Tool Wear in Milling of Medical Grade Cobalt Chromium Alloy - Requirements for Advanced Process Monitoring and Data Analytics

Computer Aided Design (CAD), Computer Aided Manufacturing (CAM) and Computer Numerical Control (CNC) are platform technologies in high end manufacturing. However, the machining process on the CNC Machine Tool is generally the main source of loss of component accuracy, precision and extraneous effects on surface finish and integrity. Moreover these 'losses', and therefore costs, only increase in cutting processes due to the inherent modes and mechanisms of progressive and catastrophic tool wear. In high end manufacturing sectors, these losses are also exacerbated by the use of 'difficult-to-cut (DTC)' materials while more stringent specifications apply and higher levels of process capability are demanded. The use of Cobalt Chromium (Co-Cr-Mo) alloys in the Medical Device sector is indicative of the many challenges. However, notwithstanding the importance of the application, there are few publications on the fundamental mechanisms in cutting this alloy, other than by the present authors. This paper builds on our research to date by reporting some preliminary results on tool wear progression in CNC milling of the Co-Cr-Mo alloy conforming to ASTM F75. It also assesses the feasibility of real time tool wear monitoring on a Mori Seiki NMV1500 CNC Machining Centre using the MTConnect communication standard. The results obtained through MTConnect are provided by embedded sensors within the machine tool and are correlated with a laboratory piezoelectric dynamometer. The results from both methods, obtained at two cutting speeds, are also related to observed tool wear progression and the cumulative volume of material removed. The results are discussed in terms of the potential and limitations of using of MTConnect and the machine tools embedded sensors, for monitoring of the process and the onset of tool wear.