Compensation for thermal deformation on sonotrodes

A sonotrode for an ultrasonic welding apparatus, the sonostrode comprising:

• a lower portion of length u and an upper portion of length o,
• the upper portion and the lower portion being arranged adjacent to each other on a longitudinal axis of the sonotrode, and a total length of the sonotrode in a direction of the longitudinal axis being u+o,
• the lower portion having a sealing surface oriented perpendicular to the longitudinal axis,
• the sealing surface configured to contact with a material to be processed,
• wherein the lower portion has a slot,
• wherein the slot extends from the sealing surface to a side of the lower portion opposing the sealing surface, such that the lower portion of the sonotrode is divided into a plurality of segments which lie adjacent to each other in a direction perpendicular to the longitudinal axis, the slot having two slot walls, and a spacing between the two slot walls tapering in the direction of the sealing surface.