Failure Mode and Effects Analysis Lawrence Hallett
Jan 14, 2015
Failure Mode and
Effects Analysis
Lawrence Hallett!
Purpose
How to conduct an FMEA.
OriginFailure mode and effect analysis (FMEA) was one of the first systematic techniques for failure analysis. It was developed by reliability engineers in the 1950s to study problems that might arise from malfunctions of military systems
Definition of FMEA
A Failure Mode and Effect Analysis uses a disciplined technique to identify and help eliminate product and process potential failure modes.
o By ID of potential failures o Assessing the risks caused by failure modes and Identify
corrective actions o Prioritizing corrective actions o Carry out corrective actions
Most COMMON Types of FMEA's
Design (Potential) Failure Modes and Effects Analysis-DFMEA • Focus is on potential design- related failures
and their causes. !
Process (Potential) Failures Modes and Effects Analysis-PFMEA • Focuses is on potential process failures and
their causes.
PFMEA's!
● Focus is on potential process –related failures and their causes. ▪Main drive is to understand the process through the identification of as many potential failures as possible.
o e.g. Incorrect material used
● PFMEA typically assumes that the design is sound.
● Development of Recommended Actions is targeted at eliminating the Root Cause of the potential failures.
PFMEA's benefits•Identifies Process Functions and Req’s!•Identifies potential failure modes!•Assesses effect of failure!•Identifies causes of failures!•Identifies process controls!•Identifies confirmed Critical Characteristics!•Provides an objective base for action
PFMEA's outputs
PFMEA's - who prepares it
•A team effort - including!•Manufacturing/production!•Engineering!•Design !•Quality!•Test!!
•However it is a moving feast
Related Documents
PFMEA
Three Parts: ●Process Flow Diagram (PFD) ●Process Failure Mode and Effects
Analysis (PFMEA) ●Process Control Plan (PCP)
Product Definition:Key Product Characteristics, DFMEA
Process Definition:Process Flow Diagram (PFD),
Failure Mode Analysis:PFMEA
Control Strategy:Control Plan,Error proofing
Customer Requirements:
Manufacturing:Work Instructions & Process Monitoring
Information Flow
SOR, Vehicle Tech Specs, System Technical Specs
Product and Process Characteristics
DFMEA/PFMEA Information Interrelationships
DFMEA Design FMEA
Process Flow Diagram
PFMEA Process FMEA
Boundary (Block) Diagram, P- Diagram,
Etc.
Design Verification Plan & Report
(DVP&R)
Process Control Plan
Process Function/Requirements
Process Flow Diagrams● The Process Flow
Diagram provides a logical (visual) depiction of the process that is being analyzed.
12
● The SAE/AIAG PFMEA guidelines describe two methods of defining process functions. Either or both may be used.
● Process Functions may be described in terms of: ▪The product features/characteristics that are
created or
▪The process actions that are performed ● Process functions should be identified in detail
as necessary to provide information for the PFMEA to develop effective Process Controls
Process Function / Requirement
13
● Consider a simple operation to drill a hole in a metal part
● The product characteristics & requirements are: ▪Hole size: 4.00 mm +/- 0.13 ▪Hole Location:
X = 28.0 mm +/- 0.2 Y = 15.0 mm +/- 0.2 ▪Perpendicular to surface, no burrs, etc.
● The process operation must create these product characteristics and meet the requirements
Process Function / Requirement
XY
4.00
●To drill the correct hole size in the specified location, the process must: ▪Position and hold the part ▪Align the part fixturing
with the drill position ▪Assure the correct drill
bit size is used ▪Set and control drill speed ▪Anticipate tool wear and
schedule preventive maintenance
● If the Function/Requirement is defined in the PFMEA as “Drill Hole” could any of these be missed?
Process Function / Requirement
Process Flow Diagram (PFD)
● Process Flow Diagram is the foundation ▪ The process must be defined step by step, including
interfaces ▪ The PFD provides the structure to document what product
characteristics and requirements (OUTPUTS) are affected by a given operation and how these characteristics and sources of variation are controlled (INPUTS)
▪ PFD is a graphical representation of every possible path a part can take through the anticipated manufacturing process
▪ A well defined PFD establishes the foundation for the PFMEA
● Helps in developing equipment specifications. ▪ How will the process control non-conforming material? ▪ How and when will inspections be performed, what is
required? ▪ How and when will parts be re-introduced into the
process?
