maintenance mgmt chapter 19

7/31/2019 Maintenance Mgmt Chapter 19

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Chapter 19

MaintenanceManagement


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Mahadevan (2007), Operations Management: Theory & Practice, Pearson Education

Maintenance ManagementDecision making context

Maintenance management is

A systematic approach to upkeep of resources

Using decision making tools

To improve the efficiency and effectiveness of the operatingSystem

Important Decisions in Maintenance Management include:

Should we repair a machine or replace it with a new one?

Should we do preventive maintenance of the available resourcesas opposed to reacting to breakdowns occurring in the system?

At what frequency should preventive maintenance be done and

what is the cost implication of the decision? Can we assure a certain level of system availability? What factors

influence system availability?

Are there any lessons to be learnt from the recent success ofJapanese approaches to maintenance management?


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Maintenance ManagementLinkages with other OM functions

Maintenance & Aggregate Production Planning

Scheduling of maintenance activities interacts closelywith APP exercise in an organisation

Maintenance & Operations Scheduling One of the key assumptions in scheduling is the

extent of availability of resources for operations .Maintenance function determines how well theassumptions about resource availability are made andhow reliable the assumptions are

Maintenance & Quality Control

A good maintenance management could contributesignificantly to quality assurance and vice versa


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Vicious Cycle of Maintenance

Multiple resources

available centrally

Reduced emphasis on

maintenance due to availability of

more than one machine

No significant

impact on resources

availability initially

Maintenanceof resources

further neglected

Resources availability

begins to drop

drastically

Identify

Bottleneck resources

Build additional

capacity in the

system


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Bath Tub CurveFailure rate of equipment over its life cycle

InfantMortality

Phase

Wear OutPhase

Useful Life Period (Constant failure rate)

F

ailureRate

Time


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Maintenance ManagementPerformance Metrics

Equipment breakdowns Breakdowns can be measured in terms of the

frequency and the severity

Mean Time Between Failure (MTBF) MTBF is the expected time of the arrival of a

failure

Mean Time to Repair (MTTR) MTTR is the expected time for restoring the

equipment back to the working condition

Availability Availability is defined, as the fraction of the time

the equipment is available for productive use

(MMTB

MTAt


7/29Mahadevan (2007), Operations Management: Theory & Practice, Pearson Education

Effective Maintenance ManagementSome requirements

Equipment Catalogue

Maintenance Policy & Manual

Troubleshooting Mechanisms Fault Tree Analysis

Maintenance Information System

Equipment History Cards



Troubleshooting MechanismAn illustration using Microwave Oven

X X X

X

X X

X

X X X X

X

X X X X

X X X

Checktoseethat ovenventilationportsarenot choked

Usecorrect time/cookingpower level

Donot operatewithopenempty

Reset Clock

Turnor stir food

Usemicrowave-safecookwareonly

CompletelyDefrost food

Ovenwill not start

Err Displays

Arcingor sparking

Incorrect time

Unevenlycookedfoods

Overcookedfoods

Undercookedfoods

Ispower chordplugged?

Isdoor closed

Cookingtimenot setPressSTOP/CLEAR

Improper defrosting

PossibleCause

Problems



Troubleshooting MechanismAn illustration using 2-line phone

Symptom Remedy

You hear five short error beepswhen you press Line 1 orLine 2button.

Make sure you set up the base phone correctly Move the handset closer to the base phone Replace the handset to the base phone for a while

to charge the battery pack

The telephone does not connect

at all, even though the numberthat you have dialed is correct.

Make sure the dialing mode is set correctly

Before dialing, make sure that you can hear thedial tone

You hear interference duringconversation

Move the handset closer to the base phone PressChannelon the handset for a channel that

gives better reception Place the base phone away from noise resources

The Charge lamp does notlight up when you place thehandset on the base phone

Wipe the charge terminals with a soft cloth forbetter contact of the charge terminals

Make sure the handset is placed on the base phoneproperly

The battery duration is short

The battery pack was charged less than 12 hours(due to power failure etc.)

