A new approach to thermally induced volumetric error compensation

Abstract

A traditional model for thermally induced volumetric error of a three-axis machine tool requires measurement of 21 geometric error components and their variation data at different temperatures. Collecting these data is difficult and time consuming. This paper describes the development of a new model for calculating thermally induced volumetric error based on the variation of three error components only. The considered error components are the three axial positioning errors of a machine tool. They are modelled as functions of ball-screw nut temperature and travel distance to predict positioning errors when the thermal condition of the machine tool has changed due to continuous usage. It is assumed that the other 18 error components remain identical to the pre-calibrated cold start values. This assumption is justified by the fact that the machine tool’s thermal status significantly affects three axial positioning errors that dominate machining errors for a machine tool after its continuous use. To demonstrate the effectiveness of the proposed model two types of machining jobs, milling and drilling, on a three-axis horizontal CNC machining centre are simulated and the machined part profiles are predicted. The results show that the thermally induced volumetric error was reduced from 115.40 to 45.37 μm for the milled surface, and the maximum distance error between drilled holes for the drilling operation was reduced from 38.69 to −0.14 μm after compensation.