Lobed preparatory blank for cold extruding a cup-shaped article with hollow polygonal interior

摘要

The invention relates to the cold extrusion of a part having a polygonal interior and a cylindrical exterior. Instead of the usual process of forcing a polygonal punch into a billet in a single extrusion step, the new method employs a plurality of extrusion steps, first forming a lobed preparatory blank and then in a second extrusion step providing a punch and die combination whereby the external lobes of the intermediate part are forced radially inwardly. In the second extrusion step a polygonal punch is used to provide the proper polygonal interior surface. A cooperating die is provided with an upper lobed cavity for receiving the lobed preparatory blank and this die is oriented with respect to the polygonal punch so that the interior lobes of the die are exactly opposite the flats of the polygonal punch. Below the upper lobed cavity of the die is a cylindrical cavity of smaller diameter and between the two is a conical surface which directs the metal of the lobes inwardly into the die cavity opposite the flats of the polygon. The preferred polygon is a hexagon.