Coupling Analysis Of Deformation And Chatter And Cutter Orientations Planning In Five-axis Milling

The aerospace thin-wall parts represented by blisks and blades have the advantages of high specific strength and lightweight.However,aerospace thin-wall parts usually use difficult-to-machining materials,and have the characteristics of complex surface,weak stiffness and time-varying dynamic characteristics,which are prone to machining deformation and chatter,which will affect the surface machining quality and accuracy of the workpiece.Therefore,this paper studies the deformation and stability of thin-walled parts in milling.The main work of this paper is as follows:(1)Cutting force modeling and analysis.Firstly,the differential element cutting force model is established,the basic idea of which is that each cutting edge of the tool can be divided into several differential elements along the tool orientation direction,and the resultant force is obtained by integrating the cutting force on the differential element in the cutter-workpiece engagement(CWE)region.Then,to improve the calculation accuracy of cutting force,based on the principle of chip formation and considering the curvature of the free surface,the CWE region of the free surface machined by ball-end milling is calculated by the analytical method.Finally,the slot cutting experiment of titanium alloy plate is carried out,the cutting force coefficients are identified by the variable coefficient method,and the cutting force model is completed.(2)The coupling of machining deformation and chatter with time-varying dynamic parameters is considered.Firstly,the material removal process is analyzed,and the time-varying dynamic parameters considering material removal at different tool location points were are obtained based on the finite element method and perturbation method.Then the global stiffness matrix of the model is extracted based on the finite element method,and the machining deformation is solved according to the generalized Hooke law and the cutting force model.Then,according to the milling dynamic equation,the milling stability region is solved based on the semi-discrete method(SDM).Finally,the CWE region is iteratively calculated by studying the coupling relationship between machining deformation and chatter,and the cutting force model is modified.(3)Tool orientation optimization is carried out for machining deformation and chatter.In this paper,it is proposed that the smaller the absolute value of the eigenvalue of the state equation is,the more stable the machining is and the better the machined surface quality is.Firstly,based on the Pareto multi-objective optimization theory,the tool orientation optimization space of the key points is obtained by using the NSGA-II to minimize the absolute values of the eigenvalues in the machining deformation and stability domain.Then,in order to realize the smooth movement of the machine tool,the optimization results are searched from the tool orientation optimization space based on the Dijkstra algorithm to minimize the change of A-axis and C-axis rotation angles of the machine tool.Finally,the optimization efficiency of the whole tool path is improved by interpolating the tool orientation on the quaternion sphere.(4)The blade optimization processing experiment was completed.Based on the proposed multi-objective optimization algorithm,the optimized tool path was generated,and the tool path before and after optimization was verified by simulation,and machining experiment was carried out.By comparing the blade machined with the optimized tool orientation with the unoptimized blade,the deformation of the blade is obviously reduced,and there is no chatter on the surface,which verifies the effectiveness of the deformation and chatter coupling optimization algorithm proposed in this paper.