In the previous article, we examined the basic logic of OEE and the seven major losses that reduce overall equipment effectiveness.
OEE shows where production capacity is being lost. Measurement alone, however, does not remove the loss.
The next step is to determine where the loss comes from. Is it a sudden failure or a long-standing chronic problem? What is the symptom, and what is the actual root cause? Where should improvement efforts be focused first?
In this article, I move from OEE thinking to practical improvement. I examine how loss structure analysis, Kaizen, Pareto analysis, 5 Why and cause-and-effect diagrams help direct actions to the right place.
How planned production time is reduced step by step
| Time level | What it means | How the next level is formed |
|---|---|---|
| Available hours | The time during which the equipment could in principle operate during a day or month. | Starting level |
| Loaded time | The time during which the equipment is planned to be in productive use. | Available hours − planned maintenance and other planned stops |
| Actual operating time | The time during which the equipment is actually operating. | Loaded time − downtime |
| Net operating time | Operating time after losses caused by minor stops and reduced speed have been removed. | Actual operating time − minor stops − speed losses |
| Value-adding operating time | The time during which the equipment produces an accepted output without correction or rework. | Net operating time − time lost to quality defects, corrections and rework |
Causes of losses
Eliminating losses requires an understanding of their nature.
TPM examines losses particularly from the perspective of declining machine and production process performance.
Losses can be divided into two main categories.
1. Random losses
A random loss occurs when there is a sudden and significant change in operating conditions.
It usually appears as the complete failure of one or more equipment components and as a visible interruption to production.
A random failure may appear to be an isolated event. Behind it, however, there may be a chronic problem that has developed over a long period and was not detected or removed in time.
The aim of a TPM programme is to prevent sporadic failures by addressing their underlying causes.
2. Chronic losses
A chronic loss exists when there is a continuing gap between the actual performance of the equipment and its theoretical optimum.
The machine may be running, but its operation is slower, less stable or of lower quality than it should be.
A chronic loss usually develops over time. It may result from wear, inadequate maintenance, accepted abnormalities or underperformance that has gradually become normal.
Chronic losses are often more difficult to detect than sudden failures because people become accustomed to abnormal performance.
Focused continuous improvement: using Kaizen to reduce losses
Loss structure analysis, together with OEE calculations, provides direction for TPM improvement work.
Not every problem can be solved at once. Attention must therefore be focused first on the losses that have the greatest impact on equipment effectiveness, production capacity and quality.
The problem-solving tools must also be selected according to the nature of the problem.
The eight quality tools form a commonly used toolkit for identifying and structuring problems and finding their root causes.
Figure 1. Eight quality tools for identifying and understanding problems and determining root causes.
OEE data should be collected by the operational team by shift and by production line.
A check sheet can be used to collect the data. It is a quick and practical way to record recurring problems at the workstation.
The data from the check sheet is transferred to a Pareto table. This makes it possible to build a loss structure analysis and identify the problems that should be addressed first.
The data should be used for improvement, not for comparing shifts, production lines or individuals.
The original seven loss categories do not always describe the causes of problems in sufficient detail.
More detailed analysis may then be required. Improvement work can be focused using tools such as Pareto charts, scatter diagrams, histograms, cause-and-effect diagrams and the 5 Why method.
A tool should not be selected simply because it belongs to the methodology. It should be chosen according to the problem being solved.
5 Why takes the analysis from symptom to root cause
5 Why is a simple way to continue asking questions until the corrective action goes beyond removing the visible symptom.
Oil on the floor is an observation.
The first response might be to replace the leaking seal. If the investigation ends there, however, the same damage may recur.
By continuing to ask why, it may become clear that the seal was damaged by metal particles in the oil. The particles entered the system through a damaged strainer. The strainer had been positioned where falling parts could damage it.
The root cause is therefore not merely the damaged seal or strainer. The underlying problem lies in the machine design and the protection of the strainer.
The corrective action is to redesign the machine or install a guard that prevents falling parts from damaging the strainer.
If only the damaged component is replaced, the same failure may return.
Recurring hose failure on a mobile machine
The same principle applies to the maintenance of mobile machinery.
A failed hydraulic hose can easily appear to be an isolated fault. The machine stops, oil leaks and the hose is replaced. Once the new hose is installed, the machine returns to work.
If a hose in the same area fails again, the cause may not be a poor-quality hose or bad luck. A chronic structural problem may be behind the failure.
The hose may rub against the frame or an adjacent component. It may bend too sharply when a boom or joint reaches its end position. Inadequate clamping may allow the hose to move under pressure pulsation. The hose may also be stretched as the machine moves or exposed to heat, rocks or other external damage.
The first repair returns the machine to operation. It does not remove the cause of the failure if the new hose is installed in the same way and in the same damaging environment.
Root-cause analysis may lead to rerouting the hose, adding support points, improving protection or modifying the structure. It should also be checked whether the same risk exists in other machines of the same model.
In this case, Kaizen does not mean replacing one hose or repairing one machine. Improvement is achieved only when the recurring failure results in a permanent change to the machine, the maintenance instructions, the spare-parts solution or the wider fleet.
A cause-and-effect diagram makes the chain of causes visible
A cause-and-effect diagram can be used when a problem may have several possible causes or combinations of causes.
In the following example, contamination was found inside hydraulic blocks delivered to production.
The analysis showed that contamination entered the blocks because of inadequate protection during storage and transport.
As a result of the project, the entire storage, packaging and transport chain for the blocks was changed so that the components remained clean throughout the process.
The corrective action was not limited to cleaning one contaminated block. The process that created the problem was changed.
Once the solution has been implemented, its effect must be monitored through OEE data. Only follow-up can show whether unplanned interruptions decrease and whether the actions have the intended effect.
From measurement to action
The strength of OEE is not the percentage figure alone.
Its value comes from directing the discussion to the right questions:
- where production capacity is being lost
- what causes the loss
- where corrective action should be focused first
From a maintenance perspective, it is important to distinguish a sudden failure from a chronic problem.
A sporadic failure must be repaired.
A chronic loss must be identified, investigated and removed at its root cause.
Kaizen connects these steps into practical improvement work. OEE shows the loss, problem-solving tools help identify its cause, and follow-up shows whether the change produced the intended result.
In a factory, an observation often arises on the production line and enters a shared process through the shift team, the improvement team or daily management.
In mobile machinery maintenance, an observation may arise far from the organisation, in the work of a single operator or technician. If the observation, investigated cause and proven solution do not enter a shared process, the same problem will later be solved again on another machine or at another site.
Methods alone are therefore not enough. A clear process is also needed for handling observations, making decisions, assigning responsibilities and following up implementation.
In the next article, Pentti Enlund examines the management structure of continuous improvement, the responsibilities of different roles, and how an individual observation or proposal moves from identification to decision, implementation and shared organisational learning.
About the author
Pentti Enlund is a Value Engineering specialist. In this article series, he examines TPM, OEE and Kaizen through value, cost and production capacity: where performance is lost, where costs arise and how improvement work should be focused in practice.