PFD Example
PFD Feeds PFMEAIdentify the Function(s)
● Function is a description of what the Process does to meet the requirements ➢Related to process specification and product
characteristics ➢Comes from the PFD operation description column
● Functions can be described as: ➢Do this operation… ➢To this part or material… ➢With this tooling or equipment…
Potential Failure Mode
Potential Failure Modes
Often missed
Potential Effect of Failure
Example
Failure Modes
Effect of Failure
Case assembled but not to the correct height
Fails height check causing rework(3) if not detected Connector corrosion leading to intermittence premature part failure(8)
Potential Effects
of Failure
Potential Effects
of Failure
Severity Ranking
Severity
Potential Cause of Failure
Cause of Failure
How to identify Cause of Failure
Developing CausesAlways assume a direct correlation between cause and failure i.e if the cause occurs then the failure mode occurs
Assumptions
Assumptions
Occurrence
How to identify Occurrence
Occurrence Evaluation Criteria
Probability of Likely Failure Rates Over Design Life Ranking Failure
SUGGESTED OCCURRENCE EVALUATION CRITERIA
Very High: Persistent failures
High: Frequent failures
Moderate: Occasional failures
Low: Relatively few failures
Remote: Failure is unlikely
≥ 100 per thousand vehicles/items
50 per thousand vehicles/items
20 per thousand vehicles/items
10 per thousand vehicles/items
5 per thousand vehicles/items
2 per thousand vehicles/items
1 per thousand vehicles/items
0.5 per thousand vehicles/items
0.1 per thousand vehicles/items
≤ 0.01 per thousand vehicles/items
10
9
8
7
6
5
4
3
2
1
Current controls
Current Controls
2 types of controls Prevention Prevent the Cause/mechanism or failure mode/effect from occurring or reduce their rate of occurrence !Detection Detect the cause/mechanism and lead to corrective action
How to identify process controls
Current Controls
Detection ranking
Detection Rankings
Risk Priority Number
Analysis Of Risk
▪ RPN / RISK PRIORITY NUMBER ▪ What Is Risk? ▪ Probability of danger ▪ Severity/Occurrence/Cause
Evaluation by RPN Only
▪ Case 1 o S=5 O=5 D=2 RPN = 50
▪ Case 2 o S=3 O=3 D=6 RPN = 54
▪ Case 3 o S=2 O=10, D=10 = 200
▪ Case 4 o S=9 O=2 D=3 = 54
WHICH ONE IS WORSE?
Example
▪ Extreme Safety/Regulatory Risk o =9 & 10 Severity
▪ High Risk to Customer Satisfaction o Sev. > or = to 5 and Occ > or = 4
▪ Consider Detection only as a measure of Test Capability.
Actions taken
Actions
Re-rating RPN After Actions Have Occurred
Re-rating RPN After Actions Have Occurred▪ Severity typically stays the same. ▪ Occurrence is the primary item to reduce / focus on. ▪ Detection is reduced only as a last resort. ▪ Do not plan to REDUCE RPN with detection actions!!!
o 100% inspection is only 80% effective! o Reducing RPN with detection does not eliminate failure mode,
or reduce probability of causes o Detection of 10 is not bad if occurrence is 1
Outputs
● PCP will be based on the previous activities in PFD and PFMEA.
● Review the PFMEA information developed & supplied and use to identify: ▪ Specific controls that may be needed due to the
information added ▪ Identify which controls are Product or Process
o Note any Special Characteristics o Identify evaluation methods, frequency and Control
Methods o Note Reaction Plans (particularly related to NC parts)
Process Control Plan
Process Control Plan Example
Part/ Process Number
Process Name /Operation Description
Machine, Device, Jig,
Tools for Mfg.
CharacteristicsSpecial Char. Class.
Methods
Reaction PlanNo. Product Process
Product / Process Specification /
Tolerance
Evaluation Measurement
Technique
SampleControl MethodSize Frequency
300 Initiate weld sequence /
Perform TIG weld of frame parts.
Robotic Arm controller.
TIG welders.
Weld beads per design specification.
Tube welds meet pull test with failure in parent material.
Pull test using test fixture 20-1.
1 pc.
Per shift.
Hydraulic pull test instruction TI21-01 Process monitoring form PMF-20-01
Quarantine material since last good pull test.
Good welds, no visible defects.
yes Weld appearance meets visual standard.
