| The upper edge strip of the butt ribs of large aircraft wings is processed by large 7050 aluminum alloy die forging.The die forging has large dimensions and complex structure form,which will produce intricate residual stress in the production process,and the subsequent processing deformation is extremely difficult to control,resulting in the deformation of the parts after processing cannot meet the design requirements.In this dissertation,7050 aluminum alloy forgings used to make integral structural parts of wing-body ribs of large aircraft were taken as the research object,carried out the research on the distribution law of quenching residual stress of forgings,sectional cold pressing to reduce the residual stress of forgings,and evaluation of residual stress control effect of forgings based on processing deformation control.The main work includes four aspects.(1)The finite element model for quenching residual stress analysis of7050 aluminum alloy wing-body rib forgings was established,and the distribution law of quenching residual stress of 7050 aluminum alloy wingbody rib forgings was obtained.On this basis,the finite element model for quenching stress analysis of several types of special-shaped section forgings(L-shaped,T-shaped and cross-shaped and strip test pieces)with similar section shape of wing-body rib forgings was established,and combined with experiments,The distribution law of quenching residual stress of this kind of special section forging was obtained.(2)Using the finite element method,the influence rule of the cross section geometry size on the quenching residual stress of the wing body rib forgings was obtained,and the mathematical regression prediction model of the internal residual stress field of the wing body rib forgings that can be used in the engineering site was established.The model is based on the standard X-ray diffraction surface stress measurement,and the internal stress of the forgings can be quickly obtained according to the geometry size of the forgings and the quenching process conditions.(3)The finite element model for residual stress analysis of 7050 aluminum alloy wing-body rib forgings during sectional cold pressing was established.The effects of asymmetric contact in the process of sectional cold pressing,nonlinear superposition caused by the overlap of cold pressing areas and other factors on the residual stress reduction effect of forgings were studied.The results showed that after five steps of cold pressing,the overall residual stress of forgings was significantly reduced,and the residual stress reduction rate in the rib area was more than 70%,The residual stress reduction rate in the wing area is more than 85%;The unsymmetrical factors in the cold pressing process make the residual stress distribution of forgings after cold pressing show the characteristics of unsymmetrical and non-uniform.The performance analysis of the forging sample shows that the overall performance and design performance of7050 aluminum alloy wing-body rib parts after the residual stress is eliminated by the multi-step cold pressing process meet the design requirements of the aircraft.(4)The finite element model for the analysis of the milling deformation of forgings was established.The residual stress obtained by using the good quenching and cold pressing process parameters was used as the initial stress of the wing body rib forging.Combined with the final target shape of the wing body rib forging,the milling process plan was designed,the processing parameters were optimized,and the processing deformation experiments of the forging under different machining allowance conditions were simulated.The results show that the maximum deformation difference of the structural parts after processing is very small,The simulation results are verified by the processing deformation experiments of the scaled parts.The process deformation verification experiment of wing-body rib processing shows that the deformation tolerance after machining meets the design requirements. |
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