fmea new
TRANSCRIPT
FMEA
Introduction
What is FMEA ?
• Means to assure that potential failure modes and their
associated cause and mechanism, have been addressed
though earlier detection.
• A tool for design and process engineers.
• “Before-the-event” action NOT an “After-the-fact”
exercise.
FMEA Application Case 1 : New designs, new technology, or new process.
Case 2 : Modification to existing design or process.
Case 3 : Use of an existing design or process in a new
environment, location or application.
Do not forget “Rule of Ten”
Design
FMEA
SPC
PPM
At
Supplier
end
Proces
s
FMEA
Design
and
developm
ent
Advanced
product
quality
planning
Purchasing Use
Manufac
turing
Manufacture Customer
Rs.1/- Rs. 10/- Rs. 100/- Rs. 1000/-
SPC
PPM
At
prodn
Rs. 10,000/- Prevention cost Internal failure cost External failure
Potential
defect
Internal
defect
External
defect
CO
ST
O
F Q
UA
LIT
Y
Nature of cost
Ratio of cost
Defect Stage
Defect report
point
Product flow
stage
Evaluation
mechanism
FMEA Stage
Process
Flow
Design
Product
Brief
Product
Concept
Product
Proto
Design
Product
Proto Build
System,
Sub system,
Part Design
Product
PILOT Build
Product
Start of
Production
+ Review
Of issues
At Proto
+ Review
Of issues
At Pilot
Potential Failure Mode & Effects Analysis Sequence
PFMEA - SEQUENCE
Application
Application Design
FMEA
Process
FMEA
Purpose Meeting specification /
Customer & Legal
requirements.
Production in compliance with
drawing
Responsibility Design and development Production / Mfg Engg.
Objective Avoiding design failures Avoiding failures during process
planning, production implementation
Timing for
commencement
Before or at design concept
finalization
Before or at feasibility stage or prior
to looking for production
Period of review Prior to the first trial run Prior to any investment
FMEA first
completion
Prior to production drawing
release for tooling
Prior to bulk production
Step # Step details
1 Define Project Scope
2 Brainstorm all potential failure modes
3 Identify the potential effects of failures
4 Determine severity rankings
5 Identify the causes of failures
6 Determine Occurrence rankings
7 Identify the current controls
8 Determine the detection rankings
9 Evaluate Risk Priority Numbers(RPN)
10 Prioritise corrective actions.
FMEA STEPS
• Formulate cross functional team
• Understand customer/process requirements.
• Define start and end of process
• All team members walk and observe the process.
• Get the „process worker‟ to explain the
operation/process under review.
• Make notes/observations.
Defining Scope of FMEA is CRITICAL!
1. PFMEA Process Scope
1. Design FMEA Block Diagram Example
Switch on/off
C
Housing
A
Bulb
Assembly
D
Plate
E
+
Attaching Method
1. Skip Fit 4. Snap Fit
2. Rivets 5. Compressive Fit
3. Thread
2
3
4
Spring
F
--
Batteries
B
4
5 5
5
System Level
Subsystem Level Component Frame
Bicycle Frame Upper Frame Design Objectives: 1. Minimum 3000 hours of riding without need for maintenance and 10000 hours of riding for design life . 2. Accommodates male adults comfortably to the 99.5th percentile 3. ...etc.... Function1: * Ease of use Potential failure model(s): * Difficult to steer * difficult to pedal Function2: * Provide reliable transportation Potential failure model(s): * Chain break frequently * Tire require frequent maintenance Function3: * Provide comfortable transportation Potential failure model(s): * seating position is not comfortable
Function1: * provide stable attachment for seat support Potential failure model(s): * Structural failure of seat support * Excessive deflection of seat support . Function 2: * Provide pleasing appearance. Potential failure model(s): * Finish (Shine ) deteriorates * Paint chips
Function 1: * Provide structural support Potential failure model(s): * Structural Failure * Excessive deflection Function 2: * Provide dimensional control for correct finished fame geometry Potential failure model(s): * Length of frame mounting point too long * Length of frame mounting point too short Function 3: * Support frame assembly production methods (welding) Potential failure model(s):
