Cumulative quantity control charts for monitoring production processes

Abstract

Two commonly used statistical quality control charts, the c-chart and u-chart, 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 does not have the shortcoming of the c- and u-charts of showing up false alarm signals too frequently. The CQC-chart does not require rational subgrouping of samples (which is necessary for the c- and u-charts), and is appropriate for monitoring automated manufacturing processes.