Correcting thermal errors

Dr. Scott Smith, University of North Carolina at Charlotte, suggests some remedies for correcting thermal errors which occur in machine tools. At least three options exist for attempting to correct these thermal errors, including brute-force temperature control, thermal modeling and temperature measurements and direct measurement of position errors. The brute-force option requires removing the heat before it can change the geometry of the machine. The spray of the coolant over the work zone, tool and workpiece helps keep temperatures more constant. In the thermal-model-and-temperature-measurement strategy, a mathematical model of the machine's thermal behavior is created. Using the model in steady-state conditions, the measurement of the temperature in a few critical locations on the machine is enough to predict positional errors caused by the temperature change. Transformation of the part program into the new machine geometry corrects for the thermal errors in near-real time.