Maintenance Methodology Introduction: What is maintenance and why is it performed? Past and current maintenance practices in both the private and government sectors would imply that maintenance is the actions associated with equipment repair after it is broken. The dictionary defines maintenance as follows: “the work of keeping something in proper condition; upkeep. ” This would imply that maintenance should be actions taken to prevent a device or component from failing or to repair normal equipment degradation experienced with the operation of the device to keep it in proper working order.
Unfortunately, data obtained in many studies over the past decade indicates that most private and government facilities do not expend the necessary resources to maintain equipment in proper working order. Rather, they wait for equipment failure to occur and then take whatever actions are necessary to repair or replace the equipment. Nothing lasts forever and all equipment has associated with it some predefined life expectancy or operational life. For example, equipment may be designed to operate at full design load for 5,000 hours and may be designed to go through 15,000 start and stop cycles.
The need for maintenance is predicated on actual or impending failure – ideally, maintenance is performed to keep equipment and systems running efficiently for at least design life of the components. The curve can be divided into three distinct: infant mortality, useful life, and wear-out periods. MAJOR MAINTAINENCE METHODS: Every facility that produces a consumer product has some requirement for maintenance or upkeep of their machinery. Depending upon the product and, to some extent, the size of the facility, this maintenance activity may be continuous in nature or periodic. Some maintenance activities may consume a ignificant portion of the facility expenses and manpower. Facility maintenance activities generally fall into three categories: Breakdown, Preventive, and Predictive. Each category has particular costs associated and specific benefits. Reactive Maintenance (Breakdown Maintenance): Reactive maintenance is basically the “run it till it breaks” maintenance mode. No actions or efforts are taken to maintain the equipment as the designer originally intended to ensure design life is reached. ?Advantages: • Low cost. • Less staff. ?Disadvantages: • Increased cost due to unplanned downtime of equipment. Increased labor cost, especially if overtime is needed. • Cost involved with repair or replacement of equipment. • Possible secondary equipment or process damage from equipment failure. • Inefficient use of staff resources. Advantages to reactive maintenance can be viewed as a double-edged sword. If we are dealing with new equipment, we can expect minimal incidents of failure. If our maintenance program is purely reactive, we will not expend manpower dollars or incur capital cost until something breaks. Since we do not see any associated maintenance cost, we could view this period as saving money.
The downside is reality. In reality, during the time we believe we are saving maintenance and capital cost, we are really spending more dollars than we would have under a different maintenance approach. We are spending more dollars associated with capital cost because, while waiting for the equipment to break, we are shortening the life of the equipment resulting in more frequent replacement. We may incur cost upon failure of the primary device associated with its failure causing the failure of a secondary device. This is an increased cost we would not have experienced if our maintenance program was more proactive.
Our labor cost associated with repair will probably be higher than normal because the failure will most likely require more extensive repairs than would have been required if the piece of equipment had not been run to failure. Chances are the piece of equipment will fail during off hours or close to the end of the normal workday. If it is a critical piece of equipment that needs to be back on-line quickly, we will have to pay maintenance overtime cost. Since we expect to run equipment to failure, we will require a large material inventory of repair parts. This is a cost we could minimize under a different maintenance strategy.
Preventive Maintenance: •Advancement on a breakdown maintenance program is a preventive program. •This periodic approach to maintenance has little continuous activity associated with it – It involves scheduling a regular outage, usually on an annual basis, where the entire machine train or plant is shutdown, or removed from production, for careful inspection and routine replacement of specific parts. •This method has the highest cost for replacement parts because the facility may have a separate program or department with the sole purpose of maintaining an inventory of spare parts and scheduling outage activity. Maintenance costs are reduced because the “annual outage” or “turn around” is usually scheduled for a period when the product demand is low. •Additional cost savings are realized because manpower and any heavy equipment are scheduled. Preventive maintenance can be defined as follows: Actions performed on a time- or machine-run-based schedule that detect, preclude, or mitigate degradation of a component or system with the aim of sustaining or extending its useful life through controlling degradation to an acceptable level. The U. S.
