The U.S. Army Combat Capabilities Development Command Army Research Laboratory (CCDC-ARL) has awarded $25 million to the Worcester Polytechnic Institute (WPI) to continue developing and advancing a cold spray 3D printing technique which could have applications repairing vehicles and military equipment in the field.
With a strong background and experience in powder metallurgy and computational tools for materials design—as well as the $25 million in military funding—WPI is well positioned to disrupt metal AM research for defense applications. Interestingly, this is not the first time the university has received significant funding from the Army, as it previously received nearly $30 million to develop projects in the same area.
The recently announced $25 million will specifically support a research endeavor focused on cold spray additive manufacturing. The technique essentially builds up layers of metal out of metal powder by using pressurized gas. The gas causes the metal powders to accelerate to near supersonic speeds, the impact of which causes the metal particles to adhere to the metal substrate (or preceding printed layer).
Because the cold spray AM technique does not rely on melting or fusing metal powders, the process is more versatile and can even be reduced to a portable applicator, facilitating its use in the field for repairs and such.
“The Army is interested in cold spray 3D printing as a repair technique,” explained Danielle Cote, assistant professor of materials science and engineering and director of WPI’s Center for Materials Processing Data, the principal investigator for the ARL project. “It’s cheaper to repair a part than to replace it, and you get the equipment back in service faster. The Army’s primary interest is unit readiness. If you’re on a mission and need to move quickly to a safer place, and a critical part on your vehicle breaks, you’re stuck unless you can repair it quickly. That’s where cold spray comes in.”
New cold spray alloys
With the Army funding, WPI researchers will focus on developing, characterizing and testing new alloys for cold spray 3D printing. In the cold spray process, the quality and properties of the metal powder are paramount, as the metal does not require melting or heat treatment.
The team will study powders using a set of new tools and equipment bought with the ARL funding, including a scanning electron microscope and energy dispersive spectroscopy unit (SEM/EDS), a synchronous laser diffraction and dynamic image particle analyzer to understand powder morphologies and nanoindenters for measuring nano-scale mechanical properties.
The research team will also collaborate with a number of subcontractors, such as the University of California Irvine, the University of Massachusetts Lowell, Penn State and Solvus Global, a recent spinoff of WPI which will provide commercially available powders that have been modified using thermal processing treatments and other techniques to meet the researchers’ specifications. That is, though the cold spray powders do not need heat treatment, they can be “fine tuned” with the precise application of heat using a method pioneered at WPI.
“This expertise is part of the reason the ARL continues to support WPI,” Cote added. “We have discovered that the properties of metal powders can be significantly enhanced with thermal processing, and that is what we are looking to do with this new award.”
WPI Computational models
WPI has also developed a number of computational models which will facilitate the study of the powders and the thermal processes required to obtain certain properties. The computational models draw from extensive databases of metal properties which were compiled in previous ARL-funded projects at the university.
As Cote said: “You can do this through trial and error, but it is much more effective to design new alloys and thermal processing protocols with our models, and then test them to verify their properties. WPI’s modeling capabilities and experience are what sets us apart from other research teams.”
In the field and beyond
Cold spray additive manufacturing and the ability to custom design cold spray powders could offer huge advantages to the military, as the technology could enable soldiers to repair broken equipment or produce replacement parts on the fly.
The research team highlighted the case of helicopter gearboxes which are need of frequent repairs. “If you need to replace a part like that, it can take months or even years, and the cost is significant—assuming that the part is available or even still being made,” Cote said. “To repair a gearbox with cold spray, you need alloys with high strength, toughness and ductility. Our methodology will enable us to develop powders that can be used to effectively repair or even manufacture parts like that and get helicopters back in the air quickly.”
Though the project has received backing from the U.S. Army, WPI’s cold spray process and metal powders could also have much broader applications, in industrial manufacturing settings and beyond. For instance, WPI is investigating the ability of using cold spray to apply antibacterial copper coatings to equipment as well as exploring the use of multi-axis robots to further automate the process for industrial settings.
“I think there is much potential for this technique,” Cote concluded. “With the work we will be doing with powder development, in robotics, and in a number of other areas, I think we are going to go a long way with cold spray. There really are endless possibilities.”