Method of making weakening lines in sheet metal

Abstract From the Canadian patent

A new sequence of steps provides more control in the formation in sheet metal of weakening lines of the type characterized by an integral yet fractured section. Basically, the method employs in making so-called easy-, open can ends for example:, 1) peripherally forming a closure in the sheet metal; 2) coining or scoring a profile surface of the closure not to, the depth required for fracture but to establish residuum, thickness along the desired line; 3) next, overforming the closure at least in part to integrally fracture the residuum along that coined line; and 4) lastly, swaging to seal or tighten edges of the fractured section.