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

This work investigates the gas-assisted extrusion and deposition of viscoelastic polymer flow in Direct Ink Writing (DIW) additive manufacturing, aiming to reveal the effect of auxiliary gas on the strand deposition process. The Exponential Phan-Thien Tanner model is utilized to describe the rheological behavior of the viscoelastic polymer. The influences of the normalized gas inlet velocity (Ug/V) and Weissenberg number (Wi) on the flow morphology and internal stress of the polymer deposited strands have been explored. The results show that at low Ug/V conditions, the formation of voids near the nozzle wall leads to intermittent separation of the ink from the nozzle, increasing instability of the deposited strand. When the Ug/V is sufficiently high, a stable gas lubrication layer forms between the nozzle wall and the polymer ink, which improves the uniformity of the velocity and stress distribution within the polymer deposited strand. Additionally, higher Wi causes the morphology of the deposited strand shift from “long-tail” to “towering short-tail” due to elastic rebound without gas assistance, and the rebound viscoelastic ink adheres to the nozzle outer wall. While under gas-assisted conditions, the auxiliary gas effectively isolates the polymer ink from the nozzle wall, thereby significantly improving the deposition stability of the polymer ink. Notably, the critical Ug/V for successful gas-assisted DIW increases with Wi. These findings indicate that the gas-assisted method can effectively enhance printing efficiency and improve deposition stability, providing a better understanding of how gas-assisted techniques optimize the DIW deposition processes, particularly under challenging high-elasticity conditions.