High power ultrasonic technology can currently count on a number of industrial applications. Ultrasonic welding, which is a standard joining technique in many applications on plastics, has few but well established metal applications, such as copper wires, pipes and connectors welding, or, considering spot welding of aluminium thin sheets, is attractive for the automotive industry field, where it could represent a possible cost effective alternative to resistance spot welding, clinching or self‐pierce riveting. The present experimental study is addressed to this kind of application in order to evidence the effects of welding parameters and, most of all, their interactions on the tensile strength of tensile–shear spot welded lap joints. Relevant results have been achieved by dedicated and non‐conventional instrumentations applied to the welder for measuring and controlling the process parameters. The best static performance has been taken as an input for the second part of the study regarding the fatigue behaviour and the joints failure modes.