Effects of Drill Vibrations on Cutting Forces and Torque

Drill bit vibrations can have an adverse affect on drilling performance resulting in lobed holes, burr formation and tool breakage. An analytical model for predicting torque, thrust and radial forces in drilling has been developed. The model includes the effects of the drill bit transverse deflections which lead to variations from the mean values in the cutting forces. Simulations for a drill, exhibiting increasing elliptical translational motion due to drill vibrations, indicate a significant increase in the ranges of the torque and thrust while maintaining essentially constant mean values. The same qualitative trends are also observed experimentally. The model, when drill vibrations are negligible, reduces to previous models for predicting the mean torque and thrust in drilling. The mean drilling torque and thrust values predicted are in good agreement with experimental data and with previously published models.