A simultaneous control scheme for mean and fraction non conforming in small process variation

Abstract

ABSTRACTIn situations where 6σ is much smaller than the spread in specifications, the conventional p-chart is not applicable for monitoring a lower fraction non conforming process. In 6σ processes, a drift of the process mean is often allowed within at most 1.5σ from the target, and a modified control chart is a useful alternative to the usual chart. This paper proposes a ZP control chart as a more efficient alternative to the conventional p-chart, and a simultaneous control scheme for mean and fraction non conforming in small process variance is discussed.