Yield Loss Mapping on Paper Container Lines: FAQ

A plant knew it lost four per cent of output but not where any of it went, so every attempt to fix it became an argument. This FAQ covers what yield loss mapping is, where to measure, how to attribute a loss to a station, how to read the map, and how yield relates to overall equipment effectiveness.

What is yield loss mapping on a paper container production line?

Yield loss mapping on a paper container production line is the practice of recording the good output at each station boundary and attributing the difference between consecutive points to the station between them, which replaces one plant-level scrap figure with a set of located losses a team can act on. The map records good units rather than defects, since counting what passed is easier to verify and adds up cleanly from station to station. Losses that leave no visible reject, such as material trimmed away or containers downgraded to a lower grade, are captured too, because they appear as a gap between the material that entered and the containers that shipped. A map is kept during production, not reconstructed from a monthly report, so a new loss shows up in days.

Where should you measure losses on a container line?

Losses on a container line should be measured at a small number of station boundaries rather than at every operation, because too many points cannot be maintained and too few cannot locate the loss, and the points should sit where the product is easily countable after a transfer. Four points cover most lines: after forming, after sealing or rim curling, after the quality check, and after packing, with the total material in and the total saleable containers out as the frame around them. Each point should record good output, so the difference between consecutive points is the loss created in between. A plant that has never mapped its line can start with these four points and add detail only where a loss proves large enough to need it.

How do you know which station actually causes a loss?

The station that causes a loss is the one between the two measurement points where the good-output count falls, not the station where the defect is first noticed, because defects created upstream are often detected later, which sends a plant to the wrong machine. This distinction is the whole point of mapping. A mark created on a warm wall just after forming may not be caught until the quality check, which makes the quality check look responsible when the transfer rail is the cause. Mapping assigns the loss to the interval, so the investigation starts in the right place. Where the loss is not visible, such as trimmed material, it appears in the gap between the final count and the material input, which is a signal to examine the trimming and handling rather than the product checks.

How should a yield loss map be read and used?

A yield loss map should be read by size to find the largest loss and by concentration to find losses that sit in one station rather than spread across several, because the two patterns need different responses, and the map should also be watched for losses that move downstream after a fix. A large loss concentrated at one station is usually an engineering fix, while a smaller loss spread across the line is usually a setup or training issue. A loss that grows over a shift often points to heat or tooling wear, which links the map to the cycle count. Read this way the map becomes a weekly decision about which single station to work on next, and a monthly view of the whole chain shows whether a fix has simply pushed the loss further along the line.

How does yield loss mapping relate to OEE?

Yield loss mapping relates to OEE by supplying the quality figure that OEE needs, since OEE combines availability, performance and quality and cannot be calculated accurately if the quality loss is unknown, and a mapped line can show which station creates the loss, so the quality term becomes a target rather than a description. The mapping also supports the performance term, because losses linked to stops and slow cycles appear at the same boundaries. Because both measures depend on counters and checks, the registration and calibration of that equipment matters for both. A plant that maps yield and measures OEE from the same data ends up with one consistent picture of where output goes, rather than two numbers that disagree.

Prepared by 燕七.