Thermal Analysis Of High-speed Motorized Spindle With Ball Bearing

Motorized spindle unit is the core component of processing equipment, in which the drive motor is built to eliminate the transmission devices. So the processing error caused by the factors such as the vibration and inertia of transmission can be avoided. However, the built-in motor and the high speed bearing will produce a large amount of heat that can’t be released effectively in the process of operation, which will seriously affect the machining accuracy due to the thermal displacement. Therefore, it is significant to analyze the hot state of the motorized spindle unit to provide evidences for the design and improvement of motorized spindle.This paper takes the high speed motorized spindle as the research object to analyze the main heat sources, in which the motor is placed between two front and one rear angular contact ball bearings. Based on the rolling bearing analysis theory, the kinematic relationship among the various components of the ball bearing is analyzed to obtain relative tangential speed between the ball and the bearing raceways and the spin angular velocity of the ball, which are used to compute heating consumption of the bearing by the local heat calculation method. It is found that the influence of the bearing speed on thermal consumption is greater than that of axial load, and the ball’s spin is the main form of the ball bearing heating. The heating power of the motor is calculated based on the asynchronous motor’s rated power and efficiency factor. Heat transfer theory is applied to compute the boundary parameters of the simplified model of spindle. On the basis of aforementioned analysis, the steady-state and transient-state analysis are done respectively by ANSYS under a certain speed with no load. The temperature distribution shows that the highest temperature appears in the iron core of the motor rotor. To get the stress distribution and thermal displacement distribution along the axial direction of the motorized spindle, the results of steady-state thermal analysis are used as temperature load to do thermal-structure coupling analysis. The results show that the maximum axial displacement appears at the front end of the spindle, and the maximum axial stress appears on the contact point between the ball and the outer ring of the front bearing.Finally, an experiment is performed by a no load spindle to verify the accuracy of the simulation results. After the motorized spindle runs for a certain time, the temperature of outer wall of the spindle and inner wall of the spindle is measured using a multimeter and a temperature sensor. The deviation between experimental results and the theoretical values is within 10%, which illustrates the theoretical method is reliable.