In today's competitive market place it is important for manufacturers of aircraft parts to be able to respond quickly to the demands of your customer. This requires flexibility and speed in the development of new or redesigned aircraft parts. One way to achieve this is to develop Knowledge Base Engineering (KBE) tools that shorten the design and production lead-time. In this paper a KBE tool is described with which geometry of moulds used for rubber forming of thermoplastic composite movable ribs can be generated. This KBE tool is part of a larger Design and Engineering Engine of an aircraft movable. The KBE tool uses information stored within the tool to generate the mould geometry and information about the mould. People not familiar with mould design can operate the KBE tool, making mould design a cheaper and, because the mould design is automated, less time consuming process. The knowledge stored in the tool consists of expert knowledge on the positioning and sizing of critical features of the rib mould. This knowledge is transformed from raw knowledge into practical design rules and practical models. Finally the models and knowledge are packaged in a KBE tool. The KBE tool consists of several features that together form the rib mould. Negative or positive mould can be modeled by changing just one input parameter. The features needed for using the mould in the rubber forming process are also positioned using user-defined parameters. This results in a tool that is flexible but fast in generating rib moulds. Generation of a rib mould typically costs 2 minutes.@en