Malfunctions and other disturbances in the production process can never be fully prevented; therefore, the system carries out scheduling with the help of a float before and a float after production. In the material master record, you define the floats before and after production using a scheduling margin key.
The float times serve the following purposes:
- Float before production
The float before production performs the following functions in the production order:
- It can compensate for delays when the material components are staged. Alternatively, if there is a capacity bottleneck at the work centers involved, you can move the production dates forward in the future. In this way, it serves as a float for capacity leveling.
- The system calculates the scheduled start by adding the float before production to the basic start date.
- Float after production
The float after production performs the following functions in the production order:
- It can compensate for unexpected interruptions in the production process by preventing the scheduled finish from being delayed.
- The system calculates the scheduled finish by subtracting the float after production from the basic finish date.
Time Elements in Lead-Time Scheduling
Let's get an overview of used time elements and their sequence.
Duration of Operations
The duration of an operation consists of a maximum of the following time components:
- Queue time:
In addition to the floats before and after production, you can define an operation float in the form of a queue time. The queue time is used to compensate for malfunctions and delays within an operation and is the interval between the earliest and latest dates of the operation. During each scheduling run, the system calculates the earliest and latest dates for the individual operation segments. You can maintain the queue time in both the work center and the operation. However, the system only schedules with the queue time in the work center if you do not maintain the queue time in the operation. If you reduce the lead time of an operation, the system can shorten the standard queue time as far as the minimum queue time.
- Setup time:
This is the time needed to prepare the work center for operations to be performed there and is part of the lead time.
- Processing time:
This is the time required to process a material in an operation. It depends on the order quantity and does not contain a setup or teardown time. The processing time is part of the execution time.
- Teardown time:
This is the time required to restore a work center to its normal state after the system has processed the operations and is part of the execution time.
- Wait time:
This is the time between the end of the execution time and the start of the move time. In the SAP ERP application, the process-related wait time can be the maximum wait time and minimum wait time. The minimum wait time is used in scheduling, and the maximum wait time is used for information purposes.
You can use the Teardown/wait simul. field in the Interoperation times section of the Operation Details screen to specify whether to consider the teardown and the wait times as simultaneous or consecutive operation segments in scheduling. If both the times are simultaneous, the lead time of the operation is reduced. The system schedules the wait time without taking the factory calendar into account. The wait time, therefore, can be scheduled daily from 00:00 to 24:00.
Move Time
In addition to the operation segments, you can define a move time. The move time is the time required to move a material from one work center to the next. The move time always occurs between two operations and is assigned to the preceding operation.
You can maintain the move time in the individual operations or in Customizing per location group in the move time matrix. In the Interoperation times section of the Operation Details screen, you can enter a minimum and a standard move time.
If reduction measures are carried out, the system schedules the operations using the minimum move time. It determines the move time with the help of the move time matrix only if you do not enter move times in the Interoperation times section of the Operation Details screen.
You can combine work centers (which are in close proximity to one another) into location groups. You can define location groups in Customizing and assign a work center to a location group on the Scheduling screen of the work center. In the move time matrix, you can specify planned values for the move time within a location group or from one location group to another. For each entry, you can specify a minimum and a standard move time.
You can use the operation segments and the move time to determine the execution time, lead time, and interoperation time of an operation.
You can schedule the material requirement from the earliest start date (you can change this in Customizing). You can display the capacity requirement for the earliest or latest start date depending on the Customizing settings.
For external operations, you can specify the delivery time in days and schedule these operations on the basis of the Gregorian calendar.
Time Components and Their Origins
Let's have a look at the different time elements which exist inside Work Center or Routing.