Manufacturing Capacity Planning

Let's turn our attention to the connected flow manufacturing environment. This environment is characterized by the operation time (set-up, run, tear-down) consuming 80% or more of the total throughput time. Work cells, short material transportation dis­tances, small queues, point-of-use material storage, and Kanbans are commonly found in this environment, and often times, work orders are not issued to production.

The choice of capacity planning techniques in this environment depends primarily upon two factors—product mix and variation in volume. If the product mix scheduled through a resource does not vary much, or if all products consume approximately the same amount of that resource per unit, capacity planning can be done by merely increasing or decreasing future available capacity in proportion to the total product volume anticipated.

Figure 5 is a typical short term capacity plan for a connected flow environment for similar products. Note that capacity is planned in product units rather than hours, since each product consumes approximately the same amount of resources, and the schedule is arranged to level the load on the plant in terms of product output. Mid to long term plans would show capacity requirements in terms of product output that would be similar to—if not identical to—the Master Schedule.

It is this situation that has led to the notion that JIT plants don't need to do any capacity planning, they just use the Master Schedule. It is merely semantics. They still do plan capacity, just in different terms. If the Master Schedule indicates an anticipated increase in output, then an increase in capacity must be arranged in advance. That is the essence of capacity planning.

If the capacity requirements vary noticeably with changes in product mix, or if volume changes are irregular, then a more detailed capacity planning and scheduling technique is necessary. In this case, the CRP technique as described above for the disconnected flow environment may be used, but the process itself might be somewhat simplified by using abbreviated routings (often one step), fewer work centers (cells), and no released shop orders (scheduled receipts, in MRP terms). In fact, some flow environments use only RCCP as the capacity planning technique if the limitations of that process noted above are not an issue.

except that the resources consumed per unit vary by product. In this situation, the capacity planning process is essentially the same as CRP. The scheduled quantity is multiplied by the resource required per unit and a total capacity required is aggregated from all of the product scheduled for the period (in this case, daily.) Note that the load on the plant has been leveled in hours now rather than in product units.

In the connected flow environment, input is inseparably linked to output. Thus, the need for classic Input/Output Control is elimi­nated. However, output against plan is monitored very closely in such environments, so I suppose one could say that Output Control is being used. Again, it is semantics.

Regardless of the environment—MRP II or JIT, disconnected flow or connected flow, fabrication or process—every manufac­turing company needs to plan capacities. The further forward that a company can look to reveal potential imbalances between

available capacity and required capacity, llic better they will \><-. able to correct the situation and avoid the rush arid chaos -.<, prevalent in many companies. The process for doing this is fundamentally the same in all companies:

1. Run the Master Schedule up against a set of data that will predict the capacity required to do it by time period.

1. Compare the results of step 1 to the capacity that is expected to be available in each period.

3. Initiate action to correct imbalances identified in step 2.

What differs is the level of detail that is employed to do the job. That varies with the environment.

Examine your situation carefully. Don't reject a technique or process because someone said it didn't apply, you don't under­stand it, or you tried it once (probably incorrectly) and it didn't work. Employing the proper techniques properly (the redundancy is intentional) is the key to winning the global competitive war.

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