Navy pioneered preventive maintenance as a means to increase the reliability of their vessels. ?Advantages: • Cost effective in many capital-intensive processes. • Flexibility allows for the adjustment of maintenance periodicity. • Increased component life cycle. • Energy savings. • Reduced equipment or process failure. • Estimated 12% to 18% cost savings over reactive maintenance program. ?Disadvantages: • Catastrophic failures still likely to occur. • Labor intensive. • Includes performance of unneeded maintenance. • Potential for incidental damage to components in conducting unneeded maintenance.
Depending on the facilities current maintenance practices, present equipment reliability, and facility downtime, there is little doubt that many facilities purely reliant on reactive maintenance could save much more by instituting a proper preventive maintenance program. Predictive Maintenance: Predictive maintenance can be defined as follows: Measurements that detect the onset of system degradation (lower functional state), thereby allowing causal stressors to be eliminated or controlled prior to any significant deterioration in the component physical state.
Results indicate current and future functional capability. Basically, predictive maintenance differs from preventive maintenance by basing maintenance need on the actual condition of the machine rather than on some preset schedule. Activities such as changing lubricant are based on time, like calendar time or equipment run time. For example, most people change the oil in their vehicles every 3,000 to 5,000 miles traveled. This is effectively basing the oil change needs on equipment. ?Advantages: •Increased component operational life/availability. Allows for preemptive corrective actions. •Decrease in equipment or process downtime. •Decrease in costs for parts and labor. •Better product quality. •Improved worker and environmental safety. •Improved worker morale. •Energy savings. ?Disadvantages: •Increased investment in diagnostic equipment. •Increased investment in staff training. •Savings potential not readily seen by management. No concern is given to the actual condition and performance capability of the oil. It is changed because it is time.
This methodology would be analogous to a preventive maintenance task. If, on the other hand, the operator of the car discounted the vehicle run time and had the oil analyzed at some periodicity to determine its actual condition and lubrication properties, he may be able to extend the oil change until the vehicle had traveled 10,000 miles. This is the fundamental difference between predictive maintenance and preventive maintenance, whereby predictive maintenance is used to define needed maintenance task based on quantified material/equipment condition.
Reliability – Centered Maintenance: The Changing World of Maintenance: Over the past twenty years, maintenance has changed, perhaps more so than any other management discipline. The changes are due to a huge increase in the number and variety of physical assets (plant, equipment and buildings) which must be maintained throughout the world, much more complex designs, new maintenance techniques and changing views on maintenance organization and responsibilities. Maintenance is also responding to changing expectations.
These include a rapidly growing awareness of the extent to which equipment failure affects safety and the environment, a growing awareness of the connection between maintenance and product quality, and increasing pressure to achieve high plant availability and to contain costs. Maintenance people have to adopt completely new ways of thinking and acting, as engineers and as managers. At the same time the limitations of maintenance systems are becoming increasingly apparent, no matter how much they are computerized. Reliability – Centered Maintenance:
Since the 1930’s, the evolution of maintenance can be traced through three generations. RCM is rapidly becoming a cornerstone of the third generation, but this generation can only be viewed in perspective in the light of the first and second Generations. The First Generation: The First Generation covers the period up to World War II. In those days industry was not very highly mechanized, so downtime did not matter much. This meant that the prevention of equipment failure was not a very high priority in the minds of most managers. At the same time, most equipment was simple and much of it was over-designed.
This made it reliable and easy to repair. As a result, there was no need for systematic maintenance of any sort beyond simple cleaning, servicing and lubrication routines. The need for skills was also lower than it is today. The Second Generation: Things changed dramatically during World War II. Wartime pressures increased the demand for goods of all kinds while the supply of industrial manpower dropped sharply. This led to increased mechanization. By the 1950’s machines of all types were more numerous and more complex. Industry was beginning to depend on them.
As this dependence grew, downtime came into sharper focus. This led to the idea that equipment failures could and should be prevented, which led in turn to the concept of preventive maintenance. In the 1960’s, this consisted mainly of equipment overhauls done at fixed intervals. The cost of maintenance also started to rise sharply relative to other operating costs. This led to the growth of maintenance planning and control systems. These have helped greatly to bring maintenance under control, and are now an established part of the practice of maintenance.
