FIELD: expanding tube end portions. SUBSTANCE: method comprises use of attachment including a large number of cams moving radially relative to central axis between removal position and outer opened position. Cams have outer surfaces arranged one near another at removal position of cams with cross section in the form of arc-shaped ring for engaging with inner surface of tube end. Radial distance between outer surfaces of cams and central axis increases from inlet side of cams to their opposite end. Tube end is expanded successively by several steps at relatively small displacement of cams; cams are removed and introduced deeper into tube end before each expansion step. Cams may be moved radially by distance less than limit radial expansion value of tube end portion. EFFECT: enhanced efficiency of method due to increased reliability of apparatus. 2 cl, 4 dwg
