Characterization of machine tools under dynamic conditions

Characterization of machine tools to determine its errors is an important preliminary step towards investigating the 'error profile' of the machine. A Computer Numerical Control (CMC) machine tool was characterized by determining the quasistatic and dynamic errors according to ASME B5.54 -1992 standard. Laser interferometer, autocollimator, electronic differential levels were used in determining the quasistatic errors of the three orthogonal axes. Performance evaluation of the CMC machine, consisting of machine hysteresis, temperature variation error (TVE), repeatability test and spindle drift test, were carried out. Dynamic testing were performed on an Aluminum Alloy 7075-T6 test piece. The temperature variations at nineteen different strategic locations on the machine tool were monitored throughout the dynamic test. A Coordinate Measuring Machine (CMM) was used in inspecting the machined workpiece deviations from part specification. Statistical regression analysis of the temperature variations on the machine structure identified the locations of the significant thermal sources during machining process. The study revealed high values of quasistatic errors, implying that the slides and traverse components of all three axes are worn-out and need overhauling. The spindle bearings recorded high temperatures and run-out, also indicating the need for overhaul. Significant temperature sources were Z axis top bearing, spindle shaft top and bottom bearing and back of the machine. It was observed that dynamic characterization did not quite follow predictions of static characterizations.