When a planned order is created by MRP, the basic dates are calculated according to the in-house production time defined on the material master. Additionally, MRP can read and explode the routing to calculate the operation dates. The planned order production dates can be then calculated according to the operation dates and the basic dates can be even adjusted to match the production dates, depending on the customizing settings.
The production dates calculated with the routing data are more accurate than the basic dates, however, this is a complex calculation and, depending on the number of operations defined on the routing, can lead to performance issues and a long MRP execution. The performance is even worse when lead time scheduling is used in combination with planning mode 2 or 3, since the routing of each planned order of each material will be read and scheduling will be carried out again.
The question here is:
Do we really need such accurate dates for a planned order?
Maybe an even better question is:
Is it worth to have a longer MRP execution to have the production dates calculated?
Considering that the planned order is merely a planning element and that it will generally be later converted to production or process orders (unless we are using repetitive manufacturing), it is usually only a big advantage to have the operation dates calculated for a planned order in the following scenarios:
- Capacity leveling is executed for planned orders;
- Variant configuration is used and there are dependencies on the routing, which may affect the results of lead time scheduling;
- Repetitive manufacturing is used with a rate routing/reporting point;
If these scenarios are not used, then we can simply run MRP without lead time scheduling and use the planned order basic dates only, in order to improve the MRP run performance. After the conversion to production or process order, the routing will be exploded and the operation dates will be calculated.
What about the accurate planned order dates calculated with lead time scheduling?
On the material master tab Work Scheduling we have the option to inform the lot size dependent in-house production time, which means that the planned order basic dates will be calculated according to the planned order size.
In addition, transaction CA97N can be used to calculate the in-house production time according to the routing and update this information directly on the material master. It means that the planned order basic dates will as accurate as the basic dates calculated with lead time scheduling.
I need lead time scheduling because I’m running capacity leveling for planned orders!
Ok, in this case lead time scheduling is really necessary. However, capacity leveling is generally carried out on the short term horizon. If this is the case, perhaps you convert planned orders to production or process orders earlier, in order to run capacity leveling only with production/process orders.
That way, you don’t need to run lead-time scheduling during the MRP run and the performance can be improved.
If you still decide that it is necessary to run capacity planning with planned orders, on the customizing transaction OPU5 it is possible to define an horizon for detailed scheduling. This horizon should be no longer than the capacity planning horizon. That means, you don’t need to run detailed scheduling for a planned order that is 6 months in the future, if you only run capacity leveling for one month in the future.
Where can I find more information about the system behavior?
On the following notes you can find more information about the functionalities mentioned on this blog, such as MRP performance, lead time scheduling and planning mode:
|206666||MRP: Control parameters during planning|
|204517||MRP: Typical causes of performance problems|
|156115||Consulting: Scheduling of planned order for recipe|
|152319||Consulting: Scheduling of planned order for routing|
|78867||MD01: Documentation on the planning mode|