Northwestern engineers have devised a new two-step method for printing 3-D metals and alloys. The new fabrication process trades in the common large metal powder beds and energy beams for liquid inks and furnaces, creating, what Northwestern Univ. called, a cheaper, faster, and more uniform printing process.
Standard methods of 3-D printing metallic objects use an energy beam, such as a laser or electron beam, which scans a powder bed. Layer by layer, the beam fuses powder particles together. After completion, unfused powder is sloughed away from the 3-D object.
Instead, the Northwestern researchers, who published their findings in Advanced Functional Materials, developed liquid inks comprised of metal or mixed metal powders, solvents, and an elastomer binder. The liquid ink—printed via a syringe-extrusion process—solidifies and fuses with previously extruded material at room temperature.
“We used a biomedical polymer that is commonly used in clinical products, such as sutures,” said Ramille Shah, who is an assistant professor at the McCormick School of Engineering and the Feinberg School of Medicine. “When we us it as a binder, it makes green bodies that are very robust despite the fact that they still comprised a majority of powder with very little binder. They’re foldable, bendable, and can be hundreds of layers thick without crumbling. Other binders don’t give those properties to resulting 3-D printed objects. Ours can be manipulated before being fired. It allows us to create a lot of different architectures that haven’t really been seen in metal 3-D printing.”
After printing, the object is sintered in a furnace. The process, according to the researchers, leads to more uniform structures.
Additionally, the process works on a variety of metals, including metal mixtures, alloys, and metal oxides and compounds. The team believes the method can be used to print batteries, solid-oxide fuel cells, medical implants, and mechanical parts for rockets and airplanes, among other uses.
The team even used iron oxide (rust) in a print. When the green body was produced, they used hydrogen in a chemical reduction step to produce iron.
“This opens up possibilities of using very cheap oxide powders rather than corresponding expensive metal powders,” said study co-author David Dunand, the James N. and Margie M. Krebs Professor of Materials Science and Engineering. “It’s hard to find something cheaper than rust.”