Use Backward scheduling if you know the due date for a work order, and need to determine when the work order should be released to the shop, in order for the job to be completed on time. This method is most appropriate if you have a deadline for the completion of a work order and must adjust your schedule to complete the job on time.
You can select the Backward scheduling method by selecting Backward in the Scheduling Method field on the Work Order Entry Scheduling tab. You are prompted to enter the due date for when the work order must be completed. The release date for the work order is then calculated automatically.
After a work order is scheduled, you can reschedule all or a part of the work order by entering the first step affected on the Work Order Entry Scheduling tab. The First Step Affected field allows you to enter the step to which to reschedule the work order. If the step entered is the first step of the work order, the release date calculated is the planned release date of the entire work order. If the step entered is not the first step, individual steps are rescheduled from the last step back to the specified step.
If a new operation step is entered or modified for an existing work order, the first step affected must be equal to or less than the lowest numbered new or modified step.
Example 1
A work order consists of two steps; the first step requires 10 hours at work center A, and the second step requires 18 hours at work center B. Work center A has a capacity of 8 hours per day, and work center B has a capacity of 16 hours per day. For simplicity, assume that work center A operates 8 hours per day, and work center B operates 16 hours per day. If the due date for the work order is 5/14/03, the steps are scheduled as follows.
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5/14/03
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16 hours
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5/13/03
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8 hours
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2 hours
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5/12/03
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2 hours
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This schedule shows that the work order release date is 5/12/03; therefore, the scheduled start date for the first step is also 5/12/03, and the start date for the second step is 5/13/03. Note that 8 hours were scheduled for the first step on 5/13/03 even though 2 hours were scheduled for the second step. This is because work center B's 16-hour shift allows the 2 hours to be processed without taking any time away from work center A's 8-hour shift.
Example 2
In this example, Example 1 is expanded by including an overlap percentage of 40 percent for the second step. Because the completion date for the second step is 5/14/03, the start date for the first step must be determined by backward scheduling the time required for the first step, multiplied by the inverse of the overlap percentage or by 60 percent. Because 60 percent of 10 hours is 6 hours, 6 hours must be backward scheduled from the start of the second step. When the start date is determined for the first step, the Forward scheduling method is used to schedule the full 10 hours.
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5/14/03
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4 hours
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16 hours
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5/13/03
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6 hours
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2 hours
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The start date of 5/13/03 is determined by backward scheduling 6 hours from 5/13/03.
For more information, see:
Scheduling
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