Failure Modes and Effects Analysis (FMEA)
FMEA injects rigor into the design of products and processes that prevents defects, mistakes, errors and variation.
By Jay Arthur
In a business world focused on success, it’s often difficult to get people to think about failure. It sounds so defeatist. But the wise quality engineer knows that anticipating and preventing possible failures is the key to success.
FMEA was developed by the Army in the 1940s. FMEA is a method to identify possible failure points, their frequency, severity, detectability, and take actions to prevent them, beforebuilding a product or implementing a process. They can be used in manufacturing, services, healthcare, banking, virtually any business. FMEAs can be used on a system (e.g., car), subsystem (e.g., braking subsystem) or part level (e.g., disc brake). FMEAs also serve as a starting point for developing control plans.
An oil leak in a car may happen frequently, but a drip or two isn’t going to be that severe. A gasoline leak, even a small one, no matter infrequent, could have a high severity and cause a car fire. Similarly, a medical procedure such as a vaccination might have a high frequency, but low severity. Something as simple as installing an IV, if done incorrectly, can cause a blood stream infection with a corresponding high severity. Anticipating and mitigating these potential fail points is the key to smooth, flawless operation.
There are two types of FMEAs—Design FMEAs (DFMEA) and Process FMEAs (PFMEA). Design FMEAs help anticipate failures in product designs. Process FMEAs help anticipate failures in procedures.
For several decades, the Automotive Industry Action Group (AIAG) has produced standards for creating DFMEAs and PFMEAs (FMEA Handbook 4th Edition). The AIAG is a consortium of the big three automakers that standardize automobile safety and quality. In the last couple of years, the AIAG has worked with VDA (Verband der Automobilindustrie), the German association for automotive manufacturers to establish a shared standard (AIAG & VDA FMEA Handbook 1st Edition). The two versions are similar, but different. The 4th edition has six DFMEA templates and eight PFMEA templates with varying numbers of fields per template. The new 1st edition has three DFMEAs and six PFMEAs. While the new AIAG & VDA FMEA handbook is coming into common use, there’s still a lot of older versions in use. Both share common failure modes and causes.
Potential Failure Modes (DFMEA)
No function
Partial function
Degradation of function
Overachievement
Intermittent function
Unintended function
Wrong part installed
Delayed function
Failure Causes (DFMEA)
Inadequate design, components, material, geometry, etc.
System interactions
Changes over time, fatigue, wear
Inadequate design
User error, misuse, abuse
Hard to manufacture
Failure causes (PFMEA) reflect common root cause analysiscauses – operator, machine, method, material, measurement, environment.
Here's how to fill out an FMEA 4th Edition template:
Identify each Part or Process Step.
Identify Potential Failure Modes - All of the manners in which the part or process could fail: cracked, loosened, deformed, leaking, oxidized, overlooked, etc.
Identify any Potential Effect(s) of Failure - Consequences on other systems, parts, or people: noise, unstable, inoperative, impaired, injury, death, etc.
Rank Severity of the Effect (1-10) from none to “hazardous without warning” (Table/Figure 1).
Evaluate Potential Cause(s) / Mechanism(s) of Failure - List every potential cause and/or failure mechanism: incorrect material, improper maintenance, fatigue, wear, etc.
Rank the Possibility of Occurrence (1-10) - remote (6-sigma) to high (3-sigma).
List Your Current Design Controls - List prevention and detection activities to assure design adequacy and prevent or reduce occurrence.
Rank Your Ability to Detect a Failure Using these Controls (1-10) from almost certain to absolute uncertainty.
Calculate the risk-priority number (RPN) for each part or step RPN = severity * occurrence * detection. (This calculation was replaced with an Action Priority (AP) matrix in the new FMEA handbook.)
Design Recommended Improvement Action(s) - Design additional actions to reduce severity, occurrence and detection ratings. Severity of 9 or 10 requires special attention.
Assign Responsibility & Target Completion Date for implementing designed improvements.
Monitor Actions Taken and effects on RPN/AP.
Method: Gather a team and use Post-it notes to capture each element in each row of the FMEA. Then transcribe it into a template for distribution. While it can seem grueling to identify and diagnose each potential failure mode, it’s a lot less grueling than a failure of a process or a part.
PFMEA 4th Edition Example (Figure 1)
New FMEA 1st Edition (Figure 2-3)
The newly introduce FMEA forms add fields and columns to the original FMEA. The FMEA analysis is similar. The updated AIAG & VDA FMEA 1st Edition handbook describes a Seven-Step approach that guides design, development and process, along with monitoring and FMEA system response:
Planning and Preparation: Develop a FMEA project plan.
Structure Analysis: Using a visual method, decide which product or process that will be analyzed.
Function Analysis: For both your Design (DFMEA) and Process (PFMEA), choose which functions will be performed, along with HOW you will evaluate their performance(s).
Failure Analysis: What is/are the failure mode(s)? And what effects or causes these failures?
Risk Analysis: Assign severity of risk, along with occurrence and detection of the cause of failure. This estimates your level of design or process risk.
Action Priority (Figure 4) is based on combinations of Severity, Occurrence, and Detection ratings in order to prioritize actions for risk reduction. Note: (AP replaces RPN): Assign a value (1-10) for each severity/occurrence/detection (New 1st Edition). AP will be automatically assigned as a High/Medium/Low Priority.Optimization: Based upon your Risk Analysis from step 6, decide which aspects of your FMEA will require actions that reduce your risk. And what are those actions?
Results and Documentation: Document your findings! How did you reduce risk, and what were the actions taken? Create a comprehensive report that shows your findings.
FMEA injects rigor into the design of products and processes that prevents defects, mistakes, errors and variation. It’s a key element in Design for Six Sigma (DFSS). Wouldn’t you rather build it right the first time? FMEAs can help.
