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A process for forming an improved deep drawn and ironed metal shell for use as a pressure vessel having selectively controlled wall thicknesses to impart additional strength to predetermined portions of the improved metal shell. A stepped mandrel is utilized in conjunction with at least one ironing

A process for forming an improved deep drawn and ironed metal shell for use as a pressure vessel having selectively controlled wall thicknesses to impart additional strength to predetermined portions of the improved metal shell. A stepped mandrel is utilized in conjunction with at least one ironing die to fabricate the improved metal shell.

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1. A process for forming an improved pressure vessel, comprising the step of: forming an initially flat piece of virgin metal having a particular thickness into a pressure vessel during a single stroke, ironing and drawing operation using a cylindrical mandrel having a multiple stepped, external

1. A process for forming an improved pressure vessel, comprising the step of: forming an initially flat piece of virgin metal having a particular thickness into a pressure vessel during a single stroke, ironing and drawing operation using a cylindrical mandrel having a multiple stepped, external side-wall profile with a first end and a second end; a first portion adjacent the first end having a first axial length and a first external diameter; a second portion adjacent the second end having a second axial length and a second external diameter, the second diameter being substantially similar but less than the first diameter; and a third portion located between the first and second portions, the third portion having a third axial length substantially greater than the first and second axial lengths and a third external diameter greater than the first and second diameters, wherein the pressure vessel formed has a multiple, stepped, internal side-wall profile corresponding to the multiple, stepped external side-wall profile of the mandrel with a first closed end and a second open end; a first portion integrally formed adjacent the first end having a first axial length and a first thickness; a second portion adjacent the second end having a second axial length and a second thickness, and the second thickness being substantially similar but less than the first thickness; and a third portion located between the first and second portions, the third portion having a third axial length substantially greater than the first and second lengths and a third thickness less than the first and second thicknesses. 2. The process as recited in claim 1, wherein the third thickness is in the range of approximately 25% to 65% of the thickness of the virgin metal. 3. The process as recited in claim 2, wherein the third thickness is approximately 45% of the thickness of the virgin metal. 4. The process as recited in claim 3, wherein the second thickness is approximately 75% of the thickness of the virgin metal. 5. The process as recited in claim 4, further comprising the step of trimming the second open end of the pressure vessel to provide a final, well-defined edge at the second open end thereof. 6. The process as recited in claim 5, wherein the forming step further comprises using a plurality of ironing rings. 7. The process as recited in claim 6, wherein the first thickness is less than or equal to the thickness of the initially flat piece of virgin metal.