Ultrasonic spot welding (USW) of multilayer metal sheets is a critical process of lithium battery manufacturing. However, inconsistent weld quality is still an issue in multilayer USW which makes the online quality monitoring very necessary to provide rapid and reliable feedbacks of each workpiece’s weld quality. In this work, the displacement of the sonotrode in the clamping direction was monitored by a high-frequency displacement sensor in order to establish the relationship with the weld quality. Features of displacement signals were analyzed combined with changes in the plastic deformation and welding qualities which were characterized by the laser scanning confocal microscopy, the optical microscopy and the electron backscattered diffraction (EBSD). Besides, effects of welding parameters on the displacement signal were studied. Finally, the relationship between the displacement signal, the plastic deformation and the weld quality was established which can be used for the online quality monitoring of the multilayer USW.

多层金属板的超声波点焊（USW）是锂电池制造的关键过程。但是，多层USW中仍然存在焊接质量不一致的问题，这使得在线质量监控对于提供每个工件的焊接质量的快速可靠反馈非常必要。在这项工作中，用高频位移传感器监测超声波发生器在夹紧方向上的位移，以建立与焊接质量的关系。分析了位移信号的特征，并结合了塑性变形和焊接质量的变化，通过激光扫描共聚焦显微镜，光学显微镜和电子背散射衍射（EBSD）表征了这种变化。此外，研究了焊接参数对位移信号的影响。最后，