Abstract: A machine for corrugating a metal foil strip includes a form gear having identical cavities along its perimeter that is driven intermittently by an electronically controlled rotary servomotor to index successive cavities to a forming station. During each dwell of the form gear, a form tooth of a punch unit at the forming station is driven by an electronically-controlled linear servomotor into the cavity to at least partly form a corrugation in the strip. During each operating stroke of the punch unit, a hold finger clamps the immediately outgoing node of the corrugation that just left the forming station against the immediately outgoing tooth of the form gear, thus preventing any part of the outgoing corrugation from being pulled back into the cavity and ensuring that the next corrugation is formed solely from a segment drawn in from the incoming foil.