Abstract
Spot ultrasonic welding (USW) of metals is used in mass production to join thin metal plates and / or wires and robustness of the welding process and minimizing the variation in quality characteristics of the joints are important factors. The joint quality depends on a number of factors including the design of welding tool. In this study, tools with tooth heights of 0.1 and 0.4 mm were used to produce spot welds of 0.8 mm-thick copper plates. The effect of tool tooth height on the quality of the welded samples was estimated based on a comparison of their linear weld density (LWD), normal strains in the weld spot, microstructure of samples, as well as the strength characteristics. It was established that tooth height has a weak effect on the LWD which correlates with compressive strains in the weld spot and achieves about 40 % under tooth imprints. More importantly, the distance between the areas of high weld density is half as much after USW with the tool with fine teeth than after USW with the tool with coarse teeth. Regardless of the selected welding tool fine grains form in the joint zone and submicrometer-sized pores present between the fine grains. USW with a tool with coarse teeth was accompanied with an increase in fraction of area occupied by fine grains and formation of regions with mechanical interlocking of material in joint zone. The average fracture loads of weld samples obtained using the tools with different tooth heights are similar and amount to approximately 2000 N. However, the variation coefficient of the test results is by a factor of 2.4 smaller after ultrasonic welding using the tool with fine teeth. Thus, optimizing the knurl height of flat welding tools can be an effective method for improving the stability of properties of ultrasonically welded joints.
Funding
1. state assignment of IMSP RAS - 124022900006-2
2. Part of experimental data was obtained during the accomplishment of a project supported by the Russian Science Foundation - 22‑19‑00617