A Study On Prediction Method Of Milling Chatter For Thin-walled Titanium Alloy Parts

With the development of the aerospace industry,the technology of thin-walled parts milling has been applied more and more widely in this field.However,the low rigidity components,large quantities of material removed in machining progress,are in the risk of the instability of the progress.Therefore,how to realize the target which makes the machining of thin-wall workpiece high accuracy,high efficiency and high stability becomes an urgent problem to be solved.In this research study,the thin-walled parts such as impellers have a similar dynamic character as the tools’ in the milling progress.Thus,it is not accurate enough to reflect the variation of stability in machining by only taking the tool’s or workpiece’s dynamic character into account.And when the impeller is under milling,the materials removed will be so much that the workpiece’s dynamic character can varies in the machining progress.It is not accurate to predict the stability of the whole machining process only by using the modal data measured before machining.According to this,both the dynamic characters of the tool and workpiece have been studied to get their effects on the stability.The finite element analysis was applied to calculate the modal data of thin-walled parts and impeller in each milling stage.Then the most appropriate milling condition of thin-walled parts’ cutting can be determined by using the multi-objective constrained optimization method.The contents in this paper are showed as follow in details.(1).In this paper,the geometry of the ball-end milling tool was divided several infinitesimal elements in the axial direction and the milling force model of ball-end milling tool was built.Based on the model,the milling force model in three axes was built as well.Then according to the thin-walled part’s milling force model,by taking the slope angle of tools in the milling progress which simulated the tool’s position in machining.And then the milling force model in multi-axes had been built.(2).Based on the discretization idea in the finite element analysis method,the planar quadrilateral element and three dimensional hexahedral element model was built to analyze the modal character of workpiece and calculate its modal parameters.Furthermore,a modal test was conducted to verify the accuracy of the finite element models.For the impeller,considering its geometric features,The three dimensional shell element was used to analyze and calculate the modal characteristics of the blade.And all these were verified by experiment.(3).The effects of both tool’s and part’s dynamic characteristic were studied based on relative transfer functions.Firstly,the transfer functions of the tool and workpiece were calculated respectively.Then the milling system’s relative transfer function can be obtained by adding the ones of tool and workpiece.Thus the stability lobe diagrams can be elaborated to analyze the variation of the critical condition of milling.(4).According to the above results,the multi-objective constrained optimization of which the goal is the best machining surface quality and maximum material removal rate was built by selecting the stable machining condition as constraints.The most optimal machining parameters and cutting conditions can be obtained by calculation.