Design and Process FMEA

FMEA systematically identifies how something could fail, what the consequences would be, how likely it is, how well it would be detected, and what should be done about it. It is preventive: its value depends entirely on being done early enough to change something.

Design FMEA

Examines the product design. Failure modes are ways the design could fail to perform its function — a component fractures, a seal leaks, software returns an incorrect value, a connector disengages under vibration. Actions change the design: material, geometry, tolerance, redundancy, or the requirement itself.

Process FMEA

Examines the manufacturing or service process, assuming the design is as specified. Failure modes are ways the process could fail to produce conforming output — hole drilled undersize, wrong component fitted, torque not applied, step omitted, wrong material used. Actions change the process: error-proofing, controls, sequence, tooling, detection.

Timing determines value

A design FMEA conducted after the design is released documents risks that can no longer be economically addressed. A process FMEA conducted after production starts becomes a record of problems already occurring. Both are common and both waste most of the method's value — which is why FMEA belongs in the project plan with a deadline that precedes design freeze and process sign-off respectively.

An FMEA produced to satisfy a customer requirement, after everything is fixed, is an expensive way of writing down what you already know.