Abstract
In this paper we addressed key challenges in engineering an instrumentation system for sensing and signal processing for real-time estimation of two main process variables in the Fused-Filament-Fabrication process: (i) temperature of the polymer melt exiting the nozzle using a thermocouple; and (ii) polymer flowrate using extrusion width measurements in real-time, in-situ, using a microscope camera. We used a design of experiments approach to develop response surface models for two materials that enable accurate estimation of the polymer exit temperature as a function of polymer flowrate and liquefier temperature with a fit of . The live video stream of the deposition process was used to compute the flowrate based on a road geometry model. Specifically, a robust extrusion width recognizer algorithm was developed to identify edges of the deposited road and for real-time computation of extrusion width, which was found to be robust to filament colors and materials. The extrusion width measurement was found to be within 0.08 mm of caliper measurements with an value of 99.91% and was found to closely track the requested flowrate from the slicer. This opens new avenues for advancing the engineering science for process monitoring and control of FFF.
Highlights
Fused filament fabrication (FFF) continues to be among the most widespread additive manufacturing (AM) processes for making polymeric functional prototypes and, in several cases, end-use parts
With the IR camera mounted at a fixed distance from the extruder, as shown in Figure 3a, molten polymer was extruded in free air for all runs in the experimental design for a period of 60 s, which is an adequate time to measure steady-state temperature dynamics
∆TIR = TL − TIR is the temperature difference between the liquefier temperature measured by axial thermocouple and temperature of the polymer exiting the nozzle measured using the IR camera
Summary
Fused filament fabrication (FFF) continues to be among the most widespread additive manufacturing (AM) processes for making polymeric functional prototypes and, in several cases, end-use parts. In an FFF process, a thermoplastic feedstock, usually available as spooled filament, is fed into the hot-end portion of an extrusion system, where it is heated, melted, and forced through a nozzle. Some of the current challenges in industrializing AM are variability in product quality and the need for rapid qualification of parts. In-situ process monitoring via process sensing and process control has recently gained a lot of attention from researchers and is the most important venue for realizing the challenge of industrialization and the development of robust AM processes
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