Fluid Mechanics of Slot Coating in Layered Manufacturing

This paper addresses the fluid mechanics of the slot-coating process within the context of the layered manufacturing system. The investigation was carried out to assist with the design of a novel slot-coating-based liquid-layer-formation subsystem. This subsystem, when used as a part of a lithography-based Rapid Layered Composite parts Manufacturing (RLCM) system, successfully solves some of the difficulties encountered in the formation of thin layers from a highly viscous fibre-photopolymer composite liquid. In addition to an analytical model, the paper presents a numerical model based on a volume of fluid (VOF) algorithm. The algorithm allows (1) solution of non-steady-state problems, (2) tracking of the free surface of the fluid undergoing large deformations, and (3) easy modification of model’s domain to facilitate experimentation with coater geometry. Results from a set of simulated experiments are reported which show the relationship between the liquid coat height and several design and process parameters. Examination of cross-sections of test parts built on an RLCM prototype system confirmed the ability of the new coater design to form solid layers of good quality.