Effects of nozzle design on CFRP print quality using Commingled Yarn

Additive Manufacturing with Continuous Fibers (AM-CFRP) results in products with high strength/stiffness at low mass. As such the process holds great promise to be part of obtaining goals in fuel economy for automobiles and aircrafts. AM is able to create products with highly complex 3D geometries, not possible with other production processes. However, there are still many drawbacks to AM process variants with continuous fibers like shape limitations and high void content and low delamination resistance in the printed product. At the University of Twente research has been dedicated on using commingled yarns as a feedstock for AM-CFRP. Before using the yarn, pultrusion is used to transform it to a consolidated filament, which allows for using a FDM-type deposition setup in the AM-CFRP process. The resulting filaments thermal and mechanical properties differ from standard AM-CFRP feedstock, affecting process settings and deposition results. This paper describes the research on the interaction between feedstock, nozzle design and print settings on microstructure, mechanical performance and dimensional stability of extruded feedstock and printed products. It is shown that nozzle designs developed for thermoplastic materials function suboptimal and that the nozzles to be designed should be conceptually different regarding shaping, heating and depositing the filament.