Maintenance is the combination of all technical and associated administrative actions intended to retain an item in, or restore it to, a state in which it can perform its required function. Many companies are seeking to gain competitive advantage with respect to cost, quality, service and on-time deliveries. The effect of maintenance on these variables has prompted increased attention to the maintenance area as an integral part of productivity improvement. Maintenance is rapidly evolving into a major contributor to the performance and profitability of manufacturing systems. In fact, some see maintenance as the "last frontier" for manufacturing.
In their article "Make Maintenance Meaningful" P.K. Kauppi and Paavo Ylinen describe the bulk of maintenance procedures as being as:
As shown in Figure 1, six maintenance programs are identified within the maintenance hierarchy, each representing an increased level of sophistication.
Reactive maintenance (also known as corrective maintenance) involves all unscheduled actions performed as a result of system or product failure. Basically, it is an attempt to restore the system/product to a specified condition. The spectrum of activities within this level are (1) failure identification, (2) localization and isolation, (3) disassembly, (4) item removal and replacement or repair in place, (5) reassembly, and (6) checkout and condition verification. This approach is mainly a response to machine breakdowns. Unfortunately, many manufacturers are still in a reactive mode of operation. Their main objective is to ship the product. If their manufacturing equipment breaks down, they fix it as quickly as possible and then run it until it breaks down again. This is an extremely unreliable process and is not the best way to maximize the useful life span of one's assets. It leaves machine tools in a state of poor repair and can cause the production of out-of-tolerance parts and scrap. Because of its unpredictable nature it can easily cause disruptions to the production process.
Scheduled maintenance utilizes a previously developed maintenance schedule for each machine tool. This is much like an oil change on an automobile that takes place every three months or 3,000 miles, whichever comes first. While this is a broadly practiced technique in many manufacturing organizations, it does possess some distinct disadvantages. The scheduled maintenance may take place too soon, while the machine still operates well (15-20 percent of all components fail after a predictable time), or it may come too late if the machine fails before the scheduled maintenance time. In some cases, the machine may still be running but producing unacceptable parts. Scheduled maintenance can be considered a part of preventive maintenance known as fixed-time maintenance (FTM). Preventive maintenance is discussed later.
Predictive maintenance involves performing maintenance on a machine in advance of the time a failure would occur if the maintenance were not performed. Of course, this means that one must calculate when a machine is predicted to fail. In order to do this, the firm must collect data on variables that can be used to indicate an impending failure (vibration, temperature, sound, color, etc.). This data is then analyzed to approximate when a failure will occur and maintenance is then scheduled to take place prior to this time. By seeking the correct level of maintenance required, unplanned downtime is minimized.
Preventive maintenance encompasses activities, including adjustments, replacement, and basic cleanliness, that forestall machine breakdowns. Preventive activities are primarily condition based. The condition of a component, measured when the equipment is operating, governs planned/scheduled maintenance. Typical preventive maintenance activities include periodic inspections, condition monitoring, critical item replacements, and calibrations. In order to accomplish this, blocks of time are incorporated into the operations schedule. One can easily see that this is the beginning of a proactive mode rather than a reactive one. The purpose of preventive maintenance is to ensure that production quality is maintained and that delivery schedules are met. In addition, a machine that is well cared for will last longer and cause fewer problems.
Current trends in management philosophy such as just-in-time (JIT) and total quality management (TQM) incorporate preventive maintenance as key factors in their success. JIT requires high machine availability, which in turn requires preventive maintenance. Also, TQM requires equipment that is well maintained in order to meet required process capability.
Preventive maintenance is also seen as a measure of management excellence. It requires a long-term commitment, constant monitoring of new technology, a constant assessment of the financial and organizational tradeoffs in contracting out versus in-house maintenance, and an awareness of the impact of the regulatory and legal environment.
The resulting benefits of preventive maintenance are many. Some of them are listed below:
Total productive maintenance (TPM) is preventive maintenance plus continuing efforts to adapt, modify, and refine equipment to increase flexibility, reduce material handling, and promote continuous flows. It is operator-oriented maintenance with the involvement of all qualified employees in all maintenance activities. TPM has been described as preventive maintenance with these three factors added: (1) involving machine operators in preliminary maintenance activities by encouraging them to keep machines clean and well lubricated; (2) encouraging operators to report indications of incipient distress to the maintenance department; and (3) establishing a maintenance education and training program.
Developed in Japan, TPM places a high value on teamwork, consensus building, and continuous improvement. It is a partnership approach among organizational functions, especially production and maintenance. TPM means total employee involvement, total equipment effectiveness, and a total maintenance delivery system. In order to achieve this, machine operators must share the preventive maintenance efforts, assist mechanics with repairs when equipment is down, and work on equipment and process improvements within team activities. Tennessee Eastman found that another employee, such as an equipment operator, with minimal training, could do 40 percent of the traditional maintenance mechanic's work. Another 40 percent could be performed with additional training, but still below the certified level. Only 20 percent of the maintenance tasks actually required a certified mechanic's skills. They also reported that as much as 75 percent of maintenance problems can be prevented by operators at an early stage. This frees maintenance personnel to be responsible for the tasks that require their critical skills, such as breakdown analysis, overhaul, corrective maintenance and root cause analysis. This places them in a "consultant" role with the operators allowing them to:
Of course, for all of this to work, the firm must have an organizational culture which supports a high level of employee involvement. Businesses must be willing to provide the necessary training in order to allow production personnel to perform the required tasks.
