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horizon provides a planned load for a specific use. However, a horizon is required for ensuring we do not promise delivery dates that cannot be met is of special importance. The time horizon for such a decision has to include all the orders already received (both released and not released to production) that might compete for the capacity required for the new received order. The important parameter is the realistic expectation of the market regarding the due date. If we assume that a client submitting an order expects to get it no later than the standard lead time of that industry, then the horizon must include all orders to be delivered within the standard lead time. We might need to extend that horizon just a little to cover for a peak load that would force quoting a somewhat later due date.

There is definitely no wish for extending the horizon significantly more than the clients’ expectations for response time to an order. It could be that some orders in the logbook have dates further out into the future, due to some clients wishing to ensure the availability of capacity for their orders. Nevertheless, do we need to consider those orders when we check the feasibility of delivering an order just received? Only when such an order enters the planning horizon should the capacity required for that order be considered.

What benefit does the planned load give? The most important information to deduce from the planned load is the approximate prediction regarding the time a new order will be processed by the CCR (the weakest link). Such information is critical for judging a “safe date” for completion of the order. It is only a gross approximation of the time the CCR would really process the order because our data are not necessarily precise and we do not guarantee the sequence of processing at the CCR. In addition, in order to obtain the planned load we simply add the load on the CCR of every order to be delivered in the horizon. Therefore, we have actually assumed that the CCR would not have idle time. See Fig. 9-2. Thus, the timing when a new order would have the chance to be processed by the CCR is far from being accurate, but it can serve as a gross assessment. All we need to know is what due date is safe enough to promise completion of the order. For that, we need the planned load and to add to it a certain time buffer, as we’ll soon see.

FIGURE 9-2 Demonstrating the calculation of the planned load.

Technically, the planned load looks like a schedule. It is generated by taking all the planned orders to be delivered and adding the required time the CCR has to invest on the timeline. The end of the planned load is a date—the approximate date when the CCR would finish processing all the currently known orders. In Fig. 9-2, this date is 06/13/10. The important aspect of this date is that this almost arbitrary sequence is not forced on the CCR. The CCR is expected to follow the general priorities of BM and when some customer orders are stuck upstream, then other orders are to be processed early and the delayed customer orders would get higher priority when they show up at the CCR.

To demonstrate further that the planned load is not a schedule, let’s review the following example. Suppose that we are in a re-entrant environment where the order goes through the same resources several times. In the planned load, all the accumulated time the CCR has to invest in that order appears once. This view definitely does not provide a realistic schedule as the order is processed by the CCR several times and in-between these separate processing times other resources would be used to process this order. Suppose there are four machines, M1→M2→M3→M4, and a typical order goes through this sequence of resources six times. No matter which one of the four machines is the weakest link, there will be six times where the CCR would work on the order. Therefore, when such an order is put on the timeline of the CCR, it is placed on one continuous location where all the required capacity for six operations is included. On one hand, such a description