Processing method for metal plate

A method for processing a metal plate comprising:

• a first step including using a first die set to form a recess in the metal plate, the recess having an outer periphery, a bottom, and a side extending between the outer periphery and the bottom, wherein the recess forms a curved surface;
• a second step including using a second die set, which is different from the first die set, a) to form a protrusion in the metal plate, the protrusion extending up into the recess, and b) to press a portion of the side, that is not part of the protrusion, toward a center of the recess;
• and
• a third step of forming a plurality of recesses in the metal plate, the third step including using a third die set, which is different from the first die set and from the second die set, a) to extend the protrusion further up into the recess, and b) to press the portion of the side further towards the center of the recess,
• wherein the plurality of recesses are formed adjacent to each other on the metal plate and are separated by the protrusion.