Generally stability is not in question for producer firms. A continuous change is available in such firms. Planned productions and issued orders cannot always actualize 100%. That is to say, orders may not be supplied or the order amounts can be changed because of the capacity constraints, gross requirements can be changed because of raw material lacking or customer amount demands can be changed. Because of all these reasons main production plans can be changed; and the firms may have to change material plans because of all these cases.
Therefore, MRP has to adapt these changes and the requirement planning has to be updated all the time. There are some methods to adapt MRP to changes and provide its up-to-dateness. Regenerative method and Net Change are the methods that are used mostly. According to frequency of replanning, one of these methods can be used in LOGO application.
Regenerative Method
In this method Material Requirement Planning is restructured periodically. This method necessitates recalculating inventory levels of materials take place in main production plan, recalculating gross and net requirements for the planned productions and necessitates BOM Explosion of the materials.
Regenerative is a method that mostly stands for plannings which are not done frequently. This method is preferred when there are no too many reasons for a company to perform re-planning. Consequently, Regenerative Method is applied weekly or monthly ranges.
Because of systematic controls, faulty data existence is nearly impossible in the system. In this type of systems, the changes done on requirement planning can only be seen after a new MRP phase.
Net Change Approach
By this method, the requirement calculations for all materials are not done periodically; the calculations are done only when a change in main production plan occurs.
If any unplanned case occurs in any time (for example, late or an early received order, increase in customer demand/order amounts, BOM renewals because of engineering changes), a partial requirement planning is done for the materials that will be affected by these changes.
The advantage of the Net Change system is that the system is updated instantly by the instantaneous changes. However, a wrong net change application can spoil the previously formed plans entirely.
A change in an upper level can have serious effects on order and production amounts of materials in lower levels.
Because main production plan is not regenerated in net change method, the previous plan errors are continued.
Net change is mostly preferred in more changeable environments when more stable environments prefer regenerative method.
To sum up, these steps are followed for MRP Net Change system operation:
- Master Production schedule (MPS) and product requirements are determined by taking company orders and demands into account.
- Bills of materials determine the gross requirements for each product by starting from level 0.
- Based on MPS, MRP Net Change suggests the necessary orders and production orders to be given by using product tree and inventory information.
- In accordance with determined changes, renewing operation is done by using appropriate method.