| The Six Big Losses |
| Introduction |
In the operation of a machine six types of waste are distinguished. These are called losses, because they lead to a decrease in the effectiveness of the machine or equipment. |
| Overview of the Six Big Losses |
| Types of Losses |
The Six Big Losses |
| Time Loss (=decrease in availability) |
1. Breakdowns
2. Waiting |
| Speed Loss (=decrease in performance) |
3. Minor stoppages
4. Reduced speed |
| Quality Loss (=decrease in quality) |
5. Scrap
6. Rework |
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| Time Loss |
Time loss is defined as the time during which the machine should be producing, but is not: no products are coming out of the machine. Basically, it refers to two types of losses: breakdowns on the one hand and waiting on the other.
The OEE Toolkit has a special registration for waiting time on a machine due to supply and transport problems in the line. This type of loss is defined as a line restraint.
| Loss |
Description |
| Breakdowns |
A sudden and unexpected machine breakdown or failure results in loss of production time. The cause of the malfunction may be technical as well as organizational (e.g. operational error, poor maintenance). OEE registers the way the breakdown manifests itself. |
| Waiting |
Production time is also lost when the machine is waiting. The machine can be waiting for many reasons, e.g. because of a changeover, maintenance or lunch break. In case of a changeover, the machine usually has to be shut down for some time in order to change tools, dies, or other parts. SMED (Single Minute Exchange of Die) defines the changeover time as the time between the last good product of the previous series and the first good product of the new series. For the OEE, the changeover time is the time when the machine does not generate any products. |
| Line restraint |
Waiting due to supply and transport (conveyor) problems in a production line or series of linked manufacturing processes is classified as a specific type of waiting: the line restraint. Because stoppages in this category originate somewhere in the production line and not in the machine itself, this category of loss of effectiveness can be left out of the OEE measurement of the machine. |
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| Speed loss |
Speed loss implies that the machine is operating but not at its maximum speed. There are two types of speed losses:
| Loss |
Description |
| Minor stoppages |
When a machine shows short interruptions and does not have a constant speed, a smooth flow of production will not occur. These minor stoppages and the subsequent loss of speed are generally caused by small problems, such as products blocking sensors or getting stuck in the conveyor belts. These frequent hitches can drastically diminish the machine’s effectiveness.
Note: In theory minor stoppages are a type of time loss. However, being very short (usually shorter than 5 minutes) they are not registered as a time loss. |
| Reduced speed |
Reduced speed is the difference between the actual set speed and the theoretical or design speed (also known as the Name Plate Capacity). There is often a considerable difference between what people think the maximum speed is and the theoretical maximum speed. In many cases, the production speed has been optimized in order to prevent other losses such as quality rejects and breakdowns. Losses due to reduced speed are, therefore, often ignored or underestimated. |
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| Quality loss |
Loss of quality occurs when the machine makes products that are not good first time. Two types of quality losses are distinguished:
| Loss |
Description |
| Scrap |
Scrap are those products that do not meet the quality specifications even if they can be sold as ‘sub-spec’. The objective is ‘zero defects’: always manufacture a good product first time.
A specific type of quality loss are the start-up losses. These losses occur when:
- upon starting-up the machine, the production is not stable right away and the first products do not meet the specifications;
- the production at the end of a production run is no longer stable and the products no longer meet the specifications;
- a number of products are no longer counted as part of the production order and, consequently, are considered a loss.
These are usually hidden losses, which are often considered to be unavoidable. The scale of these losses can be surprisingly large. |
| Rework |
Rework products are also products that do not meet the quality specifications first time, but can be reprocessed into good products. At first sight reworking products does not seem to be such a bad thing, for you can still sell the product at the normal price. However, the product was not right first time and is therefore a quality loss just like scrap. |
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