Necking method, necking apparatus, and battery manufacturing device

A necking apparatus, configured for forming a necked portion on a shell with an open end, comprising:

• a first roller, configured to feed in a radial direction of the shell to form an annular groove on the shell;
• a second roller, configured to feed in the radial direction of the shell to form a necked portion and a flanged portion on the shell;
• an inner mold, configured for supporting the shell from interior of the shell;
• and
• a press fitting structure disposed around the inner mold,
• wherein the first roller has a first surface and a second surface opposite in its axial direction, and the second roller has a third surface and a fourth surface opposite in its axial direction, wherein the third surface is farther from the open end than the fourth surface, and a plane where the third surface is located is between the first surface and the second surface,
• the first roller and the second roller are disposed on a circumference of the inner mold, and
• the press fitting structure is configured to:
• clamp the open end together with the inner mold when the first roller is fed in the radial direction of the shell, to limit outward movement of the open end.