On April 28, 2024, it is reported that a student team called AeroForge at Rice University in the United States had developed a cold spray metal 3D printing device. The device relies on pressure and speed (rather than temperature) to manufacture metal parts, which helps to significantly reduce costs and improve the quality of manufacturing or repairing one-time complex metal parts, thereby expanding the scope of metal additive manufacturing technology.
Why is this $5,000 a disruptive price? Antarctic Bear learned that Titomic, a cold spray metal 3D printing manufacturer based in Melbourne, sold its flagship product, the high-pressure cold spray system, to Sabanci University in Turkey for A$2.4 million (US$1.6 million) in the first half of 2024.
At present, they have successfully used the device to deposit copper and proved the feasibility and potential of this prototype. The project won the "Excellence in Capstone Engineering Award" and first place in the annual "Willy Revolution Award for Outstanding Innovation." In addition, the AeroForge team's project also won this year's Hershel M. Rich Invention Award, which is given to students or faculty in the Rice University Department of Engineering in recognition of their original inventions.
College students develop new cold spray metal 3D printing equipment.
Team members pointed out that traditional metal 3D printers generally use lasers to melt metal powder into a specific shape, but melting can affect the performance of the product. Cold spray technology has been used for coating, which uses speed instead of heat, basically rapidly accelerating metal particles so that they adhere to the substrate and deform. The system designed by the team aims to achieve this goal through 3D printing technology.
Applications of the device include manufacturing and repairing complex metal parts, such as those used in industrial assembly lines, vehicles, or aircraft. Industries that rely on metal parts, such as automobiles, oil and gas, and defense, will suffer significant losses due to supply chain disruptions. The team hopes that its device can provide a viable, low-cost alternative for manufacturing or repairing parts on demand.
Team member Davis Thames first proposed the idea of using a cold spray metal 3D printer to his teammates nearly a year before the start of Rice's senior design class and explained the advantages of using this technology over welding. "Typically, repairs can only remove material as you reshape the metal part," he said. "With this process, you can add material and then work it back. In welding, for example, different melting temperatures can cause uneven material properties. This equipment doesn't have that problem."
The equipment includes a gas tank that delivers high-pressure nitrogen to the system; a controller that adjusts valves and monitors pressure and temperature; a pressure vessel that heats the gas to 450°C (842°F); a powder feeder that injects metal powder into the nozzle at a precise rate; and a custom nozzle.
Team member Julianna Dickman explained: "While the gas does get heated, it's still a cold spray system because, when the gas meets the metal powder in the nozzle, the gas expands out of the nozzle and cools rapidly, while the metal powder doesn't melt or is affected by the temperature. The temperature only increases the gas's velocity, which transfers its momentum to the metal powder, which can then accelerate to our substrate and attach to it."
Challenges and innovations faced
A lot of the team's efforts focused on reducing costs, as many metal 3D printers cost more than $1 million. The AeroForge team built their device for less than $5,000.
In addition to reducing costs, the team has made important progress in safety and technological innovation. They use internal processing to manufacture parts, such as pressure vessels and nozzles, to reduce costs and ensure the availability of specific parts. The team also worked with Rice University's Environmental Health and Safety Department to ensure that technical testing meets safety guidelines and implemented a complex monitoring system and data recording system to ensure safety. In addition, the team conducted multiple safety checks and performed a large number of code iterations to ensure the effective operation of the equipment.
Tungsten carbide and spraying technology
The application of tungsten carbide (WC) in the field of 3D printing is mainly concentrated on thermal processing technologies such as binder jetting and laser melting deposition, because these technologies can better handle the high melting point and hard and brittle characteristics of WC materials.
In contrast, cold spray technology (Cold Spray), as an additive manufacturing method that does not rely on thermal energy to melt materials, is based on the principle of using high-speed airflow (usually exceeding the speed of sound) to accelerate solid particles to a high kinetic energy state, and then impact the surface of the substrate to form a tightly bonded coating. Since it does not involve the melting process of the material, cold spraying is very challenging for materials such as tungsten carbide that have an extremely high melting point (about 2870°C) and are hard and brittle.
Nevertheless, with the continuous advancement of cold spray technology, especially the in-depth study of particle acceleration mechanism, particle-substrate interaction and post-processing technology, the application of tungsten carbide in cold spraying has gradually shown its potential, especially in the field of surface coating and repair. In order to effectively use tungsten carbide in cold spraying, it may be necessary to:
Nanonic or micronized WC particles: Reducing the particle size can increase the particle's deformability and help achieve better bonding at low temperatures.
Pretreatment and post-treatment techniques: Use appropriate substrate pretreatment and post-coating heat treatment methods to improve the bonding strength between the coating and the substrate and the overall performance of the coating.
Composite material preparation: Form a composite powder with WC and other metal or alloy materials that are easy to spray (such as nickel, cobalt, etc.), and use these materials as a bonding phase during the cold spray process to promote the effective deposition and bonding of WC particles.
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