Initial tool wear and process monitoring during titanium metal matrix composite machining (TiMMC)

When machining titanium metal matrix composites (TiMMCs), the abrasiveness of the reinforcement particles of this material leads to numerous machinability challenges, namely severe tool wear and poor machined surface quality. This paper aims to study the initial tool wear and the phenomena occurring during machining of titanium metal matrix composites. Initial wear refers to tool wear that occurs early in the cutting process. When the tool life is relatively short, the initial wear could significantly influence the remaining machining process. Therefore, a better understanding of the initial tool wear mechanisms and characteristics could lead to solutions extending the tool life, thereby improving the cutting process and production efficiency. Hence, the flank tool wear was assessed and thoroughly investigated using a scanning electron microscope (SEM), an energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). A tool condition monitoring system (TCMS) for online tool wear evaluation was employed to detect the transition times between wear stages during the machining process. Based on results, the types of wear in the initial zone were characterized. Abrasion, adhesion and cracking are considered as the critical morphological changes. The reduction of workpiece surface damage and tool wear rate could be related to the formation of a protective layer as a thermal barrier at the first transition time, when the initial tool wear ends and the steady state wear region begins. This moment, as the first transition time can be a short period, less than 15 s, which was detected by fractal analysis of force and vibration signals during machining of TiMMCs. The clear signatures of the transition times were suggested by the results of the fractal analysis.