Failure Modes and Effects Analysis Paper

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Failure Modes and Effects Analysis Page 1

Failure Modes and Effects Analysis

David M. LittleTyco Electronics [email protected]

General Description of FMEAFailure mode and effects analysis (FMEA) is a systematic procedure paralleling the

mental discipline of the design process. The procedure is divided into three parts,

system FMEA, design FMEA and process FMEA. These FMEAs should be completed

prior to release of the product to manufacturing, between the concept and

development design reviews, and should include customer specific requirements

as applicable.

1. INSTRUCTIONS FOR CONDUCTING FAILURE MODE AND EFFECTS ANALYSIS

1.1. Documenting the FMEA

The FMEA is documented by the completion of the top portion (header) of the

applicable QMD Forms. The other blocks are completed as needed. The

assignment of an FMEA Number by the business unit is optional. Other forms may

be used to document the FMEA provided they are acceptable to the local business

unit or the customer. Computer software providing the ability to document and

update the FMEA may be used in lieu of the more traditional paper forms if

desired.

1.2. Component (Process)

Identify and list all components of the product or (process steps) under study.

Include part name and number. A very simple product may consist of only one

component, whereas a complex product might have numerous components.
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1.3. Component (Process) Function

Specify the intended function(s) of the component (process step) with respect to

each functional requirement of the product, whether it is an individual

component or a component within a complex product, and also whether/how it

applies to process function(s).

1.4. Failure Mode

Describe each potential failure mode identified. The assumption is made that

failure could occur and not necessarily will occur. A review of the quality history

of similar products (processes) including any design or process FMEAs is

recommended as a starting point.

1.5. Effect(s) of Failure

Describe the failure in terms of what the customer (internal and/or external)

would notice or experience. The description must be stated as specifically as

possible.

1.6. Severity of Failure (S)

Evaluate the severity of each potential failure using a scale of 1 to 10. A 1

indicates the failure would be relatively minor, and a 10 indicates severe total

failure. See Figures 1, 4 or 7 for suggested severity ratings to be used in FMEAs.

1.7. Cause(s) of Failure

List all of the causes assignable to each failure mode. Care should be taken to

assure that the list is inclusive so that remedial efforts will be aimed at all

pertinent causes.


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1.8. Frequency of Occurrence (O)

The occurrence rating is based on the probability of the failure cause occurring,

and in absence of active intervention, leading to the failure mode. Evaluate the

frequency of occurrence using a scale of 1 to 10. A 1 indicates a low frequency,

and a 10 indicates very frequent failure. See Figures 2, 5, or 8 for suggested

occurrence ratings to be used in FMEA's.

1.9. Prevention Controls

List methods utilized which will prevent or reduce the likelihood of occurrence of

the failure cause or the failure mode/effect. These controls will affect the

frequency of occurrence rating (see Paragraph 1.8.) and must be considered when

evaluating frequency of occurrence. In design, examples of prevention controls

are use of design standards, use of existing components with established history

of good performance, use of design features to eliminate or reduce likelihood of a

given failure mode, etc. In process, examples of prevention controls include error

proofing, process capability and performance analysis prior to production, design

of experiments (DOE), preventive maintenance, etc.

1.10. Detection Controls

List the methods utilized which will detect the failure cause in time to take

corrective action or which will detect the failure mode before the failure effect

results. Detection controls must be considered when evaluating the detection

rating (see Paragraph 1.11.). In design, examples of detection controls include

engineering analysis such as finite element analysis (FEA), tolerance analysis,

testing, etc. In process, examples of detection controls are inspections,

workmanship standards, etc.


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1.11. Detection (D)

Estimate the probability that the failure would be detected before it reaches the

customer using a scale of 1 to 10. A 1 indicates a high probability that the failure

would be detected before reaching the customer. A 10 indicates a low probability

that the failure would be detected before reaching the customer. Customers

includes both internal users such as downstream manufacturing processes and

external users such as the purchasing customer. QIP Inspection should not be

considered for design FMEAs unless 100% inspection is utilized. A Quality

Inspection Plan can be used for process FMEA. See Figures 3, 6, or 9 for suggested

detection ratings to be used in FMEAs.

1.12. Risk Priority Number (RPN)

The product of the estimates of severity, occurrence and detection (SxOxD) forms

a risk priority number which provides a priority of the potential failure modes.

These estimates are relative only, having no significance in absolute terms. The

purpose is to identify which potential failure modes are most likely to cause

problems either internally or for the customer. In general, higher risk priority

numbers indicate more serious consequences. The RPN provides a means of

ranking failure modes in order of their relative importance.

