Chip evacuation force modelling for deep hole drilling with twist drills

Chip evacuation is the main difficulty of deep hole drilling process. For deep hole drilling with large depth-to-diameter ratio over 10, drilling force increases significantly with the drilling depth due to the friction and pressure reaction between the continuing generated chips and the drill flutes as well as the hole wall. In practical deep hole drilling process, overlarge drilling depth will cause drill breakage due to the low rigidity of the deep-hole twist drill, while using too small drilling depth is inefficient. The existing methods for drilling depth optimization are still faced with troubles, including lack of prior knowledge input of the monitoring method and difficult to measure or calibrate model parameters of the prediction model. To overcome these problems, a novel and practical chip evacuation force model for deep hole drilling is developed in this paper. Firstly, the chip evacuation forces in deep hole drilling are derived based on the elemental chip flow method, with the expression including three chip evacuation force coefficients for the practicability of the model. Then, the chip evacuation force coefficients are calibrated in a set of drilling tests under different cutting parameters, and the relations between chip evacuation force coefficients and cutting parameters are investigated with range analysis and analysis of variance. Finally, validation experiment results show that the proposed chip evacuation force model is able to predict the drilling force with increasing drilling depth in deep hole drilling, and the maximum drilling depth can be obtained accurately with the error less than 3%.