Abstract: Disclosed is a tube-enlarging press in which clamping units are provided for preventing the fins and tubes used in a heat exchanger, from being buckled. The clamping units are provided with a through-hole for permitting the passage therethrough of mandrels falling outside of the area of the fin when the mandrels are lowered during the tube enlarging process. Therefore, the arrangements and preparations for replacement of the mandrels can be omitted.

Abstract: A method of production of a part formed with an opening wherein a metal strip material is subjected to rolling at its outer peripheral portion to have its thickness slightly reduced and shape the metal strip material into a ring-shaped blank, and at least one of inner and outer peripheral portions of the ring-shaped blank is drawn by a press to form at least one flange. The metal strip is supported in coil form on an uncoiler and payed out therefrom and subjected to a straightening before being subjected to rolling. When the metal strip material is rolled, its inner side is wrinkled. The ring-shaped blank is cut and a projection is formed at one end portion and superposed on the other end portion to be joined by electric spot welding to provide a completed ring-shaped blank. When the blank is drawn to form the flanges, by virtue of the wrinkles and thinned outer peripheral portion, the thickness of the part becomes substantially uniform.