Study On Initial Residual Stresses And Their Effects On Milling Distortion For Thick Aero-Aluminum-Alloy Plate

The machining distortion is one of the neck problems during the manufacture of the aero integrated-structure parts. The study work in the dissertation is an important part of the Tenth Five-Year Defence Advanced Research Project of"study on control technology of the machining distortion for complex structure parts"supported by PLA General Armament Department of China. Theoretical analysis and experimental study are carried out on the initial residual stresses and their effects on milling distortion for thick aero-aluminum-alloy plate. The main work completed in the dissertation is as follows.1. The measurement method of residual stress distribution in thick aluminum alloy plate is studied.Aiming at the difficult problem to measure residual stress distribution in thick plate, a new method is proposed -- modified layer removal method, based on existed measurement theories and according to the characteristics of thick pre-stretched aluminum alloy plate. The new measurement theory is deduced in detail by using elasticity theory. A new approach is provided to measure the residual stress in the thick plate.2. The residual stresses in pre-stretched aluminum alloy plates are successfully measured and analyzed.The measurement precision and applicability of the modified layer removal method are analyzed and evaluated by experiments. The residual stresses in the thick aluminum alloy plates of LY12, B95п.чand 7050T7451 are measured, and the results are analyzed and compared. The data obtained lay a basis for prediction of the machining distortion caused by the residual stresses.3. Mechanism of the milling distortion caused by initial residual stress of workpiece is analyzed.Formulae of stress re-distribution and distortion by stress releasing during milling process are deduced by elasticity theory. The calculation software is developed for the formulae. The key problems in 2D FEM simulation such as the initial stress loading, simulation of material removal, constraint transformation, etc. are solved, and 2D FEM simulation model is built to analyze the milling distortion caused by the residual stress. The FEM model is verified by the elasticity theory. Some machining cases are simulated by using of the FEM model. The machining distortion caused by residual stress are analyzed and summarized using the simulation results.4. The milling distortion of frame shaped part is predicted and analyzed.Based on its characteristic analyzed, the 3D FEM simulation technique for the...