Evaluation of high-speed end-milling dynamic stability through audio signal measurements

The progress of high-speed milling is limited by premature tool failure, spindle bearing wear and dynamic instabilities. Relative vibrations between tool and workpiece exert a great influence on the process results. Machining operations are influenced by the dynamic behaviour of the machine-tool structure and by the dynamics of the cutting process. In this paper, the influence of the machining parameters on the stability of high-speed end-milling is investigated through simulations and experiments. The stability evaluation was based on the workpiece surface finish and on the audio signals measured with a unidirectional microphone. Vibration signals were detected even for low immersion cuts. The simulation results were close to the experimental ones for the high immersion condition. There was a correlation between the simulated and experimental chatter frequencies, although the latter deviated more from the natural frequency of the system. In general the regenerative vibrations limit the maximum axial depth of cut for a stable cut; however, the forced vibrations are also important for low immersion cuts due to the low degree of engagement between the tool and workpiece and the sudden variations in the cutting forces.