Collaborative Research: Microwave Heating of Carbon Nanotube Coatings to Enable Rapid Welding in 3D-Printed Polymer Structures

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One of the most critical problems in additive manufacturing of plastic components is poor part strength caused by weak interfacial welding between the deposited polymer layers. Uniform heating of the manufactured part cannot solve this problem because it can cause warping of the 3D-printed structure that affects the mechanical reliability of three-dimensional (3D) printing as a plastic manufacturing technique. This research examines a novel manufacturing process where a thin coating of carbon nanotubes (CNTs) is deposited on the plastic filaments used in 3D printing. Microwave exposure of the printed parts causes the CNTs to heat that allows for localized polymer melting at the welds, resulting in markedly improved mechanical strength of the part. If successful, the additive manufacturing technology enabled by this project has the potential to overcome the current disparity between traditionally manufactured polymer parts such as injection molding, extrusion molding and machining as compared to parts printed with additive manufacturing techniques. Specifically, this work uses a combination of experimentation and computation to measure and model the response of CNT-loaded polymer films in order to directly capture the coating thermal dynamics. This will be done using a combination of alternating current dielectric measurements, infrared imaging, and finite-element modeling (combining radio frequency heating and heat transfer in thin coatings). This will be followed by a scaled-up investigation of the coating, material extrusion, and controlled microwave exposure processes to demonstrate how this concept translates to an additive manufacturing context, with an emphasis on strength improvements (as measured on vertically printed tensile bars) and reliability. The microwave exposure will be carried out using simultaneous infrared imaging and real-time adjustment of forward power to yield consistent, specified heating treatments. The intellectual significance of the work stems from the translation of microscale CNT heating to processing-structure-property relationships for welds in complex, macroscale 3D printed structures. This work will have a strong impact on multiple scientific and engineering fields including polymer physics, nanomaterial percolation, microwave physics, plastics processing, advanced manufacturing.