Light Assisted Hybrid Direct Write Additive Manufacturing of Thermosets

In the past recent years, numerous studies have been conducted regarding the importance of thermoset additive manufacturing. Thermosets is an important class of polymers which cross-link during the curing process forming and irreversible chemical bond. Thermosets mark unique mechanical properties including, high temperature resistance, strong chemical bond, and structural integrity and therefore these materials find wide range of applications currently. Additive manufacturing of these materials allows fabrication of these materials in complex geometries which make them suitable for applications where part customization is needed. Thermoset materials can be additively manufactured using two major technologies: Direct Ink Writing (DW) and Vat polymerization. Direct ink writing method is based on the extrusion of thermoset material through a nozzle, layer by layer until the final object is formed and thermopolymer is cured under heat after printing. In this method, desirable mechanical properties can be achieved, however, with this method high resolution part fabrication very complex geometries cannot be achieved. This is due to the longer curing time of the thermoset polymer, which can affect the printing process, and the final shape of the printed object. On the other hand, Vat Polymerization technique is based on curing the photopolymer resin, by exposing it to Ultraviolet (UV) light. This method can achieve very smooth and accurate finishes of complex geometries, due to the fast curing of photopolymer. However, the mechanical properties of the photopolymers are weaker than the thermally cured polymers used in the DW method. In addition, polymer structures fabricated via VAT photopolymerization technique show time dependent mechanical performance which limits their reliability and usage of these materials for structural applications. Therefore, this study focuses on the combination of the Direct Ink Writing and the VAT polymerization additive manufacturing processes into a new hybrid thermoset additive manufacturing technique which allows the additive manufacturing of complex geometries, while maintaining high mechanical properties. Combination of these two methods is performed by mixing thermally curing epoxy with relatively small amount of photopolymer resin. Using the direct ink writing, the mixture is extruded though a nozzle and 3D printed on the printbed. Simultaneously, the deposited ink is exposed to the UV light enhancing the yield strength of the printed material and partially curing it. Therefore, thermally curing epoxy is used to obtain the desirable mechanical properties, while the addition of the photopolymer resin allows the thermoset mixture to solidify the printed ink almost instantly, when exposed to the UV light. In this study, we will investigate the optimal mixture amount of these two different polymer types and characterize the mechanical properties of the 3D printed structures.  Therefore, this novel technique has great potential to find immediate applications where mechanical properties, and component complexity are both desired.