In thermoplastic AM, the bonding between layers of a composite may not be strong because the material is heated up for printing and quickly cools down. Celik’s thermoset AM process delivers a more isotropic result; the printing “ink” is composed of nanoclays or silica, mixed with a thermoset resin and then with the carbon fibers right at the nozzle. “It becomes a gel type of material, and when you extrude it on a surface it has enough strength to keep its shape,” he explains. The gel in each layer fuses well to the layer underneath, and when the part is completed, it is put in an oven to cure overnight.
The isotropic properties are also improved because of the use of the shorter carbon fibers. During the extrusion process, the fibers in the printing ink tend to align in the direction of the printing, reducing the strength in other directions. Since the shorter fibers don’t align as much as longer ones, the thermoset composites in Celik’s process show 80% strength in the transverse direction.
With all of these changes, Celik realized an impressive improvement in the carbon fiber content of the printed thermoset composite. “Instead of 5% to 6% fiber, we could now fabricate materials with 46% carbon fiber by volume,” he explains. The material is as strong as metal, but 80% lighter than steel and 50% lighter than aluminum.
Celik believes the lightweight thermoset composite parts produced through this AM process will be able to replace heavier metal components. In addition, with 3D-printed composites, aircraft manufacturers could re-engineer components. Only the parts that require structural integrity have to be solid; in other areas, honeycomb configurations could be used to further reduce an aircraft’s weight.
Several Department of Defense agencies have already expressed an interest in Celik’s work. While aerospace may be the first industry to use the technology, he sees additional applications in transportation and other industries, especially if the cost of producing carbon fiber can be reduced.
From 3D printing to advances in materials, the variety of R&D going on today reflects the many possibilities that composites offer for aircraft and spacecraft of the future.