This paper deals with knowledge integration during product design. An integrated design approach is presented based on two phases: The initial design and the detailed design phase. Those two phases must be as concurrent as possible. Nevertheless, minimal structural definition of the product is necessary prior to manufacturing process planning as part of the detailed design phase. During the initial design phase, the structural technology is chosen according to the product main functions. This phase aims at defining minimal functional data that are used as a starting point for other knowledge integration in the detailed design phase. During the detailed design, other people that are actively involved in the product development process evaluate the product with their own point of view and their own tools. This paper presents the use and the limits of two features-based tools for process planning knowledge integration: a What-if system and a CAPP system. Both tools make an analysis of the product. As a result of these analyses, designers add new data to the product definition. Thus, the design solution is progressively defined. A Cooperative Design Modeller supports this knowledge integration and gathers the data provided by the What-if and the CAPP systems.