A quick switching sampling system by variables for controlling lot fraction nonconforming

Abstract

This article develops a new sampling scheme by variables inspection, namely a quick switching sampling (QSS) system based on the process yield index for lot determination when the quality characteristic is normally distributed with two specification limits. The QSS system can provide a flexible sampling procedure by switching decision policies, normal inspection and tightened inspection. The operating characteristic curve of the proposed QSS system is derived and required to pass through two designed points, acceptable quality level and limiting quality level for satisfying risks simultaneously suffered by the producer and the consumer. The proposed sampling system’s performance is investigated and a comparison with the conventional variables single sampling (VSS) plan is also examined. The results indicate that the proposed system outperforms the VSS plan by requiring a smaller sample size for inspection while retaining the same protection. For practical purposes, the plan parameters’ tables are provided on the basis of various selected quality requirements and risks. Finally, we demonstrate the proposed sampling system using an example taken from a silicone LED lens industry.