Feed rate effects in freeform filament extrusion

3D printing technologies have evolved drastically in the last decade. Professional grade 3D printers produce very high quality parts largely because they have been optimized for use with just a few different materials and do not allow the user to change process parameters. Conversely, Freeform Filament Extrusion (FFE) is a technology that has emerged as a favorite of hobbyists due to widespread availability of low cost open architecture machines that permit extensive experimentation with any number of materials. The FFE 3D printing process operates by feeding thermoplastic filament through a heated nozzle while the nozzle "draws" the desired pattern one layer upon the next. The output from these hobby style FFE 3D printers is often less than ideal in large part because users lack an understanding of how critical process parameters affect the speed and diameter of polymer filament as it exits the nozzle. This research focuses on the issue of unwanted deformation of the extruded polymer during 3D printing. As a first step, the feeding mechanism of an FFE 3D printer was studied in order to find the slippage (loss) between the feeding mechanism and the filament. The relationship between feed screw rotational speed and and volumetric flow rate through the nozzle tip was then established. With known volumetric flow rates, the cross sectional profiles of printed lines were measured using a laser profilometer. This information provides an indication of suitable nozzle head translation speeds for each feed screw rotational speed. Lastly, this study considers the effect of die swell in the extrusion process and concludes that the stand-off distance should be varied to avoid unwanted deformation of the extruded filament.