DFMEA - manual.pdf

1

Failure Mode and Effect Analysis

Lecture 2-3Design FMEA

2

FMEA

• The definition of "customer" for a Design FMEA can be the . . . .

REPAIR CENTER

MANUFACTURING

NEXT ENGINEERINGGROUP

END USER

Customer Defined

2

3

FMEA

• The Design FMEA is a living document and should be initiated at or by the design concept finalization, be continually updated as changes occur throughout the phases of product development, and be fundamentally completed along with the final drawings.

Drawings

Living Document

4

FMEA

A Design FMEA is an analytical technique utilized by product or process designers as a means to ensure that, to the extent possible, potential failure modes and their associated causes have been considered and addressed.

What is DFMEA?

3

5

FMEA

• Aiding in the objective evaluation of design requirements and design alternatives

• Increasing the probability that potential failure modes and their effects on system operation have been considered in the design / development process.

• Providing additional information to aid in the planning of thorough and efficient design test and development programs.

The Design FMEA supports the design process in reducing risk of failures by:

Design FMEA

6

FMEAThe Design FMEA addresses design intent and assumes the design will be manufactured to this intent.Potential failure modes / causes which can occur during the manufacturing or assembly process are not included in a Design FMEA. Their identification, effect, and control are covered by the Process FMEA. The Design FMEA does not rely on process controls to overcome potential weaknesses in the design, but it does take the technical and physical limits of the manufacturing process into consideration.

DFMEA Assumptions

4

7

FMEA

• Planning Phase– Timing: early in the design process– Purpose: quick visibility of most obvious weak points

• Development Phase– Timing: design and preliminary component specs are

available– Purpose: expansion of planning phase

• Verification and Introduction Phase– Timing: completion of engineering model and start of

Customer testing– Purpose: final failure modes and risk assessment prior

to production

DFMEA Phases

8

FMEA

CONCEPT

ENG PROTOTYPE

DEVELOPMENT

The FMEA develops in complexity and detail as the product progresses through the design phases

Time Phase

5

9

FMEA

HARDWARE

BOTTOM-UP

TOP-DOWN

FUNCTIONAL BLOCK

RELIABILITY BLOCK

Technique - Listed Items

10

FMEASystem Breakdown ConceptSystem A composite of subsystems whose functions

are integrated to achieve a mission or specific output

Subsystem composite of assemblies whose functions are integrated to achieve a specific activity necessary for achieving a mission

Assembly a composite of subsystems

Component a composite of piece parts

Piece Part least fabricated item, not further reducible

Interface the interactions point(s) necessary to produce the necessary effects between system elements (interfaces transfer energy/information, maintain mechanical integrity, etc.

6

11

FMEAFunctional vs. Geographic

• Functional– Cooling system– Propulsion system– Braking system– Steering system

• Geographic– Engine compartment– Passenger compartment– Dashboard / Control Panel– Rear end– etc.

Interface components If an engine-driven belt powers both a water pump and a power steering system, be sure to include it as part of one, or as a separate interface element.

12

FMEASystem Breakdown Example

ETC . . . .TRANSMISSION

ETC . . . .ENGINE

BATTERYGENERATORPLUGSCOILDISTRIBUTOR

SPARK / IGNITION

CARBURATORAIR

STORAGEDELIVERY

FUELPROPULSION

RADIATORWATER PUMPCOOLANTHOSES, CLAMPSTHERMOSTAT

COOLINGAUTOMOBILE

SUBASSEMBLYASSEMBLYSUBSYSTEMSYSTEM

7

13

FMEAFunctional FMEAsFocus on the functions that a product, process, or

service is to perform rather than on the characteristics of the specific implementation. When developing a functional FMEA, a functional block diagram is used to identify the top-level failure modes for each functional block on the diagram.

14

FMEA

MOUNTING DECK, COVER

BASE DECK STAMPED COVER COVER SEAL TAPE SEAL

FUNCTIONAL BLOCK

Much of a complex product can be analyzed by looking at functional blocks rather than individual items

Functional Block

8

15

FMEA

P RE AM P

FILTER

AM P (AGC)

S LIM M ING

A to D

DECODE

CONTROL BUFFER

HOS T

HEAD

RELIABIL ITY BLOCK

Reliability Block

16

FMEADetailed FMEAs

Focus on the characteristics of specific implementations to ensure that designs comply with requirements for failures that can cause loss of end-item function, single-point failures, and fault detection and isolation.

9

17

FMEA

BASE FINAL ASSY

UNIT ASSY

MOTOR ASSY

MOTOR POLE ASSY

MOUNTINGBRACKET

MOTOR POLE

MOTOR POLE SPACER

MACHINE SCREW

MAGNET

HARDWARE

Handbook pg. 14

FMEA follows the hardware BOM from the bottom-up, or the top-down

Technique - Hardware

18

FMEAInterface FMEAs

Focus on the interconnections between system elements so that the failures between them can be determined and recorded and compliance to requirements can be verified..

