Prediction And Experimental Study On Machining Stability Of Thin-Walled Workpieces

Thin-walled workpieces that due to their material saving,light weight and compact structure are widely used in aerospace,weaponry,precision instruments,life and many other fields.However,the processing of thin-walled workpieces is a difficult problem in the material processing field.The reasons are that compared with the traditional processing,the stiffness of the thin-walled workpiece has a large gap with the rigidity of the processing system,and the machining process cannot be regarded as the coupling between the rigid workpiece and the rigid spindle and the thin-walled workpiece has poor processability.During the machining process,the deformation of the thin-walled workpiece is larger than that of its own size,and it has structural nonlinearity.Therefore,the whole machining system is the coupling of the flexible workpiece and the rigid spindle;usually it is considered that when the relationship between the thickness h of the plate and the minimum plane span b of the plate satisfies the relationship h/b<1/6,it can be called a sheet,so the loss of the quality and rigidity of the thinwalled workpiece are not negligible during the machining.The influence of factors such as elastic deformation of the workpiece and dynamic change of cutting force makes the workpiece highly susceptible to chattering,which greatly affects the surface precision and surface quality.Therefore,the research on milling stability of thin-walled workpieces has great research value and significance.In this paper,the thin-wall workpiece milling system is taken as the research object,analyzes the system's dynamic characteristics and predicts its stability.The main research contents are as follows.Based on the advantages and disadvantages of transfer matrix method and impedance coupling substructure method,the transfer matrix method based on Timoshenko beam theory and the substructure method based on Euler-Bernoulli beam theory are established.The relevant software is used to simulate the spindle and analyzes the error size and calculation speed of each method to solve the natural frequency.The influence of the average length-to-diameter ratio of the main axis on the natural frequency error solved by the substructure method is also studied.A finite element model of the workpiece system is established to solve the frequency response function of the workpiece system.The time-varying workpiece dynamic characteristics caused by the workpiece being cut during the cutting process of the workpiece system are studied in combination with the thin-walled workpiece dynamic analysis method and modal modification method.The frequency response function of the spindle system is used to solve the dynamic characteristics of a specific spindle system,draw the stability lobes of the spindle system,and consider the influence of the tool tip length to diameter ratio,the cutting force coefficient and the number of tool teeth on the stability of the system.The stability of the workpiece system is plotted and the modal correction method is used to consider the influence of cutting position,workpiece thickness and path of the workpiece on the stability of the system.Finally,the coupling model of the workpiece-spindle is established.The stability of the coupled system and the spindle system are compared to study the influence of the coupled system on the stability.A mathematical model of dynamic cutting force is established,the cutting thickness model in the classic literature is given,and the cutting thickness model in the actual machining process and the cutting thickness model considering the deformation of the main shaft are derived.Finally,experiments were performed to solve the cutting force coefficient,and the error range of the model was verified.The Von Karman large deformation theory and thin plate theory are used to establish the differential equation of nonlinear motion of the cantilever thin plate.The incremental harmonic balance method is introduced in detail.The method is used to solve the nonlinear differential equation of the cantilever thin plate,and the nonlinearity of the workpiece material to the workpiece system is considered.And consider the effect of workpiece material on the nonlinear vibration of the workpiece system,and then consider the effect of workpiece thickness,external excitation frequency and cutting force on the nonlinear vibration of the system.The research in this paper predicts the stability of thin-walled workpiece milling.It can not only serve the research and development of high-end machine tools but also optimize the surface precision and processing quality of thin-wall workpiece milling in the aerospace and automotive industries.