In modern production systems, the product, or the ser- vice, and the maintenance requirements are major out- puts: that is to say, in parallel with the production process is the maintenance process. Maintenance is a system whose activities are carried out in synergy with those of the production systems. Figure 4.3 shows the relationship between different objectives relating to these processes. Production systems usually con- vert inputs (raw materials, energy, workload, etc.) into a product that satisfies customer needs. The mainte-
4The European Standard CEN/TR 15628:2007 Maintenance – qualification of maintenance personnel classifies three differ- ent categories of maintenance personnel: the European Main- tenance Technician, the European Maintenance Supervisor, and the European Maintenance Manager. All categories are charac- terized in terms of competences and responsibilities.
Planning
Execution
Control &
supervision
Objectives
Strategies
Responsabilities
Input
Feedback
Improvements and revisions
Resources
Services
Management
Maintenance support system
Fig. 4.2 Maintenance management
Fig. 4.3 Production and maintenance processes.
(Duffuaa et al. 1999)
PRODUCTION
PROCESS OUTPUT
FEEDBACK
MAINTENANCE NEED INPUT
PRODUCTION CAPACITY
MAINTENANCE PROCESS
nance system, as a mix of know-how, labor, and spare parts, together with other resources aims to maintain equipment in a good working order, i. e., able to pro- vide the appropriate level of production capacity. In a maintenance system, feedback control, planning, and organization activities are very critical and strategic issues. The first of these deals with the production sys- tem and control of maintenance activity (e. g., work- load emission, spare parts management).
Consequently, various actions must be taken to con- trol production and maintenance activities and to re- solve breakdowns. Moreover, these activities must be planned in advance whenever possible. Clearly the first aim of maintenance action in downtime periods, dur- ing an unexpected breakdown, is to put the plant back into working order: the planning phase is skipped and
the maintenance work is carried out as soon as pos- sible. This is breakdown/corrective maintenance. In this situation the maintenance work must be completed quickly, or must be postponed until the next stop, sim- ply leaving the system to run till the next scheduled recondition. In this second case, the definitive mainte- nance work is scheduled in a previously planned stop period.
Maintenance activities are so numerous and com- plex that they require effective management and well- structured organization. The starting point is the syn- chronized control of the production system that not only involves monitoring equipment but also mainte- nance control, planning, and organization, with a lot of subactivities. This is illustrated in Fig. 4.4 and sum- marized as follows:
MAINTENANCE PROCESS
INPUT OUTPUT
FEEDBACK CONTROL
PLANT CONTROL WORK CONTROL INVENTORY CONTROL COST CONTROL QUALITY CONTROL PLANNING
MAINTENANCE PHILOSOPHY MAINTENANCE LOAD FORECASTING MAINTENANCE CAPACITY
MAINTENANCE ORGANIZATION
ORGANIZATION JOB DESIGN TIME STANDARDS WORK MEASUREMENT PROJECT MANAGEMENT
FACILITIES LABOR EQUIPMENT SPARES MANAGEMENT
OPERATIONAL MACHINES EQUIPMENT
MONITORING
Fig. 4.4 Characteristics of the maintenance process. (Duffuaa et al. 1999)
• Plant control. Control of system performance relia- bility and collection of on-field data for breakdowns and repair processes by the application of sensors or human checks.
• Work control. The maintenance workload is influ- enced by the maintenance strategy adopted and is supported by well-designed control of the workload based on an effective reporting system.
• Inventory control. This activity deals with spare parts management and with all the tools and equip- ment used in maintenance work.
• Cost control. Maintenance usually consumes large amounts of money. There are two fundamental cost factors: the direct cost of investment, i. e., invest- ment in production resources (e. g., plant, equip- ment, employees), and indirect costs caused by lack of production. It is extremely important to have an effective and continuous cost control process.
• Quality control. The main aim of quality assur- ance of a process or a product is to measure several variables representing a range of specifications, as stated by the Six Sigma quality strategies, for ex- ample, and policies applied to production/logistic system management and optimization.
The check and control process of the production system generates a large amount of useful data for planning the maintenance work. In particular, during the maintenance planning process it is necessary to as- sume some decisions involving:
• Maintenance philosophy. Several maintenance policies have been developed by practitioners and are discussed in the literature (see Chap. 9). Since no strategy is significantly more effective than the others, this problem usually deals with the identification of the best mix of strategies and policies in order to obtain the best global result (e. g., minimization of production costs).
• Maintenance load forecasting and capacity. Main- tenance requires the simultaneous use of several re- sources (e. g., manpower, spare parts, equipment).
Consequently, the load forecasting process is essen- tial to obtain the desired level of maintenance sys- tem performance. Critical aspects of maintenance capacity include the identification of the optimum number of craftsmen and their skills and the main- tenance of the required tools.
After the control and planning of maintenance pro- cesses has been carried out, the next step is to design the maintenance system correctly. This requires the in- tegration of several aspects:
• Job design. A variety of complicated tasks, called
“jobs,” are usually required to maintain a produc- tion system. Each job must be designed correctly.
The most important instrument for job design and management is the maintenance work order (illus- trated in detail in Chap. 7): it contains all the de- tails of the work required, e. g., its location, and all the skills and tools required. The work order is the
main instrument used in monitoring, planning, and reporting all maintenance activities. Moreover, in maintenance job design the evaluation of the du- ration of a generic activity is an extremely criti- cal issue. To measure and estimate this duration, method time measurement and the Maynard opera- tion sequence technique are two examples of effec- tive decision-supporting tools.
• Work measurement. Each maintenance job requires various resources and generates costs. The target of the workload analysis is to evaluate and control these costs. The ultimate aim of the maintenance process is to minimize the total cost of the produc- tion system.
• Project management. Maintenance activities are frequently part of a general development plan for the production system. Project management tech- niques are very useful in supporting the mainte- nance planning activities and effecting maintenance work (Gantt charts, critical path methods, program evaluation review technique, heuristics for project scheduling and sequencing).
In conclusion, the monitoring phase is the starting point of all maintenance activities. In particular, the performance measurement of a production system can be effectively supported by reliability and availability theory and evaluation.