5. The 7 Steps of Effective Maintenance
There are considerable differences in the way different companies tackle Effective Maintenance. A company that already has an excellent maintenance system will implement it differently from a company that has been working all-out to meet a high level of demand and has not had the time or resources to put much of a maintenance system in place.
Companies that find themselves in the second situation usually struggle to understand what they should do first. In such a case, the use of a pilot model line is strongly recommended.
5.1 Selecting a Model Line
The purposes of introducing the activities on a model line are threefold:
(1) To raise the maintenance engineers’ awareness of what Effective Maintenance entails
(2) To educate the operating department
(3) To achieve concrete results (fewer failures, etc.)
Also, since it is impractical for all of the maintenance engineers to be involved in the model line activities, a special team should be formed with the numbers available.
The next step is to select the model line. Bearing in mind the purposes listed above, the model line should be selected from the following standpoints:
(1) How badly the equipment has deteriorated
(2) The number of machines (the size of the line)
(3) The importance of the line for production
(4) The level of skill of the maintenance engineers (5) The number of people in the team
(6) The level of Autonomous Maintenance on the line
Taking these five factors into account, it is important that the maintenance engineers get hands-on experience and treat the model line activities as an essential part of their duties. For this reason, the model line should be selected only after careful consideration of the role and workload of each person in the team.
5.2 The Step-by-Step Approach
The steps involved in the activity will now be explained in detail. This practical programme for reducing failures consists of five strategies implemented in five phases, expressed in the form of seven steps.
The seven steps are intensely practical – the important thing is to work out precisely what needs to be done. This is essential, because no action takes place on the basis of abstract thinking alone.
Step 1: Assess the current situation
This activity could be described as initial cleaning by maintenance engineers; as well as identifying every minor equipment defect that could be a source of failure, it enables them to check for themselves through failure analysis the reasons why each failure was bound to occur. It also allows them to develop their understanding of how the equipment is constructed and how it works.
(2) Main activities
- Identifying and correcting visible and hidden equipment defects
- Tagging minor equipment defects and removing the tags by correcting the defects or improving the equipment (simple defects are rectified at this step)
- Analysing failures (in particular, stratifying the causes of failures)
− Analyse each failure on a separate sheet of paper and classify its cause as inadequate basic conditions, inadequate operating conditions, insufficient restoration, leaving deterioration untended, sporadic failure, design weakness, maintenance error, operating error, etc.
- Monitoring the number of tags applied and removed
- Collecting baseline data on number of sporadic failures, quality defect rates, MTBF and MTTR
- Using failure maps
- To lead into Step 2, formulating an improvement plan for the equipment defects identified
By identifying concealed and obvious equipment defects and analysing failures, find out what kinds of failures are concentrated on which parts of the equipment, and acquire hands-on experience of the extent of the deterioration under which the equipment is being operated. Also, to lead into Step 2 by formulating an improvement plan for the equipment defects identified.
Step 2: Reverse deterioration and eliminate weaknesses
To restore the equipment and make improvements in order to eliminate the problems identified in Step 1. To continue analysing failures and painstakingly tracking down their causes to ensure they can be prevented from recurring. Also, carrying out corrective maintenance to prolong the lifetimes of short-lived sections and components at the same time as raising the level of maintenance skill.
(2) Main activities
- Eliminating forced deterioration and correcting existing deterioration. Think about restoring before improving.
- Painstakingly tracking down the causes of failures (using techniques such as Why- Why Analysis, FTA, FMEA, and P-M Analysis)
- Ensuring that no failures can recur
- Carrying out corrective maintenance to prolong the lifetimes of short-lived sections and components
- Considering handing over responsibility for some checks to Autonomous Maintenance
- Stratifying restoration and improvements, and monitoring progress against plans Improving the maintenance department’s maintenance skills
- Identifying which parts are to be maintained by means of standards (leading into Step 3)
In this step, the equipment is brought back into tip-top condition through restoration and improvement, and failures and quality defects are reduced dramatically. Short-lived components are also made to last longer through corrective maintenance.
