System of manufacturing injection molded article and metal mold

A method of manufacturing an injection-molded article by using a single injection manifold having first and second flow channels serially connected between an injection nozzle and a cavity formed in a metal mold to provide single injection,

• the second flow channel being located downstream of the injection nozzle,
• the first flow channel being continuously connected to a downstream end of the second flow channel and located upstream of the cavity;
• the method comprising the steps of:
• injecting a single shot of molten resin from the injection nozzle into the second flow channel and the first flow channel in this order;
• heating a first part of the single shot of molten resin to a prescribed high level in the first flow channel;
• keeping temperature of a second part of the single shot of molten resin in a prescribed second level near a flowable limit of molten resin lower than the prescribed high level in the second flow channel;
• ejecting the first and second parts of the single shot of molten resin into the cavity in this order by newly injecting a next single shot of molten resin from the injection nozzle into the second flow channel and the first flow channel in this order;
• and
• forming a skin layer of the injection molded article with the first part of the single shot of molten resin and a core layer of the injection molded article with the second part of the single shot of molten resin in the cavity by generating a fountain flow in the cavity with the first and second parts of the single shot of the molten resin based on a difference in temperature between the first and second parts of the single shot of molten resin.