Abstract: The temperature of machine tool spindle supported by rolling bearings will increase when the rotating speed goes up, which brings the change of bearings preload and restricts the spindle speed. A method is put forward to adjust spindle bearing preload automatically according to the thermal expansion characteristic of materials. Based on the analysis of the heat generated during speed increasing by friction power loss, a temperature field model is built. The spindle thermal-deformation induced by temperature rise is calculated by using finite element analysis, and according to the difference of thermal expansions of two metal materials, a mathematical model of temperature difference versus displacement is established. The solution of the bearing supporting structure design parameters is set up by using two kinds of metal materials with different thermal expansion characteristics. The simulation and calculation results indicate that the spindle speed range can be increased effectively, and the speed increases from 2.5 kr/min to 3 kr/min on a real machining center.

Key words: Automatic adjustment, Finite element analysis, Spindle bearing preload, Thermal expansion characteristics of meterial