Maintenance: definition, key tasks, and effective strategies

The technical development of the past decades has been rapid; specialized plants have become more and more complex and powerful and are now the backbone of our economy and society. It is, therefore, all the more critical that these plants are always in perfect operating condition and function without failures. This is where the topic of maintenance comes into play.

What is maintenance, and what measures does it include?

The purpose of maintenance is to ensure the preservation or restoration of the functionality of technical objects such as machines. In technical terms, maintenance is the totality of measures to maintain the target condition and determine and assess the actual situation.

Maintenance, in turn, includes several technical and administrative areas of action, which are explained in the following section.

The tasks of maintenance

Measures for determining and assessing the actual condition and investigating the causes of wear and tear
- Measuring
- Testing
Measures to maintain the target condition and to delay the reduction of the existing wear stock
- Cleaning
- Lubricate
- Refilling
- Readjustment
- Preservation
Measures to restore the target condition
- Repair
- Replace
Measures to improve the actual condition of the system/increase performance
- Evaluate
- Analyze
- Check
- Decide

Finding the right maintenance strategy

In today’s business environment, it is essential to develop a maintenance strategy. Besides this type of strategy, there are others such as:

Corporate strategies
Business area strategies
Sales strategies
Investment strategies

Before we go into the concept of maintenance strategy in more detail, we must first explain the concept of strategy in general.

A precise plan of one’s course of action is designed and implemented to achieve a specific goal with a strategy.

The purpose of the maintenance strategy, in general, is for management to set specific maintenance goals that are then to be achieved.

Maintenance objectives include, for example, extending the life expectancy of a machine, property, or piece of equipment, maintaining a specified condition, etc. A budget is set for the maintenance strategies, which must be taken into account.

What types of maintenance strategies are there?

Maintenance strategies are divided into different classes or types.

These include:

Damage-dependent maintenance strategy
Preventive maintenance strategy
Prospective maintenance strategy
Deferred maintenance strategy
Periodic maintenance strategy
Condition-based maintenance strategy

Each of these strategies is explained in more detail below

Damage-dependent maintenance

The damage-dependent maintenance strategy is also called reactive or breakdown maintenance. The damage-dependent maintenance strategy is one of the original forms of maintenance. As soon as something is damaged or defective, it must be repaired. With this strategy, the deliberate aim is for something to break. No preventive measures are taken to preserve the machine, property, or equipment. If a breakdown should occur, it is necessary to react quickly to continue production promptly and keep the costs within manageable limits. Otherwise, there is a risk of too long downtimes and costs.

The damage-based planning strategy has few advantages but numerous disadvantages.

Advantage:
- Neither additional technology for analysis nor tools for planning are needed, in which investments would otherwise have to be made
Disadvantages:
- Damage, which can quickly become expensive, cannot be avoided by this strategy because there is no planning in advance
- This strategy massively shortens the service life of machines and equipment
- It is not possible to plan the work sensibly with this strategy
- The primary focus of this strategy is on eliminating the damage that has occurred
- The failure of a machine or a device cannot be predicted. Therefore, due to the possible lack of spare parts, extended downtime can occur, which would result in high follow-up costs
This strategy is used in the following areas:
- In machines where damage to persons can be ruled out
- For devices that can be repaired cheaply or entirely replaced for a low budget
- For appliances that do not need to be repaired often
- This strategy is worthwhile when there is no data on the condition of the affected machine or device

Preventive maintenance strategy

Preventive maintenance is also called planned maintenance. The main objective of this strategy is to reduce the risk of machine and equipment failures to a minimum. Routine preventative maintenance is carried out according to predefined intervals or usage guidelines. The operating conditions of the machines are not taken into account. Are replacing a car timing belt after a certain number of kilometers or changing a light after certain operating hours are examples of this. To introduce a systematic preventive maintenance or maintenance strategy, it is necessary to have a precise knowledge of the service life and deterioration of the machines and equipment.

Prospective maintenance

The prospective maintenance strategy is also called predictive maintenance. As long as the machines work and produce at the desired rate, everything is acceptable within the supply chain. This can work well, but it does not have to. In this case, we are at the damage-dependent maintenance described above.

The whole thing becomes problematic if the machines are defective more often. In the long run, it then quickly becomes expensive for the company. With the introduction of Industry 4.0 at the latest, it will become problematic for companies to pursue a damage-based maintenance strategy. The competition is not sleeping. Competitors who rely on big data, artificial intelligence, and machine learning will be ahead in the future with the help of predictive maintenance.

Predictive maintenance is one of the most critical maintenance strategies. With this strategy, equipment and machine are monitored continuously, i.e., during operation. This determines when the machine or device needs to be serviced. Prospective maintenance is based on estimates obtained through analyses and evaluations of the various machine parameters.

Predictive maintenance is intended to save costs, as work only needs to be carried out when necessary. This is why predictive maintenance is also referred to as condition-based maintenance. Networked machines can use the condition data of these machines to gather information from the sensors. The information obtained is then combined digitally with data from the MES (Manufacturing Execution System) or the ERP (Enterprise Resource Planning). This makes it possible to predict inspection and maintenance times for the machines accurately. One method of using predictive maintenance is predictive analytics.

Maintenance is only carried out at the time when it is necessary. Maintenance is not carried out after fixed intervals or damage. This saves resources and maintenance costs.

Predictive maintenance is mainly used in the care of wind turbines and their turbines and the automotive sector. In these areas, for example, vibrations that appear suspicious, imbalances, and material defects are detected with the help of predictive maintenance.

