Operational Modal Analysis-Based Control of Cutting Modes in Turning

Turning, like any cutting process, is performed in a closed machining system and is always accompanied by chatter. Increasing cutting speed to improve productivity was constrained by increased vibration amplitude, resulting in negative outcomes. The cutting mode control technology presented in this article ensures chatter-free machining based on operational modal analysis (OMA) results and is relevant. The technology was based on representing the machining system as a 2nd-order oscillatory element with one degree of freedom. Identification of the dynamic parameters of this oscillatory element, which replaces the machining system, was automatically performed in the developed software application, which calculates the element’s dynamic parameters from the frequency response function of the vibration acceleration signal obtained during operational modal analysis. Specialized software was developed to simulate the cutting process in a machining system in both the time and frequency domains, including stability diagram (SD) design. The SD design for a given feed rate is automatically implemented in the “cutting depth – spindle speed” coordinates using a new stability criterion for systems with closed positive feedback via a delay argument function. The system was considered stable if the Nyquist diagram did not pass through the point with coordinates [+1, 0] on the complex plane. The verification of the adequacy of the developed technology was based on the Ra and Rz roughness parameters of the machined surface under various cutting conditions specified in the SD, fully confirming its effectiveness in ensuring chatter-free machining. Particularly, the roughness parameter Rz of the machined surfaces at the same cutting depth and feed rate decreased by 1.3–1.8 times.