The 28th Maintenance Group Additive Manufacturing Flight at the Ellsworth Air Force Base conducted its first restoration of an active flying aircraft in May and repaired an overwing faring slip joint using metal cold spray (kinetic consolidation) technology. The very first demonstration of on-aircraft structural repair using metal cold spray AM technology had been conducted successfully at the USAF base in September 2019.
In this first application on an active aircraft, the slip joint had to be repaired to enable vertical movement within the wing contours, both up and down. In the same manner, of which a hinge holds a door in position as it is opened and closed, the slip joint does a similar job for the B-1’s wings.
“During cold spray, we used helium gas to accelerate the particles to a speed of Mach 3,” said Brian James, the 28th MXG additive manufacturing chief engineer. “Upon impact, the particles become the substrate, forming a strong mechanical bond.”
In 3dpbm Research’s comprehensive market report on the Metal AM Market Opportunities and Trends, cold spray technology is considered part of the family of cold consolidation metal AM technologies, which also includes ultrasound consolidation by Fabrisonic and friction consolidation (based on friction stir welding) by MELD Manufacturing. Promoted by Australian companies SPEE3D and Titomic, as well as German company Impact Innovations and US-companies VRC Metal Systems and in development at GE Additive, cold spray technology is currently the most market-ready (although UAM has been available even longer) and is gaining widespread adoption especially for use in the armed forces for on-demand and even in-the-field repairs.
What normally takes weeks or months of time to order, ship and remove the old component and install the new part, can now be done in mere hours or days by using cold spray technology, said James. Annually, the Additive Manufacturing Flight saves the Air Force approximately $2 million.
“The only other alternative to fixing the slip joint, if we didn’t use cold spray, would be to remove and replace the part, which would cost roughly $500,000 and [take] 8 weeks to remove,” added James.
The 28th Bomb Wing established the Air Force’s initial field-level additive manufacturing flight in 2019, which utilizes new technologies that are cost-effective and can restore aging aircraft components. Using the cold spray process saves time and cuts costs by roughly 98% compared to the original method of replacing aircraft parts.
For the past seven years, Ellsworth worked alongside VRC Metal Systems, a company that specializes in the manufacturing of cold spray machinery, cold spray-related process work development and research, and development of new cold spray applications for government and commercial applications. During this time, the VRC Raptor Cold Spray machine was developed and helped the base accomplish part restoration historical feats.
“We spent a lot of time and effort designing this system,” said Rob Hrabe, the VRC Metal Systems chief executive officer and co-founder. “Seeing it used on an aircraft that can benefit from such cost savings and time improvement makes all of the effort over the years worth it.”
In the very first demonstration cold pray application at Ellsworth, that took place less than two years ago, the 28th Maintenance Squadron Additive Manufacturing Rapid Repair Facility repaired simulated corrosion damage on the wing of a B-52 Stratofortress static display at the South Dakota Air and Space Museum using the GEN III High-Pressure Cold Spray unit.
This event began as just an idea to see how the rapid repair section could improve cold spray repair procedures. In the past, corrosion would be blended out, then painted over. During a Cold Spray repair, the corrosion is removed through the previous procedure, then filled in with the aluminum material. Once filled, technicians sand down the new aluminum until it is flush with the original surface.
The entire procedure demonstrated different ways cold spray can be used. It also showed that the GEN III, manufactured by VRC Metal Systems in Rapid City, can be transported to any aircraft. Additionally, the ability to move this system allows technicians to work on the aircraft in a safe and productive manner.
Numerous agencies collaborated to complete this first-of-its-kind repair on the B-52, such as VRC Metal Systems, Air Force Life Cycle Management, the University of Dayton Research Institute, the South Dakota School of Mines and Technology, and the Army Research Lab. Additionally, units from Ellsworth, including the 28th Medical Group Bioenvironmental flight and 28th Civil Engineer Squadron units collaborated on this effort.
Together, these organizations acquired a variety of data, including air samples, during the procedure. This will aid the Air Force in determining what is required to do future on-aircraft Cold Spray repairs on the flight line.