Two major processing steps occur during requirements planning:
First, the system determines the uncovered net requirement quantities for each individual day in the planned horizon. It does this based on the stocks that have to be taken into account, the requirements and the firmed receipts.
Then, during the lot-size calculation, the system creates procurement proposals for all net requirements and, depending on the lot size parameters, net requirements can be covered exactly, split or combined into one procurement proposal.
The safety stock that is available is a special case because the net requirements calculation interprets it as stock and as requirement and receipt.
First it is taken into account as a stock because it is used to cover the first requirements on the time axis. Only when the available part is consumed does the system calculate the net requirements for the corresponding day. Since this first net requirement should also balance out the available safety stock, the first net requirement is increased by the available part of the safety stock, which means that at this point, the safety stock itself is a requirement that is to be procured.
For example (due to the complexity of the lot size Customizing and the different requirement/stock situations that are possible, we can only describe one scenario as an example):
Safety stock: 10 pieces
Safety stock available for planning: 100 %
Stock/requirements situation:
Date | MRP Element | Receipt/Requirement | Available Quantity |
MAY/01/08 | Stock | 0 | |
MAY/01/08 | Safety Stock | 10- | 10- |
JUN/02/08 | PIR | 3- | 13- |
JUL/01/08 | PIR | 3- | 16- |
AUG/01/08 | PIR | 3- | 19- |
SEP/01/08 | PIR | 3- | 22- |
OCT/01/08 | PIR | 3- | 25- |
NOV/03/08 | PIR | 3- | 28- |
DEC/01/08 | PIR | 3- | 31- |
During net requirements calculation, the system determines the following
net requirements while taking the safety stock available for planning into
account:
Date Requirement
02.06.2008 13 (10 is safety stock planned as a receipt + 3 for the req on May/01/08)
01.10.2008 12 (3 for July, 3 for Aug, 3 for Sept making it 9 and this is covered by 100% of safety stock and so it takes the next reqt for Oct’08 3 units and makes it 12 and stops there).
Based on these net requirements, the system then carries out the lot size calculation:
a) No rounding: If no rounding is used, the system creates receipt elements with the value of the net requirements for these dates. Material shortages occur only up to the value of the safety stock.
b) Rounding = 5: In this case, the system creates a receipt of 15 for JUN/02/08, that is 2 more pieces than are necessary. These 2 pieces are consumed in the next net requirement so that on OCT/01/08 only 10 are required instead of 12. If 100% of the safety stock is available for planning, no receipt element is required/created. Due to the rounding, the next receipt would be required on NOV/03/08 and not on OCT/01/08 (as was determined in the net requirements calculation). However, this cannot be determined when the lot size planning is carried out. The next receipt is created on the next date that is determined in the net requirements calculation. However, in this example, there is no other net requirement calculated for the original net requirements calculation after OCT/01/08 because only two net requirements (on JUN/02/08 and OCT/01/08) are available without a rounding value. Therefore, the MRP creates only one receipt on JUN/02/08. It does not create any more after that. Only when more requirements are added to the time axis is the next receipt created at a later date.
Problems may occur if, due to roundings, minimum lot size or firmed lot sizes, the lot size calculation carries out procurement beyond the mere filling of the part of the safety stock that is available. In this case, the net requirements quantities and dates that are calculated no longer match the resulting available quantities on the time axis, which causes delayed requirement coverages after the material has been planned.
Note that a useful lot size calculation can only be carried out after the net requirements calculation is completed because otherwise, processes such as the rescheduling check, lot combination and so on do not work correctly. However, if safety stocks are available, the net calculation at the time of the safety stock consumption must assume a procurement of a certain value to ensure that the subsequent net requirements are calculated correctly. Since the amount of this "scheduled receipt" is not known, the system assumes the simplest case (EX - exact balancing of the safety stock at the time of the consumption). Any deviations from this procedure in the lot size calculation can cause incomprehensive procurement and rescheduling proposals.
Solution
It is not possible to change the program since material requirements planning is based on the concept of the separation of net requirements and lot size calculation.
Therefore, we recommend that you do not use the safety stocks that are available for planning in connection with firmed lot sizes, minimum lot sizes or roundings.
<End of SAP Note>
Hope the information was useful. Please point out any other points of interest which can be added to this document to make it more meaningful.
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.
User | Count |
---|---|
2 | |
2 | |
2 | |
2 | |
2 | |
2 | |
2 | |
1 | |
1 |