Punching is a process that removes a scrap slug from the metal workpiece each time a punch enters the punching die. As a result of this process, there is a hole left in the metal workpiece. Punched material is most normally done in sheet, roll material and flat stock. The punching process produces multiple size holes in a quick amount of time. The punch diameter is what determines the size of the hole. Commonly punched materials include aluminum,  mild and stainless steel, copper and titanium.