Patent ID: 8226404

Claim:
An undercut processing mechanism ( 30 ) in a molding device ( 1 ) for molding an article (P) to be molded with a stationary mold ( 11 ) and a movable mold ( 14 ), the molded article (P) having an undercut portion (P 3 ) formed inside it in a circumferential direction thereof at a time of punching out the molded article (P) and brought to a detachable state, comprising: an undercut mold core ( 60 ) comprising plural split cores ( 61 ) that line one another in an entire circumferential direction to correspond in position to an inner peripheral surface of the undercut portion (P 3 ), the split cores ( 61 ) comprising inner split cores ( 61 a ) and outer split cores ( 61 b ) formed to line alternately, the inner split cores ( 61 a ) abutting on one another and formed on an inner side and the outer split cores ( 61 b ) coming close to one another along an outer side of the inner split cores ( 61 a ) when the split cores ( 61 ) have been reduced in diameter toward an center axis of the undercut portion (P 3 ); slide members ( 50 ) radially disposed and opposed to the center axis of the undercut portion (P 3 ) in a state in which each of the slide members ( 50 ) supports each of the split cores ( 61 ) of the undercut mold cores ( 60 ) on a leading end thereof; a holder ( 40 ) provided integrally with the stationary mold ( 11 ) or movable mold ( 14 ) for housing the slide members ( 50 ) slidably between a molding position at which the split cores ( 61 ) supported on the leading ends of the slide members ( 50 ), respectively, line one another in the entire circumferential direction and a demolding position at which the split cores ( 61 ) are reduced in diameter one another toward the center axis of the undercut portion (P 3 ); guide means ( 46 ) disposed in the holder ( 40 ) for guiding, at the time of punching out the molded article (P), the slide members ( 50 ) to move simultaneously in a punching-out direction parallel to the center axis of the undercut portion (P 3 ) and in a direction escaping from the undercut portion (P 3 ) toward the center axis of the undercut portion (P 3 ), respectively, along an inclination direction from the molding position to the demolding position; and ejector pins ( 27 ) driven in the punching-out direction to project out, wherein the holder ( 40 ) is integrally provided with the movable mold ( 14 ) in a state in which leading ends of the ejector pins ( 27 ) are movably guided, the slide members ( 50 ) have proximal ends thereof connected slidably in the escaping direction to the leading ends of the ejector pins ( 27 ), and the guide means ( 46 ) comprises guide holes ( 46 ) which are formed in the holder ( 40 ) and along which the slide members ( 50 ) are movably guided in the inclination direction, with midway portions of the slide members ( 50 ) passing through the guide holes ( 46 ).