Method of manufacturing sandwich molded product, injection molding machine, and sandwich molded product

A method of manufacturing a sandwich molded product, the method employing at least two molds capable of forming a mold cavity to mold the sandwich molded product, the method comprising:

• a base layer molding step that injection-fills the mold cavity with a base layer resin to mold a base layer;
• a first expansion step that causes the volume of the mold cavity to expand to a specified quantity such that a certain space is formed between an outer surface of the base layer molded by the base layer molding step and an inner surface of the mold;
• a first injection-filling step that injection-fills the space formed by the first expansion step with a first resin which is a foamable resin to fill the space with the first resin;
• a second expansion step that, after the start of the first injection-filling step, causes the mold cavity to expand to a specified quantity such that the space is further expanded, thereby foaming the first resin and molding a foam molded product which has a skin layer and a foamed layer formed within the skin layer;
• and
• a second injection-filling step that, after completion of the first injection-filling step and after the completion of the second expansion step, injection-fills a second resin into the foamed layer of the foam molded product by penetrating the skin layer.