In this paper, the framework for a sheet metal part design and manufacturing assessment environment is presented. Based on an investigation of the characteristics of sheet metal part design, form feature methodology is employed to facilitate design and provide information for assessment. The tasks, rules, and the significant items for manufacturing assessment are identified and formalized into a knowledge base with object-oriented techniques. The knowledge base is used for design assessment including evaluation for compatibility with press-working processes, modification of preliminary designs into better ones given cost considerations, and evaluation to avoid defects and failures. To support on-line design evaluations, a part model is constructed by extracting the required feature and connectivity data from a CAD database. The research is concentrated on box-type sheet metal parts primarily made by cutting (e.g., shearing, blanking, punching, etc.), bending, flanging, and local stretching. These parts are produced by both stampers and fabricators.