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NPS researcher explores 3D printing with extremely viscous materials

A recent addition to NPS' Department of Mechanical and Aerospace Engineering, Dr. Emre Gunduz continues his research into cutting-edge, direct-write 3D printing with extremely viscous materials.

Dr. Emre Gunduz arrived at NPS in July, ready to continue his cutting-edge work with the 3D printing of extremely viscous materials. This work is the culmination of two years of research and testing completed by Gunduz and his colleagues at Purdue University, where they set out to find a way to improve the flow of extremely viscous materials (for comparison, think the consistency of cookie dough) in direct-write 3D printing.

Generally, direct-write 3D printing uses either pliable materials - such as clay - which are then pushed through a syringe via piston or compressed air, or works via thermoplastic extrusion, in which meltable polymers (such as polylactic acid) are pushed through a heated nozzle in order to form pre-programmed shapes.

As such, both types of direct-write 3D printing depend on the ability to get the materials through the printer’s nozzle—and to get them through at a regulated rate in order to produce an accurate, consistent end product. This can be problematic in projects that require finer nozzle sizes, since smaller sizes mean more restriction when it comes to the flow of printing material. The increased pressure required to remedy this causes friction, which causes excessive heat. This, in turn, alters the flow, often negatively affecting the precision with which one can operate the printer. As a result, achieving high resolution products becomes difficult, and using these systems on materials that are sensitive to heat or friction is extremely problematic.  

The latter issue is one with dire implications for military organizations looking to capitalize on the convenience and potential cost-savings that 3D printing can offer. In defense industries, this is especially true in the case of one of the viscous materials that Gunduz’s method was designed for and tested on: solid propellants (such as those used in missiles and the booster rockets for the space shuttle).

In order to avoid the heat (and consequent thermal excursions) that would be produced by increased friction during the 3D printing of the viscous materials that make up these propellants, Gunduz devised a method to apply ultrasonic vibrations to the nozzles of 3D printing devices, using transducers to resonate in such a way that it separates the viscous materials from the nozzle walls and allows them to flow, unobstructed, through the nozzle.

According to Gunduz, “Everything is arranged so that the resonating frequency of the system is matched, to get the optimum amount of vibrations.”

These high-frequency, ultrasonic vibrations (about 30 kilohertz or 30,000 times per second) push on the inner walls of the nozzle. By using this technique, Gunduz can apply an acceleration of about 60,000 Gs in the nozzle, which creates a force great enough to pull the printing material off the surface of the nozzle walls. The detached materials then move around the nozzle in a step-wise motion, exiting it without necessitating increased pressure and the resultant friction and heat that accompany it.

Gunduz’s method is a game-changer in several ways. It will allow for the printing of viscous materials in existing high-performance systems that previously lacked the ability to print these materials. Additionally, the control and accuracy that are now available when printing these materials allow for the printing of arbitrary shapes—an especially advantageous function in the case of solid propellants, which can now be geometrically designed in ways that produce a more directed and controlled burn.

Similarly, Gunduz proposes that other applications have much to offer in the customization and optimization of military uses of the technique. For example, in the case of missile use, it would allow personnel to print the exact amount of propellant needed for mission requirements, thus eradicating waste and stretching often strained budgets even further. On a Navy vessel, where everything is at a premium, use of the system could increase efficiency by eliminating the need for the storage of propellant in excess of what is specifically required for a particular mission. On long deployments, the printer’s other potential capabilities—such as the printing of biomedical devices, food, and personalized pharmaceuticals—could also contribute to improvements in operations and streamlining of current systems.

As one of the newest members of NPS' Department of Mechanical and Aerospace Engineering, Gunduz will be continuing to develop materials that are most suitable to this approach to 3D printing. He is currently planning on offering courses focused on this type of manufacturing, with the possibility of developing a certificate program at NPS. Gunduz believes this will be an important addition to NPS' training offerings—especially as 3D printers become more commonly used within the military. As such, he is looking forward to training and collaborating with the greater NPS community: “My goal is to train the students on these so they know what’s going on, how they can use these systems, and how they can improve them through research work.”

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