Research On Residual Stresses And Deformation Of Thin-walled Precision Rotary Parts Induced By Machining

With the development of aerospace technology, better performances of aviation components such as stable precision, long life and low cost becomes more and more important, which bring forward stricter demands for the capacity of some key parts. Due to the advantages of light in weight, material saving and compact structure, thin-walled parts are extensively used in aerospace and precise instrument industry in the past few years. However, owing to the low stiffness caused by the special structure, deformation is easily generated in the process of machining thin-walled parts influenced by cutting forces, cutting heat and clamping. A new distribution of residual stresses will emerge after the coupling of the initial residual stresses left by previous processes and the cutting induced residual stresses. All these factors will impact the long-term stability of performance and precision of parts. Therefore, in order to improve the quality and capacity of aerospace thin-walled parts, the object of the thesis is to predict and control the machining deformation and residual stresses of thin-walled rotary parts by means of theoretical analysis, finite element simulation and scientific experiment on the basis of researching the status quo of thin-walled parts machining at home and abroad.After analyzing the status quo of residual stresses and machining deformation of thin-walled parts at home and abroad, a prediction mathematical model of cutting force considering the three affecting regions nearby the rake face, tool edge and flank face is established on the basis of Johnson-Cook's flow stress model. The strain and strain rate of material are introduced into this model to better match the fact of large strain and high strain rate exists in the cutting process. Oxley's mathematical formula is given. And the influencing rules of tool parameters and cutting parameters on cutting forces are studied using the previously established mathematical model. By means of cutting experiments, the validity of the model is proved.Based on the established cutting force model, a prediction mathematical model of cutting induced residual stresses considering the cutting region, tool edge radius and tool flank wear is established combined with the temperature model and the rolling/sliding contact analysis model raised by Jaeger. The influencing rules of tool parameters and cutting parameters on cutting induced residual stresses are studied using the established mathematical model. By means of cutting experiments, the validity of the model is proved.According to the elastic-plastic finite element theory, a 3D finite element cutting model is established using the ABAQUS software. By means of finite element simulation, the influencing rules of tool parameters and cutting parameters on cutting force, cutting heat and cutting induced residual stresses as well as the influencing rules of different machining processes on the distribution of residual stresses are studied. And unanimous results can be found in simulation, mathematical model prediction and experiment.A theoretical prediction model of thin-walled parts machining deformation considering initial residual stresses, cutting force and cutting heat is established based on the above cutting force model, temperature model and residual stresses model, which is then used to predict the machining deformation of thin-walled rotary parts in cutting process. ABAQUS is used to simulate the heat treatment processes of thin-walled rotary parts, the distribution of initial residual stresses in simulation is the same as the heat treatment experiment, which proves the validity of finite element simulation. The birth-death element technology of ABAQUS is introduced into the simulation of thin-walled rotary parts machining deformation; the simulation results are unanimous with the theoretical prediction results. Meanwhile, the machining deformation under two different ways of clamping is simulated.Finite element simulation and general rotation experiment design method are combined to make the simulation experiment planning. Genetic algorithm is applied in the parameter identification of cutting induced max residual stresses prediction model. A prediction model with the advantages of significant regression, easy expression and convenience in analyzing the influencing rules of cutting parameters on cutting induced residual stresses is given. Cutting parameters are optimized with the constraint of the maximum residual stress. The results of influencing rules of cutting parameters on residual stresses are unanimous in prediction model, theoretical model and cutting experiments.