Multiple-process performance analysis chart based on process loss indices

Control chart techniques have been widely used in the manufacturing industry for controlling and monitoring process performance and are practical tools for quality improvement. When dealing with variable data, one usually employs the (X) over bar chart and R chart ( or S chart) to detect the process mean and process variance change. These charts are easy to understand and effectively communicate critical process information without using words and formulae. In this paper, we develop a new multiple-process performance analysis chart (MPPAC), using the process loss index L-e to control the product quality and/or reliability for multiple manufacturing processes. Upper confidence bounds are applied to the L-e MPPAC to ensure the capability groupings are accurate, which is essential to product quality assurance. The L-e MPPAC displays the multiple-process relative inconsistency and process relative off-target degree on one single chart in order to provide simultaneous capability control for multiple processes. We demonstrate the applicability of the proposed L-e MPPAC incorporating the upper confidence bounds by presenting a case study on some liquid-crystal display module manufacturing processes, to evaluate the factory performance.