Transcript Failure Mode and Effects Analysis

FMEA Fundamentals
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.
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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.
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.
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The Simple Form
Process Failure
Step
mode
Potential Effect
of failure
Potential
Current
Sev
cause
Occ control Det RPN
Recommended
action
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.
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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.
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
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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
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FMEA can …
– Objective evaluation of readiness
– Helps manufacturing in process and test
development
– Documents risks
– Assess resources, tooling, and maintenance
Desc:
Jacking Pinion
Part No. 103.02
Size:
36 x 63
Wt:
6027
Teeth:
7
Pitch:
.26 DP
Receive material
C/T =
Incoming inspect
C/T =
P2000 or P3000
Saw gash teeth
C/T = 4 hrs
757
Mill to length
Center
Drill
Drill & tap
C/T = 5 hrs
942
Saw shaft end
C/T = 9 hrs
321
Rough turn
C/T = 10 hrs
321
Finish turn &
thread
C/T = 28 hrs
854
Maag cut teeth
C/T = 30 hrs
Heat Treat
NQTT
757
Drill
C/T =
C/T = 10 hrs
463
Spline
C/T = 10 hrs
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
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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.
Severity Criteria
Effect
Criteria: Severity of Effect
Hazardous May endanger machine or assembly operator. Very high severity ranking when a potential failure mode affects
without warning safe item operation and/or involves noncompliance with government regulation. Failure will occur without warning.
Ranking
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 High
Major disruption to production line. 100% of product may have to be scrapped. Item inoperable, loss of primary
function. Customer very dissatisfied.
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High
Minor 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.
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Moderate
Minor 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.
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Low
Minor 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.
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Very Low
Minor 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.
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Minor
Minor 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 Minor
Minor 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 Criteria
Probability 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
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1 in 20
≥ 0.67
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1 in 80
≥ 0.83
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1 in 400
≥ 1.00
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1 in 2,000
≥ 1.17
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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
Very High: Failure is almost
inevitable.
High: Generally associated with
processes similar to previous
processes that have often failed.
Moderate: Generally associated
with processes similar to previous
processes which have experienced
occasional failures, but not in major
proportions.
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Detection Criteria
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
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Low
Low likelihood current control(s) will detect failure mode
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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 Certain
Current control(s) almost certain to detect the failure mode. Reliable detection controls are known with similar
processes.
1
Detection
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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
French Press Coffee
Process
Step
Obtain beans
Potential
Recomm
Failure Effect
Potential
Current
ended
mode of failure Sev cause Occ control Det RPN action
Grind beans
obtain water
boil water
Steap grounds
Filter mother liquor
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Practice
1. Break into groups
2. Handouts
 SOD rating charts
 A4 with FORM
3. Discuss
4. Questions?
Roadmap
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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
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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
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Poor control procedures
Improper equipment maintenance
Bad recipe
Fatigue
Lack of safety
Hardware failure
Failure to enforce controls
Environment
Stress connections
Poor FMEA’s
Questions to Help Identify Causes
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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.
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Man
Machine
Method
Measurement
Material
Mother Nature (Mileau)
Almost all errors are caused
by humans
Source
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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
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Response
Establish a routine
Training for behavior modification
Standardizing procedures
Training engagement and attentiveness
Training skill building,
Basic education, life experience
Discipline
Process Control Examples
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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
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Marking
Training and educational safeguards
Visual checks
Gage studies
Preventive maintenance
Automation (real time control)
Statistical Process Control (SPC)
Post-process inspection or testing
Typical Process Documents
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Visual aides
Work instructions
Inspection instructions
Inspection records
SPC records
Equipment operating instructions
Training records
Traceability records
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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?