Rice University students in Houston, Texas, have developed a cold spray metal 3D printing device that relies on pressure and velocity rather than temperature to create a metal part. Their work could help expand the repertoire of metal additive manufacturing techniques, bringing down cost and enhancing the quality of making or repairing one-off complex metal parts.
Team AeroForge members used the device to successfully deposit copper, demonstrating the viability and potential of their prototype. The project won an Excellence in Capstone Engineering Award and first place in the Willy Revolution Award for Outstanding Innovation at the annual Huff OEDK Engineering Design Showcase in April, 2024.
Team AeroForge’s project is also the recipient of this year’s Hershel M. Rich Invention Award, presented to Rice engineering students or faculty members for “original invention development.”
“Traditional metal 3D printers generally use a laser to melt metal powder into a particular shape, but melting can really impact the properties of your product,” said Aasha Zinke, student team member. “Cold spray technology, which has been used for coatings, uses velocity instead of heat, basically accelerating metal particles so fast that they adhere to and deform onto a substrate. The system that we’ve designed aims to accomplish that in a 3D printing capacity.”
There are advantages of using the cold spray metal 3D printer over welding. “Typically, with repairs, you can only remove material as you reshape a metal part,” said Davis Thames, who first pitched the idea for the project to a teammate almost a year prior to the start of the senior design class. “But with this process, you can add material and then machine it back down. With welding, for instance, varying melting temperatures may result in uneven material properties. We don’t have that issue with this device.”
The device consists of a gas tank that feeds high-pressure nitrogen gas into the system; controls that regulate valves and monitor pressure and temperature; a pressure vessel that heats the gas to 450 Celsius (842 Fahrenheit); a powder feeder designed to dispense metal powder into a nozzle at a precise rate; and a custom nozzle.
While the gas does get heated, it is still a cold spray system because when the gas meets powder in the nozzle, it is expanded out of the nozzle and cools very quickly. The particles never melt; they really never see temperature ⎯ the temperature only serves to increase the speed of the gas, which imparts its momentum on the metal powder, which can then accelerate to the substrate and adhere.
A lot of the team’s efforts were focused on reducing costs since most metal 3D printers can cost over $1 million. Team AeroForge built its device for less than $5,000. One of the biggest innovations was making the system less expensive, machining many of its parts in-house, for instance, the pressure vessel, because it is potentially dangerous. Other parts, like the nozzle, are proprietary and couldn’t be found elsewhere. The nozzle was very difficult to manufacture and the team had to develop new processes to make it.
Metal powders are dangerous if inhaled, and working pressurized gas also adds another layer of safety considerations. The team worked with the environmental health and safety department at Rice to make sure it abided by all guidelines during testing. One of the safety specifications is that no one is allowed to be in the room while the system is in operation. To ensure safety, the team implemented a complex monitoring system and a three-part data logging system.
The team also implemented many security checks. For example, there’s a hierarchy in which the switches can be opened. Communication with the device is done wirelessly, which required a lot of code iteration to make sure it that works effectively.
Image – A student working on the prototype. Courtesy of: Gustavo Raskosky/Rice University.
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