Handle bar assembly
Front Wheel assembly
Real wheel assembly Lower front tube
Sprocket assembly
Seat assembly Lower rear tube
Chain assembly Sprocket tube
1. PFMEA process scope
Step # Step details
1 Define Project Scope
2 Brainstorm all potential failure modes
3 Identify the potential effects of failures
4 Determine severity rankings
5 Identify the causes of failures
6 Determine Occurrence rankings
7 Identify the current controls
8 Determine the detection rankings
9 Evaluate Risk Priority Numbers(RPN)
10 Prioritise corrective actions.
FMEA STEPS
2. Potential Failure Mode
• Potential Failure Mode is defined as the manner in which a
component, subsystem, or system could potentially fail to
meet the design intent.
• The assumption is made that the failure could occur, but
may not necessarily occur. A recommended starting point
is a review of past things-gone-wrong, concern reports, and
group “brainstorming”.
• Typical failure modes could be, cracked leaking,
fractured, oxidized, no signal, drift, etc. ( Described in
physical or technical terms, not as symptom noticed by the
customer).
2. Potential Failure Mode - examples
• Bent
• Cracked
• Contaminated
• Loosened
• Leakage
• Damaged
• Deformed
• Gouged
• Misaligned
• Corroded
• Broken Tooling
• Wrong Tooling
• Wrinkled
• Scratched
• Humidity
• Handling Damage
Step # Step details
1 Define Project Scope
2 Brainstorm all potential failure modes
3 Identify the potential effects of failures
4 Determine severity rankings
5 Identify the causes of failures
6 Determine Occurrence rankings
7 Identify the current controls
8 Determine the detection rankings
9 Evaluate Risk Priority Numbers(RPN)
10 Prioritise corrective actions.
FMEA STEPS
3. Potential Effect(s) of Failure
• Effect of failure mode on the customer (s).
• Describe effects of failure in terms of what customer(s) might
notice or experience.
Customer Effect
End user In terms of product / system
performance e.g. noise,
inoperative, poor appearance.
Next operation/ In terms of process/ operation
subsequent performance e.g. fitment problem,
damage
Operation/
location
3. Potential Effect(s) of Failure
• Example could be :
- For end user : Noise, rough, inoperative, leaks,
unstable, erratic operation, etc.
- For next/ subsequent operations: does not fit, can not
mount, damages equipment, excessive tool wear, etc.
Step # Step details
1 Define Project Scope
2 Brainstorm all potential failure modes
3 Identify the potential effects of failures
4 Determine severity rankings
5 Identify the causes of failures
6 Determine Occurrence rankings
7 Identify the current controls
8 Determine the detection rankings
9 Evaluate Risk Priority Numbers(RPN)
10 Prioritise corrective actions.
FMEA STEPS
4. Determining Severity
Severity is an assessment of the seriousness of the effect of
the potential failure mode to the next component, subsystem,
system or customer if it occurs. Severity applies to the effect
only. A reduction in Severity Ranking index can be effected
only through a design change. Severity should be estimated
on a “ to “ scale.
4. Suggested PFMEA Severity Ranking
Effect Criteria : Severity of effect
This ranking result when a potential
Failure mode result in a final customer
and/or a manufacturing/assembly plant
defect .The final customer should always
be considered first if both occur, use the
higher of the two severities.
(Customer Effect)
Criteria : Severity of effect
This ranking result when a potential Failure
mode result in a final customer and/or a
manufacturing/assembly plant defect .The
final customer should always be
considered first. if both occur, use the
higher of the two severities .
(Manufacturing/ Assembly Effect)
Rankin
g
Hazardous
Without
warning
Very high Severity ranking when a potential
failure mode affect safe vehicle operation
and/or involves noncompliance with
government regulation without warning
Or may endanger operator(machine or
assembly without a warning
10
Hazardous
With
warning
Very high Severity ranking when a potential
failure mode affect safe vehicle operation
and/or involves noncompliance with
government regulation with warning
Or may endanger operator(machine or
assembly with a warning
9
Very High Vehicle/item inoperable (loss of primary
Function)
Or 100% of product may have to be scrapped
or vehicle item repaired in department with a
repair time greater than one hour
8
High Vehicle/item operable but at reduce level of
performance customer very dissatisfied
Or product may have to be a stored and a
portion(less than 100% )of scrapped or
vehicle item repaired in department with a
repair time greater than one hour.
