Explanation of the
”Six Big Losses”

One of the main targets with TPM and OEE program is to reduce and/or eliminate what is called the Six Big Losses.

 

The coupling between Six Big Losses and OEE

One of the main targets with TPM and OEE program is to reduce and/or eliminate what is called the "Six Big Losses" – the most common reasons to productivity losses within manufacturing. In the table below the Six Big Losses are listed and you’ll see how they are connected and related to factors in the OEE calculation.

 

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Handling of the Six Big Losses

Now that we know what the Six Big Losses are and some of the events that contribute to these, we are ready to focus on how to measure and correct them. To categorize the data makes the stop event data easier to follow up, and if it occurs in real-time it’s even simpler.

Downtime

The elimination of unplanned Downtime is critical in order to improve OEE. Other OEE factors can’t be improved if the manufacturing is down. It is not only important to know how much Downtime you have but also when, and the root cause to the downtime, that is usually called Reasons. Once you have data around Downtime and the Reasons you can finally make a Reason tree where you group and build up to see the biggest contributing Reasons. With that knowledge you can then reduce the largest factors first and work your way down.

Changeovers

Changeover is measured as the time between the last correct unit until the first correct unit has been produced after the changeover. This includes major adjustments and/or reheating required to get an acceptable product result which meets the quality requirements. Measurements of time for Changeover is important and many companies are using creative methods to reduce it. It can be carts with all necessary tools or parts needed for the specific changeover and all marked to make it easy to make the adjustments.

Micro stops and Reduced speed

Micro stops and Reduced speed is one of the most difficult parts of the Six Big Losses to both measure and monitor. Cycle time analysis can be used to handle this type of losses. In the most manufacturing processes you have to implement automatic data gathering in order to be able to measure the cycle time. This is since the cycles are fast and are repeating themselves. By comparing all made cycles against an Ideal Cycle time and through matching of the data of micro stops a total loss due to speed can be calculated. The reasons for Micro stops and Reduced speed are often very different and that is why you should measure them separately.

Waste and Rework

Waste and Rework are divided since the root cause is usually different. Units that require extra work in order to pass should be classed as waste in the OEE calculation. The tracking of the waste during a process or shift can help you in the analysis since there is often a pattern.
A Six Sigma program have an overall goal to reach a level of waste that is below 3 to 4 units per million units. This is used to reach the target of “almost perfect” quality.

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