Process fmea breakfast

Failure Mode and

Effects Analysis

Lawrence Hallett!

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

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 - who prepares it

•A team effort - including!•Manufacturing/production!•Engineering!•Design !•Quality!•Test!!

•However it is a moving feast

PFMEA

Three Parts: ●Process Flow Diagram (PFD) ●Process Failure Mode and Effects

Analysis (PFMEA) ●Process Control Plan (PCP)

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

Pencil Assembly

Using a simple mechanical pencil -conduct a Process FMEA

Process Function/Requirements

Process Flow Diagrams● The Process Flow

Diagram provides a logical (visual) depiction of the process that is being analyzed.

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

Severity Ranking

Severity

Potential Cause of Failure

Cause of Failure

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

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