Analysis Of Machining Distortion Of Aluminum Alloy Prestretched Plates Based On Residual Stresses

Machining distortion has been a major challenge in China and world airframe industry which costs billion of losses in profit every year. The challenge in aerospace monolithic component is particularly outstanding, although the production capacity of aluminum alloy thick plate increased rapidly in China in recent years, machining distortion and performance problem result of China needs to import aluminium alloy thick plate for aviation at the same time of aluminum alloy thick plate overcapacity. The material removal of aluminum alloy thick plate caused rebalancing of residual stress is an important factors of machining distortions in aerospace monolithic component, but the residual stress of aluminum alloy thick plate formation in its production process is not controlled by the manufacturing process. Therefore, the paper mainly analyzed from two aspects, that is, aluminum alloy thick plate production and machining distortion caused by material removal. Based on the research status of aluminum alloy thick plate and aerospace monolithic component, by the means of experimental testing, mechanical modeling, numerical simulation, and so forth, emphases of research are on the quenching and prestretching process, the analytic formula of workpiece distortion caused by residual stress relaxation is derived. Finally, Python scripting language is used for quenching and prestretching process on ABAQUS for custom-made application development. The main work contents are as follows:1. The discretization method is employed to separate the aluminum alloy thick plate into levels. The equivalent plastic strain can be defined for every level according to the residual stresses during quenching. The formula of non-uniformity of yield strength and elasticity modulus are derived, the yield strength model with less than 2%difference is formulated as a function of the equivalent plastic strain. Moreover, the curve of elasticity modulus is fitted according to the variation of elasticity modulus with plastic deformation. By considering the non-uniformity of yield strength as well as elasticity modulus, the pre-stretching is simulated for the residual stresses when the conditions of the pre-stretching ratios are 1.8%, 2.2% and 2.5%, respectively. In comparison to unproposed method, whether the distribution or the magnitude the residual stresses obtained by the proposed method are more good agreement with the experimental measurements.2. The equivalent force stress hypothesis and equivalent stress in rolling direction hypothesis is used to the analysis of workpiece distortion caused by residual stress release. The analytic formula of workpiece distortion caused by residual stress relaxation and equivalent stress in rolling direction after material removal is derived based on mechanics, geometry and mathematics. The comparison result of analytic formula method with finite element method shows that their result are very similar and the analytical formulas derived in this paper are correct.3. Aiming at the tedious process of finite element modeling and a large number of quenching simulation parameters, a custom-made application program is development to realize rapid modeling of quenching and prestretching. The feasibility of the custom-made application is verified by operational example.