1. Failure Mode and Effect Analysis
(FMEA)

2. What is Failure Mode and Effect Analysis (FMEA)?
FMEA is a quality audit procedure which aims to anticipate failure in a product’s functional design.
“Failure” may be the result of design, manufacturing process, or use.

3. FMEA The aim of FMEA is to anticipate: What might fail
What effect this failure would have
What might cause the failure

4. FMEA The significance of the failure is assessed against:
The probability of failure
An assessment of the severity of the effect of that failure
The probability of existing quality systems spotting the failure before it occurs

5. Where Does FMEA Occur? Concept FMEA Design FMEA Process FMEA Planning
Development
System-Level
Design
Detail
Design
Testing and
Refinement
Production
Ramp-Up
Concept FMEA
Design FMEA
Process FMEA

6. Design Project FMEA Design FMEA’s should cover:
all new components
carried over components in a new environment
any modified components
Mandatory on all control and load carrying parts

7. Design Project FMEA
“Failure” - a component or system not meeting or not functioning to the design intent
Design intent - may be stated in terms of MTBF, load or deflection, coat thickness, finish quality, etc.
“Failure” need not be readily detectable by a customer

8. FMEA Process Identify a failure mode
Determine the possible effects or consequences of the failure
Assess the potential severity of the effect
Identify the cause of failure (take action!)
Estimate the probability of occurrence
Assess the likelihood of detecting the failure

9. Failure Mode
Failure mode - the manner in which a component or system failure occurs (doesn’t meet design intent)
Potential failure modes
Complete failure
Partial failure
Intermittent failure
Failure over time
Over-performance failure

10. Failure Mode
Question to be asked: “How could the component or system fail?”
Examples: Consider failure modes of a penlight’s function defined as “Provide light at 3  0.5 candela.”
No light
Dim light
Erratic blinking light
Gradual dimming light
Too bright

11. Failure Mode - Identification
List potential failure modes for the particular part or function
assume the failure could occur, however unlikely
Sketch free-body diagrams (if applicable), showing applied/reaction loads. Indicate location of failure under this condition.
List conceivable potential causes of failure for each failure mode

12. Failure Mode – Effects
For each failure mode, identify the potential downstream consequences of each failure mode (the Effects)
Procedure for Potential Consequences
Beginning with a failure mode (FM-1) – list all its potential consequences
Separate the consequences that can result when FM-1 occurs: “Effects of FM-1”
Write additional failure modes for remaining, depending on circumstances
Add these to list of failure modes

13. Failure Mode – Effects Team brainstorms failure modes and effects
Example: Analyzing penlight bulb
Premature burnout – user could trip, fall, be injured
While used in eye examination, bulb might explode, resulting in injury

14. Failure – Severity
To analyze risk, must first quantify the Severity of the Effects
Assume that all Effects will result if the Failure Mode occurs
Most serious Effect takes precedence when evaluating risk potential
Design and process changes can reduce severity ratings

15. DFMEA Severity Table Severity of Failure Rank
Hazardous – No warning: Unsafe operation, without warning 10
Very high: Product inoperable; loss of primary function
8, 9
High: Product operable, but at a reduced level
6, 7
Low: Product operable; comfort or convenience items at reduced level
4, 5
Minor: Fit/finish, squeak/rattle don’t conform; average customer notices
2, 3
No effect 1

16. Failure Mode – Causes
After Effects and Severity addressed, the Causes of Failure Modes must be identified
In Design FMEA (DFMEA), design deficiencies that result in a Failure Mode are Causes of failure
Assumes manufacturing and assembly specifications are met
Process FMEA (PFMEA) has similar investigation
Causes are rated in terms of Occurrence
Likelihood that a given Cause will occur AND result in the Failure Mode

17. Failure Mode - Occurrence
Estimate the probability of occurrence on a scale of (consider any fail-safe controls intended to prevent cause of failure)
Consider the following two probabilities:
probability the potential cause of failure will occur
probability that once the cause of failure occurs, it will result in the indicated failure mode

18. Failure Occurrence - Ranking
Occurrence Criteria Ranking
Remote: unreasonable to expect failure (1)
Low: similar designs have low failure rates (2,3)
Moderate: similar designs have occasional moderate failure rates (4, 5, 6)
High: similar designs have failed in the past (7,8,9)
Very high: almost certain failure, in major way (10)

