Rapid and scalable additive manufacturing of thermoset polymer composites

Additive manufacturing (AM) has recently been transformed into a robust manufacturing paradigm for rapid, cost-effective, and reliable manufacturing of fiberreinforced thermoset polymer composites. Among various AM techniques, direct ink writing (DIW) technique offers exceptional ability for constructing scalable 3D composite structures with a high resolution and rapid production rates. In the conventional DIW technique, composite parts are created by thermal post-curing of a thermoset resin ink in an oven at elevated temperatures to obtain a highly crosslinked polymer network. The long and energy-intensive curing processes often required for curing the monomer limits the applications of this approach to layer-by-layer printing of simple 2D geometries. In addition, the conventional approach is not suited to creating large structures, as the uncured material in the earliest deposited layers reaches a flow state, resulting in loss of print fidelity or even the collapse of printed parts. Alternative in-situ curing approaches during the printing process are promising for highrate and scalable AM of thermoset polymer composites. To date, a handful of AM techniques based on in-situ curing have been developed using UV-curable thermoset resins. However, these techniques are not yet applicable for creating structural components due to the poor mechanical performance of the matrix, as well as incomplete curing of the resin in the presence of light absorbing reinforcements. In this work, we present a novel technique that can realize fast and energy-efficient fabrication of high-performance polymer composites using a thermoresponsive thermoset resin system. Our technique involves feeding resinous inks filled with discontinuous carbon fiber (CF) reinforcements from the nozzle of a printing robot and directing thermal stimulus toward the extruded material. The thermal stimulus is configured to rapidly and locally heat the composite material and instantaneously rigidize the extruded material. Using our novel printing technique, we demonstrate AM of tall composite structures using conventional layer-by-layer printing, which is difficult to achieve using existing techniques. In addition, instantaneous and localized curing of the thermoset matrix resin allows for the manufacturing of freeform structures (in-air printing), eliminating the need for support materials and tooling. We have shown that we can manufacture fully cured, void-free, and high-performance composites with printing speeds up to 1.5 m/min without requiring post‐treatment or post‐curing steps.