Flow simulation and experimental validation of polymer extrusion using additively manufactured carbon fiber reinforced PEEK dies

Recent developments in polymer additive manufacturing (AM) have enabled composite materials and tough polymers such as Carbon-Fiber (CF)-reinforced Polyether-Ether-Ketone (PEEK), to be processed by Fused Filament Fabrication (FFF). CF-PEEK is a particularly strong and highly thermal resistant material that can overcome the limitations of polymer AM dies used in polymer profile extrusion with high demanding process conditions. Furthermore, AM offers flexibility by enabling streamlined die design which results in more flow balance and lower die head pressure compared to the flat die design. Flow simulations were performed in this study to predict the die head pressure and melt flow velocity across the profile extrusion section. The die design profile used for simulation has a cross section composed of two circular features connected by a horizontal line and non-uniform wall thickness. The flow simulation was validated by experimental testing of CF-PEEK AM dies in a single screw extruder operated at five different screw speed settings. The input for the simulations was the mass flowrate which was calculated from actual experiments depending on the mass of polymer extrudates and the corresponding extrusion time for each screw speed. The flow simulation includes a non-isothermal model that couples the polymer melt flow and the heat transfer across the melt. The viscosity model coefficients of the extruded materials (polypropylene, PP, and acrylonitrile butadiene styrene, ABS) used in the simulation were obtained from actual rheology testing. The simulation results indicate that the deviation of die head pressure from experimental testing is within 1-13% for PP and within 22-29% for ABS.