19. Example DFMEA Occurrence Table
Probability of Failure
Failure Rates
Rank
Very High: Failure almost inevitable
> 1 in 2 10
1 in 3 9
High: Repeated failures
1 in 8 8
1 in 20 7
Moderate: Occasional failures
1 in 80 6
1 in 400 5
1 in 2000 4
Low: Relatively few failures
1 in 15,000 3
1 in 150,000 2
Remote: Failure unlikely
< 1 in 1,500,000 1

20. Current Controls Design controls grouped according to purpose
Type 1: Controls prevent Cause or Failure Mode from occurring, or reduce rate of occurrence
Type 2: Controls detect Cause of Failure Mode and lead to corrective action
Type 3: Controls detect Failure Mode before product reaches “customer”

21. Detection Detection values are associated with Current Controls
Detection is a measure of Type 2 Controls to detect Causes of Failure, or ability of Type 3 Controls to detect subsequent Failure Modes
High values indicate a Lack of Detection
Value of 1 does not imply 100% detection

22. Criteria: Likelihood of Detection
DFMEA Detection Table
Detection
Criteria: Likelihood of Detection
Rank
Absolute Uncertainty
Design Control does not detect, or there is no Design Control 10
Very Remote
Very remote chance Control will detect 9
Remote
Remote chance Control will detect 8
Very Low
Very low chance Control will detect 7
Low
Low chance Control will detect 6
Moderate
Moderate chance Control will detect 5
Moderately High
Mod. High chance Control will detect 4
High
High chance Control will detect 3
Very High
Very high chance Control will detect 2
Almost Certain
Control almost certain to detect 1

23. Reducing Risk
The fundamental purpose of the FMEA is to recommend and take actions that reduce risk
Adding validation or verification can reduce Detection scoring
Design revision may result in lower Severity and Occurrence ratings
Revised ratings should be documented with originals in Design History File

24. Design Project FMEA - Results
Risk Priority Number (RPN)
RPN = Severity x Occurrence x Detection
Mathematical product of the seriousness of a group of Effects (Severity), the likelihood that a Cause will create the failure associated with the Effects (Occurrence), and an ability to detect the failure before it gets to the customer (Detection)
Note: S, O, and D are not equally weighted in terms of risk, and individual scales are not linear

25. Non-Intuitive Statistical Properties of the RPN Scale
Incorrect Assumption
Actual Statistical Data
The average of all RPN values is roughly 500
The average RPN value is 166
Roughly 50% of RPN values are above 500
(median is near 500)
6% of all RPN values are above 500
(median is 105)
There are 1000 possible RPN values
There are 120 unique RPN values

26. Criticality Criticality = Severity x Occurrence
High Severity values, coupled with high Occurrence values merit special attention
Although neither RPN nor Criticality are perfect measures, they are widely used for risk assessment

27. Interpreting the RPN No physical meaning to RPN
Used to “bucket problems”
Don’t spend a lot of time worrying about what a measure of “42” means
Rank order according to RPN
Note that two failure modes may have the same RPN for far different reasons:
S=10, O=1, D=2: RPN = 20
S=1, O=5, D=4: RPN = 20

28. Actions Actions taken are the important part of FMEA
Change design to reduce
Severity (redundancy?)
Occurrence (change in design, or processes)
Detection (improve ability to identify the problem before it becomes critical)
Assign responsibility for action
Follow up and assess result with new RPN

29. FMEA Benefits Systematic way to manage risk Comprehensive Prioritizes
Problems
Based on qualitative assessment
Unwieldy
Hard to trace through levels
Not always followed up

30. FMEA Levels CFMEA – 1 (Concept) DFMEA – 2 (Design) PFMEA – 3 (Process)
Failures in the concept (inability to achieve performance)
Detection
Ability to find the failures (i.e., use of historical data, early models, etc.)
DFMEA – 2 (Design)
Failures in current design (performance)
Detection
Highlighting failures during the detail design phase
PFMEA – 3 (Process)
Failures in production process
Finding the errors in the production line

31. Relationships (CFMEA, DFMEA, PFMEA)

32. FMEA

33. FMEA

34. END