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A yield percentage is the expression of a yield standard which is declared for an operation when performed on a particular machine. This is also called standard yield. When creating a new operation on the routing for a work order, the yield percentages always default to 100% for that operation. The yield percentage is always a step yield: that is, it declares a standard percentage of the output quantity to the input quantity. For example, an operation with a step yield of 98.5% will output 985 good parts for every 1000 parts it receives. The cumulative yield for a shop work order is the product of the step yields of all operations in the routing for that work order. For example, if a work order has an operation with a step yield of 99.7% and another with a step yield of 97.4% and any remaining operations at 100%, its yield is 97.1078% (.974 x .997 x 1.00 x ... x 1.00). The Scheduler and Yield Percentages A work order is released for a certain quantity. In general only the first operation in the routing sequence is scheduled to produce this quantity. The scheduler determines that the quantity for each subsequent operations is the original work order quantity times the cumulative yield for all operations prior to that operation. As an example, suppose that the first operation of a routing has a standard step yield of 95%, and that all remaining operations have step yields of 100%. Suppose that the unit run time for the first operation is 0.1 hours, the unit run time for the second operation is .2 hours, and that the original work order quantity is for 100 parts. The scheduler will schedule 10 hours for the first operation and 19 hours for the second operation. The 19 hours for the second operation arises out of 95 good parts coming from the first operation. The material from the remaining 5 parts is assumed to be lost. Actual yield percentages Once the shop floor begins to work on a shop work order, actual yields can be determined. If the PROSPAC user configures the system to record what actually happens on the shop floor, the actual quantities completed for each operation are taken from the timecards, or their equivalent, and used by the scheduler to schedule remaining uncompleted operations. In this case the scheduler uses the last quantity completed on a completed operation, instead of the original work order quantity, to compute the input quantities for each of the remaining uncompleted operations. If the PROSPAC user does not record actual quantities complete for each operation from the shop floor, the scheduler reverts to using the original work order quantity to compute the input quantities for each of the remaining uncompleted operations. |
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