Calculating Production Dates (Lead Time Scheduling) (SAP Library - Material Requirements Planning (PP-MRP))

Calculating Production Dates (Lead Time Scheduling)

Implementation Options

If the basic dates calculation is not exact enough for your needs, you activate the calculation of production dates using lead time scheduling.

Prerequisites

You have created a routing for the material.

You have assigned a scheduling margin key to the material in the material master.

You can define the scheduling margin key in Customizing for MRP by choosing Define floats (scheduling margin key).

You have maintained the following parameters for lead time scheduling in Customizing for MRP by choosing Define scheduling parameters for planned orders:

Scheduling levels - to differentiate between detailed, rough-cut, and rate-based scheduling
Parameters for determining the routing
Parameters that determine if and how scheduling is carried out
Parameters that determine if and how basic dates are to be adjusted

Process Flow

In lead time scheduling, the precise production times, that is, the production start date and the production finish date, are specified for materials that are produced in-house. Capacity requirements are also created during lead time scheduling and the date, on which the components must be provided, is also determined.

The production dates are determined using the routing. The system hereby uses the floats that are allocated to the material via the scheduling margin key in the material master. These floats include the float before production and the float after production, as well as the extra time factors specified in the routing such as the queue times, setup times, labor times, machine times, and so on.

The system normally executes the lead time scheduling with backwards scheduling and starts from the determined order finish date. The system only switches to forward scheduling and starts from the order start date, if the times in routing are substantially shorter than the times in the material master and the determined production start date is therefore further in the future than necessary.

The system calculates the float after production using the order finish date and thus determines the production finish date. Starting from the production finish date, the individual operations of the routing are then scheduled backwards. The starting date of the first operation is the production start date.

The float after production is the number of workdays that are planned as a buffer between the production finish date and the order finish date. This serves to compensate for interruptions during production to avoid displacing the order finish date.

The system checks whether the production start date is later than the order start date. If you have determined that the order start dates are to be adjusted in lead time scheduling in Customizing for MRP (IMG activity Define scheduling parameters for planned orders), the system subtracts the float before production from the production start date to calculate the new order start date. If you do not want the system to adjust the order start date, the system will not change the old order start date.

The float before production is the number of workdays that are planned as a buffer between the order start date and the production start date. By using this float, delays in material staging do not cause delays in starting production. Additionally, if there are capacity bottlenecks or delays in an incoming sales order, the production dates can be brought forward.

The system checks whether the production start date is earlier than the order start date and, if necessary, determines new production dates. To do this, you must determine a possible time reduction in two places:

To reduce the floats before and after production, you must define the reduction for the plant, the planning type and, if necessary, for a production scheduler in Customizing for MRP.
To reduce the times in the operation, you must assign a reduction strategy to the operation in the routing.

The system must set an order finish date so that the material is available for the start of production. Therefore, the order finish date always lies after the production finish date. If you have not maintained a float after production, the order finish date always lies exactly one day after the production finish date.

If the in-house production time is much less than a day and if you want the material to be available for the production finish date, then you maintain the in-house production time in the material master record with zero (the float after production likewise with zero). Then, the production date is the same as the order finish date.