Optimal machine design for 20 kHz applications for which the joining process must be precisely performed by several sonotrodes in a single weld process. The rigid sonotrode support is realized by means of individual alignment modules and allows for accurate positioning even at large weld forces. Contrary to conventional designs, the weld stroke is performed by the anvil. During this stage, the plastic parts to be welded are moved against the stationary sonotrodes. Thus, it is possible to obtain machine cycle times of less than 10 seconds.