During a polymer-additive manufacturing technique called laser sintering, a high-temperature laser is run across a bed of polymer powder to form a pre-designed, computer-generated shape. This process is repeated multiple times with new layers of powder and laser energy until a 3-D part is complete.
While experimenting with high-temperature polymer resins, Koerner and his team found that the polymers printed well, but when they removed the pieces from the powder bed for post-processing, the material would essentially “melt into puddles,” proving useless.
To counteract this issue and better enable molecules to entangle and form a shape under the heat of the laser, Koerner suggested adding carbon fiber filler to the resin material as a means of enabling better energy transfer from the laser to the matrix. The carbon fiber would cause the laser to heat the material much faster by absorbing the laser energy and conducting heat much faster than with the polymer alone.
As a result, the researchers successfully printed high-temperature polymer composite sample pieces in multiple configurations, in what, to their knowledge, are the highest temperature capable, polymer composite parts made by additive manufacturing to this day.
“High-temperature materials are notoriously hard and expensive to process, even using conventional manufacturing techniques,” said Dr. Jeffery Baur, a principal materials engineer at AFRL. “Since they typically wind up being used in military specific applications, there is not a large supplier base for these types of materials. This breakthrough will enable us to additively manufacture high temperature, composite parts in a cost-efficient manner. Moreover, high temperature polymer composite parts that are small and have complex features will be extremely beneficial and advantageous not only for the Air Force but have the potential to be a game-changer throughout industry.”
The team successfully printed a number of test coupons and brackets with the novel material and plan to demonstrate the ability to print larger parts as the next step in their process. Preliminary test data indicates that the material can withstand elevated temperatures, but further testing and qualification of the material is needed prior to implementation on Air Force platforms.
Nevertheless, this is a significant breakthrough in additive manufacturing with huge, cost saving benefits for the Air Force over the long term.
“This is a high, value-added capability for the Air Force,” said Baur. “We are excited about this breakthrough and look forward to seeing the impacts over the future.”