Performance evaluation for systems of pooled machines of unequal sizes: Unbalancing versus balancing

This research explores the appropriateness of unbalancing the workload per machine in certain types of flexible manufacturing systems (FMSs) configured as pooled machines of unequal sizes. Studies are conducted to examine the applicability of following an objective to unbalance workloads when solving the FMS planning problems of selecting part types to be machined together and determining their production ratios. Simulation is used to compare unbalancing and balancing on realistic, detailed models of flexible flow system (FFSs). The experiments are constructed to evaluate the impact of operational factors such as blocking, transportation, buffer utilizations, fixture requirements of various types, and different workload distributions among the machine types. The research results indicate that the aggregate and theoretically optimal unbalanced workloads provided by Stecke and Solberg (1981, 1985) using a closed queueing network model can be appropriate in a realistic FMS. Production rate and system and machine utilizations can all be higher when unbalancing workloads in systems of pooled machines of unequal sizes. It is also observed that: (1) system performance in terms of system utilization or production rate is sensitive to the appropriate number of pallets in the system, when either unbalancing or balancing; and (2) unbalanced part mix ratios conversely can lead to balanced machine utilizations among unequally sized pooled machine types. Overall system utilization seems to be more sensitive to the number of pallets in the system when unbalancing than when balancing. Further research needs are also noted.