The invention relates to an ultrasonic metal welding device and a method for welding electrical conductors using a compression chamber that is adjustable at least in height and that is delimited on opposite sides by a section of a sonotrode as a first delimiting surface and by at least one section of a counter electrode (156) as a second delimiting surface, wherein for welding, the counter electrode and the sonotrode are displaced relative to one another. The counter electrode used is one that comprises sections (152, 154) of geometrically different working surfaces or is composed of at least two sections that are displaceable relative to one another.