To enhance the insertable property of a pipe in a boss, and to suppress wear and damages of the pipe inserted in the boss.
A burring die includes a first plate, a second plate arranged opposite to the first plate to hold a platy workpiece between the first plate and itself, and a burring punch arranged so as to pierce a prepared hole in the workpiece from the side opposite from the first plate with respect to the workpiece, and be insertable in a burring hole. The burring punch is formed in a columnar bar shape, and has a small diameter part 51 on a distal end side, a large diameter part 52 on a proximal end side, and an diametrically enlarged part with the outside diameter of the small diameter part 51 being expanded to the outside diameter of the large diameter part 52. The outside diameter d1 of the small diameter part 51 is smaller than the hole diameter d2 of the prepared hole, and the outside diameter d3 of the large diameter part is formed to be larger than the hole diameter d2 of the prepared hole. The axial-direction section of the diametrically enlarged part 53 is curved.
AJIKI NAOJI
KANAI YASUYUKI
SUGIYAMA TAKETOSHI
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