Proportional Distribution of Buffer

Use

The total buffer of an order is the difference between the order end date and the latest end date of the last operation in the order in accordance with forward scheduling. This also includes transport and wait time (TWT), if active. In an open-loop scenario, the buffer may differ over time, meaning that no work center is guaranteed the initial buffer that it was granted the first time an order is scheduled. In an order with several work centers, if the first work center(s) in the MRO chain postpones the start of the order, later work centers may experience buffer shortages if the ROC date keeps declining. The worst case would be that the order is not completed on time. To avoid such situations, the CMC uses a formula built on arithmetic progression to distribute buffer among all work centers involved in processing the order. The CMC provides a formula for proportional and progressive distribution .

Proportional distribution distributes the available buffer among all work centers involved in an order in proportion to the duration of the operation(s) in each work center. This means that operations that have a long duration get a larger share of the buffer than operations with short duration.

Prerequisites

In Customizing of CMC order codes , you have set the stretch factor to zero or you have left the field blank.

Example

To distribute the available buffer proportionally, the CMC performs the following calculations:

  1. determines the ROC for the material number:

    Material 4711-A has a ROC of 8 days

  2. adds the ROC to the current date to calculate the latest end date of the order:

    August 1 st plus 8 days = August 9th

  3. reads the standard duration of each operation in the order:

    Operation 1 = 10 hours

    Operation 2 = 8 hours

    Operation 3 = 16 hours

  4. calculates the total duration for the whole order:

    10 + 8 + 16 = 34 hours

  5. compares the total duration with the latest end date to get the total buffer:

    Total duration = 34 hours

    Current date to latest end date = 64 working hours (dependent on factory calendar, capacity, TWT, and so on)

    Total buffer: 64 - 34 = 30 hours

Depending on whether you select a compressed or non-compressed view of the operations the system does the following:

Note Note

The compressed view of the CMC is where the CMC bundles sequential operations from the same work center and displays them in one line. In the non-compressed view the CMC displays each operation in a separate line.

End of the note.
Non-Compressed View

The CMC considers each operation individually, and determines the following:

  • position of each operation in the order

  • duration of each operation in the order

  • the stretch factor equals zero or blank

  • the total number of operations in the order

Using this information, the CMC does the following

  1. It takes the standard duration of each operation and adds this to the sum of the operation position minus 1 multiplied by the stretch factor:

    Operation 1: 10 + ((1-1) x 0) = 10 hours

    Operation 2: 8 + ((2-1) x 0) = 8 hours

    Operation 3: 16 + ((3-1) x 0) = 16 hours

  2. It takes the total number of operations in the order and multiplies this by the number of operations minus 1:

    3 x (3-1) = 6 hours

  3. It multiplies this by the stretch factor defined in Customizing for Order Codes and Priority Rules:

    6 x 0 = 0 hours

  4. It divides the result of step 3 by 2:

    0 / 2 = 0 hours.

  5. It adds 34 (total standard duration of all work centers):

    34 + 0 = 34 hours

  6. It determines the available buffer for each operation by multiplying the results from step 1 by the total available buffer divided by the result from step 5:

    Operation 1: 10 x 30 / 34 = 8.8 hours

    Operation 2: 8 x 30 / 34 = 7.1 hours

    Operation 3: 16 x 30 / 34 = 14.1 hours

  7. cumulates the standard duration and the buffer above for each operation to determine the latest date of each operation

Compressed View

The CMC considers each work center individually, and determines the following:

  • position of each work center in the order

  • duration of total consecutive operations in the work center

  • the stretch factor equals zero or blank

  • the total number of work centers in the order

Using this information the CMC does the following:

  1. It takes the standard duration of the consecutive operations in the work center and adds this to the sum of the work center position minus 1, multiplied by the stretch factor:

    Work center A: 18 + ((1 - 1) x 0) = 18 hours

    Work center B: 16 + ((2 - 1) x 0) = 16 hours

  2. It takes the total number of work centers in the order and multiplies this by the number of work centers minus 1:

    2 x (2-1) = 2 hours

  3. It multiplies this by the stretch factor defined in Customizing for Order Codes and Priority Rules:

    2 x 0 = 0 hours

  4. It divides the result of step 3 by 2:

    0 / 2 = 0 hours.

  5. It adds 34:

    34 + 0 = 34 hours

  6. It determines the available buffer for each work center by multiplying the results from step 1 by the total available buffer, and divides this by the result from step 5:

    Work center A: 18 x 30 / 34 = 15.9 hours

    Work center B: 16 x 30 / 34= 14.1 hours

  7. The latest end date of each work center is the sum of the standard duration of the consecutive operations in that work center plus the calculated available buffer for that operation:

    Work center A: 18 + 15.9 = 33.9 hours

    Work center B: 16 + 14.1 = 30.1 hours