The piston of akiyumureta, the resin molded article which has the undercut section production manner null of the resin molded article which uses formation die and its formation die which form

摘要

PROBLEM TO BE SOLVED: To provide a resin molding, whose neck portion consisting of a projected part has a high strength and an undercut part, and a mold for molding the resin molding. ;SOLUTION: In this resin molding 20, the strength of a resin consisting of a neck portion 23b comprising a projected part 23 is enhanced by molecular orientating the resin to the extending direction of the neck portion 23b. A resin mold 10 is equipped with a gate part 16, which is equipped with a gate port and a gate passage 16a and which partitions at least the apex part of a cavity for forming a head portion 23a, undercut forming parts 17, which fit to the outer periphery of the gate part and the tip part of which partitions a cavity forming the head portion 23a and at least some part of the neck portion 23b together with the gate part 16 and which are devided into a plurality of pieces along the expanding direction of the gate passage 16a and can displace radially, and an engaging part 18, which can move relative to the undercut forming parts 17 so as to clamp the undercut forming parts 17 towards its central part side in order to close its tip part.;COPYRIGHT: (C)1999,JPO