Example Product: 12V Electric Water Pump (EWP) for engine cooling
Why this product? It mixes mechanical, electrical, and electronics—great for showing interfaces, controls, EMC, sealing, NVH, and durability risks in one example.
Product Snapshot (Context for All Steps) #
- System context (vehicle cooling loop, interfaces to hoses/ECU/power/ground)
- Key requirements & targets (e.g., 20–120 L/min, head ≥ X kPa, 9–16 V, −40 to 125 °C, IP67/69K, ≤ Y dBA, service life ≥ Z hours, EMC per OEM spec, zero visible leaks)
- High‑level architecture (housing, impeller, shaft, bearings, mechanical seal, BLDC motor, rotor/stator, PCB, Hall sensor, connector, O‑rings)
Step 1: Planning & Preparation #
Goal: Define scope, team, timing, and inputs so DFMEA starts right.
Inputs: Program charter, customer specs, CAD maturity, BOM rev, past LL (lessons learned), warranty field data (if any), regulatory/EMC norms.
Activities:
- Define item scope & boundaries (in/out of DFMEA), assumptions, lifecycle phases considered.
- Identify interfaces (coolant, electrical, mechanical mounts, thermal, EMC, software/firmware).
- Form cross‑functional team (design, systems, EE, ME, materials, test, quality, manufacturing rep).
- Plan evidence sources (calculations, FEA/CFD, tolerance stacks, DVP&R, simulations).
Outputs/Artifacts: DFMEA plan page, boundary statement, interface list, timing with APQP gates, role matrix (RACI).
Visuals/Templates: Scope card, boundary box, interface register, kickoff checklist.
Hands‑on task: Fill the DFMEA cover sheet + scope/boundary section for the EWP.
Step 2: Structure Analysis #
Goal: Make the product’s structure explicit to anchor functions & failures.
Activities:
- Create Design Structure Tree (System → Subsystem → Components).
- Draw Functional Block Diagram (FBD) with energy/material/signal flows.
- Map interfaces (coolant in/out, 12 V supply, ground, ECU PWM, mounting).
Outputs/Artifacts: Structure tree, FBD, interface matrix.
EWP Example Tree: EWP → {Housing, Impeller, Shaft, Bearings, Seal, Motor (rotor/stator), PCB, Hall sensor, Connector, O‑rings}.
Hands‑on task: Build the structure tree + simple FBD for the EWP.
Step 3: Function Analysis #
Goal: Translate structure into functions, requirements, and interfaces.
Activities:
- For each element, list Function → Requirement/Target (measurable).
- Include interface functions (seal coolant, mate connector, dissipate heat, meet EMC).
- Mark special characteristics (safety, regulatory, CTQs).
Outputs/Artifacts: Function‑Requirement table, P‑Diagram (inputs, noise factors, control factors, outputs).
EWP Examples: - Impeller: “Deliver flow Q at ΔP ≥ X at RPM Y; cavitation margin ≥ M.”
- Seal: “No visible leakage at P, T, and life Z; chemical compatibility with coolant.”
- PCB: “Drive motor at PWM command; over‑current protection ≤ Amax; meet CISPR‑25 limits.”
Hands‑on task: Draft the P‑Diagram + a function/requirement sheet for 5 key EWP parts.
Step 4: Failure Analysis #
Goal: Derive failures from functions; link effects and causes across levels.
Activities:
- For each function, define Failure of Function (what not happening/over‑happening).
- Capture effects at next‑higher level and vehicle/customer level; assign Severity.
- Trace next‑lower level causes; keep chains tight & specific.
Outputs/Artifacts: Failure chains (Cause → Failure Mode → Effect), initial S ratings.
EWP Sample Chains:
- Failure Mode: “No/low coolant flow” → Vehicle Effect: engine overheat → S=10
Causes: Impeller press‑fit slip; rotor demagnetization; stuck bearings; firmware duty cap. - Failure Mode: “Leak at seal” → Effect: coolant loss/environmental spill → S=8
Causes: Seal wear; material incompatibility; runout; assembly damage. - Failure Mode: “EMC radiated emissions high” → Effect: ECU interference → S=9
Causes: Layout loop area, missing common‑mode choke, poor shielding/grounding.
Hands‑on task: Build three full failure chains for the EWP.
Step 5: Risk Analysis #
Goal: Evaluate risk using S‑O‑D; drive Action Priority (AP) decisions.
Activities:
- List current prevention controls (design margins, DFSS calcs, material specs, FEA/CFD, derating, tolerance stack) that influence O.
- List current detection controls (DVP&R tests: flow/pressure map, leak/burst, endurance, NVH, thermal shock, salt spray, HALT, EMC, software‑in‑loop/HIL; design reviews; simulations) that influence D.
- Assign O and D per AIAG‑VDA criteria; compute AP (H/M/L) to prioritize.
Outputs/Artifacts: Risk‑rated DFMEA rows with S/O/D/AP.
EWP Sample Rows (illustrative): - “No flow at high ambient” — S=10, O=4 (current margin minimal), D=6 (late detect via endurance) → AP: High
- “Seal leak after 500h” — S=8, O=5 (abrasive coolant risk), D=5 (leak test @ DV only) → AP: High
- “EMC radiated > limit” — S=9, O=3 (layout rules applied), D=4 (bench pre‑scan) → AP: Medium
Hands‑on task: Rate three prioritized rows and justify each rating from controls.
Step 6: Optimization #
Goal: Define actions that reduce risk (prefer O and D improvements), then re‑evaluate.
Activities:
- Propose Recommended Actions (owner, due date, expected effect on O/D).
- Examples for EWP:
- Increase impeller‑shaft interference & add spline (reduce O).
- Upgrade seal to FKM + finish control on shaft (reduce O).
- Add current‑limit + soft‑start, ferrite beads, CM choke, ground stitch vias (reduce O/D for EMC).
- Conformal coat PCB + conformal keep‑outs (reduce O for corrosion shorts).
- Add in‑line leak test @ end‑of‑line fixture (reduce D).
- After completion, Re‑evaluate O/D, update AP, and close items with objective evidence (test reports, updated calcs, PPAP records).
Outputs/Artifacts: Action tracker, revised DFMEA rows, before/after AP chart.
Hands‑on task: Convert one High‑AP row to Medium/Low with concrete actions and re‑ratings.
Step 7: Results Documentation #
Goal: Package results for decisions, audits, and feedback to future programs.
Activities:
- Compile DFMEA Summary Table (open H‑APs, residual risks, special characteristics).
- Cross‑link to DVP&R (which risks are verified/validated where).
- Record risk acceptance rationale (management/customer sign‑off).
- Capture Lessons Learned and publish to knowledge base for reuse.
- Ensure change management linkage (ECN/PLM references).
Outputs/Artifacts: DFMEA Report PDF, Summary Table, LL entry, sign‑off record.
Hands‑on task: Draft a one‑page summary for the EWP DFMEA with three key insights.
