Patent ID: 8661867

Claim:
A container manufacturing method comprising: setting a metal billet into a forming container with a gap between the metal billet and an inner wall of the forming container, a top portion having a top cross-sectional area, and a bottom portion having a bottom cross-sectional area smaller than the top cross-sectional area, only the bottom portion of the metal billet having at least one plane on a side surface thereof; forming an extended section which engages with an end portion of an inlet of the container by pressing a pressing backward side of the metal billet with a large punch having an outer diameter substantially equal with or larger than the outer diameter of the metal billet; and pushing a boring punch into the bottom portion continuously after penetrating the boring punch through the top portion and bending the plane towards the inner wall so as to hot-dilate the metal billet, to make an outer diameter of the bottom portion of the metal billet equal to an outer diameter of the top portion of the metal billet located in the container before the step of penetrating the boring punch through the top portion and pushing the boring punch into the bottom portion.