PFMEA Structure Analysis

Updated on September 6, 2025

5 min read

🧭 Why Structure Analysis? #

Before rating risks, you need a complete, visual map of how the process works: the sequence of operations, where/what is measured, and the interfaces (Man, Machine, Method, Material, Measurement, Environment) that can create variation. This becomes the backbone for Function → Failure → Risk in later steps.

🎯 Objectives of Step 2 #

Create a rev-controlled PFD covering all operations, inspections, transports, and storages.
Build a Process Structure Tree from line → stations → tools/fixtures/gages/parameters.
Prepare a 6M Interface Register that will seed failure causes in Step 4.
Define data & traceability points that support detection controls and reaction plans.

📦 Deliverables (what “done” looks like) #

PFD Rev-A (with symbols legend, rework/quarantine loops, inspection/test points)
Process Structure Tree (hierarchical view with tools/gages/critical parameters)
6M Interface Register (station-wise 6M factors to watch)
Data/Traceability Map (what gets stored where in MES/PLM)

1) Process Flow Diagram (PFD) #

🔖 Symbols Legend

▣ Operation (assembly/processing)
◯ Inspection/Test (in-process or EoL)
➝ Transport (manual or conveyor)
▤ Storage/Buffer (WIP)
⟲ Rework Loop / ⛔ Quarantine (nonconforming flow)

🗺️ Line Flow (Rev-A)

▣ OP01 Incoming & Kitting
   ➝ Serial assignment, kit verify (scanner)
▣ OP02 Bearing Press (housing/shaft)
   ◯ In-station depth/force check
   ➝
▣ OP03 Shaft Sub-Assembly (prep/lube/clean)
   ➝
▣ OP04 Stator Into Housing (orientation/seating)
   ◯ Vision orientation check
   ➝
▣ OP05 Rotor/Impeller Press-Fit
   ◯ LVDT depth + force signature (100%)  → Data to MES
   ➝
▣ OP06 Mechanical Seal Installation
   ◯ Vision orientation + cleanliness gate
   ➝
▣ OP07 PCB Handling & Potting (ESD controlled)
   ◯ Potting mass/time & cure log; ESD verification
   ➝
▣ OP08 Connector Fit / Electrical Join (if applicable)
   ◯ Pull/vision check (sampled or 100% per CTQ)
   ➝
▣ OP09 Housing Closure & Screw Torque
   ◯ DC tool trace (torque/angle 100%)  → Data to MES
   ➝
◯ OP10 Pre-Leak Screening (air decay/pressure hold)
   ↳ If FAIL → ⟲ Rework/Repair Cell → Retest
   ➝
◯ OP11 Electrical Spin Test (current draw/run-up)
   ↳ If FAIL → ⟲ Repair Cell → Retest
   ➝
◯ OP12 Final Leak & Flow/RPM Test (EoL)
   ↳ If FAIL → ⛔ Quarantine → MRB/8D
   ➝
◯ OP13 Final Inspection (label/visual/pack audit)
   ➝
▣ OP14 Pack & Ship  → ▤ FG Storage/Dispatch

Notes

SC checkpoints: OP05 depth/force (🎯), OP06 orientation/cleanliness (🔧), OP09 torque (🎯), OP12 leak (🔧) & flow (🔺).
Recipe-locked tests: OP10 & OP12 (limits controlled; daily master part).
No scan → no progress enforced at OP05, OP09, OP12.

2) Process Structure Tree (Line → Stations → Tools/Gages → Parameters) #

EWP Final Assembly & EoL Line (Line-EWP-01)
│
├── Cell A: Sub-Assemblies
│   ├── OP02 Bearing Press
│   │     ├─ Fixture: BP-01 (hard-stop, guided)
│   │     ├─ Press: Servo PRS-20
│   │     └─ Gages: Depth LVDT; Force sensor
│   ├── OP03 Shaft Sub-Assembly
│   │     └─ Tools: Clean bench; Lint-free kits; Lube dispenser
│   └── OP04 Stator Into Housing
│         ├─ Fixture: ST-Align-03
│         └─ Vision: ORI-Cam-V2 (orientation)
│
├── Cell B: Critical Fits & Sealing
│   ├── OP05 Rotor/Impeller Press-Fit
│   │     ├─ Press: Servo PRS-30 (force vs. distance)
│   │     ├─ Fixture: PF-Guided-02 (hard-stop)
│   │     └─ Gages: LVDT depth; Force signature
│   └── OP06 Mechanical Seal Installation
│         ├─ Fixture: SealGuide-01 (chamfers/pilot)
│         └─ Vision: ORI-Cam-V1; Cleanliness gate (particle counter)
│
├── Cell C: Electronics & Closure
│   ├── OP07 PCB Handling & Potting
│   │     ├─ ESD: Mats/straps/monitor
│   │     ├─ Dispenser: Pot-Disp-05 (mass/time)
│   │     └─ Cure: Oven CUR-01 (profile logged)
│   ├── OP08 Connector Fit/Join
│   │     └─ Tools: Crimp/solder station; Pull tester; Vision
│   └── OP09 Housing Closure & Screw Torque
│         ├─ DC Tool: Atlas-QS (torque/angle trace)
│         └─ Socket ID sensor; Thread start guidance
│
└── Cell D: Test & Release
    ├── OP10 Pre-Leak Screening (Air)
    │     └─ Bench: Leak-AIR-100 (air decay; daily master part)
    ├── OP11 Electrical Spin Test
    │     └─ Stand: Spin-ELEC-20 (current draw/run-up)
    ├── OP12 Final Leak & Flow/RPM Test
    │     └─ Bench: LeakFlow-WET-300 (ΔP & duty; curve storage)
    ├── OP13 Final Inspection
    │     └─ Station: VIS-FINAL (labels/visual/pack audit)
    └── OP14 Pack & Ship
          └─ Pack line; Label printer; Verification scanner

