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.