Manufacturing method of rectangular battery can

A manufacturing method of a rectangular battery can having a rectangular cross-section parallel to a bottom plate by drawing and ironing a blank of aluminum alloy, comprising:

• a first step of ironing the blank thereby forming an interim cup including
• an oval or a rectangular interim bottom whose area is larger than the bottom plate of the rectangular battery can,
• an inclined wall tilting obliquely upwardly that is formed continuously from each longitudinal end of the interim bottom,
• a short side wall that is formed continuously from the inclined wall, and
• a long side wall that is formed continuously from a curved corner formed on each lateral end of the interim bottom;
• a second step of drawing or drawing and ironing the interim cup thereby deforming the interim cup such that each boundary between the interim bottom and the inclined wall is gradually displaced toward a longitudinal end of the bottom plate of the rectangular battery can, and that a width of the interim bottom in a direction along a minor axis is adjusted to a width of the bottom plate of the rectangular battery can in a direction along a short side;
• and
• a third step of ironing or drawing and ironing the short side wall and the long side wall that is executed after the second step thereby thinning thicknesses of the short side wall and the long side wall,
• wherein the second step is executed to
• eliminate the inclined wall by bending the inclined wall at a right angle with respect to the bottom plate thereby shaping the inclined wall into a part of the short side wall, and
• eliminate the curved corner by bending the long side wall thereby shaping the curved corner into a corner bent at a right angle with respect to the bottom plate.