Challenges in Additively Manufactured Thermoset Continuously Reinforced Composites

Continuously-reinforced composite additive manufacturing (CC-AM) is set to revolutionize the manufacturing and design of high-strength, low-weight structures. Longitudinal tensile strengths of CC-AM have been reported exceeding 1500 MPa with minimal porosity, making this system a candidate for scale-up and structural applications. However, there remain a number of morphological non-idealities that are unique to the CC-AM process that limit the performance of a complex AM build. These can be categorized into material non-idealities (fiber clustering, resin-rich zones, matrix quality) and topological constraint non-idealities (joint design constraints, minimum path radius, tow cuts). Furthermore, for UV snap-cured carbon fiber CC-AM, limited penetration of the UV radiation through the carbon fiber tow presents a challenge to achieving optimal in-situ curing. The present work lays out these challenges both in a general sense, with specific case examples for material built with the CF3D system (Continuous Composites Inc.) using T-1100 12K carbon fiber tows and a UV snap curing acrylate resin. Most of the issues highlighted are inherent to CC-AM, and so most of the recommendations for future development to mitigate the various non-idealities are expected to translate to other CC-AM technologies, such as those employing a thermoplastic polymer matrix.