Thermal Performance Analysis And Optimization Of Motorized Spindle

High speed motorized spindle technology has been developing together with the development and demand of high speed CNC machine tools. The performance of the motorized spindle has direct influence on the precision and stability of machine tool. Its dynamics and thermal characteristics play a key role in the operation of CNC machine tools. As a result, it is necessary to analyze and research in the heat generation and heart transfer of motorized spindle, so that it is possible to build the model to compute the spindle's thermal distribution. This will work as reference for motorized spindle design.The heat source and means of heat transfer inside motorized spindle are firstly determined. Then on the basis of heat transfer theory and rolling bearing analysis theory, the model to compute the heat generation, heat convection and bearing thermal contact conductance are established. After this, data for finite element analysis is computed. Finally, ANSYS software is used for steady-state, transient-state and thermal-structure coupled field analysis. Optimization is undertaken with thermal deformation as the objective variable. More detailed job is as below:Firstly, the heat sources are determined after exploring the internal structure and operational characteristics. Based on the rolling bearing analysis theory, the method to compute the rolling bearing's torque and angular velocity are acquired. These can lead to calculate the heat generation of the bearings. As for the motor inside the spindle, the way to compute its heat generation is established based on the working torque and motor efficiency. The way to compute thermal contact conductance between the bearing ball and raceway is obtained by analyzing the contact conditions between them. Finally, the method to obtain the heat convection coefficient between the spindle and different types of heat sinks are built based on heat transfer theory.After establishing the thermal model of motorized spindle, the value of heat generation rate, heat convection coefficient and thermal contact conductance under different spindle speed is computed. The data is applied to the spindle's finite element model as thermal load and boundary condition. For the rated speed, the steady-stated thermal analysis is undertaken and for the acceleration process the transient-steady thermal analysis is carried out. After this, the result of steady-stated analysis is used as the input for thermal-structure coupled field analysis, from which the thermal induced deformation of the spindle is obtained. Finally, optimization of the spindle structure is conducted with the distance between the machining end and bearings as the design variable and the thermal induced deformation of machining end as objective variable.