Apparatus for cold forming recesses in the heads of screw fasteners

Abstract

A recess is formed in a screw head by a cold forming technique employing a two piece punch which includes an outer member having an axial bore formed therethrough which receives and carries an inner, concentric punch pin for movement within the bore. The pin is mounted within the bore to have freedom of movement within certain limits. The forward end of the outer member has a surface or cavity shaped therein which corresponds to the general shape of the screw head to be formed and is large enough to accommodate the screw head when fully formed. The forward end of the punch pin has a nib formed thereon which is shaped to form the desired screw recess when impacted into the screw head. The pin is impacted into the screw head metal by driving it forwardly from its rear exposed end. The rear end of the pin presents a relatively small driving area disposed closely to the axis of the punch pin which reduces substantially resistance to the movement of the pin so that it may seek the path of least resistance through the metal during the cold forming procedure. The pin is withdrawn from the cold formed recess by engagement of a shoulder on the carrier with a cooperative shoulder on the pin. The shoulders engage along a relatively small area which is disposed closely to and symmetrically about the axis of the pin to enable the pin to move about and seek the path of least resistance during withdrawal.