Drill wear monitoring using a constrained-motion drilling dynamometer and aluminum witness sample

This paper describes drill wear monitoring using the combination of a constrained-motion drilling dynamometer (CMDD) and aluminum witness sample. The drill wear state is assessed using the increase in torque and thrust force measured by the CMDD while drilling an aluminum witness sample. The drill is worn using the selected workpiece material and holes are intermittently drilled in the aluminum witness sample to determine the wear state. The hypothesis is that there is a direct link between the wear state and witness sample torque and thrust force increase, independent of the workpiece material. Therefore, a single model that relates tool wear to torque and thrust force increase can be calibrated and implemented for other drills and materials. The witness sample approach demonstrates good agreement between the predicted increase in force magnitude and the experimental results. A mechanistic drilling torque and thrust model is also described and a linear regression approach is defined to obtain the coefficients. The growth in these coefficients with drill wear state is examined and it is observed that one coefficient was highly sensitive to the wear state.