A. Sarmah, A.G. Crowley, S.K. Desai, G. Zolton, M.J. Green
Texas A&M University,
Keywords: direct ink writing, radio frequency heating, thermosetting resin, free-form processing
Summary:Direct Ink Writing (DIW) is an extrusion-based additive manufacturing method where the print medium is a liquid-phase ‘ink’ dispensed out of small nozzles and deposited along digitally defined paths. Conventional DIW methods for thermosetting resins rely on the use of viscosifiers, novel crosslinking chemistries, and/or long curing schedules in an oven. Here, we demonstrate the use of a co-planar radio frequency applicator to generate an electric field which can be used to rapidly heat and cure DIW-printed, nano-filled composite resins. This method avoids the need of an oven or post-curing step. The proposed process consists of a layer-by-layer, print-and-cure cycle which allows for printing of high-resolution, multi-layer structures. Every extruded layer is partially cured using RF before depositing the next layer; this allows the printed part to maintain structural integrity without buckling under its own weight. The process enables both increased throughput and decreased touch time relative to traditional part manufacturing. Commercial epoxy resin with varied nano-filler loadings were examined as DIW candidates. Rheological characterization was used to assess both curing kinetics and printing behavior. After printing, the thermo-mechanical properties, surface finish, and shape retention of RF-cured samples were evaluated and found to be comparable against samples conventionally cured in an oven. This method of manufacturing establishes RF heating as a suitable alternative to conventional methods, facilitating rapid, free-form processing of thermosetting resins without a mold.