Safety Time in Planning – The Time Float
Planning as we know is never smooth and is always subjected to deviations. Options to smoothen the effects exist and in SAP they take up the forms of
- ‘Quantity float’ to take care of variability in demand and/or production and
- ‘Time float’ to take care of uncertainties in timing of demand and/or production and also supply variability into account like unreliability of vendor deliveries affecting the overall production plan.
Most often discussions in the PP forum revolve around the quantity float provided as static and dynamic safety stocks and little attention is paid or discussed on time floats. This documents aims at explaining the functionality of how a time float can be utilised in relevant business scenarios.
Quantity floats have been discussed earlier as in the documents as below:
Static Safety stock: Safety Stock and its Availability for Planning Purposes
Dynamic Safety stock: Dynamic Safety Stock – The Quantity Float
(As a side note, in actual production we also have the floats provided which we see under the Schedule Margin Key).
In SAP, in addition to static and dynamic safety stocks used commonly with MRP procedure, we also have the ‘minimum’ safety stock along with Automatic Safety stock that is provided for usage with the Reorder planning procedure.
- Quantity float–>Static Safety stock, Dynamic Safety stock, Automatic Safety stock and Minimum Safety stock. (Of these, Static and Minimum safety stocks can be again categorized as ‘manual’ whereas the other two are ‘automatic’ options).
- Time float–> Safety Time.
Safety time in SAP Material master MRP2 view:
While using the safety time, we have the option to include all requirements or only the independent requirements (PIR/Sales order) to be taken into account. A blank option/selection by default switches off the functionality.
Either we can enter either the Safety time period profile field or the Safety time/act coverage field in the material master.
Safety time period profile is set in the configuration to include safety time in days in addition to safety time in percentage (ie as a fraction).
Safety time/actual coverage is only to include whole number of days.
Preference is for the ST period profile and if it is not there the system considers the Safety time/act coverage value for calculations.
For our discussion we will consider the option of using the ST profile and for Independent Requirements alone in the material master as below.
Initial PIR status without the Safety time in material master: (before the safety time indicator has been actually set)
Post Safety time settings the PIR has been scheduled as below:
Even though the requirement is split the requirements date is not changed.
1st PIR is 100.
ST period profile is 3 days and 20%.
So 100 is split as 80 and 20.
2nd PIR is 200
So 200 is split as 160 and 40 respectively.
Execute MRP now.
Consider the PIRs on 01/03/2013 which are split as 20 and 80 respectively.
The Planned order for 80 is available on 26/2/2013 and that for 20 on 25/02/2013.
Three working days before 1st Mar’13 is 26th Feb’13.
80% of PIR is planned for this day and balance 20% gets carried over to the previous day which is 25th Feb’13.
If we do not maintain any ST period profile and instead the safety time/actual coverage in the material master, we will not see any split of planned orders on 2 consecutive working days and instead the shift will be on a single day as it is obvious.
If the planner needs to see which proposal corresponds to which demand as it is not easier to infer because of the shift, the following can be done in MD04.
By default the requirements do not change and by using SettingsàSettingsàDates tab
Under Safety time choose Option On.
Display is as below:
Repeat the exercise with other assemblies/subassemblies existing under your FG material and try to set the safety time indicator in the mrp view as option 2 (safety time for all requirements) and then observe the results. In addition to the PIR shift scenario we have seen in this discussion it should in addition shift the dependent requirements downstream for instance.
There are many research works/white papers available on the web discussing on time vs quantity floats based on multiple business factors.
A sample discussion on the topic:
Do try to read more on the topic in other sources/forums which would give you more information from a business point of view. Such things would help in your project to discuss about all these effects/impacts with the business planner/s to decide on which one to use/suggest.