An ultrasonic rotary welding apparatus and methods of using the same are disclosed. The ultrasonic welding device includes an ultrasonic horn and an anvil. The ultrasonic horn is constrained by a mounting system. The mounting system permits the horn to exhibit two degrees of freedom. The first degree of freedom permits translational motion in a direction perpendicular to the longitudinal axis of the horn. The second degree of freedom permits rotation about an axis perpendicular to both the longitudinal axis of the horn and the direction of translational motion.