An assessment of quasi-static and operational errors in NC machine tools

This paper reports the results of a comparative study of predictive error modeling and machining-cycle machine tool accuracy. The total positional error due to geometric accuracy errors was modeled for a particular type of NC machine tool. Subsequently, the NC machine tool was tested for geometric accuracy for repeatability, small-load hysteresis, linear displacement accuracy, straightness, roll, pitch, yaw, and spindle drift. The measurements were then used as input parameters in the error model to predict the total resulting error. Machining was performed next on an aluminum workpiece, and a set of sensors was used for on-line force, torque, and temperature data acquisition. The finished workpiece was post-process inspected for all dimensions on a coordinate measuring machine. An analysis of data from the model, post-process measurements, and static geometric accuracy machine tool characterization parameters indicates significant shifts in machine performance under actual cutting conditions. Based on the findings, some important research issues are presented.