This paper proposes a model for representing knowledge about design for net shape manufacturing (NSM) and a means of applying the model to conduct simultaneous engineering. The three major issues that the designers have to balance are: 1) user requirements, 2) process constraints, and 3) candidate designs. We view the goal of design for NSM to be achieving the best possible compatibility among these three issues. Expert designers develop skilled know-how of achieving good compatibility. This paper conceptualizes this knowledge as compatibility-data (c-data) and constructs a knowledge-base CKB. Further, we present two methods that use the CKB to help designers. The first method is the compatibility-based classification system (CCS) which, given the user requirements and the process constraints, searches the CKB for candidate designs. The second is the design assessment system which utilizes the concept of design compatibility analysis (DCA). Given a partial or full description of all the three issues, DCA evaluates the overall compatibility and gives suggestions for improvement, i.e., to modify the design, to respecify the process, or to negotiate the user requirements. Both methods accommodate hardness of constraints, the degree to which the constraints must be satisfied. Using these systems, designers can rapidly generate sound part designs that satisfy requirements and are producible. We illustrate our model by an example: injection molded composite shells for electrical connectors.