Production orders are always scheduled at order creation. As prerequisite, routings with operations and work centers must be maintained and scheduling parameters must be defined in Customizing.
Scheduling of Planned and Production Orders
In the context of production planning, the following scheduling methods are available:
- Determination of basic dates
- Lead time scheduling
The determination of basic dates is only available for planned orders. Alternatively, you can use lead time scheduling. For production orders, only lead time scheduling is available.
When using the determination of basic dates, the system calculates the start and end day of the order based on data maintained in the material master (in-house production time). However, no operation times are calculated.
When using lead time scheduling, the system calculates exact start/end dates and times (including seconds) on order level based on operation duration data maintained in the routing. Furthermore, the system also creates capacity requirements on operation level which you can use for capacity planning. Since lead time scheduling is based on the routing (which contains exact information about operation duration), this approach leads to reliable planning data.
From a business perspective, also using lead time scheduling for planned orders results in more reliable planning data. Furthermore, due to the fact that, when converting a planned order into a production order, the lead time scheduling is executed anyway, SAP recommends to also use lead time scheduling for planned orders to prevent the calculated dates changing significantly when converting the planned order into a production order.
Scheduling Time Elements of a Production Order
Depending on your business requirements, you can schedule orders either forwards or backwards in time: In forward scheduling, a production order is scheduled forwards in time starting from the basic start date (for example, manually entered or copied from the planned order); in backward scheduling, a production order is scheduled backwards in time starting from the basic finish date (for example, manually entered or copied from the planned order).
The above graphic shows all the possible elements contributing to the total lead time of a production order: The total lead time of a production order lies between the basic start date (BS) and the basic finish date (BF) and is represented by the upper green bar in the figure. The float before production lies between the basic start date (BS) and the scheduled start date of the first operation (SS), and the float after production lies between the scheduled finish date of the last operation (SF) and the basic finish date (BF). By specifying sufficient buffer times, you obtain better production stability as you can react to any unforeseen events that may occur in the production process. However, if your buffer times are too high, your production resource utilization might decrease. If necessary, for example in case of delays of other orders or a machine breakdown, the buffer times can be automatically reduced by the system.
In the Customizing activity Define Scheduling Margin Keys, you define the floats for order scheduling. Afterward, you assign the key to the material master of the manufactured product.
The degree of reduction is maintained in reduction strategies in Customizing.
The operations are scheduled in the order of their operation numbers. In the case of forward scheduling, the system starts from the lowest operation in ascending order. In the case of backward scheduling, the system starts from the highest operation in descending order. Each operation has the time elements queue time, setup time, processing time, teardown time, wait time, and move time. The sum of all time elements (except move time) defines the lead time of an operation. The queue time and the move time serve as time buffers for the operations. Similar to order buffer times, they can also be reduced if necessary.
As you can see in the figure, the queue time lies between the earliest start (ES) and the latest start (LS) of an operation. The wait time lies between the earliest finish (EF) and the latest finish (LF) of an operation. Let us consider two extreme scenarios: In the first scenario, the queue time is completely consumed. In this case, the worker begins setting up the work center at the latest possible point in time. In the second scenario, the queue time is not consumed at all. In this case, the worker begins setting up the work center at the earliest point in time. Henceforth, each operation has an earliest and a latest start and end date. If the order is executed as planned, the actual operation start date will lie somewhere within this time horizon.
Wait time is usually used to define the time the next operation must wait until it can be started, for example, if paint needs to dry before the next operator can touch the manufactured material. Move time is used to define the time required to move the manufactured material from one work center to the next one. Although the move time is a time element shared by two subsequent operations, it is always attributed to the first operation. Starting from the latest finish (LF), the system adds wait and move time, respectively, to calculate the earliest start (ES) date of the next operation. The latest finish (LF) date of the last operation in the order corresponds to the scheduled finish (SF) date of the order.
After the manufactured good is produced, it must be moved from production to the warehouse. This time is usually represented using the goods receipt processing time.
If a production order is created with reference to a sales order, the basic finish date of the production order is determined in backward scheduling on the basis of the scheduling of the sales order. The time segments of sales order scheduling (for example, pick/pack, load, and transit time) are also shown in the figure.
Please refer to the video below for a simple scheduling example in the system.
For more information regarding the scheduling of individual orders, please also refer to the SAP Application Documentation.
Calculation of Setup, Processing, and Teardown Times
As discussed in the previous section, the system schedules each operation of the order (provided that the respective control key is set up accordingly). However, we have not discussed yet how the system calculates the duration of each operation. As shown in the figure, the durations of the setup time, the processing time and the teardown time of an operation are calculated based on formulas which are assigned in the work center. The total duration of an operation is the sum of setup time, processing time, and teardown time.
Let us consider the following example: For a production operation, a setup time of 60 minutes is required. For each manufactured item, the worker needs 15 minutes. After finishing the operation, the work center must be cleaned for 30 minutes. This information is maintained as standard values in the operation. These standard values are used together with the work center formulas and the operation quantity to calculate the total operation duration. In our example, the formulas are defined as follows:
- Setup formula: The setup duration is only required once per manufacturing operation.
- Processing formula: The processing duration scales linearly with the number of manufactured items (operation quantity).
- Teardown formula: The teardown duration is only required once per manufacturing operation.
In our example, we manufacture 10 bikes (operation quantity). Using the formulas and the operation standard values, we obtain the following durations:
- Setup duration: 60 min
- Processing duration: 150 min (10 bikes x 15 min per bike)
- Teardown duration: 30 min
In total, the operation duration is 240 min. When using, for example, forward scheduling, the system adds this duration to the specified operation start time to calculate the operation end date.
In addition to operation durations, the system also calculates capacity requirements for each operation (provided that the respective control key is set up accordingly). The calculation of capacity requirements follows a similar approach as the calculation of duration.
For more information about the calculation of capacity requirements of operations, please refer to the SAP Application Documentation.
In this demonstration, you will see the following process steps:
- Create a production order.
- Analyze the scheduling of the order.