Framework for dynamic tolerance control in discrete part manufacturing

The traditional means of tolerance control in manufacturing based on static pre-production tolerance chart analysis to set in process tolerance, followed by conventional process control activities to maintain required tolerances, present several limitations. This tolerance management strategy may be too rigid for current and future, integrated automated manufacturing environments. This paper presents a framework, and discusses elements required to create and implement global, dynamic tolerance management when machining discrete parts. A graph based representation of machining sequence and new mathematical models for both the pre-production deterministic and stochastic tolerance distribution are presented. Use of feedback from sensors to enable use of an on-line stochastic tolerance chart to evaluate actual yield is discussed. Actual yield will then be the basis upon which necessary corrective actions, globally optimized over the whole set of machining operations, are undertaken to close the loop.