PURPOSE: To execute effectively forming of a collar part of a collared through- part by an operation of once, by forming a tapered part on a punch, decreasing gradually a gap between the punch and die inner hole, and providing a means for aligning automatically the punch by an operation of a magnet.
CONSTITUTION: A tapered part 35 is formed on an ironing punch 34, and a gap between the punch 34 and a die inner hole 11 is decreased gradually as the punch 34 goes in. The first magnet 44 is embedded in the bottom face of the punch 34, and the second magnet 46 is provided on a bottom face 45 of an opposed punch holding case 32. A repelling action is generated between both the magnets 44, 46, the punch 34 is aligned, and it is held so as to be movable in a state that a flange part 38 had been pressed against the inside surface of a detaining edge part 42. When a die 10 is made to go into the inner hole 11 of the punch, a tip tapered part 36 spreads out a prepared hole 48 of a thin plate base material 50, and extrudes its opening edge part to the die 10 side. An extruded cylindrical part is ironed between the tapered part 35 of the punch 34 and the die inner hole 11, and a collared through-hole 54 of uniform thickness having a collar part 52 of prescribed height is formed.
SAITOU KANJI
FUKUDA YASUHIRO
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