PROBLEM TO BE SOLVED: To securely punch a metal plate 5 without causing burr, crack, and so on without strictly managing a clearance.;SOLUTION: A punch 3 has on a leading-end face of a punch body 11 a projection 12 having a projecting curved face 16 abutting on a metal plate 5. An annular flat face 13 around the projection 12 and a side face 14 of the punch body 11 form a corner part 15 for punching the metal plate 5. The corner part 15 is rounded so as to have a radius of 0.2 mm or larger but 0.8 mm or smaller. By pushing the metal plate 5 into a die hole 6 of a button die 2 by means of the projecting curved face 16, tensile stress is applied to the metal plate 5. By causing the rounded corner part 15 to advance into the die hole 6 in that state, the metal plate 5 is punched.;SELECTED DRAWING: Figure 1;COPYRIGHT: (C)2019,JPO&INPIT
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