To provide a tube expansion method capable of preventing tip cracks when expanding a tube.
This tube expansion method comprises: a curling step for forming the edge part 14 where the entire circumference of a tube end is bent outward at least 90° or more; a concentric tube-expansion step where a tube stock 11 including the edge part 14 is expanded outward in the radial direction on the same center; and a cutting step where the edge part 14 is cut. A preliminarily expansion step for expanding the tube stock 11 outward in the radial direction may be provided before the curling step. Furthermore, an eccentrically tube expansion step for further expanding the concentrically expanded tube by deviating the center may be provided after the concentrically tube expansion step. This method is suitable to work a fuel injection tube which is mounted on automobiles.
COPYRIGHT: (C)2009,JPO&INPIT
Yuji Nakata
Mori Tadayoshi
Koji Miwa
Hiroshi Nagata
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