The expanded DPMO interface for capturing the compounding effect of process mean and variability as a new paradigm for process evaluation and improvement

摘要

This paper explores the gap between the existing conceptual notion of defects per million opportunities (DPMO) as part of process improvement initiatives and its applications to real-world engineering processes. The current way of obtaining the DPMOs documented in the literature is problematic since it strictly assumes that there will be a shift in the process mean over time, while process variability remains unchanged. Accordingly, it does not account for shifting process standard deviation. This may not be the case in real-world practices. This paper offers several unique contributions to the Six Sigma body of knowledge by expanding the existing DPMO and process fallout concepts, ultimately leading to process improvement. First, this paper considers the process fallout resulting from shifting standard deviation while keeping the mean the same. Second, the process fallout is examined when shifting both the process mean and standard deviation over time. Third, standard process capability indices are then modified to incorporate both mean and standard deviation shifts. Finally, the paper is extended to dual quality characteristics to obtain a better understanding of the integrated effects of correlations on the DPMO and process fallout.