A method of manufacturing a monolithic component having internal wall(s), including separately placing uncured composite material on a mold parts, placing the mold parts on a support plate with a portion of the uncured composite material extending between and in contact with the adjacent mold parts, interconnecting the adjacent mold parts through a connection allowing limited relative movement on the support plate along a direction corresponding to a thickness of the uncured composite material therebetween, biasing the adjacent mold part toward each other along the limited relative movement to provide a compressive force on the uncured composite material extending therebetween, and curing the composite material to obtain the monolithic component with each internal wall being formed between adjacent mold parts. The bias causes the adjacent mold parts to move toward each other as the thickness of uncured material extending therebetween reduces during curing. A tool assembly is also discussed.