Regimes of droplet train impact on a moving surface in an additive manufacturing process

In jetting-based additive manufacturing, one or more droplet trains are deposited on a moving surface to fabricate layers in an additive approach. The impact behaviour of the droplets onto the surface defines the final fabricated layer properties in terms of geometry and surface finish. This paper reports on such behaviour when depositing a solution of a bio-degradable resin towards an ultimate goal of fabricating bone implants in an additive manufacturing process. The solution was jetted via a fixed single nozzle continuous piezoelectric printhead on a moving surface. The effect of two main process parameters, jetting frequency and substrate linear velocity, on the impact behaviour was investigated. Quantitative analysis was undertaken to investigate the droplet formation characteristics and droplet/surface interactions. The phenomena associated with the interaction at the front of the advancing liquid layer were correlated with the process conditions. The result was a classification of the droplet train/moving surface interactions into three main regimes depending on the droplet impingement characteristics and the surface motion.