Process for forming a deep drawn and ironed pressure vessel having selectively controlled side-wall thicknesses

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.