Single-server aggregation of a re-entrant flow line

On-time delivery performance of a semiconductor manufacturing system depends on the cycle time distribution of lots produced in the manufacturing network. A detailed simulation model of the manufacturing system that can predict the cycle time distribution may be helpful in performance improvement activities, but requires considerable development and maintenance effort. To reduce development and maintenance effort, an aggregate model has recently been developed that is a lumped-parameter representation of a manufacturing workstation. The lumped-parameters are directly determined from arrival and departure events measured at the workstation in operation. In this paper, we investigate under which conditions the previously developed aggregate model can be used to model a re-entrant flow line of workstations, motivated by semiconductor manufacturing. We find that the range of throughput levels for which accurate cycle time predictions are obtained increases for increasing process time variability, and decreases for increasing network size.