IMPROVING CUSUM CONTROL CHARTS VIA QUALITY-ORIENTED STATISTICAL TOLERANCING

A new systematic method for concurrent design of process quality, statistical tolerance (ST) and control chart is presented. A set of standardized process quality indices (PQIs)for variables is introduced for meeting the measurement and evaluation to process yield, process centering and quality loss. To develop a quality-oriented SPC approach, a standardized interface between process quality indices system and the parameter design of Cumulative Sum (CUSUM control charts is needed. The two-dimensional array form ST (C-p*, delta*) is presented for selecting a set of parameters (k, h) with suitable ARL(0) and ARL(1) to realize the optimal control for a process toward a predetermined quality target. A case study shows the detail procedure of this concurrent design for PQIs, ST and SPC parameters. The process quality, statistical tolerance, sampling plan with confidence interval for CUSUM chart can be concurrently designed under the guideline of quality-oriented statistical tolerancing and SPC technique. The predetermined PQIs can be assured via this CE approach under certain condition (process parameters are known or unknown) with a preset confidence probability.