Analytical Modeling Method Onto Thermal Deformation Errors Of Precision Spindle Unit

As an important functional part of high-end CNC machine tools,the thermal deformation error at the end of precision spindle is an important factor that causes the machining error of machine tools.The formation mechanism of thermal error of spindle can be summarized as follows: During operation,the heat generated by the internal motor and bearing in high-speed operation cannot be timely and effectively dissipated,which leads to the temperature rise of spindle structure.The thermal elastic deformation of spindle caused by the temperature rise will directly affect the end accuracy of spindle,and then affect the comprehensive accuracy/accuracy stability of high-end CNC machine tools.Therefore,the establishment of a reliable thermal error model at the end of the spindle unit is of great significance to improve the positive design level of the thermal balance of the spindle structure and the machining accuracy/accuracy stability level of China's high-end CNC machine tools.In this paper,by analyzing the mechanism of thermal error of precision spindle unit,based on the model of thermal deformation of rolling bearing structure for spindlerelative thermal displacement of inner and outer rings,the linkage model of relative thermal displacement of inner and outer rings of rolling bearing-the thermal deformation error at the end of spindle unit is established.The high-precision temperature information is obtained by the thermal-fluid-solid coupling simulation modeling method,and the bearing force load information is obtained by the force balance relationship.Finally,the thermal error model of the precision spindle unit considering the thermal deformation of the bearing structure is constructed.Firstly,based on the theory of thermoelasticity,a temperature rise-thermal deformation model of a thick-walled ring elastomer,which mainly considers the influence of temperature rise,radial pressure of inner and outer circumference and axial pressure of end face.Based on the model,the thermal deformation model of angular contact ball bearing and cylindrical roller bearing for spindle is established.Based on the thermal deformation of bearing structure,the force load-relative thermal displacement model of high-speed angular contact ball bearing and cylindrical roller bearing is constructed.Then,through the Fluent Flow module in the Ansys Workbench simulation platform,the thermal-fluid-solid coupling simulation model of the precise temperature field of the precision spindle unit is established,and the temperature rise information of the bearing at different times is extracted.On the one hand,the force of the spindle bearing is obtained through the force balance analysis.According to the force load-relative thermal displacement model of the inner and outer rings,which considers the thermal deformation of the bearing structure,the radial linear thermal error and the angular thermal error of the spindle are solved.On the other hand,the temperature of Fluent Flow module is transmitted to State Structural module through Ansys Workbench,and the thermal-structure coupling simulation model of spindle rotation unit is established in State Structural to simulate the axial linear thermal error at the end of spindle.Finally,based on the thermal error model of the precision spindle unit,taking the spindle experimental conditions as a reference,the change rule of the thermal error at the end of the spindle at different speeds is studied,and the model is verified by the spindle temperature and thermal error test experiments.The results show that the thermal error model established in this paper can effectively predict the linear thermal error of the spindle end in the vertical direction,the thermal error of the rotation angle and the linear thermal error of the axial direction,and has high analysis accuracy,which provides theoretical support for the subsequent thermal balance design and thermal error suppression technology.