Non-Newtonian modeling of contact pressure in fused filament fabrication

Abstract

Strategy for reducing molecular ensemble size for efficient rheological modeling of commercial polymers Journal of Rheology 65, 43 (2021); https://doi.org/10.1122/8.0000125 Rheology discussions: The physics of dense suspensions Journal of Rheology 64, 1501 (2020); https://doi.org/10.1122/8.0000174 Yielding, thixotropy, and strain stiffening of aqueous carbon black suspensions Journal of Rheology 64, 955 (2020); https://doi.org/10.1122/8.0000028 Rheology of thermoplastic vulcanizates (TPVs) Journal of Rheology 64, 1325 (2020); https://doi.org/10.1122/8.0000108 The weakly nonlinear response and nonaffine interpretation of the Johnson-Segalman/Gordon-Schowalter model Journal of Rheology 64, 1409 (2020); https://doi.org/10.1122/8.0000122 Strain shifts under stress-controlled oscillatory shearing in theoretical, experimental, and structural perspectives: Application to probing zero-shear viscosity Journal of Rheology 63, 863 (2019); https://doi. Abstract The nozzle pressure was monitored in a fused filament fabrication process for the printing of high impact polystyrene. The contact pressure, defined as the pressure applied by the newly deposited layer onto the previous layer, is experimentally calculated as the difference between the pressure during printing and open discharge at the same volumetric flow rates. An analytical method for estimating the contact pressure, assuming one-dimensional steady isothermal flow, is derived for the Newtonian, power-law, and Cross model dependence of shear rates. A design of experiments was performed to characterize the contact pressure as a function of the road width, road height, and print speed. Statistical analysis of the results suggests that the contribution of the pressure driven flow is about twice that of the drag flow in determining contact pressure, which together describe about 60% of the variation in the observed contact pressure behavior. Modeling of the elastic and normal stresses at the nozzle orifice explains an additional 30% of the observed behavior, indicating that careful rheological modeling is required to successfully predict contact pressure.