Abstract
The study deals with the search for the usable critical length of the block hom provided several slits in a stepped rectangular block. The horn is used to weld two long parts in an ultrasonic plastic welder, and its vibration characteristics are not clear because of its complex configuration. On the condition that a shape and size of cross section of the horn is constant, the FEM vibration analysis of the horn is executed under a variety of lengths of the horn, numbers of the slits, and shapes of the slits. The amplitude distribution on the small end surface of the horn, where it is an evaluation factor of the horn's usability, is examined from the results analyzed. As a result, it is confirmed that the usable critical length of the horn is 690 mm.
