Abstract: Apparatus for forming circumferential corrugations in a thin wall tube to produce a cylindrical bellows. The tube is supported on a rigid sleeve to prevent distortion, but is free to move axially as each corrugation is formed by an expanding mandrel which extends through a circumferential channel in the sleeve to form a complete ring. The mandrel is composed of interfitting wedge elements, alternate elements of which move radially more than the others to accommodate the expansion and contraction, a common multiple cam actuator providing the driving force on all elements simultaneously.