2.3. Operation Sequences and Dates of a Production Order

2.3.1. Domain-Specific Knowledge

2.3.1.1. Operation Sequences and Parallelization

The operations of a production order can be completed sequentially or parallelized.

In case of a sequential completion the subsequent operation to an operation is only started, after it was completely finished.

../_images/sequential.svg

2.3.1 Sequential operation sequence handling

It happens quite often, that an operation B can only be started after its predecessing operation A has been completed, because it might manufacture the components that are needed in the subsequent operation.

Operations that are independent of each other can also be completed parallelized, as long as there are enough capacities available.

../_images/parallel.svg

2.3.2 Parallelized operation sequence handling

2.3.1.2. Scheduling

The scheduling takes place during the planning of a new production order and is lodged in the ERP-System. Several factors play a role in the scheduling.

It has to be checked, if additional components have to be ordered from external sources and therefore if the delivery date as well as the release date have to be rescheduled or be considered, respectively.

The milestones of one’s own processing have to be determined, under consideration of the safety margin before production [1] and the safety margin after production [2]. These dates determine the maximum time frame for the production.

../_images/continuous-scheduling.svg

2.3.1.3. Lead Time Scheduling

The Lead Time Scheduling is the determination of start and end dates of the single operations of a production order. Based on the milestones it is either forward scheduled or backward scheduled, respectively.

The earliest start time (/EST) and the earliest end time (/EET) are forward scheduled, based on the order start date.

The latest start time (/LST) and the latest end time (/LET) are backward scheduled based , based on the order finish date.

The following example is used to explain how the continuous scheduling is determined forward or backwards, respectively.

An order with the number 4711 has three operations. The order start date is Sunday 22:00 o’clock and the order finish date is the following Tuesday at 12:00 o’clock.

Shift breaks are only on Monday from 12:00 o’clock until 14:00 o’clock and from 22:00 o’clock until 24:00 o’clock.

The operations are defined as follows:

Operation 4711 0010 4711 0020 4711 0030
Target Quantity 4 pc(s) 4 pc(s) 4 pc(s)
Target Time per Unit 1 h 2 h 2 h
Target Setup Time 2 h 4 h 2 h
Target Teardown Time 2 h    
Wait Time 2 h    
Queue Time      
Minimum Send Ahead Quantity   2 pc(s)  

Note

Because there is a minimum send-ahead quantity for operation 4711 0020, it must be kept in mind that a minimum lead time has to be met.

The minimum offset time is calculated as follows:

\[ \begin{align}\begin{aligned}Minimum\ Offset\ Time = Minimum\ Send\ Ahead\ Quantity\\\times\ Target\ Time\ per\ Unit\end{aligned}\end{align} \]

For the example this means the minimum offset time is calculated as follows:

\[Minimum\ Offset\ Time = 2 * 2\ h = 4\ h\]

Attention

Breaks or free shifts prolong only the execution times (setup, processing, teardown) and thus also the lead time, but not the transitional periods (queue time, wait time, move time).

Forward scheduling is based on the order start date and backward scheduling is based on the order finish date. This results in the earliest times for forward scheduling and the latest times for backward scheduling.

2.3.1.3.1. Results

Operation 1000 0010 1000 0020 1000 0030
Earliest start date Su, 22:00 Mo, 10:00 Mo, 18:00
Earliest end date Mo, 06:00 Tue, 02:00 Tue, 06:00
Latest start date Mo, 04:00 Mo, 16:00 Tue, 00:00
Latest end date Mo, 12:00 Tue, 08:00 Tue, 12:00
2.3.1.3.1.1. Forward Scheduling
../_images/forward-scheduling.svg

2.3.3 Forward Scheduling

Scheduled start date with forward scheduling So, 22:00 o’clock
Scheduled end date with forward scheduling Tue, 06:00 o’clock
2.3.1.3.1.2. Backward Scheduling
../_images/backward-scheduling.svg

2.3.4 Backward Scheduling

Scheduled start date with forward scheduling Mo, 04:00 o’clock
Scheduled end date with forward scheduling Tue, 12:00 o’clock

2.3.2. The Digital Image in FORCE Bridge API

GET productionOrders/{productionOrderId}

Request the details of an production order.

GET operations/{operationId}/scheduledDates

Request the scheduled dates of an operation.

GET productionOrders/{productionOrderId}/operationSequence

Request all operations of a production order and their predecessors and successors.

PUT productionOrders/{productionOrderId}/schedulingResult

Update production order scheduling result.

Hint

All time formats correspond to ISO 8601.

2.3.3. Tutorials

2.3.3.1. Get the Scheduled Dates of an Operation

Solution: show/hide

Java

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        GetOperationScheduledDatesRequest scheduledDatesRequest = new GetOperationScheduledDatesRequest(operationId);
        OperationScheduledDatesResponse operationScheduledDatesResponse = operationClient.getScheduledDates(scheduledDatesRequest);

/../_code/java/src/test/java/com/forcam/usage/operations/ScheduledDatesTest.java

Footnotes

[1]The float before production is a starting buffer for possible delays in staging and capacity bottlenecks to adjust the production dates of an order.
[2]The safety time is an end buffer to intercept unforeseen disturbances in the production process.