Transcript Document

Failure Mode and Effects
Analysis (FMEA)
Additional material to execute
FMEA exercise
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)
Failure Mode and Effects Analysis
Abbreviated Approach
Item
Potential
Failure
Mode
Function
Potential
Effect(s) of
Failure
S
e
v
C
l
a Potential Causes/
s Mechanisms(s)
s
Failure
O
c
c
u
r
Current
Controls
Prevention/Detection
D R
e P
t
e N Recommended
c
Action(s)
Actions Results
Responsibility
& Target
Completion Date
Actions
Taken
S O D R
e c e P
v c t N
What can be done?
What
are the
Effect(s)?
How
bad
is it?
- Design changes
How
often
does
it
happen?
What are the
functions, features
or requirements?
What can go
wrong?
- Partial/ Over/
Degraded
Function
- Unintended
Function
- Special controls
- Changes to standards,
procedures, or guides
What are
the Cause(s)?
- No Function
- Intermittent
Function
- Process changes
How can this
be prevented
and detected?
How
good is
this
method
at
detecting
it?
Who is going
to do it and
when?
What did they
do and what
are the
outcomes
FMEA (cont.)
Item/Function Potential Potential S C Potential Cause(s)/
Failure Effect(s) e l Mechanism(s) of
(9)
Mode
of failure v a failure
s
(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
FMEA SEVERITY EVALUATION CRITERIA
CRITERIA: Severity of Effect
RANK
Hazardouswithout
warning
Very high severity ranking when a potential failure mode affects safe vehicle
operation and/or involves noncompliance with government regulation without
warning
10
Hazardouswith
warning
Very high severity ranking when a potential failure mode affects safe vehicle
operation and/or involves noncompliance with government regulation with
warning
9
Very High
Vehicle/item inoperable (loss of primary function).
8
High
Vehicle/item operable but at a reduced level of performance. Customer very
dissatisfied.
7
Moderate
Vehicle/item operable but Comfort/Convenience item(s) inoperable. Customer
dissatisfied.
6
Low
Vehicle/item operable but Comfort/Convenience item(s) operable at a reduced
level of performance. Customer somewhat dissatisfied.
5
Very Low
Fit & Finish/Squeak & Rattle item does not conform. Defect noticed by most
customers (greater than 75%).
4
Minor
Fit & Finish/Squeak & Rattle item does not conform. Defect noticed by 50% of
customers.
3
Very Minor
Fit & Finish/Squeak & Rattle item does not conform. Defect noticed by
discriminating customers (less than 25%).
2
None
No discernible effect.
1
(D,F,GM. FMEA, 2001)
EFFECT
Very high severity ranking when a potential failure
mode affects safe operation and/or involves
noncompliance with regulations without warning.
Or may endanger operator without warning.
Hazardouswith warning
Very high severity ranking when a potential failure
mode affects safe operation and/or involves
noncompliance with regulations with warning.
Or may endanger operator with warning.
Very high
Product/item inoperable, with loss of primary
function. Or 100% of product may have to be
scrapped or repair time >1h.
High
Moderate
Product/item operable, but at reduced level of
performance. Customer dissatisfied. Or product
may have to be sorted and less than 100%
scrapped. Repair time between 0.5 and 1h.
Product/item operable, but comfort/convenience
inoperable. Customer dissatisfied. Or a portion
(less than 100%) of the product may have to be
scrapped with no sorting. Repair time less than 0.5h
Ranking
10
9
8
7
6
In the third edition this table is presented in two columns but the information is the same
(customer effect and manufacturing/assembly effect).
Hazardouswithout
warning
PROCESS
-----------------------------------------------------Criteria: SEVERITY of Effect
(D,F,GM. FMEA, 2001)
Effect
Low
Very Low
Minor
Very Minor
None
Product/item operable, but comfort/convenience
operable at a reduced level. Or than 100% of the
product may have to be reworked with no sorting.
Repairing off-line.
Fit and finish/squeak and rattle item does not
conform. Defect noticed by most customers
(greater than 75%). Or product may have to be
sorted with no scrap, and a portion (less than 100%
reworked.
Fit and finish/squeak and rattle item does not
conform. Defect noticed by 50% of the customers.
Or a portion (less than 100%) of the product may
have to be reworked with no scrap. On-line but outof-station.
Fit and finish/squeak and rattle item does not
conform. Defect noticed by discriminating
customers (less than 25%). Or a portion (less than
100%) of the product may have to be reworked
with no scrap. On-line but in-station.
No discernible effect. Or slight inconvenience to
operation or operator, or no effect.
5
4
3
2
1
(D,F,GM. FMEA, 2001)
FMEA (cont.)
Item/Function Potential Potential S C Potential Cause(s)/
Failure Effect(s) e l Mechanism(s) of
(9)
Mode
of failure v a failure
s
(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.
Product/
function
Name of the item and its
intended function
(purpose/objective).
