Study On Nonlinear Dynamic Characteristics Of Dynamic Damping Boring Bar System

With the rapid development of machinery manufacturing industry,there is more and more demanding of parts' precision.Because of the specificity of its processing sectors,not only the vibration caused by high-frequency boring operations reduces the machining precision and cutting efficiency,but also the noise generated by the vibration is harmful to the physical and mental health of workers.The primary goal of this work is to develop mathematical models for two and three degree of freedom dynamic vibration damping boring bar system by considering the nonlinear factors of the rubber ring and damping fluid in the damping boring bar system.Based on nonlinear vibration analysis theory,the bifurcation diagrams,maximum Lyapunov index diagrams,Poincaré maps,phase diagrams,safe basin,basin of attraction are obtained by means of numerical calculation method.Both the effect of the system dynamics parameters on the system vibration characteristics,the sensitivity of the system vibration to the initial value,the local and global dynamic stability of the system are studied,which can provide a theoretical basis for design and parameter optimization of damping boring bar system.The main research contents of this paper are as follows:The discrete dynamic model of two degree of freedom dynamic damping boring bar system is established,where the damping coefficient and nonlinear damping force are calculated.The vibration equation of a dynamic damping boring bar system with a rubber ring and a damping fluid is obtained.The system bifurcation and chaos characteristics with the change of system parameters of external excitation frequency,damping mass,rubber ring stiffness,damping coefficient,are studied with the help of bifurcation diagram,phase diagram and Poincaré diagram.It is found that the amplitude of the external excitation increases sharply and system vibration is transient instability when the frequency of the external excitation is near 0.5.The system motion alternates between the period 1 motion and the quasi period motion with the external excitation frequency increasing.When the stiffness coefficient of the rubber ring,the damping coefficient of the damping liquid,the mass of the damping block are smaller,the bifurcation characteristics,such as saddle node bifurcation,doubling bifurcation,Hopf bifurcation and torus doubling bifurcation,become very complicated.The vibration of system is relatively stable when they are larger.It is found that,under the condition of a certain size of damping block,the vibration stability of the system is enhanced when the mass of the damping block is more than 0.5 times.Therefore,in practical application,the vibration of the damping boring bar can be effectively suppressed by using the mass block with larger density.The safe characteristics of the system are studied by calculating the safe basin,and the erosion process of the safe basin is analyzed when the external excitation frequency and damping coefficient change.It is found that the system safe basin is subject to varying degrees of erosion with the change of system parameters.In order to analyze the sensitivity of the system vibration to initial value,the basin of attraction of the system is calculated numerically,and the local and global dynamic stability of the system are studied.The results show that the phenomenon of coexistence of attractors,including period and period,period and chaos,coexist in the process of parameter variation.The nonlinear dynamic model of three degree of freedom vibration damping boring bar system considering the nonlinear factors of rubber ring and damping fluid is established,and the dynamic parameters of the system are calculated.The effects of the external excitation frequency,the mass of the damper,the stiffness coefficient of the rubber ring and the damping coefficient on the vibration characteristics of the system are analyzed.