Finally, the amount of capital tied up in fixed assets together with a sharp increase in the cost of that capital led people to start seeking ways in which they could maximize the life of the assets. The Third Generation: Since the mid-seventies, the process of change in industry has gathered even greater momentum. The changes can be classified under the headings of new expectations, new research and new techniques. Downtime has always affected the productive capability of physical assets by reducing output, increasing operating costs and interfering with customer service.
By the 1960’s and 1970’s, this was already a major concern in the mining, manufacturing and transport sectors. In recent times, the growth of mechanization and automation has meant that reliability and availability have now also become key issues in sectors as diverse as health care, data processing, telecommunications and building management. Greater automation also means that more and more failures affect our ability to sustain satisfactory quality standards. Finally, the cost of maintenance itself is still rising, in absolute terms and as a proportion of total expenditure.
In some industries, it is now the second highest or even the highest element of operating costs. As a result, in only thirty years it has moved from almost nowhere to the top of the league as a cost control priority. Maintenance and RCM: From the engineering viewpoint, there are two elements to the management of any physical asset. It must be maintained and from time to time it may also need to be modified. This suggests that maintenance means preserving something. On the other hand, they agree that to modify something means to change it in some way.
This distinction between maintain and modify has profound implications which are discussed at length in later chapters. However, we focus on maintenance at this point. The fact that every physical asset is put to service is because someone wants it to do something. In other words, they expect it to fulfill a specific function or functions. So it follows that when we maintain an asset, the state we wish to preserve must be one in which it continues to do whatever its users want it to do. Maintenance is simply is “Ensuring that physical assets continue to do what their users want them to do”.
What the users want will depend on exactly where and how the asset is being used. This leads to the following formal definition of Reliability-centered Maintenance: “Reliability-centered Maintenance is a process used to determine the maintenance requirements of any physical asset in its operating context In the light of the earlier definition of maintenance” “A process used to determine what must be done to ensure that any physical asset continues to do whatever its users want it to do in its present operating context. ”
RCM – The seven basic questions: The RCM process entails asking seven questions about the asset or system under review: ?What are the functions and associated performance standards of the asset in its present operating context? ?In what ways does it fail to fulfill its functions? ?What causes each functional failure? ?What happens when each failure occurs? ?In what way does each failure matter? ?What can be done to predict or prevent each failure? ?What should be done if a suitable proactive task cannot be found? Functions and Performance Standards:
Before it is possible to apply a process used to determine what must be done to ensure that any physical asset continues to do whatever its users want it to do in its present operating context, we need to do two things: Determine what its users want it to do ; ensure that it is capable of doing what its users want to start with. This is why the first step in the RCM process is to define the functions of each asset in its operating context, together with the associated desired standards of performance. What users expect assets to be able to do can be split into two categories: 1.
Primary functions: It summarizes why the asset was acquired in the first place. This category of functions covers issues such as speed, out-put, carrying or storage capacity, product quality and customer service. 2. Secondary functions: It recognize that every asset is expected to do more than simply fulfill its primary functions. Users also have expectations in areas such as safety, control, containment, comfort, structural integrity, economy, protection, efficiency of operation, compliance with environmental regulations and even the appearance of the asset. 3. Functional Failures:
The objectives of maintenance are defined by the functions and associated performance expectations of the asset under consideration. But how does maintenance achieve these objectives? The only occurrence which is likely to stop any asset performing to the standard required by its users is some kind of failure. This suggests that maintenance achieves its objectives by adopting a suitable approach to the management of failure. The RCM process does this at two levels: ?First, by identifying what circumstances amount to a failed state. ?Second, by asking what events can cause the asset to get into a failed state. . Failure Modes: As mentioned in the previous paragraph, once each functional failure has been identified, the next step is to try to identify all the events which are reasonably likely to cause each failed state. These events are known as failure modes. “Reasonably likely” failure modes include those which have occurred on the same or similar equipment operating in the same context, failures which are currently being prevented by existing maintenance regimes, and failures which have not happened yet but which are considered to be real possibilities in the context in question. . Failure Effects: The fifth step in the RCM process entails listing failure effects, which describe what happens when each failure mode occurs. These descriptions should include all the information needed to support the evaluation of the consequences of the failure, such as: What evidence that the failure has occurred ?In what ways it poses a threat to safety or the environment ? In what ways it affects production or operations ?What physical damage is caused by the failure ?What must be done to repair the failure. 6. Failure Consequences:
A detailed analysis of an average industrial undertaking is likely to yield between three and ten thousand possible failure modes. Each of these failures affects the organization in some way, but in each case, the effects are different. They may affect operations. They may also affect product quality, customer service, safety or the environment. They will all take time and cost money to repair. A great strength of RCM is that it recognizes that the consequences of failures are far more important than their technical characteristics.
