A comparative evaluation of sequential set point adjustment procedures fortolerance control

The machining of complex parts typically involves a logical and chronologic al sequence of n operations on m machine tools. Because manufacturing datum s cannot always match design datums, some of the design specifications impo sed on the part are usually satisfied by distinct subsets of the n operatio ns prescribed in the process plan. Conventional tolerance control specifies a fixed set point for each operation and permissible variation about this set point to insure compliance with the specifications. Sequential toleranc e control (STC) uses real-time measurement information at the completion of one stage to exploit the available space inside a dynamic feasible zone an d reposition the set point for subsequent operations. This paper introduces an extension of STC that utilizes the variability of the operations to sca le the problem data and further enhance the ability of STC to optimize the production of an acceptable part.