Determination of inner and outer modulation dynamics in orthogonal cutting

Many efforts have been devoted in the past to the identification of the dynamic behavior of the cutting process. Nevertheless, there have been no consistent results due to the inherent complexity of the cutting process, and the methodological and experimental errors involved. Among the problems to be solved, the experimental realization of the double modulation is the most difficult one. Present approaches use elaborate instrumentation and assume the delayed inner modulation for the outer modulation. This assumption may not hold under all circumstances and it will be modified in this paper. The present method approaches the cutting process as a one-input one-output process consisting of the inner modulation and dynamic cutting force component. The application of bivariate time series models give the transfer function of the inner modulation dynamics. The outer modulation dynamics’ effect on the cutting process is subsequently determined from the disturbance noise dynamics. The theoretical background for the proposed approach along with a new modeling strategy has been introduced in detail. The experimental verification of the theoretical postulates and the identification of the cutting process dynamics were carried out using actual data collected from an orthogonal turning process of a tubular workpiece. External white noise excitation was used and the experimental setup was designed to minimize the errors caused by inertia and disturbances. Although the proposed method requires prior knowledge of the machine tool structure, it requires a comparatively simple experimental procedure and minimizes the possible errors associated with the signal processing task.