Cumulative quantity control charts for monitoring production processes

Two commonly used statistical quality control charts, the c-chart and u-cha rt, are unsatisfactory for monitoring high-yield processes with low defect rates. To overcome this difficulty, a new type of control chart called the cumulative quantity control chart (CQC-chart) is introduced in this paper. The CQC-chart can be used no matter whether the process defect rate is low or not, and when the process defect rate is low or moderate the CQC-chart d oes not have the shortcoming of the c- and u-charts of showing up false ala rm signals too frequently. The CQC-chart does not require rational subgroup ing of samples (which is necessary for the c- and u-charts), and is appropr iate for monitoring automated manufacturing processes.