Engineers Demo Value of Cold Spray Repairs to Naval Aviation

January 25, 2017

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The Marine Corps Assistant Deputy Commandant for Aviation (Sustainment), William E. Taylor, visited Fleet Readiness Center Southwest (FRCSW) Jan. 23 to learn more about cold spray additive technology.

Engineers and artisans from FRCSW did a demonstration and briefing for Taylor and Marine Corps aviation representatives from Camp Pendleton, California. The cold spray technique is saving the Naval Aviation Enterprise time and money in repairing aircraft components and returning them to the fleet, improving readiness across the Navy and Marine Corps.

"This has a lot of promise," Taylor said.

Cold spray is an additive, solid-state thermal spray process which can restore components' critical dimensional features lost due to corrosion, wear, or mechanical damage. It works by taking powdered metal alloys customized for the need of the specific part to be repaired and spraying it onto the metal of the damaged component, creating a mechanical bond. The process creates a low-porous or nonporous surface without making any heat-induced changes to the substrate.

Explained more in layman's terms, the process bonds metal to metal in a relatively low-heat environment, filling in any corrosion or other damage in machine parts. Repairs often take less time and are safer, too. To use a traditional chrome coating, for example, takes 20 hours to cover a part with 20 mL of metal; cold spray can do it with a tungsten/carbide/cobalt alloy in about two minutes. The process also eliminates the health hazards posed and safety precautions required using traditional methods.

The repaired parts come out stronger and less prone to mistake. According to Luc Doan, a materials engineer at FRCSW, of the approximately 150 parts repaired using cold spray so far, none have been returned for another repair. Additionally, none have resulted in machine rejections. With traditional methods, approximately 20-40 percent are machine rejected.

Conrad Macy, a secondary power Fleet Support Team (FST) engineer for Naval Air Systems Command (NAVAIR), explained the parts can endure at least 10 times more stress and impact than traditional parts. It might be more, but at that point engineers stopped trying to test the damage limits.

Macy is the impetus behind bringing cold spray to naval aviation. In his job working with the fleet making repairs to aircraft, he became tired of throwing away expensive parts because of minor damage. He felt sure some process could fix the parts, so he began searching for it. About six years ago, through a Small Business Innovation Research (SBIR) project, he found what he needed with cold spray. The SBIR with Inovati sealed the deal, showcasing the applicability of cold spray to increase fleet readiness by refurbishing previously scrapped components. Often, these components are in demand across naval aviation, but have long lead times.

Inovati's cold spray technique is called Kinetic Metallization. Cold spray can encompass a variety of techniques; this one uses low-pressure helium or nitrogen and a sonic nozzle to accelerate particles. The combination of low pressure and sonic gas speed significantly decreases gas consumption compared to conventional cold spray processes while still achieving high particle velocities, according to the company. It also wastes less material compared to other cold spray machines and techniques, according to the Navy.

This less expensive, faster method of repair has saved more than $1 million on one part alone. The F/A-18's Aircraft Mounted Accessory Drives (AMADs) cost approximately $168,000 each. Damage to one part of the AMAD would previously result in scrapping the entire drive, but with the repairs available through cold spray, 10 have been refurbished and sent back to the fleet for a savings of about $1.6 million.

To bring the process to naval aviation, Macy worked with engineers at FRCSW to explore different options. The team brought an Inovati machine to its laboratory environment three years, and its success led to installation of another machine in the production shop at FRCSW in December 2015.

FRCSW is the main depot for all variations of the F/A-18, so most of the parts it has repaired using cold spray have been for that platform. However, it has also been used for E-2, F-5, CH-53 and H-1 parts, as well as for the LM2500 ship engine.

Engineers now are pressing forward with future applications for the technology, including on V-22 window sills. Macy is exploring through another SBIR the use of a rotating nozzle in the cold spray machine. The current machine has a fixed nozzle, which works well for easily rotated parts, but not as well for bulkier ones. Though that change requires a hitherto unknown design, the engineers have no doubt they will determine the necessary techniques.

"We're going to be successful," Macy said.

Source : US Navy