Coupled Thermo-Chemical Modeling of Frontal Polymerization-Assisted Additive Manufacturing of Thermoset Polymer Components

Abstract

Frontal polymerization (FP) is a localized and self-propagating exothermic polymerization reaction process that cures thermoset resins rapidly with the need of only a small amount of initial heat input for front initiation. FP has demonstrated its potential for various applications related to polymer and polymer composite manufacturing due to its energy-efficiency and rapid curing ability of thermosets. Recently, it has been used for additive manufacturing (AM), where a traveling front cures the ink instantaneously as it is being extruded, allowing supportless printing of complex structures without post-print curing. While the current FP-based AM experimental works demonstrate its great potential, determining certain printing parameters through trial and error remains a crucial challenge, which hinders its large-scale applications. To thoroughly understand the interaction between the printing parameters and the front behavior and subsequent printing process, and eventually guide the optimal design of printing process, numerical modeling of the FP-assisted AM process is necessary. We adopt an element activation approach and establish a coupled thermos-chemical finite element model for simulating continuous FP-assisted AM printing, which accounts for both the coupled thermos-chemical phenomenon and the dynamic ink deposition in a real printing process. Element activation allows elements addition and transformation from air to ink in the simulation domain along a preset printing path at certain velocity. A coupled thermo-chemical partial differential equation system is solved over the continually updated printing domain to simulate the heat diffusion and polymerization reaction during the printing process. The model is validated by comparing the front temperature evolution from simulation and the IR camera measurements in experiment. The validated model illustrates the self-regulative front behavior of the front and the system under certain conditions. Furthermore, the validated model is adopted to study the relationship between the front and substrate temperature over layers under various printing velocities and layer lengths, and shed light on optimal printing parameters selection.