Production orders are always scheduled when the order is created. As a prerequisite, routings with operations and work centers must be maintained, and for the order types, scheduling parameters must be defined in SAP Central Business Configuration at plant level.
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 previous 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 can occur in the production process. However, if your buffer times are too high, your production resource utilization can 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.
Float before production and the float after production are defined in the configuration activity, Define Floats (Scheduling Margin Key), which we explain later in this lesson.
The strategies for automatically reducing the floats are defined in the configuration activity, Define Scheduling Parameters for Production Orders, which we explain in this lesson.
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.
The queue time, wait time, and move time are defined in the routing. The setup time, processing time, and teardown time are calculated when the order is created based on the operation standard values and formulas of the assigned work centers. The configuration activities for defining the standard values and the formulas are explained in the unit, Applying Product-Specific Configuration for Master Data.
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 lies 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 must 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 based on 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.
Refer to the course code S4C40, which is a prerequisite for this course, if you want to learn more about production order scheduling.