Modeling Chip-Evacuation Forces in Drilling for Various Flute Geometries

In this paper, a chip-evacuation force model is presented to predict the torque and thrust required to evacuate the chips during drilling for various flute geometries. The model considers the chips in the flutes as granular solids and determines the chip-evacuation thrust and torque from the normal and lateral pressure distributions in the chips that fill the flutes. The model requires two coefficients of friction that are established via a calibration procedure. The critical depth for the process is determined by setting a threshold value on the chip-evacuation torque, which is based on the onset of chip-clogging. The effectiveness of the chip-evacuation force model in determining the chip-evacuation thrust and torque and predicting the critical depth has been assessed via a set of validation experiments using both standard and parabolic drills. The parabolic drill produced lower chip-evacuation forces and increased critical depths relative to the standard drill. While the standard drill has a modestly larger effective flute cross-sectional area for most of the flute length, the parabolic drill has a significantly smaller contact area between the chips and the flute surface, which is the main reason for the superior chip-evacuation performance of the parabolic drill.