Patent ID: 7121447

Claim:
An ultrasonic welding apparatus, comprising: an ultrasonic sonotrode; a backing plate in opposite relationship to the ultrasonic sonotrode; actuating means for displacement of the ultrasonic sonotrode and the backing plate relative to each other for pressing flat workpiece portions therebetween for welding thereof, the sonotrode and the backing plate having respective mutually facing surfaces, wherein the surface of said sonotrode includes at least one portion provided with projections and at least one smooth portion, wherein the surface of said backing plate includes at least one portion provided with projections and at least one smooth portion and wherein said smooth portions and said portions with projections are arranged to provide that said smooth portions press against a part of the workpiece portion to which forces are applied to a weld formed by said backing plate and said sonotrode, and wherein said portion of the surface of the sonotrode, which is provided with said projections, is disposed in opposite relationship to a smooth portion of the surface of the backing plate.