In-process simulation of the extrusion to support optimisation and real-time monitoring in fused filament fabrication

A simulation model is presented in this work, capable to predict temperature and velocity of the extrudate as well as the compressive force acting on the filament in a fused filament fabrication (FFF) machine operating with a Bowden extruder. The simulation model is developed for future incorporation into a larger on-machine apparatus designed for process monitoring and adaptive control and destined to the fabrication of high value-added parts. The simulation model captures mechanical aspects of the extruder (including slippage at the drive gear, filament compression into the hot end), as well as temperature and pressure changes within the extrusion chamber, where the filament is liquefied and transformed into the extrudate. The model is implemented so that it can react to changes in the part program as it is being executed, offering predictions on the extrusion process that can be compared with sensor measurements. The simulation model is implemented in prototype form and calibrated on a multi-sensor FFF machine working with a PLA filament within a range of predefined operating conditions (heating temperatures and print feed rates). Load cells, high-speed optical imaging and infra-red thermal imaging of the extrudate mounted on the FFF machine are used to verify the predictions of the simulation model.