Characterisation of abrasive water-jet process for pocket milling in Inconel 718

Experiments were carried out in Inconel 718 in order to investigate the possibility of using the abrasive water-jet process for producing 3D features such as pockets. A design of experiments approach was taken, considering variables such as water pressure, nozzle stand-off distance, traverse speed, nozzle orifice diameter, abrasive mass flow rate and tool-path step over distance. The experimental variables were related to depth of cut and pocket geometry. Statistical analysis was carried out in order to develop mathematical models which include process variable interactions and quadratic terms. This led to models with high correlation and prediction power which allow a better understanding of the process and can form the base for further process optimisation. The models were validated with additional experiments and showed good agreement with the water-jet system. The results showed that water pressure has a non-linear behaviour and is of paramount importance for controlling the depth of cut and geometrical errors. Additionally, nozzle diameter and the interaction between feed rate and abrasive mass flow are critical factors affecting the depth of cut.