Predecessor-Successor Processing of Operations and Manufacturing Orders

Max Delay, Operation Successor Processing, and Overlapping Operations and MOs

Key Concepts

A Successor Operation is an operation in a single manufacturing order that requires material from a predecessor operation. This relationship is defined in the Alternate Path of the manufacturing order. A successor operation cannot start until the predecessor operation is complete or partially complete if overlapping operations are used. 

Similar to the concept of successor operations, a Successor Manufacturing Order is a manufacturing order from the same or different job that requires materials from a given manufacturing order. The successor manufacturing order cannot schedule to start before the material will be available for the predecessor manufacturing order.

Many options allow manufacturers to define how predecessor and successor operations and manufacturing orders interact with each other. These include Max Delay, Operation Successor Processing, and Operation Overlap. 

Max Delay

Setting the Max Delay will enforce a specific amount of time that can pass before the Successor Operation must be run. For this feature to work, however, all of the following must be true:

  • In Settings | System Options | Scheduling, the "Max Delay" option must be enabled.
  • The predecessor and successor operations are limited to a single activity.
  • The predecessor operation is limited to a single successor.
  • The successor operation is limited to a single predecessor.
  • All activities scheduled on the resource where the successor operations are scheduled must have a max delay relationship with a predecessor operation.
  • The use of helper or secondary resources is not compatible with Max Delay.

Operation Successor Processing

Another way is to go into the "Advanced" tab of the operation and set the Successor Processing to the desired effect.

  • Successor Processing: Allows control over whether the successor operation must be scheduled on the same resource as its predecessor operation. The use of this feature requires that the routing be linear within the predecessor and successor operation.
    • Keep Successor: This means that the successor operation will try to be scheduled on the same resource as the predecessor operation.
    • Keep Successors; No Interrupt: This means that not only will the successor operation try to end up on the same resource, but it will also try to end up as the very next operation scheduled on the resource. 

Note: Successor Processing and Default Resources Compatibility

By default, the scheduler will attempt to keep successor operations on the same resource as the predecessor operation if possible; keep successor is always attempted.

However, if a Default Resource is specified for the successor operation, the scheduler will never attempt to keep successor operations on the same resource.

  • Time Limit: This functions similarly to the max delay, and using either one will determine whether or not predecessor and successor relationships must run on the same resource. If so, then the operation successor processing should be used. If not, then max delay should be used. 

For Successor Processing to work, however, the following must be true:

  • Predecessor and Successor Operations are limited to a single activity.
  • The resource that the predecessor is scheduled to must also be able to perform work for the successor.
  • The resource requirements, including capabilities and number of helper resources, must match exactly between the predecessor and successor.

Overlapping Operations

If an operation does not have to wait for its predecessor to finish before starting, the operations can be set to allow "Overlapping." This will cause both operations to finish more quickly since they are completed in parallel. The Overlap Options are defined under the Alternate Path tab of the Job dialog. Note: You must specify the Overlap Type for each Path Node.

  • No Overlap: The entire predecessor operation must be completed before the successor operation can begin.
  • Transfer Qty: The successor operation can begin once the first operation has produced a specified quantity (specified in the OverlapTransferQty field of the operation mappings).
  • Transfer Span: Successor operations can begin after the predecessor operation has been running for a specified time (specified in the OverlapTransferHrs field in the Alternate Path Node mappings).
  • At First Transfer: The successor can start once a specified number of items is produced and transferred to inventory (specified in the TransferQty field of the Item mappings).
  • Transfer Span After Setup: The successor can begin after the OverlapTransferHrs plus any Setup time.
  • Percent Complete: The successor can begin after the predecessor operation has been completed to a percent (specified in the OverlapPercentComplete field in the Alternate Path Node mappings). 

Overlapping Manufacturing Orders

Overlapping manufacturing orders are similar to overlapping operations because they allow successor processes to begin before the predecessor has completed its run. However, the overlap is dictated almost entirely by the material availability and when the products and materials are considered available. Therefore, the overlapping manufacturing orders must have a successor and predecessor relationship defined. 

The product being produced by the predecessor manufacturing order's specific operation sets when that product is considered available for successor manufacturing order's operations to use as a material. To set this relationship, use the "Inventory Available Timing" field of the Product tab of the Job dialog:

  • At Operation Run Start: This option sets PlanetTogether to assume that the total Output Quantity of the operation's product is available at the very beginning of that operation's run time. Using this option will allow the successor manufacturing order to complete overlapping at the beginning of this operation.
  • At Operation Material Post-Processing End: The operation's Run and Material Post-Processing times must all elapse before the product is considered available in inventory.
  • Based on Item Transfer Quantity: Similar to the Transfer Quantity in overlapping operations, this option specifies a Transfer Quantity that, once reached, will set the product to be available in inventory. 

Related Articles

Max Delay

Alternate Paths

Job Dialog