Failure Mode and Effects Analysis

FMEA Fundamentals

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Objective

• Understand FMEA is a risk assessment tool– Present an overview of FMEA– Review history of the tool– Introduce terms, structure, types of FMEA’s– Present a road map for construction

• To get a little practice with this tool.

Failure Modes Effects Analysis is …

A systematic approach used to examine potential failures and prevent their occurrence.

The analysis generates a relative risk ranking to each failure mode.

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History of FMEA

Developed in the 60’s by NASA to identify single point failures on the Apollo project. SPF = any single piece of equipment that, if it fails, can bring your entire operation to a halt. (managed with redundancy)

US Navy adopted it in the 70’s for weapons programs.

In the 80’s, the automotive industry implemented FMEA and required its suppliers to do the same.

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Overview

• Applied during the early stages of product, process, or design.

• FMEA begins by defining the functions a part or process is supposed to perform. (Flowchart)

• Brainstorming is used to identify failure modes• This process helps predict problems and

provides a method to rank most likely failure modes.

The Simple Form

Process Step

Failure mode

Potential Effect of failure Sev

Potential cause Occ

Current control Det RPN

Recommended action

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FMEA Terms

Failure Mode Any way in which a process could fail to perform a required function or fail to meet a measurable expectation– Effect Consequence of a failure. Ranked by

severity.– Severity The level of seriousness of the effect of a

failure. A “10” represents most severe. A “1” represents least severe.

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FMEA Terms

Cause Source of a failure mode; means by which a particular element of the process results in a failure mode. Ranked by probability of occurrence. – Occurrence The likelihood that a particular cause

will happen and result in that particular failure. A “10” is near certainty. A “1” is a remote chance of occurrence.

Current Controls All means of detecting the cause or the failure mode before it reaches the customer.– Detection Our ability to detect a failure. A “10”

implies the current control will not detect a failure. A “1” suggests detection is nearly certain.

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FMEA Terms

Risk Priority Number Results from the multiplication of the three rankings. (SxOxD) Ranges from 1 to 1000. Failure modes with high RPN’s indicate a high risk of failure.

Recommended Actions Those corrective actions identified and implemented to reduce the most serious risks.

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FMEA Process

• Inputs – Drawing and specifications– Other customer requirements– Process technical procedures– Warranty or nonconformance history– History or hysteria

• Outputs – Risk Priority Number (RPN) = severity x occurrence x

detection– List of actions to prevent causes or to detect failures– History of actions taken and future activity

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Types of FMEA’s

• Design – Performed on design criteria focusing on how

each requirement can fail. Goal is to maximize design quality, reliability, cost and maintainability

• Process – Performed on each step of a process and how it

can fail.• Equipment

– A special PFMEA focusing on equipment failure

FMEA can …

– Objective evaluation of readiness– Helps manufacturing in process and test

development – Documents risks– Assess resources, tooling, and maintenance

757Mill to length

CenterDrill

Drill & tap

321Rough turn

Heat TreatNQTT

757Drill

P2000 or P3000Saw gash teeth

942Saw shaft end

321Finish turn &

thread

854Maag cut teeth

463Spline

988Deburr

616OD grind

Final inspect Pack Ship

Receive material Incoming inspect

C/T = C/T = C/T = 5 hrs C/T = 10 hrs C/T = C/T = 10 hrs

C/T = 4 hrs C/T = 9 hrs

C/T =

C/T = 30 hrsC/T = 28 hrs

C/T = 3 hrs

C/T = 10 hrs

C/T = 8 hrs C/T = C/T =

Desc: Jacking PinionPart No. 103.02Size: 36 x 63Wt: 6027Teeth: 7Pitch: .26 DP

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Recommended Actions

• Corrective action should focus on those highest concerns as ranked by the RPN.

• The intent is to reduce the occurrence, severity and/or detection rankings

• Improving detection control is typically expensive.

• Emphasis should be placed on preventing, rather than detecting, defects.

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FMEA is appropriate when …

• New products or processes are being designed• Existing designs and processes are being changed• Existing designs or processes will be used in new

applications or environments• Completing a root cause analysis or improvement

project, to prevent recurrence of the problem• Update an FMEA - as information changes, as high

priority failure modes are addressed

FMEA fails, when …• One person is assigned to do the FMEA alone. • The SOD (rating scales) are not customized so that they are meaningful to

your company. • The design or process expert is either not included on the FMEA team or is

allowed to dominate the FMEA team. • Members of the FMEA team have not been trained and become frustrated

with the process. • The FMEA team gets bogged down with the minute details . • Rushing through the generation of potential failure modes in a hurry to move

on to the next step of the FMEA, possibly overlooking significant but obscure failure modes.

• Listing practically the same effect for every failure mode • Stopping once the RPNs are calculated • Not reevaluating when new failures occur.

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Severity Criteria

Effect Criteria: Severity of Effect Ranking

Hazardous - without warning

May endanger machine or assembly operator. Very high severity ranking when a potential failure mode affects safe item operation and/or involves noncompliance with government regulation. Failure will occur without warning.

10

Hazardous - with warning

May endanger machine or assembly operator. Very high severity ranking when a potential failure mode affects safe item operation and/or involves noncompliance with government regulation. Failure will occur with warning.

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Very HighMajor disruption to production line. 100% of product may have to be scrapped. Item inoperable, loss of primary

function. Customer very dissatisfied.8

HighMinor disruption to production line. Product may have to be sorted and a portion (less than 100%) scrapped.

