AN INTRO TO RELIABILITY

By Bijli VM

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

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RELIABILITY

QUALITY & RELIABILITY

GARVINS 8 DIMENSIONS OF [PRODUCT]

QUALITY

◦ PERFORMANCE

◦ FEATURES

◦ RELIABILITY

◦ CONFORMANCE

◦ DURABILITY

◦ SERVICEABILITY

◦ AESTHETICS

◦ PERCEIVED QUALITY

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QUALITY & RELIABILITY

RELIABILITY IS A SUBSET OF

QUALITY

OR

RELIABILITY IS A TOOL TO

ENSURE ‘QUALITY’4

Understand the different similar

looking terminologies

What is Reliability?

What is Reliability? (Simplest

defn) It is the guarantee that the product will

work over its designed life

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

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

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

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%

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

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

OPTIMUM RELIABILITY (trade

off)

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?

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

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

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 Good management practice

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

Reliability is usually represented in a

graph vs time

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 optimisedmaintainability, availability and safety and quality levels at desired confidence levels and at competitive prices

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

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

THANK YOU ALLThank You Mr Dimitri Kececioglu