Study of the print behavior of fillers in the material extrusion printing process

Abstract

Fused filament fabrication (FFF) with filled polymers has grown popularity due to the improved material properties. However, nozzle clogging is observed for higher filler contents, resulting in a failed print. Based on the flow behavior and filler orientation in an FFF nozzle, an experiment varying nozzle diameter, filler size, resin viscosity, and volume content is designed. Clogging of sphere-filled and fiber-filled polymers is investigated in a custom nozzle flow test device (NOFT). The ratio between nozzle diameter and filler diameter was found to have the highest effect on nozzle clogging. Sphere-filled polycarbonate was found to clog for ratios $\frac{D}{d}\leqq6.2$. A distribution in the ratio of Stokes‘s drag force to extrusion force was found to describe intermittent clogging of sphere-filled polymers. The flow behavior in an FFF nozzle was investigated with respect to nozzle diameter, filler size, resin viscosity, and volume content. A viscosity model to predict material printability was derived, based on the observations of the different factors studied and the required volume flow rate.