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Quality Management – Prof. Schmitt Exercise 09

Failure Mode and Effects Analysis E 09 page 0© WZL/IPT

© WZL/Fraunhofer IPT

Exercise Quality Management09 Failure Mode and Effects Analysis

Dipl.-Ing. Dipl.-Wirt. Ing. Michael Vorspel-Rüter

Dipl.-Ing. Dipl.-Wirt. Ing. Michael Vorspel-RüterGroup Business Excellence & DevelopmentDepartment Quality ManagementChair of Metrology and Quality ManagementSteinbachstr. 25 (ADITEC), D-52074 Aachen, Tel.: +49 (0)241 80-20717Fax: +49 (0)241 80-22671Email: [email protected]: http://www.wzl.rwth-aachen.de



Seite 1© WZL/Fraunhofer IPT

Example - FMEA Design

Execution of a design FMEA based on the example of a:

corkscrew




What is FMEA?FMEA = Failure Mode and Effects Analysis

or:Fehler-Möglichkeits- und Einfluss-Analyse

FMEA is a quality planning technique, i.e itis used in INNOVATIVE development and manufacturing processes

To forecast and reveal possible failures and to avoid them by implementing appropriate measures.

To document know-how (e.g. What can go wrong at which point in turning process? What parameters are important?).Inter-departmental interface for the exchange of expert knowledge (Personal communication is encouraged).

Targets:




Basic Methodology of FMEA

Definition ofContents

Preventive Application

Team Work

Systematic approach

Basic Methodologyof FMEA Effectiveness of FMEA

E.g. Reducing the cost of quality(source T. Pfeifer)

Actual status

Target statusFPC

TC

FC

FPC

TC

FC

are preconditionsfor

Legend:FPC = Failure Prevention CostFC = Failure CostTC = Testing Cost




FMEA – Failure Costs

Cos

ts p

er F

ailu

re

Planning Idea to product

Process planning

Demand onstock

Final inspection

Product in use

System-FMEAProduct

-,101,-

10,-

100,-System-FMEAProcess

FMEA is a preventive approach, i.e. weaknesses arerecognized and eliminated at an early stage




FMEA – Teamwork

Decision finding in team

Preparation in centers of competence

Team selection (example)

responsible permanentlyinvolved

temporarilyinvolved

design moderatorprocessplanningquality

assurance

development

procurement

Task of the moderator:•Project planning and - organisation•Documentation, evaluation•Assure methodological correctness•Moderation of conversation

Used information (e.g.):• Tolerance Analysis, dimensioning• process feasibility• failure lists• techn. drawing




FMEA Process

II Description of the object to be analysed• What should be included in the analysis?• What is the relation between the object and

the environment?• Clear definition of focus and borders of

investigation?

III Functional Analysis• Functions• Malfunctions• Interface functions

IV Identification of potential failures• Potential failures• Potential effects of failures• Potential causes for failures

V Evaluation of failures• Significance grade• Occurrence probability grade• Detection evaluation grade

VI Measures• Identification of weak points• Definition of measures• Responsibility and schedule

VII Updating• measures already implemented• Estimation of residual risk• Field FMEA

I Organisational preparation• Choose processes / products f. FMEA• Build up teams• Specify dates




To Task I: FMEA Checklist (e.g.)

FMEA-criteria: Weighting Evaluation Result Evaluation Result

Degree of Innovative developmentinnovation New type of design

Use of new materialsNew manufacturing techniquesOther conditions of useNo similar product on market

Technology Critical processComplex product

Legal Statutory regulationsrequirements Safety part

In this example: The corkscrew is more important

57759

107

108

10

1536219

1052

5352130181063

1004020

342

1241117254

5142859

1049204040

220

Cork- screw knife




To Task II: Description of the object to be analysedII.1:Identify the system structure

SE

SE

SE

SE

SE

SE

SE

SE

SE

SE

SE

SE

SE

.

.

.

Level of structureA B C D

SE: System elements

II.2:Identify the level of analysis

SE

SE

SE

SE

SE

SE

SE

SE

SE

SE

SE

SE

SE

.

.

.

Level of structureA B C D

SE: System elements




To Task III, IV: Definition of functions and malfunctionsIII.1:Identify the function of every system element

Systemelement

Function 1

Function 2

Function 3...

III.2: Specify potential malfunctions

Systemelement

Malfct. 1

Malfct. 2

Malfct. 3...

