FMEA Types and steps involved

FMEA means Failure Mode and Effects Analysis. There are 3 types of FMEAs. 

1. System FMEA (SFMEA)
2. Design FMEA  (DFMEA)
3. Process FMEA  (PFMEA)

SFMEA is for System and used to analyze the failures of the end product in a customer's system. It focuses on the potential failure modes associated with the functions of the end product. 

DFMEA begins with the development of information to understand the system, subsystem or component being analyzed and defines their functional requirements and characteristics. It focuses on potential failure modes associated with the function of each system, subsystem or component being analyzed. 

PFMEA is used to analyze manufacturing and assembly processes. It focuses on process inputs. 

FMEA Processes - Steps Involved 

There are 13 steps in creating an FMEA. Please find the attached diagram.

Step 2: Define the Function 

What is the system, the sub system or process steps supposed to do in view of customer requirements?

Step 3: Determine Potential failure modes

Possible categories in which a function can go wrong:- No function, Partial function, Intermittent function and Unintended function. 

Step 4: List Potential failure effects 

Examples: Noise, Loss of fluid, Loss of function, Loss of system, Rough surface, poor appearance, Customer dissatisfied, Intermittent operations, Unpleasant odor, Potential safety hazard, No/Low output. 

Step 5: Assign Severity Ratings

Assess the seriousness of the effect.

Step 6: List all potential causes of the failure mode.

Step 7: Assign Occurrence Ratings

Rate the occurrence based on the likelihood that a specific root cause will occur.

Step 8: Define Current Design/Process Controls

Detecting the cause and subsequent failure mode prior to production and prevent the cause from occurring. Example- Lab test, Load test, Field test, Fleet test, Design review, Final test, Gauging, Operator training, Method sheets, Work instructions, Maintenance, Environmental test, Fail/Safe features, Warnings, Error proof by design, setup verification etc.

Step 9:  Assign Detection Settings.

Rate the detection based on each detection control mentioned.

Step 10: Calculate RPN

RPN = Severity of the effects * Probability of occurrence * Ineffectiveness of design/process verification.

Step 11: Develop an Action Plan to address high RPNs

Order of priorities :

1.  High Severity
2.  High Multiple
3.  High RPN

Note: RPN threshold values should not be a target.

Step 12 - Take Action

•  Define the necessary actions in order to reduce occurrence and/or detection of the failure mode.
• Redesign the product to reduce severity.
• Determine the list of recommended actions.
• Assign a person responsible with a due date foe each task.

Examples of Recommended actions: Revise design, revise test plan, revise material specification, reliability testing, finite element analysis, training, process instructions etc.

Step 13: Reevaluate the RPN

Reevaluate all the three ratings - severity, occurrence and detection and calculate the new RPN.

Reason for the Failure of FMEAs

• Only one person is assigned to complete the FMEA.
• Not customizing the rating scales with business units specific data, so that they are meaningful.
• The design or process expert is not included in the FMEA or is allowed to dominate the FMEA team.
• Members of the FMEA team are not trained in the use of FMEA, and become frustrated with the process.
• The FMEA team becomes bogged down with minute details of design or process, losing sight of the overall objective.
• Rushing through identifying the failure modes to move on to tht next step of the FMEA.
• Listing the same potential effect for every failure.
• Stopping the FMEA process when the RPNs are calculated and not continuing with the recommended actions.
• Not reevaluating the high RPNs after the corrective actions have been completed.

Thank you for reading this article.