Operator evaluation to Visual Std TB20-VS1
100% Each piece.
Visual inspection OWI #20-01.
Remove part and send to repair.
Weld voltage yes 24 Volts AC +/- 2.0 volts
Machine Control
100% Each weld cycle.
Closed-loop machine control.
Scrap part & Re-start welder.
Weld voltage yes 24 Volts AC +/- 2.0 volts
Visual Once each
Shift start or change-over or maint. event.
Set-up OWI #20-02 & Form PMF-20-02 Periodic maintenance per PM-WI #20.
Scrap current part. Shut down.Notify maintenance.
Inert gas flow rate
yes 5 cubic feet / min.+/- 0.5 cfm
Visual twice Per shift. Operator cleans gas cup twice per shift PM-WI-20. Process monitoring form PMF-20-01
Notify maintenance.
Inert gas flow rate
yes 5 cubic feet / min.+/- 0.5 cfm
Visual of verification of Flow Meter
Once each
Shift start or change-over or maint. event
Set-up OWI #20-02 & Form PMF-20-02. Equipment Calibration Procedure #368
Quarantine material since last good pull test.Notify maintenance.
Form 818-1 (Rev 12Apr02)
CONTROL PLAN Control Plan No:Part Number/Latest Change Level Key Contact/Phone Date (Orig.) Date (Rev.)
Customer Part Number Core Team Customer Engineering Approval/Date (If Req'd.)
Part Name/Description Supplier/Plant Approval/Date Customer Quality Approval/Date (If Req'd.)
Supplier/Plant Supplier Code Other Approval/Date (If Req'd.) Other Approval/Date (If Req'd.)
Prototype Pre-Launch Production
Process Control Plan Example
Initiate weld sequence / Confirm Wire feed rate
Initiate weld sequence / Confirm Weld voltage
Initiate weld sequence /Perform TIG weld of
frame parts.
Initiate weld sequence / Confirm Inert Gas flow
rate
Scrap part & Re-start welder
Closed-loop machine control.
Each weld cycle.
100%Machine Control
300 mm / minute +/- 10 mm / min.
yesWeld wire feed rate
Scrap part & Re-start welder
Closed-loop machine control.
Each weld cycle.
100%Machine Control
24 Volts AC +/- 2.0 volts
yesWeld voltage
Notify maintenance.
Operator cleans gas cup twice per shift PM-WI-2500. Process monitoring form PMF-20-10
Per shift.twiceVisual5 cubic feet / min.+/- 0.5 cfm
yesInert gas flow rate
Remove part and send to repair.
Visual inspection OWI #20-010.
Each piece.
100%Operator evaluation to Visual Std TB20-VS1.
Weld appearance meets visual standard.
yesGood welds, no visible defects.
Scrap current part.Shut down.Notify maintenance.
Set-up OWI #20-020 & Form PM-20-020 Predictive maintenance pinch roller replace @ 180 days.
Shift start or change-over or maint. event
100%Operator setup check and verification
300 mm / minute +/- 10 mm / min.
yesWeld wire feed rate
Quarantine material since last good pull test. Notify maintenance.
Set-up OWI #20-02 & Form PM-00-02. Equipment Calibration Procedure #368
Shift start or change-over or maint. event
Once each
Visual verification of Flow Meter
5 cubic feet / min.+/- 0.5 cfm
yesInert gas flow rate
Scrap current part. Shut down.Notify maintenance.
Set-up OWI #20-02 & Form PM-20-02 Periodic maintenance per PM-WI #20.
Shift start or change-over or maint. event
Once each
Visual24 Volts AC +/- 2.0 volts
yesWeld voltage
Quarantine material since last good pull test.
Hydraulic pull test instruction TI41-01 Process monitoring form PM-20-010
Per shift.
1 pc.
Pull test using test fixture 20-1.
Tube welds meet pull test with failure in parent material.
Weld beads per design specification.
Robotic Arm TIG welders
and controllers.
300.
.!Robotic Arm TIG welders
!Initiate weld sequence / Close and latch curtain
300
FrequencySize
Reaction PlanControl Method
SampleEvaluation Measurement
Technique
Product / Process Specification /
ToleranceProcessProductNo.
MethodsSpecial Char. Class.
CharacteristicsMachine,
Device, Jig, Tools for Mfg.
Process Name /Operation Description
Part/ Process Number