Step 3: Set specialized maintenance standards and help the operating department to establish provisional Autonomous Maintenance standards
To keep the equipment in the improved condition achieved in Steps 1 and 2, the maintenance work must be organised in the form of standards. Preventive maintenance is then started in accordance with these. To begin with, periodic (time-based) maintenance is used.
(2) Main activities
- Examine each machine in turn and identify the parts that should be subjected to preventive maintenance
- Also identify everything that needs to be cleaned, lubricated, or otherwise attended to as part of routine daily maintenance
- Draw up a preventive maintenance (mainly periodic maintenance) standard for each machine
- Specify exactly what the operators are supposed to do under Autonomous Maintenance and what the maintenance engineers are supposed to do under Effective Maintenance
- Start by using provisional standards for checking and replacement intervals
- Prepare a maintenance calendar and begin faithfully implementing whatever has been decided
The main task in Effective Maintenance is to overhaul the equipment based on the results of checking and inspecting it. Begin by identifying the routine daily maintenance tasks that must be performed (including cleaning and lubricating), and clearly indicate on the standards who is responsible for carrying out these tasks. Preventive maintenance should start with periodic (time-based) maintenance; the first thing that needs to be done is to set up and begin implementing a system for maintaining the equipment and replacing parts at specified intervals.
Step 4: Take action against equipment weaknesses
Although we start by trying to eliminate ‘function-stoppage failures’ (catastrophic failures that cause a machine to stop working entirely), our eventual goal is also to eliminate ‘function-reduction failures’ (failures where the machine keeps on working but at a lower level of performance). In other words, we want to maintain the equipment in such a way as to eliminate product quality defects as well as breakdowns. In this step, we identify the relationships between quality defects and the functional sections or components of the machine, and try to restore these sections or components to perfect condition by comprehensive checking and overhauling. This is what is meant by performing quality maintenance.
(2) Main activities
- Continue to deepen the understanding of how the equipment is constructed and how it works
- Learn how, and in accordance with what principles, the machine processes the product
- Perform a comprehensive inspection with the aim of identifying minor defects in everything associated with the equipment, including jigs, tools, fixtures and so on
- Clearly understand the product’s quality characteristics
- Keep investigating until all the equipment components that determine the quality of the product (i.e. the parts to be maintained) have been identified.
- In practice, this means pinpointing the quality components through the use of P-M Analysis
Given that quality is built into the product by the equipment, it is clear that equipment maintenance must also have a significant effect on product quality. In this step, it is important to identify the relationships that exist between the equipment’s functional sections and components and the quality characteristics of the product. From now on, equipment maintenance must incorporate quality maintenance in accordance with these principles. P-M Analysis is a particularly powerful tool for clarifying the relevant relationships.
Step 5: Make checking and overhauling more efficient
To ensure that preventive maintenance (principally periodic maintenance) is faithfully carried out and reduce the labour-hours required, by adding maintenance tasks relating to the quality function sections and components identified in Step 4 into the provisional standards prepared in Step 3, and making these tasks easier and more efficient to complete.
(2) Main activities
- Draw up a QM Matrix showing the relationships between quality defects and equipment functions
- Ensure that all the items to be maintained and controlled are incorporated into the Effective Maintenance and Autonomous Maintenance standards and faithfully implemented
- Improve awkward checks to make them easier to perform
- Continue to develop the maintenance calendar, consolidate checks (integrate several checks into a single one to reduce their number), and extend the intervals between checks
- Increase reliability by increasing the number of periodic maintenance items on the basis of deterioration measurements
- Reduce maintenance costs by overhauling at the unit level and only replacing those parts that have deteriorated beyond the acceptable limit
- Reduce the time and cost of overhauls by standardising parts, etc.
