Method and apparatus for drawing sheet metal can stock

Method for drawing pre-coated flat-rolled sheet metal can stock into a one-piece cup for use in the manufacture of a two-piece cylindrical can, comprising

• providing can stock of preselected gage flat rolled sheet metal pre-coated on both its planar surfaces with an organic coating, both such organic coating surfaces being lubricated with draw lubricant,
• cutting a circular blank of predetermined diameter from such can stock,
• providing cupping means including
• draw die means,
• cupping punch means, and
• clamping ring means,
• disposing such draw die means on one planar surface side of such circular blank,
• such draw die means including
• a cupping cavity having a centerline axis,
• can stock clamping means limited to a planar clamping surface, and
• a compound curvilinear cavity entrance zone between such cavity and planar clamping surface,
• such cavity entrance zone including a compound curvilinear surface having a radius of curvature of about five times starting thickness gage for such sheet metal,
• such die means cupping cavity having an internal side wall in symmetrical relationship about such centerline axis of the cupping cavity and of circular configuration in a plane perpendicularly transverse to such axis,
• disposing such cupping cavity with its centerline axis intersecting the geometrical center of such circular blank, with
• such die means planar clamping surface being disposed radially exterior of and contiguous to such cupping cavity entrance zone in a plane which is perpendicularly transverse to the centerline axis of the cupping cavity,
• disposing such cupping punch means and clamping ring means on the remaining opposite planar surface of such circular blank;
• such cupping punch means presenting a substantially cylindrical configuration punch,
• aligning such punch for relative movement into such cupping cavity along a travel path in which its centerline axis is directionally coincident with the centerline axis of the cupping cavity,
• such punch including
• an end wall symmetrically disposed in relation to such punch centerline axis presenting a peripheral surface defining a plane which is perpendicularly transverse to such axis,
• a substantially cylindrical configuration peripheral side wall symmetrically disposed with relation to the centerline axis of such punch, and
• a compound curvilinear transition zone between such punch end wall planar surface and such punch cylindrical side wall,
• selecting such punch side wall to have a predetermined diameter which is about 25% to 40% less than such predetermined diameter of such circular blank,
• selecting a surface area for such punch curvilinear transition zone to be as large as possible in relation to punch diameter while avoiding forming buckles in such sheet metal of preselected gage during a cup drawing operation;
• disposing such clamping ring means to circumscribe such punch providing can stock clamping means limited to a planar clamping surface radially exterior of and contiguous to such punch for clamping such can stock in a plane which is perpendicularly transverse to the centerline axis of such punch,
• providing relative movement of such punch into such cupping cavity with such circular blank being clamped radially exterior of such punch and cavity solely between said planar clamping surfaces of the draw die means and clamping ring to draw form a cup-shaped work product,
• such cup-shaped work product having
• a closed end wall having a periphery lying in a plane perpendicularly transverse to its centerline axis,
• a substantially cylindrical side wall having a predetermined diameter which is about 25% to 40% less than such circular blank diameter, and
• a compound curvilinear juncture between such cup end wall and side wall having an interior surface area corresponding to such preselected surface area of such cupping punch curvilinear transition zone,
• such cup side wall having a uniform height in extending from such closed end wall toward the axially opposite open end of such cup,
• interrupting such relative movement of such punch into such cupping cavity to provide
• flange metal extending about substantially the full periphery of such cup at its open end,
• such flange metal being disposed in a plane which is substantially perpendicularly transverse to the centerline axis of such cup.