Additive manufacturing (AM) of lightweight and energy-efficient composites using continuous carbon fibers and thermosetting polymers offers great opportunities for advancing composite manufacturing with design flexibility, low cost, reliability and repeatability, with potential use in a wide range of applications. However, to date there has been no AM technique reported to process continuous carbon fibers and thermosetting polymers for direct 3D printing. The temperature-dependent viscosity of thermosetting polymers suffers a significant decrease before the composite suddenly turns into a solid, making it difficult to infuse the polymer into the fiber structure and quickly cure the composite into a solid while retaining the desirable pattern during the additive manufacturing process. Here, we overcome these difficulties and report a dynamic capillary-driven AM approach, called localized in-plane thermal assisted (LITA) 3D printing, with a controllable viscosity and degree of curing of polymer to enable its fast and near-simultaneous infusion and curing to implement in situ solidification of composites into arbitrary shapes. Using the LITA technique, we developed a robotic system consisting of a uniquely designed printing head and an automated robot arm, yielding a 3D printer that enables us to print a composite on 2D and 3D substrates or in free space. The printed composite had high fiber volume fraction (60%) and degree of curing (95%) with high mechanical strength (810 MPa) and modulus (108 GPa).
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