System Identification of Fused Filament Fabrication Additive Manufacturing Extrusion and Spreading Dynamics

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University of Texas at Austin


In fused filament fabrication additive manufacturing, polymer extrusion and spreading dynamics affect build quality in both surface finish and mechanical properties. The state of the art in extrusion modeling and control is identification and compensation of a fixed first order pole with a linear model of the system. However, physical nonlinearities cause deviation of this pole in practice. To advance the aim of slicing using accurate nonlinear dynamic models, this work presents a system and procedure for automated measurement of dynamic bead extrusion. The system uses a belt printer, iFactory3D One Pro, with nozzle tilted 45 degrees from the build belt, and a snapshot 3D scanner. Single layer prints in polylactic acid (PLA) are scanned and then automatically ejected. The gcode for the single bead print holds the gantry speed fixed or extrusion speed constant while the extrusion flow rate or gantry speed is varied as a step input signal in space. The experiment design matrix varied two variables: gantry speed and extrusion flow rate. Time constants are fitted to bead area signals that are extracted from the scan data to obtain nonlinear models. Depending on the experiment condition, the percent difference between the highest time constant and the lowest time constant ranged from 279% to 61%, confirming the high nonlinearity of the extrusion system in FFF 3D printers. Additionally, measurements are performed on a cartesian 3D printer with a 2D scanner to test applicability of the methods to a general audience and verify observed trends. It was observed that larger steps in extrusion velocity for a constant X-Axis velocity, yielded smaller time constants, while the same steps in velocity using a constant extrusion velocity condition with variable X-Axis velocity, yielded the opposite trend. Moreover, the time constants for a step up in extrusion velocity yielded higher overall values in time constant when compared to step down conditions.


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