Economic Design of A Dynamic CCC – r Chart for High-Yield Processes

Abstract Recently, Ohta et al. [Quality and Reliability Engineering International 17: 439-446, 2001] have studied the economic design of CCC (Cumulative Count of Conforming)- r charts for high-yield processes assuming a fixed hazard rate. Generally, however, the hazard rate is varying over time. With the ageing of a process, the hazard rate gets first gradually smaller, while during the last stage of the wear-out process, the hazard rate increases. For such processes, the Weibull distribution is used to model the circumstances. In this paper, we discuss an economic design of a dynamic CCC – r chart with time-varying parameters. Concretely, we propose a process control model for a Weibull distributed-shock model and determine the initial values and dynamic decision rules for the time-varying parameters of the CCC–r chart, that is, the required number of nonconforming observations r , the sampling interval h , and the lower control limit LCL maximizing the expected profit per unit time derived from the process. Finally, we compare the profits obtained applying a dynamic CCC – r chart with those obtained with a traditional static CCC – r chart.