As a manufacturer, it's important to understand how many items are passing through your production processes cleanly without any defects, as defects can be costly in terms of wasted components and rework. The first pass yield tells you the overall proportion of units that achieve this benchmark. The higher the FPY, the better your production quality.
TL;DR (Too Long; Didn't Read)
Calculate first pass yield by dividing the number of "good" units you produce by the number of units entering the production process.
What Is First Pass Yield?
First pass yield is a mathematical formula used for measuring quality and performance in manufacturing. Specifically, it shows you how many items are moving through the production process without any problems. An FPY of 98 percent, for example, tells you that 98 percent of items are moving through the system without any issues. Two percent of your items are scraps or reworks, which can be a time and cost burden on final production. The higher the FPY, the more efficient your production processes.
How to Calculate First Pass Yield
The formula is fairly straightforward:
First pass yield = number of "good" units of products completed with no scrap or rework / total units of products entering the process
Suppose, for example, you have 10,000 units entering the production process. One hundred and fifty are scrapped or reworked, which means that 9,850 are finished first-time to specification. First pass yield is 98.5 percent (9,850/ 10,000).
First Pass Yield for Multiple Production Processes
The above equation gives the first pass yield for a single production process. You can also calculate the total FPY where an item moves through multiple processes en route to final specification. The equation now is:
First Pass Yield = process 1 yield x process 2 yield x ...process 'n' yield
Consider now an operation that has three processes. The first process has a first-time production yield of 98.5 percent, the second has a first pass yield of 94 percent and the third has a first pass yield of 97 percent. The total FPY is 0.985 x .0.94 x 0.97 which equals 0.898 or 89.8 percent. That means that one out of every 10 products will not make it through your entire system without needing rework. The total number of processes has an impact here as the more processes you have, the greater the chances of making a mistake.
First Pass Yield Limitations
The problem with FPY is it turns on the number of scraps and reworks you've identified. These can be hard to spot, especially if your front-line workers are operating as "hidden factories," fixing problems as they go or helping out their co-workers upstream. When items are fixed within a process, they won't show up as a defect and your first pass yield rate will look better than it actually is. Make sure you have a proper measurement system in place to properly track and define these issues.
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