Patent ID: 7309229

Claim:
An injection-molding mold die for injecting a molten material at a predetermined pressure into a cavity formed by clamping the mold die, comprising: a cylinder having (a) a continuous whole cylinder shape, (b) a hollow formed therein, (c) an opening formed at the end thereof, having the hollow extending thereto, and (d) an external peripheral surface defining a part of the cavity, and (e) an undercut-forming section forming a shape on the external peripheral surface, from which formed shape the mold die is unable to be separated in the mold die separation direction; and a diameter-enlarging member which enters the hollow through the opening so as to enlarge the external diameter of the cylinder and which can relatively advance to or retreat from the hollow, wherein the diameter-enlarging member lies in the hollow when the mold die is clamped and exits the hollow when the mold die is opened, and wherein the cylinder comprises a metal having a longitudinal elastic modulus greater than the value of the predetermined pressure, and the external diameter enlarged by the insertion of the diameter-enlarging member is reduced when the diameter-enlarging member exits the hollow.