Abstract: A method of corrugating a metallic pipe which achieves an increase in the limit of tube expansion ratios. First, a heated part is formed by heating a local part of an outer periphery of a pipe in a circumferential direction by a high frequency coil. Next, the heated part is located within a forming surface of a forming die, and an axial compressive stress is applied to the pipe. Thus, the heated part is expanded while restricted by the forming surface. Therefore, even when the axial length of the heated part is increased, formability is stabilized and the tube expansion ratio can be raised.

Abstract: The present invention can provide a method and an apparatus for bending a pipe whose bending cross section has reduced compressed ratio, reduced reduction ratio of area and reduced reduction in thickness and in which bending can be conducted at the desired curvature. In the present invention, both edges of the pipe bending portion are arrested and grasped, a center of one bending edge is set to be the axis and a revolution axis is amounted on it, a rotation axis is mounted at a center of the other bending edge and gears are installed on the revolution axis and the rotation axis so as to engage each other so that the driving is driven to the gear on the rotation axis. The rotation axis revolves having the radius to be the distance from the rotation axis to the revolution axis and at the same time the rotation axis rotates on its axis having the radius of the gear in response to the revolution angle.

Abstract: There is disclosed a technique characterized by the following steps. An axial load is applied from both ends of a primary tube while locally heating the primary tube by use of a high frequency coil in the peripheral direction, and the heated portion is thereby bulged. The application of load is stopped almost concurrently with termination of the heating process. The heated portion is forcibly cooled with a cooling liquid, thus molding one crest. Then the primary tube and the high frequency coil are relatively moved. The next crest is formed by repeating the foregoing steps. Such operations are consecutively repeated in the axial direction of the primary tube, thereby obtaining a corrugate tube formed with crests having a large amount of bulge and a small pitch.