Importance

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Abstract

The exemplary embodiments provide a die set comprising a knockout punch and a necking die for necking-in a metal container preform. In an axial direction from front to back of the die, the die has an inwardly tapering in-feed surface, a forming radius, a generally cylindrical land having a die bore diameter, a discharge surface and a relief surface having a diameter larger than the die bore diameter. The land has an axial length of less than 0.1 inch. It is believed that such a length limits the number of metal contacts with the land (rebounds between the knockout punch and the land) to one or two as a metal container preform is necked in the die in conjunction with a knockout punch having a punch diameter that provides a gap between the knockout punch and the land. While the gap may be larger than the topwall thickness of the metal of the preform within the gap, it may alternatively be the same as, or smaller than, the thickness (by up to 10%), to effect re-resizing of the container wall. The exemplary embodiments also provide a method of necking a container preform using such a die.

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First Claim