How Work Orders are Scheduled

Oracle Manufacturing uses unconstrained scheduling engine in the background to schedule work orders during create and certain update actions. In addition, the scheduling engine is also used to compute the manufacturing lead time of a product based on its primary work definition.

The scheduling engine uses the information provided at the resource definition, work order operation resource level and the resource's calendar to determine the resource's start date and completion date for in-house operations. While scheduling work orders, resources are assumed to have infinite capacity and the scheduling engine disregards loads on the resources from other work orders. It rolls up the resource dates to determine the start and completion dates of each in-house operation. For supplier operations, the scheduling engine uses the lead time information specified at the operation level to calculate the start and completion date of the operation. Eventually the operation dates are rolled up to determine the work order dates. The required date of the operation items are updated to the start date of its operation. The following types of scheduling methods are supported by the scheduling engine:

Forward Scheduling
Backward Scheduling
Midpoint Scheduling

Forward Scheduling: When a work order is forward scheduled, the scheduling engine uses the start date of the work order as an input to determine the start and completion dates for each scheduled resource (for in-house operations), the start and completion dates for each operation and eventually the completion date of the work order. The application automatically performs forward scheduling when the start date of a work order is provided. Forward scheduling is also used by the lead time calculation program to determine the manufacturing lead time of the product.

Backward Scheduling: When a work order is backward scheduled, the scheduling engine uses the completion date of the work order as an input to determine the start and completion dates for each scheduled resource (for in-house operations), the start and completion dates for each operation and eventually the start date of the work order. The application automatically performs backward scheduling when the completion date of a work order is provided.

Midpoint Scheduling: When a work order is midpoint scheduled, the user selects an operation to perform midpoint scheduling by specifying either the operation start date or the operation completion date. If Midpoint scheduling is performed from the operation start date, all the prior operations are backward scheduled while the selected operation and succeeding operations are forward scheduled. If Midpoint scheduling is performed from the operation completion date, all resources of the prior operations and the selected operation are backward scheduled while the succeeding operations are forward scheduled.

The following actions trigger scheduling or rescheduling of work orders:

Create Work Orders: When work definition is specified, application automatically performs either forward or backward scheduling depending on whether start date or completion date is provided.
Update Work Order - Start Date or Completion Date: Updating one of these date nulls out the other and application automatically performs either forward or backward scheduling.
Update Work Order - Work Definition name or Work Definition Date or Work Order Quantity: Updating any of these fields on the work order triggers the application to prompt forward scheduling or backward scheduling method to reschedule the work order.

The following attributes influence the scheduling behavior:

Quantity: The work order quantity influences the scheduled duration of a work order.

For discrete manufacturing, the work order quantity is considered for calculation of the work order operation resource dates when the resource's Basis Type is Variable.

For process manufacturing, the work order batch quantity is considered for calculation of the work order operation resource dates by scaling the work order operation resource usage from its work definition batch when its Basis Type is Variable.

For manufacturing lead time calculation of an item using discrete manufacturing work method, the lot size specified in the item definition is considered.

For manufacturing lead time calculation of an item using process manufacturing work method, the output quantity of the standard batch defined in the primary work definition is considered.
Work Order Start Date or Completion Date: Serves as the anchor point to perform forward or backward scheduling.
Work Order Operation / Execution Sequence: Scheduling engine considers the operation sequence to schedule the operations and it’s resources. However, in the case of released work orders with resequenceable operations, the execution sequence will be considered instead of the operation sequence.
Work Order Operation Start Date or Completion Date: Serves as the anchor point to perform midpoint scheduling.
Work Order Operation Resources Sequence Number: Resources which have unique sequence numbers within an operation are scheduled sequentially in the ascending order. Resources which share a common sequence number within an operation are considered as simultaneous resources and are scheduled in parallel.
Work Order Operation Resources Name: Used by the scheduling engine to determine the work center resource calendar to schedule the resources.
Work Order Operation Resources - Required Usage: Used by the scheduling engine to schedule the resource duration.
Work Order Operation Resources - UOM: Used by the scheduling engine to schedule the resource duration. The resource usage is converted from the specified unit of measure to the scheduling unit of measure using the profile Hour Unit of Measure (ORA_RCS_HOUR_UOM). The UOM set in this profile must belong to the UOM class specified in the other profile SCM Common: Default Service Duration Class (RCS_DEFAULT_UOM_CLASS_CODE_FOR_SVC_DURATION). For any scheduled resource, it's recommended that this profile be set to a UOM class that represents units of measure for Time.
Work Order Operation Resources - Scheduled Indicator: Resources which have Scheduled = Yes are considered by the scheduling engine to compute the duration of the resource. The resources which have Scheduled = No aren't scheduled and assumed to have the zero duration, such that the resource's planned start date = planned completion date. For the resources that have Scheduled = No or defined with zero duration, work order scheduling doesn’t consider the calendar work times.
Work Order Operation Resources - Assigned Units: The required usage of the resource is divided by the assigned units to compute the scheduled duration of the resource.
Work Center Resources - Available 24 Hours Indicator: Resources which have this indicator set to No are scheduled within the shifts associated with it. Resources which have this indicator set to Yes, are assumed to be available 24 hours.
Work Center Resources - Efficiency and Utilization Percentages: The scheduling engine inflates the required usage of a resource if its efficiency and, or utilization percentages are less than 100%.
Work Center Resources - Shift Assignments: Scheduling engine considers the availability of resources based on the shifts assigned to the work center resource. In the case of work centers with override calendars, the scheduling is based on the availability of resources of the override calendar that's effective for the scheduling date.
Work Center Resource Availability: Scheduling engine considers the shift exceptions and work center resource exceptions to determine the availability of resources within shifts assigned to it.
Work Center Override Calendars: In the case of work centers with override calendars, the scheduling is based on the availability of resources of the override calendar that's effective for the scheduling date.
Supplier Operation Lead Time Attributes: For supplier operations the scheduling engine uses the Fixed Lead Time, Variable Lead Time, and Lead Time UOM information provided at the operation level to calculate the start and completion dates of the operation. In the case of work centers with override calendars, the scheduling of supplier operations is based on plant calendar only.
Maximum Scheduling Duration in Months: Scheduling engine considers this plant parameter setting to determine the maximum allowed scheduling duration for a work order when its created or updated.
Plant Time zone: The plant time zone represents the time zone where the plant is geographically located and its identified by the setting in Manage Organization Parameters using the FSM task Manage Inventory Organizations. The shifts and its timings defined for the calendar associated to the manufacturing plant is interpreted in this plant time zone. Scheduling of work orders are carried out in this time zone.
User Time zone: Though this time zone doesn't influence the scheduling logic, it influences the value displayed in the date time fields on the work order. This plant parameter should be set to the time zone of the user accessing the Manufacturing application by navigating to Set Preferences and then Regional.

