Example Line: 12V Electric Water Pump (EWP) Final Assembly & End‑of‑Line (EoL) Testing
Why this line? It covers press‑fits, seal installation, electronics handling, torqueing, leak & flow tests, poka‑yokes, and data collection—perfect to teach prevention/detection controls, AP, and Control Plan linkage.
Process Snapshot (handoff from DFMEA) #
- From DFMEA to PFMEA: critical characteristics handover (🔺Safety, 🔧Regulatory, 🎯CTQ)
- High‑level line map (typical 12–18 steps):
Incoming inspection → Bearing press → Shaft sub‑assembly → Mechanical seal install → Stator into housing → Rotor/impeller press‑fit → PCB assembly & potting → Connector fit → Housing closure & torque → Leak test → Electrical test → Flow/RPM test → Final inspection → Pack & ship - Key process constraints: takt time, station cycle times, CTFs (critical‑to‑function), ESD/cleanliness, traceability needs
Step 1: Planning & Preparation (incl. 5T) #
- InTent: Reduce process‑induced risk for EWP to meet CTQ, safety, regulatory
- Timing: APQP gates; PFMEA start with draft PFD ready; iterate through Run@Rate
- Team: Mfg/Process Eng, QE (moderator), Maintenance, Operator, IE, SQE, Test Eng, EHS
- Task: Analyze EWP final assembly & EoL test (out of scope: upstream supplier processes unless critical)
- Tool: PFMEA sheet (AIAG‑VDA), PFD, characteristics matrix, Control Plan template, MSA/SPC plan
- Inputs: DFMEA summary, special characteristics list, drawings/specs, work instructions, past lessons learned, line layout, CP/CTQs, gage list, MSA status, capability baselines
Deliverables: 5T worksheet, PFMEA plan page, RACI, document list.
Step 2: Structure Analysis #
- Build the Process Flow Diagram (PFD) with part/operation/inspection/transport/storage.
- Create Process Structure Tree: Line → Stations → Tools/Fixtures/Gages.
- Map interfaces: Man–Machine–Method–Material–Measurement–Environment (5M/6M).
- Identify special processes (press‑fit, sealing, potting, torque).
Deliverables: PFD (rev‑controlled), process structure tree, interface register.
Step 3: Function Analysis #
- For each operation: define process step function + requirement/target
(e.g., Torque fasteners to 4.0±0.3 N·m; press‑fit depth 12.00±0.05 mm; leak ≤ 0.5 ml/min @ 1.5 bar; ESD < 100 V; cleanliness ISO 16232 class X). - Assign process characteristics (PCs) & link product characteristics (from DFMEA).
- Flag special characteristics (🔺, 🔧, 🎯) and measuring methods (GR&R status).
- Draft reaction plans placeholders for later Control Plan.
Deliverables: Process Characteristics Matrix (op‑by‑op function/req/SC/measurement), initial gage list + MSA plan.
Step 4: Failure Analysis #
- For each operation, write failure mode as a deviation of the step function
(e.g., “press‑depth undersize,” “seal lip damaged,” “torque low,” “potting voids,” “connector mis‑seat,” “ESD event not controlled,” “leak test skipped,” “flow below spec”). - Effects: on next operation, line scrap/rework, and end‑user (vehicle/customer). Assign Severity (S) anchored to customer impact.
- Causes: 5M/6M based, specific & verifiable (worn punch, wrong fixture, batch mix‑up, uncalibrated gage, operator method variation, ESD mat resistance high, humidity out of range).
- List current prevention controls (PFMEA) and current detection controls (checks/tests/poka‑yokes).
Deliverables: Complete cause–mode–effect chains per op.
Step 5: Risk Analysis (S‑O‑D & AP) #
- Rate Severity (S) from effects; Occurrence (O) from cause frequency & prevention; Detection (D) from detection method capability & timing.
- Use Action Priority (AP) tables (H/M/L) to decide where action is needed.
- Typical examples:
- Mechanical seal damage → Coolant leak → S=8; O=5 (manual install, sharp edge risk); D=6 (late leak test) → AP=H
- Under‑torque screws → Loosened joint → S=9; O=3 (DC tool with strategy); D=3 (OK/NOK trace) → AP=M
Deliverables: Rated PFMEA rows with justifications.
Step 6: Optimization (Actions & Re‑evaluation) #
- Define recommended actions (owner/date/expected O or D impact). Prioritize AP=H, then M.
Examples:- Add hard‑stop & depth sensor to press‑fit; SPC on depth; golden sample verification.
- Introduce ESD monitoring with interlocks; weekly audits; wrist‑strap testers.
- Convert manual seal install to guided fixture + chamfer + vision pre‑check.
- Upgrade leak test to earlier station + final audit; add auto‑result lockout to MES.
- Tooling PM: MTBF tracking; error‑proofed bit selection (RFID sockets).
- Implement, collect evidence (capability, MSA, test reports), then re‑rate O/D and update AP; document residual risk acceptance if needed.
Deliverables: Action tracker; before/after S‑O‑D/AP snapshot; evidence pack.
Step 7: Results Documentation #
- Compile PFMEA Summary Table (open AP H/M, residual risks, special characteristics, top actions closed).
- Publish/update the Process Control Plan (link every significant risk to a control, method, frequency, reaction plan, records, responsibility).
- Ensure traceability: PFMEA ↔ PFD ↔ Control Plan ↔ Work Instructions ↔ Check sheets ↔ MSA/SPC studies ↔ Calibration records ↔ Maintenance plans.
- Prepare PPAP artifacts: PFMEA, Control Plan, MSA, Capability (Cp/Cpk), Gage list, Layout inspection, Initial Process Studies, PSW.
- Capture Lessons Learned for future lines and suppliers.
Deliverables: PFMEA report set (PFMEA, PFD, Control Plan, LL, sign‑offs).
Wrap‑Up: Checklists, Metrics & Audit Readiness (optional but recommended) #
- Completeness checklist across 7 steps (scope, PFD, PCs/SCs, S‑O‑D/AP, actions, CP linkage, evidence).
- Process health metrics: %AP‑H closed, ndc≥10 on critical gages, Cpk≥1.67 for safety/CTQ, FPY, DPMO, audit scores.
- Audit pack index: doc codes, revisions, storage location (PLM/SharePoint/MES).
