A DFMEA (design FMEA) asks how the product can fail to do its job even if it is built exactly to the drawing. Its causes are design decisions: material, geometry, tolerances, specified torque. A PFMEA (process FMEA) asks how the manufacturing or assembly process can fail to build the part to the drawing. Its causes are process factors: machines, methods, operators, material handling, measurement. Design engineering owns the DFMEA and finishes it before design release. Manufacturing and quality engineering own the PFMEA and finish it before production launch.
| DFMEA (design) | PFMEA (process) | |
|---|---|---|
| Question | Can the design, built to print, fail to perform its function? | Can the process fail to build the part to print? |
| What you analyze | Systems, subsystems and components, and their functions | Process steps and operations, and their purposes |
| Typical failure mode | Joint loosens in service; seal leaks at low temperature | Bolt under-torqued; seal installed twisted; hole drilled off position |
| Typical causes | Material choice, geometry, tolerance stack, specified values | Machine settings, tool wear, method, operator error, fixturing, incoming material |
| Prevention controls | Design standards, proven designs, simulation, tolerance analysis | Error-proofing, setup verification, preventive maintenance, process parameters |
| Detection controls | Design verification: analysis, prototypes, validation tests | Inspection, in-station monitoring, gauging, end-of-line tests |
| Owner | Design or product engineering | Manufacturing, process and quality engineering |
| When it is done | During design, before release to production tooling | During process design, before PPAP or production launch |
| Main outputs | Design changes, test plans, special characteristics | Process changes, control plan entries, work instruction content |
Both documents use the same seven-step structure described in the AIAG & VDA FMEA Handbook: planning and preparation, structure analysis, function analysis, failure analysis, risk analysis, optimization, and results documentation. Both rate severity, occurrence and detection, and both end with actions. What changes is the thing being analyzed.
In a DFMEA the structure is the product: vehicle, system, component, feature. In a PFMEA the structure is the process: line, station, operation, and the work elements inside it, often grouped as people, machine, material, method, measurement and environment. If your PFMEA rows read like design concerns (“wall too thin”), they belong in the DFMEA. If your DFMEA rows read like shop-floor errors (“operator forgets washer”), they belong in the PFMEA.
The documents are a chain, not two separate exercises. The DFMEA identifies which product characteristics matter most, and those become special characteristics on the drawing. The PFMEA then asks how each process step could fail to deliver those characteristics, and the control plan records how the process controls them. Work instructions carry the result to the operator.
Severity should travel with the effect. If the DFMEA rates “sensor bracket loosens, signal lost” at severity 8, a PFMEA failure mode that leads to the same end effect should also carry severity 8. Different severity numbers for the same effect are a common audit finding. The FMEA guide walks through the rating scales.
A company that is design-responsible for a product needs both. A build-to-print supplier, who makes parts to a customer’s drawing, normally owns only the PFMEA, though it should ask the customer which characteristics are special. IATF 16949 lists design FMEAs among product design outputs and process FMEAs among manufacturing process design outputs, so automotive suppliers are expected to produce whichever matches their responsibility. Medical device makers usually handle design risk under ISO 14971 and may use a PFMEA as one input to process risk control.
Start from a PFMEA worksheet that already has the AIAG-VDA columns, then rank actions with Action Priority. See RPN vs Action Priority for how that ranking differs from the older RPN.
Occurrence and detection ratings should rest on data, not opinion. In a DFMEA, occurrence comes from field history of similar designs and from how proven the design approach is. In a PFMEA it comes from process data: scrap history, defect rates and capability. A characteristic with a Ppk of 1.67 earns a lower occurrence rating than one at 1.0; see Cpk vs Ppk and the process capability calculator.
Detection ratings depend on whether the measurement can be trusted. A gauge that cannot tell good parts from bad does not earn a strong detection rating, which is why a gage R&R study belongs in the PFMEA evidence file. Both documents feed the PPAP package, and the quality core tools guide, the pillar for this cluster, shows how they connect.
Example: A fictional sensor bracket bolted to a housing with one M8 bolt. Function: hold the sensor in position under vibration. End effect if it fails: signal lost, severity 8 in both documents.
Result: Severity is identical because the end effect is identical. The DFMEA action is a design change (bolt grade or torque spec); the PFMEA action is process control. Neither document can fix the other’s cause.
The DFMEA starts first because the PFMEA needs to know which characteristics matter. They overlap in practice: process engineers should join DFMEA reviews to flag features that will be hard to make.
Usually not, because it has no design authority. It does need a PFMEA and should get the list of special characteristics from the customer’s drawing or DFMEA.
No. The PFMEA analyzes what can go wrong and why. The control plan lists the controls that run in production. Controls chosen in the PFMEA should appear in the control plan.
ISO 9001 requires risk-based thinking but does not name FMEA. IATF 16949 and many automotive customer requirements do expect design and process FMEAs.
The AIAG & VDA handbook adds a supplemental FMEA for monitoring and system response, which looks at how a system detects and reacts to failures while the product is in use. It extends the DFMEA; it does not replace the PFMEA.
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