Chad Duty, Associate Professor of Mechanical, Aerospace and Biomedical Engineering at the University of Tennessee, wants to create a world of stronger, lighter and cheaper products. From the moment he first saw a 3D printer in action in the mid 1990’s, he set himself on the course to change the way products are designed and manufactured. Additive manufacturing (3D printing) puts new material only where it is needed, which allows manufacturers to create complex shapes and take full advantage of material properties with less waste.

Traditional manufacturing approaches for a typical Lockheed Martin F-22 Raptor result in a buy-to-fly ratio of 11:1. That means 11 times as much material must be purchased to create the plane than actually flies on the plane after construction. The traditional “subtractive manufacturing” approach starts with large chunks of raw materials, and cuts away any waste material that’s not part of the final geometry that performs the function – similar to a sculptor chipping away at a big granite block. For the Raptor, that translates into buying over 110,000 lbs of raw stock titanium to produce 10,000 lbs of final components that go on the plane – resulting in over 100,000 lbs of waste with every plane. While material cost is only part of the F-22’s $132 million price tag, that’s still a massive amount of wasted raw material to make one aircraft.

 3D printing technology has grown rapidly over the course of the last decade. Researchers and engineers have designed increasingly complex parts and more people have access to 3D printers than ever before. There are three F’s in 3D printing; form, fit and function. Form is in reference to how the part feels, fit to how the part fits with other parts of the assembly, and function is about how well the part actually works. As the accuracy of printers has improved over the years, control over the shape and geometry of a part (form and fit) have been demonstrated.  So Duty’s research is focused primarily on the final frontier of functionality; printing components that not only work in the real world, but combining 3D design with advanced materials to accomplish things that plastics have never done before.

Although it will likely be decades before we’re directly printing an F-22 Raptor, Duty has partnered with the Oak Ridge National Laboratory to develop high temperature carbon-fiber reinforced plastics that can be used in the manufacture of advanced composite parts for the aerospace industry.  If his research is successful, both the time and cost to produce such complex composite parts can be decreased by an order of magnitude.  

Specifically, Duty’s team is working to identify the fundamental properties of a material that make it “printable” on a 3D printer. Not all plastics can simply be melted and extruded on a 3D printer, especially when considering high performance plastics that can operate at elevated temperatures and contain fiber reinforcements. Duty’s “Printability Model” is based on the fundamental viscoelastic and rheological properties of these materials (i.e. how the material squishes and flows) to identify the appropriate conditions for 3D printing and the effect that additives like carbon and glass fiber might have on the final part performance. This type of insight is critical for companies that are advancing the uses of 3D printing: from material suppliers, to printer manufacturers, to end users such as Boeing.

The future of this research includes:

●      “Printability” Model: A model that shows engineers what materials (polymers & composites) can successfully be 3D Printed based on fundamental measurements.

●      Liquid Nails: A patent-pending approach for 3D Printing that uses “liquid nails” to improve the bond between printed layers. This has traditionally been the weakest link in 3D printed structures.

●      Controlling Distortion: As plastic solidifies, it shrinks. For 3D printing, this produces a large amount of distortion, especially for large parts. Duty’s research is working to change the print paths and the local material composition to develop methods for controlling distortion in a printed part.

●      High Temperature Tooling: Aerospace and automotive companies use large and complex molds (or “tools”) to define the shape of composite parts, which are formed at high temperatures and pressures in a device called an autoclave. In collaboration with ORNL, Duty’s group is using the high temperature materials they’re developing to print and test these tools for production, cutting the time and money required for making components significantly.

●      Fatigue Life: Several applications where 3D printing of metals is attractive are limited by fatigue behavior.  Duty’s group has been investigating how different printing conditions affect the microstructure of the material, and how this in turn affects the fatigue life of high performance titanium parts.

3D printers make artistic designs on a computer come to life, but the technology is limited. Traditionally, the products made by 3D printers are relatively flimsy and don’t have a great deal of strength and durability. Chad Duty, Associate Professor of Mechanical, Aerospace and Biomedical Engineering at the University of Tennessee, is experimenting with high temperature carbon-fiber reinforced plastics to make stronger, lighter and cheaper products than can be used to create anything from a Boeing 777 airplane to a Shelby Cobra sports car.