1.13. Recommended Action

Using the RPN and the results of the potential failure mode verification studies,

determine which failure modes need action. Enter a brief description of the

action on the FMEA form. Items, which require further action, shall be

documented using Action Item Form or other documentation methods acceptable

to the local business unit or the customer and their status shall be monitored as a


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part of the design review process. Items requiring no corrective action may be

noted as none on the FMEA form.

1.14. Area or Individual Responsible and Completion Date

For each recommended action, identify the responsible area or individual that

will complete the action and an expected completion date.

1.15. Action Taken

Following completion of the recommended action, enter any results or design

(process) changes. Include reference to any ECs, engineering or test reports, and

supporting documentation.

1.16. Severity, Occurrence, Detection and Risk Priority Number

A. For any completed recommended action, use these columns to re-evaluate

the probability of severity, occurrence, and detection to determine the new RPN.

B. To reduce the severity number, the cause or entire failure mode must be

eliminated. To reduce the occurrence number, remove or control the cause of the

failure mode through design (process) changes. To reduce the detection number,

new or improved verification or prevention techniques must be implemented.

2. FMEA RECORDS

2.1. System FMEA, design FMEA and process FMEA record files may also be

maintained by business unit and responsible team function as follows:

A. Design assurance (development/product engineering) function.

B. Quality/reliability engineering function.

C. Process/manufacturing engineering function.


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2.2. System FMEA, design FMEA and process FMEA revisions, updates, and/or

corrective actions, must be issued and distributed to the business unit and

responsible team functions listed in Paragraph 2.1. above.

FMEA System Example is provided after the text.

System FMEA

A system FMEA identifies potential failure modes, effects, and causes that may

prevent a system from meeting all of its system objectives. The system FMEA is a

process that analyzes the customers requirements/characteristics relative to

their intended function to ensure that the resultant product meets customer

needs and expectations. When potential failure modes are identified, action must

be initiated to eliminate or reduce their occurrence. Risk assessment via the use

of risk priority numbers is completed in order to prioritize the actions.


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See last page for revision history:PROJ ECT NAME PROJ ECT NO. PART NO. ORIGINAL DFMEA DATE: DFMEA REV.

RELIABILITY ENGR. DESIGN/PRODUCT ENGR. MANUFACTURING ENGR. TEST ENGR.

COMPONENT or

SUBASSEM.

COMPONENT

FUNCTION(S)FAILURE MODE(S)

EFFECTS OF

FAILURE

SEV

SCLASS

CAUSE(S) OF

FAILURE

OCC

O

PREVENTION

CONTROLS

DETECTION

CONTROLS

DET

D

RPN

OSD

RECOMMENDED

ACTION(S)

ConfidentialFAILURE MODE AND EFFECTS ANALYSIS - SYSTEM

APPROVED

Revison History:

Revision Date Responsible Engineer Description


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FMEA Design Example is provided after the text.

Design FMEA

A Design FMEA identifies potential failure modes, effects, and causes that may

prevent a new design from meeting all of its design objectives. The design FMEA is

a process that analyzes the product's design characteristics relative to their

intended function to ensure that the resultant product meets customer needs and

expectations. When potential failure modes are identified, action must be

initiated to eliminate or reduce their occurrence. Risk assessment via the use of

risk priority numbers is completed in order to prioritize the actions.


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COMPONENT or

SUBASSEM.

COMPONENT


EFFECTS OF

FAILURE

SEV

SCLASS

CAUSE(S) OF

FAILURE

OCC

O

PREVENTION

CONTROLS

DETECTION

CONTROLS

DET

D

RPN

OSD

RECOMMENDED

ACTION(S)

ConfidentialFAILURE MODE AND EFFECTS ANALYSIS - DESIGN

APPROVED

Revison History:



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FMEA Process Example is provided after the text.

Process FMEA

A Process FMEA identifies potential failure modes, effects, and causes that may

prevent the manufacturing processes from producing a new design that meets all

of its design objectives. It is a process that identifies potential process variables

in order to focus controls for prevention or detection of potential failures. The

process FMEA is to be considered a living' document that is changed and updated

as the process evolves and matures. Risk assessment via the use of risk priority

numbers is completed in order to prioritize preventative and detection actions.


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PROCESS STEPPROCESS STEP


EFFECTS OF

FAILURE

SEV

SCLASS

CAUSE(S) OF

FAILURE

OCC

O

PREVENTION

CONTROLS

DETECTION

CONTROLS

DET

D

RPN

OSD

RECOMMENDED

ACTION(S)

APPROVED

ConfidentialFAILURE MODE AND EFFECTS ANALYSIS - PROCESS

Revison History:



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