Modeling Chip-Evacuation Forces and Prediction of Chip-Clogging in Drilling

One of the fundamental difficulties of the drilling process is the evacuation of the chips from the drilled hole. As the hole depth increases, the chips tend to cluster together and clog the flutes, causing increased forces, poor hole quality, elevated drill temperatures, and drill breakage. In this paper, a model for chip evacuation has been developed to predict the force and torque arising from the evacuation of the discontinuous chips. The model considers the pressure on a differential chip section being created by the forces required to push the chips out of the hole. The two coefficients of friction required by the model are established via a calibration procedure. The effectiveness of both the calibration and the force models has been assessed via a set of validation experiments. The model can be used to predict the depth when chip-clogging occurs, indicating the need for a pecking cycle, and the depth where the drill experiences an excessive amount of torque, which may result in drill breakage.