Method of manufacturing a closure unit made of sheet metal or plating and container having a closure unit obtained thereby

A method of manufacturing a closure unit formed of sheet metal and containing a holding ring having a ring area bounding a central opening and comprising three substantially flat superjacent and folded sections for attachment with a membrane, said method comprising the step of:

• performing in a single deep-drawing operation predetermined shaping and punching operations upon a blank from which there is formed the closure unit wherein said step of performing in a single deep-drawing operation said predetermined shaping and punching operations upon the blank forming the closure unit comprises the steps of:
• punching out the blank for the closure unit, peripherally shaping a holding ring and cupping a central portion of the blank to form a substantially cup-shaped part, punching out the bottom of the substantially cup-shaped part to provide a central opening, rolling predetermined sections back into the substantially cup-shaped part, and flattening the rolled-back sections adjacent the central opening;
• wherein said steps of punching out the blank, peripherally shaping a holding ring and cupping a central portion of the blank, and punching out the bottom are performed during a travel path of a tool in a given direction;
• and said steps of rolling and flattening are performed during a travel path of said tool in a direction which is reverse to said given direction.