19. Advanced Production Planning and Scheduling Systems

In this chapter, we present algorithms for a number of functions of the production planning framework presented in Chap. 5. We focus on models for integrated Capacity and Master Production Planning, Job Planning and Resource Group Loading, and Shop Floor Scheduling and Control. At the Master Production Planning level, we exploit a simple Linear Programming formulation to set appropriate capacity levels and in particular to decide whether a temporary expansion of capacity is needed (e.g., through overtime work). With the same formulation, we decide what end-items are to be produced in which period. By applying the lead time offset procedure that is the heart of Materials Requirements Planning, and using the Bill of Materials information, the same is done on the level of part manufacturing (basic level). Essential in the above procedure are two parameters, the effective overall capacity of each manufacturing shop and the final assembly department, often indicated as the maximum throughput, and the lead times needed to complete a part or product in each department. A significant portion of these lead times may in fact be waiting times in front of individual workstations that are busy. To minimize these waiting times, workload control norms are often used which in turn may influence the effective capacity. An essential question then is what these workloads should be in order to match a desired throughput and production lead time. That question is answered by exploiting a Closed Queueing Network approach that explicitly determines the relation between a preset work-in-process level, throughput and the resulting lead times (advanced level). Finally, we exploit a detailed shop floor scheduling procedure, called the Shifting Bottleneck approach, that basically serves to ascertain that internal due-dates, following from the above defined internal manufacturing lead times are indeed met (state-of-the-art).