The following scenarios list some of the errors when scheduling a work order:

Work center resources without shift assignments: When a work center resource isn't a 24 hour resource and isn't assigned to any of the shifts of the production calendar, then the scheduling engine can't derive the availability of this resource and hence will error out. The most likely cause for such as situation is when you associate a new calendar to the plant in Manage Plant Parameters task and forget to reassign the existing work center resources to the new shifts.

Plant calendar effective dates aren't enough: If the work order quantity is such that the sum of resource duration of all operations are computed to be larger than the calendar effective dates, then scheduling will error out. For example, when a user manually creates a work order by specifying a start date and a large work order quantity, the calendar's effective end date should be greater than the work order completion date calculated based on the work order's resource duration. Likewise, when Supply Planning creates a work order by specifying the completion date, the calendar effective start date must be lesser than the work order start date calculated based on the work order's resource duration.

Plant parameter of maximum scheduling duration is violated: Scheduling will error out if the computed duration of the work order is greater than the parameter value set for the Maximum Scheduling Duration in months in Manage Plant Parameter.

Schedule Work Orders Manually

Now, you can manually schedule or reschedule manufacturing work orders based on the scheduling method that you select on the user interface.

You can create work orders manually or through supply chain planning, or maintenance programs using the scheduling method value as default scheduling. The work orders are always scheduled automatically with no gap or overlap using the user interface. However, you can now schedule work orders manually to enable gap or overlap between operations or resource when you select the scheduling method value as user or external scheduling.

You can perform the following when you schedule the work orders manually:

Select the work order scheduling method
Schedule work orders manually
- Manual update of work order attributes
- Manual update of work order start and completion dates
- Manual update of work order operation start and completion dates
- Manual update of work order resource start and completion dates

Select the work order scheduling method

The scheduling method is displayed at the work order header for work orders. You can select one of the following two values:

Default Scheduling

This scheduling method is the default option when a work order is created through the user interface.
User or External Scheduling

When you select this scheduling method, you can schedule or reschedule the work order manually by updating the work order dates, operation dates, and resources dates. Also, the firm check box is automatically selected, and you can optionally deselect the firm flag.

Schedule work orders manually

Manual update of work order attributes
If you update the work order quantity, then the work order isn't rescheduled. However, the material and resource requirements are recalculated.
If you update the work definition name or date, then the scheduling method is automatically updated as default scheduling and the work order is automatically scheduled. The work order is re-exploded with the details of the new work definition.
Manual update of work order start and completion dates
You can use this scheduling method only in the user interface. However, the FBDI and REST services continue to work with the default scheduling method.

Manual update of work order operation start and completion dates
You can manually update the start and completion dates of the work order operations. The unconstrained scheduling won't be invoked if your scheduling method is User or External Scheduling. However, the work order start and completion dates gets synchronized with the earliest operation start date and the latest completion date, if they are outside the work order start and completion date.

Manual update of work order resource start and completion dates
You can manually update the start and completion dates of the work order resources. The unconstrained scheduling won't be invoked if your scheduling method is User or External Scheduling. However, the work order operation start and completion dates and the work order start and completion dates gets synchronized with the earliest resource start date and the latest resource completion date, if they are outside the work order or operation dates.

During work order execution, if you resequence the operation, then the work order wouldn’t be automatically scheduled if the scheduling method is User or External Scheduling.

Oracle Fusion Cloud Supply Planning, including Production Scheduling will consider manually scheduled work orders during scheduling. If Oracle Supply Planning, including Production Scheduling update the work order dates, Oracle Fusion Cloud Manufacturing will honor the recommendations.