Prediction of extrudate deposition regimes from rheology and printing kinematics using computational fluid dynamics

The growing adoption of 3D-printing techniques highlights the need for a fundamental understanding of how printing and material parameters influence process efficiency and product quality. This study examines the combined effects of kinematic and rheological parameters on the deposition of soft materials. A virtual tool based on a non-conformal coupling mesh and volume-of-fluid method is developed to capture nozzle motion and emulate the deposition of a single extrudate, assuming Newtonian behavior under isothermal conditions. Extrudate deposition experiments with polylactic acid serve as benchmarks for the simulations. An advanced shape retention index (ASRI) is introduced to quantitatively link printing parameters to extrudate geometry. The roundness of the deposited extrudate varies with viscosity: it either increases or decreases depending on the speed ratio (nozzle flow speed U to nozzle movement speed V) and the normalized gap height (print-bed-to-nozzle distance h relative to nozzle diameter D). The ASRI correlates with the Bond (Bo) and Ohnesorge (Oh) numbers through a power law using either Bo/Oh or Bo2Oh as variables, revealing two deposition regimes: a free state, where h/D is large, and a constrained state, where extrudate height is limited by the nozzle gap. The transition between regimes depends on U/V. The ASRI provides a predictive framework for extrudate shape evolution, capturing the interplay between printing parameters and material flow.