Combining Q chart with statistical tolerancing for process monitoring and designated quality

Q charts allow practitioners to monitor, with a known and predictable false-alarm rate, for shifts that may occur in the early history of the process, in spite of the uncertainty about the values of the process mean and variance. In order to assure designated process quality in short production runs and in the early phases of long runs, a new approach to combine the Q charts with quality-oriented statistical tolerancing technique is presented. When the statistical parameters are unknown, we can use Q chart to adjudge whether the process is stable from the second sample, and the judgment will be more accurate along with more samples. So long as the samples meet the minimum data N-min for assuring designated process quality with a determined confidence probability 1-alpha, we can estimate the values of C-p and k, and predict whether the process is capable to designated process quality.