Research On Cutting Mechanics And Dynamics Of Five-axis Machining Of Deep Cavity Surface Based On Basis Transformation

The core parts with the characteristics of deep cavity surface are widely used in major equipment in petroleum,chemical,aerospace and other fields.The space in this type of parts is relatively narrow,and the cutter system has long overhang and weak rigidity.Material of parts has poor machinability and heavy cutting force during the process.It is prone to chattering during machining,resulting in poor surface quality.In order to avoid chatter,the machining parameters selected are often very conservative,which seriously reduces the equipment utilization.It is of great significance to study the cutting mechanics and dynamics of this type of parts to optimize the machining process and machining parameters,and improve the surface machining quality and the machining efficiency.Therefore,the contact geometry between the cutter and the deep cavity surface is analyzed in the five-axis machining based on the research idea of base transformation.Considering the material cutting characteristics,a mechanical model of the ball-end mill is established.Combined with the modal parameters of the cutter system identified by trial cutting experiments,a milling force prediction model and a vibration stability prediction model for five-axis machining of deep cavity surface are proposed.The main research contents are as follows:(1)Based on the idea of base transformation,a five-axis machining analysis method for deep cavity surfaces is proposed.Each cutter location point of the five-axis machining of deep cavity surface is discretized into five-axis machining of workpiece with simple geometry.The relationship between the cutter coordinate system,cutter axis,feed and workpiece is parameterized.An abstract two-dimensional space is constructed with new bases,and the mapping relationship between the cutter location points of five-axis machining of deep cavity surface and the space point set is established.The results of cutting mechanics and dynamics research of cutter location points are stored evenly in corresponding space.Then the prediction of milling force and vibration stability of five-axis machining of deep cavity surface can be simplified as an efficient data extraction of cutter location points.(2)Taking the five-axis machining of deep cavity surface as the research objects,the contact geometry between cutter and workpiece is analyzed with analytical method.In oblique plane five-axis machining and concave crescent cylinder five-axis single root clean-up machining,the previous tool path sweep surface,the current tool path sweep surface,the cross section,the surface to be processed,etc.,are expressed analytically.The boundary of the cutter workpiece engagement(CWE)is obtained by intersecting of the space surfaces.Based on the CWE limitation method and the space limitation method,two analytical algorithms of in-cut cutting edge(ICCE)for five-axis machining of deep cavity surface are proposed.Compared with experiments,solid modeling method and discrete method,the analytical method can balance both efficiency and accuracy.(3)Considering the dynamic mechanical characteristics and mesoscale scale effect during material cutting,the milling force model of ball-end mill is established.The forces in the first deformation zone and the third deformation zone are analyzed for the oblique cutting of discrete cutting edge element.The plastic shear flow stress considers the strain hardening,strain rate strengthening,thermal softening and mesoscopic scale effect during cutting,and a dislocation density correction experiment is designed.The linear relationship is used to approximate the relationship between the friction coefficient and the cutting thickness,cutting speed and rake angle.The cutting thickness considers the influence of cutter run-out.In the experiment of five-axis machining of deep cavity surface,the measured force and the predicted force agree well in amplitude and trend.(4)A modal parameter identification method for cutter system is proposed,and a vibration stability prediction model for five-axis machining of deep cavity surfaces is established.Based on the zero-order analytical method,combined with the chatter frequency and the limit depth of cut obtained during the experiment,a series of stiffness,natural frequency and damping ratio are calculated,and the optimal modal parameters are further selected.The identification method has been verified by the hammer test,and it can reflect the modal characteristics of the cutter system under working conditions.Combining dynamic milling force and modal parameters,the vibration differential equation of weak rigid cutter system is constructed.The complete discretization scheme is used to solve the eigenvalues of the transfer matrix,and the vibration stability of the machining system is judged with Floquet theory.The effects of machining parameters such as rotation speed,cutting depth,step distance,feed speed and cutter axis vector on vibration stability are analyzed.In the experiment of five-axis vibration stability of deep cavity surface,the measured results are consistent with the predicted results.