process and apparatus for injection molding of molded parts made from plastic material having at least one cavity , which includes : a ) injection of plastic melt from an injection unit along a melt flow path into the cavity of an injection - molding die ; b ) injection of a fluid into the still molten plastic material , so that the latter is pressed against the walls of the cavity ; c ) allowing the plastic material to solidify until the latter forms the molded part in self - supporting manner ; and d ) releasing the molded part from the cavity of the injection - molding die .