Breakfast session introducing FMEA

1. Failure
Mode and
Effects
Analysis
Lawrence Hallett!

2. Origin
Failure 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

3. 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.

4. 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.

5. 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

6. PFMEA's - who
prepares it
•A team effort - including!
•Manufacturing/production!
•Engineering!
•Design !
•Quality!
•Test!
!
•However it is a moving feast

7. PFMEA
Three Parts:
● Process Flow Diagram (PFD)
● Process Failure Mode and Effects
Analysis (PFMEA)
● Process Control Plan (PCP)

8. 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

9. Pencil Assembly
Using a simple mechanical pencil -conduct a Process FMEA

10. Process Function/Requirements

11. Process Flow Diagrams
● The Process Flow
Diagram provides a
logical (visual)
depiction of the
process that is being
analyzed.

12. PFD Example

13. PFD Feeds PFMEA
Identify 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…

14. Potential Failure Mode

15. Potential Failure Modes
Often missed

16. Potential Effect of Failure

17. 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)

18. Potential
Effects
of
Failure

19. Severity Ranking

20. Severity

22. Potential Cause of Failure

23. Cause of Failure

24. Developing Causes
Always assume a direct correlation between cause and failure
i.e if the cause occurs then the failure mode occurs

25. Occurrence

26. 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

27. Current controls

28. 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

29. How to identify process controls

30. Current Controls

31. Detection ranking

32. Detection Rankings

33. Risk Priority Number

34. Analysis Of Risk
▪ RPN / RISK PRIORITY NUMBER
▪ What Is Risk?
▪ Probability of danger
▪ Severity/Occurrence/Cause

35. 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?

36. 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.

37. Actions taken

38. Actions

39. Re-rating RPN After Actions Have Occurred

40. 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

41. Outputs