Order review/release and lot splitting in drum-buffer-rope

The drum-buffer-rope (DBR) planning and control system is relatively new in the published literature. As such, many issues relating to various operating policies have yet to be resolved. In this paper, we look at three such policies. First we study selected order review/release (ORR) methodologies that have appeared in the published literature to be used as the rope component in DBR. Secondly, we study the impact of lot splitting by breaking process batches into numerous transfer batches. Lastly, the impact of capacity balance between the bottleneck resource and non-bottleneck resources are modelled. A simulation model of an existing V plant that manufactures pliers is constructed. Results indicate that the appropriate choice of each operating policy is a function of the shop performance criteria felt to be important by management. No previous paper has studied the feasibility of using the various ORR methodologies in a DBR environment. We show that the performance of each is dependent on other conditions within the shop. Likewise, the impact of lot splitting has yet to be studied. We found that splitting process batches into smaller transfer batches nearly always improved shop performance criteria. Further, simulation results indicate that shop inventory levels necessary to achieve comparable service levels is a function of the capacity balance between bottlenecks and non-bottlenecks, i.e. capacity slack. As capacity slack increases, thereby reducing capacity balance, shop inventory levels show a corresponding decrease.