Correlation between tool flank wear, force signals and surface integrity when turning bars of Inconel 718 in finishing conditions

Inconel 718 is commonly used in critical components such as turbine discs, where turning, drilling, milling and broaching are common machining operations. In these components, fatigue life should overcome standard values and, for this reason, working conditions in finishing operations are carefully chosen taking into account surface integrity issues. Process monitoring can help assuring the component quality. In this paper, signals coming only from forces sensor and spindle power were correlated with tool flank wear and surface integrity when turning Inconel 718. Results showed that: 1) force signals showed a remarkable correlation with tool wear state; 2) some signals, like passive force were more sensitive to tool wear; 3) there was a good correlation between external and internal signals; 4) some surface integrity defects were observed from the very beginning of machining tests.