Failure Mode and Effects Analysis (FMEA)

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Failure Mode and Effects Analysis (FMEA)

• Additional material to execute FMEA exercise

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Definitions Failure Mode is the way in which
the failure is manifested. Failure effect is
the consequence of the failure. Failure cause
is what induces the failure.
Escalante (2003)
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Failure Mode and Effects Analysis Abbreviated
Approach


C
D
Actions Results
S
R
l
e
e
Current
P
Responsibility
a
Item
Potential
Potential
t
v
N
Controls
s
Recommended
Target
e
Failure
Effect(s) of
s
Actions
c
Action(s)
Completion Date
Function
Mode
Failure
Prevention/Detection
Taken
What can be done?
How bad is it?
What
- Design changes
are the
Effect(s)?
What did they do and what are the outcomes
- Process changes
How often does it happen?
What are the functions, features or requirements?
- Special controls
- Changes to standards,
procedures, or guides
What can go wrong?
What are
the Cause(s)?
- No Function
How good is this method at detecting it?
- Partial/ Over/
Degraded
Function
Who is going to do it and when?
- Intermittent
How can this
Function
be prevented and detected?
- Unintended
Function
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FMEA (cont.)
Item/Function Potential Potential S C
Potential Cause(s)/ Failure Effect(s) e
l Mechanism(s) of Mode of failure
v a failure s
(9)
(10)
(11)
(14)
(12) (13)
(9) Name of the item and its intended function
(purpose/objective). (10) Include specific
problems, failures, defects (anti-functions) of
the analyzed system() and its functions. Use
physical terms. (11) The effect of failures in
the function of the analyzed system, as they
would be perceived by the customer
(internal/external). (12) Evaluation of the
severity of the effect of the failure to the
next system or to the internal/external
customer. Sometimes large values of severity can
be reduced by means of design reviews
that compensate or mitigate the resulting
severity.
() subsystem or component
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FMEA SEVERITY EVALUATION CRITERIA
EFFECT
CRITERIA Severity of Effect
RANK
Very high severity ranking when a potential
failure mode affects safe vehicle operation
and/or involves noncompliance with government
regulation without warning
Hazardous- without warning
10
Hazardous- with warning
Very high severity ranking when a potential
failure mode affects safe vehicle operation
and/or involves noncompliance with government
regulation with warning
9
Vehicle/item inoperable (loss of primary
function).
Very High
8
Vehicle/item operable but at a reduced level of
performance. Customer very dissatisfied.
High
7
Vehicle/item operable but Comfort/Convenience
item(s) inoperable. Customer dissatisfied.
Moderate
6
Vehicle/item operable but Comfort/Convenience
item(s) operable at a reduced level of
performance. Customer somewhat dissatisfied.
Low
5
Fit Finish/Squeak Rattle item does not
conform. Defect noticed by most customers
(greater than 75).
Very Low
4
(D,F,GM. FMEA, 2001)
Fit Finish/Squeak Rattle item does not
conform. Defect noticed by 50 of customers.
Minor
3
Fit Finish/Squeak Rattle item does not
conform. Defect noticed by discriminating
customers (less than 25).
Very Minor
2
None
No discernible effect.
1
6
In the third edition this table is presented in
two columns but the information is the
same (customer effect and manufacturing/assembly
effect).
(D,F,GM. FMEA, 2001)
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(D,F,GM. FMEA, 2001)
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FMEA (cont.)
Item/Function Potential Potential S C
Potential Cause(s)/ Failure Effect(s) e
l Mechanism(s) of Mode of failure
v a failure s
(9)
(10)
(11)
(14)
(12) (13)
(13) Indicates any special characteristic
(critical, key, major) that will require special
controls. Some of the D, F, GM special symbols
can be used. (An indication of criticality is
when severity is 9 or 10, being the occurrence
and detection geater than 3. (Stamatis,
1995)). (14) Describe what causes the failure
modes. Discover the root causes.
9
S
C
Potential causes/ mechanism of failures
Potential failure mode
Potential failure effects
Product/ function
e
l
v
a
s
Name of the item and its intended function
(purpose/objective).
Include specific problems, failures, defects
(anti- functions) of the analyzed system() and
its functions. Use physical terms
The effect of failures in the function of the
analyzed system, as they would be perceived by
the customer (internal/external)
Describe what causes the failure modes. Find the
root cause.
Typical causes
Use field data, previous FMEAs, warranties, etc.
Incorrect material spe- cified, Inadequate
design life assumption, Over-stressing
Insufficient lubrication capability
Examples
Begin with previous FMEAs, brainstorming. Use
technical terms. Examples Cracked,
loosened, fractured, leaking...
Noise, erratic operation, unstable, inoperative...
Typical mechanisms
Wear, fatigue, corrosion
Summary of FMEA
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FMEA (cont)
(15) (16) (17) (18)
(19) (20)
(15) Frecuency of the cause from 1 to 10.
Statistically assigned if having information
about similar components, systems or sub-systems.
Otherwise use the following table. (16) List
the verification/validation design activities or
others related activities. The prevention
controls are preferred. Its recommended to use
two columns to define the two types of controls
(P) for prevention, (D) for detection.
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Probability of
Likely Failure Rates Over Design
Ranking