10

19

FMEADFMEA Form

20

FMEAWorksheetFMEA WORKSHEET PRODUCT: ENGR PG

TYPE: DESIGN PROCESS OTHER____________ ITEM:

FUNCTION POTENTIAL EFFECTS OF POTENTIAL VERIFICATION ORFAILURE MODE FAILURE S CAUSES O CURRENT CONTROL E RPN

11

21

FMEA

PRODUCT: FMEA NO.

PROCESS/OPERATION: PAGE OF

DESIGN (OR PROCESS) FMEAPLANNING REFERENCE: DATE: BY:

Oklahoma CityPOTENTIAL POTENTIAL S POTENTIAL O CURRENT D RPN ACTION CORRECTIVE RESPONSIBILITY ACTION RESULTING

FUNCTION FAILURE MODE EFFECTS OF CAUSE(S) OF CONTROLS PRIORITY ACTION & DATE DUE TAKENFAILURE FAILURE S O D RPN

DETECTIONOCCURRENCESEVERITY RPN = S x O x D

ENGINEER WITH PROGRAM TEAM3.DESIGN ENGINEER

(MANUF ENGINEER)1.

DESIGN ENGINEER, MANUFACTURING

ENGINEER, QUALITY ENGINEER,

RELIABILITY ENGINEER2.

DFMEA Steps - Teams

22

FMEAGround Rules

1. Do not consider all conceivable failure modes

2. Initially write the failure mode as loss of function

3. Decide on the approach - function or hardware

4. Develop each column of the FMEA independently.

12

23

FMEAFunction

Common problems• Not all functions are identified• The description is not exact or concise• The description is not in direct language

FMEA WORKSHEET PRODUCT: ENGR PGTYPE: DESIGN PROCESS OTHER___________________ ITEM:


24

FMEAPotential Failure Mode

• The manner in which the item (product, component, system) could potentially fail to meet the design intent.

• Assume that the failure mode could occur but may not necessarily occur.

• Potential failure modes should be described in “physical” or technical terms, not as a symptom noticeable by the customer



13

25

FMEAEffects of Failure

• Describe in terms of what the customer might notice or experience

• State clearly if safety or compliance to regulations is an issue.

• Keep in mind the hierarchical relationships between parts, subsystems and systems.



26

FMEASeverity of Effect

• An assessment of the seriousness of the effect.

• Only applies to the effect• If several effects exist for a failure mode,

choose the worst case severity.• Rank on a scale of 1-10



14

27

FMEASeverity of Effect DesignSEVERITY EVALUATION CRITERIA

Severity of EFFECT Ranking

Improbable, minorUnreasonable to expect that the minor nature of this failure would cause any real effect on the overall performance

1

LowThe failure is insignificant and the user is only minimally affected 2The product is fully functioanl and the failure is viewed as a nuisance item 3ModerateFailure causes customer dissatisfaction in the form of annoyance 4Failure notices by customer requires correction 5Customer notices slight performance degradation 6HighLoss of some product function but not of system performance 7Product inoperable or fails to meet performance criteria 8

ExtremePotentailly hazardous affect. possibly safety-related 9Product safety of liability hazard 10

28

FMEASeverity – Another Example

15

29

FMEAPotential Causes

• For each potential failure mode, list all possible causes

• Goal is to get to root cause, or to a reasonable place to break the cause-effect chain.

• Rotate columns is necessary. If the team starts finding causes of causes, “promote” the original cause to potential failure mode.



30

FMEATesting the Relationships

• Use the following to see if you got the relationships in the proper sequence:

IF cause THEN failure modeHOW DO I KNOW? effect

16

31

FMEA

FAILUREMODE

LIKELY CAUSES LIKELY EFFECTS

ACTIONS

TRIGGER

PREVENTIVECONTINGENT

- ADAPTIVE- CORRECTIVE

Cause-Effect Model

32

FMEAOccurrence

• The likelihood that a specific cause will occur and result in the failure mode.

• Rank on a scale of 1 - 10



17

33

FMEAOccurrence of Cause DesignOCCURRENCE EVALUATION CRITERIA

Probability the CAUSE will occurPossible

Failure Rate (DPPM)

Ranking

Remote

Failure is unlikely. No known failures associated with almost identical designs <1 in 106 1(<1)

Very LowOnly isolated failures associated with similar designs < 1 in 20,000 2

(<50)LowOccassional failures associated with similar designs <1 in 4,000 3

(<250)ModeratePrevious designs have experienced problemsor occassiona lfactory out-of control conditions 1 in 1,000 4

1 in 400 51 in 80 6

HighSimilar designs have experience problems which have led to stop-ship conditions 1 in 40 7

1 in 20 8ExtremeFailure almost inevitable 1 in 8 9

1 in 2 10

34

FMEAOccurrence – Another Example

18

35

FMEAEngineering Verification

• The activities that will assure the design adequacy for the failure mode / cause

• If the design FMEA is done very early, it may not be possible to determine the engineering verification



36

FMEAEffectiveness

• The ability of the proposed design control to detect the potential cause.

