the present invention relates to a method and apparatus for molding plastic articles . more specifically , the present invention is directed to a staged sequentially separated apparatus for injection molding of plastic panels having a flap or tab molded therewith in a single molding and forming step . the present invention provides , among other things , a method and an apparatus for forming an injection molded part with an undercut , the undercut lying generally in a plane of a major portion of the part , the undercut having an open elongate opening and being positioned between an elongate integrally molded tongue and panel . the apparatus comprising a first mold half with a first mold cavity defining surface , a second mold half with a second mold cavity defining surface , a tongue member carried by the second mold half and projecting into a mold cavity . the tongue member having generally opposing facing surfaces spaced from the first and second mold cavity surfaces for forming opposite face of a molded part undercut . the apparatus also comprising means to selectively effect movement of the transverse mold insert relative to at least a portion of the remainder of the second mold half .