Fmea Design

Nathan & Nathan Consultants Pvt. Ltd. NNCPL/PPT/005 1.

DESIGN FMEADESIGN FMEA

to the

Training Seminar on

FAILURE MODE & EFFECT ANALYSISFAILURE MODE & EFFECT ANALYSIS

DFMEADFMEA


DESIGN FMEADESIGN FMEAF

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OriginUS-Space program and defence safety system in 1960’s

Common Definitions Function :

Function of the item being analysed to meet the Design intent. Includes information regarding the environment in which this system operates.

Failure Mode:

A ‘Failure Mode’ is the manner in which a component, assembly or system could potentially fail to meet the design intent. Typical failure mode may includes, not limited to :

Yield; Fatigue; Material Instability; creep; wear; corrosion;

Cracked Deformed; Leaking.


DESIGN FMEADESIGN FMEAWhat is FMEA?

FMEA is a systemised group of activities to:

1. recognise and evaluate the potential failure of a product /

process and its effects

2. identify actions which could eliminate or reduce the chance

of potential failure occurring

3. document the process

Why FMEA ?

1. For a company policy where continuous improvement is

emphasized for its product, process

2. FMEA is a living document

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A Who should do FMEA?

1. Cross Functional Team Effort – with a leader

2. Team of knowledgeable individuals Ex. Expertise in Design,

Mfg., Assly., Quality., etc.

3. Team should include representatives of sub-contractors and/or

customers

When FMEA should be done ?

1. Essence is timeliness

2. Pro-Active rather than reactive

3. Before process failure mode occurs



ME

A Advantages of FMEA

1. Avoids late change crisis

2. Reduces or eliminates chance of

implementing corrective change

3. excellent technique for preventive action

4. interactive process which is never ending

Types of FMEA

1. System FMEA – Power transmission system

2. Design FMEA – Axle shaft

3. Process FMEA – Heat treatment



ME

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FMEA shall consider special characteristics Aiming defect prevention rather than defect detection Use FMEA manual & CFT approach

Potential – Design FMEA

Potential Means ‘Anticipated’

It is an analytical technique to assure that potential failure

mode and their associated causes have been considered and

addressed.


DESIGN FMEADESIGN FMEADesign FMEA supports the Design process in reducing the risk of failures by :

Aiding in the objective evaluation of design requirements and design

alternatives Aiding in the initial design for manufacturing and assembly requirements Increasing the probability that potential failure modes and their effects on

system and vehicle 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 Developing a list of potential failure modes ranked according to their effect

on the "customer", thus establishing a priority system for design

improvements and development testing Providing format for recommending and tracking risk reducing actions. Providing future reference to aid in analysing field concerns, evaluating

design changes and developing advanced designs.

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DESIGN FMEA - BLOCK DIAGRAMHelps to analyze the inter-relationship between various parts/subsystems within each subsystem/ system.

Example :

2

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4 1 4

5 5

SWITCHON/OFF

C

HOUSINGA

BATTERIESB

BULBASSEMBLY

D

PLATEE+

SPRINGF

COMPONENTS

A. HOUSINGB. BATTERIES (2 D CELL)C. ON/OFF SWITCHD. BULB ASSEMBLYE. PLATEF. SPRING

ASSEMBLY METHOD

1. SKIP FIT2. RIVETS3. THREAD4. SNAP FITCOMPRESSIVE FIT


DESIGN FMEADESIGN FMEAIT

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CLICK HERE

FOR FMEA FORMAT

CLICK HERE


DESIGN FMEADESIGN FMEAIT

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System Level Sub system level Component level

Bicycle

DESIGN OBJECTIVE

1 Minimum 3000 hr. of riding withoutneed for maintenance & 10,000 hr.of riding for design life2 Accommodates mate auditscomfortably to the 99.5 th percentile3 etc.

