AFRL Looks to Fine Tune process of 3D Printing Composite Inks
July 25, 2019
AFRL’s Polymer Matrix Composites Materials and processing research team has been working toward 3D printing complex parts that will be lighter and less expensive for the Air Force. The team has added 100-300 microns long chopped fibers into the polymer. The chopped fibers for producing a structure with continuous fibers will have high and equal distribution, reducing cracks in the structure, one of the team’s main objectives. Withstanding higher operating temperature is another objective.
“If we could print something and then add some type of surface finish, in theory it would take less time and be less expensive,” said Andrew Abbott, PMC M&P team member.
It was tested and found that when the polymer is agitated or shaken up, the substance in the epoxy breaks down and it becomes more of a liquid. When 3D-printed to make an object, it sets or gels, much like toothpaste. The beads that exit the printed nozzle are laid down so that they fuse together. Once a layer of the beads is laid down, another layer is printed on top of these and the layers fuse together, eventually creating a part with the desired shape.
The laying down of the beads explains why the materials currently used in the 3D-printing process cannot be used for Air Force needs. Thermoplastics are used during typical 3D-printing, which lead to poor bonding between printed layers and cracks in the structure due to a weak cross link of particles. Hence, the team uses thermosets with better fatigue behaviour and mechanical robustness of the resulting printed composite parts. Next, continuous fiber composite parts are created so that the beads are made stronger with equal distribution.
“One of the research team’s visions is to explore and see what’s possible in 3D-printing of composites. Complexity is something that you can do with 3D-printing that you will have a hard time doing conventionally. But to make this happen we need to understand the detailed physics and chemistry that is happening during the process,” Dr. Hilmar Koerner, PMC M&P research lead, explained.
The team has partnered with National Synchrotron Light Source II at Brookhaven National Laboratory to further examine the parts they produce, in order to better understand why composites fail between beads and layers.
An X-ray beam is produced using Brookhaven’s 11-1D beamline instrumentation to collect data at up to 9,000 images per second. The X-ray beam hits the 3D-printed with millisecond time resolution and micron spatial resolution. They look at how fast nano-sized particles flow to see how they align and assemble. It allows the researchers to simultaneously look at the structure and the dynamics of the 3D-printing ink during processing. This way of analysing composite inks is the first of its kind.
“This study in particular highlighted the use of this technique of real-time ‘visualization’ of nanoscale ordering and mobility inside materials during 3D-printing, which is an exciting capability that will likely be applied more routinely in the future,” Lutz Wiegart, beamline scientist at Brookhaven National Laboratory said.
Source: Wright-Patterson AFB