Abstract
The article presents the tightened-normal-tightened acceptance sampling plan, using the process capability index C-pk. The parameters of the proposed plan are obtained by solving an optimization problem, such that the producer's risk and the consumer's risk are satisfied simultaneously for several specified combinations of acceptable quality level and limiting quality level, respectively. The plan parameters are tabulated and discussed for industrial use, when the fractions non-conforming beyond the lower and the upper specification limits are symmetric or asymmetric. We validate the effectiveness and use of the proposed plan with an actual example. The efficiency of the proposed plan is compared with published and resubmitted sampling plans with the same AQL and LQL values. The proposed plan provides smaller ASN than the single sampling plan and the resubmitted sampling plan under the same values of AQL and LQL.