IV: Linking of malfunctions to the failure net

Level of structure (e.g.)A B C

FE F FC

Malfct.B.1

Malfct.A.1

Malfct.A.2

Malfct.A.n

.

.

.

Malfct.C.1

Malfct.C.2

Malfct.C.m

.

.

.

FE : Failure EffectF : FailureFC : Failure Causes




To Task V: Evaluation

Failure Effect Failure Failure Causes

RnS RnD RnO

Significance Detection evaluation grade

Occurrence probab. evaluation grade

Failure Chain

Risk numbers

!

Hint: Evaluation follows the actual implemented measures consider initial measures!

Malfct. B.1

Malfct. A.1

Malfct. A.2

Malfct. A.n

.

.

.

Malfct. C.1

Malfct. C.2

Malfct. C.m

.

.

.




To Task V: Evaluation of failures

Risk Priority Number = RnO x RnS x RnD

Measure of existence of a weak point extends from 1 (low risk)

to 1000 (high risk)

How likely is this failure cause?Probability that the cause of this failure occur from

1 (improbable) to 10 (probable)

How severe is this failure effect?The effect of the failure on the customer from 1 (no effect) to 10

(e.g. endangering safety of the customer)

How likely is it that this failure cause will be detected?Probability that the failure cause will be discovered prior to delivery to

customer from 1 (probable) to 10 (improbable)




To Task VI: Risk minimisation procedureRisk analysis based

on implemented measures

End

No

Yes

Risk minimisation

Risk?

Measureswith date

and competence

Specify

Introduce

Review

Remedial

Effect limiting

Detection




To Task VI: Risk identification I

Risk-Identification is based on classified, partly subjective evaluations.

Risk Identification cannot be done on the basis of fixed rules or limits.

Risks can only be prioritised relatively to each other.

The following methods of risk-identification and determination of appropriate measures must therefore be verified from the engineers point of view.




To Task VI: Risk identification IIIdentify necessity for measures

Pareto- Analysis(cover 80%)

Specify limit valuesfor the risk

E.g.:RPN > 124 and

RN 'significance' > 8 &RN ‚occurrence‘ > 3

Risk evaluation Failure causes Measures

O S D1 1 1 Ideal condition (target) no measures (nm)1 1 10 insignificance, rare failure nm1 10 1 Failure does not reach user nm1 10 10 Failure reaches user yes10 1 1 frequent failure, identifiable, expensive yes10 1 10 frequent failure, reaches user yes10 10 1 serious, frequent failure yes10 10 10 difficulties yes, yes, yes !!!

%Sum(%)

0

10

20

30

40

50

60

70

80

90

100

ID 1 ID 2 ID 3 ID 4 ID 5




To Task VI: Pareto Chart (e.g.)

97,25,5404

100

91,7

80,5

63,3

Sum (%)

100726Total

2,8205

11,2813

17,21252

63,34601

%RPNID

0

10

20

30

40

50

60

70

80

90

100


%Sum(%)

0

50

100

150

200

250

300

350

400

450


abs.Sum(%)

80%

80%

Chart of RPN- %

Chart of absolute RPN(combined with %)




To Task VI: Determination of measuresBasis: The RPN- priorised chains of failures.

For each single risk number (RNS, RND, RNO) specific measures can be determined (see below).

For the reduction of Total- RPN it usually makes sense,first to reduce the single RN with highest scores by appropriate measures.

Note measures always with the responsible person and date!

Failure effect Failure cause

RNS RND RNO

Effect limiting Detection Remedial

Failure chain

Risk numbers

Measures

Significance Detection evaluation grade

Occurrence probab. evaluation grade




Example Corkscrew

Casing

Spiral shaft

Rivets

Levers




Step II. 1 (and II. 2) Identification of system structure

Corkscrew

Spiral shaft

Lever

Casing

Rivet

Gear rod

Cork thread

Bore- hole

Thread

Rivet hole

Guidance

Construction

Cases

Level of structure A Level of structure B Level of structure C




Step III. 1 Identify functions of every system element

Corkscrew

Spiral shaft

Casing

Gear rod

Cork thread

Rivet hole

Guidance

to pull cork as a whole

to centerto transmit tractive force

Positioning on bottlesto center spiral shaft

to retain rivets

Form closure with lever

form closure with cork (transmit tractive f. to the cork)

