| 摘要 |
PROBLEM TO BE SOLVED: To provide a tube end flattening-expanding method with which crack generation in an expanded portion is suppressed even with a steel tube of high strength when the opening part of a steel tube end is flattened and expanded. SOLUTION: An expanding tool 10 comprises a flattening die 12 having the inner wall 13 of V-shaped section, and the flattening-expanding die 11 of triangular section which is fitted to an inner side of the flattening die, and a steel tube end opening part is pressed into the top portion of the expanding die 11. The outer side surface of an end part of the steel tube M is abutted on the V-shaped inner wall 13 of the flattening die, and the steel tube at the portion abutted on the V-shaped inner wall 13 is forcibly reduced/flattened. By further pressing the steel tube, the flattening degree is heightened by the V-shaped inner wall 13, and the triangular side part of the expanding die 11 is pressed in the major diameter direction of the flattened steel tube to give expanding deformation to a tube stock in the major diameter direction. The steel tube is then formed into the shape with the flat end opening part expanded in the major diameter direction on the whole. COPYRIGHT: (C)2004,JPO&NCIPI
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