Method and apparatus for forming unobstructed holes in hollow hydroformed metal parts

Abstract

Method and apparatus for forming unobstructed holes in a hydroformed metal part employs a punch having a peripheral side conforming to the desired hole shape and an end face having a central cutting edge with a high point that contacts on closure of a hydroforming die with an unsupported wall section of the part initiating a stress riser therein. During forming of the part, the hydraulic pressure forces the above wall section outward against this high point increasing the magnitude of the stress riser. The punch is advanced while maintaining the hydraulic pressure causing the above high point to fracture this wall section at the stress riser and the above cutting edge to then split and cut this wall section to form oppositely facing cut edges in this section. Simultaneously, oppositely angled cutting edges at opposite ends of the central cutting edge and at the punch end face periphery then cut this wall section in directions away from the oppositely facing cut edges to form oppositely extending slugs. As the punch continues to be advanced, contoured portions of the punch end face with the aid of the hydraulic pressure contact the slugs to provide a seal to maintain the hydraulic pressure while bending the slugs as they are being cut into the interior of the part. The peripheral side of the punch with further punch movement engages the slugs with an interference fit to maintain the hydraulic pressure and forces the slugs into positions forming an unobstructed hole in the part while remaining integral therewith.