Master Scheduling
Part 3 of 5

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Inclusiveness: The Master Production Schedule should consider all demands for products and services. This usually includes customer orders, sales forecasts, and distribution requirements. There are other demands that also should be included in the Master Production Schedule. These are interplant demands, export plans, spare parts, and other demand sources.
The strategies embodied in the Production Plan generate important objectives that should be included in operations detail plans and execution. Additionally, the material and capacity availability frequently limit the options of the master scheduler. A factor often overlooked is how the interaction between booking customer orders and consum­ing the forecast can sometimes distort the real demand.

Most understand the idea that there is not a "perfect forecast." Yet many use this as an excuse to accept the current level of forecast accuracy. It is important to realize that small increases in forecast accuracy can significantly stabilize schedule changes and reduce inventory in the entire supply chain.
Stability: Frequent changes to the Master Production Schedule inside the cumulative lead time can destroy the integrity of the entire Manufacturing Resource Planning system. Those charged with the responsibility for execut­ing the detail plans are constantly faced with changing priorities. They soon loose confidence with the information generated by the Material and Capacity Requirements Plans. This ties back to the principle of interactive perfor­mance discussed earlier. Consider the foreman who was asked what reports he got to help him decide what to work on each day. He replied that he received a schedule, a priority list, and a hot sheet. When asked which did he use when deciding what to work on he replied, "I work on the stuff I have parts for!"

An important technique to help stabilize the Master Pro­duction Schedule is to establish and maintain time fence policies. Gaining control by using time fences can be a very helpful tactic but their effective use requires the coopera­tion of Top Management to enforce them. The first time fence is the cumulative lead time of the Master Production Schedule products. This establishes the minimum plan­ning horizon. In most situations the planning horizon will extend beyond the cumulative lead time to give greater visibility to plan long lead time items. The manufacturing orders that fall inside the cumulative lead time should be scheduled receipts or firm planned. It is critical that the master scheduler controls the plan inside the cumulative lead time fence.

Other important time fences are the firm, mix, and rate fences that should control the changes to the Master Production Schedule. Changes outside the cumulative lead time generally cause few problems and have little impact on costs. Inside the cumulative lead time it is important to set the rate of production based on the commitments for raw materials. The decision made at this critical point should control the total volume of production. Once raw materials are converted into specific items and assemblies, the mix of different products that can be produced gets smaller. Frequently different styles, colors and special labeling will limit flexibility of what finished products can be made. Finally, usually near the end of the manufactur­ing cycle, the schedule should be firm and change only with Top Management's approval. Changes made within these fences add more cost the closer the item is to being completed. When changes are necessary, it is important that management knows the cost impact of these decisions.

Feasibility: One "golden rule" of Master Scheduling is that it should always be realistic. Simply put, this means that when something gets scheduled there should be a very good possibility that the materials and capacity will be available. A bottleneck that is several levels deep in the product structure can control the production flow through all down stream (toward the end item) operations and stages of production. This is frequently a very difficult situation to coordinate.

Material Requirements Planning is a backward scheduling procedure driven by the need date of a component's parent item. Additionally Material Requirements Planning as­sumes that infinite capacity is available to convert compo­nents into subassemblies. The traditional Manufacturing Resource Planning approach is to provide a Rough Cut Capacity Plan that suggests the load condition in critical work centers. Armed with this "rough cut" information, the master scheduler is to rearrange the Master Production Schedule for the products creating the overload condition. This can be an extremely difficult task. Especially when the items need to be master scheduled in the future and the capacity problem is near term and several levels down in the product structure.

There are tactical initiatives like Finite Forward Schedul­ing that can help synchronize scheduling. Yet the fact remains that most companies do not have Master Schedul­ing in place thereby rendering the use of Finite Forward Scheduling inoperative.

To be Continued