汽车轻量化板材的平底无铆振动连接塑性变形行为及其损伤机理的研究

Lightweight materials, manufacturing technology and the car body structure optimization are the three main approaches to achieve the lightweight constructions. The lightweight materials, such as aluminum or magnesium alloys, are widely utilized in the automotive industry for the weight reduction. The flat-clinching of the lightweight sheets, one of the advanced joining technologies, has been a hot research topic abroad, but there is no relevant literature in China. Here, a new manufacturing technology, called vibratory flat-clinching, is proposed to join two lightweight sheets in the vibration field coupling with plastic deformation. First, deformation mechanisms and damage evolution mechanisms are revealed and the formation condition of the interlocking is obtained in vibratory flat-clinching. The mechanisms of effect of vibration frequency and amplitude on joining two sheets are then revealed when the interlocking is influenced by material flow, friction, stress field, strain field, displacement field and velocity field. Third, the reasonable process parameters (including the shape and dimension of joining tools, vibration frequency and amplitude, speed and displacement of the punch) to join the lightweight sheets by different material and thickness in vibratory flat-clinching are obtained. Furthermore, the experimental equipment and computer control system in vibratory flat-clinching are developed to join the two lightweight sheets. The corresponding experiments are investigated and the strength predictive model is established. Lastly, performance assessment systems of the joint are developed to evaluate the joint quality.

实现汽车轻量化的三个途径分别是材料、工艺与结构，因此诸如铝合金、镁合金等轻质的汽车板材在汽车中获得了广泛的应用，且轻量化板材的平底无铆塑性连接先进工艺技术是国外该领域的研究热点，而国内未见相关研究的报道。为此本项目提出一种在振动场、塑性变形力场的耦合作用下，实现双层板材平底无铆振动塑性连接的新工艺；揭示该平底无铆振动塑性连接的机理和材料内部的损伤机理，获得该无铆塑性连接时S形机械锁的形成条件；揭示振动频率与振幅对双层板塑性连接时的材料流动、摩擦状况、应力场、应变场、位移场、速度场的影响机制；获得不同材质和厚度的双层板材平底无铆振动塑性连接时模具形状及尺寸、振动频率及振幅、冲压速度和冲压行程等合理工艺参数；研制出适用于双层轻量化板材无铆塑性连接的实验装置及其计算机控制系统，并开展相应的实验研究；建立双层板材平底无铆振动塑性连接点的强度预测模型，进一步获得双层板材塑性连接质量评价指标。

实现轻量化的三个途径分别是材料、工艺与结构，因此诸如铝合金、镁合金、钛合金等轻量化板材在汽车、飞机等交通工具制造领域获得了广泛应用，且轻量化板材的连接技术成为国内外研究的热点，本项目针对轻量化板材的平底无铆连接塑性变形机理及流变行为进行系统深入的研究。.基于DEFORM-2D有限元分析软件，开展了双层轻量化板材的带有台阶形压边圈的平底无铆大塑性连接成形工艺的数值分析，指出在双层板材之间要获得高质量的平底无铆大塑性变形连接，铆接头剖面应为倒置形状的机械锁；进一步揭示了平底无铆塑性连接在双层板材之间获得倒置Ω形状的机械锁的过程中应力场、应变场、速度场、损伤场的演化过程及材料流动行为。通过正交试验法对平底无铆连接过程中的五种因素进行模拟方案组合，确定了冲头圆角半径、拔模斜度、压边圈内半径、压边圈圆角半径和冲头的冲压速度对铆接头几何参数中互锁值影响的权值顺序；获得了不同的冲头形状、不同的压边力对铆接头几何参数中互锁值和颈厚值的影响规律，进一步确定了该倒置Ω形状的机械锁的合理尺寸。.设计了平底无铆塑性连接的交流伺服成形设备中的模具、动力源及计算机控制系统，研制出了平底无铆塑性连接的交流伺服成形设备；建立了伺服控制系统中的摩擦模型、动力源、执行机构的数学模型及仿真模型，通过试验验证了该平底无铆成形设备及其伺服控制系统的可靠性。.开展了厚度为1.5mm、2.0mm、2.5mm的Al5052、Al6061和Q235三种材质双层板材的平底无铆塑性连接试验；在INSTRON实验机上开展了铆接头的抗拉试验和抗剪试验，分析了抗拉试验和抗剪试验中板材铆接头的不同失效形式，揭示了底厚值、板材的材质及厚度、压边圈的形状及压边力对铆接头强度的影响规律；综合考虑互锁值、底厚值和颈厚值对铆接头强度的影响，建立了平底无铆塑性铆接头抗拉强度与抗剪强度的预测公式。与外凸铆接头的无铆塑性连接铆接头相比，平底无铆塑性连接的铆接头的抗拉强度提高了53.6%，抗剪强度提高了4.13%，连接效果足满足工程实际应用要求。