- Begin researching and utilising commercially-available diagnostic equipment
- Promote various management techniques (spare-parts management, maintenance planning management, maintenance information management, maintenance budget management, etc.)
This step consists of putting together a system for the maintenance tasks and effecting improvements to streamline those tasks. A programme of inspection and repair is rolled out in accordance with monthly and weekly maintenance schedules based on a maintenance calendar. In conjunction with this, various management activities (spare- parts management, maintenance planning management, maintenance information management, maintenance budget management, and so on) for promoting Effective Maintenance are carried out. The study of predictive maintenance is also commenced with a view to compensating for the weaknesses in periodic maintenance.
Step 6: Perform comprehensive equipment diagnoses
In this step, equipment diagnostics are employed to add predictive maintenance to the maintenance mix in order to monitor trends in the state of deterioration of the equipment and identify the optimal point in time for maintenance. Predictive maintenance is used for sections of the equipment that have failed seriously in the past or that would cause serious damage if they failed now.
(2) Main activities
- Identify sections of the equipment that have failed seriously in the past or that would cause serious damage if they failed now
- Identify the parts of each machine that are to be subjected to predictive maintenance
- Find out what diagnostic equipment is available on the market and make use of it
- Study the patterns of natural deterioration and the parameters available for measuring it
- Use simple diagnosis to perform trend monitoring and periodically carry out precision diagnosis. Monitor the data.
- Try to develop the company’s own original diagnostic devices (using various types of sensor)
- Begin by using vibration diagnosis to detect abnormal levels of vibration
- Develop equipment diagnostic experts
- Train all maintenance engineers in equipment diagnostics
The main purpose of predictive maintenance is to assess how much longer a piece of equipment is going to keep working for. As well as using hands-on activities to develop the ability to judge how much life is left in a machine or component, the subject should be studied thoroughly in order to acquire the ability to develop the best possible diagnostic techniques for the company.
Step 7: Implement predictive maintenance and roll out to other equipment
The programme is then rolled out to all the equipment that requires it, based on the experience and results obtained so far. To accomplish this effectively, the focus should be kept on the key points of the steps carried out so far. In other words, the level of restoration and improvement of the equipment should be checked, maintenance standards should be formulated, and time-based and predictive maintenance applied to the parts that need it.
(2) Main activities
- The maintenance department prepares inspection and maintenance standards for all existing equipment that requires them
- The rollout procedure is as follows:
- Survey the level of restoration and improvement of the equipment being addressed
- Painstakingly improve any parts that have been neglected or have not been dealt with satisfactorily
- Identify every item to be checked, including those relating to product quality
- Prepare the inspection and repair standards
- Put together a maintenance calendar and carry out preventive maintenance
- Implement the maintenance standards as far as possible on all equipment that requires them
- Continue to maintain the equipment in accordance with the standards while progressively enhancing those standards
The lines that require this approach include all equipment subject to preventive maintenance as identified when the equipment was prioritised.
5.3 Horizontal Replication of Equipment Management and Quality Management to Other Lines
Only half the potential results will be achieved if Effective Maintenance is not pursued hand-in-hand with Autonomous Maintenance. The results achieved on the model line should be rolled out to other lines only after full consensus has been achieved with the operating department about who is to be responsible for which tasks. In practice, however, this has to be done while still attempting to cope with a high level of sporadic breakdowns.
The matrix shown below indicates what is being controlled under Effective Maintenance and Quality Maintenance, and the method of controlling it, from the equipment management and quality management aspects. This matrix also reinforces the point that the principal feature of Quality Maintenance is keeping quality defects at zero.
6 Activities within Effective Maintenance
6.1 Examples of Activities within Effective Maintenance
Effective Maintenance is a comprehensive programme that brings together a wide range of different maintenance activities under a single umbrella. An example of this is shown below. MP information management, spare-parts management and predictive maintenance are outlined separately.
