A device for ultrasonically welding metal parts includes a sonotrode whose head can be excited by a vibration generator to produce vibrations. The sonotrode is connected to the vibrator with a screw connection provided on one side of the sonotrode. The sonotrode head may have at least one welding surface relative to the torsion axis on the circumference side. An anvil having a counter/compacting surface may be arranged opposite the welding surface of the sonotrode in a stationary position. The welding surface and the compacting surface may delimit a compaction space to receive parts to be welded. The entire sonotrode may be excited to produce torsional oscillation with a negligibly small longitudinal vibration component.