Mathematical modeling and experimental study of material flow and torque in the extrusion-based additive manufacturing of granulated polymer

• The focus of the paper is on the use of granulated materials in an extrusion chamber for FDM 3D-printing, instead of pr-formed filaments, which allows for material variety, cost reduction, and weight scalability. • A detailed mathematical model for the material flow in the screw-based extrusion system is presented and is used for estimation of the required torque for any specific nozzle output. • The model can be extended for use of various polymers in the screw-based FDM process. • The extrusion-based injection system is built up and is used in a test setup for validating the model results, which shows good correlation. Fused deposition modeling (FDM) method is one of the most common additive manufacturing techniques for printing polymer parts. However, it requires pre-formed filaments for printing which limits the variety of the materials that can be printed. The alternative is direct melting of granulated polymer pellets in an extrusion chamber and deposition of the extruded to make parts. This method opens the way for using various materials including almost all polymers and polymer-metal or polymer-ceramic composites in direct or indirect additive manufacturing. However, there are challenges in setting the parameters of the extruder and adjustment of the material flow. This article presents an analysis of material flow in the extruder used for direct pellet-printing of Acrylonitrile butadiene styrene (ABS) parts. The material in the extruder is divided into the melting and the melted zones. In the melting zone, the thickness of the melt increases gradually, whereas in the melted zone, pressure gradient is developed in the fully melted polymer. Characteristic specifications of extruder such as operating pressure, screw rotational speed, material flow and the required torque for rotating the screw are derived for extruding ABS polymer. The extrusion-based injection system was built up and is used in a test setup for validation of the simulation results. Good correlation between the experimental and theoretical results is obtained.