Ultrasonic Welding of Aluminum 6111: Reliability and Maintainability Study of Robot Mounted C-Gun Welding System

Ultrasonic metal welding (USW) is a promising joining method for aluminum automotive body construction applications. During USW, aluminum weldments are joined together by applying high frequency vibrations while holding the parts together with a moderate clamping force. In an effort to further the development of USW for high volume robotic body construction applications, a reliability and maintainability study was performed using a robotic welding cell installed in the Ford Research and Innovation Center. The robot was equipped with a modified Sonobond ultrasonic metal welder, which was mounted on a C-frame. The study consisted of welding fully overlapped 550 mm × 350 mm × 0.9mm thick AA6111-T4 aluminum panels with 330 welds on each panel until 100,000 welds were made. Consistency in welder operation was monitored by welding fully overlapped AA6111-T4 aluminum strips (25mm wide × 550 mm long × 0.9mm thick) at the end of each day’s welding and then tensile testing the strips in a T-peel configuration. There was no statistical difference in average T-peel strength over the course of the 100,000 weld study. There was also no degradation noted in lap shear failure loads between samples welded at the end of the 100,000 weld study and those generated before initiation of the study. Reliability of the USW process during this study was monitored by periodic inspection of the robot and welder joints, attachments, fittings, tip, anvil, clamps, cables, etc. Only very minor wear of the welder tip and anvil contact surfaces were noted after the study was completed. However, during the study, after 82,000 welds a small piece of aluminum was removed from between the tip grooves, even though the weld strength was unaffected by the presence of the aluminum. There were no failures of any mechanical or electrical parts during the study. In addition, primary voltage and current signals of the ultrasonic welder’s power controller were periodically recorded during the weld study and it was determined that there was no change in the electrical behavior of the welder.