The RCM process classifies these consequences into four groups, as follows: ?Hidden failure consequences: Hidden failures have no direct impact, but they expose the organization to multiple failures with serious, often catastrophic, consequences. Most of these failures are associated with protective devices which are not fail-safe . ?Safety and environmental consequences: A failure has safety consequences if it could hurt or kill someone. It has environmental consequences if it could lead to a breach of any corporate, regional, national or international environmental standard. Operational consequences: A failure has operational consequences if it affects production (output, product quality, customer service or operating costs in addition to the direct cost of repair) ?Non-operational consequences: Evident failures which fall into this category affect neither safety nor production, so they involve only the direct cost of repair. Failure management techniques are divided into two categories – ?Proactive tasks: These are tasks undertaken before a failure occurs, in order to prevent the item from getting into a failed state.
They embrace what is traditionally known as ‘predictive’ and ‘preventive’ maintenance, although we will see that RCM uses the terms scheduled restoration scheduled discard and on-condition maintenance. ?Default actions: These deal with the failed state, and are chosen when it is not possible to identify an effective proactive task. Default actions include failure-finding, redesign and run-to-failure. RCM divides proactive tasks into three categories, as follows: •Scheduled restoration tasks. •Scheduled discard tasks. •Scheduled on-condition tasks. ?Scheduled restoration and scheduled discard tasks: Scheduled restoration entails remanufacturing a component or overhauling an assembly at or before a specified age limit, regardless of its condition at the time. •Similarly, scheduled discard entails discarding an item at or before a specified life limit, regardless of its condition at the time. •Collectively, these two types of tasks are now generally known as preventive maintenance. •They used to be by far the most widely used form of proactive maintenance. •However for the reasons discussed above, they are much less widely used than they were twenty years ago. Scheduled On-condition tasks: •The continuing need to prevent certain types of failure, and the growing inability of classical techniques to do so, are behind the growth of new types of failure management. •The majority of these techniques rely on the fact that most failures give some warning of the fact that they are about to occur. •The new techniques are used to detect potential failures so that action can be taken to avoid the consequences which could occur if they degenerate into functional failures.
They are called on-condition tasks because items are left in service on the condition that they continue to meet desired performance standards. RCM recognizes three major categories of default actions: ?Failure-finding: Failure-finding tasks entail checking hidden functions periodically to determine whether they have failed (whereas condition-based tasks entail checking if something is failing). ?Redesign: Redesign entails making any one-off change to the built-in capability of a system. This includes modifications to the hardware and also covers once-off changes to procedures. No scheduled maintenance: As the name implies, this default entails making no effort to anticipate or prevent failure modes to which it is applied, and so those failures are simply allowed to occur and then repaired. This default is also called run-to-failure. Level of Repair Analysis: Introduction: Level of Repair Analysis (LORA) is used by the United States Department of Defence as an analytical methodology used to determine when an item will be replaced, repaired, or discarded based on cost considerations and operational readiness requirements.
Process: •LORA analysis establishes who and where each unit will be repaired and determines if it is more cost effective to discard an item than attempt to repair it. •While this kind of analysis seems costly and unnecessary, at enterprise scales over many years, significant cost savings can be realized. •For example, the LORA process may discover that replacing a part actually costs hundreds of times that amount, when all cost are considered (maintenance manpower, warehousing facilities, shipping, etc. ).
