At Purdue University, Indiana, Professor Jeffrey Rhoads, assistant professor Emre Gunduz and colleagues have been leading research into 3D printed propellants, pyrotechnics and solid rocket fuel. Termed “energetic materials”, this focus has led the group to launch their own faculty spin off company, Next Offset Solutions Inc., focusing on overcoming emerging challenges in national security, defense, and energy.
Next Offset Solutions’ most recent development is high-viscosity 3D printing, as recently discussed in Additive Manufacturing journal.
“It’s like the Play-Doh press of the 21st century,” explains Professor Rhoads.
“We have shown that we can print these energetic materials without voids, which is key. Voids are bad in energetic materials because they typically lead to inconsistent, sometimes catastrophic, burns.”
As explained by Purdue PhD candidate Monique McClain, the university is renowned for its excellent propulsion program, encompassing several centers of excellence for advances in aerospace. Previously, this program has overseen the development of FDM 3D printed reactive material, and inkjet 3D printed “functional materials” which are both projects of new company Next Offset Solutions Inc.
Published online in November 2017, the group’s inkjet project succeeded in 3D printing thermite, a non-explosive pyrotechnic metal powder commonly used by the military in hand grenades used to partially destroy equipment, and stealth operations.
With high-viscosity 3D printing, the group unlocks a new potential method for fabricating some of the most challenging energetic materials.
High viscosity 3D printing
Viscous materials are incredibly challenging to process via 3D printing. This, explains assistant professor Gunduz, is due to friction, “It’s hard to print those kinds of materials, especially at very high rates, and high resolution because of issues with the nozzles. You can’t really push them through […] The problem there is the friction.”
The group’s high viscosity 3D printing methods works to dispel the friction between a thick material paste and its extrusion nozzle. This is achieved by adding an ultrasonic probe to the nozzle which vibrates, separating the material from the walls of the nozzle and allowing it to “snake” through.
According to Gunduz, “The results were really striking because its a new diagnostic. Nobody has characterized a viscous flow in a channel like this.”
The path to commercialization
As a proof of concept, the team successfully 3D printed a range of viscous materials using this method, including a metal-polymer composite, clay, and fondant icing. With potential cross-industry applications, in electronics, biomedical devices, pharmaceuticals and explosives, the method has now been patented, and the team continues to investigate new potential materials.
A paper discussing the approach titled “3D printing of extremely viscous materials using ultrasonic vibrations” is published online in Additive Manufacturing journal. It is co-authored by I. E. Gunduz, M. S. McClain, P. Cattani, G. T.-C. Chiu, J. F. Rhoads and S. F. Son.
Through Next Offset Solutions, the method is offered as part of the company’s R&D capabilities. Still in the early stages, its vision is “To serve as a recognized, trusted authority capable of solving the emergent technical challenges of the national security and defense sectors.”
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Featured image shows Monique McClain, Purdue PhD student, and the group’s high viscosity 3D printer. Photo via Purdue University