• Rank on a scale of 1 - 10



19

37

FMEAEffectiveness of Design Verification

EFFECTIVENESS EVALUATION CRITERIA

Effectiveness of the Verification Activity Ranking

Very EffectiveDesign evaluation controls will detect a design weakness prior to production release 1

2HighControls will have a good chance of detecting design weakness 3Will be detectable after release but before build 4

ModerateControls may detect design weakness before initial shipment 5Will be detected prior to shipment to customer 6

LowControls not likely to detect design weakness and must wait for larger volume 7

8Very LowControls will probably not detect falure 9Controls cannot ir will not detect failure 10

38

FMEAEffectiveness (Detection)

20

39

FMEA

Occurrencex Severity

x EffectivenessRPN = O x S x E

Risk Priority NumberFMEA WORKSHEET PRODUCT: ENGR PGTYPE: DESIGN PROCESS OTHER___________________ ITEM:


40

FMEA

Priority RPN rangeA OVER 200B 100-199C 26-99D 1-25

Final ranking (or risk assessment) in order of importance

Action Priority

21

41

FMEA

A 8 4 3 96

B 4 8 3 96

SAME RESULT

Handbook pg. 29

Failure

Mode

Seve

rity

Occur

rence

Effecti

vene

ssRPN

Shortcomings of RPN Method

42

FMEA

A 8 4 3 96

B 4 8 3 96

Failure

Mode

Seve

rity

Occur

ence

Effecti

vene

ssRPN

FOCUS ON SEVERITY

Shortcomings of RPN Method

22

43

FMEAAnother Scoring Approach

FMEA “Area Chart”*

HIGH PRIORITY

MEDIUMPRIORITY

LOW PRIORITY

1 2 3 4 5 6 7 8 9 10

10987654321

OCCURRENCE

SEVE

RIT

Y

* Failure Modes and Effects Analysis, Paul Paladay, PT Publications, 1995

44

FMEA

The design must be improved based on the results of the FMEA study.

A well-developed Design FMEA will be of limited value without positive and effective corrective actions.

Actions

23

45

FMEA

Component misspecification due to communication problemsUnenforceable specs - can’t be verified with present technologyImproper specs - “standard conditions” can be a trap! OR specs for past products no longer sufficient for new ones

What problems do we encounter with specifications?

Specifications

46

FMEAFMEA Homework 2

• Complete a design FMEA for the product shown on the next page

• Use the forms provided on the web page, or create forms of your own. If your company already has FMEA forms, you may use them for this exercise.

• Concentrate on the function / failure mode / effect and cause columns. Make up something (within reason) for the engineering verification and scoring.

• Each person is to submit an FMEA.• Submit the FMEA to me attached to e-mail.

Assignment is due 4/2/2004.

24

47

FMEA

ADHESIVE

ADHESIVE-FREEAREA

TOP VIEW SHOWING LABEL IN PLACE

RECESSED AREA

FMEA Homework 21. Evaluate the design of a pressure-sensitive adhesive label attached to an instrument case.2. The case contains sensitive electronic components that cannot be exposed to contamination from particles or vapors, including possible contamination from the pressure-sensitive adhesive. 3. The hole is used for final adjustment and is covered with a pressure-sensitive label. To keep the inside of the case from being exposed to possible contamination from the adhesive, the label was designed with a no-adhesive area.4. The final adjustment of the components is intended for the factory only and must not be done by the consumer.5. Remember that you are product designers and not process engineers at this point, however, the process engineer on your team says that a manufacturing constraint exists, the labels must be attached by hand by an operator on an assembly line.6. List any process concerns that you will want to consider as part of a later process FMEA.

48

FMEADesign FMEA FormPRODUCT: FMEA NO.

PART / SYSTEM: PAGE OF

DES IGN FMEA DRAWING REFERENCE: DATE: BY:

S O E R PN R ES U LTIN G

S O E RP N

EFFECTIVENESSEVERITY OCCURRENCE RPN = S x O x E

P ART OR S YS TEM

DESIGN VERIFICATION

ACTIVITES

EFFECTS OF FAILURE -LOCAL,

NEXT LEVEL, END USERFUNCTION(S)

POTENTIAL CAUSES OF

FAILURE

POTENTIAL FAILURE MODE

ACTION

RECOMMEN. CORRECTIVE

ACTIONS

RESPONSIB & DUE DATE

ACTIONS TAKEN

Documents

DFMEA - manual.pdf