🔍 Introduction
Most FMEAs stop at the surface when identifying causes—listing vague entries like “operator error” or “material defect.” But to truly reduce risk, you need to go deeper.
That’s where advanced failure cause modeling comes in.
By building detailed cause chains, using Ishikawa integration, and exploring multi-layered cause analysis, you strengthen your FMEA’s value—and the effectiveness of your recommended actions.
In this article, we’ll explore practical ways to go beyond the basics and model causes like an expert.
🧱 1. The Standard Cause Structure in FMEA
In AIAG-VDA FMEA, the “Cause of Failure” is the root of risk analysis.
| Element | Purpose |
|---|---|
| Function | What the item should do |
| Failure Mode | How it fails to perform |
| Cause | Why it fails |
| Effect | What happens when it fails |
However, many FMEAs stop at Level 1 causes. For example:
- Failure Mode: “Leakage”
- Cause: “Seal not installed properly”
That’s helpful—but not deep enough.
🌳 2. Cause Trees: Building Multi-Layered Root Causes
A Cause Tree (or Failure Chain) expands each failure cause into sub-causes until you reach the actual root.
🧠 Example:
Failure Mode: Bolt is loose
Primary Cause: Torque not applied correctly
→ Sub-cause: Operator skipped torque step
→ Sub-cause: Torque tool was not calibrated
→ Sub-cause: Calibration plan not followed
✅ Now you can assign prevention actions at:
- Operator level (training, mistake-proofing)
- Tool level (calibration)
- System level (checklist enforcement)
💡 This traceable breakdown is especially helpful during audits and problem solving.
🐟 3. Integrating Ishikawa (Fishbone) into FMEA
You can use an Ishikawa (Cause & Effect) Diagram to brainstorm causes before documenting in the FMEA.
Typical Cause Categories:
- Man – Operator skill, fatigue, attitude
- Machine – Equipment settings, wear, calibration
- Material – Incorrect spec, shelf life, contamination
- Method – Work instructions, sequence, tools
- Measurement – Gages, inspection frequency, MSA
- Environment – Temperature, humidity, lighting
✅ Use the Ishikawa tool in cross-functional workshops to explore causes for each key failure mode.
📌 4. Categorizing Causes for Better Control Selection
You can classify causes based on their nature to decide whether prevention or detection is best suited.
| Cause Type | Control Strategy |
|---|---|
| Human Error | Mistake-proofing, training (Prevention) |
| Machine Fault | TPM, sensor-based detection (Detection) |
| Design Weakness | Robust design, simulations (Prevention) |
| Method Gap | SOP review, standardization (Prevention) |
💡 Add cause type as an extra column in your FMEA for better filtering and action planning.
🔄 5. Cause Linking Across DFMEA → PFMEA
One of the strengths of advanced FMEA modeling is the ability to link causes between design and process.
Example:
- DFMEA Cause: Housing flatness out of spec
- PFMEA Cause: Fixture not locating part correctly
- Link: Poor design leads to high process sensitivity
👉 This helps in aligning design changes with process improvements and avoiding “throwing the problem over the wall”.
🔧 6. Using Software Tools for Cause Modeling
Advanced FMEA tools like APIS IQ RM and PLATO SCIO allow:
| Feature | Benefit |
|---|---|
| Cause chaining | Model Level 1 → Level 2 → Level 3 |
| Ishikawa diagrams | Built-in brainstorming tools |
| Object linking | Reuse causes across FMEAs |
| Visual mapping | Better communication in reviews |
💡 If you’re still using Excel, build a custom visual with indentation or color-coding to show multiple cause layers.
🧠 7. Real-World Case: EV Battery Leak
Failure Mode: Battery housing leak
Initial Cause (PFMEA): Sealant missing
Cause Tree:
- Robot failed to apply sealant
- Vision sensor failed to detect gap
- Calibration was skipped
- Maintenance checklist incomplete
Action Plan:
- Add sealant presence detection sensor (Detection)
- Add daily calibration checklist for vision sensor (Prevention)
- Revise maintenance SOP and train technician (Prevention)
✅ This multi-level root cause modeling improved detection and reduced recurrence in future batches.
✅ Summary
| Advanced Cause Modeling Helps You… |
|---|
| Identify true root causes, not just symptoms |
| Plan layered actions with real impact |
| Communicate risks clearly to leadership and customers |
| Strengthen PFMEA and DFMEA linkages |
| Improve audit and customer feedback scores |
FMEA is not just about documenting failure—it’s about understanding why things fail, so you can prevent them effectively.
📥 Bonus Download:
📄 [FMEA Cause Tree Template + Ishikawa Brainstorming Sheet] (Insert your download link)
🔁 Coming Up Next in the Series:
Post #9: FMEA Moderation Techniques for Cross-Functional Teams
🔗 Internal Links to Add:
/fmea-in-apqp-projects//modular-family-fmea//fmea-software-overview//dfmea-vs-pfmea/
