Abrasive Water Jet Cutting (AWJC) of Co-Cr-Mo alloy investment castings in the medical device industry

Investment castings (usually involving ceramic based shells) have traditionally been separated from the mould tree using an abrasive cutting operation. While material removal rates are relatively high, the process unfortunately suffers from poor accuracy control that often necessitates further finishing operations. Following an overview of key considerations in investment casting including tree configurations and gate profile, the paper details experimental work to investigate the feasibility of abrasive waterjet cutting (AWJC) as an alternative to grinding for component cut-off. The workpiece material was a high strength cobalt-chromium-molybdenum alloy (ASTM F-75) commonly used for orthopaedic implants. Preferred AWJC cutting parameters were established for material thicknesses up to 30 mm. Specimens of 13 mm and 30 mm thickness were cut through at maximum traverse speeds of 220 mm/min and 80 mm/min respectively. Abrasive grit embedment was observed primarily at the top surface and exit region of the cut. The effect of investment casting refractory shells on the AWJC process was examined. In addition, a comparative analysis of performance and cost with alternative cutting methods was also performed.