高强铝合金关键航天薄壁构件柔性渐进成形机理与精度控制

Targeting to solve the critical problems related with small batched manufacturing of high-strength aluminum alloy thin-wall components in aerospace field, such as lower formability with complicated geometry, long forming procedure, lower accuracy control and inefficient production, a new flexible incremental sheet forming process is proposed and to be developed to dynamically integrating external energy field synchronously generated by laser beam on the localized forming zone, with systematically analyzing the macro/micro forming mechanism to realize high-efficiency incremental sheet forming and control the forming quality in macro/micro scales. Process innovation, constitutive modeling, high efficiency numerical simulation and microstructure analysis will be conducted to: (1) investigate the microstructure evolution laws with dynamic external energy field focused at the localized forming region, the hardening mode with cyclic loading and damage/fracture evolution mode; (2) reveal the intrinsic relationships among the geometric features (global feature and boundary feature) of the sheet metal components and the preformed configuration, loading path and numbers of forming pass; (3) further find the macro/micro mechanisms and the relationship with process parameters which results in dramatic increase of the formability; (4) finally work out the implementation method to flexibly form the typical aerospace sheet metal parts and the strategies to control the dimensional accuracy by geometric compensation oriented loading path and surface quality. The research results will certainly provide theoretic support and technical reference for the in-depth industrial application of advanced incremental sheet forming in the aerospace field.

针对高强铝合金整流罩等航天关键薄壁结构件成形特性差、成形道次多、精度控制难和生产效率低的问题，提出在动态变形区域同步叠加能量场的柔性渐进成形新方法，可显著提高材料的成形特性和变形的均匀性。深入分析材料的宏微观变形机理，实现高强铝合金钣金构件的高效渐进成形和宏微观质量的有效控制。拟通过工艺实验与方法创新、本构模型建模、数值仿真计算、成形机理和微观组织分析建模结合的方法，揭示高强铝合金在动态局部热/力循环加载条件和摩擦作用下板料的微观组织演化规律、非线性硬化规律和破裂/损伤演化规律；明晰不同宏观几何特征与中间构型、加载策略和工艺参数的关系；探究渐进成形极限变形程度显著提高的宏微观力学机制及其与宏观参数的内在联系；提出渐进成形尺寸精度补偿算法和表面质量控制策略，实现高强铝合金整流罩样件的渐进成形制造，为更多航天钣金薄壁件的高效柔性成形制造探索可行的新技术通道。

基于航天高强铝合金复杂钣金构件小批量、高效、低能耗的柔性制造需求和材料成形特性差的问题，提出了板料柔性渐进成形的整体解决方案。从如何提高铝合金板渐进成形的成形能力/成形质量/成形效率、板料渐进成形评价和微观组织演化，以及样件试制，开展了理论分析、工艺试验、数值仿真与电镜观测。重要成果有：（1）提出了二次螺旋曲线加工轨迹和点接触加工轨迹生成方法、三层板渐进成形新方法和自由渐进成形新方法，可显著提高成形质量和变形能力，降低几何偏差，缩短成形时间；（2）构建了兼顾成形特性与表面质量的搅拌摩擦渐进成形工艺窗口和兼顾宏观特性与微观组织的搅拌摩擦渐进成形最佳工艺窗口，3种铝合金的应用验证具有显著效果。（3）提出了以降低厚向晶粒梯度提高制件强度为目标的两道次双面搅拌摩擦渐进成形新方法、多道次渐进成形与轨迹补偿的阶梯特征铝合金钣金件几何精度控制方法和具有尖楞特征钣金件的单点两道次双面渐进成形与轨迹补偿的几何精度控制方法，实验验证具有较好的效果。（4）提出了用于评价板料渐进成形表面质量、成形载荷及其分量、几何扭转角的解析预测方法，可以用于指导工艺参数与设备选择，以及加工轨迹的优化。（5）建立了考虑温度和应变速率影响的韧性断裂准则和修正的GTN韧性断裂准则，以及工具头等效压缩几何模型，实现了铝合金搅拌摩擦渐进成形的数值仿真，揭示了损伤的非连续跳跃性变化和渐进成形断裂FLC模式有别于传统板料成形的FLC。（6）揭示了铝合金搅拌摩擦渐进成形过程中的动态再结晶与析出强化效应，以及室温渐进成形时的晶粒碎化、空洞演化与沿厚度方向被拉长从而延缓厚向破裂的特性。（7）制作了AA2024航天口框样件、AA5052三棱锥形钣金件、AA2024直壁深腔钣金件和Ti6Al4V航空发动机风扇叶片叶尖加强边样件。本项目发展了板料渐进成形工艺；为提高铝合金板的成形能力、破解成形质量与加工效率的矛盾提供了一系列新方法；为改善铝合金成形件的强度与塑性提供了新思路。