Study On Deformation Prediction Theory And Methods Of The Aerospace Thin-walled Components During Precision Milling Process

At present,airframes are widely made of monolithic thin-walled components for the sake of weight reducing and strength ratio improvement.However,due to factors such as cutting force induced flexible deflection,dynamic vibration and non-uniform residual stress distribution induced distortion,precision machining of these low-rigidity thin-walled parts has been providing a serious challenge for engineers.In this article,the models and methods for predicting the precision milling deformation errors are systematically invested by means of theoretic analysis,mechanics modeling,finite element simulation and experiments verification.Firstly,based on large deformation theory and virtual work principle,a three-dimensional(3-D) thermo-elastic-plastic coupled finite element analysis(FEA) model is constructed to investigate the high-speed milling(HSM) processes of 7050-T7451 aluminum alloy.Several key FEA techniques,such as finite element mesh model,material constitutive model,chip separation criteria,frictions on the tool-chip interface and 3-D heat conduction governing equations,are analyzed and implemented to improve the accuracy and efficiency of the FEA simulation.A HSM case is simulated with the 3-D FEA model.The detailed calculated results are presented and analyzed,including the chip's geometric shape and its evolution processes,the stress,strain,cutting forces, and temperature distributions in the workpiece,tool and chip,as well as the residual stresses distributions on the machined surface.Secondly,based on two typical cutting force predicting models,namely the rigid model and the flexible model,a numerical simulation procedure is developed to evaluate cutting forces under different cutting conditions.The precision and validity of the prediction models are verified by the milling force experimental measurements.Then,a semi-artificial thermocouple device is developed to explore the dynamic cutting temperature variation rules in high-speed milling of A17050-T7451 aluminum alloy.Also, a cutting temperature empirical formula is constructed by means of orthogonal experimental design and multivariate linear regression analyses.Thirdly,based on the dynamic cutting force model,a method for obtaining the stability lobes is developed.The modal parameters are identified by the finite element modal analyzing.The predicted stability lobes are used to determine the optimal cutting conditions to suppress chatter phenomenon during the high speed milling process.Finally,the thin-walled workpiece distortion prediction model is systematically invested. Several key influencing factors,such as initial residual stress,cutting loads,fixture, cutting path and sequence are considered.The fields of the stress and temperature distribution rules during the thin-walled parts machining process,as well as the residual stress distribution laws,are detailed analyzed.The thin-walled workpiece local flexible deflection prediction research is mainly focused on two factors:cutting path and force. Based on two typical cutting force predicting models,a numerical simulation procedure is developed to evaluate the flexible deflections in both symmetry and step-symmetry milling process.