飞机蒙皮拉伸成形加载轨迹设计及优化

Optimization of loading trajectory for skin stretch forming process

加载轨迹是决定飞机蒙皮拉伸成形质量的关键因素.首先对双曲度单凸蒙皮变形最大截面采用应变控制方法,通过解析分析公式推导设计拉形加载轨迹范围;然后将各加载参数转化为拉形设备中夹钳和工作台运动参数,并作为设计变量;最后采用最优化理论与算法和有限元数值模拟相结合的方法,以减小卸载回弹提高贴模度为研究目标,以单元最大主应变和厚度减薄率为约束条件建立最优化数学模型,采用序列二次规划的优化方法确定最合理的拉形加载轨迹;对优化结果进行实验验证,实验结果和优化结果相吻合.分析表明加载轨迹优化后,成形零件的贴模度、应变分布与厚度的均匀程度均有明显提高.

Loading trajectory is the key factor in skin stretch forming. First the loading trajectory of double curve skin was designed through the analytic method, then the parameters were changed to the machine＇s instructions which were used as design variables. The method of combining finite element analysis and optimization algorithms was proposed to acquire the reasonable loading trajectory. Optimization mathematics model was set up in order to reduce springback and improve the fittability. The reasonable loading trajectory was found through the numerical simulation and sequential quadratic programming optimization algorithm under the restrictive of maximal thickness strain. Experiment was done according to the reasonable loading trajectory. Both numerical simulation and experiment results show that the precision, strain distributing and thickness uniformity of skin are improved greatly.