Numerical investigation on the viscoelastic polymer flow in material extrusion additive manufacturing

Abstract

In this paper, high-fidelity direct numerical simulations (DNSs) are carried out to explore the behavior of viscoelastic polymer flow in direct ink writing (DIW) additive manufacturing. The impact of ink elasticity on the stress for the strand deposition process has been examined. The exponential Phan-Thien Tanner (PTT) model is used to characterize the shear-thinning viscoelastic rheological behavior of polymeric fluids, and the gas-polymer interface is captured by the volume of fluid (VOF) method. Focusing on the extrusion and deposition of polymer, the effects of ink elasticity represented by the Weissenberg number (Wi), normalized printing speed and gap height on the formation of the printed strand have been studied. The results indicate that the polymer flow out of the nozzle is quite stable with time, and the polymeric stress balance is disturbed in the middle of the printed strand. For high Wi, the strand has significant deformation and an obvious large head (the earliest printed bulge in the deposited strand), whereas a larger normalized printing speed leads to a large stress region. In particular, a small normalized gap height has a squeezing effect on the deposited strand, and a visible depression in the middle of the strand can be obtained for large heights. Additionally, the degree of polymer deformation exhibits a major monotonic dependence on the normalized printing speed and gap height. The nonlinear relationships between the maximum stress components and process parameters show that the maximum stress decreases with Wi, but different printing speeds and gap heights have almost no effect on the stress components in the build platform-normal direction. The above analysis contributes to the inference of the deformation effects in different flow states, which can provide guidance to DIW additive manufacturing.