Thermal characteristics analysis of machine tool spindle with adjustable bearing preload

The spindle is the key functional part of the machine tool, and the thermal deformation caused by the heat generation of the bearing seriously affects the machining accuracy. This article studies the thermal characteristics of spindle using a variable preload system and an external liquid cooling system, by analyzing the temperature rise mechanism of the machine tool. Firstly, a novel variable preload device for bearings has been designed, which enables adjustable output force direction. Based on the variable preload performance of the device, an integrated thermal analysis model of the spindle variable preload was established to simulate the temperature field and thermal displacement field of the spindle under the variable preload condition. And then, a modular external cooling system was innovatively used on the spindle housing to further reduce thermal deformation of the spindle. By establishing a thermal-flow-structural coupling analysis model of the spindle, the overall thermal characteristics of the spindle under the combined influence of variable preload bearing and modular external cooling system were analyzed in detail. The simulation results indicate that the thermal gradient and deformation of spindle with variable preload and external liquid cooling are lower than those of spindle with a constant preload, while the degree of thermal optimization gradually increases as the spindle speed rises. The accuracy of the simulation was verified by the temperature rise experiment of the spindle, which provides a foundation for engineering application.