With the help of the Internet of Things, mathematical algorithms are used to analyze the behavior of components that are at risk of wear or have to withstand demanding conditions. For example, the probability of a failure of bearings can be accurately predicted.

Pharmaceutical and food industries or paint shops are all industrial sectors where the failure of these machines would cause significant problems.

The maintenance of this maintenance strategy is expensive because sophisticated tools are used. Therefore, this strategy is beneficial when machines or equipment are critical from a safety or cost perspective. This applies, for example, to:
- Infrared thermographic
- Vibration analyzes
- Oil analyzes
- Testing of materials, such as ultrasound, eddy current, etc.
With the predictive maintenance strategy, the maintenance measures are derived from the qualitative condition of the machine and the predicted wear progression. The wear progression is predicted based on deterioration parameters. Deterioration parameters are critical figures on the wear and tear or deterioration of a property or machine. The influencing variables of the deterioration parameters include wind, precipitation, temperature, and human factors such as traffic or vandalism.
- In machines that cause high costs if they break down
- In machines that already have corresponding sensors or where the technical prerequisites for the required sensors are already in place
Innovative software for system maintenance detects changes in general conditions. This includes, for example, a defect in a cooling system that can lead to an engine problem. Through a prediction algorithm of the software, the probability of failure is predicted, and the machine user is forewarned.

Through such clever software, predictions can be made during an operation about the maintenance requirements that will arise in the future, and the deployment of service personnel can be better planned accordingly. The software learns from every error message and feedback from the machine. It then modifies the model accordingly. Over time, thanks to the software, the calculated failure predictions become more and more accurate. This makes it possible to learn about potential faults in advance.

What is a deferred maintenance strategy?

With this strategy, as soon as the damage occurs, it is not repaired immediately. Instead, the repair is postponed for the time being and planned for later due to the given maintenance guidelines. This strategy is usually used by companies that have to cut costs due to liquidity bottlenecks. In the long run, however, this strategy does not prove successful.

Periodic maintenance

With this strategy, maintenance is planned and carried out based on a maintenance contract or calendar. The company often establishes the timing of care on the specifications of the respective manufacturer or empirical values. This maintenance strategy aims to minimize machine breakdowns and to carry out repairs before the machine breaks down.

Advantages:
- Compared to the damage-based maintenance strategy, this strategy is better as there is less downtime
- Consequential damage due to defects in the machines is reduced
- Fewer total breakdowns
Disadvantages:
- Maintenance is always carried out based on the maintenance contract or calendar. It does not matter if the machine needs care or not
- This strategy is not so easy to plan
The periodic maintenance strategy is used in similar areas as the damage-dependent maintenance strategy. This strategy is used primarily when manufacturer specifications have to be met. This makes sense if there are still warranty claims on the machine or the device. It should be noted that maintenance is always proper, regardless of the strategy used. This includes, for example, oil changes or the replacement of worn parts. In this way, additional defects and downtimes can be avoided.

Condition-oriented maintenance

This strategy takes two approaches. As with the periodic maintenance strategy, regular maintenance is carried out. In addition, the condition of the machines is checked at regular intervals. In this way, possible sources of faults are detected and eliminated in advance. This maintenance is carried out at regular intervals or continuously. Condition monitoring is used for this purpose. In addition, this maintenance strategy requires that specific parameters such as pressure, filling level, etc., are monitored. Industrial maintenance work can then be planned and carried out based on this data.

Advantages:
- Defects in machines occur less frequently because wearing parts are replaced more often. This leads to less consequential damage
- Measures can be planned better because repairs are detected and eliminated at an early stage
- Total failures are kept within limits
Disadvantages:
- In the beginning, this strategy leads to high acquisition costs, since for example measuring equipment must be purchased
- With large machine fleets, the expenditure is correspondingly high
- There is a risk that machines are maintained unnecessarily and too early. This leads to unnecessary costs

What is Condition Monitoring?

Condition monitoring means monitoring the condition of a machine. Various parameters, such as speed, volume, temperatures, pressure, vibrations, and fill levels, are regularly

and filling levels are measured and recorded at regular intervals. These values are used to determine and evaluate the condition of the machine.

Condition monitoring offers companies in the manufacturing sector the opportunity to better understand their machines’ condition and react more quickly to signs of wear or changes in the devices. As a result, machine maintenance can be better planned. The needs of the machines are monitored in real-time. In emergencies, it is, therefore, possible to react quickly and take appropriate safety measures. The device works more efficiently, and safety is increased. Breakdowns are reduced to a minimum.

In many cases, condition monitoring is used in conjunction with predictive maintenance. However, condition monitoring also plays a significant role in predictive maintenance. In this way, irregularities in the machines can be quickly detected and remedied before (expensive) damage occurs. Since the application of condition monitoring is vast, the demand for intelligent and efficient condition monitoring systems (CMS) is correspondingly high. Effective condition monitoring systems analyze faults and find the causes. This maximizes the service life of the machine. Raw materials, costs, and energy are saved.

In summary, condition monitoring enables the precise detection of faults, promotes preventive action, optimizes maintenance intervals, leads to less machine downtime, and better and more reliable production.

Which strategy is best?

There is no such thing as the perfect maintenance strategy. Instead, it makes sense to combine several of the methods listed. For example, it is common for many companies to have regular maintenance in addition to a chosen strategy, combining, for example, the predictive maintenance strategy with the periodic maintenance strategy.