Failure mode and effects analysis (FMEA)

Each failure mode gets rated 1 to 10 on three scales: severity of the effect, likelihood of occurrence, and likelihood the current controls detect it before it escapes. Multiplying them gives a risk priority number (RPN); the newer AIAG-VDA handbook replaces raw RPN with action priority tables, partly because teams gamed RPN by inflating detection scores. Either way the discipline is the same: list the ways it can fail, rank them, act on the top.

The DFMEA versus PFMEA split matters. A DFMEA drives design for manufacturability decisions while geometry is still cheap to change. A PFMEA examines a specific process at a specific plant, which is why a generic PFMEA copied across sites is a red flag. Both are core deliverables inside APQP, written during development and updated whenever the design or process changes.

For procurement, a supplier's PFMEA is a window into process maturity. Ask for it before award: does it cover every operation, do high-severity items (9 and 10) get design-side action regardless of RPN, and has it been revised after past escapes and root cause investigations? An FMEA written once to pass a quality assurance audit and never touched again predicts exactly nothing.

Frequently asked questions

What is FMEA?

Failure mode and effects analysis (FMEA) is a systematic method for identifying how a design or process can fail, scoring each failure mode for severity, occurrence, and detection, and working the highest risks first. The output is a ranked worklist that drives design and process changes rather than a report that gets filed.

What is the difference between a DFMEA and a PFMEA?

A design FMEA (DFMEA) asks how the product can fail in use and drives design decisions while geometry is still cheap to change. A process FMEA (PFMEA) asks how manufacturing can produce a bad part, and it examines a specific process at a specific plant, which is why a generic PFMEA copied across sites is a red flag.

How is an FMEA risk priority number calculated?

Each failure mode gets rated 1 to 10 on severity, occurrence, and detection, and multiplying the three gives the risk priority number (RPN). In one stamping example, a burr failure mode scored severity 6, occurrence 4, detection 5 for an RPN of 120; adding an inline vision check dropped detection to 2 and the RPN to 48. The newer AIAG-VDA handbook replaces raw RPN with action priority tables, partly because teams gamed RPN by inflating detection scores.

Does a low RPN mean no action is needed?

Severity overrides the arithmetic. High-severity items rated 9 or 10 warrant design-side action regardless of RPN: in one connector DFMEA, a retention failure scored severity 9 because the device loses function in the field, so the team designed in a positive lock rather than relying on assembly inspection, even though occurrence was low.

How should buyers use a supplier's FMEA?

A supplier's PFMEA is a window into process maturity, and it is worth requesting before award. Check whether it covers every operation, whether high-severity items get design-side action regardless of RPN, and whether it has been revised after past escapes. One buyer found a machined-housing PFMEA covering 12 of 30 routing steps and untouched for three years, which said more about the supplier's quality system than the audit slide deck did.