2. QUALITY & RELIABILITY
QUALITY
•Conformance to specifications
•Fitness for intended use
(Juran)
•Meeting or exceeding
customer expectations
(Deming)
•Conformity to standards set by
industry or organisation that
must align with customer needs
2
RELIABILITY
7. What is Reliability? (Simplest
defn)
It is the guarantee that the product will
work over its designed life
8. What do you understand by
reliability?
For my mobile phone
I want a reliability of x%
95%
For a period of y (hrs/ days/ cycles)
2 yrs
9. CASE HISTORIES OF COST
REDUCTION THROUGH RELIABILITY
HP reduced service costs by about
70% while increasing the sales by
25% for a measuring instrument
T-38 Airplane: 1960-1962
◦ Cost of reliability effort: $ 15,00,000
◦ Savings over 3 years: $ 3,20,00,000
Minuteman I Missile System
◦ 30% reduction in failure rate
◦ $ 16,00,00,000 savings over 10 years
10. CASE HISTORIES OF COST
REDUCTION THROUGH RELIABILITY
Texas Instruments
◦ $ 8 million spent
Reliability of 800 types of semiconductors
improved from one failure in 2,500 hrs to > one
failure in 25,000 hrs
11. Significance of Reliability
No. of
components
in series
100
250
500
1,000
10,000
100,000
Individual Component reliability
99.999%
Equipment Reliability
99.90%
99.75%
99.50%
99.01%
90.48%
36.79%
99.99%
99.01%
97.53%
95.12%
90.48%
36.79%
0.01%
12. Significance of Reliability
Farm Tractor
Model Year
1935
1960
1970
1980
1990
No. of Critical
Components
1200
2250
2400
2600
2900
Tractor
Reliability Per
Year (av.
component
reliability is
99.99%)
88.70%
79.90%
78.70%
77.10%
74.80%
No. of tractors
failing per year
per 1,000
tractors
113
201
213
229
252
13. Cost Escalation of Products
Re 1 Concept Phase
Rs 10 Design Phase
Rs 100 Development Phase
Rs 1,000 Manufacturing Phase
Rs 10,000 Support Phase
15. Reliability answers questions
like
What is the probability of my radar
encountering a failure during my
exercise sortie of 50 days?
Which are the most critical spares I
need to stock as OBS/ B&D for my
sonar?
What is the expected life of my FCS?
16. Reliability answers questions
like
How much will the average life time
increase, if I add redundancy to my
SDN server?
How many missiles should I have to
ensure destruction of the target?
What is the probability of my car not
breaking down during the first
10,000kms or 3 years which ever is
lowest
17. How is Reliability beneficial? (for
engineers)
Predict PRODUCT/ PROCESS failures
Understand why failures occur
Improves the product/ process in an
objective way
Creates optimised Test Plans
Predicts spare parts requirement
Plan maintenance activities and
schedules
Risk based decision making with spare
consumption data
Good engineering practice
18. How is Reliability beneficial? (for
managers)
Lowers manufacturing costs
◦ Less overtime, rework, downtime, audits &
inspection
Lowers life cycle costs
◦ Warranty costs, product recalls, customer
dissatisfaction
Ensures product/ process capability
Produces evidence for dependability
claims
Insight into contractual compliance
Risk based decision making
19. DEFINITION OF RELIABILITY
◦ (1) conditional probability at a given
◦ (2) confidence level that the equipment will
◦ (3) perform its intended function satisfactorily or
without failure i.e. within specified performance
limits
◦ (4) at a given age
◦ (5) for a specified length of time, function period
or mission time when used in a manner and for
the purpose intended
◦ (6) while operating under the specified
application and operation environments with their
associated stress levels
(Reference: Reliability Engg Handbook by Dimitri Kececioglu) 19
21. RELIABILITY ENGG
DEFINITION
Provides the theoretical and practical tools
whereby the probability and capability of parts,
components, equipment, products, subsystems,
and systems to perform their required functions
without failure for desired periods in specified
environments, i.e. their desired optimised reliability,
can be specified, predicted, designed in, tested,
demonstrated, packaged, transported, stored,
installed and started up, and their performance
monitored and fed back to all concerned
organisations, and any needed corrective actions
taken, the results of these actions being followed
through to see if the units reliability has improved,
and similarly for their desired and optimised
maintainability, availability and safety and quality
levels at desired confidence levels and at
competitive prices
22. The Concept of System
Effectiveness
System Effectiveness is the product of
◦ Operational Readiness
◦Mission Reliability
◦ Design Adequacy
SE = OR*RM*DA = Nac
Nt
Nac – No. of systems that accomplish all designed for mission
objectives when called upon to do so at a point in time
Nt – Total no. of systems in hand
23. System Effectiveness
What should be the total no. of missiles
on hand when Nac = 100 such missiles
are required to destroy a target given
that
◦ OR = 0.98
◦ RM = 0.95
◦ DA = 0.90 Nt = ?
SE = Nac/ Nt = OR*RM*DA=0.98*0.95*0.90=0.8379
0.8379= Nac/ Nt = 100/ Nt
Therefore Nt = 100/0.8379
i.e. 119 missiles
