Lot synchronization in make-to-order shops with order release control: an assessment by simulation

Lot splitting is an important strategy for avoiding the starvation of workstations, for accelerating the progress of jobs, and ultimately for improving overall due date performance. While lot splitting has received much attention in the extant literature, the use of alternative lot transfer policies that determine how the flow of lots through the production system is synchronised has been largely neglected. This study uses simulation to assess the performance of different lot synchronisation policies at release and different lot transfer policies on the shop floor in a ConWIP (Constant Work-In-Process) controlled job shop. The results suggest that different approaches should be applied at the release and shop floor levels. While lots should be synchronised in some form at order release, their progress on the shop floor should not be synchronised. Instead, lot coordination should be executed by dispatching in accordance with repetitive lots logic. The results further highlight that if lot progress is synchronised in systems that limit the workload, then lot release should also be synchronised. Otherwise, blocking may occur if lot progress on the shop floor depends on the release of lots, which in turn depends on lot progress. These findings have important implications for research and practice.