Designing a Variables Two-Plan Sampling System with Process Loss Consideration

Acceptance sampling had become an essential practical tool for quality assurance application, closely related with incoming inspection. Acceptance sampling plans provide the decision rule for product acceptance to meet the preset product quality required by the vendor and the buyer. As today’s modern paradigm of quality improvement, reduction of variance from the target value is the guiding principle as well as reduction on fraction of defective. The pm C index particularly adopts the loss function approach, which distinguishes product quality by increasing penalty to products deviating from the target. This paper proposes variables two-plan sampling system based on process capability index pm C that takes into account departures from target value as well as changes in the process variation. The operating procedure and the conditions to determine the plan parameter are provided. The plan parameter of the proposed sampling plans determine effectively by solving the two nonlinear equations simultaneously. The behavior of the proposed two-plan sampling system is also discussed. For practical purpose, table of the required sample size and the corresponding critical acceptance value under various parameter settings is provided.