带筋钛型材热拉弯宏微观变形机理及精确成形调控

Curvilinear titanium components with stiffener are high performance structures in a new generation of large airplane. They can be used to realize the best matching of thermal and potential properties between composite panel and metal frame. These components are traditionally machined from forged billets, and then bump formed. The buy-to-fly ratio is only about 30:1-10:1 and the machining cost is very high. Meanwhile, crack often occurs and forming quality is difficult to be realized. So this kind of high performance components is hindered to be used massively in the new type of aircraft. In this project, the linear friction welding is introduced and hot stretch bending process of titanium profile with welded stiffener is developed in order to enhance buy-to-fly ratio, improve the forming quality and cut the cost. The research focuses on three important scientific aspects: (1) non-uniform material flow behavior and defect formation mechanism of hot stretch bending for titanium profile with stiffener, (2) internal stress variation of profile with stiffener when hot stretch bending, (3) microstructure evolution mechanism in welded area under multi-field coupling excitation conditions. The main research contents are as follows: (1) material flow behavior and forming defects, (2) residual stress distribution, (3) microstructure evolution mechanism and mechanical property of welded area during hot stretch bending process, (4) process control and optimization of hot stretch bending. The macroscopic and microscopic deformation mechanism of hot stretch bending process for profile with welded stiffener will be revealed. The shape forming and microstructure control of the process will be realized. The research has an important academic significance to develop the inter-discipline of welding and forming. The proposed new technology is useful for realizing low-cost green manufacturing of titanium curvilinear frames of new aircraft.

带筋钛合金曲率构件是新一代大型飞机实现复材蒙皮与金属骨架之间热和电位特性良好匹配的高性能结构，目前采用锻造毛坯+数控加工+增量热压弯复杂工艺，材料切削量大、利用率极低（仅3.5%-10%），开裂等缺陷难以控制，精度性能难以保障，制约了该结构的应用。项目将热拉弯成形与线性摩擦焊组合，发展基于焊筋型材成形钛曲率构件的新工艺，以提高材料利用率和成形质量、降低制造成本。围绕带筋钛型材自阻热拉弯过程非均匀材料流动及缺陷形成机理、热拉弯复杂加载条件下焊筋型材成形过程内部应力变化规律、电/热/力多场耦合激励条件下焊筋区域微观组织形态演化机制等科学问题，从材料流动行为及成形缺陷、残余应力分布及影响规律、焊缝微观变形及力学性能、成形工艺调控与优化等方面开展研究，揭示带筋钛型材热拉弯变形机理，实现工艺过程形性调控。项目成果可丰富焊接与成形学科交叉理论，为新一代大型飞机低成本绿色制造提供解决途径。

新一代大型飞机为了减轻重量，提高经济性，大量采用碳纤维复合材料蒙皮壁板。钛与碳纤维复合材料的强度、刚度、热特性匹配良好，能获得很好的减重效果。同时，由于二者的电位比较接近，不易产生电偶腐蚀，因此，与复合材料蒙皮相连接的承力骨架大量采用钛合金曲率构件。传统带筋钛合金曲率构件工艺（如锻造+数控加工法）从坯料上直接加工出带筋构件，数控加工量很大，材料利用率极低，仅为3.5%~10%左右，材料及数控加工成本极高；工艺过程复杂，制造过程中非均匀变形导致零件残余应力大，均需制造专用复杂工装对零件进行热校形，工装成本极高。.本项目将热拉弯成形与线性摩擦焊组合，提出了基于焊筋型材成形钛曲率构件的新工艺，即首先通过线性摩擦焊在等截面钛合金型材上焊接局部筋条，形成焊筋变截面毛坯，然后通过基于自阻加热的型材热拉弯蠕变工艺实现其精确成形，最后通过少量数控加工得到高性能带筋钛合金曲率构件，实现了减少工序、提高材料利用率，显著降低制造成本的目的。.围绕带筋钛型材热拉弯过程非均匀材料流动及缺陷形成机理、热拉弯蠕变复杂加载条件下焊筋型材成形过程内部应力变化规律、电/热/力多场耦合激励条件下焊筋区域微观组织形态演化机制等科学问题，从带筋钛型材自阻加热拉弯过程材料流动行为及成形缺陷、焊筋结构热拉弯蠕变后残余应力形成机制及影响规律、热拉弯蠕变成形过程中焊缝微观变形机制及组织性能、焊筋钛型材热拉弯蠕变成形工艺调控方法等方面开展了研究，揭示了焊筋钛型材热拉弯宏微观变形机理，建立了成形过程调控与优化方法，研发了柔性随形加热工装，研制出典型钛合金主承力曲率框试件。发表论文11篇；授权发明专利4项；培养研究生6名（其中1名获得北航优秀博士论文）；获得中国航空学会科技进步一等奖1项；实现成果转化1项。.项目研究对丰富和发展焊接与塑性成形学科交叉理论具有重要学术意义，且所提出的新工艺可为实现新一代大型飞机的低成本绿色制造提供先进实用的方法和技术。