Operation Overlap

General Information

The constraint based scheduling (CBS) flow is enhanced with the additional feature, operation overlap. The purpose of this feature is to allow users to define and let operation overlap take effect in their production schedule. In the existing flow, if the operations are defined as Not Parallel, you cannot start the second operation till the preceding operation reaches its end time. The operation overlap feature allows you to schedule the operations that are not parallel to start earlier than the preceding operation's scheduled end time.

The meaning of the term Operation Overlap is how early a succeeding operation is allowed to start in relation to its latest preceding operation or operations start time. You can define the operation overlap time on a succeeding operation on the routing and/or shop order operation line. The overlap time will be possible to define as either a percentage of the preceding operations scheduled manufacturing lead time or as a number of units (i.e., the time it takes the preceding operation to produce an X number of units). If an overlap time is defined on the first operation in an operation structure (i.e., no defined preceding operation), the defined overlap time will not have any effect.

Operation Overlap Process

The overlap time can be specified in the CBS Overlap field on the Routing Template/Routing Template Operation tab. The Overlap Unit list can be used to define the time either as a percentage or as a number of units.
Example: Assume A and B are two non parallel operations. The overlap time for B is 10 and the overlap unit is percentage. (A is the first operation). B will start after ten percent of A's manufacturing lead time is over. If the overlap unit is units, then B will start only after A has produced ten of units.
When routing operations are created based on a routing template operation, the overlap information will be automatically transferred to the new operation.
The CBS Overlap and CBS Overlap Unit fields can also be found in the Routing /Routings, Shop Order/Operation, Interim Order/Operation windows. When an order operation is created based on a routing revision, the overlap information will be automatically transferred to the order operation line. However, you can modify the transferred information. The same information will be transferred to the CBS server when the order operation is created and the defined overlap information will take effect. 

 Different scheduling scenarios are described below:

• In this scheduling scenario, we have two operations defined in the routing/shop order as Not Parallel. 

• In this scheduling scenario, we have three operations. Operation 10 is Not Parallel and 20 and 30 are defined as Parallel. 

• In this scenario, we have four scheduled operations. Operation 10 and 40 are not parallel,  and 20 and 30 are defined as Parallel.

Operation Run Rate

It will not be possible to finish the succeeding operation before the preceding operations scheduled end time + transportation time +  time it takes the succeeding operation to manufacture the last delivered overlap quantity from its preceding operation. 

This method is used in order to prevent succeeding operations with faster run rates, ending at the same time or earlier than the preceding operation.

Buffered Operation Reporting

Where operation overlap exists and some quantity is reported on an operation, the schedule is updated to show the remaining quantity for that operation. This happens only if Buffer Operation Reporting is enabled in Scheduling Basic Bata/Shop Order Scheduling/Buffered Operation Reporting tab and the Adjust Schedule Due To Shop Floor Reporting check box is selected in the Scheduling Basic Bata/Shop Order Scheduling/Scheduling Servertab. When an operation is reported out of sequence, its preceding operation will also be updated in the schedule, assuming that the overlap quantity has been completed.
 

Example 1: After reporting 30% of OP 10, it will be rescheduled with a new start time. OP 20 can still overlap after 50% of OP 10 is scheduled to finish.

Example 2: OP 10 has not been reported yet but 30% has been reported on OP 20. A new overlap percentage will be calculated as Previous Overlap - Reported Quantity (assuming that the same quantity has been reported on OP 10 as well).

Therefore the new overlap will be 20% and the remaining operation time for OP 20 will be reduced by 30% because of the reported quantity. OP 20 will not be scheduled to start directly after the new calculated overlap because then it will be completed before OP 10, whereas it is not allowed to be completed before the finish time of OP 10 plus the time it takes to manufacture the last delivered quantity from OP 10 to OP 20. See Operation Run Rate above.