Key Parameters (examples):

OP05: Depth 12.00±0.05 mm, peak force window X–Y kN, signature match (corr ≥ Z).
OP06: Seal orientation OK, shaft Ra ≤0.30 µm, cleanliness pass.
OP09: 4.0±0.3 N·m (angle monitored), tool batch/ID captured.
OP12: Leak ≤0.5 ml/min @1.5 bar; Flow ≥35 L/min @ ΔP 20 kPa @ 80% duty; temperature compensation logged.

3) 6M Interface Register (seed for causes in Step 4) #

Station	Man	Machine	Method	Material	Measurement	Environment
OP05 Press-Fit	Operator certification; fatigue	Servo press drift; fixture wear	Press profile & hard-stop; lube method	Impeller ID spread; shaft OD	LVDT stability; force sensor cal	Temp affects dimensions
OP06 Seal Install	Handling technique	Nest alignment; vision lighting	Chamfer/lube procedure	Seal hardness lot; contaminants	Vision false accept; particle counter	Humidity/cleanliness class
OP07 Potting	ESD discipline	Dispenser repeatability; oven	Mass/time recipe; cure profile	Potting resin lot age	Scale GR&R; oven probe cal	Temp/humidity shifts
OP09 Torque	Tool usage consistency	DC tool accuracy; socket ID	Strategy (torque/angle), thread start	Screw length/finish	Tool audit; GR&R	Oil mist influencing torque
OP10 Pre-Leak	Setup steps	Bench valves/seals	Test cycle (stabilize/measure)	Air dryness; O-rings	Master leak stability	Ambient temp/pressure
OP12 Final Leak/Flow	Fixturing care	Pump stand leaks	Recipe lock; curve rules	Test media quality	Flow meter GR&R; temp comp	Media temp; supply pressure

Keep this register tab next to the PFD; you’ll reference it directly when writing causes in Step 4.

4) Station Specs (excerpt pages you can drop into your workbook) #

📄 OP05 — Rotor/Impeller Press-Fit (Critical)

Inputs: Shaft, impeller, lube (spec), clean housing.
Tools/Fixtures: Servo PRS-30, PF-Guided-02, LVDT, force sensor.
Characteristics: Depth 12.00±0.05 mm (🎯); Peak force X–Y kN; Signature match ≥Z.
Verification: 100% LVDT + force signature; SPC X̄-R every 30 pcs.
Traceability: Serial, depth, peak force, curve, OK/NOK to MES.
Reaction (pointer): Out of spec → stop cell; quarantine last good lot; verify gage; check fixture; 8D if trend.

📄 OP06 — Mechanical Seal Install (Regulatory)

Inputs: Seal (lot-controlled), shaft finish Ra ≤0.30 µm, lubricant.
Tools: SealGuide-01, ORI-Cam-V1, particle counter.
Checks: 100% vision orientation; cleanliness gate; random Ra audit.
Traceability: Orientation result, lot IDs.
Reaction: Fail → rework/replace; clean cell audit; lot containment if repeated.

📄 OP09 — Housing Closure & Torque (CTQ)

Tools: DC tool Atlas-QS with socket ID; thread start aid.
Spec: 4.0±0.3 N·m + angle window; 100% trace.
Data: Curve + OK/NOK tied to serial; daily tool audit.
Reaction: Under/over-torque → rework + visual thread check; pattern check; tool calibration review.

📄 OP12 — Final Leak & Flow (Safety/Release)

Bench: LeakFlow-WET-300; recipe lock; daily master part.
Specs: Leak ≤0.5 ml/min @1.5 bar (🔧); Flow ≥35 L/min @ ΔP 20 kPa @ 80% duty (🔺); temp comp.
Data: Full curve & limits to MES; station status heartbeat.
Reaction: Fail → Quarantine; MRB; parameter audit; fixture leak check; 8D.

