Dome made of aluminum alloy; particularly intended to form the bottom of a tank; and method of manufacturing it

A method for producing a dish of rounded shape, open at its top, of a weldable aluminum alloy, particularly for producing the bottom of a tank, the method comprising:

• (a) providing a mold having an interior face cavity that corresponds to the shape of said dish, said mold being closed at its top and open at an opposite end from said top;
• (b) forming a blank in the shape of a cone frustum by bending and welding a flat piece of an untempered aluminum alloy having a shape of a portion of an annulus;
• (c) inserting said blank completely into said mold, so that:
• said blank has an initial position that is concentric with said mold,
• an exterior frustoconical face of said blank faces said interior face of said cavity,
• a small base of said blank rests on said interior face of said cavity near the top of said mold, and
• a large base of said blank is close to said interior face of said cavity near the opening of said mold;
• (d) arranging a deformable pressing wall peripherally inside said blank, against an interior face of said blank and near the small base;
• (e) applying heat and pressure to said blank and said deformable pressing wall during a first phase, to cause:
• said blank and said deformable pressing wall in contact therewith to bend toward the interior face of said cavity, and
• said blank to progress toward the top of said mold and conform to the shape of said cavity's interior face;
• (f) halting progression of said blank and said deformable pressing wall toward the top of said mold, when said blank and said deformable pressing wall reach a predetermined position of conformity with said cavity;
• (g) applying said heat and pressure during a second phase to:
• mold said exterior face of said blank to the shape of said interior face of said cavity, and
• press said deformable pressing wall against said interior face of said blank and thereby contribute to molding said exterior face of said blank;
• (h) extracting said blank, which is formed into said rounded dish having an opening at the top, from the mold.