Advanced Planning and Scheduling: Scheduling Details

In this topic, you will read about scheduling details in advanced planning and scheduling (APS).

Scheduling Method

In conjunction with the constraint date, this determines the sequence by which the operations of the production order are scheduled. You can select any of the following scheduling methods in the Scheduling Method box on the General tab of the Production Order Maintenance (AM201500) form:

• Finish On: The operations are scheduled backwards from the constraint date. Production orders created from a sales order, or orders created as linked orders from a parent order, has this value selected by default. For sales orders, the constraint date is one day earlier than the scheduled ship date.
• Start On: The operations are scheduled forward from the constraint date.
• User Dates: This value provides you with the ability to define the start and end dates of the production order. This is a way for the user to override the manufacturing lead times or to use any calendar dates including non-working days.

Constraint Date

This is a particular date by which the production order is needed or needs to be started. It is only entered when the scheduling method is either Finish On or Start On.

You specify the constraint date on the General tab of the Production Order Maintenance (AM201500) form.

Dispatch Priority

Dispatch priority is used in APS to load the production orders and operations in priority sequence. Orders with the same priority are loaded by the constraint date. Orders with the highest priority are scheduled first. One (1) is the highest priority and ten (10) is the lowest.

You specify the dispatch priority on the General tab of the Production Order Maintenance (AM201500) form.

Infinite Capacity Planning

Production order operations starting and ending dates are calculated solely on the basis of operation duration. In APS, the system uses infinite capacity planning for production orders whose end date is beyond 120 days from the date when the planning is initiated.

Also, the system uses infinite planning when creating planning orders during material requirements planning. For more details about calculating operation and production order dates, see MRP Configuration: System Settings.

Finite Capacity Planning

Production orders can be scheduled and rescheduled respecting the capacity and current load of work centers, machine, and tools and the availability of materials. If the scheduling method is Finish On, the operations are scheduled backwards until the calculated operation start date is in the past. From that point the sequence is reversed and the operations are forward-scheduled.

Operations are always scheduled in contiguous blocks skipping over non-working hours and schedule breaks. See the following example:

• A work center has capacity available today starting at 11 a.m. with a noon to 1 p.m. lunch break and a shift ending at 5 p.m.; so 5 hours remaining capacity and 8 hours available tomorrow.
• The schedule blocks are 1 hour.
• An operation has a duration of 9 hours.

The following table shows the schedule blocks consumed by the operation.

Finite scheduling may result in the following issues:

• Gaps may appear between operations when a resource is not available on the desired time slot. For example, an operation requires 8 hours of a resource and a contiguous block of time is not available for the next operation. This may not be the desirable when the next operation must be started immediately after completion of the previous operation.
• The calculated finish date of the production order may be after the required date for a sales order or linked production order.
• If all material is not available for the order, either in stock or allocated from a supply order, the order will not be scheduled.
• If machine scheduling is used, the machine may not be available although the work center is available.
• If tool scheduling is used, the tools required may not be available although the work center is available and the machine is available.

For more information about the calculation of the duration of operations, see Advanced Planning and Scheduling: Operation Lead Time.

Firm Scheduling of Production Orders

You can prevent a production order from being rescheduled if strict production dates are important for the production order (for example, because of the commitment with the customer). You can firm the order—that is, fix the production dates. When you run finite scheduling of production orders, the system does not reschedule the firmed production orders.

To firm any number of production orders, on the Rough Cut Planning (AM501000) form, you do the following:

1. Select the check box in the unlabeled column of each row that contains a production order to be firmed.
2. In the Action box of the Selection area, select Firm.
3. Click Process on the form toolbar. The system firms the dates of the processed production orders and changes the schedule status of the orders to Firm.

To undo firm for a production order, you perform the same steps but select the Undo Firm action.

Firm production orders are hidden from the Rough Cut Planning form by default—that is, the Exclude Firm Orders check box in the Selection area is selected—but you can display these orders by clearing the check box.

You can also firm production orders by using the Production Schedule Board (AM215555) form.