If this part is replaced hundreds of times per year, over the course of many years, then there may be an opportunity to save money by adjusting the repair process to leverage this economy of scale (reliability improvements, component repair, etc). •This analysis drives the maintenance support for each repairable unit analyzed. LORA is the most important physical supportability analysis business decision made during acquisition of a system. •The LORA process starts by identification of the options where maintenance can be performed.
It is common for systems to use 2 or 3 levels of maintenance. LORA produces a decision for each item within the system, indicating where each maintenance action for the item will be performed. Systems in Manufacturing Manufacturing System Defined “A collection of integrated equipment and human resources, whose function is to perform one or more processing and/or assembly operations on a starting raw material, part, or set of parts” Equipment includes •Production machines and tools •Material handling and work positioning devices •Computer system
Manufacturing System is been divided into four ways: Is all manufacturing the same? For most people, the word will conjure up pictures of production and assembly lines making very large numbers of products – such as motor cars, televisions, compact discs, clothes and so on. You may wish to ask the following questions: * Is the type of manufacturing system used to produce cars the same as the one that makes jeans? * Is a ball-point pen made in the same way as the furniture in your home? * Are manufacturing systems the same across the world – in different countries and cultures?
Because of the very broad range of products that are manufactured, several different types of manufacturing system have evolved. Each system meets the unique demands and characteristics of the product and the market in which it will eventually be sold. There are a number of ways in which manufacturing systems can be classified: a. Process or continuous production: This is where the plant or factory may run twenty-four hours a day, for weeks or months on end, stopping only for maintenance or when breakdowns occur.
This type of production is normally found in industries such as chemical processing, food production and steel making, and in China for example, with the making of chopsticks. Products that depreciate quickly, or are in high demand are often continuously produced. The output from the plant is normally expressed in weight or volume of goods produced, rather than in numbers of products made. The cost of the equipment used in this form of production is likely to be very high, as it is likely that it will have been made specially.
Because many of these processes are automated, labour costs are generally low. Most of the operations undertaken in mass production are repetitive and can become very tedious for human workers, who may feel they have little decision-making power or control over the outcome of the final product. Bored or disillusioned workers are likely to make mistakes. Many companies have made great investments of time and money to enhance the quality of work life for their operators by using a system of job rotation, and through making teams of workers responsible for the quality of what they produce.
Quality circles are composed of groups of workers who meet on a regular basis to discuss and solve quality problems. They investigate causes of faults, recommend changes, and then take corrective action. In this way, workers are motivated to take pride in their work and become involved in maintaining quality standards. Waste from defectively made products is reduced dramatically, whilst productivity and quality are increased. Robots are used increasingly for manufacturing and assembly tasks – they produce more consistent quality, are generally faster, do not become tired or ask for holidays! ) Mass production: Large quantities are againinvolved in mass production, but in this case it is individual products that are manufactured – for example, motor cars, ‘white goods’ such as refrigerators and washing machines, personal stereo systems etc. As with continuous production, highly specialised and therefore expensive machines are used. The variety of the product manufactured is kept to a minimum where possible to minimise any changes necessary to the tooling, which will take time and therefore cost money.
Most of the operations undertaken in mass production are repetitive and can become very tedious for human workers, who may feel they have little decision-making power or control over the outcome of the final product. Bored or disillusioned workers are likely to make mistakes. Many companies have made great investments of time and money to enhance the quality of work life for their operators by using a system of job rotation, and through making teams of workers responsible for the quality of what they produce.
Quality circles are composed of groups of workers who meet on a regular basis to discuss and solve quality problems. They investigate causes of faults, recommend changes, and then take corrective action. In this way, workers are motivated to take pride in their work and become involved in maintaining quality standards. Waste from defectively made products is reduced dramatically, whilst productivity and quality are increased. Robots are used increasingly for manufacturing and assembly tasks – they produce more consistent quality, are generally faster, do not become tired or ask for holidays!
In mass production systems equipment, labour and supply of materials and components are highly organised (increasingly through the use of computers to monitor and control processes) to ensure a smooth flow of work through the factory and thereby minimise the cost of making each product. (c) Batch production: This type of manufacturing makes products in specific quantities. These made be made in one production run, or in batches to be repeated at certain times. A batch can range from 2 or 3 products to a hundred thousand or more.
