IE0324 Quality Engineering
Topic 6B:
Failure Mode
and Effects Analysis (FMEA)
1
Quality Tools
FMEA
 Failure Mode and Effect Analysis (FMEA) is an analytical technique that combines the
technology and experience of people in identifying foreseeable failure modes of a
product, service, or process, and planning for its elimination.
 FMEA consists of a group of activities intended:
1. to recognize and evaluate the potential failure of a product, service, or process and its
effects
2. identify actions that could eliminate or reduce the chance of the potential failure occurring
3. document the process.
 FMEA is initially before-the-event action requiring a team effort to alleviate most easily
and inexpensively changes in design and production.
 There are two types of FMEA:
1. Design FMEA
2. Process FMEA
https://www.weibull.com/basics/fmea.htm
FMEA
■ “Failure modes” means the ways, or modes, in which something might fail.
Failures are any errors or defects, especially ones that affect the customer,
and can be potential or actual.
■ “Effects analysis” refers to studying the consequences of those failures.
■ Failures are prioritized according to 1) how serious their consequences are,
2) how frequently they occur and 3) how easily they can be detected.
■ FMEA is used during design to prevent failures.
■ FMEA is used for control, before and during ongoing operation of the
process. Ideally, FMEA begins during the earliest conceptual stages of design
and continues throughout the life of the product or service.
WHEN TO USE FMEA
1. When a process, product or service is being designed or redesigned,
after quality function deployment (QFD).
2. When an existing process, product or service is being applied in a new
way.
3. Before developing control plans for a new or modified process.
4. When improvement goals are planned for an existing process, product
or service.
5. When analyzing failures of an existing process, product or service.
6. Periodically throughout the life of the process, product or service
FMEA
FMEA PROCEDURE
■ Preparation for the FMEA
1. Design tree/process map: identify all of the different
components of a product/design
2. Function tree: identify all of the function for overall
design/process and each component the design
3. Failures: determine ways each function can fail
■ * https://www.youtube.com/watch?v=M0Ej466IfZs
FMEA PROCEDURE
1. Identify the scope of the FMEA.
– Is it for concept, system, design, process or service? What are the
boundaries? How detailed should we be? Use flowcharts to identify
the scope and to make sure every team member understands it in
detail.
2. Assemble a cross-functional team of people with diverse knowledge
about the process, product or service and customer needs.
– Functions often included are: design, manufacturing, quality,
testing, reliability, maintenance, purchasing (and suppliers), sales,
marketing (and customers) and customer service.
FMEA PROCEDURE
3.
Develop process map and identify the functions of your scope from .
– Ask, “What is the purpose of this system, design, process or service? What do our
customers expect it to do?”
– Name it with a verb followed by a noun.
– Usually one will break the scope into separate subsystems, items, parts, assemblies or
process steps and identify the function of each.
4.
For each function, identify all the ways failure could happen.
– These are potential failure modes. If necessary, go back and rewrite the function with
more detail to be sure the failure modes show a loss of that function.
5.
For each failure mode, identify all the consequences on the system, related systems,
process, related processes, product, service, customer or regulations.
– These are potential effects of failure. Ask, “What does the customer experience
because of this failure? What happens when this failure occurs?”
FMEA PROCEDURE
6. Determine how serious each effect is. This is the severity rating (S).
Severity is usually rated on a scale from 1 to 10, where 1 is
insignificant and 10 is catastrophic. If a failure mode has more than
one effect, write on the FMEA table only the highest severity rating
for that failure mode.
7. For each failure mode, determine all the potential root causes. Use
tools classified as cause analysis tool, as well as the best
knowledge and experience of the team. List all possible causes for
each failure mode on the FMEA form.
8. For each cause, determine the occurrence rating (O) . This rating
estimates the probability of failure occurring during the lifetime of
your scope. Occurrence is usually rated on a scale from 1 to 10,
where 1 is extremely unlikely and 10 is inevitable. On the FMEA
table, list the occurrence rating for each cause.
FMEA PROCEDURE
9.
For each cause, identify current process controls. These are tests, procedures
or mechanisms that you now have in place to keep failures from reaching the
customer. These controls might prevent the cause from happening, reduce the
likelihood that it will happen or detect failure after the cause has already
happened but before the customer is affected.
10. For each control, determine the detection rating (D). This rating estimates how
well the controls can detect either the cause or its failure mode after they
have happened. Detection is usually rated on a scale from 1 to 10, where 1
means the control is absolutely certain to detect the problem and 10 means
the control is certain not to detect the problem (or no control exists). On the
FMEA table, list the detection rating for each cause.
