CFD analysis and prediction of suction force during the pulling-up stage of the continuous liquid interface production process

Continuous liquid interface production (CLIP) is a novel constrained-surface curing approach that, due to its surprisingly fast fabrication speed, is shown to have the potential to revolutionize manufacturing. However, until now, it has not been possible to reliably fabricate parts with large cross-sectional area due to the large stress generated in the cured layer that results from the suction force of the liquid resin during the pulling-up stage. In this work, a systematic computational fluid dynamics (CFD) analysis was performed to investigate the resin flow behaviour in the micro-gap between the new cured layer and the resin tank during the pulling-up stage of the CLIP process, under various operational conditions. COMSOL software package was used to calculate hydrodynamic balance during the pulling-up stage using the so-called 'deformed geometry' technique along with the boundary condition of a moving wall and transient analysis. Using the numerical method, local instantaneous negative pressures in the resin flow field under various operational conditions were obtained. The results show that the magnitude of the negative pressure varies with the stage hoisting speed and acceleration, thickness of the oxygen-inhibited zone, cross-sectional area, and the slip at the interface between liquid resin and the bottom of the resin tank, and that the transient vacuum effect is significant enough to possibly damage the fabricated parts. Based on the simulation conclusions, some suggestions for optimizing operational conditions to reduce the suction force and thus improve the reliability of the CLIP process have been proposed. (C) 2019 Author(s).