Novel real-time monitoring method of depths of cut and runout for milling process utilizing FFT analysis of cutting torque

For smart manufacturing systems, it is required to monitor the cutting process in real-time to recognize the present state of the process. In this study, a novel method to monitor important parameters (i.e., axial/radial depths of cut and end mill runout) in the square end milling process by analyzing frequency components of the cutting torque is proposed. The proposed method assumes easily achievable information about the cutting conditions (i.e., spindle speed and feed rate) and tool parameters (i.e., helix angle, nominal radius, and number of flutes) as the given inputs. The presented method only utilizes measured torque data and the given inputs; therefore, it does not require any previously tuned information (e.g., specific cutting forces). From the perspective of the cutting torque model, analytical relationships between the process parameters to monitor and the frequency components of the cutting torque are clarified. On the basis of the mathematical expressions derived from the model, the proposed method offers a monitoring scheme of axial/radial depths of cut and runout. In addition, an index is suggested to offer information on reliability of the monitored outputs to the user. As results of experimental tests, the proposed method successfully monitored axial/radial depths of cut and runout and evaluated the reliability of the outputs.