Injection molding method using void inducing pin and mold therefor.

摘要

A void inducing member 40 having a gas discharging part 44 formed to a shape whose sectional area is made smaller toward its acute top end is provided in a mold at at least one position corresponding to a cavity 30 defining the thick wall portion of a molded resin part 90. After the cavity 30 is filled with a resin melt 50 by full-shot injection, compressed gas is supplied from a gas supply source 60 through the gas discharging part 44 into the resin melt 50. The resin skin layer being formed in contact with the top end of the void inducing member 40 is easily broken through by the compressed gas, and fine gas bubbles serving as a void nucleus 51 are inserted into the resin melt 50. The void nucleus 51 is expanded to a void 52 having a size corresponding to the volumetric shrinkage of the resin melt 50. Since the growth of the void 52 compensates for the volumetric shrinkage of the resin melt 50, no defects such as sink marks are formed on the surface of an obtained resin part 90. <IMAGE>