Abstract 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.

中文翻译：

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预弯铝合金板加工变形建模与仿真

摘要 在当前的商用航空工业部门中，通过铣削薄型和大型飞机蒙皮在预弯曲的金属板上形成凹槽以减轻重量并保持结构完整性。由于弯曲残余应力分布不对称，预弯板在加工过程中容易发生变形。本研究采用理论与数值方法相结合的方法对加工变形的机理进行了分析。分析模型是基于拉伸弯曲过程的回弹分析建立的，考虑弯曲残余应力和加工引起的应力的耦合效应。数值模型是结合壳单元和子模型分析技术构建的。此外，一系列金属板被弯曲成圆柱形轮廓并依次铣削以在内表面形成浅口袋，以验证理论和模拟模型。通过比较实验结果与预测结果与加工深度和加工应力相关的加工变形，发现初始弯曲残余应力分布呈不对称的“N”形或“Z”形，即不同于传统的对称“M”或“∩”分布。此外，变形变化趋势受到弯曲残余应力和压缩加工应力的耦合效应的影响。通过比较实验结果与预测结果与加工深度和加工应力相关的加工变形，发现初始弯曲残余应力分布呈不对称的“N”形或“Z”形，即不同于传统的对称“M”或“∩”分布。此外，变形变化趋势受到弯曲残余应力和压缩加工应力的耦合效应的影响。通过比较实验结果与预测结果与加工深度和加工应力相关的加工变形，发现初始弯曲残余应力分布呈不对称的“N”形或“Z”形，即不同于传统的对称“M”或“∩”分布。此外，变形变化趋势受到弯曲残余应力和压缩加工应力的耦合效应的影响。