Research on the motorized spindle’s thermal properties based on thermo-mechanical coupling analysis

High speed, powerful motorized spindle is one of the most important assemblies in high speed CNC machine tool. The motorized spindle mounts a built-in frameless motor in its structure and can gain very high rotary speed and high torque. It is rigid, compact and precise. This structure also has shortcomings. The heat dissipation of the built-in motor is very difficult. The angular contact ball bearings often get very high temperature rise when rolling at high speed. These shortcomings make the spindle unstable and short life. Modern high speed motorized spindles have these serious reliability problems which delay their acceptance in industry. In this paper, heat sources of heat generated by the spindle are analyzed. Thermo-mechanical coupling model for FEA on the motorized spindle is developed. Complicated boundary conditions for the FEA of the spindle system are described carefully. The heat convection coefficient of every boundary condition is calculated. The temperature field and thermal deformation of the spindle system are simulated by FEA software ANSYS. Main factors which influence the thermal properties are investigated carefully. Experiment on a custom-built motorized spindle is performed, which is very consistent with the simulation result. At last, two innovative methods are presented to improve the thermal properties of motorized spindle. The simulation on the modified spindle system indicates the innovative methods are effective.