Failure

Life

Very High
³
10

100 per thousand vehicles/items

Persistent
failures


50 per thousand vehicles/items

9


High
20 per thousand vehicles/items

8

Frequent

failures


10 per thousand veh
icles/items

7


Moderate
5 per thousand vehicles/items

6

DESIGN OCCURRENCE EVALUATION
Occasional
failures


2 per thousand vehicles/items

5



1 per thousand vehicles/items

4


Low Relatively
0.5 per thousand vehicles/items

3

(D,F,GM. FMEA, 2001)
few failures


0.1 per thousand vehicles/items

2


Remote


1

0.01 per thousand vehicles/items

Failure is

unlikely


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FMEA (cont)
(15) (16) (17) (18)
(19) (20)
There are 2 type of controls according to its
importance i) Prevention. To prevent the
cause/mechanism or the effect/failure mode, or
reduce its occurrence. ii) Detection. To detect
the cause/mechanism or the effect/failure mode
by either analytic of physical
methods. Preventive controls are related to the
reduction of OCCURRENCE and not to the evaluation
of DETECTION
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DFMEA (cont)
(15) (16) (17) (18)
(19) (20)
(17) Is the evaluation associated to the best
detection control listed in the design control
(relative evaluation for every individual
FMEA). A scale from 1 to 10 is used. The
suggested evaluation criteria is shown in the
following table. (18) (Risk Priority Number).
Evaluation of the designs risk. Varies between 1
and 1000 RPN (S)x(O)x(D)
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(D,F,GM. FMEA, 2001)
15
(No Transcript)
16
FMEA (cont)
(15) (16) (17) (18)
(19) (20)
(19) Attention should be focused on high values
of severity, and high RPN, and in general,
independently of the RPN when the severity is 9
or 10. The goal is first to reduce severity,
then reduce ocurrence, and last to reduce
detection. It is desirable that the recommended
actions reduce the risk and increase customer
satisfaction by means of an improved design.
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FMEA (cont)
(15) (16) (17) (18)
(19) (20)
-Only the design reviews can reduce
severity. -To reduce occurrence the causes or
failure mechanisms must be eliminated or
controlled through design reviews. -To improve
detection, the design verification and
validations actions should be increased. If
there are no actions, write none. (20) Define
the responsible person and the completion date.
18
O
D
Responsibility target completion date
Current design controls (prevention/detection)
c
e
Recommended actions
u
t
r
e
r
c
List the design verification and validation
activities. Include current control like field
tests, laboratory studies and prototype testing
applied to this or to similar designs. There are
2 type of controls according to its importance
i) Prevention. To prevent the cause/mechanism
or the effect/ failure mode, or reduce its
occurrence. ii) Detection. To detect the
cause/mechanism or the effect/ failure mode by
either analytic of physical methods.
Determine and apply improvement actions. If they
are not necessary write the word none To
reduce occurrence the causes or failure
mechanisms must be eliminated or controlled
through design reviews. To improve detection,
the design verification and validations actions
should be increased. If there are no actions,
write none. Its preferable to reduce -in
that order, severity, occurrence and detection
Define the responsible person and the
completion date
Summary of FMEA (cont.)
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FMEA
(21)
(22)
(21) Register the implementation date and a brief
description of the action taken. (22) After the
implementation of the corrective actions,
re-evaluate the severity, occurrence and
detection. If necessary repeat steps 19-22.
Dont forget the follow up actions.
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ACTION RESULTS
S
O
D
R
e
c
e
P
Actions taken
v
u
t
N
r
c
Register the implementation date and a brief
description of the action taken. Re-evaluate RPN.