1. Product Data Management Implementation Guide
  2. Operation Start Dates

Operation Start Dates

The system calculates the operation start dates with the average number of hours per operation.

For a fixed lead time, the system calculates the operation hours using:

  • Level lead time.

  • Hours per work day.

  • Number of employees per operation.

  • Number of operations.

You must schedule the hours per operation according to the resource units within the entire level lead time to ensure that the start date of the first operation equals the start date of the work order. When the job moves to a different work center in the same day, the system decreases the resource units available by the percentage of the work day remaining. The system does not use resource units on the due date of the work order. Instead, it assumes that the order was completed at the end of the previous day.

For each operation, the system then schedules this average time into the appropriate work center, based on the available hours from the Work Center Resource Units table (F3007). The system schedules the last operation due date on the day before the work order due date.

The system uses this formula to calculate average time per operation:

Level lead time × work hours per day × employees or machine number of operation sequences (blank operation sequence codes only) = average time per operation.

The work hours per day are retrieved from the Manufacturing Constants table (F3009).

The calculation uses these values:

  • Work order due date: May 1

  • Average time per operation: 25 hours

  • Operations in the routing instructions:

    • OP40 WC 200-204 due April 30 start April 27

    • OP30 WC 200-101 due April 27 start April 24

    • OP20 WC 200-204 due April 24 start April 21

    • OP10 WC 200-101 due April 21 start April 17

    • WC Resource Units 200-204: 8

    • WC Resource Units 200-101: 8

To determine variable lead times, the system schedules the actual hours from the work order routing instructions according to the same resource unit rules used for fixed lead time.

The system uses the prime load code to determine the hours to use. The hours are then applied to the Work Center Resource Units table, similar to fixed lead time. The system applies the queue time from the work order routing instructions at the beginning of an operation and the move time at the end of an operation.