Potential
failure mode
Include specific
problems, failures,
defects (antifunctions) of the
analyzed system(*)
and its functions. Use
physical terms
Potential
failure effects
The effect of failures in the
function of the analyzed
system, as they would be
perceived by the customer
(internal/external)
Use field data, previous
FMEAs, warranties, etc.
Examples:
Begin with previous
FMEAs, brainstorming. Noise, erratic operation,
unstable, inoperative...
Use technical terms.
Examples:
Cracked, loosened,
fractured, leaking...
Summary of FMEA
S
e
v
C
l
a
s
Potential causes/
mechanism
of failures
Describe what causes
the failure modes. Find
the root cause.
Typical causes:
Incorrect material specified,
Inadequate design
life assumption,
Over-stressing
Insufficient lubrication
capability
Typical mechanisms:
Wear, fatigue, corrosion
FMEA (cont)
O
Current
c
design
u
controls
r (Prevention &
r
Detection
(15)
(16)
D
e
t
e
c
R
P
N
(17) (18)
Recommended
Responsibility
actions
& target
completion
date
(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. It’s recommended to
use two columns to define the two types of controls: (P) for prevention,
(D) for detection.
High:
Frequent
failures
Moderate:
Occasional
failures
Low: Relatively
few failures
Remote:
Failure is
unlikely
Likely Failure Rates Over Design
Life
100 per thousand vehicles/items
Ranking
50 per thousand vehicles/items
9
20 per thousand vehicles/items
8
10 per thousand vehicles/items
7
5 per thousand vehicles/items
6
2 per thousand vehicles/items
5
1 per thousand vehicles/items
4
0.5 per thousand vehicles/items
3
0.1 per thousand vehicles/items
2
 0.01 per thousand vehicles/items
1
10
(D,F,GM. FMEA, 2001)
DESIGN OCCURRENCE EVALUATION
Probability of
Failure
Very High:
Persistent
failures
FMEA (cont)
O
Current
c
design
u
controls
r (Prevention &
r
Detection
(15)
(16)
D
e
t
e
c
R
P
N
(17) (18)
Recommended
Responsibility
actions
& target
completion
date
(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
DFMEA (cont)
O
Current
c
design
u
controls
r (Prevention &
r
Detection
(15)
(16)
D
e
t
e
c
R
P
N
(17) (18)
Recommended
Responsibility
actions
& target
completion
date
(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 design’s risk. Varies
between 1 and 1000: RPN= (S)x(O)x(D)
Detection
Criteria: Likelihood of DETECTION by Design
Control
Ranking
Absolute
Uncertainty
Design Control will not and/or can not detect a potential
cause/mechanism and subsequent failure mode; or there
is no Design Control.
10
Very Remote
Very remote chance the Design Control will detect a
potential cause/mechanism and subsequent failure
mode.
9
Remote
Remote chance the Design Control will detect a
potential cause/mechanism and subsequent failure
mode.
8
Very Low
Very low chance the Design Control will detect a
potential cause/mechanism and subsequent failure
mode.
7
Low
Low chance the Design Control will detect a potential
cause/mechanism and subsequent failure mode.
6
(D,F,GM. FMEA, 2001)
Moderate
Moderate chance the Design Control will detect a
potential cause/mechanism and subsequent failure
mode.
5
Moderately
High
Moderately high chance the Design Control will detect
a potential cause/mechanism and subsequent failure
mode.
4
High
High chance the Design Control will detect a potential
cause/mechanism and subsequent failure mode.
3
Very High
Very high chance the Design Control will detect a
potential cause/mechanism and subsequent failure
mode.
2
Almost
Certain
Design Control will almost certainly detect a potential
cause/mechanism and subsequent failure mode.
1
FMEA (cont)
O
Current
c
design
u
controls
r (Prevention &
r
Detection
(15)
(16)
D
e
t
e
c
R
P
N
(17) (18)
Recommended
Responsibility
actions
& target
completion
date
(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.
FMEA (cont)
O
Current
c
design
u
controls
r (Prevention &
r
Detection
(15)
(16)
D
e
t
e
c
R
P
N
(17) (18)
Recommended
Responsibility
actions
& target
completion
date
(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.
O
c
u
r
r
Current design
controls
(prevention/detection)
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.
D
e
t
e
c
R
P
N
Recommended
actions
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”.
It’s preferable to reduce -in that
order, severity, occurrence and
detection
Summary of FMEA (cont.)
Responsibility
& target completion
date
Define the responsible
person and the completion
date
FMEA
ACTION RESULTS
Action Taken S O D
e c e
v u
t
r
c
(21)
R
P
N
(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. Don´t
forget the follow up actions.
ACTION RESULTS
S
e
Actions taken
v
Register the implementation date and a
brief description of the action taken.
Re-evaluate RPN.
O
c
u
r
D
e
t
c
R
P
N