The Structure of an Effective Maintenance system
6.2 A System for Maximising Production Effectiveness
Figure 6.29 Example of a System For Maximising Production Effectiveness
6.3 Spare Parts Management
6.3.1 The aims of spare parts management
The basic aims of spare parts management are listed below, although the way it is implemented must be tailored to the specific characteristics of the factory.
(1) Promote improvements such as standardisation and unitisation of components, longer working life, and better reliability, as an integral function of spare parts management.
(2) To minimise downtime, ensure that parts required for breakdown repairs or planned maintenance are always available and ready for use.
(3) Cut stock levels, prevent deterioration of parts in stock, and seek to reduce purchasing and storage costs, through effective management of technology and materials.
6.3.2 Classification of spare parts, and storage and restocking methods
Figure 6.30 shows a system for classifying spare parts, and available storage and restocking methods aimed at achieving the above objectives. As the figure shows, stock levels and purchasing costs should be minimised by using restocking and purchasing methods such as consignment stocks, periodic restocking visits by suppliers, ad-hoc ordering based on unit-cost agreements, and so on.
6.3.3 Some common problems with spare parts management, and hints for solving them
(1) Spare parts are often stored chaotically in separate departments, and new ones are mixed up with worn-out ones. The first step is to identify all unnecessary items and remove them.
(2) Reusable parts should always be refurbished before ordering new ones.
(3) Each part used should be considered to decide whether it should be kept permanently in stock or not, based on the following guidelines (see Figure 6.31):
- Components required for unexpected breakdowns should be kept permanently in stock unless a standby machine is available.
- As a rule, any spare part that can be planned for in advance should not be kept permanently in stock. However, if a part is used more than 3 or 4 times a year, it should be kept permanently in stock in order to reduce purchasing costs. Any parts whose delivery lead time is longer than the planned maintenance interval should also be kept permanently in stock.
- Refurbished parts should be kept permanently in stock for use as spares.
(4) Deciding order points, order quantities and order numbers required for routine management of permanently stocked parts
Maintenance materials can be managed on a fixed-quantity or fixed-number basis, depending on the form they take and how they are consumed. Fixed-number management is more common. To avoid stock-outs, it is particularly important to set the minimum stock levels at values that allow for the maximum foreseeable variations in amounts used and delivery lead times. The maximum stock level is determined by the minimum stock level plus an order volume set according to the purchase frequency. If problems with parts storage are to be spotted and dealt with at an early stage, then the actual storage locations must be clearly labelled, showing the order points, order quantities and order numbers (see Table 6.10).
(5) Storage locations
These should be set up for ease of use, to minimize transportation and handling. The frequency of use and restocking system employed for each part should be taken into account when deciding where it is to be stored. Specialized parts unique to a particular machine should be kept as close as possible to that machine. Duplication of storage should be avoided by having a centralized system for large common parts and a distributed storage system (with satellite stores in different locations) for small items.
Figure 6.31 Deciding which Parts to Keep Permanently in Stock
Table 6.10 Consumption Models and Corresponding Standards
(6) To reduce purchasing administration and storage costs, it is desirable to advance the purchasing and supply system, wherever possible, from ad-hoc ordering based on unit cost agreements, to periodic restocking visits by suppliers, to supplier-owned storage systems, and finally, to supplier outlet systems. Management and purchasing costs should be reduced as indicated by flow diagrams (1) (2) and (3) in Figure 6.32.
(7) Efforts should be made to standardise component configurations, dimensions and manufacturers, and reduce the variety of components used.
(8) Identifying the equipment where each and every component is used would generate excessive processing costs, so this should only be done for larger commercially available components and materials. For such items, the relevant equipment and the required quantity should be noted on memos, which can then be used to sort items according to where they are to be used, when accepting delivery of parts orders at the end of the month. This need not be done for parts unique to particular equipment, as it is obvious where these are to be used. In either case, if the location where the part is to be used is identified when processing orders, the resulting data can be used effectively in managing the equipment budget. To reduce the administrative workload, small commercially available components and materials should be treated as a common item in the equipment budget, rather than being specifically assigned to the equipment where they are used.
