Gas-assisted extrusion of viscoelastic polymer flow in direct ink writing additive manufacturing

In this work, direct numerical simulations are carried out to study the gas-assisted extrusion of viscoelastic polymer flow in direct ink writing (DIW) additive manufacturing. The exponential Phan-Thien-Tanner constitutive model is used to characterize the shear-thinning viscoelastic polymer flow, and the gas-polymer interface is captured by the volume of fluid method. The effects of gas inlet velocity and polymer elasticity [denoted by the Weissenberg number (Wi)] on the gas-assisted extrusion of the polymer flow have been investigated. The results show that the auxiliary gas inlet can form a protective layer between the polymer and the nozzle wall, thereby eliminating the effects of wall slip. This mechanism effectively reduces the swell ratio, increases the extrusion speed as well as decreases the internal stress of the polymer. However, this is only applicable to certain gas flow rates, and the gas with too high inlet velocity increases the risk of polymer rupture. Adjusting the gas inlet velocity can minimize the internal stress of the polymer ink, thereby achieving optimal printing quality and forming accuracy. In addition, the polymer with higher elasticity has more significant swelling deformation, which exhibits a larger depression at the gas inlet region, leading to a higher risk of rupture. Higher Wi not only decreases internal stress within the polymer but also results in a larger region with high tr(Θ) values, which indicates a greater degree of ink deformation and thus severely impacts the printing resolution and accuracy. This study benefits to offer guidance to the gas-assisted DIW additive manufacturing.