Ultrasonic welding apparatus having plurality of sonotrodes

An ultrasonic welding apparatus for ultrasonic machining of a material comprising at least two sonotrodes (3, 4) and a converter device (6, 7, 8) which converts an electrical AC voltage into an ultrasonic vibration and causes the at least two sonotrodes (3, 4) to perform ultrasonic vibration, wherein the at least two sonotrodes (3, 4) are so arranged that the material to be machined is disposed between them during the machining operation and can be machined at the same time by the at least two sonotrodes (3, 4), wherein the converter device (6, 7, 8) excites the first sonotrode at a frequency fs1 and the second sonotrode at a frequency fs2, wherein fs2 is greater than fs1, characterised in that there is provided at least one third sonotrode (5), wherein the third sonotrode (5) is so arranged that the material to be machined is positioned between at least one sonotrode (3) on the one hand and at least two sonotrodes (4, 5) on the other hand during the machining operation and wherein preferably the total surface area of the sonotrode (3) positioned on one side of the material to be machined approximately corresponds to the total surface area of the sonotrodes (4, 5) positioned on the other side of the material to be machined.