Modified Chip-Evacuation Force Modeling and Chip-Clogging Prediction in Drilling of Cortical Bone

Abstract

Chip clogging is one of the fundamental issues faced by the dentists during the drilling of cortical bone. The chip clogging can lead to significant increase in temperature, thrust force and torque, and can even cause the drill bit to break. In this study, a modified chip-evacuation model to estimate the thrust force was developed for drilling of the cortical bone. First, the modified chip-evacuation force model with two parameters was developed based on the flute geometry. A set of drilling tests was conducted to calibrate the model parameters. Secondly, the parameter models were established as functions of spindle speed and feed, and the coefficients were then determined through nonlinear-regression analysis. The importance of cutting parameters on the model parameters was investigated via analysis of variance. Thirdly, the validity of the force model was analyzed by experimental results. Subsequently, based on the gradient of the chip-evacuation force, the chip-clogging prediction was conducted, and the prediction accuracy was assessed by the validation tests. Finally, the effect of cutting condition on the chip clogging was explored. The modified chip-evacuation force model proved to be an effective tool for predicting the thrust force, and the chip clogging could be estimated accurately with a relative error less than 10%. The spindle speed and the feed both had significant effects on the chip-evacuation force and chip clogging. The modified model could provide a better approach to finding how a pecking cycle can be implemented, and then, it can assist surgeons in selecting cutting conditions. INDEX TERMSChip clogging, chip-evacuation force, drilling of cortical bone, twist drill. NOMENCLATURE F z Chip-evacuation force. F z (0) Initial cutting force. λ Ratio between the lateral and axial pressure. D Drill diameter. A 0 Half flute area. µ f Coefficient of friction between the chip and the flute. µ w Coefficient of friction between the chip and the hole wall. l f Effective contact length of the chip element with the flute face. l h Effective contact length of the chip element with the flute heel. The associate editor coordinating the review of this manuscript and approving it for publication was Ming Luo .l w Effective contact length of the chip element with the hole wall. θ Angle between the flute face and the plane formed across the flute. z Dimensionless depth. z Hole depth. P Pressure intensity along the chip flow direction. κ, ξ Parameters of the chip-evacuation force model. F model Fitting value of the chip-evacuation force from the force model. F exp Processed thrust force from the drilling experiment. α 0 , α 1 , α 2 , α 3 Regression coefficients of κ model from the polynomial regression. α 0 , α 1 , α 2 , α 3 Regression coefficients of κ model from the logarithmic polynomial regression.