports that no specific standard practice for cold spray application has been developed yet by any of the prime engine OEMs. To address this, he says, StandardAero will deploy “a trial/testing matrix” to perform an analysis on all applicable materials it estimates it will need to use. “This trial/testing matrix will use testing results or standard requirements from previously approved thermal spray materials,” he says. “For example, we’ll use the tensile and macro-analysis requirements for Inconel 718 [a high-strength, corrosion-resistant nickel chromium] thermal spray material for our testing basis for Inconel 718 cold spray. We will work with the OEMs for the application of cold-spray technology to meet the repair characteristics they have established.”

AAR’s Scott Ingold adds that the company introduced cold-spray technology to extend the life of the integrated lower control actuator on the U.S. Army’s Boeing CH-47 Chinook helicopter. “Unlike thermal spraying technologies, the powders used are fused—not melted—through kinetic energy,” he says. “This prevents the part from being exposed to heat, which introduces weakening stress into the component. For this reason, thermal spraying techniques cannot be applied to certain materials such as magnesium, so this technology introduces repairs for parts where there was previously no possibility of repair.”

Also pushing the boundaries of engine component repair, Evendale, Ohio-based GE Aviation is developing a cold metal transfer process for application to restore seals on rotating engine parts.

“This material-additive technology is a unique, low-heat process that allows us to build up worn areas on many types of components,” says Scott Fentress, GE Aviation’s general manager- component repair. “Metal is applied quickly in very small droplets, lowering the amount of heat transferred to the part. After the metal transfer, modest final machining is needed to restore surface finish and final dimensions.”

Lower heat means less thermal stress and distortion are introduced during the repair, says Fentress. This increases repair yield, since there is less chance of cracking than when using hot metal transfer methods, he adds.

GE expects to make its first repairs using cold metal transfer within the first six months of 2016, initially on the Inconel 718 rotating seals on its GE90-94B, Fentress says.

Airlines operating from deserts or in salt air environments are at higher risk of engine component erosion—especially within the high-pressure compressor airfoils. To combat that, MTU Maintenance recently introduced MTUPlus ERCoateco, an improved erosion and corrosion-resistant nanotechnology coating that provides resistance to particle as well as fluid erosion.

“We developed ERCoateco drawing from many years of PVD [physical vapor deposition] technology know-how and field experience,” says Frank Seidel, senior manager-repair engineering for MTU Maintenance in Germany. “Cost savings will be achieved through a scrap rate reduction of up to 30%, a decreased specific fuel consumption of up to 0.5%, reduced CO2 emissions and increased on-wing times,” he adds.

MTU Maintenance also has developed advanced plasma-sprayed coatings for combustors, tailored particularly to the needs of desert operators, he says. This involves the application of an additional chemically optimized top coating that reacts with molten sand and crystallizes the CMAS (calcium-magnesium-aluminum-silicates) on top of the base coating system. “In a variety of isothermal and thermal cycle tests, our MTU coating showed a significant increase in CMAS resistance and lifetime durability compared to the current standard YSZ [Yttria- stabilized zirconia] coatings,” he says.

MTU spends about 10% of its annual 160 million R&D expenses on repair development, including machining, surface treatments, dimensional restorations and testing applications. “In addition, we are developing data management tools which allow us to evaluate and use the findings of our repair activities for the future. Also, we are aiming at a high yield rate and a reduction of the scrapping process,” says Seidel.

At Pratt & Whitney, dimensional restoration has been driving new welding technologies. One of these is a replacement for tungsten inert gas (TIG) welding. “It reduces the time normally involved with the TIG welding process by as much as 75% and is applicable to a wide range of nonstructural parts on which we previously did TIG welding,” says William Brindley, manager for manufacturing and aftermarket technology at the engine OEM’s East Hartford, Connecticut, headquarters.

Brindley explains that the new welding method was introduced three years ago to address degradation due to wear. “We have used this new dimensional welding method to restore the part’s surface to the point where it meets the original design specs, and we are continuing to expand its use on a wider range of materials.”

Brindley also cites the company’s solid-state friction welding as a ground-breaking method for replacing component structural features, enabling repairs that could not be done prior to its introduction four years ago.

“Friction welding does not melt material to achieve a weld,” he says. “It allows us to maintain much of the critical microstructure of the original base metal and therefore maintain much of the original material’s mechanical properties. For many alloys this is not achievable with standard fusion welding methods, like TIG.”

In addition to recently introduced repair schemes, future repair technologies are being actively researched. “We have four to five projects going on right now that focus on ending repetitive repair issues—mostly on nacelles,” says Jim Epperson, Spirit AeroSystems’ senior engineering manager- global customer support and services. “Our R&D is also being applied to the evolving major airframe composite structures of the new-generation jets. In that regard, we are finding that if a certain repair technology applies to one type of component, it can likely apply to such major structures as fuselages and wings.”

StandardAero Component Services’ Tim Mathis reports that his company is shifting its focus toward composite parts repair technology. He says the ratio of metal to composite engine parts repaired by the company is currently 80/20. But that could reach a 50/50 split within a decade.

“The challenge is, how do we get ready to repair the new composite engine parts that we don’t even know about yet?” says Mathis. “That means addressing issues involving equipment and technology, as well as those for composite parts inspections, layup and the more sophisticated machining methods that will be required.”

Preparations are in progress on ceramic matrix composites (CMC), which, Mathis points out, are not used in legacy engines, and thus have no available repairs. He predicts that CMC applications will be with combustor liners, fan cases and hot-section components, including blades, vanes, shrouds, nozzles and exhaust.

But as repair technology increases in complexity, intellectual property access will become a greater issue. “Intellectual property has always been a decisive factor for our repair development,” says MTU Maintenance’s Seidel. “In fact, we believe this situation has gotten more challenging over the past few years due to the strong OEM dominance of the aftermarket. Yet there is still room for new ideas and solutions.”

However, Oliver Wyman’s Doan believes that most MROs lack the infrastructure to develop repairs without intellectual property access.

“Developing new repair technology mandates a thorough understanding of the technology and data—such as the data pertaining to stress analysis. That’s why more MROs will have to partner with OEMs going forward. The new technology is coming in fast; the old technology is leaving fast.” 

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