Predicting the rotating tool-tip dynamics in mechanical micromachining using modal testing

This study presents an experimental methodology to predict the tool-tip dynamics including rotational effects in micromachining. In this approach, the ultra-high-speed spindle dynamics (i.e. the FRF matrix at the spindle tip) at different spindle speeds are obtained experimentally. Since the modal test are performed on a rotating tool, measured response includes unwanted error motions as well as the dynamic response to the excitation. Therefore, a frequency domain filtering algorithm is designed to isolate the dynamic response. Then, the experimentally obtained spindle dynamics are coupled with the tool dynamics calculated using the spectral-Tchebychev technique to predict the tool-tip dynamics. The developed approach/methodology is demonstrated on a micro machine tool incorporating miniature ultra-high-speed spindles (with air bearings), and a tungsten carbide tool blank. The predicted tool-tip dynamics are validated by direct measurements; it is concluded that the presented unified modeling approach can be used to accurately determine the tool-tip dynamics.