7
Moderate Vehicle? Item operable but Comfort/
convenience item(s) inoperable.
Customer dissatisfied.
Or a portion (less than 100%) of the product may
have to scrapped with no sorting, or vehicle/item
repaired in repair department with a repair time less
than a half- hour.
6
Low Vehicle/item operable but comfort/
convenience item(s) operable at a
reduced level of performance.
Or 100% of product may have to be reworked, or
vehicle/item repair off-line but does not go to repair
department.
5
Very low Fit and finish/squeak and rattle item
does not conform. Defect noticed by
most customers. (greater than 75%)
Or 100% of product may have to sorted, with no scrap
and a portion (less than 100%) reworked.
4
Minor Fit and finish/ squeak and rattle
item does not conform. Defect
noticed by 50% of customers.
Or a portion (less than 100%) of the product may have
to be reworked, with no scrap, on-line but out-of-
station.
3
Very minor Fit and finish/ squeak and rattle
item does not conform. Defect
noticed by discriminating
customers (less than 25%)
Or a portion (less than 100%) of the product may have
to be reworked, with no scrap, on-line but in-station.
2
None No discernible effect. Or slight inconvenience to operation or operator, or
no effect.
1
4. Suggested PFMEA Severity Ranking
Step # Step details
1 Define Project Scope
2 Brainstorm all potential failure modes
3 Identify the potential effects of failures
4 Determine severity rankings
5 Identify the causes of failures
6 Determine Occurrence rankings
7 Identify the current controls
8 Determine the detection rankings
9 Evaluate Risk Priority Numbers(RPN)
10 Prioritise corrective actions.
FMEA STEPS
5. Potential Causes(S)/ Mechanism(s)
of Failure ( Design) • Potential Cause of Failure is defined as an indication of a design weakness, the consequence of which is the failure mode.
Typical failure causes may include: - Incorrect Material Specified.
- Inadequate Design Life Assumption
- Over-stressing.
- Insufficient Lubrication Capability.
- Poor Environment Protection.
- Incorrect algorithm.
- In progress tolerance specified.
• Typical failure mechanisms may include:
Creep Fatigue Wear Corrosion
5. Potential Cause(s) of Failure
• Every conceivable failure cause assignable to each
potential failure mode.
• Specific causes where remedial efforts can be aimed.
• Examples
- Part missing or mis-located,
- Improper torque,
- Improper welding,
- Inaccurate gauging, etc.
- Inadequate lubrication,
- Chip on located, etc.
Step # Step details
1 Define Project Scope
2 Brainstorm all potential failure modes
3 Identify the potential effects of failures
4 Determine severity rankings
5 Identify the causes of failures
6 Determine Occurrence rankings
7 Identify the current controls
8 Determine the detection rankings
9 Evaluate Risk Priority Numbers(RPN)
10 Prioritise corrective actions.
FMEA STEPS
6. Occurrence(O)
• Occurrence is the likelihood that a specific cause/ mechanism
will occur.
• Removing or controlling one or more of the causes/mechanism of the failure mode through a design change is the only way a reduction in the occurrence ranking can be effected.
• Estimate the likelihood of occurrence of potential failure cause mechanism on a “1” to “10” scale. Questions such as the following should be considered:
- What is the service history/field experience with similar components or subsystems?
- Is component carryover or similar to a previous level component or subsystem?
Contd…
6. Occurrence(O) (contd…)
- How significant are changes from a previous level component or subsystem?
- Is component radically different from a previous level component ?
- Is component completely new ?
- Has the component application changed?
- What are the environmental changes?
- Has an engineering analysis been used to estimate the expected comparable occurrence rate for the application?
