When the injection molded parts have cavities, bosses and other structures, after molding, the molded parts of the cavities and bosses will prevent the plastic parts from being ejected from the mold, and the molded parts of the cavities and bosses must be withdrawn before ejection . These parts are generally made to be movable. When the mold is opened, all the molded parts on the side are pulled out in an orderly manner. After removing the obstacles, the plastic parts are ejected, and the side car parts are restored to their original positions when the mold is closed.