Gas-assisted technique benefits to enhance the print efficiency and quality in extrusion-based additive manufacturing, while the deposition flow highly depends on the print speed and the gap distance between the nozzle and platform. In this work, high-fidelity numerical simulations are performed to study the viscoelastic polymer flow in gas-assisted direct ink writing (DIW) additive manufacturing. The exponential Phan–Thien–Tanner model is employed to characterize the shear-thinning rheological behavior of viscoelastic polymers, and the volume of fluid approach is utilized to track the gas–ink interface. The effects of the normalized print speed (Up/V) and normalized gap distance (HG/D) on the deformation and stress of the deposited filament under gas-assisted conditions have been investigated. The results show that under gas-assisted conditions, the filament morphology shifts from local accumulation to stretching and thinning as Up/V increases. Lower Up/V prolongs residence time and promotes elastic swelling at nozzle corners, whereas high Up/V raises shear and enhances elongation but may cause underfilling. Additionally, lower HG/D restricts polymer flow, induces wall adhesion, and even leads to unstable voids. Appropriately increasing HG/D helps to effectively reduce the shear stress and stress concentration as well as improve the leveling property under gas-assisted conditions. Compared to the case without gas assistance, auxiliary gas provides external confinement and a gas-shear boundary that reduces the frictional resistance near the nozzle. A reasonable selection of Up/V and HG/D contributes to achieving optimal gas-assisted effects. These findings can provide guidelines for gas-assisted DIW additive manufacturing.
Ye et al. (Wed,) studied this question.
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