2. RELIABILITY - LESSON ONE
Overview:
Application of Reliability in different industries
Importance of Reliability – Cost Impact
Bathtub curve
Predictability vs. Failure Mode Avoidance
P-Diagram
Strategies for Improvement
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3. QUOTES
―A man who lacks reliability is utterly useless.‖
Confucius (551-479)
―Engineering is the science of economy, of
conserving the energy, kinetic and potential,
provided and stored up by nature for the use of
man. It is the business of engineering to utilize
this energy to the best advantage, so there may
be the least possible waste.‖
Willard A. Smith (1908)
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4. RELIABILITY - DEFINITION
Wikipedia - the ability of a system or
component to perform its required functions
under stated conditions for a specified period
of time.
ASQ – the probability that an item can
perform its intended function for a specified
interval under stated conditions
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6. RELIABILITY - COMPARISON
Reliability field
Nuclear Aerospace Medical Consumer Products
Reliability Criteria
# units in field 00 000 00000000 00000000
Quality of field records:
Failed units excellent excellent Reasonable>good fair
Unfailed units excellent excellent none none
Units lost to follow-up no no often yes
Noise space simple moderate complicated complicated
Competing risks no no yes yes
Key Reliability redundancy, redundancy, intervention robustness,
Strategy intervention intervention some intervention
Key reliability measure probability probability cure rate and side effects distance from failure modes
Memo: Design improvement yes yes no yes
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7. WHY IS RELIABILITY IMPORTANT ?
Safety
Customer Satisfaction
Warranty Costs
Reputation
Repeat Business
Cost Analysis
Customer Requirements
Competitive Advantage
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8. RELIABILITY IMPROVEMENT PROCESS
Set goals & requirements (customer driven)
Perform an assessment
Testing
Data collection
Failure reporting, analysis and corrective
action system (FRACAS)
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9. VOCABULARY
Mean Time to Failure (MTTF)
Mean Time Between Failures (MTBF)
Hard Failures – product function ceases
Soft Failures – degraded to unacceptable level
Failure rate
Hardware Breakdown Structure
FMEA – Failure Modes, Effects & Analysis
SPC – Statistical Process Control
DOE – Design of Experiments
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10. LIFE CYCLE COST
―It’s unwise to pay too much, but it’s foolish to
spend too little‖— John Rustin
Present Value vs. Future Value of money
Acquisition Costs
Sustaining Costs
Cost Breakeven
Include Cradle-to-Grave costs converted to
NPV models
http://www.barringer1.com/pdf/LifeCycleCostSummary.pdf
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11. LIFE CYCLE COST
$30,000
$25,000
$20,000
C
o
$15,000
s Product A
t
Product B
$10,000
$5,000
$0
1 2 3 4 5 6 7 8 9
Years in Service
Product B has a lower acquisition cost but needs repaired more often and at
greater expense 1
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12. RELIABILITY RELATED COSTS
Prevention activities - intended to ensure that
processes work without fail, such as failure mode
and effects analysis, training and preventive
maintenance
Appraisal activities - how well processes such as
product and process approvals are actually working
via activities such as inspection and testing
Failure costs - related to failures that do occur and
are further classified as internal (failure identified
before it reached the customer) or external
(detected after reaching the customer). The time
and expense of reprocessing failed products or
services and investigating failures could fall into
either failure category, depending on when the
event occurs. Warranty costs are decidedly
external failures. 1
16. RELIABILITY PREDICTABILITY
Reliability is the probability that an item can
perform its intended function for a specified
interval under stated conditions, However:
We do not have access to all products in the
field, particularly those that have not failed
We cannot specify a period of time to
measure reliability
We cannot specify a set of operating
conditions
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17. RELIABILITY IS FAILURE MODE AVOIDANCE
Reliable products are robust and mistake free
Failure modes of our products are primarily that
something breaks or performance degrades
Avoiding failure modes will decrease the
probability of failure
Reliability prediction is not easy for many
industries
We need to reduce variation and the sensitivity
to noise (ie. Six Sigma and P-diagram)
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18. P-DIAGRAM
P-Diagram
Noise Factors
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2
3
Input Signal Ideal Function
System
Error State
Control Factors 1
1 2
2 3
3
4
5
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19. P-DIAGRAM DEFINITIONS
Ideal Function – primary intended function of
the design
Input Signal – energy which is put into the
system to make it work
Error State – undesirable output of the
system
Control Factors – features that can be
controlled by design or process
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20. NOISE FACTORS
Sources of disturbing influences that can
disrupt ideal function, causing error states
which lead to quality problems
Product variations
Changes over time/usage
Customer duty cycle
External environment
System interactions
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21. P-DIAGRAM EXAMPLE
P-Diagram
Self contained jet pack Noise Factors
1. Fuel volatility
2. Wind
3. Temperature
Input Signal Ideal Function
Throttle position System Lifts person off ground
Error State
1. No ignition
Control Factors
1. Material properties 2. Flame too large
2. Design
3. Manufacturing process
4. Assembly process
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22. FMEA
Bring P-Diagram
List error states (potential failure modes)
Ties together P-Diagram and Testing
Living and changing document
Discovery, legal document
Ultimate failure mode avoidance document
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23. TESTING
Captures the effects of noise factors over useful
life
Generates a measurable event
Generates a failure of degradation of the ideal
function
Generates results which are directly correlated
with real-world performance
Can be accelerated for reliability improvement
experiments (HALT, HASS)
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25. STRATEGIES FOR IMPROVEMENT
Change the design concept
Make basic current design assumptions
insensitive to the noises (beef up design, use
Design of Experiments, redundancy)
Reduce or remove the noise factor(s)
Insert a compensation device
Send the error state/noise elsewhere else
where it will do less harm (disguise effect)
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26. FRACAS
Failure Reporting, Analysis and Corrective
Action System
Prioritizes field failures
Root Cause Investigation Teams
Needs input from Team members
Drives problems to closure
Documentation in central location
Closed Loop System
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27. SUMMARY
Application of Reliability in different industries
Importance of Reliability – Cost Impact
Bathtub Curve
Predictability vs. Failure Mode Avoidance
P-Diagram
Strategies for Improvement
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28. WHERE TO GET MORE INFORMATION
Reliasoft - http://www.reliasoft.com/
RIAC -
http://src.alionscience.com/src/training.do
Hobbs Engineering -
http://www.hobbsengr.com/
ASQ Reliability Div. - http://asq.org/reliability/
SRE - http://www.sre.org/
You’ll find many more on the web….
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29. REFERENCES
Dr. Tim Davis -“Science, engineering, and
statistics”. Applied Stochastic Models in
Business and Industry, 2006, Vol. 22, Issue 5-
6, pp. 401-430
Dr. Vasiliy Krivstov
Dr. Paul Barringer
Reliasoft
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