A comparative evaluation of sequential set point adjustment procedures for tolerance control

The machining of complex parts typically involves a logical and chronological sequence of n operations on m machine tools. Because manufacturing datums cannot always match design datums, some of the design specifications imposed on the part are usually satisfied by distinct subsets of the n operations 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 tolerance control (STC) uses real-time measurement information at the completion of one stage to exploit the available space inside a dynamic feasible zone and reposition the set point for subsequent operations. This paper introduces an extension of STC that utilizes the variability of the operations to scale the problem data and further enhance the ability of STC to optimize the production of an acceptable part.