An ultrasonic welding system. The system includes an ultrasonic transducer assembly having a horn and a first transducer and a second transducer arranged to impart ultrasonic energy into the horn. The horn has a first part-interfacing surface and a second part-interfacing surface opposite the first part-interfacing surface. An actuator assembly is operatively coupled to the ultrasonic transducer assembly and configured to cause rotation of the horn. A controller is configured to: cause the actuator assembly to rotate the horn so that the first part-interfacing surface applies the ultrasonic energy to a first part along an entire length of the first part-interface surface while a first ultrasonic energy is applied through the horn via the first transducer to cause the first part-interfacing surface to vibrate back and forth along its entire length as the first ultrasonic energy is applied by the first transducer to the horn.