Aircraft are produced using small batch production – agricultural machinery, furniture, machine tools, buses and lorries (other examples needed here) are made in larger numbers. In a batch production manufacturing system, each piece of equipment may be used to make several different products. This means that the machinery used must be far more versatile than that used in mass production. The workers who operate them are likely to be more skilled. In an attempt to increase versatility and flexibility in batch production processes, manufacturing cells are increasingly used.
Manufacturing cells are normally groups of machines, normally involving sheet metal forming or machining operations, with each piece of equipment performing a different operation on a component. The machines can be retooled and regrouped for different product lines within the same family of parts. The cells are typically attended by one operator overseeing the group of machines, although increasingly they are becoming computer controlled, employing robots for materials handling. In a large factory, many batches of different products of varying quantities, scheduled for different customers and delivery dates, will be processed at any one time.
This can pose some serious problems of planning involving the use of machines and the personnel to operate them if orders are to be met on time. The use of computer controlled machines and computerised production control and management systems are increasingly used in an attempt to bring down the costs of production. Systems that are able to respond quickly and effectively to changes in product manufacture are known as flexible manufacturing systems. FMS integrates all the major elements of manufacturing into a highly automated system.
It normally consists of a number of manufacturing cells, each containing an industrial robot serving several CNC machines, and an automated materials handling system – all linked to a central computer. FMS systems are highly automated and are capable of optimising each step of the total manufacturing operation. These steps may include one or more operations or processes, such as machining, grinding, cutting, forming, heat treatment and finishing, as well as handling raw materials, inspection and assembly. These automated systems of batch production are able to operate on a continuous basis. ) Jobbing production: Also known as custom manufacturing. This system of manufacturing produces normally one product at a time, normally to a single customer’s specification. Highly skilled workers and general purpose equipment are used. Problem-solving and trouble- shooting are necessary because each product presents new challenges. Products that are custom-manufactured are normally very expensive, and might include large yachts, space satellites, oil rigs and special purpose machine tools. Just-in-Time (JIT) anufacturing is a system that can be applied to continuous, mass, batch and jobbing production. JIT was developed in Japan to eliminate the waste of materials, machines, labour, money and stocks held (known as ‘inventory’) throughout the manufacturing system. The JIT idea has the following goals: • purchase supplies of materials and components from outside suppliers just in time to be used • produce parts just in time to be made into subassemblies • produce subassemblies just in time to be assembled into finished products. • produce and deliver finished products just in time to e sold. Using JIT principles means that the sizes (or ‘lots’) of materials and components purchased or manufactured are likely to be smaller. It is therefore easier to spot any defects or faults. The advantages of using JIT are: • low costs associated with inventory (stocks held on shelves) • fast detection of defects in production or in delivery of supplies, and lower scrap loss • reduced need to inspect parts to ensure they meet specification • less reworking of parts • high quality parts at low cost. COMPUTER -INTEGRATED MANUFACTURE
Computers are now used in many ways in the design and manufacture of products. With sophisticated hardware and software, manufacturers are now able to: • improve product quality • minimise manufacturing costs • reduce product development time • make better use of materials, people and machinery • maintain a competitive edge in the domestic and international marketplace Where the traditionally separate functions of research and development, design, production, assembly, inspection and quality control are all linked through the use of information technology, this is known as computer integrated manufacturing.
It is not just the use of computers that is important – it is the way that a company’s operations are planned and integrated that brings success. Elements of a computer integrated systems include: • computer-aided design and draughting (CADD) – allows for the conceptualisation of new products more easily • computer-aided manufacture (CAM) – involves monitoring and controlling the manufacturing operations • computer-aided process planning – (CAPP) such as estimating costs or the time taken to perform a certain manufacturing operation • management information systems for marketing, finance, payroll etc.
CHOOSING AN APPROPRIATE TYPE OF MANUFACTURING SYSTEM Choosing the most appropriate type of manufacturing system for a particular product will depend upon the following factors: • the volume (quantity) to be produced • availability of necessary equipment and machinery, or appropriately skilled workers • the type of product to be made • the life cycle or durability of a product • the production philosophy of the organisation