The punch contacts the work piece material supported by the die & a pressure buildup occurs. When the elastic limit of the work material is exceeding, the material begins to flow plastically. The punch penetrates the work material & the blank is displaced into the die opening a corresponding amount. A radius is formed on the top edge of the hole & the bottom edge of the blank according to figure Compression of the slug material against the walls of the die opening burnishes a portion of the edge of the blank according to figure At the same time the plastic flow pulls the material around the punch, causing a corresponding burnished area in the work material. Further continuation of the punching pressure then starts fractures at the cutting edge of the punch & die. Under ideal cutting conditions, the fractures will meet & the remaining portion of the slug edge will be broken away. A slight tensile bar will be formed along the t...
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