| 摘要 |
PROBLEM TO BE SOLVED: To prevent the generation of burr on a blank by a slit between divided nibs of a forging and heading tool. SOLUTION: The forging and heading tool is composed so that plural small pieces of nibs having the same shape of approximately isosceles trapezoid are combined into an annular shape and held in a case and a die hole 4 is formed with a regular polygonal upper die part 41 which is formed on the inside of the small pieces of nibs and lower die part 71 which is recessed into a nib receiving base 7. In each small piece 3 of nib before assembling, an angleαformed by crossing extended limes of both slaut sides is smaller than the angle dividing 360 deg.C by the number of the small pieces 3 of nibs. In a state where the small pieces of nibs are held in the case 1, slant sides 31, 31 of adjacent small pieces 3, 3 of nibs are pressed and brought into contact with each other over the entire side by elastic deformation due to clamping force with the case 1 and pressing force which acts on the butt faces of the adjacent small pieces of nibs are stronger as it goes closer to the die hole.
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