Maintenance Mgmt Chapter 19
Transcript of 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
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Effective Maintenance ManagementSome requirements
Equipment Catalogue
Maintenance Policy & Manual
Troubleshooting Mechanisms Fault Tree Analysis
Maintenance Information System
Equipment History Cards
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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
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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
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Maintenance ManagementAlternatives
Routine Inspection
Preventive Maintenance
Condition Monitoring Breakdown Maintenance
Planned Shutdown/Major Overhauls
Equipment Replacement
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Breakdown Vs Preventive MaintenanceTrade-offs
Cost of
PM
Cost of
BD
Total
Cost
Level of PM activity
C
ostofMaintena
nce
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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
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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
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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/-
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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/-
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Preventive Maintenance PolicyExample 19.3. Graphical Illustration
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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
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Equipment ReplacementDecision Tree
A
B
C
1
New After
2 Yrs
After
4 Yrs
End of
6 Yrs
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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
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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
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Rotable Spares Parts PlanningA queueing theory representation
Maintenanceof spares
ReconditionedSpare ready
for use
Spares in usein equipment
Failed spareswaiting for
Maintenance
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Maintenance ConsumablesService Level
A B C
V 95% 97% 99%
E 90% 92% 95%
D 85% 90% 95%
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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
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TPM Prize winnersIndian Scenario
Source: http://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.