Study On Chatter Stability Analysis Of Thin-walled Cylinder Workpiece In Turning Operations

Because of thin wall thickness and weak stiffness,the machining of thin-walled cylindrical cylinder has always been the focus and difficulty of mechanical industry.Under the action of dynamic cutting force,the workpiece and the tool contact point is easy to occur strong chatter,so that the workpiece surface left vibration marks,seriously affect the machining efficiency and surface accuracy.In the process of machining,the cutting system is a time-varying system due to the constant removal of the workpiece material and the change of the cutting position of the tool.Therefore,from the perspective of dynamic modeling,considering the effects of timevarying thickness and time-varying position,this paper analyzes the inherent characteristics of thin-walled cylindrical cylinder workpiece in turning,and transforms the problem of vibration system stability into the problem of selecting the value of critical cutting width.The stability limit diagram is used to predict the machining stability,so as to better predict the machining chatter before the actual machining.The main research contents of this paper include:1)The dynamic equation of the stationary state of thin-walled cylindrical cylinder workpiece is established.The beam function method was used to solve the inherent characteristics of the workpiece under two kinds of boundary conditions: fixed supportedsimply supported and fixed supported-fixed free.and the natural frequencies and corresponding mode shapes were obtained.The finite element software was used to carry out modal analysis on the workpiece,and the natural frequency and corresponding mode shape of the workpiece in the static state were obtained,and the comparison was made to verify the correctness of the finite element model.By analyzing the variation of natural frequency of thin-walled cylindrical cylinder workpiece with different thickness-diameter ratio and length-diameter ratio,it is found that the natural frequency of the workpiece decreases with the decrease of the thickness and the increase of the length of the workpiece,but the mode shapes of each order will migrate.It lays a foundation for solving and verifying the natural frequency in the subsequent stability analysis.2)Based on the regenerative chatter mechanism,the delay differential equations of single and two degrees of freedom thin-walled cylindrical turning systems are established,using analytic method and discrete method to deal with time delay,respectively for the stability limit diagram.By comparing,found that the discrete method allows direct prediction in any stable cutting condition stable state,namely stronger applicability half a discrete method,more general.For the single degree of freedom turning chatter system dynamics model,according to the corresponding stability limit expression,the influence law of different machining parameters on the vibration system stability is analyzed.For the dynamic model of two-degree-of-freedom turning chatter system,the influence of parameter matching difference between the tool and the workpiece on the stability is emphatically studied,so as to find an optimal turning condition,which can effectively avoid chatter while processing with high efficiency.3)Considering the influence of time varying factors in the cutting process,the variation law of the natural frequency of the workpiece under single cutting was analyzed.For the workpiece with time varying,the finite element model was established and the finite element limit diagram was obtained.Through simulation analysis,it is found that reverse turning can effectively improve the stability of turning weak points.Through the analysis of the timevarying workpiece model,it is found that the stability of the coupling system tends to decline in general,but fluctuates upward in local parts.Time-varying modeling and stability analysis of workpiece parameters can accurately predict the occurrence location of flutter to a certain extent,which provides reference for the follow-up online monitoring and control.The turning experiments of thin-walled cylinder workpiece on the CA6140 were carried out to verify the correctness of the time-varying stability limit diagram.According to the test results,it is found that the cutting width can be selected by using the stability prediction diagram of the 2DOF coupled vibration system to predict the chatter incidence more reliably.4)Based on the theoretical analysis of the chatter stability of thin-walled cylinder workpiece in turning,the software for predicting the chatter stability of tool-workpiece turning is developed.The software directly materializes the theoretical analysis results and assists the processor to find a larger stability region before actual processing,and be able to calculate the corresponding maximum cutting width under the specified spindle speed.The development of the software can facilitate the engineering application,save the cost of theoretical research,and realize the visibility,accuracy and high efficiency of thin-wall cylinder turning stability.