A fluid-dynamics-based analysis of droplet coalescence in Arburg Plastic Freeforming: A case study with polycarbonate

This study investigates the coalescence behavior of bisphenol A polycarbonate droplets in the Arburg Plastic Freeforming additive manufacturing process through a computational framework that integrates thermal, rheological, and mechanical analyses. Using FLOW-3D simulations, the influence of extrusion temperature on droplet morphology, thermal field evolution, and interfacial bonding was examined. The polymer was modelled as a non-Newtonian, shear-thinning fluid with temperature-dependent viscosity, and the bonding potential was quantified using a William-Landel-Ferry (WLF)-based equivalent time at the glass transition after contact initiation, along with a numerically estimated tensile strength. Results reveal that higher extrusion temperatures promote greater spreading and wetting, enlarge the initial contact area, and extend the viscoelastic activation window, thereby improving interfacial coalescence. An equivalent time analysis based on WLF theory and a tensile-strength numerical evaluation reflects a balance between thermal input and spreading-driven post-contact cooling, rather than a purely monotonic temperature effect. These findings provide an Arburg Plastic Freeforming-specific numerical framework for analyzing local contact evolution, thermal history, and interfacial bonding potential between adjacent droplets. The results should be interpreted as local, probe-based indicators of bonding kinetics under a canonical two-droplet configuration.