激光冲击铆接成形及其机械冶金复合作用机制

Deformation based mechanical clinching for sheet metals is an important branch of modern plastic forming. However, it is often with low joint strength and inapplicable to ultrathin sheets, which seriously limit its industrial applications. Based on the fact that the joint performance depends on the joint structure and interface, a new joining method with high joint strength, so called laser shock clinching, is proposed in this project, which applies laser induced explosive plasma and shock pressure to the ultrathin sheets and deforms them into undercuts. Mechanical interlock and metallic bonds are generated synchronically during plastic deformation. By designing and controlling laser shock processes, similar or dissimilar sheet metals among copper, aluminum, titanium can be joined simultaneously with mechanical clinching and metallurgical welding. In order to evaluate the effects of forming conditions on the joint structures and interfaces, the form-fit and force-fit joints, and their formation mechanisms will be investigated by experiments and numerical simulations. The coupling analysis on multi-material plastic flowing process under high strain rate will be also conducted, together with SEM, DSC and other metallographic examinations, to study the interfacial behaviors such as expansion, slipping, atomic diffusion, and microstructural evolution. By stretching, shearing, bending, and micro-hardness tests, joint performance and defects in joints will be experimentally studied. The main purpose of this project is to reveal the mechanical-metallurgical mechanism of laser shock clinching, and to describe its technology and theory.

板材无铆钉铆接是现代塑性成形技术的重要方向，而低连接强度和对超薄材料的欠适应性是限制其工程应用的关键瓶颈。本项目基于结构连接形式和界面连接性质对连接性能的决定性，提出通过脉冲激光所致的爆炸等离子体和高压冲击波，将超薄板材塑性成形为互锁铆合结构，并实现界面原子结合，进行高强度无铆钉铆接的新方法。选择铜、铝、钛等板材，主动设计与控制激光冲击过程，完成同质和异质材料的同步铆合与焊合；通过工艺实验和数值模拟，从型面几何配合和力配合角度，研究结构互锁形式及其塑性成形机制，量化工艺条件和材料性能与连接结构和连接性质的关联性；通过多体材料高应变率塑性流动耦合分析，结合SEM、DSC等手段，研究铆接成形中的界面扩张、高速剪切、原子扩散和组织演变，阐明界面冶金结合的力学和材料学原理；采用拉、剪、弯、微观硬度等试验，研究材料铆接性能与缺陷，以期揭示机械冶金复合作用的铆接机制，并形成激光冲击铆接成形理论与技术。

板材无铆钉铆接是现代塑性成形技术的重要方向，而低连接强度和对超薄材料的欠适应性是限制其工程应用的关键瓶颈。本项目基于结构连接形式和界面连接性质对连接性能的决定性，提出通过脉冲激光所致的爆炸等离子体和高压冲击波，将超薄板材塑性成形为互锁铆合结构，进行高强度无铆钉铆接的新技术。通过搭建的激光冲击铆接成形实验系统以及研制的多工艺参数匹配的铆接成形模具，并采用工艺实验、数值模拟、结构表征等方法，研究了板材与预制孔板激光冲击铆接、双层/三层、同质/异质板材激光冲击铆接、渐进式激光冲击线铆接、板材激光冲击焊/铆接复合连接等研究，分析了各种工况下的材料流动规律、板材连接机制，测试了接头力学性能，归纳了铆接缺陷模式，量化了工艺条件和材料性能与连接结构和连接性质的关联性，并在材料流动、组织演变、微观硬度等方面阐明了缺陷产生原理。多材料耦合流动模拟及实验现象表明，由于激光冲击波在两层材料上的不同传播，下层箔材易于产生颈部破裂而上层箔材则更易产生底部破裂，而上下两层材料的厚度差异会显著影响塑性成形特性，即当下层箔材厚度略小于上层箔材时，材料易于流动为互锁结构；对铆接接头进行拉伸剪切测试，发现互锁尺寸和颈部厚度共同决定连接强度；互锁结构同样决定着接头的失效形式，在服役状态下，上层箔材倾向于产生拉脱，下层箔材则更容易产生颈部剪切破裂。激光冲击焊/铆复合连接研究表明，冲击焊接呈环形冶金连接区域，并在光斑中心区域造成环形鼓包，冶金结合界面处的显微硬度低于材料基体；对比焊接、铆接、焊/铆复合连接试样的力学性能，发现焊/铆复合连接试样的剪切强度明显高于纯焊接及铆接试样，且焊铆复合连接试样具有更好的能量吸收特性。本项目还发明了激光驱动液压胀形的板材铆接、半空芯铆钉激光冲击成形及同步铆接、空芯铆钉实芯化以提高铆接强度等方法，项目提出并实现的板材激光冲击铆接成形新技术，具有成形速度快、连接性能好、无冲头成形、无铆钉连接等特点，具有原始创新和源头创新性，具有重要的科学意义和工程应用前景。