Optimal Testing: Data Management for Enhanced Quality, Reliability and Yield Improvement
Project & Quality Management Quality Management Reliability.
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Transcript of Project & Quality Management Quality Management Reliability.
![Page 1: Project & Quality Management Quality Management Reliability.](https://reader033.fdocuments.us/reader033/viewer/2022061607/56649dda5503460f94ad14c5/html5/thumbnails/1.jpg)
Project & Quality Management
Quality Management
Reliability
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Reliability Management
Why is it needed?
• Reliable operation of critical equipment
• Planning of maintenance activities
• Improved ‘quality’ of an item
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Reliability Management
Reliability management is concerned with performance and conformance over the expected life of the product
“the probability that a product or a piece of equipment performs its intended function for a stated period of time under specified operation conditions’”
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Definition of Reliability
The definition has four important elements:
• Probability
• Time
• Performance
• Operating conditions
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Definition of Reliability
Probability• A value between 0 and 1• Precise meaning
e.g. probability of 0.97 means that 97 of 100
items will still be working at stated time
under stated conditions
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Definition of Reliability
Performance• Some criterion to define when product has
failed
e.g. bearing clearances in an engine or amount
of emissions from a car
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Definition of Reliability
Operating conditions• These describe the operating conditions that
correspond to the stated product life. e.g. for a car engine this might mean
→ Speed→ Loading→ Effects of an expected amount of
misuse such as over-revving and stalling.
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Reliability Measurement
This is based on the Failure Rate
i.e.TimeOperatingTotal
FailedItemsrateFailure
Some products are scrapped when they fail e.g. hairdryer
Others are repaired e.g. washing machine.
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Failure rate over the life of a product
The failure rate is expected to vary over the life of a product – ‘Bathtub Curve’
Time
Fa
ilu
re R
ate
A
C
D
B
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Bathtub Curve
A-B Early Failure• ‘Teething’ problems. Caused by design/material
flaws
B-C Constant Failure• Lower than initial failure rate and more or less
constant until end of life
C-D End of life failure• Failure rate rises again due to components
reaching end of life
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Simplifying Assumption
• Exponential distribution of failure rate is assumed. This means that the failure rate remains constant over life of product
• Bathtub curve becomes a straight line
Calculating Failure Rate
Time
Fa
ilu
re R
ate
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Calculating Failure Rate
Failure rate TimeOperatingTotal
FailedItems
usually expressed by the Greek letter lambda ()
The probability of a product surviving until time (t) is given by the following function:
Reliability at time (t) =
e is the exponential function
te
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Procedure
To establish reliability of an item:
• Conduct a series of tests until a number of
them fail.
• Calculate failure rate (Lambda).
• Calculate reliability for a given time using
Reliability at time (t) = e-t
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Example
Trial data shows that 105 items failed during a test with a total operating time of 1 million hours. (For all items i.e. both failed and passed).
The failure rate 41005.1
1000000
105 x
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Example
Find the reliability of the product after 1000 hours i.e. (t) =1000
Reliability at 1000 hours:
R(1000) = 0.9
te
)10001005.1( 4 xxe
Therefore the item has a 90% chance of surviving for 1000 hours