6. Determine Occurrence Rating
Suggested Evaluation Criteria: Design
Probability of failures Possible Failure Rates Ranking
Very High: persistent failures ≥ 100 per thousand vehicles/ item. 10
50 per thousand vehicles/ item. 9
High : Frequent failures 20 per thousand vehicles/ item. 8
10 per thousand vehicles/ item. 7
Moderate :occasional failures 5 per thousand vehicles/ item. 6
2 per thousand vehicles/ item. 5
1 per thousand vehicles/ item. 4
Low : Relatively few failure 0.5 per thousand vehicles/ item. 3
0.1 per thousand vehicles/ item. 2
Remote : Failures is Unlikely ≤ 0.010per thousand vehicles/ item. 1
Process FMEA Suggested PFMEA occurrence evaluation criteria with Ppk values
Probability Likely Failure Rates * Ppk Ranking
Very High: Persistent Failure ≥ 100 per thousand pieces < 0.55 10
50 per thousand pieces. ≥ 0.55 9
High : Frequent Failures 20 per thousand pieces. ≥ 0.78 8
10 per thousand pieces. ≥ 0.86 7
Moderate : Occasional Failures 5 per thousand pieces. ≥ 0.94 6
2 per thousand pieces. ≥ 1.00 5
1 per thousand pieces. ≥ 1.10 4
Low : Relatively Few Failures 0.5 per thousand pieces. ≥ 1.20 3
0.1 per thousand pieces. ≥ 1.30 2
Remote : Failure us unlikely ≤ 0.01 per thousand pieces. ≥ 1.67 1
6. Determine Occurrence Rating
Step # Step details
1 Define Project Scope
2 Brainstorm all potential failure modes
3 Identify the potential effects of failures
4 Determine severity rankings
5 Identify the causes of failures
6 Determine Occurrence rankings
7 Identify the current controls
8 Determine the detection rankings
9 Evaluate Risk Priority Numbers(RPN)
10 Prioritise corrective actions.
FMEA STEPS
7. Current Controls (Design)
• List the preventing, design validation/verification (DV), or
other activities which will assure the design adequacy for
the failure mode and/or cause/ mechanism under
consideration.
• Current controls are those that have been or are
being used with the same or similar designs.
Three types of Design Controls:
- prevent the cause/mechanism of failure mode effect
from occurring, or reduce their rate of occurrence.
- detect the cause/mechanism and lead to corrective
actions, and
- detect the failure mode.
7. Current Design Controls (contd…)
Prevention (P) e.g. building redundancy,
Design oriented failsafe arrangement, Pokayoke,
• control
Detection (D) e.g. lab test, design
oriented verification, road test, inspection
etc
• Specify „P‟ & „D‟ controls in separate columns. If one column is used
for current design control, specify „P‟ or „D‟ before each control.
Types of Process Controls Affects
Prevent the cause / mechanism or
failure mode / effect from occurring
or reduce their rate of occurrence.
Occurrence Ranking
Detect the cause / mechanism &
lead to Corrective Actions.
Detection Ranking
Detect the failure mode. Detection Ranking.
7. Current Process Controls
Step # Step details
1 Define Project Scope
2 Brainstorm all potential failure modes
3 Identify the potential effects of failures
4 Determine severity rankings
5 Identify the causes of failures
6 Determine Occurrence rankings
7 Identify the current controls
8 Determine the detection rankings
9 Evaluate Risk Priority Numbers(RPN)
10 Prioritise corrective actions.
FMEA STEPS
8. Detection (d)
• Detection is an assessment of the ability of the
current design controls, to detect a potential cause
/mechanism (design weakness), or
• The ability of the current design controls to detect
the subsequent failure mode, before the component,
subsystem Or system is released for production.
• In order to achieve a lower ranking generally the
planned design control has to be improved.
8. Detection Ranking Suggested Evaluation Criteria: For Design detection
Detection Criteria : Likelihood of Detection by Design Control Ranking
Absolute uncertainty Design Control will not and/or can not detect a potential causes /mechanism an
subsequent failure mode ; or there is no design control
10
Very Remote Very remote chance the Design Control will detect a potential causes /mechanism and
subsequent failure mode .
9
Remote Remote chance the Design Control will detect a potential causes /mechanism and
subsequent failure mode .
8
Very low Very low chance the Design Control will detect a potential causes /mechanism and
subsequent failure mode .
