Research On Milling Residual Stress Prediction And Machining Distortion Control Technology Of Aerospace Structure Parts

Lightweight integral structural parts are widely applied in all kinds of aerospace products.However,due to the influence of material internal residual stress,structure size,thin-walled structure,material removal rate and overall stiffness,excessive distortion is prone to occur after the machining of structural parts,which affects its service performance.It is of great significance to study the distortion of aerospace structural parts and put forward the corresponding control technology to improve product quality and production efficiency as well as control machining cost.In this paper,investigations are performed on residual stress prediction and deformation control technology in milling of aluminum alloy aerospace structure parts.First,residual stress solution algorithm based on radial return method is studied aiming at the prediction of orthogonal cutting residual stress.Comprehensively considering the influence of mechanical load and thermal load in orthogonal cutting,plastic stress is updated based on the radial return method,and the analytical prediction model of residual stress in orthogonal cutting is established The theoretical model is verified by cutting experiments of aerospace aluminum material.Results show that compared with the existing calculation methods,all stress components in radial return method are updated without a priori assumption of elasticity.The calculation process of radial return method satisfies the consistency condition of plasticity.The residual stress prediction model established by radial return method can effectively avoid stress mutation and yield drift,and has high prediction accuracy.Second,a residual stress prediction model in milling is established based on the residual stress prediction model in orthogonal cutting.Considering the characteristics of transient variable thickness oblique cutting in the milling process,the mechanical and thermal stresses are calculated based on three-dimensional elastic contact mechanics and moving periodic changing milling heat source model.The milling residual stress is solved by radial return method developed in Chapter2.Measurement experiments of milling temperature and residual stress of aerospace aluminum alloy are carried out to verify the established model.Based on the experimental results of residual stress in milling bottom surface,a surface stress distribution model is established.The key influencing factors of the residual stress in milling are clarified.Results show that in side milling,the ploughing effect of the cutting edge on the machined surface is greater than the shearing effect of the cutting tool on the workpiece material.The feed per tooth influences the residual stress through the joint action of mechanical stress and thermal stress;the residual stress value increases with the increase of cutting speed.The key influencing factors of the residual stress on bottom milling are milling depth,milling width,feed per tooth and cutting speed in the order from strong to weak.Third,aiming at the challenges of milling vibration thin-walled parts,a vibration suppression method based on the shear thickening characteristics of corn starch is proposed.Through the milling vibration experiments of aerospace aluminum alloy thin-walled structures under different concentrations of corn starch suspension,it has been proved that corn starch suspension has a significant inhibitory effect on milling vibration.To further explore the vibration suppression mechanism,a milling dynamic model considering the characteristics of cornstarch suspension is established,and the theoretical results are verified by experiments.The theoretical and experimental results show that the milling vibration of thin-wall structure part can be effectively suppressed by the corn starch suspension.When the concentration of corn starch suspension reaches 48%,the vibration amplitudes are reduced by more than 90%,and fine surface machining quality is obtained.Further analysis of the vibration reduction mechanism shows that the shear thickening property of corn starch suspension under high frequency intermittent milling loads is the main reason for vibration suppression and distortion reduction.Finally,comprehensively considering initial residual stress,machining residual stress and structural characteristics of aerospace structural parts,a machining distortion prediction model caused by residual stress is established,and the model is verified by machining experiments.On this basis,a distortion control method combining machining allowance control with the effect of corn starch suspension is proposed.Machining distortion measurements are carried out to verify the effectiveness of the distortion control method on three kinds of typical aerospace aluminum structural parts.Results show that the bending distortion occurs under the joint action of the initial residual stress and the machining induced residual stress.The influence of initial residual stress is dominant on the machining distortion.By the distortion control method proposed in this paper,the machining distortions of three typical aerospace structural parts are significantly reduced,which proves that the distortion control technology proposed in this paper can effectively reduce the machining distortion of aerospace structural parts.