Keywords: polymers, thermoset polymer resins
Summary:The spreading of a liquid droplet or cylindrical lament on a solid substrate is an important process for a range of industrial applications such as ink-jet printing technologies, coating, and additive manufacturing. One particular example is direct ink writing (DIW), which involves the dispensing of polymer resins, either as a continuous lament or as droplets onto a printing platform using a programmable dispensing/deposition head to form a complex 3D geometry. The printing parameters and the chemorheological properties of the resin control the final printed part fidelity and quality. DIW printing of themoset polymers typically involve the deposition of resins with complex time-dependent rheology, i.e. the viscosity of the resin changes with polymerization. For the purpose of setting printing parameters, it is highly desirable for the deposited materials to have a predictable and stable shape with minimal voids or gaps between dispensed resin. Therefore, understanding the way that deposited droplets and laments spread during printing is of paramount importance to controlling the printing process. In this work, we develop computational tools to simulate the free interface of a deposited thermoset resin droplet or cylindrical bead as a function of time and cure. The thermoset chemorheological properties are measured and serve as inputs into process parameters and non-Newtonian constitutive models. The shape of the bead is tracked as a function of time with different kinetic polymerization rates to de ne a printability space. Numerical simulation results are compared to experimental results when possible to validate the model and demonstrate predictability. In conclusion, we demonstrate scaling laws that allow for prediction of final drop shape given the chemorheological properties of a resin and DIW printing parameters that significantly reduce the printing parameters space and ensure high print quality.