7
Low Low chance the Design Control will detect a potential causes /mechanism and
subsequent failure mode .
6
Moderate Moderate chance the Design Control will detect a potential causes /mechanism and
subsequent failure mode .
5
Moderate High Moderate High chance the Design Control will detect a potential causes /mechanism and
subsequent failure mode .
4
High High chance the Design Control will detect a potential causes /mechanism and
subsequent failure mode .
3
Very High Very high chance the Design Control will detect a potential causes /mechanism and
subsequent failure mode .
2
Almost Certain Design Control will almost certainly detect a potential causes /mechanism an subsequent
failure mode .
1
Suggested PFMEA Detection Evaluation Criteria
Detection Criteria Inspection
Types
Suggested Range of Detection Method Rank
A B C
Almost
Impossible
Absolute certainty of non detection X Cannot detect or is not checked 10
Very remote Control will probably not detect X Control is achieved with indirect or Random check only 9
Remote Control have poor chance of
detection
X Control is achieved with Visual inspection only 8
Very low Control have poor chance of
detection
X Control is achieved with double visual inspection only. 7
Low Control may detect X Control is achieved with charting methods, such as SPC. 6
Moderate Controls may detect X Control is based on variable gauging after parts have
left the station, or Go/No Go gauging performed on
100% of the parts after parts have left the station.
5
Moderate
High
Controls have a good chance to
detect
X X Error detection in subsequent operation, or gauging
performed on setup and first-piece check( for set-up
causes only).
4
High Controls have a good chance to
detect
X X Error detection in-station, or error detection in subsequent
operations by multiple layers of acceptance : supply, select,
install, verify. Cannot accept discrepant part.
3
Very high Controls almost certain to detect. X X Error detection in station ( automatic gauging with
automatic stop feature). Cannot pass discrepant part.
2
Very high Controls certain to detect. X Discrepant parts cannot be made because item has
been error proofed by process/product design.
1
Inspection Types: A. Error-proofed B. Gauging C. Manual Inspection
8. Detection Ranking
Step # Step details
1 Define Project Scope
2 Brainstorm all potential failure modes
3 Identify the potential effects of failures
4 Determine severity rankings
5 Identify the causes of failures
6 Determine Occurrence rankings
7 Identify the current controls
8 Determine the detection rankings
9 Evaluate Risk Priority Numbers(RPN)
10 Prioritise corrective actions.
FMEA STEPS
9. Determine Risk Priority Number (RPN)
- Risk Priority Number (RPN)
= Severity x Occurrence x Detection
- To be used for prioritization of corrective actions.
- Ranges between 1 and 1000.
- Regardless of RPN value, special attention should be
given when severity is high.
FMEA Model
Potential Failure
Mode Cause of Failure
Current
Design/Process
Control
Effect of
failure
Frequency of
Failure
Possibility of finding
failure or Cause of
failure
Severity
Rating Occurrence
Rating
Detection
Rating
Step # Step details
1 Define Project Scope
2 Brainstorm all potential failure modes
3 Identify the potential effects of failures
4 Determine severity rankings
5 Identify the causes of failures
6 Determine Occurrence rankings
7 Identify the current controls
8 Determine the detection rankings
9 Evaluate Risk Priority Numbers(RPN)
10 Prioritise corrective actions.
FMEA STEPS
10. Recommend Action(s)
• The intent of any recommended action is to reduce any
one or all of the occurrence, severity, and/or detection
rankings.
• An increase in design validation/verification action will
result in a reduction in the detection ranking only.
• A reduction in the occurrence ranking can be effected
only by removing or controlling one or more of the cause
mechanisms of the failure mode through a design change.
• Only a design revision can bring about a reduction in the
severity ranking
• Examples include revised design geometry, and /or
tolerance, revised material specifications, modify the mfg
process
10. Prioritise & implement action(s)
• Enter a brief description of the actual action and effective date.
Resulting RPN
• Estimate & record resulting S,O,D and RPN rankings.
• Resulting RPNs should be reviewed and new set of actions
should be decided accordingly till the desired RPN is not
achieved.
• This ensures FMEA is a Living Document,
• FMEA can also be updated as and when new failure modes
are discovered.