The usable life of the battery has expired andneeds replacement



Maintenance ManagementAlternatives

Routine Inspection

Preventive Maintenance

Condition Monitoring Breakdown Maintenance

Planned Shutdown/Major Overhauls

Equipment Replacement



Breakdown Vs Preventive MaintenanceTrade-offs

Cost of

PM

Cost of

BD

Total

Cost

Level of PM activity

C

ostofMaintena

nce



Maintenance AlternativesImplications

Routine

Inspection

Preventive

Maintenance

Predictive

Maintenance

Breakdown

Maintenance

Major

Overhaul

Equipment

Replacement

Impact on the equipments working condition

Little Substantial

Co

stofmaintena

nce



Preventive Maintenance PolicyOptimal PM Cycle

CPM = Average cost of preventive maintenance for one unit ofthe equipment

CBD = Average cost of a breakdown maintenance for one unit ofthe equipment

M = Number of units of the equipment requiring maintenance

n = Number of periods in the planning horizonpi = Probability of breakdown in the ith period after

preventive maintenanceBi = Number of breakdowns during a PM cycle of durationi

B1 = M * p1

B2

= M * (p1

+ p2) + B

1* p

1

Bi = M * (p1 + p2 + p3 + . . . + pi)+ B1 * pi-1 + B2 * pi-2 + . . . + Bi-1 * p1

Cost of preventive maintenance for a PM cycle of i = M * CPM

Cost of breakdown maintenance for a PM cycle of i = Bi* CBD



Preventive Maintenance PolicyExample 19.3.

Monthfollowing PM

(a)

Probabilityof

breakdown(b)

(a) * (b)

1 0.10 0.10

2 0.15 0.30

3 0.30 0.90

4 0.20 0.80

5 0.15 0.75

6 0.10 0.60

Sum 3.45

MTBF for one sewing machine= 3.45 months.

In other words, the number

of breakdowns for onemachine per month = 1/3.45.

For 200 machines, thenumber of breakdowns everymonth = 200/3.45 = 57.97

The cost of pure breakdown maintenance policy = 57.97 * 950 = Rs. 55, 072/-



B1 = M * p1= 200 * 0.10 = 20B2 = M * (p1 + p2) + B1 * p1= 200 * (0.10 + 0.15) + 20 * 0.10 = 52

PMCycle

No. of BDsBD Mtce.

costPM Mtce.

costTotal costof Mtce.

Cost of maintenance (per month)

PM BDTotal ofthe two

1 20.00 19,000.00 60,000.00 79,000.00 60,000.00 19,000.00 79,000.00

2 52.00 49,400.00 60,000.00 109,400.00 30,000.00 24,700.00 54,700.00

3 118.20 112,290.00 60,000.00 172,290.00 20,000.00 37,430.00 57,430.00

4 175.62 166,839.00 60,000.00 226,839.00 15,000.00 41,709.75 56,709.75

5 234.89 223,147.40 60,000.00 283,147.40 12,000.00 44,629.48 56,629.48

6 298.69 283,757.59 60,000.00 343,757.59 10,000.00 47,292.93 57,292.93

Preventive Maintenance PolicyExample 19.3.

The optimal PM cycle for the garment manufacturer is 2 months

Cost of preventive maintenance per sewing machine = Rs. 300/-Cost of breakdown maintenance per sewing machine = Rs. 950/-



Preventive Maintenance PolicyExample 19.3. Graphical Illustration

-

10,000.00

20,000.00

30,000.00

40,000.00

50,000.00

60,000.00

70,000.00

80,000.00

90,000.00

0 1 2 3 4 5 6

PM Cycle (months)

Totalcostofmaintenance(R

s)

Total of the two Preventive maintenance cost Breakdown maintenance cost



Equipment ReplacementDecision Tree

A

B

C

1

New After

2 Yrs

After

4 Yrs

End of

6 Yrs



Spare Parts Management

Types of Spares

Capital Spares

Insurance Spares

Rotable Spares

Maintenance Consumables

Use of Queueing Theory models forspare parts planning

VED Classification of spare inventory



Spare Parts PlanningInsurance Spares

Cu = The per unit cost of the spareCs = The per unit cost of shortage of the spareS = The per unit salvage value of the spareN* = Optimal number of units to be stockedPi = The probability that the demand for the spare is iunits

TC(N) = Total cost of stocking N insurance spares

10

(*)(**)(

Ni

is

N

i

iuiPCiNPSNCNTC

The optimal number of spares to be stocked can be identified by checkingthe following pair of equation for alternative values of N from 0.

