| This research investigates chip ejection and formation in the drilling process. The chip ejection mechanism of discontinuous chips, chip thickening in deep hole drilling, spiral chip and string chip forming mechanism, and chip breaker in drilling are analyzed. An analytical model is developed to predict the smoothness of chip ejection, the optimum helix angle for chip transport, and the effect of chip initial speed on chip ejection. Drilling experiments have been conducted to validate the chip ejection speed and chip clogging estimated by the model. The variation of chip thickness across the drill cutting edge is observed. The chip thickness increases with the drilling depth. An analytical model is developed to evaluate and predict the effect of chip thickening on cutting forces. Based on this chip thickening mechanism, it is found that the increase of drilling forces in deep hole drilling is caused by chip thickening besides chip rubbing against the hole wall. The relationship between chip thickness and chip force is validated by drilling experiments. Two models are developed to predict the spiral and string chip formation, respectively. Based on the level of bending due to the chip generation at the cutting edge and deflection by the flute, these models qualitatively investigate relationship of the point angle and flute helix angle on the average chip length. Drilling experiments validate the chip length for spiral and string chip predicted by both models. Several chip breakers for drilling are analyzed. Drilling experiments show the performance of these chip breakers is limited. One new chip breaker is designed and its performance is validated by drilling of the AISI 1018 steel, which is ductile material. |
