Light assisted hybrid direct write additive manufacturing of thermosets

In the past recent years, numerous studies have beenconducted on additive manufacturing of thermosets andthermoset composites. Thermosets are an important class ofpolymers used in engineering applications. Monomer units inthese material systems irreversibly cross-link when externalstimuli or a chemical crosslinking agent is applied in terms ofthe curing or photopolymerization process. Thermally curingthermosets mark unique mechanical properties including, hightemperature resistance, strong chemical bond, and structuralintegrity and therefore these materials find wide range ofapplications currently. However, direct write additivemanufacturing of these material systems at high resolution andat complex geometries is challenging. This is due to the slowcuring rate of thermally curing thermoset polymers which canadversely affect the printing process, and the final shape of theprinted object. On the other hand, VAT Polymerization additivemanufacturing, which is based on curing the photopolymer resinby Ultraviolet (UV) light, can allow the fabrication of complexgeometries and excellent surface finish of the printed parts dueto the fast curing rate of photopolymers used in this technique.Mechanical properties of photopolymers, however, are usuallyweaker and more unstable compared to the thermally curingpolymers used in the direct write additive manufacturingmethod. Therefore, this study focuses on taking the advantagesof these two thermoset additive manufacturing methods byutilizing both the thermally cured epoxy and photopolymer resinstogether. Using the direct writing, the resin mixture is extrudedthough a nozzle and the final 3D object is created on the printbed. Simultaneously, the deposited ink is exposed to the UV lightenhancing the yield strength of the printed material and partiallycuring it. Therefore, thermally cured epoxy is used to obtain thedesirable mechanical properties, while the addition of thephotopolymer resin allows the thermoset mixture to partiallysolidify the printed ink when exposed to the UV light. The resultsachieved in this study showed that, the hybrid additivemanufacturing technology is capable of fabricating complex andtall structure which cannot be printable via additivemanufacturing method. In addition, mechanical properties of thehybrid thermoset ink are comparable to the thermally curedthermoset polymer indicating the great potential of the lightassisted, hybrid manufacturing to fabricate mechanically strongparts at high geometrical resolution.