Grey Quality Envelop Control Charts

Globalization has made the life cycle of new products shorter and shorter. Quality control methodology including quality control charts has to evolve to face the sparse data availability challenges. Accordingly, managerial team needs to use interval quality indices. The Grey quality envelop proposed in this paper is an interval-valued function composed of a pair of upper bound function and lower bound function extracted from the information contained in the quality index sequence of the production system and thus will offer a dynamic boundary for the product quality index control purpose. Furthermore, small sample impacts on control chart is discussed and control chart based on small sample asymptotics is discussed