Lecture # 7:Lecture # 7:

MAINTENANCE & RELIABILITYMAINTENANCE & RELIABILITY

Humayun Akhtar Awan

RIPHAH INTERNATIONAL UNIVERSITY, ISLAMABADRIPHAH INTERNATIONAL UNIVERSITY, ISLAMABAD

OPERATIONS MANAGEMENTOPERATIONS MANAGEMENT

WORLD WORLD CLASS CLASS

RELIABILITYRELIABILITY

EVERYTHING RIGHT, FIRST TIME, EVERY

TIME

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)

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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.

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