| Cutting chatter is one of the main reasons that reduce the quality of machining,limit cutting efficiency,affect the life of machine tools and tools,and even lead to accidents.Therefore,the research and analysis of dynamic response characteristics of cutting chatter is of great theoretical significance and practical value in engineering for revealing the mechanism of cutting chatter and realizing the prediction and control of cutting chatter.In this dissertation,the dynamics modelling,numerical simulation and experimental method are used to study the nonlinear dynamic characteristics of cutting chatter in turning process based on the basics theory and method of nonlinear dynamics.The dynamic response characteristics of turning chatter system under the influence of different factors are analyzed,it is found that turning chatter system has periodic motion,multi periodic motion,quasi periodic motion,chaotic motion,or coexistence of multiple motion process.The main research contents and results of this dissertation include the following:(1)Based on the mechanism of regenerative cutting chatter,a new dynamics model of single degree of freedom regenerative turning chatter under the influence of the tool thermal deformation is established.The effects of different degrees of tool thermal deformation on the dynamic characteristics and bifurcation characteristics of turning chatter system are compared and analyzed,by comparing the bifurcation diagram and dynamic response diagram of tool chatter displacement changing with cutting speed under the influence of different tool thermal deformation,and the tool thermal deformation will lead to the earlier instability in turning system.(2)A novel two degrees of freedom model for an orthogonal turning process is developed based on considering the thermal distortion of the tool and the workpiece,by using the bifurcation diagram of the displacement of turning chatter system and Poincaré section,the results suggest that thermal deformation will affect the dynamic response characteristics of turning chatter system,leading to the occurrence of chaotic motion in advance and the corresponding parameter range of chaotic motion increases,especially for high-speed turning.In addition,thermal deformation will affect the initial balance position of turning chatter system.(3)By comparing and analyzing the bifurcation diagram,phase diagram andPoincaré section of tool chatter displacement changing with the feed speed under different workpiece speeds based on a more comprehensive two degrees of freedom orthogonal turning model,with the increasing of workpiece speed and feed speed,the chatter displacement of tool in cutting direction increases,but the chatter displacement of tool in feed direction decreases.Furthermore,the stick-slip phenomenon only appears in the cutting direction.(4)With a new proposed three degree of freedom dynamic model of cutting chatter,the nonliear dynamics of model’s bifurcation diagram,time sequence diagram and power spectrum of tool chatter displacement in three directions are analyzed.It is found that with the change of workpiece speed,tool chatter shows multiple dynamic response characteristics in the feed direction and cutting direction,but only chaotic motion in the axial direction of workpiece.The higher the speed of workpiece,especially in the axial direction of workpiece,the chatter displacement of the tool could be obviously restrained.(5)Based on the improved two degree of freedom dynamics model of friction cutting chatter,the effects of different cutting speeds and tool rake angle on the dynamic response and bifurcation characteristics of tool chatter are studied,the results show that under the action of different cutting speeds and tool rake angles,the tool with higher cutting speeds has better stability;the stick-slip phenomenon disappears in the process of tool chatter;the larger contact stiffness is conducive to reduce the chatter displacement of the tool,the contact stiffness and cutting speed have a certain impact on the dynamic response and bifurcation characteristics of tool chatter.Moreover,for the lager cutting speed,the cutting tools display robustness to the contact stiffness.(6)Based on a new proposed single degree of freedom turning process model,in this work,the effects of the regenerative and the frictional cutting force on the tool bifurcation characteristics are investigated.It is found that that the vibration amplitude of the tool increase and the chatter vibration happened earlier as the regenerative cutting force increases.Meanwhile,the vibration amplitude of the tool is reduced due to the increase of the frictional cutting force,however,it affects the original equilibrium position of the tool.(7)Using the three-way dynamic turning force test system,the dynamic response characteristics of cutting force in three directions under the influence of spindle speed and feed speed are studied by experiments.The experimental results show that the dynamic turning force has the characteristics of periodic motion,bifurcation andchaotic motion in different degrees,which indirectly shows that the cutting chatter system will have periodic motion,chaotic motion and bifurcation behavior in the turning process. |
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