The use of CNC machine tools, together with decreasing lot sizes and stricter tolerance prescriptions, has led to changes in sheet-metal part manufacturing. In this paper, problems introduced by the difference between the actual material behaviour and the results obtained from analytical models and FEM simulations are discussed against the background of the required predictable accuracy in small-batch part manufacturing and FMS environments. The topics are limited to those relevant to bending along straight lines. Applications of analytical and empirical models in the area of CAPP and adaptive control are discussed. Process planning for sheet bending, however, should not be treated as an individual task but must be related to other process-planning tasks. An integrated CAPP system for sheet metal, part-s, is introduced briefly.