Study On Prediction Of Residual Stress And Machining Distortion For Monolithic Thin-walled Structural Components

The distortion of Aerospace Monolithic thin-walled Components is always one of difficulties puzzling the aviation industry, and it has greatly academic and engineering value to predict and manipulate machining distortion of thin-walled structural components. Therefore, a deep study is carried out on the quenching of aeronautical aluminum alloy blank taking aeronautical aluminum alloy 7075-T7 as an example. Utilizing finite element simulation and experiment verification, the stress-elimination-process of pre-stretching and the milling process of multi-frame monolithic components are also studied considering the main reason of the machining distortion.Firstly, residual stress is an important factor that results in machining distortion. To get a blank with quenched residual stress, the temperature field and stress field in quenching process are simulated by applying a sequentially coupled procedure. The variation law of the blank surface and center temperature in quenching process and temperature gradient born in the cooling process are predicted. The trend of residual stress in quenching process and the distribution of residual stress after quenched are simulated. Through analyzing that the distribution of residual stress and elastic and plastic strain after quenched in a midsection, the cause of quenched residual stress is verified once again.Secondly, the process of residual stress-elimination of pre-stretching is simulated. The influence of pre-stretching on residual stress of blank and plastic strain is analyzed. The distribution of residual stress and plastic strain in different pre-stretching magnitude are analyzed, the result indicated that the blank is stretched about 3%, the magnitude of plastic strain is about 2.4%, and the quenched-stress is removed about 89.5%. The mechanism of residual stress-elimination of pre-stretching is verified by contrast with the distribution of residual stress and plastic train.Then, the machining deformations caused by the release and re-distribution of original residual stresses are studied by the finite element method. The simulation of layered material removal is researched by using the birth and death element technology, as well as the workpiece deformation in different layer-stripping depth and the rule of residual stress release and re-distribution in the process of material removal are studied. A proportional part model is designed based on a multi-frame monolithic component from a plane, and the deformation of the model induced by residual stress in different pre-stretching magnitude is analyzed.Finally, the key techniques of finite element model for the milling machining distortion are studied, including the loading of original residual stress, the reasonable description of cutting parameter, the loading of milling force and milling temperature and the implementation of dynamic feed process. The rule of machining distortion in the role of single factor is simulated respectively. The prediction model of workpiece deformation in the role of multi-factor coupling is established. The integral machining deformation of two-frame structure component is predicted. By optimizing machining parameters, the machining distortion of workpiece is reduced. To validate the prediction model, a same dimension component is machined in a five axis machine center and its deformation is measured on a Three Coordinate Measuring Machine.