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Operation Management
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Lecture # 7:Lecture # 7:
MAINTENANCE & RELIABILITYMAINTENANCE & RELIABILITY
Humayun Akhtar Awan
RIPHAH INTERNATIONAL UNIVERSITY, ISLAMABADRIPHAH INTERNATIONAL UNIVERSITY, ISLAMABAD
OPERATIONS MANAGEMENTOPERATIONS MANAGEMENT
Columbia, Discovery, Atlantis, Endeavour Example of RELIABILITY failure: Challenger in 1986 (NASA almost shut down) Columbia has done 86 million miles, but is scheduled for 77 more voyages till retirement Maintenance requires scheduling for 01 million moving parts to ensure reliability 600 computer generated maintenance jobs, with hundred of tasks during three month turn around period between flights
NATIONAL AERONAUTICS & SPACE NATIONAL AERONAUTICS & SPACE ADMINISTRATIONADMINISTRATION SPACE SHUTTLE SPACE SHUTTLE
PROGRAMMEPROGRAMME
INTRODUCTIONINTRODUCTION The results of failure can be disruptive, inconvenient,
wasteful and expensive in terms of money & human lives Machine and product failures can have far-reaching
effects on an organization’s operation, reputation and profitability, whether it is an office or production floor
The objective of maintenance and reliability is to maintain the capability of the system while controlling costs. A good maintenance system drives out system variability
Maintenance Maintenance includes all activities involved in keeping a system’s equipment in working order
Reliability Reliability is the probability that a machine part or product will function properly for a specified time under stated conditions
Interdependency of operator, machine and mechanic is a hallmark of maintenance and reliability
RELIABILITYRELIABILITY Systems are composed of a series of individual
interrelated components, each performing a specific job. If any one component fails to perform, for whatever reason, the overall system can fail. The Chain is just as strong as the Weakest Link
Two tactics:Two tactics:Improving Individual componentsProviding redundancy
IMPROVING INDIVIDUAL IMPROVING INDIVIDUAL COMPONENTSCOMPONENTS
Because failure do occur, understanding their occurrence is an important reliability concept
As the number of components in a series increases, the reliability of the whole system declines very quickly
To measure reliability in a system in which each component may have its own unique rate of reliability, the following equation is used:
System Reliability RRss = R = R11 X R X R22 X R X R33 X ……. X R X ……. X Rnn
Component Reliability is a design issue. The basic unit is Product Failure Rate (FR)
FR (%) = FR (%) = Number of FailuresNumber of Failures X 100 X 100 No. of Units TestedNo. of Units Tested
FR (N) = FR (N) = Number of Failures_______________Number of Failures_______________ No. of Unit-hours of Operating TimeNo. of Unit-hours of Operating Time
Mean Time between failures (MTBF) = _____ Mean Time between failures (MTBF) = _____ FR(N)FR(N)
11
PROVIDING REDUNDANCYPROVIDING REDUNDANCY
To increase reliability, Redundancy is added
This is done by use of addition “Backup” components in parallel
If one component fails, an alternate arrangement is in placeProbability of
first component
working
Probability of
second component
working+
Probability of
second component
Not workingX
(0.8) + [(0.8) X (1-0.8)] = 0.96
MAINTENANCEMAINTENANCETwo types of maintenance:
Preventive Maintenance:Preventive Maintenance:A plan that involves routine inspections, servicing and keeping facilities in good condition to prevent failure & to keep the system working without interruptions
Breakdown Maintenance:Breakdown Maintenance:Remedial Maintenance that occurs when equipment fails and must be repaired on an emergency or priority basis
Two tactics:Two tactics:Implementing or improving preventive
maintenanceIncreasing repair capabilities or speed
IMPLEMENTING OR IMPLEMENTING OR IMPROVING PREVENTIVE IMPROVING PREVENTIVE
MAINTENANCEMAINTENANCE Preventive Maintenance implies that we can determine when a system will need service or repair
For some products, failure in initial stages is possible, called Infant MortalityInfant Mortality. This is due to improper use by customer mostly. So firms test products for this prior to shipment and sometimes after sales service includes installation and training
Equipment history and replacing parts or components before the time specified by OEM to be maintained Maintenance Required Time of Maintenance Cost of Maintenance Inventory of spares Emergency spares supplier
INCREASING REPAIR INCREASING REPAIR CAPABILITIES OR SPEEDCAPABILITIES OR SPEED
Because reliability and preventive maintenance are seldom perfect, most firms opt for some level of repair capability
Enlarging or improving repair facilities can get the system back in operation faster
A good maintenance facility should have the following 06 features: Well-Trained personnel Adequate Resources Ability to establish a repair plan and priorities Ability and authority to do material planning Ability to identify the root cause of breakdown Ability to design ways to extend MTBF Equipped In-house maintenance facility or external
vendors
TOTAL PRODUCTIVE TOTAL PRODUCTIVE MAINTENANCEMAINTENANCE
It combines TQM with strategic view of maintenance from process equipment design to preventive maintenance
It involves the concept of reducing variability through employee involvement and excellent maintenance records
It also involves: Designing machines that are reliable, easy to operate and easy to
maintain Emphasizing total cost of ownership when purchasing machines,
so that service and maintenance are included in the cost Develop preventive maintenance plans that utilizes the best
practices of operators, maintenance departments and depot services
Training workers to operate and maintain their own machines High utilization of facilities, tight scheduling, low
inventory and consistent quality demand reliability. Total productive maintenance is the key to quality
TECHNIQUES FOR TECHNIQUES FOR ESTABLISHING MAINTENANCE ESTABLISHING MAINTENANCE
POLICIESPOLICIESTwo other OM techniques have proven beneficial to establishing maintenance policies: Simulation & Expert Systems
Simulation helps in complex maintenance and reliability decisions. Failure of parts, components and systems can be simulated using a physical, graphic or mathematical model.
Expert Systems are computer programs that mimic human logic to assist staff in isolating and repairing various faults in machinery and equipment.