Modeling And Analysis Of Thermal Error Of Machine Tool Spindle System

Machine tools as the manufacturing mother machine of mechanical products,its processing quality and efficiency directly affect the production technology level of other mechanical products.CNC machine tool is the most basic equipment in manufacturing industry.CNC machine tool industry has become one of the basic,pillar and combat readiness industries of the national economy.Its level has become an important symbol to measure a country’s comprehensive national strength and industrial modernization.At the same time,with the wide application of new alloy materials in aerospace,energy and other fields,as well as the increasing demand for processing efficiency in manufacturing industry,high-speed machining is becoming an important development trend of machine tools.High-speed machining can improve production efficiency,improve processing quality,reduce processing costs and realize the processing of difficult-to-process materials.Therefore,in order to achieve high-speed machining,the spindle needs to achieve higher speed.Therefore,the spindle system is the core component of machine tool,and its working performance under high-speed operation directly determines the working performance of machine tool.As the core parts of machine tools,spindle components will produce significant temperature rise and thermal deformation at high speed,which directly affects the accuracy of machine tools,and even cause damage to machine tools.On the surface of data research,the thermal error of machine tool is one of the biggest error sources of NC machine tool.Especially in precision machine tool,the load in the process of processing is very small,so the thermal deformation of spindle is larger,which can reach 60%-70%of the total machining error of parts.Therefore,reducing the thermal error of spindle is very important to improve the processing accuracy of CNC machine tools.In this paper,the thermal characteristics of the precision horizontal machining center THM6350 are analyzed,and the thermal error model of the spindle is established.Firstly,based on the theory of heat transfer and thermoelasticity,the mathematical model of temperature field of machine tool spindle is established,and the calculation methods of heat generation and thermal boundary conditions of spindle assembly bearing are studied theoretically.According to the actual working conditions,the finite element model of temperature field of spindle assembly of precision horizontal machining center is established.The temperature field of spindle assembly is analyzed under twelve rotational speeds ranging from 500 r/min to 6000 r/min.The distribution of temperature field and thermal deformation field of spindle assembly is obtained by thermal characteristics.When the spindle speed is 2000 r/min,4000r/min and 6000 r/min,the temperature field and thermal deformation of the key points of the spindle assembly of the precision horizontal machining center are measured and analyzed experimentally.The accuracy of the modified finite element model and its applicability to different working conditions are verified by comparing the measured temperature and thermal deformation of the key points of the spindle assembly with the calculated results of the finite element method under different working conditions.According to the existing thermal characteristic model of spindle system and the theory of thermal stiffness,the temperature field data of 4000r/min machine tool at the time of reaching thermal equilibrium,i.e.180 min,are taken as initial samples to identify the key thermal stiffness of spindle,which provides a basis for the next digital thermal error modeling.Finally,according to the principle of BP neural network modeling,data acquisition and BP neural network model training were carried out for six key points under twelve rotational speeds of 500r/min-6000r/min spindle of precision horizontal machining center,which had been established and verified accurately.The final prediction results show that the maximum error percentage is-0.2006%,which proves that the BP neural network has a good fit for the thermal error modeling data of the spindle.The thermal error model of spindle with high precision and good robustness is the key to realize the software compensation of thermal error of NC machine tools.The calculation and analysis process of this subject provides a digital theoretical analysis and modeling method for the thermal error modeling of spindle components of machine tools.Although it is a digital thermal error modeling and analysis for the spindle system of THM6350 precision horizontal machining center,its results and results are as follows:The improved method provides a reference for the digital modeling of the thermal characteristics,performance and thermal errors of spindle assemblies of this kind of machine tools in the future,and has great engineering generalization significance.