Implementation of viscosity and density models for improved numerical analysis of melt flow dynamics in the nozzle during extrusion-based additive manufacturing

Abstract

Fused Filament Fabrication (FFF) is an Additive Manufacturing (AM) process that builds up a part via layer by layer deposition of polymeric material. The purpose of this study is to implement viscosity and density models for improving the assessment of melt flow behavior inside the nozzle during deposition. Numerical simulations are carried out for different combinations of important process parameters like extrusion velocity Ve, extrusion temperature Te, and filament material (Acrylonitrile Butadiene Styrene (ABS) and Polylactic Acid (PLA)). Cross-Williams–Landel–Ferry (Cross-WLF) viscosity and Pressure–Volume–Temperature (PVT) density models are incorporated to get realistic results. Distribution of printing parameters like pressure, temperature, velocity and viscosity inside the nozzle are observed at steady state and their relationship with the print quality is discussed. Effect of the PVT model on polymer deposition is illustrated by comparing it with deposition considering a constant density. Velocity profiles are obtained for the different cases considered and locations where the flow is fully developed, along the axial distance of the nozzle, are determined and termed as stable zones. A direct correlation between the position of the developed melt flow profile and printing quality is established and the best combination of printing parameters is proposed for ABS and PLA. Extended stable zones are obtained for the polymer melt in the nozzle at Ve = 60 mm/s, Te = 220 °C for ABS and Ve = 30 mm/s and Te = 195 °C for PLA and hence, these can be considered as the optimum values of the printing parameters.

About 3D Printability of Thermoplastic Collagen for Biomedical Applications

“…Since the dynamic viscosity determines the printability of the material, the material becomes more printable as the temperature increases. In their studies on the parameters for optimal extrusion, Mishra et al [ 22 ] and Gopi et al [ 23 ] came to similar conclusions as in the present study. According to Duty et al [ 19 ], the material can be successfully deposited if the calculated pressure drop (Δp needle tip ) is less than the maximum system pressure for a given flow rate (Q).…”

“…This low strength could be related to the pore size of the scaffold of 1922.77 ± 10.76 µm. Seidenstuecker et al [ 31 ], Han et al [ 32 ], and Ai et al [ 22 ] showed in their studies that the optimum pore size for better mechanical properties is between 160–500 µm. Both honeycomb structures show higher maximum failure load and have higher compressive strength compared to the scaffolds with line filling.…”

An Electroconductive, Thermosensitive, and Injectable Chitosan/Pluronic/Gold-Decorated Cellulose Nanofiber Hydrogel as an Efficient Carrier for Regeneration of Cardiac Tissue

“…The viscosity of the hydrogels decreases by increasing the shear rate by two to three orders of magnitude, making them suitable for injection and self-healing [ 54 ]. The viscosity values are also within the applicable range for extrusion through nozzles [ 55 ]. The effect of AuNPs is distinguishable at relatively low shear rates (<3 s −1 ).…”

The Comparison of Medical Grade PP with Common Grade PP in Injection Moulding Process

“…The effects of shear rate and temperature on viscosity are considered in this 6-parameter model. This model, like the Bird-Carreau model, accounts for both Newtonian and shear thinning [19]. The generic Cross equation is used to simulate the shear thinning component, which is a common and older alternative to the Bird-Carreau-Yasuda model [19]:…”

“…The well-known form of the Cross model can be expressed as Eq. ( 13) if the infinite shear rate viscosity is insignificant [19].…”