Thermal Error Prediction And Compensation Of Vertical Machining Center Spindle

In the fine and high speed machining process, the heat produced by the friction of bearing, guide rail and ball screw changed the temperature of the machine part. Because of the thermal expansion and contraction principle, the displacement field of the machine parts changed. The thermal deformation of the machine heavily affected the machining precision. A crucial measurement to improve the accuracy is to reduce the thermal deformation of the machine tool. Analyzing the thermal characteristics of the machine tool, presenting effective compensation model can reduce the machining error and improve the machining accuracy.Because of lots of heat produced by the machine tool spindle under high-speed operation, the machining accuracy of machine tools largely depends on the accuracy of machine tool spindle. The produced heat of the bearing of the spindle transfer to the spindle and the handle, which could lead to the thermal deformation of the spindle, so machining accuracy is affected. Therefore, it’s crucial important to compensate the thermal error of the machine tool spindle.In this paper, thermal characteristics experiment and analysis were conducted on the vertical machining center spindle system. Based on the analyzed results, the thermal error compensation model based on exponential function, the thermal error compensation model based on time series analysis and the hybrid thermal error compensation model based on residual analysis of the machine tool spindle were presented to reduce the effect of thermal deformation. The main contributions of this dissertation are shown as follows:(1) Designed the thermal characteristic analysis experiment of the machine tool spindle, measured the thermal deformation of the machine tool spindle, the temperature of the end of the spindle and the ambient temperature. Analyzed the experimental data, studied the change law of the temperature field and the thermal deformation of the spindle.(2) On the basis of thermal characteristics analysis of machine tool spindle, the thermal error compensation model based on exponential function was presented. A verification experiment was designed to verify the effectiveness of the compensation model under constant speed and variable speed working conditions. This compensation model can be easily and quickly implemented in production with little investment of manpower and time. But several models are needed to be conducted to meet the demand of the processing conditions and seasonal variations. So this model lacks robustness.(3) The application of time series analysis in thermal error modeling on NC machine tools was presented briefly. How to utilize the thermal error serials surveyed to conduct the thermal error compensation model was discussed in detail. A verification experiment was designed to verify the effectiveness of the compensation model under constant speed and variable speed working conditions. This online model could reflect the periodic variation and random variation of the thermal deformation, and it had better robustness. But this model couldn’t compensate the early thermal error of the machine tool spindle.(4) By making full use of the advantages of the thermal error compensation model based on exponential function and the thermal error compensation model based on the time series analysis, the hybrid thermal error compensation model based on residual analysis was presented. A verification experiment was designed to verify the effectiveness of the compensation model under constant speed and variable speed working conditions. This model also made up for the deficiency of the former two thermal error compensation models.The research is sponsored by Independent Innovation Project of Shandong Province "Independent Innovation Project of Shandong Province" (Grant No. 2013CXH40101).