Study On Dynamic And Static Characteristics Of Hydrostatic Bearing-spindle System Of CNC Lathe

As a key equipment for the machinery equipment industry,CNC machine tools have a very important strategic position,which to a large extent reflect the level of a country’s mechanical equipment level.As the core supporting component of CNC machine tools,bearings play a crucial role in the performance of CNC machine tools.Compared with traditional bearings,the oil film bearings have high rigidity,high load capacity and other advantages,which can better adapt to the high-speed and high-precision operation of CNC machine tools.Therefore,the oil film bearings are increasingly used in production.At present,researchers have conducted a lot of research on the dynamic and static characteristics of oil film bearings,but have not fully considered the impact of processing quality and installation error.However,machining quality and installation error have similar order of magnitude with the oil film thickness,which have a obvious effect on the performance of the oil film bearings and cause a large change in the dynamic and static characteristics of the spindle system supported by the bearings.Therefore,the thesis took the actual engineering project as the background,and studied the influence of bearing system parameters,machining quality and installation error on the performance of CNC lathe spindle system.The thesis provided a theoretical basis for the design and manufacture of hydrostatic bearing-spindle systems,and improved the performance of hydrostatic bearing-spindle systems.First of all,according to the project requirements,general transformation of CNC lathe spindle system was conducted,including: process parameters,transmission scheme and spindle system structure.The modal analysis and harmonic response analysis of the lathe machine are performed to verify the rationality of the spindle system structure.Secondly,the hydrostatic bearings used in the transformed CNC machine were designed and checked for static characteristics.Using flow conservation law and transfer function analysis method,the pressure in the oil chambers of the hydrostatic bearing-spindle system was obtained,and the dynamic response model of the hydrostatic bearing was established;using single factor variable method,the influence of the diameter of the orifice,the initial clearance of the bearing,and the oil pressure to the dynamic response of hydrostatic bearings were studied.It was found that the bearing system parameters such as the diameter of the orifice,the initial clearance of the bearing,and the oil pressure have a certain degree of influence on the dynamic response of the hydrostatic bearing,the stiffness of the oil film,and the temperature of the oil.Then,mathematical models such as surface roughness,dimension error,shape error,and assembly error were established and substituted into the mathematical model of hydrostatic bearing-spindle system’s static characteristic.The influence of machining quality and assembly error to hydrostatic bearing-spindle system’s static characteristic.It was found that the most important influence on the static characteristics of hydrostatic bearing-spindle system is the assembly error,followed by the shape error,size error,and the influence of surface roughness is small.Finally,the mathematical model of hydrostatic bearing-spindle system’s dynamic characteristic was established.The influence of surface roughness,dimension error and shape error on the dynamic characteristics of the hydrostatic bearing-spindle system wers studied.It was found that the dimensional error and shape error affect the dynamic characteristics of the hydrostatic bearing-spindle system.The influence of surface roughness is small.Axial trajectory analogy experiments were carried out using an oil film bearing test bench,and the causes of axial trajectory displacement of the experimental bench were found,providing reference for the improvement of the experimental bench.The results of the research show that the bearing system parameters determine the overall performance of the hydrostatic bearing-spindle system performance,and the bearing-spindle system’s machining quality and installation error have a certain impact on it.The results of the dissertation have important reference significance for the design and manufacture of oil film bearings.