Performance of Manufacturing Systems in an Environment with Disruptions.

To better understand the mechanics of manufacturing system performance, we have formulated a model for analyzing the impacts of disruptions. A disruption is any unplanned event which interrupts the flow of product through the manufacturing process. The negative effects of disruptions include missed commitments, increased work-in-process inventories, longer intervals and higher production costs. Clearly, it is important to eliminate the occurrences of disruptions from any manufacturing environment. Moreover, with the migration towards a Just-in-Time manufacturing strategy, predictability in our manufacturing operations becomes even more critical. In this memo, we describe the disruptions model and its implementation. We introduce the concept of product-related disruptions, unplanned events which directly affect a specific product in a shop. We contrast this type of disruption with the more widely studied process-related disruptions such as machine breakdowns. Our model explicitly captures the effects of both product-related disruptions and process-related disruptions and we use the model to study their impacts on work-in-process inventory. We conducted a series of simulation studies using the model, through which we determine functional relationships between work-in-process inventory and disruption level for both product- and process-related disruptions. The disruption level is defined by two parameters: frequency of occurrence and average duration. The objective of constructing these relationships is to characterize system performance in response to disruptions. The relationships can be used to determine the potential for improvement as the disruption level is reduced.