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

The machining of complex parts typically involvesa logical and chronological sequence of n operations on mmachine tools. Because manufacturing datums cannot alwaysmatch 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 foreach operation and permissible variation about this set pointto 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 introuces an extension of STC that utilizes the variability ofthe operations to scale the problem data and further enhancethe ability of STC to optimize the production of an acceptable part.