(108a) Design and Characterization of a Compact Mixing Pellet Extruder for 3D Printing

A compact extruder for processing pellets, powder, and recycled flake is presented. The extruder is enabled by a mixing screw design having an exceptionally short length-to-diameter (L/D) ratio of 8:1 as well as double flights with variable pitch and strategically arranged counter-rotating mixing slots. These features enhance material plastication, disrupt solid bed formation, and significantly improve thermal and compositional homogeneity within the extrudate. The model-based screw design methodology is presented that uses non-isothermal, non-Newtonian simulations to refine the screw geometry for optimal energy efficiency and material throughput. Experimental validation was performed using a custom-built extruder using a 31 mm screw diameter and an instrumented nozzle including melt pressure and intrusive melt temperature sensors. Throughput and melt temperature are characterized as a function of four critical factors including the screw speed, barrel temperature, nozzle geometry, and extruder orientation. The results are compared to a 20 mm screw diameter and their respective simulations. The presented systems offer considerable advantages in terms of reduced energy usage, improved residence time distribution, and enhanced processing capabilities for complex, recycled, and bio-based polymer materials with broad implications for sustainable manufacturing in the polymer processing and additive manufacturing communities.