Study On The Formation Mechanism And Variation Law Of Roundness Error In Cylindrical Grinding

Ultra-precision grinding is widely used in the fields of national defense industry,optical lens in aerospace industry,and precision instruments processing.Ultra-precision grinding machine is the basis of processing ultra-precision grinding.Hydrostatic spindle is the core functional component of the ultra-precision grinding machine.And the dynamic characteristics of the grinding process system,which is composed of hydrostatic spindle,work-piece and fixture,have a decisive influence on the final roundness error of the work-piece.At present,the research in this field is not enough at home and abroad,so it is urgent to study on formation mechanism and influence law of the roundness error in spindle cylindrical grinding.The dynamic model of grinding process system including liquid hydrostatic grinding wheel/work-piece spindle,work-piece and fixture is established.The model fully considers the influence of spindle rotation accuracy,dynamic imbalance,static bearing stiffness/damping,and stiffness of center hole/roundness error,which is closer to the engineering practice,making calculation results more accurate.The natural frequencies and vibration modes of the system are analyzed by building model,and the correctness of the theoretical modeling method is verified by comparing with the results and experimental data of existing research.The model is numerically iterative solved by using the method of combining the Riccati transfer matrix with the Wilson-? method to realize the quantitative study of the dynamic response of the system.A new model for solving the method based on the cyclic iteration of "grinding force-transient grinding quantity" is put forward.According to the established mathematical model of grinding force and grinding depth which is changed with time,solve the transient deformation of shafting in every moment.Then according to the forming process of roundness error in cylindrical grinding,take the grinding wheel spindle and the deformation of the work-piece spindle into the next moment cyclic iteration,to obtain more accurate amount of transient grinding.The Matlab model calculation program is adopted to work out calculation program for the model,to realize the quantitative simulation in the forming transition process of the roundness error of work-piece cylindrical grinding.The research reveals the influence law of the grinding process system parameters(spindle rotation accuracy,dynamic imbalance,system stiffness(bearing stiffness,center frame stiffness and center stiffness),and the roundness error of center hole)on the roundness error of the work-piece.The research indicates that the influence of the hydrostatic bearing stiffness on the work-piece roundness error is obvious;rear center stiffness is insufficient,which needs center frame for supporting,and center frame stiffness can significantly reduce the work-piece roundness error and improve the accuracy;the center roundness had a greater impact on the machining roundness error,but the impact should be reduced as possible;the balance accuracy grade of the wheel spindle should not be less than G=1;the hydrostatic bearing rotation accuracy should be higher than 1?m.Participate in the construction of the experimental platform of grinding process system,and test the natural frequency of the spindle and the roundness error of the work-piece actual grinding.The research shows that the experimental value of natural frequency is basically consistent with the results of theoretical calculation,and the error is not more than 8%.The correctness of the theoretical analysis is verified by experiments.At the same time,the research also shows that the roundness error experiment is basically consistent with the simulation results,and the error is not more than 15%.Correctness of the theoretical model and the method is further verified by experiments.The work of this thesis provides important theoretical methods and effective ways to realize the quantitative analysis of the dynamic formation of roundness error of the work-piece cylindrical grinding and the exploration of the accuracy limit of grinding machine.It is of reference value.