Methods of and/or apparatus for punching holes in sheet metal

An improved apparatus for punching holes in sheet metal of the type wherein parent sheet metal is advanced through the nip between a punching roller and a backing roller and wherein slugs are punched from the metal to form holes therein by the punch face of punches projecting from the surface of the punching roller, wherein the improvement comprises at least one groove between lands in said backing roller aligned with the punched faces and having a base surface spaced from the punch faces so that as the slugs are punched, a slug is cracked out of the parent metal until one edge of the slug bears against the base surface of the groove at a point of contact which acts as a pivot point about which the slug pivots as force is exerted by the further action of the punch sufficiently to cause the slug to be completely separated from the parent sheet metal.

Apparatus for punching holes in sheet metal, said apparatus comprising a frame, a punching roller mounted on a shaft rotatable in said frame and carrying a plurality of punches on the cylindrical surface thereof, a backing roller mounted on a shaft rotatable in said frame and spaced sufficiently close to the cylindrical surface of the punching roller as to enable the sheet of metal to rotate the backing roller by frictional contact therewith, said backing roller having for each row of holes to be punched a groove between lands or annular rings thereon, said groove having a base disposed relative to the length of said punches and relative to said lands and said lands being spaced a distance apart substantially wider than the width of said punches so that on a sheet of metal being passed through the nip between said punching roller and said backing roller, and on said punching roller being driven, each punch punches a slug of metal so as to be cracked out of the parent metal until one edge of the slug contacts the base of said groove at a point of contact which acts as a pivot point on which the slug pivots to cause the slug to be removed completely from the parent metal by further action of the punch, with each hole being made in a substantially symmetrical depression.

A method of punching holes in sheet metal using a rotatable punching roller having a series of radial punches on a cylindrical surface thereof and a backing roller, the backing roller having for each row of holes to be made two raised annular lands and an annular groove therebetween, the groove having a bottom at a predetermined depth relative to said lands and said lands being spaced apart from said punches by a distance substantially wider than the width of the punches, said method comprising the steps of driving said punching roller running sheet metal through the nip between the punching roller and the backing roller so that the backing roller is frictionally driven by the sheet metal and so that each punch in the punching roller causes a slug of metal to be cracked out of the parent metal until one edge of said slug of metal engages the bottom of the groove of the backing roller at a fulcrum point whereupon the slug of metal fulcrums on said fulcrum point causing complete separation of the slug of metal from the parent metal, each hole made being in a substantially symmetrical depressed area of the sheet metal.