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By Root 2515 0

The relative priority of each new production order competing for being released today is based on how much replenishment is required to reach a full target level of inventory in the shop floor (including the warehouse) relative to the target level. In other words, the production orders in the queue awaiting release are getting a buffer status, similar to the orders that were released. That status serves as the relative priority of the order. The orders with the highest status would be released first. Every order that is released updates the regular planned load. Once the planned load limit has been exceeded, the daily release of orders is stopped. The rest of the queue awaiting release has to wait until the next day, and as consumption continues, their relative priority will go up accordingly.

Let’s demonstrate the mechanics of this procedure with the following example: Suppose the replenishment time is 5 days with 16 hours of CCR time every day (5 days × 16 hrs/day = 80 hours). A natural limit for the regular planned load is 80 percent of the replenishment time—64 hours. We use only 80 percent of the replenishment time assuming that this way the overall replenishment time, including the operations downstream of the CCR, would be easily maintained (the part downstream of the CCR usually takes much less time than the time to reach the CCR waiting for its turn and then being processed by the CCR). This procedure of release would avoid having too much WIP on the shop floor. Suppose that on a given day the planned load reaches 50 hours. Suppose 11 items are in the production pipeline. The relevant information is shown in Table 10-2.

As the planned load is already 50 hours and the limit is 64 hours, we can release up to 14 hours of work. Right now we need to release 19.3 hours—a little too much. The most straightforward method is to add from the highest priority, P10, then P3, then P1, P7, P5, P8. This would bring us to a total of 13.2 hours. The next, P9, would penetrate the 14 hours limit. Should P9 be released? This decision should be subject to the judgment of the person in charge (usually the master scheduler) and is not too critical. The main point is that P6, P2, and P4 would wait at least one additional day.

In most cases, a certain minimum batch is required. That must be considered in addition to the CCR load. When a minimum batch is used, then the priority is determined just by the quantity required to replenish to the target level. However, the load on the CCR needs to consider the size of the batch. For instance, if the target level is 100 and currently there are 49 on-hand and 50 in the pipeline (it could be that the 50 units are included in two production orders, not yet finished, somewhere in the shop floor, etc.). The replenishment to the target level requires only one unit, but the minimum batch is 25. The priority for releasing the next replenishment order is based on 1 × 100/100 = 1%, but the time on the CCR needs to consider a batch of 25. When the load on the CCR and the relative priorities of the other orders will permit the release of this order consisting of 25 units to the floor, the time it’ll take on the CCR is planned based on the load of processing 25 units. It may thus prevent other orders from being released on that day.

TABLE 10-2 List of the Orders in the Queue Awaiting Release

Peak and Off-Peak Behaviors

At off-peak periods, there should be no blockages to the release of small replenishment orders to the floor. When the demand starts to pick up, then monitoring the replenishment order release starts to be critical because continuing to release small daily batches increases the number of setups, creating more blockages of the flow in the shop. The impact of this algorithm is to set a limit on the actual wait time to the CCR, thus limiting WIP to a degree that will allow orders in the shop to move at a speed that is in line with the assumed replenishment time. However, at the same time there are orders that still wait to go into the shop. This means the actual replenishment time