Research On Stability Prediction Of Milling With Multiple Delays And Variable Delays

As an efficient cutting method,milling is widely used in aviation,aerospace,ship,automobile mould and key parts processing and other fields.The regenerative chatter in milling process is the main factor that affects the machining quality,the tool life and the production efficiency.The control and stability prediction of milling chatter is one of the most important challenges in the machining field.With the development of milling technology,the traditional linear theory of milling dynamics has been unable to guarantee the accuracy of the model.Considering the nonlinear factors of milling process is the premise to predict the stability of milling chatter accurately.Multiple delays and variable delays phenomenon is one of the main nonlinear sources of milling process.Therefore,the stability prediction of milling chatter with multiple time delays and variable delays is studied.The main contents include:(1)The dynamic cutting thickness model is established according to the geometric relationship of the helical end mills,the formation process of tool path and the regenerative effect.And according to the kinematic analysis and force analysis,the milling force in the milling process is determined.Finally,the dynamic equation of milling process based on regenerative effect and helix angle effect is established.(2)The stability prediction model of milling chatter based on helix angle effect is established by using the semi-discretization method,the updated semi-discretization method and the updated full-discretization method,respectively.And the stability criterion is put forward.According to the stability prediction results obtained by the above three methods,a better method is chosen as the research method of the stability in this paper.And then,the accuracy of the chosen method is verified by time domain simulation.Meanwhile,the influencing factors of stability limit are analyzed.(3)The effect of multiple regenerative effect on milling chatter stability is studied.The dynamic equations based on eccentric runout of milling cutter and intermittent cutting with large amplitude are established,respectively.The stability limit of milling chatter based on eccentric runout of milling cutter and large amplitude intermittent cutting is predicted by updated full-discretization method and Simulink simulation,respectively.According to the stability prediction results,the influence of the two phenomena on the milling chatter stability is analyzed.(4)The chatter control effect when the two methods of chatter control,namely variable pitch cutter and variable spindle speed milling,are adopted respectively or together is studied.Firstly,the dynamic models of milling process based on variable pitch cutter,variable spindle speed milling and variable spindle speed milling with variable pitch cutter are established,respectively.The updated full-discretization method is used to establish the corresponding stability prediction models.The stability prediction results under various operating conditions are obtained by MATLAB simulation.According to the stability prediction results,the influences of variation form of pitch and spindle speed modulation parameters on the stability of milling process are analyzed in down-milling or up-milling operations and high-immersion or low-immersion operations.