enable rotation to the lever

screwing in

to bring up counter moment

to allow vertical movement and rotationto prevent tilting

transmit tractive force to lever





Step III. 2 Specify potential malfunctions

Corkscrew

Spiral shaft

Casing

Gear rod

Cork thread

Rivet hole

Shaft- Guidance

Cork breaks

Difficult to turn/ impossible

slips down from bottleSpiral shaft tilted

too much play

Bottle getsdamaged

difficult to turn spiral shaft Guidance is clamping

slanty spiral shaft

no tractive force transmittable

Rivets can not be assembledRivets fall out

difficult to turn

no form closure with lever incompatible with lever

Cork gets stuck

no form closure





Corkscrew: Step IV Linking of malfunctions to the failure net

No tractive forcetransmittableCork gets stuck No form closure

with lever possibleDifficult to turn

spiral shaft Cork gets stuck Tooth profile incomp. with lever

Spiral shaft tiltedCork breaks

Shaft- Guidance has too much playBottle gets damaged

Example:

Slanty spiral shaftBottle gets damaged

Cork thread without form closure

Cork breaks

I

Malfct. B.1Malfct. A.1Malfct. A.2

Malfct. A.n...

Malfct. C.1Malfct. C.2

Malfct. C.m...

II

III

IV

V

VI




Corkscrew: Step V Valuation

This part will be processed in the exercise.

Failure Effect Failure Failure Causes

RnS RnD RnO

Significance Occurrence prob.evaluation grade

Detection evaluation grade

Effect limitingmeasures

Suggested detectionmeasures

Suggested remedialmeasures

Failure chain

Risk numbers

Measures

!

Failure Mode and Effects Analysis

Type/m odel /m anufacture/batch: Subject no.

Subject no.:

Status.:

Status

Responsibility:

Responsibility:

Company:

Company:

Dept. :

Dept. :

Date:

Date:

Control no.

Page of

System no./System element:

Function/Task:

No. Poss.Conseq.

Poss.failures

S Poss.Causes

Remedial measures

D Ident ific. Measure s

O RP N Responsibility /Due date

S= evaluation gradeSi gnifi cance D= Detectio n evalutation grade O = Occurance evaluation grad eRis k Priority Number RPN = S*D*O

System-FMEA Product System-FMEA Process 1 1




Blank VDA Form (1996)Failure Mode and effects analysis

System FMEA Product System FMEA ProcessFMEA No.:

Page:

Type/Model/ manufacture/batch:

CorkscrewSubject No.:90 HF- 10145- AAStatus:A/369 437/KC

Guarantor:

J. StudentFirma:

Dept.: MQDate:

System- No./System- element:

Possible Failure effect

Poss. Failurecauses

Poss. Failure Remedial measures

Detection measures

S O D RPN R/DNo.




Corkscrew: Pareto Chart

0

10

20

30

40

50

60

70

80

90

100

ID 1 ID 2 ID 3 ID 4 ID 5 ID 6 ID 7

5

6

4

Sum (%)

Total

7

3

2

1

%RPNID

80%




Attachment: Criteria for the evaluation grade of the System-FMEA Product

Unlikely1 Unlikely that the failure will have any perceptible consequences, customer will probably

not perceive the failure.

Low

Moderate6 Operability of the vehicle is restricted, immediate stay in the garage is not obligatory, 4 disturbance of fundamental control elements.

High8

7

Very high10

9

Severity evaluation grade S

Safety risk, violation of legal regulations.

Operability of the vehicle is constricted, immediate stay in the garage is obligatory, disturbance of the system.

Low disturbance of the system, remedy of defects near the next regular stay in the garage, disturbance of fundamental control elements.

32





Very High1 The occurred failure cause will be surely detected.

High3 Detection of the occurred failure cause is very probable and can be proved using different2 testing methods.

Moderate6 Detection of the occurred failure cause is probable; the reliability of the design cannot be 5 proved; testing methods are quiet reliable.4

LowDetection of failure causes is less probable; the reliability of the design cannot be proved.Testing methods are quiet reliable.

Unlikely

Detection of failure causes is unlikely; the reliability of design could not be proved.

Detection grade D

10

9

8

7





Unlikely1 The occurrence of the failure cause is unlikely.

Low32

Moderate654

High 87

Very high10 The failure cause occurs very often. Inadequate and unsuitable design.

9

Occurrence evaluation grade O

The failure cause occurs redundantly; problematic, immature design.

Failure cause occurs intermittently; suitable, pretty mature design.

The probability of occurrence of the failure cause is low; reliable design.

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