Finite and infinite capacity planning
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resources. This is a time-phased plan and a particular resource may be required several times during the manufacture of a product. The use of product load profiles in complex products represents an approximation of the actual load. The data is aggregated for all master scheduled items to produce a time-phased load profile for each of the resources defined. Where overloads are detected, management need to take appropriate action. Preferably, this should take the form of additional capacity, as changes to the MPS will cause instability at lower levels in the planning process. The use of RCCP allows the impact of a particular product mix with the MPS to be analysed. It allows ‘what-if’ analysis so that before the MPS is submitted to MRP, management can be reasonably sure that the plan is broadly compatible with capacity. RCCP does have limitations nonetheless:
It considers only critical resources. This is not a problem unless product mix is highly variable. It ignores WIP/component inventory of lower-level components. It does not take into account the completion of work orders. The effect of these simplifications is that RCCP is a pessimistic view of the capacity/load balance.
In practice, RCCP is often a critical element in successful master scheduling. If skilfully applied, the limitations outlined do not invalidate the technique. Some software suppliers now offer more sophisticated RCCP systems based on simulation techniques. These provide a more accurate picture of load and help to visualize the effect of product mix.
19.9.2 CRP vs RCCP CRP and RCCP have the same objective: to provide information on the load imposed on the manufacturing system. Both are infinite capacity loading approaches. That is to say, both maintain works order start and finish dates. It has been shown that these approaches contrast sharply with FCS where capacity is not exceeded, but due dates are flexible. Table 19.3 compares these two techniques. A superficial review of these two techniques would suggest that CRP is the superior technique. CRP has three major disadvantages, however: Data. CRP requires a large amount of data. With the decline of bonus systems, many companies no longer have work study departments to provide accurate routing information. Need for feedback. To provide an accurate answer, CRP requires detailed shop floor feedback. Many companies are attempting to reduce the amount of transactions that need to be made on the shop floor. Timing of information. CRP is run after MRP. Thus, if any significant overloads are detected that cannot be addressed by overtime, then it will