| 摘要 |
<p>PURPOSE:To exactly prevent the pipe end of a branch pipe part from becoming irregular, and also to save the number of times of burring, by formed a bulge part whose top is flat and trapezoidal, when forming a branch pipe of a T-pipe joint. CONSTITUTION:A blank steel plate 6 is placed on a die 7, and a U-bend punch 9 is dropped. As for the U-bend punch 9 to be used, a plug 9' is installed to a position opposed to a die branch pipe hole 12, of a semicylindrical bottom surface 8 having the same curvature as the inside surface of a base pipe part 1 of a branch pipe side piece. When the punch 9 drops, the blank steel plate 6 is curved, and a bulge part 18' whose top is flat is formed. A reduced portion by this bulge working concentrates in a bent deformation part which is in contact with a shoulder part 8'' of the plug 9', a reduced portion of a material contacting with a flat bottom surface 8' of the plug 9' is extremely small, and on the top of the bulge part 18', no biased portion is formed. Subsequently, by a conventional method, a lower hole 11 is opened in the center of the bulge part 18', and after that, a branch pipe part is formed by burring working.</p> |
