DFMEA vs PFMEA: what is the difference?
Short answer
A design FMEA (DFMEA) asks how the product can fail to meet its function because of its design, assuming it is made to drawing. A process FMEA (PFMEA) asks how the manufacturing and assembly process can fail to make the product to drawing, assuming the design is right. Both follow the same seven steps of the AIAG-VDA handbook and the same action priority logic, but they have different owners, timing and controls.
Side by side
| Aspect | DFMEA (design) | PFMEA (process) |
|---|---|---|
| Analyses | Product, system, component design | Manufacturing, assembly, logistics steps |
| Assumption | Parts are made to specification | The design is correct |
| Structure | System → subsystem → component | Process item → process step → work element (4M) |
| Typical causes | Wrong material choice, tolerance stack, insufficient strength | Wrong setting, tool wear, missing part, wrong handling |
| Controls | Design verification: calculations, tests, simulations | Prevention (poka-yoke, standard work) and detection (inspection, gauges) |
| Owner and timing | Design engineering, APQP phase 2 | Manufacturing / quality engineering, APQP phase 3 |
| Main output | Design changes, test plan, special characteristics | Control plan, work instructions, error proofing |
How they connect
Special characteristics identified in the DFMEA flow into the PFMEA, where the process must show how they are controlled. The failure effects of the PFMEA often refer back to the failure modes of the DFMEA, so the severity rating stays consistent. The PFMEA then drives the control plan: every prevention and detection control should appear there.
Common mistakes
Writing design causes into the PFMEA ("material too weak") instead of process causes, rating detection as good because the customer will find the defect, and starting the PFMEA after the line is already built.