Figure 6.32-(1) Flowchart for Managing Long Reels of Material, Using Fixed-Quantity System
Figure 6.32-(2) Flowchart for Managing Nuts and Bolts, Using Double-Bin System
6.4 Lubrication Management
Approximately 40% of machine elements are subject to rubbing and friction of some kind, and correct application of the right lubricants to these parts serves, among other things, to:
(1) Reduce friction (and hence reduce loss of power)
(2) Ensure smooth sliding movement
(3) Prevent wear
(4) Prevent overheating and seizure
(5) Provide a cooling effect
(6) Remove dirt and debris from rubbing surfaces
(7) Prevent corrosion and erosion
(8) Prevent noise and vibration
Proper lubrication can therefore help to prevent equipment underperformance or failure, as well as increasing productivity and reducing operating and maintenance costs, thereby delivering tangible economic benefits. In practice, wear, deterioration or failure of equipment can often be traced, directly or indirectly, to lubrication problems (see Figure 6.33).
Managing lubrication means managing materials and technology. Lubrication materials management involves purchasing, receiving and storing the required lubricants, paying for them, and disposing of them after use. Lubrication technology management, on the other hand, means observing the four basic rules of lubrication (using the correct lubricant, in the correct amount, by the correct method, and at the correct time), and is therefore applied on the shop floor. Some common problems relating to lubrication are discussed below, together with possible solutions.
Figure 6.33 Equipment Failures
6.5 Predictive Maintenance
6.5.1 Predictive maintenance and equipment diagnostics
Many of the machines and components of which production plant is composed, fail as a result of initial defects or sudden deterioration, or because they have come to the end of their working life. Even if they do not break down completely, their performance may decline. Failure or underperformance of this kind causes loss of production functions, with consequent effects on production efficiency, product quality and yield, and resource consumption. This can result in significant losses, so it is essential to control and sustain the performance of production equipment, and improve it where possible, during the course of regular production activities. The following maintenance methods are generally used to achieve this:
(1) Breakdown maintenance
(2) Preventive maintenance
(3) Corrective maintenance
(4) Maintenance prevention
(5) Predictive maintenance
The decision as to which of these maintenance regimes to adopt is determined by considerations such as the basic corporate philosophy, the scale of the production equipment, and the quality and quantity of labour available. In the past, firms generally tended to employ breakdown maintenance, but most have now progressed to preventive or predictive maintenance. They now monitor the state of deterioration of their production equipment and act in advance to ensure that it remains in good condition, thus preventing it from failing. They also do their best to keep up with the times by continually improving and upgrading their equipment based on the latest technological advances, allowing it to perform even better, deliver even better product quality and be maintained more effectively.
Nevertheless, a review of how preventive maintenance is actually implemented in most companies reveals that they have difficulty in determining the right intervals for equipment overhaul and repair, resulting either in over-maintenance or in unexpected breakdowns. The concept of predictive maintenance arose from the need to resolve this situation. In predictive maintenance, the mechanisms of equipment failure and deterioration are investigated in great detail, the condition of the equipment during operation is assessed, and the maintenance work done on the equipment is tailored to suit its condition. In other words, potential failures due to deterioration that demonstrates identifiable trends are predicted and dealt with before they can become actual ones.
Advances in the research and development of equipment diagnostics (see Table 6.11), a key tool for implementing predictive maintenance effectively, are encouraging a general move towards predictive maintenance nowadays. Nevertheless, when deciding what type of maintenance approach to adopt, a good balance must always be sought between the amount that has to be invested in maintenance and the profits that can be gained from production.
Table 6.11 Principal Diagnostic Techniques and their Functions
Table 6.12 Predictive Diagnostic Techniques
Table 6.13 Predictive Diagnostics and Applicable Equipment
Chapter 7. Early Equipment Management. Part 1