TPM's focus is on elimination of the major losses or inefficiencies incurred in production activities. These losses include those due to obstruction of equipment efficiency, manpower efficiency, and material and energy efficiency. Based on their link to corporate goals, targets for eliminating or reducing these losses are developed. Just as in activity-based cost accounting where cost drivers are identified, the objective of TPM is to identify variables that can demonstrate improved performance. All major equipment losses are functionally related to availability, performance, efficiency and/or quality rate so the improvement resulting from the maintenance system can be measured by its impact on overall equipment effectiveness (see below).
Beneficial results of TPM include:
As a final note on TPM, another school of thought holds that TPM can be adopted by continuous diagnostic monitoring of a machine's conditions and establishing a trend line for it. Trend lines approaching or veering into the domain that identifies poor operating conditions will trigger maintenance action.
It has been assumed that preventive maintenance programs help to ensure reliability and safety of equipment and machinery. However, tests performed by airlines in the mid-1960s showed that scheduled overhaul of complex equipment had little or no positive effect on the reliability of the equipment in service. These tests revealed the need for a new concept of preventive maintenance, which later became known as reliability-centered maintenance (RCM).
The concept of RCM is rooted in a 1968 working paper prepared by the Boeing 747 Maintenance Steering Group. A refined version appeared in 1970. Continued studies at the Department of Defense led to the 1986 publication of the "Reliability Centered Maintenance Requirements for Naval Aircraft, Weapons Systems and Support Equipment," a set of maintenance standards and procedures that certain military maintenance personnel were expected to follow. The RCM methodology was further developed and found application not only in the military and aviation, but also in the energy, manufacturing, foundry, and transport industries.
According to Bulmer, the RCM process can be considered as three separate but associated analyses: failure mode and effects analysis, consequence analysis, and task analysis. These analyses consider the specific characteristics and consequences of a failure and attempt to arrive at the optimal solution based on this information.
Total productive maintenance provides a systematic procedure for linking corporate goals to maintenance goals. This procedure calls for the consideration of external and internal corporate environments, and then the development of a basic maintenance policy congruent with the environments. Next key points for maintenance improvement are identified, which result in the definition of target values for maintenance performance. These values, referred to as overall equipment effectiveness (OEE), are a function of equipment availability, quality rate, and equipment performance efficiency, and provide a starting point for developing quantitative variables for relating maintenance measurement and control to corporate strategy.
Essentially, OEE offers a measurement tool that helps identify the real areas of opportunity within an operation. These areas have been termed the "six big losses." OEE allows the firm to break these losses into smaller components to better evaluate the impact the maintenance program is making on the operation. The six losses are:
If a company has an OEE of 85 percent or more, then it is considered to be a world-class company.
Two major trends in the development of maintenance management research have been identified: (1) emerging developments and advances in maintenance technology, information and decision technology, and maintenance methods; and (2) the linking of maintenance to quality improvement strategies and the use of maintenance as a competitive strategy.
The first major trend has to do with the impact of artificial intelligence techniques, such as expert systems and neural networks, on the formation of maintenance knowledge in industrial organizations. There is a diverse application of expert systems within the maintenance area. A number of these systems and their applications are listed below:
The second major trend is typified by the emergence of total productive maintenance, which must be incorporated into the firm's strategy. In the quest for world-class manufacturing, many industries are appreciating the need for efficient maintenance systems that have been effectively integrated with corporate strategy. It is vital that maintenance management becomes integrated with corporate strategy to ensure equipment availability, quality products, on-time deliveries, and competitive pricing. Managerial attitudes have changed toward maintenance because of the emergence of new management philosophies. In addition, social trends such as lack of capital, fluctuations in currencies, competition, quality, and environmental consciousness, have also encouraged a new focus on maintenance.
Maintenance will continue to be a major area of concern for manufacturers and other forms of business. A study of some seventy manufacturing plants found that over 50 percent of the maintenance work performed by these firms was reactive (run to failure, emergency breakdown). The balance of maintenance work was preventive or period based (25 percent), predictive or condition based (15 percent), and proactive or root-caused based (10 percent). A strong correlation has been found to exist between manufacturing cost reduction and preventive/predictive maintenance. Over a five-year period a study group of companies found that productivity improvements correlated strongly with a number of variables, one of which was preventive/predictive maintenance.
Mike Laskiewicz recommends that organizations recognize maintenance as a key department that needs to be well managed. In addition, the maintenance department should be led by a strong-minded individual who is a good motivator, technically competent, experienced and familiar with advanced industry practices. Finally Laskiewicz notes that maintenance planning must be a top priority.
R. Anthony Inman
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