)()1( NTCNTC

)()1( NTCNTC

The optimal number of spares to stock is given by:

**

0

1

0

N

i

i

s

us

N

i

iSC

CCP



Rotable Spares Parts PlanningA queueing theory representation

Maintenanceof spares

ReconditionedSpare ready

for use

Spares in usein equipment

Failed spareswaiting for

Maintenance



Maintenance ConsumablesService Level

A B C

V 95% 97% 99%

E 90% 92% 95%

D 85% 90% 95%



Total Productive Maintenance(TPM)

Total Productive Maintenance (TPM) An alternative approach to equipment

maintenance that seeks to achieve zerobreakdowns and zero defects

A successful blend of preventive maintenanceideas with the philosophy of TQM

Based on the three ideas Yaruki Motivation Yarude Competency

Yaruba Work Environment As of 2004, 65 PM prizes have been

awarded to various divisions of Indiancompanies for excellence in TPM practice



TPM Prize winnersIndian Scenario

Source: http://www.tpmclubindia.org/awards.htm
http://www.tpmclubindia.org/awards.htmhttp://www.tpmclubindia.org/awards.htm


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Overall Equipment Effectiveness(OEE): Performance Metric for TPM

*

TiOpe

OAcTiCyclTheorEfficienePerforma

*OutActu

DeOutActuaRateQuality

Overall Equipment Effectiveness =

Availability * Performance Efficiency * Quality Rate


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OEE & Six big losses

Equipment

Operating Time (A)

Loading

Time (B)

Net Operating

Time (C)

Valuable

Operating

Time (D)

1. Breakdown

2. Setup & Adjustment

3. Idling & Minor Stoppage

4. Reduced Speed

5. Defect & Rework

6. Startup

Six big losses

Downtime

Losses

Speed

Losses

Quality

Losses


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TPM Methodology

Establishing a thorough system of preventivemaintenance for the equipments entire life span

Implementation of TPM by various departmentsincluding Engineering, Operations and Maintenance

Involvement of every single employee from topmanagement to workers on the shop floor

Promoting preventive maintenance through asystem of motivation management by creating

autonomous small group activities for maintenance


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Steps for AutonomousMaintenance

Sl. No. Step Activities&Objectives

1 Initial CleaningCleantoeliminatedust anddirt; Lubricate, Discoverproblems andcorrect them

2Countermeasures at thesourc

of problems

Prevent causeof dust &dirt, Improveparts that arehard

toclean; Reducetimefor cleaning

3CleaningandLubricationStandards

Establishstandards for cleaning, lubricationetc.

4 General Inspection Discover andcorrect minor equipment defects

5 Autonomous Inspection Developanduseautonomous inspectioncheck sheet

6 Organisation&TidinessStandardiseindividual workplacecontrol methods,Developsystematic maintenancecontrol

7 Full autonomous maintenanceDevelopcompanypolicyandgoals further, Increaseregularityof maintenanceactivities


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Maintenance ManagementChapter Highlights

Maintenance management is linked to otheroperations management functions such as qualitymanagement, scheduling and aggregate productionplanning

Several performance measures are available toassess maintenance management. These includeavailability, MTBF, MTTR and overall equipmenteffectiveness.

Use of troubleshooting mechanisms, fault treeanalyses and a good maintenance managementinformation system results in effective maintenance

Several alternatives are available for maintenancemanagement. These range from simple routine

inspection to equipment replacement.


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Maintenance ManagementChapter Highlights

There are four type of spare parts in organisations.These include capital spares, insurance spares,rotable spares and maintenance consumables. Themethod of inventory planning vastly differ among

these.

Total Productive Maintenance (TPM) is a newerapproach to maintenance management that seeksto achieve zero breakdowns and zero defects. It is

based on the premise that production operatorsplay a crucial role in maintenance.

Overall Equipment Effectiveness (OEE) is used toassess the performance of TPM. By eliminating sixbig losses OEE of equipment could be improved.

maintenance mgmt chapter 19

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