Influence of thermo-mechanical deformations on the positioning accuracy of CNC machine tools

Abstract

This research aims at improving the machining accuracy of the CNC machine tools by decreasing the errors caused by the thermo-mechanical deformations and increasing the positioning accuracy of the mobile element. This work analyses and researches the effects of the thermo-mechanical deformation on the positioning accuracy of the feed kinematical linkages of the CNC machine tools that are using the indirect measuring system of the position. The analysis is focused on feed kinematical linkages having rapid speed rates, of 40 m/min, that use a preloaded bearing system of the ball screw, supported at both ends. Constructive methods are also presented for decreasing the temperature at the heat generating sources by thermo-stating both the ball screw and its bearings. Through thermostats the temperature in the ball screw and its bearings is decreased, that leads to decreasing its influence on the positioning accuracy. The thermo-stating of the ball screw makes possible to keep a constant preloading force of the two ball screw nuts and, as far as the bearings are concerned, the coolant agent is the same as the lubrication agent that leads to a smooth running and, by default, to expanding the life of the feed kinematical linkage.