Most everyone in the 3D printing industry is well aware that the future for high quality components seems to be in metal 3D printing. With that in mind, researchers have been steadily refining the process, and now a team at Northwestern University has come up with a process that even allows the use of inexpensive rust powder, which is more lightweight, offers greater stability, and is safer and more affordable in comparison to other iron powders.
Findings regarding this new process were recently discussed in a paper, ‘Metallic Architectures from 3D-Printed Powder-Based Liquid Inks,’ by Adam E. Jakus, Shannon L. Taylor, Nicholas R. Geisendorfer, David C. Dunand, and Ramille N. Shah, just published in Advanced Functional Materials. These researchers have discovered a way to create new and complex metallic architectures via 3D printing with a new class of inks that will extend to a range of metals and mixtures, alloys, oxides, and compounds.
“This is exciting because most advanced manufacturing methods being used for metallic printing are limited as far as which metals and alloys can be printed and what types of architecture can be created,” said Dr. Ramille Shah, assistant professor of materials science and engineering in the McCormick School of Engineering and of surgery in the Feinberg School of Medicine, who led the study. “Our method greatly expands the architectures and metals we’re able to print, which really opens the door for a lot of different applications.”
With the new process, researchers are able to skip numerous time intensive and expensive tasks from relying on lasers or beams, to eliminating the need for a metal powder bed. The inks are created in any size volume from small to large as solvents, powders, and a biomedical elastomer called polylactic-co-glycolic acid (PLGA) are mixed together.
“The resulting 3D-printed green-bodies can be handled immediately, are remarkably robust, and may be further manipulated prior to metallic transformation,” state the researchers in their paper. “Green-bodies are transformed into metallic counterparts without warping or cracking through reduction and sintering in a H2 atmosphere at elevated temperatures.”
Beginning as a liquid, this new 3D ink is quick to become a solid as printing progresses through a simple syringe-extrusion process at room temperature. The new process is well-suited for making structures of any size (referred to as ‘green bodies’) that can be handled directly after printing.
“We used a biomedical polymer that is commonly used in clinical products, such as sutures,” Shah explained. “When we use it as a binder, it makes green bodies that are very robust despite the fact that they still comprise 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 3D 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.”
The use of a furnace is another part of what makes this process so unique, and allows for uniform temperature that logically allows for uniform components without defects or problems often encountered like warping or cracking. Basically, the only thing limiting size of the prints is the size of the furnace. Many extrusion nozzles can be used at once (as opposed to one laser on a powder bed) to print extremely large sheets.
“To me, as a metallurgist, I’m amazed that the structure does not deform or break apart, despite shrinking extensively during densification,” Dunand said. “That is not something that I see often.”
With oxides such as rust that are then turned into metal via a reduction process, manufacturers should see numerous benefits.
“It might seem like we are needlessly complicating things by adding a third reduction step where we turn rust into iron,” Dunand said. “But this opens up possibilities for using very cheap oxide powders rather than corresponding expensive metal powders. It’s hard to find something cheaper than rust.”
The team sees this process as being conducive for the fabrication of items such as:
- Solid-oxide fuel cells
- Medical implants
- Mechanical parts for larger structures like rockets and airplanes
- Onsite manufacturing of components
This process should be garnering a great deal of attention from those interested in 3D printing with metal as it offers such an expansive application as well as versatility, considering that 3D models can be built with inks made from both single and mixed oxide powders–and this can be done with over two dozen different metal-based materials. While many have seen a new world opening through metal 3D printing, this new process shows the potential to expand it substantially further. Discuss the future of 3D printing in the Innovative 3D Ink forum on 3DPB.com.
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