Video: Purdue Team 3D Prints Highly Viscous Materials

A method for 3D printing highly viscous materials through extrusion could improve the manufacture of solid rocket fuel among other applications.

A Purdue University team has created a method to 3D print extremely viscous materials with the consistency of clay or cookie dough. This technology advance could be used for manufacturing solid rocket fuel, dental implants, pharmaceuticals and more. 

According to Emre Gunduz, assistant research professor of mechanical engineering, thermoplastic extrusion is the most common form of 3D printing but it doesn’t allow for printing high-strength materials such as ceramics and metal composites. “But the precursor for these materials are extremely viscous, and normal 3D printers can’t deposit them, because they can’t be pushed through a small nozzle,” he says. 

Most proposed solutions to this problem involve changing the composition of the materials themselves.  However, Gunduz’s solution is to apply high-amplitude ultrasonic vibrations to the nozzle itself.  “We found that by vibrating the nozzle in a very specific way,” says Gunduz, “we can reduce the friction on the nozzle walls, and the material just snakes through.”  Gunduz and his team have been able to print items with 100-micron precision using this method.

In order to visualize and study the process, team traveled to Argonne National Laboratory, outside Chicago, to conduct high-speed microscopic X-ray imaging. They were able to see inside the nozzle, and precisely measure the flow of the clay-like material. “The results were really striking,” says Gunduz. “We were able to quantify the flow, and understand how our method was actually working.” 

See footage of the process in the video below:

The research is being conducted at Zucrow Labs, the largest academic propulsion lab in the world. As such, the first practical application being explored is for solid rocket fuel.

“Solid propellants start out very viscous, like the consistency of cookie dough,” says Monique McClain, Ph.D. candidate in aeronautics and astronautics. “It’s very difficult to print, because it cures over time, and it’s also very sensitive to temperature. But with this method, we were actually able to print strands of solid propellant that burned comparably to traditionally cast methods.” McClain tested the combustion by printing 2-cm samples, igniting them in a high-pressure vessel (ranging to 1,000 psi), and analyzing slow-motion video of the burn.

For solid rocket fuels, 3D printing offers the opportunity to customize the geometry of a rocket and modify its combustion. “We may want to have certain parts burn faster or slower, or something that burns faster in the center than the outside,” says McClain. “We can do that much more precisely with this 3D printing method.”

Beyond rocket propellants, Gunduz imagines numerous uses for this new viscous material printing process, including customized dental crowns made out of ceramics and personalized drugs. 

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