POTENTIAL FAILURE MODE :1 Difficult to steer2 difficult to pedal

FUNCTION1 provide reliable transportation

POTENTIAL FAILURE MODE ( S )

1 Chain break frequency2 Tires require frequency

FUNCTIONS :

Frame

FUNCTION1 provide stable attachment for seatsupport


1 Structural failure of seat support2 Excessive defection of seat support

FUNCTIONS :

Provide pleasing appearance


1 Finish deteriorates2 Paint chips

Handle bar Assembly

Front wheel Assembly

Rear wheel Assembly

Sprocket Assembly

Upper frame

FUNCTION1 provide structural support


1 Structural failure2 Excessive defection

FUNCTIONS :

Provide dimensional control for correctfinishing frame geometry


1 Length of frame mounting points toolong

2 Length of frame mounting points are tooshort

Lower front Tube

Lower Rear Tube

Sprocket Tube

FOR DESIGN FMEA CHECKLIST

CLICK HERE


DESIGN FMEADESIGN FMEAE

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FunctionPotent

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PotentialEffect(s)of Failure

Specify the descriptionand Function of the item

ExampleItem function Occupant protection from

weather, noise and sideimpact

Support anchorage fordoor hardware



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NS Potential Failure Mode Potential

Effect(s) ofFailure

Sev

Review of the past things-gone-wrong, concerns reports, andgroup brainstorming is required.

List the failure modes those arepossible to occur against therequirements specified in theprevious column.

Apart from Engg. specification ,what would a customer considerobjectionable

ExampleCracked, Deformed, Loosened,Oxidised, Leaking



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NS Potential Effect(s) of Failure Sev

Class

List the effects of failure mode on thefunction, as perceived by thecustomer.

Describe the effects using theterminology specified in Severityrating table

For each failure mode, more than oneeffect can be listed

Example- Noise- Erratic Operation- Poor Appearance- Unstable- Intermittent Operation- Rough- Inoperative



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SeverityClass

PotentialCause(s) /

Mechanism (s)of Failure

Assess the seriousness ofthe effect in a 1-10 scale

This rating applies toEFFECT only (i.e. previouscolumn)

Safety related effectsshould be rated in Nos.9 or10

FOR SEVIORITY RANKING

CLICK HERE



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Classification

PotentialCause(s) /

Mechanism(s) of Failure

Occur

Classify special productcharacteristics (e.g. critical,key, major)



Potential Cause(s) /Mechanism (s) of Failure

Occur

CurrentProcessControl

sPreventi

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CurrentProces

sControl

sDetecti

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Indication of Designweakness, the consequenceof which is the failure mode.

Describe the causes in sucha way that can be eliminatedor controlled

Typical cause include : Incorrect material

specified Inadequate Design life

assumption Over-stressing Insufficient Lubrication

Capability

Typical Failure causes mayinclude, but not limited to

1 Incorrect materialspecification

2 Inadequate design lifeassumption.

3 Over stressing4 Insufficient lubrication

capability5 Inadequate / improper

Maintenance instruction6 Incorrect algorithm7 Improper software

specification / surfacefinish specification / travelspecification

8 Excessive heat9 Improper tolerance

specified

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Occurrence

CurrentProcessControlspreventi

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CurrentProces

sControl

sDetecti

on Estimate the probability of

occurrence on a 1-10 scale Rate against each causes Use past data as a basis

(rejection %) for ranking Document the basis of

occurrence ranking For a new design, if there is no

previous experience, use teamjudgement

Don’t consider failure-detectingmeasures while giving ranking(Prototype testing, etc.)

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FOR OCCURANCE RANKING

CLICK HERE


DESIGN FMEADESIGN FMEAEstimate the likelihood of occurrence of potential failure cause /mechanism on 1 to 10 scale. In determining this estimate,questions such as following should be considered.

1 What is the service history / field experience with similarcomponents , sub system , or systems ?

2 Is component a carryover or similar to previous levelcomponent , subsystem or systems ?

3 How significant are changes from previous level component,subsystem or systems ?

4 Is component is radically different from previous levelcomponent, subsystem or systems?

5 Is component is completely new ?6 Has the component application changed ?7 What are the environmental changes?8 Has an engineering analysis been used to estimate the

expected the comparable occurrence rate for the application ?9 Have preventive Controls been put in place ?