5) Data & Traceability Map (what to store, per station) #

Station	Data to Store	Frequency	Ties To
OP01	Kit BOM scan, serial seed	100%	MES unit record
OP05	Depth, force, curve ID, OK/NOK	100%	MES + SPC DB
OP06	Vision result, lot IDs	100%	MES
OP07	Potting mass/time, cure profile, ESD log	100%/shift	MES/ESD log
OP09	Torque/angle curve, tool ID, socket ID	100%	MES
OP10	Leak value, recipe rev, master check	100%	MES
OP12	Leak/flow curves, duty, ΔP, temp	100%	MES
OP13	Label verification, visual checklist	100%	MES
OP14	Pack audit result, pallet ID	100%	MES

Rules:

No scan → no progress on OP05, OP09, OP12.
Recipe-lock prevents unauthorized parameter changes (role-based).
Daily master checks on leak/flow benches with auto-block on failure.

6) Hand-off to Step 3 (Function Analysis) #

From this lesson you now have:

The PFD (sequence & where quality happens)
The structure tree (who/what/with-which tool)
The 6M register (interfaces that breed causes)

👉 In Step 3, convert each operation into a clear process function + measurable requirement (e.g., “Press impeller to 12.00±0.05 mm with signature within window”). These will become the anchors for failure modes in Step 4.

⚠️ Common Pitfalls (and fixes) #

Pitfall	Fix
PFD missing inspections/tests	Mark every check with ◯; add rework/quarantine flows
Tools without parameters	List measurable parameters for each tool (depth, force, torque, time, temp)
No environment factors	Add humidity/temp/cleanliness/ESD where relevant
Data not tied to serial	Enforce serialization + curve storage at OP05/09/12
Rework path unclear	Draw ⟲ loops and define who/where/how for retest

🔗 Internal Linking Suggestions #

Next: Lesson 5.3 — Step 3: Function Analysis (Process Functions, Requirements & SCs)
Templates Hub: PFD (Visio/PPT), Process Structure Tree (Excel), 6M Interface Register (Excel), Data & Traceability Map (Excel)

🧠 Pro Tip #

Treat the PFD as your risk radar. If a defect can occur and there’s no prevention or detection node shown, it won’t be controlled. Draw it now—save pain later.

Updated on September 6, 2025

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Introduction to FMEA

Foundations of FMEA

Step-1: Planning & Preparation in FMEA

Step 2: Structure Analysis in FMEA

Step 3: Function Analysis in FMEA

Step 4: Failure Analysis in FMEA

Step 5: Risk Analysis in FMEA

Step 6: Optimization in FMEA

Step 7: Results Documentation in FMEA

DFMEA in Practice

PFMEA in Practice

FMEA Linkages

FMEA Tools & Templates

FMEA Best Practices

FMEA Advanced Applications

PFMEA Structure Analysis

🧭 Why Structure Analysis? #

🎯 Objectives of Step 2 #

📦 Deliverables (what “done” looks like) #

1) Process Flow Diagram (PFD) #

🔖 Symbols Legend

🗺️ Line Flow (Rev-A)

2) Process Structure Tree (Line → Stations → Tools/Gages → Parameters) #

3) 6M Interface Register (seed for causes in Step 4) #

4) Station Specs (excerpt pages you can drop into your workbook) #

📄 OP05 — Rotor/Impeller Press-Fit (Critical)

📄 OP06 — Mechanical Seal Install (Regulatory)

📄 OP09 — Housing Closure & Torque (CTQ)

📄 OP12 — Final Leak & Flow (Safety/Release)

5) Data & Traceability Map (what to store, per station) #

6) Hand-off to Step 3 (Function Analysis) #

⚠️ Common Pitfalls (and fixes) #

🔗 Internal Linking Suggestions #

🧠 Pro Tip #

🧭 Why Structure Analysis? #

🎯 Objectives of Step 2 #

📦 Deliverables (what “done” looks like) #

1) Process Flow Diagram (PFD) #

🔖 Symbols Legend

🗺️ Line Flow (Rev-A)

2) Process Structure Tree (Line → Stations → Tools/Gages → Parameters) #

3) 6M Interface Register (seed for causes in Step 4) #

4) Station Specs (excerpt pages you can drop into your workbook) #

📄 OP05 — Rotor/Impeller Press-Fit (Critical)

📄 OP06 — Mechanical Seal Install (Regulatory)

📄 OP09 — Housing Closure & Torque (CTQ)

📄 OP12 — Final Leak & Flow (Safety/Release)

5) Data & Traceability Map (what to store, per station) #

6) Hand-off to Step 3 (Function Analysis) #

⚠️ Common Pitfalls (and fixes) #

🔗 Internal Linking Suggestions #

🧠 Pro Tip #

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