Item operable, but at a reduced level of performance. Customer dissatisfied.7

ModerateMinor disruption to production line. A portion (less than 100%) of the product may have to be scrapped (no

sorting). Item operable, but some convenience item(s) inoperable. 6

LowMinor disruption to production line. 100% of product may have to be reworked. Item operable, but some items

operable at reduced level of performance. Customer experiences some dissatisfaction.5

Very LowMinor disruption to production line. The product may have to be sorted and a portion (less than 100%) reworked.

Fit and Finish/Squeak and Rattle item does not conform. Defect noticed by some customers.4

MinorMinor disruption to production line. A portion (less than 100%) of the product may have to be reworked on-line

but out-of-station. Fit and Finish/Squeak and Rattle item does not conform. Defect noticed by average customer. 3

Very MinorMinor disruption to production line. A portion (less than 100%) of the product may have to be reworked on-line but out-of-station. Fit and Finish/Squeak and Rattle item does not conform. Defect noticed by discriminating

customers. 2

None No effect. 1

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Occurrence CriteriaProbability of Failure

Occurrence Possible Failure Rates Cpk Ranking

≥ 1 in 2 < 0.33 10

1 in 3 ≥ 0.33 9

1 in 8 ≥ 0.51 8

1 in 20 ≥ 0.67 7

1 in 80 ≥ 0.83 6

1 in 400 ≥ 1.00 5

1 in 2,000 ≥ 1.17 4

Low: Isolated failures associated with similar processes.

1 in 15,000 ≥ 1.33 3

Very Low: Only isolated failures associated with almost identical

processes.1 in 150,000 ≥ 1.50 2

Remote: Failure is unlikely. No failures ever associated with almost identical processes.

≤ 1 in 1,500,000 ≥ 1.67 1

Moderate: Generally associated with processes similar to previous

processes which have experienced occasional failures, but not in major

proportions.

High: Generally associated with processes similar to previous

processes that have often failed.

Very High: Failure is almost inevitable.

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Detection CriteriaDetection

Criteria: Likelihood the existence of a defect will be detected by process controls before next or subsequent process, or before part or component leaves the manuracturing or assembly

location Ranking

Almost Impossible

No known control(s) available to detect failure mode 10

Very Remote Very remote likelihood current control(s) will detect failure mode 9

Remote Remote likelihood current control(s) will detect failure mode 8

Very Low Very low likelihood current controls(s) will detect failure mode 7

Low Low likelihood current control(s) will detect failure mode 6

Moderate Moderate likelihood current control(s) will detect failure mode 5

Moderately High Moderately high likelihood current control(s) will detect failure mode 4

High High likelihood current control(s) will detect failure mode 3

Very High Very high likelihood current control(s) will detect failure mode 2

Almost CertainCurrent control(s) almost certain to detect the failure mode. Reliable detection controls are known with similar

processes.1

FMEA Practice

Let’s make a cup of coffee• Customer wants:

– French press– Medium roast (mild but not overly bitter)– 12 ounces … now

• Watch for:– Multiple effects for one failure mode– Multiple failure modes with a common effect– Multiple causes of a failure mode

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French Press Coffee

Process Step

Failure mode

Potential Effect

of failure SevPotential

cause OccCurrent control Det RPN

Recommended action

Obtain beans Grind beans obtain water boil water Steap grounds Filter mother liquor

Practice

1. Break into groups2. Handouts

SOD rating charts A4 with FORM

3. Discuss4. Questions?

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Roadmap

• Identify the cross-functional team• Define customer needs and expectations• Review the process or design, list functions• Brainstorm potential failure modes• Analyze potential failure modes (severity of effect,

occurrence of causes, ability to control detection)• Calculate RPN’s (risk priority numbers)• Identify actions to reduce high RPN’s• Execute on actions• Recalculate RPN’s and update FMEA

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Process Failure Causes• Omitted processing• Processing errors• Errors setting up work pieces• Missing parts• Wrong parts• Processing wrong work piece• Mis-operation• Adjustment error• Equipment not set up properly• Tools or fixtures improperly

prepared

• Poor control procedures• Improper equipment maintenance• Bad recipe• Fatigue• Lack of safety• Hardware failure• Failure to enforce controls• Environment• Stress connections• Poor FMEA’s

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Questions to Help Identify Causes• Can any equipment failures contribute to this effect?• Material faults?• Human errors?• Methods and procedures?• Software performance?• Maintenance errors or the absence of maintenance?• Inaccuracies or malfunction of the measurement device?• Environment - chemicals, dust, vibration, temperature, humidity, shock?

• Use the 6M’s to help brainstorm and organize potential causes of failures.– Man– Machine– Method– Measurement– Material– Mother Nature (Mileau)

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Almost all errors are caused by humans

Source• Forgetfulness• Errors due to misunderstanding• Errors in identification• Errors made by amateurs• Willful errors• Inadvertent errors• Errors due to slowness• Lack of standards• Surprise errors• Intentional errors

Response• Establish a routine• Training for behavior modification• Standardizing procedures• Training engagement and attentiveness• Training skill building, • Basic education, life experience• Discipline

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Process Control Examples• Standardized work instructions or procedures• Fixtures and jigs• Mechanical interfaces• Mechanical counters• Mechanical sensors• Electrical/electronic sensors• Job sheets or process routings• Bar coding with software integration and control

• Marking• Training and educational safeguards• Visual checks• Gage studies• Preventive maintenance• Automation (real time control)• Statistical Process Control (SPC)• Post-process inspection or testing

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Typical Process Documents• Visual aides• Work instructions• Inspection instructions• Inspection records• SPC records• Equipment operating instructions• Training records• Traceability records

In Summary

• FMEA is another tool when a team has knowledge of a process

• It documents “known” failures and fixes• It can be an excellent training tool

• Questions?