顺序变形的多点-柔性模复合近净成形技术机理研究

Multi-point forming process is a master method for the production in the area of aviation, aerospace, shipbuilding and other industries where curved sheet parts contain small batch, many models, and small curvature. However, the traditional multi-point forming process has some weak points, such as the so making sheet metal tends to wrinkle and have large amount of springback. In order to solve this problem, a novel near-net forming method is proposed, which is based on the sequential deformation by integrating multi-point and flexible dies. Since the normal constraints are imposed on both side of the sheet metal, the normal pressure stress and tangent tensile stress are introduced to make the pressure stress of the inner sheet less than the critical wrinkling stress, and in turn to eliminate wrinkle defect. On the other hand, the tensile stress of the outer sheet is increased, so as to reduce the springback bending moment and inhibit the springback value. Through thorough and systematic research on multi-point near-net forming law, the model for calculating the normal pressure stress and tangent tensile stress will be established to gain the variation rule of springback and curvature. Besides, the stress-strain state and its impact on the wall thickness distribution in forming process will be revealed. Furthermore, the wrinkling mechanism and its control methods will be discussed to solve the aforementioned problem in traditional multi-point forming. This research could make a certain contribution to theoretical innovation in multi-point forming field.

航空、航天、造船等行业的曲面板材零件具有批量少、型号多、曲率小的特征，适于采用多点成形工艺进行生产。传统多点成形存在板料易起皱、回弹量大的问题，影响其实际应用。为解决这一问题，申请者提出一种顺序变形的多点-柔性模复合近净成形新方法。基本原理是在板料两侧施加法向约束，引入法向压应力和切向拉应力，使板料内层压应力小于临界起皱应力，可消除起皱缺陷；使板料外层拉应力增加，可降低回弹弯矩，抑制回弹。通过对板材多点近净成形规律深入系统的研究，建立法向应力和切向应力理论计算模型，给出回弹和曲率变化规律，揭示成形过程应力应变状态及其对壁厚分布的影响，探讨失稳起皱机制及其控制方法，解决传统多点成形板料易起皱、回弹量大的难题，为多点成形领域理论创新做出一定的贡献。

为解决航空、航天等行业曲面板材零件生产中存在的板材回弹量大、易起皱难题，提出了一种顺序变形的多点-柔性模复合近净成形新方法，通过在板材上下表面施加法向约束来减小板材回弹量、抑制起皱发生。通过力学分析、数值模拟和实验，系统地研究了金属板材多点-柔性模成形规律与变形行为，主要结论如下：通过力学分析揭示了法向约束力减小板材回弹的机理，给出了板材回弹量计算模型，推导出回弹补偿解析公式。推导出法向约束力作用下板材临界起皱应力的解析公式，揭示了法向约束力抑制起皱的机理。建立了多点-柔性模成形数值模型，获得了圆柱面试件与马鞍面试件应力状态。研制出多点-柔性模成形装置，通过实验研究了1060铝合金和Q295圆柱面试件回弹规律，板材回弹量比传统多点成形分别下降了38.6%和63.5%。通过实验研究了1060铝合金马鞍面试件起皱行为，传统多点成形中试件经向最大皱纹高度为2.53mm，纬向最大皱纹高度为4.58mm，多点-柔性模成形中试件未发生起皱。