Effect of tool edge geometry in ultrasonic welding

Ultrasonic vibration was applied to a single AA1050 aluminum sheet, and relative motion between a weld tool and a specimen during ultrasonic welding was assessed. Weld tools with different knurled edges such as a trapezoidal pattern edge (trapezoidal edge) and a serrated pattern edge (serrated edge) were prepared in this study to investigate the effect of tool edge geometry on weld microstructure. Relative motion behaviors between weld tools and a specimen were analyzed with a high-speed camera and digital image correlation. A large difference was observed under the normal force of 588 N. In this condition, relative amplitude of the serrated edge was larger than that of the trapezoidal edge, and the penetration of the serrated edge was lower than that of the trapezoidal edge. In the serrated edge, plastic flow in the microstructure occurred because of a greater temperature rise. The strength of the joints welded using the serrated edge was greater than that using the trapezoidal edge. In addition, although smaller relative vibration was observed in both of the tool edges as the normal force increased, the serrated edge showed higher joint strength. These phenomena are discussed and related to the relative amplitude and penetration depth. It is suggested that the bonded area was enlarged by the plastic flow, thereby increasing joint strength.