Research On Cutting Force And Nonlinear Chatter Stability Of Ball-end Milling Cutter

Ball end milling cutter is one of the most widely used tools in the automotive,aerospace,molds and mechanical parts industries.During processing,chatter will occur under unsuitable cutting conditions,leading to excessive tool wear and even blade chipping,deterioration of machined surface quality,reduction of production efficiency and excessive noise so it is an urgent problem to be solved in mechanical processing.For this reason,this paper has carried out the research on the modeling of the cutting force and dynamics of the ball end milling cutter and the analysis of the chatter stability.The main research work includes:(1)A simplified ball-end milling force model with three degrees of freedom is established based on the Merchant the oblique cutting theory and the tool geometric model.Based on the hypothesis of differential dispersion and Merchant oblique cutting theory,the main profile coordinate system is associated with the orthogonal cutting edge curve,and the micro-cutting force model is obtained from the perspective of theoretical analysis.According to the position change relationship of the ball-end milling cutter in the machining process,the dynamic integral interval expression is obtained,and the integration obtains the ball-end milling force model.Finally,the influence of feed rate and axial cutting depth on the cutting force of ball end milling cutter is analyzed by simulation.(2)According to the regenerative chatter theory,considering the influence of the vibration displacement in the X,Y and Z directions under unstable cutting conditions on the instantaneous milling area,a nonlinear dynamic cutting force model for ball-end milling with three degrees of freedom is established.Combining the dynamic theory and the milling characteristics of the ball-end milling cutter,a three degrees of freedom nonlinear dynamics model of ball-end milling with three degrees of freedom is established,linear structural stiffness term and the nonlinear dynamic cutting force with a time lag term are introduced into the model.The dynamic characteristic parameters of the milling system are identified through the modal hammer test and stiffness test.Through time-domain simulation,the stability of milling chatter and the influence of different axial milling depths on chatter response are studied and analyzed.(3)Through test by the three-way force sensor,the ball-end milling force model is verified.Then,the displacement sensor and the force sensor are used for experiments to verify the dynamic cutting force model of the ball-end milling cutter.The vibration displacement of the tool is obtained through time domain simulation,then the dynamic model is verified by the laser displacement sensor.The stability lobe diagram is drawn to analyze the influencing factors of milling stability,and the time domain simulation analysis is performed on the points of different areas on the stability lobe diagram.Finally,the thesis discussed the influence of the stiffness of the milling system on the chatter stability.The test results show that the three degrees of freedom ball-end milling cutter nonlinear dynamic cutting force model and the ball-end milling cutter nonlinear chatter mechanical model established in this paper are valid.By simulating the established models,it can be found that the greater the axial cutting depth or feed rate,the greater the cutting force.Increasing the stiffness of the milling system can increase the stability of milling,reduce chattering,and provide theoretical support for improving the dynamic machining accuracy of ball-end milling cutters.