Abstract
Fused Filament Fabrication (FFF) has become increasingly popular due to its accessibility and rapid fabrication abilities. However, FFF cannot reliably reproduce prints and often suffers from low print quality, which negates many of its benefits. Most previous work in improving FFF has focused on optimizing print parameters, yet results still vary from print to print and printer to printer. Recently, there has been an emphasis on detecting the formation of anomalies using nondestructive methods such as infrared (IR) thermography and other imaging techniques that monitor the part in-situ. While these approaches can identify the formation of geometric anomalies, they are limited to surface and subsurface observations. Furthermore, analyzing images for anomalies is computationally expensive compared to integrated thermocouples that can be used to flag thermal anomalies. This research aims to investigate the unstudied heat transfer interactions between the print bed and cooling fan that impact part quality (e.g., warping, shrinkage, etc.) and local polymer properties (e.g., crystallinity) via thermocouples integrated into the print bed. This is accomplished by printing 1 cm PLA cubes at bed temperatures from 60 to 110°C, and by conducting no-extrusion experiments to measure the bed thermal behavior without printing. It was found that the measured bed temperatures varied spatially across the print bed, and significant interactions between the cooling fan and print bed were measured at the print location. At 100% fan speed, the central thermocouple temperature decreased by 18.53°C and 8.71°C at given bed setpoint temperatures of 110°C and 60°C, respectively. These interactions often led to print failure at high bed temperatures, as excessive cooling near the built-in thermistor caused increasing print bed temperatures at other locations. This cooling is suspected to have triggered a bed thermal runaway error at high temperatures (∼120°C). Lastly, the effect of the cooling fan on print geometry was observed by varying the layer at which the fan turned on. Turning the fan on later in the process led to severe geometric anomalies in the upper layers of the print. Ultimately, this work shows the importance of including the effect of the cooling fan on the print bed in models of the FFF process. Understanding this relationship will allow for the development of fan cooling strategies that will not interfere with printer performance or print quality, leading to consistent fabrication of higher-quality parts.
