Stretch bending is commonly used in the fabrication of profile-based shapes. However, one of the challenges in many bending-type forming processes is controlling springback upon unloading. Springback appears sensitive to upstream and in-process parameters, making prediction and control difficult. The springback problem is particularly important in forming processes where stringent control strategies are needed to assure product dimension, process flexibility and overall equipment effectiveness. In this research, we present an analytical framework for springback assessment in a stretching-controlled bending process. A new, flexible rotary stretch bending machine is designed and built, which allows the manufacture of complex-shape profiles with varying curvatures, including straight portions, with low tool investments. Furthermore, a Full Moment (FM) analytical model is developed for springback assessment. The modeling strategy employs a full moment distribution along the entire profile upon bending, introducing a stretching-controlled moment transition between different curvature portions such that the springback contribution from the plastic moment outside the theoretically bent portions is considered. Additionally, the influential factors related to material, geometry and process, including the applied stretching strains, are comprehensively considered. In this way, the modeling strategy enables accurate evaluation of springback in the flexible stretch bending process. Moreover, the proposed forming process is validated by a series of experiments conducted for a wide range of stretching levels using rectangular hollow aluminum alloy profiles. This forming strategy demonstrates high capability for controlling springback and dimensional accuracy. By comparing experiments, numerical simulations and analytical calculations, this proves that the developed FM model provides accurate and efficient assessment of springback. The average relative error provided by the FM model is 2.2%, as compared to 10.5% for a classical method used for comparison. Using the analytical model combined with numerical simulation, the crucial deformation characteristics, including stretching-dependent evolution of strain transition, are revealed. Overall, the FM analytical strategy has proven its capability as an effective tool, which can make springback knowledge more explicit, generic and reuseable for stretching-controlled bending processes.

拉伸弯曲通常用于制造基于轮廓的形状。然而，许多弯曲型成形工艺中的挑战之一是在卸载时控制回弹。回弹似乎对上游和过程中的参数敏感，从而使预测和控制变得困难。回弹问题在需要严格回弹控制策略以确保产品尺寸，工艺灵活性和整体设备效率的成型工艺中尤其重要。在这项研究中，我们提出了一种在拉伸控制，柔性弯曲过程中进行回弹评估的分析框架。设计并制造了一种新型的灵活的旋转拉伸弯曲机，可以以较低的工具投资来制造具有不同曲率的复杂形状的轮廓，包括直线部分。此外，开发了全矩（FM）分析模型用于回弹评估。建模策略在弯曲时沿整个轮廓采用了完整的力矩分布，在不同曲率部分之间引入了拉伸控制的力矩过渡，从而考虑了塑性力矩在理论上弯曲的部分之外的回弹作用。此外，还综合考虑了与材料，几何形状和工艺有关的影响因素，包括所施加的拉伸应变。这样，建模策略可以在拉伸控制的成型过程中准确评估复杂形状零件的回弹。此外，通过使用矩形空心铝合金型材针对各种拉伸水平进行的一系列实验，验证了所提出的成型工艺。这种成形策略证明了控制回弹和尺寸精度的高能力。通过比较实验，数值模拟和分析计算，这证明了所开发的FM模型可提供准确有效的回弹评估。FM模型提供的平均相对误差为2.2％，而用于比较的经典方法为10.5％。使用分析模型与数值模拟相结合，揭示了关键的变形特征，包括应变转变的拉伸相关演化。总体而言，FM分析策略已经证明了其作为有效工具的功能，可以使回弹知识更加明确，通用并且可重复用于拉伸控制的弯曲过程。