Mechanistic approach for prediction of forces in micro-drilling of plain and glass-reinforced epoxy sheets

Aerospace and automobile industries extensively use components made of plastics and fiber-reinforced plastics which require micro-machining operations including micro-drilling to be carried out. Various attempts are reported in the literature to study different strategies and model the forces in micro-drilling with a view to produce micro-holes having large aspect ratio and to reduce drill breakage. The force models are more statistical than mechanistic in approach. In the present work, an attempt is made to develop mechanistic models of thrust and torque in micro-drilling of plain epoxy sheets. Material model capturing strain rate and temperature-dependent yield strength of epoxy material and basic principles of machining are employed for this purpose. The mechanistic model for prediction of thrust and torque is validated using well-planned full factorial design of experiments. Experiments are carried out using a carbide drill of 0.5-mm diameter with three levels for speed and feed on a high-speed miniature machine tool specially developed at the laboratory. The material model is extended to glass-reinforced plastics (GRP), and drilling forces are predicted using the proposed mechanistic model. In both cases of plain and GRP sheets, the model predictions are close to the experimentally measured drilling forces.