Prediction of Cutting Forces and Tool Breakage in Milling from Feed Drive Current Measurements

Abstract

This paper describes the use of current drawn by feed drive motors for milling process monitoring. A model of a vertical milling machine feed drive control system is used to analyze cutting force measurements from the drive motors. The current and voltage limits in the amplifier, and the friction in the feed drive assembly are included in the analysis. The viability of using armature current as a cutting force measurement sensor is discussed. The pulsating milling forces are predicted from the current measurements at tooth passing frequencies which are within the bandwidth of the servo. It is shown that tool failure in milling can be detected within one spindle revolution by adaptively filtering the average current signals at tooth passing periods. The residual terms of a first order auto-regressive time series filter is found to be sensitive to the tool failure event. The tool breakage algorithm is independent of cutting conditions and the friction in the drive system.