From theory to practice : development and calibration of micro pellet extruder for additive manufacturing

Abstract

Pellet additive manufacturing (PAM) is in terms of printing process very similar to the widely used fused deposition modelling (FDM) systems. The main difference is the use of pellets instead of filament. In this study, a pellet, single screw extruder is developed. A screw design with variable pitch and depth is modelled analytically to predict the melting behavior of acrylonitrile butadiene styrene (ABS) during steady state extrusion. The extruder screw was designed unconventionally short with a length of 85 mm and a diameter of 20 mm, giving an L:D ratio of 4.25:1. The model predicted the melting profile for ABS being extruder at 235°C at 10 RPM, the result of which was confirmed to a degree by experimentation. The extrusion rate of the screw extruder was measured at barrel temperatures of 225°C to 245°C with 5°C increments and at 5 RPM and 10 RPM. The extrusion was found to increase non-linearly with barrel temperature and screw speeds. The extruder printed adequately on an FDM style motion system with minor upgrades.