In modern production systems that perform under high cost environments, even small improvements in line efficiency represents large savings over the lifetime of an assembly line. In the beginning of modern production systems, it was thought that a `perfectly balanced' line was the most efficient way to design the line. However in practice, the ideal perfectly balanced line seldom occurs, because some degree of imbalance is inevitable.
Recent studies have found that unbalanced lines with a bowl shape workload configuration can yield performance in throughput as good as, or even better than those of a perfectly balanced line. This thesis studied the "bowl phenomenon" in large unpaced assembly lines under stochastic processing times. The control variables analyzed in this study were line length, buffer capacity, task time variability, and percentage of imbalance. A full factorial experiment was designed in order to characterize the main and interaction effects, and computational simulation was used to replicate the behavior of the unbalanced assembly lines. The results of the experiment suggest that unbalancing a large assembly line in a bowl shape workload configuration could provide statistical significant improvements in throughput. Moreover, the results also suggest that the Work in Process (WIP) and the Cycle Time (CT) increase linearly as the Throughput (TR) of the line increases. Even though, the rate at which the TR increases is greater than the rate at which the WIP and CT increases, line designers and production managers need to make an important managerial decision on how much they are willing to increase the WIP and CT of their lines in order to improve the throughput when implementing a bowl shape workload configuration. Furthermore, the results suggested that as the buffer capacity and the number of workstations in the line decreases, and the coefficient of variation of the workstations increases the benefits the bowl phenomenon and the percentage of imbalance of the "best bowl configuration" increases.
In this research, the relationship between the production rate of large assembly lines with a bowl shape workload configuration and its line length, buffer capacity, task time variability, and percentage of imbalance has been studied for the first time. The results would provide valuable guidelines for line designers and managers that want to improve their assembly lines.
Library of Congress Subject Headings
Assembly-line methods--Production control; Assembly-line balancing
Industrial and Systems Engineering (MS)
Department, Program, or Center
Industrial and Systems Engineering (KGCOE)
Lopez, Christian E., "Unbalanced Workload Allocation in Large Assembly Lines." (2014). Thesis. Rochester Institute of Technology. Accessed from
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