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Current Design ControlsPrevention

Current Design ControlsDetection

Detect

RPN

Type of ControlsLevel Type

PreventionPrevention of Cause ( Design Features/Design Changes)

Detection

Detection of Cause and Lead to Correctiveaction(Simulation, Model testing)Detection of Defects(Design Verification &Validation)

List the existing controls, which can detect the causes or failuremode

If one column form is used then, the following prefixes should beused P – before each prevention control D – before each Detection control


DESIGN FMEADESIGN FMEADetection RPN

Recommended Action

Assess the probability ofcontrols listed in the previouscolumn, which will detect thecause or failure mode

While giving ranking, assumethe failure is occurred

Don’t assume ranking is lowbecause the occurrence is low

One detection ranking can beassigned to multiple controls

FOR DETECTION RANKING

CLICK HERE

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RPNRecommended Action

Responsibility & TargetCompletion

Date

Risk Priority Numberis the multiplication ofseverity x occurrencex detection.

While calculatingRPN, consider onlyhighest severity ratingof each failure mode



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Responsibility& Target

Completion DateAction Results

Policy for RPN to take action- define a target RPN and anything above that

can be considered for action. For Ex. It can be50.

- consider only high priority no. for take actionand review periodically

As a first priority, severity ranking can be reducedby elimination of failure mode by change in design

The next priority is to take action on causes toreduce occurrence ranking

consider action on controls to reduce detectionranking

Action such as , be not limited to following shouldbe considered- Review design Geometry and / or Tolerances- Revised material Specification.- DOE or other problem solving methods- Revised Test plan



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Responsibility & TargetCompletion Date

Actions

Taken

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RPN

Specify the responsibilityand target completion datefor every actions identified

During APQP, the FMEAcompletion dates should beprior to Design Release



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Action Results

Actions TakenSev

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Det RPN

Describe the verification results Where effectiveness measure is

required, specify the target dateaccordingly

After the assessment of theactions taken, re-assess thevalues of severity, occurrence,detection and RPN



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The design responsible engineer is responsible for ensuring thatall actions recommended have been implemented or adequatelyaddressed .

The design responsible engineer has several means of ensuringthat concerns are identified and that recommended actions areimplemented . they includes but not limited to followings :

1 Ensuring design requirements are achieved2 Reviewing engineering drawings & specifications3 Conforming incorporation in assembly / manufacturing

documentation &Reviewing process FMEA & Control plans


DESIGN FMEADESIGN FMEAP

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Develop the Block diagram before proceeding with Design FMEA

While deciding the effect of the failure modes of the item, consider the nextsub-assembly stage onwards upto the level of end-user

Give the occurrence rating, as far as possible, based on the existing data onsimilar previous items

While listing out the Causes/ mechanism of failure, consider the indication ofDesign weakness, which leads to the failure mode.

While deciding the actions, the priority will be to

Identify design changes leading to reduction in severity Elimination of Design causes of failure leading to reduction in occurrence If any of the above is not possible, introduction of new design controls to

reduce the detection.


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DESIGN FMEA QUALITY OBJECTIVES

1 DESIGN IMPROVEMENTS : The FMEA drives design improvement as primaryobjective.

2 HIGH REISK FAILURE MODES : The FMEA address all high risk failure modesas identified by FMEA team , with executable action plans. All other failuremodes are considered .

3 A/D/V/ OR DVP & R PLANS : the analysis / Development / validation ( A/D/V)and / or Design verification plan and report ( DVP & R ) considered the failuremode .

4 INTERFACES : The FMEA scope includes integration and interface failuremodes in both block diagram & analysis

5 LESSONS LEARNED : The FMEA considered all major “ lessons learned “ asinput to failure mode identification

6 SPECIAL OR KEY CHARACTERISTICS : the FMEA identifies appropriate keycharacteristics candidates as input to the key characteristics selection process ,if applicable due to company policy.


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ES 7 TIMING : The FMEA is completed during the “ Window of opportunity “

where it could most efficiently impact the product design

8 TEAM : The right people participate as part of the FMEA team throughout the analysis and are adequately trained in FMEA methods

9 DOCUMENTATION : the FMEA is completely filled out “ by the book ”including “ action plan ” and new RPN values .

10 TIME USAGE : Time spent by FMEA team as early as possible is aneffective & efficient use of time , with a value –added result . thisassumes recommended actions are identified as required and theactions are implemented .



Fmea Design

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