11. Optional for most industries: Ask, "Is this failure mode associated with a critical
characteristic?" (Critical characteristics are measurements or indicators that
reflect safety or compliance with government regulations and need special
controls.) If so, a column labeled “Classification” receives a Y or N to show
whether special controls are needed. Usually, critical characteristics have a
severity of 9 or 10 and occurrence and detection ratings above 3.
FMEA PROCEDURE
12. Calculate the risk priority number, or RPN, which equals S × O × D. Also
calculate Criticality by multiplying severity by occurrence, S × O. These
numbers provide guidance for ranking potential failures in the order they
should be addressed.
RPN value does not mean anything stand
alone, but its meaning is shown only in
comparison to other RPNs
FMEA Analysis
Function or
Failure Type
Process Step
Potential
Impact
What is the
Briefly outline
impact on the
Describe what
function, step
key output
has gone
or item being
variables or
wrong
analyzed
internal
requirements?
SEVERITY
Potential
Causes
OCC
Detection
Mode
DET
RPN
What are the
existing
controls that
How
either prevent
How severe is What causes
frequently is
the failure How easy is it Risk priority
the effect to the the key input
this likely to
from
to detect?
number
customer? to go wrong?
occur?
occurring or
detect it
should it
occur?
FMEA Analysis
Function or
Failure Type
Process Step
Potential
Impact
SEV
Potential
Causes
OCC
Detection
Mode
DET
RPN
What are the
existing
What is the
controls that
Briefly outline
impact on the
How
either prevent
Describe what
How severe is What causes
function, step
key output
frequently is
the failure How easy is it Risk priority
has gone
the effect to the key input
or item being
variables or
this likely to
from
to detect?
number
wrong
the customer? to go wrong?
analyzed
internal
occur?
occurring or
requirements?
detect it
should it
occur?
Tire function:
support
weight of car,
traction,
comfort
Flat tire
Stops car
journey, driver
and passengers
stranded
10
Puncture
2
Tire checks
before
journey. While
driving,
steering pulls
to one side,
excess noise
3
60
FMEA PROCEDURE
13. Identify recommended actions. These actions may be design or process
changes to lower severity or occurrence. They may be additional controls
to improve detection. Also note who is responsible for the actions and
target completion dates.
14. As actions are completed, note results and the date on the FMEA form.
Also, note new S, O or D ratings and new RPNs
Severity Rating Scale *
10
Dangerously High
Failure could injure the customer or employee.
9
Extremely
High
Failure would create noncompliance with federal regulations.
8
Very High
Failure renders the unit inoperable or unfit for use.
7
High
Failure causes a high degree of customer dissatisfaction.
6
Moderate
Failure results in subsystem or partial malfunction of the product.
5
Low
Failure creates enough of a performance loss to cause the customer to complain.
4
Very Low
Failure can be overcome with modification to the customer’s process or product but there is minor
performance loss.
3
Minor
Failure would create a minor nuisance to the customer but would have minor effects on the customer’s
process or product.
2
Very Minor
Failure may not be readily apparent to the customer but would have minor effects on the customer’s process
of product.
1
None
Failure would not be noticeable to the customer and would not affect the customer’s process or product.
Occurrence Rating Scale*
10
Very High:
Failure is almost
inevitable
9
8
1 occurrence every 3 to 4 days or a probability of 3 occurrences in 10 events.
High:
Repeated failures
7
6
More than 1 occurrence per day or a probability of more than 3 occurrences in 10 events
1 occurrence per week or a probability of 5 occurrences in 100 events.
1 occurrence every month or 1 occurrence in 100 events.
Moderate:
Occasional failure
1 occurrence every 3 months or 3 occurrences in 1,000 events.
5
1 occurrence every 6 months to 1 year or 1 occurrence in 10,00 events.
4
1 occurrence per year or 6 occurrences in 100,000 events.
3
Low: Relatively few
failures
2
1
1 occurrence every 1 to 3 years or 6 occurrences in 1 billion events.
1 occurrence every 3 to 5 years or 2 occurrences in 1 billion events.
Remote: failure is unlikely
1 occurrence in greater than 5 years or less than 2 occurrences in 1 billion events.
Detection
Example FMEA
** https://www.youtube.com/watch?v=oZ7CSFA-Jd0
Design Tree- think of
everything in your
design
Severity
Occurrence
Detection
Post FMEA
FMEA Analysis
Function or
Failure Type
Process Step
Potential
Impact
SEV
Potential
Causes
OCC
Detection
Mode
DET
RPN
Addressing Risks: SEV, Criticality, RPN
The order in which risk should be addressed:
SEV
Criticality (SEV × OCC)
RPN = SEV × OCC × DET
RPN numbers should not be used alone to prioritize risk! As a
general rule, special attention should be given to high severity,
and then to high criticality (SEV x OCC), regardless of RPN
Quality Tools
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