A workload balancing model for determining set-up time and batch size reductions in GT flow line workcells

Set-up time and batch size reductions – cornerstones of Quick Response Manufacturing (QRM) – are often viewed as pathways leading to lower work-in-process (WIP) inventory levels and reduced manufacturing lead times. However, set-up time and batch size reductions may not always yield such improvements. Increased workload due to the additional set-ups can lead to a violation of the system's capacity constraints and cause system instability, which results in increased manufacturing lead times and WIP inventory levels. A work-load balancing model in conjunction with a heuristic model is presented to determine the required set-up time reduction schemes for different levels of batch size reduction. The model is based on the Theory of Constraints to balance the flow line and limit the workload of each workstation such that each workstation meets the reserved capacity constraint. It is shown that a reduction plan determined by the workload balancing model will maintain the cell's system stability and improve its performance. Incorporating the workload balancing and simulation models, a general approach for selecting the most appropriate reduction plan is illustrated through an example of a gear manufacturing cell. The implications for management are: (1) that pre-established levels for set-up time and batch size reductions are not always effective; and (2) that effective reduction plans need to be preceded by system capacity and performance analysis to determine the effects of such reductions prior to implementation.