Non-hierarchical work-in-progress control in manufacturing

Reducing Work-In-Process (WIP) in manufacturing systems is associated with advantages such as predictable throughput times and increased manageability. To achieve this, an abundance of WIP control methods have been developed, such as CONWIP¹ and Kanban for repetitive manufacturing, and LUMS COR² and POLCA³ for high-variety manufacturing. These methods take three types of control decisions, viz., release (entry to the manufacturing system), authorization (entry to a work centre) and dispatching (order selection at a work centre). All existing WIP control methods are hierarchical by first deciding on release and authorization before making dispatching decisions, thereby letting the decision whether to produce precede over which order to produce. This hierarchy is traditionally motivated by uncertainty in information between organizational levels, but this is questionable given the advent of Industry 4.0 technologies. We develop a non-hierarchical method – termed DRACO⁴ – that simultaneously considers release, authorization and dispatching when deciding. The simulation results show that DRACO significantly outperforms LUMS COR and POLCA on mean WIP and delivery performance measures. Additional analysis also indicates that overall manageability is improved by the non-hierarchical method DRACO.