| The aero-engine is also called blade machine,so the manufacturing quality of blade directly affects the service performance and life of the engine.With the increasing requirements of bypass ratio,thrust-weight ratio and service life of aero-engine,The blade structure becomes more complex such as thin wall,wide chord,bending and sweeping.The material is more difficult to cut,and the precision and surface quality requirements are higher,which put forward more stringent requirements for blade manufacturing technology.Multi-axis NC machining is the main manufacturing method of aero-engine fan and compressor blades.However,in the process of blade precision NC milling,because of the difficult cutting materials,poor rigidity of the parts,dynamic characteristics of the cutting process and strong time-varying,it is very easy to appear chatter phenomenon,resulting in low machining accuracy and poor surface quality of the blade.Therefore,the accurate establishment of the dynamic model of thin-walled blade milling process and the effective strategy of chatter suppression are the key to achieve high-efficiency and high-quality machining of such parts.In this paper,the aero-engine blade is taken as the object,the key technologies involved in high quality NC milling of aero-engine blades,such as dynamic modeling of time-varying process system,prediction of time-varying modal parameters,optimization of tool position and process stiffness are studied.The main research contents and main innovative achievements of the paper are as follows:1.A dynamic model of single flexible milling system for thin blade is established.On the basis of analyzing the milling process model of thin-walled workpiece,the type division and dynamic modeling of milling process system are carried out.In view of the milling process system of thin-walled blade,a single flexible time-varying dynamic model is established based on the dynamic model division criterion of flexible process system.On the premise of considering the influence of cutter axis vector on the stability,a single flexible time-varying dynamic model is established.The stability domain analytical model of thin-walled blade process system is established according to the stability criterion of blade dynamic system.2.A modal perturbation prediction method for thin-walled part milling process is presented.Based on the perturbation principle,the evolution mechanism of dynamic characteristics in thin-walled blade milling and the calculation model of time-varying modal parameters prediction are proposed.The modal parameters prediction in thin-walled blade milling process is realized by the first-order perturbation method.Firstly,the blade process model is simplified and discretized along the chord length direction without losing the dynamic characteristics of the process system.The mass matrix and stiffness matrix are calculated based on the geometric parameters and material properties of the discrete element.Then,the reliability of the prediction method is verified by comparing the measured modal with the simulated value,and the real-time prediction of modal parameters under the condition of blade material removal is realized.3.Three dimensional stability region lobes for milling thin-walled part under time-varying conditions are established.Based on the modal prediction of blade material continuous removal process,a fully discrete method for calculating the lobe diagram in the stable region with the relative change of tool-workpiece position is studied.Secondly,based on the stability criterion of blade dynamic system,the three-dimensional blade lobe diagram in stable region is established,and the effects of structural characteristics,material removal process and cutter axis vector on lobe diagram are analyzed.Finally,the evolution process of three-dimensional lobe diagram under time-varying mode is analyzed by numerical calculation method,which provides a theoretical basis for the selection of optimal cutting speed in thin-walled blade machining process.4.A tool axis vector control method for thin-walled part stability cutting is developed.The transient cutting force model of the ball-end milling cutter for blade finishing and the boundary of the contact area of the ball-end milling cutter are analyzed.A fast method for calculating the contact area is proposed,and the mapping area of the contact area corresponding to different inclination angles is obtained.Finally,the correctness of the cutting force model is verified by cutting force simulation experiment.Based on the stability lobe diagram,the optimal tool axis vector parameter domain is determined,and the deflection cutting force is taken as the constraint boundary.The trend diagram of the influence of tool axis vector on the transient cutting force is analyzed,and the tool axis vector is further optimized to ensure the blade stable cutting.5.The optimization method of non-uniform allowance for thin-walled part stability cutting is proposed.The mechanism of influence of milling process allowance distribution on blade dynamic characteristics is studied.An optimization model of non-uniform allowance distribution based on eigenvalue sensitivity is proposed.Firstly,the simplified blade process model is discretized orderly along the stack direction to calculate the stiffness sensitivity of each discrete element.Secondly,according to the sensitivity distribution of each node,the analytical relationship between stiffness,sensitivity and allowance thickness distribution is established.Finally,the thickness variation at the calculated node is mapped.The final finish machining drive surface is constructed on the surface of the blade process model,and the process stiffness of the blade is enhanced.The validity of the method is verified by experiments.Finally,a comprehensive suppression strategy for milling chatter of thin-walled blades is experimentally verified.The results show that the proposed strategy can significantly improve the machining quality and precision of aero-engine blade parts. |
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