Quality is a principle issue in production management (PM). No process is perfect and the production of defective items is unavoidable. Very few studies regard the effect of the existence of defective items (EEDI) in production processes. Further, quality has been studied in isolation to high extent, of other PM domains. In this study, defect rates together with the assembly ratios of the bill of material are embedded in process charts. This facilitates the analysis of the EEDI in assembly operations and enables to quantify them. Apparently, defect rates grow dramatically in assembly operations due to the mutual effects of the assembly’s components. Hence prior quality assurance effort is motivated