Abstract: An undercut processing mechanism is attached to and used in a molding die for forming a molded product having an undercut portion, and allows demolding of the undercut portion. The undercut processing mechanism includes: a holder attached to or formed integrally with the molding die; a sliding piece configured to be slidable relative to the holder such that a mold core is moved so as to demold the undercut portion; a retaining piece configured to retain the sliding piece such that the sliding piece is slidable; and a support wall configured to support the sliding piece so as to prevent the sliding piece from being tilted when the sliding piece slides. The sliding piece forms a part of the mold core for forming the undercut portion.

Abstract: A pair of mold cores (51, 52) for molding an undercut portion (P1) in a holder (30) installed inside a movable mold (13) are connected to and supported by a retaining piece (40) which is moved in the demolding direction, and at the time of demolding, the respective mold cores (51, 52) are guided by guide means (33, 34) from the molding position, where they are contacted with each other, to the mold release position, where they are separated from each other, being moved from one end side to the other end side of the retaining piece (40), in the mutually opposite directions so as to pass each other in the back and forth direction.

Abstract: An undercut processing mechanism can facilitate punching-out of undercut portions having various shapes spreading in the circumferential direction on the inside of a molded article. Split cores (61) that form an undercut molding core (60) are supported one by one at the leading end of slide members (50) disposed radially to face the center axis of an undercut portion (P3). Each slide member (50) is housed in a holder (40) so as to be slidable between a molding position where the split cores (61) are mutually disposed in the entire circumferential direction and a demolding position where the split cores (61) are mutually reduced in diameter.