Maintenance functions can be classified into different types. Organizations select the specific type of maintenance, depending on their plans and programmes and also the specific policies of maintenance.
1. Breakdown Maintenance:
It is a traditional form of maintenance, and it requires organizations to make available a separate maintenance team. The services of this maintenance team are called upon time to time whenever there is a machine breakdown. Frequency of such services or the problem of breakdown occurrences depends on the age of the machines and plant workload, defects in the system, etc.
To understand the trend, it therefore becomes necessary for every organization to maintain machine breakdown or the failure statistics. By analysing this, it is possible to understand three different kinds of probability distribution as under:
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(a) Normal distribution
(b) Negative exponential distribution
(c) Hyper-exponential distribution
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These distributions have been outlined in detail later in this chapter with mathematical logic. What is important to understand here is that maintenance problems do not follow any uniform defined distribution pattern. In fact, they vary from case to case.
Maintenance work in case of any breakdown being time-independent, it is often difficult for an organization to decide the optimal manpower requirement. It is also often difficult to gauge the requirement of other pools of resources like spares and tools for effectively carrying out maintenance work.
2. Preventive Maintenance:
Normal wear and tear of machines can be avoided by adhering to a preventive maintenance programme. Preventive maintenance has been defined as per BS: 3811:1974 as, ‘Maintenance carried out at predetermined intervals, or to other prescribed criteria, and intended to reduce the likelihood of an item not meeting an acceptable condition.’
Preventive maintenance activities involve:
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(a) Periodic inspection to avert breakdowns and depreciation of plant
(b) Upkeep of plant by routine adjustment and repair
This helps to prolong the useful life of a plant by preventing breakdown and damage, thereby minimizing production interruptions.
The overall objective of the maintenance function is to support the operating department by keeping production equipment and facilities in proper running condition at the lowest possible cost. Preventive maintenance alone does not always prove adequate to achieve this. It also requires a huge cost and does not alone facilitate the actual investigation into the reasons for failure.
3. Corrective Maintenance:
To compensate for the failings of breakdown and preventive maintenance, the corrective maintenance policy is considered a better alternative. Corrective maintenance involves the study of equipment design and its improvements, like changes in design, substitution of more suitable components or improved materials to eliminate or to reduce the frequency of maintenance problem. Corrective maintenance tools in organizations are:
(a) Corrections, i.e., improvements in the maintenance pattern
(b) Redesign, i.e., modifications in the existing design
(c) Substitution, i.e., replacement of components with more improved versions
(d) Changes in material specifications
4. Predictive Maintenance:
The predictive maintenance approach works on the prediction of likely failures of equipment and making provision accordingly for maintenance activities ahead of probable date of failure. For successful predictive maintenance, it is necessary:
i. To monitor condition of equipment
ii. To analyse failure
iii. To collect statistical data
5. Total Productive Maintenance (TPM):
This kind of maintenance involves all employees of an organization through participation in small group activities. TPM was first introduced in Nippondenso Co. Ltd of Japan in 1969, after they experienced difficulty in preventive maintenance activities of automated equipment (with conventional maintenance crew). The important features of TPM are:
i. Activities to maximize equipment effectiveness
ii. Autonomous maintenance by operators
iii. Company-led small group activities
The TPM Programme organizes all employees from the top management to production-line workers in a company-wide maintenance system to support productive facilities. The dual goal of the programme is zero breakdowns and zero defect. Its results are tremendous.
There is an obvious elimination of breakdowns and defects, there’s an improvement in operations, and the costs are reduced. This helps to increase the productivity. In addition to all tangible benefits, it also ensures intangible benefits, which the Japanese list as the five ‘S’:
(a) Seiri (Orderliness)
(b) Seiton (Tidiness)
(c) Seiso (Purity)
(d) Seiketsu (Cleanliness)
(e) Shitsuke (Discipline)