Infusing reinforcing fibers into raw material is a key to scaling up 3-D printing to large parts—60-100 ft. in size—for aerospace. ORNL calls this broad-area additive manufacturing, and the lab has been working with Lockheed Martin and an equipment manufacturer to develop the capability, initially to produce low-cost tooling but ultimately to print structures such as the wings of a large unmanned aircraft.
Large printed parts can warp because areas with different thicknesses cool at different rates—a core technical challenge with additive manufacturing. Adding 13% by volume of chopped carbon fiber to the thermoplastic-pellet feedstock provides twice the strength and four times the stiffness, and stops parts-warping as they cool, says Love.
As a next step, ORNL is working with an equipment supplier to build the prototype of a single machine that will print plastic parts, machine them to final shape and wrap them in re-inforcing carbon-fiber tows to produce large structural components.
“We work with the equipment makers, because the OEMs want this technology throughout their supply base,” says Craig Blue, director of ORNL's advanced manufacturing program.