Finite element modeling of a micro-drill and experiments on high speed ultrasonically assisted micro-drilling

Modal characteristics of a generic micro-drill and experiments on the micro-drilling with superimposing of longitudinal ultrasonic vibration are presented. Finite element (FE) analysis is used for identification of eigenfrequencies and modes of the drill. Dynamic influence of the drill shank is discussed and a hybrid model is proposed to account for it. The model is proven to be efficient for complicated drill models and advanced analysis. A high speed ultrasonically assisted micro-drilling (UAMD) system is established with air bearings and longitudinally vibrating workpiece. During the experiments the thrust force reduction is studied as well as effects of ultrasonic vibration frequency and rotational speed. A correlation study was conducted between the thrust force measurements and simulations from a nonlinear force model. It can be seen that the current one-dimensional model is not sufficient to describe the complete behavior of the drill. The FE model and force experimental results can be utilized for a full dynamic model of the UAMD system to study vibration and the cutting mechanism in the future.