Quality is a principle subject in the industrial engineering (IE) domain. There exists no perfect process and some extent of failures, including the production of defective items is unavoidable. A defective item for the purposes of this study is one item that can be used as it is, as planned, if detected – it is either scraped, sold for lower price, reworked or repaired. Most studies focus on machine failures of various types, and very few 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 IE domains. Production process charts and product structure/bill-of-materials (BOM) are known IE concepts, but to my surprise I could find no source in the literature which notices the common basis of these two descriptions, let alone defect rates and number of defective items. This, thus, seems to be a first attempt to integrate these concepts.
The isolated study of quality impeded the understanding of the full effect of poor quality, particularly in assembly operations. While in a serial manufacturing process each item moves individually, they are joined in assemblies – there, a single defective item may disqualify a whole assembled unit. I could find no quantification of the EEDI on assembly operations, where components arrive from different sources and paths of the product structure/process chart and with different defect rates.
In this study, defect rates are embedded in process charts. In addition, the assembly ratios of the BOM are added. This integration facilitates the analysis of defect rates in assembly operations, in a way that enables to quantify these rates. 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.
