Infor LX & BPCS Manufacturing Tip of the Week: Backward Scheduling

Operations are automatically backward scheduled at shop order release time. The backward scheduling algorithm starts with the shop order due date and schedules each operation based upon the standard move and queue times in the routings and the number of days the job is expected to run at standard. The system calculates and stores the operation scheduled start date. The dates may be modified by the shop order maintenance program. The number of days that a job is expected to run an operation is dependent upon the available capacity for that work center and the total hours scheduled for that operation.

The backward scheduling algorithm also considers the shop calendar for weekends, shutdowns, holidays, and partial days.

Backward Scheduling Process

The algorithm starts with the due date of the shop order or planned order. The system makes the following calculations for each operation in the reverse sequence:

1. The number of move days is subtracted from the due date (or initial date of the previous operation) to get the due date for this operation. The move days are only used on valid shop calendar days.
2. The system uses the following calculation for the number of clock hours for the operation: Standard run or machine hrs/No. of operators + setup hours
3. The number of clock hours is spread over the available daily capacity of the work center for those given days. The system uses the following calculation for the daily capacity of the work center: Number of shifts x hours per shift x average efficiency/100
4. Each day is checked against the shop calendar; the calculation bypasses inactive days or adjusts for any changes in the work center capacity for that day.
5. Queue time days are subtracted in the same manner as move time days. The resulting date is the operation start date.

The algorithm then goes to the previous operation. When all operations have been included, the resulting date is the scheduled start date of the shop order. Note that MRP uses the item lead time to determine material requirement dates on planned orders.

George MorosesGeorge Moroses

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