The FMEA Process: 7 Steps
Step 1: Define Scope
What process or product are you analyzing? A process FMEA (PFMEA) examines manufacturing steps. A design FMEA (DFMEA) examines the product design. For lean practitioners, PFMEA is most common. Define the boundaries: which operations are included?
Step 2: Identify Process Steps
List every operation in the process. For each operation, identify: its function (what it should do), its requirements (how you know it is done correctly).
Step 3: Identify Failure Modes
For each operation: how could it fail? What could go wrong? A failure mode is the way the operation fails to meet its requirement. Example: “Hole drilled undersize,” “Sealant applied with insufficient fillet,” “Fastener installed with incorrect torque.”
Step 4: Determine Effects and Severity
For each failure mode: what is the impact on the customer (next operation, final assembly, or end user)? Rate Severity on a 1–10 scale. S=1 is no effect. S=9–10 is safety hazard or regulatory violation. In aerospace, structural failures and FOD are typically S=9 or 10.
Step 5: Identify Causes and Occurrence
For each failure mode: what causes it? Rate Occurrence (likelihood) on a 1–10 scale. O=1 means nearly impossible. O=10 means almost certain. Base ratings on actual data (defect rates, historical occurrence) when available, not gut feel.
Step 6: Identify Current Controls and Detection
What controls exist to prevent the cause or detect the failure? Rate Detection on a 1–10 scale. D=1 means the control will almost certainly detect. D=10 means no control exists or detection is impossible. SPC improves detection. Poka-yoke improves both prevention and detection.
Step 7: Determine Action Priority and Assign Actions
Use the S×O×D Action Priority table (or RPN if your organization uses the older method) to prioritize. Assign specific actions with owners, deadlines, and verification methods. After implementation, re-rate to confirm the risk has been reduced.
Rating Scales
| Rating | Severity | Occurrence | Detection |
|---|---|---|---|
| 1 | No effect | Nearly impossible (≤1 in 1,000,000) | Almost certain to detect |
| 2–3 | Minor annoyance | Very unlikely | High chance of detection |
| 4–6 | Moderate impact, rework needed | Occasional | Moderate detection capability |
| 7–8 | Major impact, customer affected | Frequent | Low detection capability |
| 9–10 | Safety hazard / regulatory | Very frequent / certain | No detection / cannot detect |
Worked Example: Sealant Application PFMEA
| Failure Mode | Effect | S | Cause | O | Current Control | D | RPN | Action |
|---|---|---|---|---|---|---|---|---|
| Insufficient fillet radius | Corrosion path at joint; rework | 7 | No standard work for technique | 6 | Visual inspection at next station | 5 | 210 | Create standard work + TWI training |
| Sealant uncured | Joint failure in service; safety | 9 | Shop temp below cure minimum | 3 | Inspector checks adhesion | 4 | 108 | Add temp monitoring + auto-alert |
| Foreign object in sealant | FOD risk; corrosion initiation | 8 | Dirty application area | 4 | Pre-seal clean per SOP | 6 | 192 | Add poka-yoke clean verification step |
| Wrong sealant type applied | Chemical incompatibility; rework | 8 | Multiple sealant types at station | 2 | Operator reads work order | 7 | 112 | Color-code sealant tubes by type; poka-yoke storage |
Priority order (by RPN): Insufficient fillet (210) → FOD (192) → Wrong type (112) → Uncured (108). The highest-RPN item gets action first — standard work and TWI training for sealant application technique.
💡 The FMEA Is a Living Document
The most common FMEA failure: it is created during APQP, filed in a binder, and never updated. A real FMEA is updated when: (1) A new failure mode is discovered in production. (2) A customer complaint reveals an undetected failure. (3) A process change adds new failure possibilities. (4) Countermeasures are implemented and ratings need to be re-scored. Review the FMEA at least quarterly or whenever the process changes.
🎯 The Bottom Line
FMEA is proactive quality — anticipating failures before they occur instead of reacting to defects after. The 7-step process identifies failure modes, rates their risk (Severity × Occurrence × Detection), and prioritizes prevention actions. Focus on high-severity items first (regardless of occurrence), drive occurrence down with process improvement, and drive detection up with SPC and poka-yoke. Keep the FMEA alive by updating it with field data and new discoveries. Next: Poka-Yoke Design — error-proofing techniques that eliminate failure modes at the source.
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