First-pass yield and the capacity effect of rework

Why it matters

A product coming out good in the end does not mean it was made right the first time. If a product needed correction, readjustment or re-inspection, it has consumed extra resources. The first-pass yield rate preserves this distinction. The denominator is the number of unique products entering the process for the first time; the numerator is those among them accepted without rework. Seeing the same product a second time is not counted as a new entry. If the product identity is not preserved, the records can show production higher than it is. As a result, both the quality indicator and the capacity calculation are distorted. For this reason the product history carries more information than the final status alone.

The rework load often stays outside the daily production table. When a worker or machine set aside for the main operation spends time again on the same part, the opportunity to make new products falls. Even if the resource is separate, the load does not disappear; it moves to another work center. In these two cases the same total time can produce different flow results. First it is explained which resource was used for how many minutes, and then the capacity on the calendar is assessed. Counting the number of units leaving a station may not show all the work spent at that station. If especially re-inspection and handling after correction are left out of scope, the extra load looks incomplete.

The final good rate is the ratio of unique products accepted at the end of the period to the first entries. It answers a different question from the first-pass rate. A high final good rate can be useful in meeting customer need, but it must not hide a low first-pass success or a heavy correction load. Scrap, products waiting for rework and products whose outcome is still open are also kept as separate states. Assuming a record that has not yet concluded to be good raises the ratio early. If the same time window and the same product set are not preserved, the comparison loses its meaning. For products that enter within the period and complete afterward, the closing rule must be written in advance.

The aim in this lesson is not simply to label rework as negative. When needed, a nonconforming product can be salvaged by a safe and verified operation. But the feasibility of the correction, the re-acceptance condition and the resource effect must be clear. Removing the final inspection to cut time, or counting a product that has been corrected as a new product, is not a solution. A lasting improvement raises the first-pass success while protecting the acceptance condition. Cost, lead time and resource load are reported as separate results. A proposal that reduces the rework quantity becomes stronger when it is shown with new data that the same source of defect does not recur later.

Formula