An Innovative Hybrid Ultrasonic Resistance Welding Process for Joining Advanced Lightweight and Dissimilar Materials

轻质结构对于提高燃油经济性和减少碳排放是非常理想的。作为轻量化的关键推动者，先进轻质材料和多材料结构的成功利用依赖于经济且可靠的连接工艺。电阻点焊（RSW）作为汽车行业应用最广泛的技术之一，由于不同的物理性能和冶金差异，不适合连接异种材料。此外，RSW 在加入最新一代先进高强度钢和铝合金方面还面临挑战。相比之下，超声波点焊（USW）显示出多种优势，但其应用受到通用超声波换能器输出功率的限制。该奖项重点关注创新的混合超声波电阻焊（URW）工艺，该工艺有效地集成了超声波和电阻焊，最大限度地发挥了每种工艺的优势。初步结果表明 URW 有望增强关节机械性能。该研究将深入推进对电场和声场之间复杂耦合机制的科学理解。由于该技术在汽车、航空航天和国防工业领域具有广泛的适用性，该项目直接影响美国的经济福利和国家安全。成功开发的 URW 工艺将显着有利于轻质结构，尤其是多材料结构的制造和组装。超声波和RSW系统固有的相似性使得现有的RSW机器人和设备很容易适应，从而促进URW广泛的工业应用。所获得的关于超声波诱发物理现象的知识将极大地有助于开发和改进各种先进制造工艺。一个具体的例子是超声波电阻增材制造。 URW工艺和微观结构演化模型增强了集成计算材料工程（ICME）在固态制造领域的应用。最后，该奖项带来的多学科教育计划将为机械、材料、冶金、控制和数据处理领域的下一代工程师和研究人员提供支持。这项研究的目的是增进对新型混合 URW 工艺所涉及的多物理热-机-电-声耦合机制的了解，揭示焊接结构演化的基本物理原理，并优化 URW 以连接先进的轻质和异种材料。假设超声波振动会在三个阶段影响 RSW：通过去除表面涂层和污染物来改变接触电阻，通过声流和空化效应影响熔化过程中的热力学和动力学条件，以及在凝固过程中细化微观结构。这项研究的范围包括： (1) 在各种条件下对 URW 进行全面的实验研究，然后进行焊缝的机械测试和多尺度表征。将建立过程-结构-属性关系； (2)通过高速热成像以及多物理建模对URW过程进行原位分析，以确定过程中的热力场。还将开发Al-Fe界面反应模型，该模型将通过受控热机械测试环境下金属间化合物（IMC）形成和生长的物理模拟进行验证。 (3) 在工艺参数、电极几何形状以及声场和电场之间的同步方面优化 URW 工艺，以最少的输入工艺能量实现理想的接头性能。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力优点和更广泛的影响审查标准进行评估，被认为值得支持。

Lightweight structures are highly desirable for improving fuel economy and reducing carbon emissions. As key lightweight enablers, successful utilizations of advanced lightweight materials and multi-material structures rely on economical and reliable joining processes. Resistance spot welding (RSW), as one of the most extensively used technologies in the automotive industry, is not suitable for joining dissimilar materials due to their different physical properties and metallurgical differences. In addition, RSW faces challenges in joining the newest generation of advanced high strength steel and aluminum alloys. In comparison, ultrasonic spot welding (USW) shows several advantages, but its applications are limited by the output power of generally available ultrasonic transducers. This award focuses on an innovative hybrid ultrasonic resistance welding (URW) process, which effectively integrates ultrasonic and resistance welding, maximizing the advantages of each process. Preliminary results show promising enhancements of joint mechanical performance with URW. The research will deeply advance the scientific understanding of the complex coupling mechanisms between electrical and acoustic fields. Since this technology has wide applicability to the automotive, aerospace and defense industries, the project directly impacts the economic welfare and national security of the United States. The successfully-developed URW process will significantly benefit manufacturing and assembly of lightweight, and especially multi-material structures. The inherent similarities of ultrasonic and RSW system make it naturally convenient to adapt existing RSW robots and equipment, facilitating widespread industrial applications of URW. The obtained knowledge on ultrasonically induced physical phenomena will deeply contribute to developing and improving various advanced manufacturing processes. One specific example is ultrasonic resistance additive manufacturing. The URW process and microstructural evolution model enhances applications of integrated computational materials engineering (ICME) in the field of solid-state manufacturing. Finally, the multidisciplinary educational program as a result of the award will empower next-generation engineers and researchers in the fields of mechanical, material, metallurgy, control, and data processing. The objectives of this research are to advance the knowledge of multiphysical thermo-mechanical-electrical-acoustic coupling mechanisms involved with the novel hybrid URW process, to reveal the fundamental physics of weld structure evolution and to optimize URW for joining advanced lightweight and dissimilar materials. Ultrasonic vibration is hypothesized to affect RSW in three stages: modifying contact resistance through removal of surface coatings and contaminations, influencing thermodynamic and kinetic conditions during melting through acoustic streaming and cavitation effects, and refining microstructure during solidification. The scope of this research includes: (1) A comprehensive experimental study of URW at various conditions, followed by mechanical testing and multi-scale characterizations of the welds. Process-structure-properties relationships will be established; (2) In situ analysis of the URW process through high speed and thermal imaging, as well as multiphysical modeling to determine the thermo-mechanical field during the process. Al-Fe interfacial reaction model will also be developed, which will be verified through physical simulations of the inter-metallic compounds (IMC) formation and growth under a controlled thermo-mechanical testing environment. (3) Optimization of the URW process in terms of process parameters, electrode geometry along with the synchronization between acoustic and electrical fields for desirable joint performance with the minimum amount of input process energy.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.