Synthesis of the 3D artefact for quick identification of thermal errors in machine tools

Abstract

A method for quick identification of spatial-variant thermal errors using onmachine measurement of a three-dimensional (3D) reference artefact is proposed. The artefact is devised to apply for the real machining operations without interfering with machining operation. To minimize the thermal effects of the environment, the artefact is made of a material with an extremely low coefficient of thermal expansion. Thermal drifts of the cutting tool edge against the workspace origin, thermal expansions of three feed axes and thermal distortions of C-shaped machine frames are calibrated simultaneously through one setup of the artefact. Comparing geometric information of the invariant artefact measured in cold and warm states, we can derive thermal error parameters without calibration of the artefact by an external measuring device. It takes less than 4 min to calibrate spatial-variant thermal errors. We can apply the calibration process using the artefact on a shop floor conveniently. The accuracy of the proposed method is confirmed through the diagonal test of ANSI/ASME B5.54. Positioning errors in the diagonal direction have been reduced from 40 μm to 10 μm after compensation of the spatial-variant thermal errors.