Ultrasonic welding device

A method of welding, comprising:

• providing first and second joining partners;
• providing a welding apparatus that comprises a sonotrode with a structured working surface;
• arranging the first and second joining partners to contact one another;
• and
• forming a welded connection between the first and second joining partners by contacting the first joining partner with the structured working surface and vibrating the sonotrode at an ultrasonic frequency;
• wherein the structured working surface comprises a plurality of apexes, a plurality of nadirs between immediately adjacent ones of the apexes, and planar sidewalls that extend between the nadirs and the apexes,
• wherein for each of the apexes the planar sidewalls on either side of the respective apex extend along first and second planes that intersect one another at an acute angle,
• wherein for each of the apexes the planar sidewalls on either side of the apex merge with one another to form an acute point at the apex,
• wherein the structured working surface further comprises a plurality of curved surfaces that extend between immediately adjacent ones of the apexes and each of the nadirs are formed by the curved surfaces, and
• wherein a vertical displacement between each of the nadirs and the apexes on either side of the respective nadir is the same throughout the plurality of apexes and the plurality of nadirs.