<p class="MsoNormal" style="text-indent: .25in">Fused filament fabrication (FFF) is a material extrusion additive manufacturing (AM) process that works well with thermoplastic polymers and is inexpensive compared to other AM processes, leading to its increasing popularity for industrial applications. However, one disadvantage of FFF parts is their anisotropic behavior, such that the FFF parts exhibit different mechanical properties based on the printing orientation, printing parameters and thermal conditions, so the mechanical performance of the parts can be unpredictable. Finite element analysis (FEA) is used to simulate the thermal histories, among other properties, involved in FFF, to estimate the extent of interlaminar bonding, or degree of fusion between two subsequent layers. If the layers of the FFF part are sufficiently fused together at high temperatures, the mechanical performance of the part improves and approaches the mechanical performance of an injection molded part that lacks distinct layers. On the other hand, if temperatures are too high, the thermoplastic may sag and cause geometrical inaccuracy. Thus, FEA is necessary to simulate the thermal conditions of the FFF process to understand and predict the mechanical performance of FFF parts. With an accurate FEA model, the FFF process can be simulated with various printing parameters, so the part can be manufactured under optimal conditions for improved mechanical performance. In this paper, several simulation cases of increasing complexity are presented within MSC Digimat-AM, and both a thermocouple and an infrared thermal imaging system are used to validate the results from Digimat-AM. First, a steady state case is conducted and simulated to corroborate the two validation tools and to calibrate the thermal emissivity value and conductivity coefficient of the thermoplastic used for testing, in this case, acrylonitrile butadiene styrene (ABS). Next, the thermal camera is tested for its response time by comparing its frame rate to the resulting thermal images. Lastly, Digimat-AM is used to simulate the FFF printing process. It was concluded that infrared thermal imaging is suitable for in-process thermal data collection during FFF printing, but with several limitations, such as low resolution, thermal radiation from the print bed due to the nozzle, and reflections of surroundings off the print bed. Thermocouples can act as aids to calibrate the thermal imaging but affect the cooling rate of the surrounding filament. Given considerable computing time, Digimat-AM can simulate the thermal profiles of different cases, but the thermal profiles are sensitive to changes in simulation parameters, such as time increment, and printing parameters, causing unexpected systematic errors or inaccurate results.</p>

Validation of a Finite Element Model for Fused Filament Fabrication Additive Manufacturing

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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