Current rise index (CRI) maps of machine tool motors for tool-wear prognostic

Abstract

Quantitative polar maps of tool-wear of cutting tools (here, chisel drills) undergoing dry machining are charted based only on transducers reporting electrical current measurements from machine (spindle and feed drives) motors. Associated with these maps are qualitative descriptions of the various modes of tool-wear afflicting the drill tools. These tool-wear maps are based a novel wear criterion developed here that relies on the % increase in motor (spindle and feed drive motors) RMS current values and is dubbed the Current Rise Index (CRI). For verification in a drilling operation application, this index is found to positively track the progressive increase in tool-wear. Utilizing this CRI and the associated polar plots, monitoring of cutting tools may be achieved simply by machine tool operator via visual monitoring of polar CRI maps generated in real-time. Naturally, such plots lend themselves to automated prognosis by common control techniques utilized in machine tool operations. Such maps may also serve as indirect means of predicting tool-wear in automated cutting operations.