Mata kuliah : J0444 - Manajemen Operasional
Tahun
: 2010
Maintainance and Reliability
Pertemuan 26
Learning Objectives
• Explain the importance of maintenance in production
systems
• Describe the range of maintenance activities
• Discuss preventative maintenance and the key issues
associated with it
• Discuss breakdown maintenance and the key issues
associated with it
• Define reliability
• Perform reliability computations
• Explain the purpose of redundancy in a system
Introduction
• Maintenance
– All activities that maintain facilities and
equipment in good working order so that a
system can perform as intended
• Two basic categories
– Building and grounds
– Equipment maintenance
Goal of Maintenance
• To keep production systems in good working order at
minimal cost
• Reasons for maintenance
– To avoid production or service disruptions
– To not add production or service costs
– To maintain high quality
– To avoid missed delivery dates
Maintenance Management
• All activities involved in
keeping a system’s
equipment working
• Objective: Maintain
system capability &
minimize total costs
© 1995 Corel Corp.
Maintenance Performance
Employee
Involvement
Maintenance
Procedures
Maintenance
Performance
© 1995 Corel Corp.
© 1995
Corel
Corp.
Good Maintenance & Reliability Strategy
• Requires:
– Employee involvement
– Maintenance and reliability procedures
• To yield:
–
–
–
–
–
Reduced inventory
Improved quality
Improved capacity
Reputation for quality
Continuous improvement
Employee Involvement
•
•
•
•
© 1995 Corel Corp.
Information sharing
Skill training
Reward system
Power sharing
Maintenance & Reliability Procedures
•
•
•
•
Clean and lubricate
Monitor and adjust
Minor repair
Computerized records
Maintenance
Procedures
© 1995
Corel
Corp.
Maintenance Benefits
Lower
operating
costs
Reduced
inventory
Improved
capacity
Faster, more
dependable
throughput
Maintenance
Continuous
improvement
Higher
productivity
Improved
quality
Reactive vs Proactive
Reactive Maintenance:
• Breakdown maintenance
– Reactive approach; dealing with breakdowns or
problems when they occur
Proactive Maintenance:
• Preventive maintenance
– Proactive approach; reducing breakdowns through a
program of lubrication, adjustment, cleaning,
inspection, and replacement of worn parts
Maintenance Reasons
• Reasons for keeping equipment running
– Avoid production disruptions
– Not add to production costs
– Maintain high quality
– Avoid missed delivery dates
Breakdown Consequences
• Production capacity is reduced
– Orders are delayed
• No production
– Overhead continues
– Cost per unit increases
• Quality issues
– Product may be damaged
• Safety issues
– Injury to employees
– Injury to customers
Total Maintenance Cost
Total Cost
Cost
Preventive
maintenance cost
Breakdown and
repair cost
Optimum Amount of
preventive maintenance
Preventive Maintenance
• Preventive maintenance: goal is to reduce the
incidence of breakdowns or failures in the plant or
equipment to avoid the associated costs
• Preventive maintenance is periodic
– Result of planned inspections
– According to calendar
– After predetermined number of hours
Example
Frequency of breakdown
Number of breakdowns
Frequency of occurrence
0
1
2
3
.20 .30 .40 .10
If the average cost of a breakdown is $1,000, and the
cost of preventative maintenance is $1,250 per month,
should we use preventive maintenance?
Example Solution
Number of
Breakdowns
0
1
2
3
Frequency of
Occurrence
.20
.30
.40
.10
1.00
Expected number of
Breakdowns
0
.30
.80
.30
1.40
Expected cost to repair = 1.4 breakdowns per month X $1000 = $1400
Preventive maintenance = $1250
PM results in savings of $150 per month
Predictive Maintenance
• Predictive maintenance
– An attempt to determine when best to perform
preventive maintenance activities
• Total productive maintenance
– JIT approach where workers perform preventive
maintenance on the machines they operate
Breakdown Programs
• Standby or backup equipment that can be quickly
pressed into service
• Inventories of spare parts that can be installed as
needed
• Operators who are able to perform minor repairs
• Repair people who are well trained and readily
available to diagnose and correct problems with
equipment
Replacement
• Trade-off decisions
– Cost of replacement vs cost of continued
maintenance
– New equipment with new features vs
maintenance
– Installation of new equipment may cause
disruptions
– Training costs of employees on new equipment
– Forecasts for demand on equipment may
require new equipment capacity
• When is it time for replacement?
Reliability
• Reliability: The ability of a product, part, or system
to perform its intended function under a prescribed set
of conditions
• Failure: Situation in which a product, part, or
system does not perform as intended
• Normal operating conditions: The set of
conditions under which an item’s reliability is specified
Reliability is a Probability
• Probability that the product or system will:
– Function when activated
– Function for a given length of time
• Independent events
– Events whose occurrence or nonoccurrence do not
influence each other
• Redundancy
– The use of backup components to increase
reliability
Rule 1
Lamp 1
.90
Lamp 2
.80
.90 x .80 = .72
Rule 2
.80
Lamp 2 (backup)
.90 + (1-.90)*.80 = .98
.90
Lamp 1
Rule 3
.70
Lamp 3 (backup for Lamp 2)
.80
Lamp 2 (backup for Lamp1)
1 – P(all fail)
1-[(1-.90)*(1-.80)*(1-.70)] = .994
.90
Lamp 1
Example Reliability
Determine the reliability of the system shown
.98
.90
.92
.90
.95
Solution
The system can be reduced to a series of three
components
.98
.90+.90(1-.90)
.95+.92(1-.95)
.98 x .99 x .996 = .966
Failure Rate
Failure Rate
Infant
mortality
Failures due
Few (random) failures
to wear-out
Time, T
Exponential Distribution
Reliability = e -T/MTBF
1- e -T/MTBF
T
Time
Normal Distribution
Reliability
0
z
Availability
• The fraction of time a piece of equipment
is expected to be available for operation
Availability 
MTBF
MTBF  MTR
MTBF = mean time between failures
MTR = mean time to repair
Improving Reliability
•
•
•
•
•
•
•
Component design
Production/assembly techniques
Testing
Redundancy/backups
Preventive maintenance procedures
User education
System design
The End