FMEA (Failure Mode and Effects Analysis): How to Do It

DFMEA (Design FMEA) analyzes the failure modes of the product design before it is manufactured: geometry, tolerances, materials. PFMEA (Process FMEA) analyzes the failure modes of the manufacturing process: machine parameters, operation sequence, handling. SFMEA (System FMEA) analyzes the complete system, including interactions between subsystems. In automotive under IATF 16949, DFMEA and PFMEA are almost always mandatory; SFMEA is used for complex systems with multiple interdependent components.

The process follows a logical sequence: (1) Identify the functions of the product or process. (2) Identify the potential failure modes of each function. (3) Identify the potential causes of each failure mode. (4) Identify the effects of each failure mode on the customer. (5) Score severity (S), occurrence (O) and detection (D) from 1 to 10. (6) Calculate the RPN. (7) Prioritize and define actions for the highest RPNs. (8) Re-evaluate after implementing the actions.

Severity (S) scores the impact of the effect on the customer if the failure occurs, from 1 (no effect) to 10 (safety risk without warning). Occurrence (O) scores the probability of the cause occurring, from 1 (remote) to 10 (very high). Detection (D) scores the ability of the current control system to detect the failure before it reaches the customer, from 1 (almost certain detection) to 10 (not detected). The RPN is the product of the three, ranging from 1 to 1000.

There is no universal threshold set by the standard; each organization defines its own criteria, typically between 100 and 125 as an alert limit. However, the more rigorous approach (recommended by the AIAG-VDA handbook) prioritizes any failure mode with a Severity of 9 or higher, regardless of the total RPN, because it implies a safety risk or regulatory non-compliance.

To reduce Severity: this can rarely be reduced without changing the product design. To reduce Occurrence: address the root cause with poka-yoke, statistical process control or a material/supplier change. To reduce Detection: improve the control system with automatic inspection, in-line sensors or increased sampling frequency. The most effective strategy usually combines occurrence reduction with improved detection.

It is a living document. It must be reviewed whenever the design, process, material or supplier changes, or when a non-conformance occurs that was not anticipated in the original FMEA. Review after an NC is especially important: if the actual failure was not contemplated, the FMEA was incomplete and must be updated to add the new failure mode.

The AIAG-VDA FMEA Handbook reference manual includes official DFMEA and PFMEA templates in Excel format, widely used in the automotive industry. Many OEM customers also provide their own mandatory template as a Customer Specific Requirement. IgeraIndustria can index your specific template and help you complete it, citing the applicable internal procedure.

IgeraIndustria does not replace the technical judgment of the cross-functional team, but it indexes your historical FMEAs and past NCs to suggest failure modes, causes and effects already documented in similar processes, speeding up the initial analysis and reducing the risk of missing already known failures.