Modeling and simulation of machining distortion of pre-bent aluminum alloy plate

In current commercial aviation industry sector, thin and large aircraft skin-panel is milled to create pockets on the pre-bent metal plate to reduce weight and maintain structural integrity. The distortion of the pre-bent plate is liable to occur during the machining process due to the asymmetrical distribution of the bending residual stress. In this study, the mechanism of machining distortion is analyzed by the combination of theoretical and numerical methods. The analysis model is established based on the springback analysis of the stretch bending process by considering the coupled effects of bending-induced residual stress and machining-induced stress. The numerical model is constructed by the combination of the shell element and the submodel analysis technologies. Furthermore, a series of metal plates are bent to cylindrical profile and milled sequentially to create the shallow pockets at the inner surface to verify the theoretical and simulation models. By the comparisons of the machining distortions related to the machining depth and machining-induced stress between the experimental results and predictions, it is revealed that the distribution of initial bending residual stress is emerged with unsymmetrical “N” or “Z” shape, which is different from the traditional symmetrical “M” or “∩” distribution. In addition, the distortion variation tendency is affected by the coupled effects of bending residual stress and the compressive machining-induced stress.