电辅助双层异型波纹管液压胀形变形协调机制及缺陷控制

Since the special-shaped structural and hard-deformed material characteristics in hydroforming of bi-layered special-shaped metallic bellows (BSB), it is easily encounter defects, such as over thinning, wrinkling, bursting, insufficient filling, etc. Thus, an electric assisted hydroforming method is adopted to reduce deformation resistance, improve formability and finally realize precision forming. In the process, the hydroforming and pulse current are imposed asynchronously. The deformation compatibility mechanism and its whole-process collaborative control as well as the defects control are two key scientific problems need to be solved urgently. The project aims to establish a 3D FE model for the BSB electric assisted hydroforming by obtaining the relationships of pulse current on stress-strain curve, temperature, texture, grain of the Inconel 625 strip. Based on the model, the deformation compatibility mechanism in the whole process is revealed and the deformation collaborative control method is achieved. Further, the defects and failure modes are analyzed. By carrying out influence studies on the defect indices, multi-objective optimization for the process parameters is implemented to obtain the stable deformation zone and realize the defects control. The validation is performed by manufacturing typical products. After finish the project, the urgent demand on bi-layered rectangular bellows may be solved and a high-performance precision forming method for special-shaped bellows is developed.

受“异型轮廓”结构特性和“难变形”材料特性的影响，双层异型金属波纹管传统液压胀形过程中极易出现材料过度减薄、起皱、破裂、充填不足等缺陷，因此，提出采用电辅助液压胀形的方法，通过变形-电流异步加载方式，降低变形抗力，提高材料塑性，解决材料精确塑性成形的技术难题。研究材料变形协调机制、进行全过程不均匀变形协同调控，实现成形缺陷控制是亟待解决的关键科学问题。本项目拟通过获得脉冲电流作用对Inconel 625高温合金带材应力应变关系、温升、组织晶粒变化的响应，建立电辅助双层矩形波纹管液压胀形全过程三维有限元仿真模型，揭示成形全过程材料变形协调机理，获得不均匀变形协同调控方法；分析变形协调失效形式和缺陷产生的原因，开展工艺研究和多目标优化计算，获得稳定成形区间并实现缺陷的控制；开展典型件实验验证，解决核电领域对双层矩形波纹管的迫切需求，发展一种异型金属波纹管高性能精确成形方法。

围绕双层矩形金属波纹管“异型轮廓”结构特征和“难变形”材料特征导致的充填不足、材料过度减薄、起皱、破裂问题，本项目在液压胀形工艺基础上，提出了基于电辅助的液压胀形、多步液压胀形、液压胀形+机械校形三种方法，通过建立仿真分析模型、分析材料变形行为，揭示了三种成形过程的材料变形特征及参数影响规律，获得了壁厚减薄率、过渡圆角段波高与不同参数之间规律性的响应。基于理论分析、仿真分析和实验，形成了成形工艺路线，对比研究了三种成形工艺的优缺点和适用范围，实现了成形缺陷有效控制，突破了异型波纹管不均匀变形协同调控这一技术难题，发展了金属波纹管成形技术，丰富了异型结构件精确塑性成形理论。.研究取得的进展包括：（1）揭示了高温合金矩形波纹管液压胀形直边段和过渡圆角段的协同变形特征、获得了工艺参数及结构参数对波纹管液压胀形的影响；（2）揭示了脉冲电流作用下高温合金的宏观力学响应、建立了“电-热-力”多场耦合的高温合金矩形波纹管电辅助液压胀形有限元模型，阐明了电流参数对矩形波纹管电流异步加载液压胀形过程的影响规律；（3）提出了多步液压胀形工艺方案，揭示了波纹管变形特征、阐明了工艺参数的影响规律、获得了优化的工艺参数组合；（4）提出了矩形波纹管“液压胀形+机械校形”复合成形的方案，揭示了其变形特征及缺陷演变规律并进行了方案优化；（5）设计加工了四种成形工艺的实验模具，研制了典型矩形波纹管，并对各成形工艺的适用性进行了评价。研究成果在本领域著名期刊IJAMT、CJA、MST等发表期刊论文10篇（其中SCI期刊5篇），并在国内学术会议上发表会议论文2篇；申请发明专利6项，其中授权5项。获2020年度中国有色金属工业科学技术奖三等奖，项目负责人入选2019年度陕西高校第三批“青年杰出人才支持计划”，培养硕士生7人。