Prediction and mechanism of surface evolution in high-pressure slurry jet micro-machining of channels

Abstract

Recent advances in abrasive water jet (AWJ) processes have enabled controlled-depth micro milling for a variety of applications, such as micro fluidic chip manufacturing. However, AWJ micro milling can be difficult to control and its successful application requires judicious selection of the process parameters. Since the mechanics of the process have not been fully understood, prediction of the machined topography arising from a set of process parameters is difficult. The present work combines computational fluid dynamics, Lagrangian particle tracking, and a deformed geometry surface evolution technique into a comprehensive model that predicts the evolving shape of micro-channels milled on 6061-T6 aluminum plates using high-pressure abrasive slurry jet machining (HASJM). Requiring calibration using only a single channel centerline depth, the model could predict the machined profiles of micro-channels milled using multiple nozzle passes with less than a 2% error. The model was also used to investigate the underlying physics of the machining process. This allowed experimental observations to be explained in terms of the changes that occur, due to the evolving eroded shape, in stagnation zone size, particle ricochet behavior, secondary slurry flow, and local particle impact angles and velocities. Overall, the work shows that such models can not only very accurately predict evolving machined topography, but also be very useful tools to understand abrasive jet machining mechanisms which occur on time scales which are too brief to be directly observed experimentally.