In the operation of a machine, there are three main types of waste that can be identified, with a further six sub-categories, generally known as the six big losses. They are referred to as losses due to the fact that they lead to a decrease in the effectiveness of the machine. The diagram below depicts this overview:
Availability Loss can be explained as the time during which the machine is not producing, when products should be produced. This can generally be for one of two reasons: breakdowns and waiting.
- A breakdown loss occurs when there is a sudden and unexpected breakdown/failure of a machine which causes in a loss in production time. The cause of this failure may be technical or organisational (for example, operational error or poor maintenance).
- A waiting loss occurs when the machine is waiting for something. This can be further divided into sub-categories: idle or line restraint.
- Firstly, when a machine is idle, it means that production time has been lost because the machine does not make any products. For example, when a changeover occurs, the machine normally has to stop producing for some time in order to change tools, dies, or other parts.
- Secondly, when a line restraint occurs, it means that the machine is standing still because of supply or transport problems on the production line. This would happen when the operator is waiting for material, either from stores or previous machines.
Performance Loss can be explained as the time during which the machine is operating, but not at its maximum speed. This can generally be for one of two reasons: minor stops and reduced speed.
- A minor stoppage loss occurs when the machine experiences short disruptions and does not operate at a constant speed. In this case, the smooth flow of production is not being achieved. This type of loss is generally caused by small problems, for example, when a product gets stuck in the conveyor belt. If these complications occur frequently, it reduces the machine’s effectiveness dramatically. Even though, theoretically, a minor stoppage is a time loss, they may not be registered as a time loss simply because they occur in very short duration (usually less than five minutes).
- A reduced speed loss occurs when a machine runs at a slower speed than it is designed to run. One reason for this occurring can be that people don't realise that the equipment is designed to run at a different speed than its current production speed. Another reason may be that the designed speed produces poor quality products.
Quality Loss occurs when the machine is not making good products the first time around, in other words, when there are defects in the products the machine is producing. This can generally be divided into two categories: scrap and rework.
- A scrap loss occurs when a product is produced which does not meet the quality specifications needed to sell the product, and it cannot be reused. In this case, scrap is a waste of material.
- A rework loss occurs when those quality specifications are not met, but the product can be reprocessed into good products. In this case, it is still considered a loss because the effort spent to process the product twice is a waste.
The Six Big Losses are forms of waste. They do not add value to the products. Instead, they reduce a machine’s effectiveness (which is measured by the OEE). To apply OEE and take part in improvement activities, it is important to use this knowledge of the different types of equipment-related losses.