Failure Mode and Effects Analysis (FMEA) Additional material to execute FMEA exercise

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 AnalysisAbbreviated Approach

Item Potential Potential

Sev

Class

Occur

Current

Detec

RPN

ResponsibilityActions Results

Failure Effect(s) of Recommended & TargetFunction Mode Failure

Potential Causes/Mechanisms(s)

FailureControls

Action(s) Completion DateDet

Occ

RPN

ActionsTaken

Sev

What are the functions, featuresor requirements?

What can go wrong?

- No Function

- Partial/ Over/ Degraded Function

- Intermittent Function

- Unintended Function

What are the

Effect(s)?

How bad is it?

What are the Cause(s)?

Howoften does

ithappen?

How can this be preventedand detected?

How good is

this method

atdetecting

it?

What can be done?

- Design changes

- Process changes

- Special controls

- Changes to standards, procedures, or guides

Prevention/Detection

Who is goingto do it andwhen?

What did theydo and what

are theoutcomes

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)(12) (13)

(14)

(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 largevalues of severity can be reduced by means of design reviews thatcompensate or mitigate the resulting severity.

(*) subsystem or component

FMEA (cont.)

Hazardous-withwarning

Very High

High

Very high severity ranking when a potential failure mode affects safe vehicle operation and/or involves noncompliance with government regulation without warning

Low

Very Low

Minor

Very Minor

None

Very high severity ranking when a potential failure mode affects safe vehicle operation and/or involves noncompliance with government regulation with warning

Vehicle/item inoperable (loss of primary function).

Vehicle/item operable but at a reduced level of performance. Customer very dissatisfied.

Vehicle/item operable but Comfort/Convenience item(s) inoperable. Customer dissatisfied.

Vehicle/item operable but Comfort/Convenience item(s) operable at a reduced level of performance. Customer somewhat dissatisfied.

Fit & Finish/Squeak & Rattle item does not conform. Defect noticed by most customers (greater than 75%).

Fit & Finish/Squeak & Rattle item does not conform. Defect noticed by 50% of customers.

Fit & Finish/Squeak & Rattle item does not conform. Defect noticed by discriminating customers (less than 25%).

No discernible effect.

10

8

7

6

3

2

1

Hazardous-withoutwarning

Moderate

4

5

EFFECT CRITERIA: Severity of Effect RANK

FMEA SEVERITY EVALUATION CRITERIA

9

(D,F

,GM

. FM

EA

, 200

1)

Effect

PROCESS ------------------------------------------------------ Criteria: SEVERITY of Effect

Ranking

Hazardous-withoutwarning

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.

10

Hazardous-with 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.

9

Very high

Product/item inoperable, with loss of primary function. Or 100% of product may have to be scrapped or repair time >1h.

8

High

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.

7

Moderate

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

6

In th

e th

ird e

ditio

n th

is ta

ble

is pr

esen

ted

in tw

o co

lum

ns b

ut th

e in

form

atio

n is

the

sam

e(c

usto

mer

effe

ct a

nd m

anuf

actu

ring/

asse

mbl

y ef

fect

).

(D,F

,GM

. FM

EA

, 200

1)

Low

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.

5

Very Low

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.

4

Minor

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 out-of-station.

3

Very Minor

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.

2

None

No discernible effect. Or slight inconvenience to operation or operator, or no effect.

1

(D,F,GM. FMEA, 2001)

(13) Indicates any special characteristic (critical, key, major)that will require special controls. Some of the D, F, GM specialsymbols can be used.

(An indication of criticality is when severity is 9 or 10, being theoccurrence and detection geater than 3. (Stamatis, 1995)).

(14) Describe what causes the failure modes. Discover the rootcauses.

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)(12) (13)

(14)

FMEA (cont.)

Product/function

Potentialfailure mode

Potentialfailure effects

S C Potential causes/mechanismof failures

e lv 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 causesthe failure modes. Findthe root cause.

Use field data, previousFMEAs, warranties, etc.

Begin with previousFMEAs, brainstorming.Use technical terms.

Examples:Cracked, loosened,fractured, leaking...

Typical causes:

Examples:

Incorrect material spe-cified, Inadequate design life assumption, Over-stressing Insufficient lubrication capability

Noise, erratic operation,unstable, inoperative...

Typical mechanisms:Wear, fatigue, corrosion

Summary of FMEA

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 relatedactivities. The prevention controls are preferred. It’s recommended touse two columns to define the two types of controls: (P) for prevention, (D) for detection.

O Current D R Recommended Responsibilityc d esig n e P actions & targ etu co n tro ls t N co m p letio nr (P rev ention & e dater D etection c

Probability of Failure

Likely Failure Rates Over Design Life

Ranking

Very High: Persistent failures

100 per thousand vehicles/items 10

50 per thousand vehicles/items

9

High: Frequent failures



7

Moderate: Occasional failures



5


4

Low: Relatively few failures

0.5 per thousand vehicles/items 3

0.1 per thousand vehicles/items

2

Remote: Failure is unlikely

0.01 per thousand vehicles/items

1

(D,F

,GM

. FM

EA

, 200

1)

DE

SIG

N O

CC

UR

RE

NC

E E

VA

LU

AT

ION

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 andnot to the evaluation of DETECTION

(15) (16) (17) (18) (19) (20)


FMEA (cont)

(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 shownin the following table.

(18) (Risk Priority Number). Evaluation of the design’s risk. Variesbetween 1 and 1000: RPN= (S)x(O)x(D)

(15) (16) (17) (18) (19) (20)


DFMEA (cont)

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

(19) Attention should be focused on high values of severity, and highRPN, and in general, independently of the RPN when the severity is9 or 10.

The goal is first to reduce severity, then reduce ocurrence, and lastto reduce detection. It is desirable that the recommended actions reducethe risk and increase customer satisfaction by means of an improveddesign.

FMEA (cont)

(15) (16) (17) (18) (19) (20)


-Only the design reviews can reduce severity.

-To reduce occurrence the causes or failure mechanisms must beeliminated 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.

(15) (16) (17) (18) (19) (20)


FMEA (cont)

OCurrent design

controls(prevention/detection)

D

Recommendedactions

Responsibility& target completion

date

c eu t

RPNr e

r c

List the design verification andvalidation activities. Includecurrent control like field tests,laboratory studies and prototypetesting applied to this orto 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 improvementactions. If they are not necessarywrite 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 thatorder, severity, occurrence anddetection

Define the responsibleperson and the completiondate

Summary of FMEA (cont.)

FMEA

(21) (22)

(21) Register the implementation date and a brief description of the actiontaken.

(22) After the implementation of the corrective actions, re-evaluate the severity, occurrence and detection. If necessary repeat steps 19-22. Don´tforget the follow up actions.

ACTION RESULTSAction Taken S O D R

e c e Pv u t N

r c

ACTION RESULTS

Actions taken

S O D Re c e Pv u t N

r c

Register the implementation date and a brief description of the action taken.Re-evaluate RPN.

Documents

Failure Mode and Effects Analysis (FMEA) Additional material to execute FMEA exercise