Step 2 – Structure Analysis in FMEA

Once Step 1: Planning & Preparation is complete, the next step in the AIAG-VDA 7-Step FMEA approach is Structure Analysis.

Structure Analysis provides a visual map of the system, subsystem, components, or process steps being analyzed.

👉 It answers the question:
“How is the product or process built, and how do its elements interact?”

Without a clear structure analysis, teams often miss critical functions, requirements, and risks.

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Objectives of Structure Analysis #

1. Identify system, subsystem, and component relationships (for DFMEA).
2. Map process steps and flows (for PFMEA).
3. Define interfaces between elements.
4. Provide the foundation for Function Analysis in Step 3.

📌 Think of Structure Analysis as the blueprint of the FMEA.

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Tools for Structure Analysis #

The AIAG-VDA Handbook recommends three main visualization methods:

1. Structure Tree

• Shows hierarchical relationships → System → Subsystem → Component.
• Example (DFMEA):
  • Vehicle
    • Electric Motor
      • Stator
      • Rotor
      • Bearings

2. Block Diagram

• Shows functional interactions between elements.
• Example (DFMEA – Electric Motor):
  • Battery → Inverter → Motor → Transmission → Wheels

3. Process Flow Diagram (PFD)

• Maps steps in a process for PFMEA.
• Example (PFMEA – Welding Process):
  1. Load parts in fixture
  2. Align position
  3. Apply electrode pressure
  4. Apply current
  5. Release & unload

📌 Choice of method depends on FMEA type:

• DFMEA → Structure Tree + Block Diagram.
• PFMEA → Process Flow Diagram.

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Example – DFMEA Structure Analysis (Electric Motor) #

• System: Electric Motor Assembly
• Subsystems: Rotor, Stator, Housing, Bearings
• Components: Windings, Laminations, Seals, Fasteners

👉 A Structure Tree helps the team see where risks could originate (e.g., winding failure inside stator).

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Example – PFMEA Structure Analysis (Welding Process) #

• Process: Spot Welding Operation
• Steps: Load → Position → Clamp → Weld → Release → Inspect
• Interfaces: Material from stamping → Assembly line transfer → Welding machine → Inspection station

👉 A Process Flow Diagram ensures the team captures risks at each step.

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Benefits of Structure Analysis #

1. Provides clarity on what is being analyzed.
2. Helps identify interfaces (where many failures occur).
3. Ensures no elements are overlooked.
4. Builds the base for Function and Failure Analysis (Steps 3 & 4).

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Common Mistakes in Structure Analysis #

• Overcomplicating diagrams → Too much detail slows progress.
• Ignoring interfaces (system-to-system or step-to-step).
• Skipping the diagram entirely → Team jumps directly to failures, causing gaps.
• Not aligning with the FMEA scope and boundaries defined in Step 1.

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Case Study – Assembly Line Bolting PFMEA #

• Scope: Bolting suspension arm to chassis.
• Structure Analysis Tool: Process Flow Diagram.
• Steps:
  1. Operator picks bolt
  2. Positions bolt in hole
  3. Applies torque with tool
  4. System checks torque value
  5. Assembly moves to next station

👉 With this structure, the team later identifies risks like bolt missing, under-torque, over-torque.

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Key Takeaways #

• Structure Analysis = visual mapping of system, components, or process steps.
• Tools: Structure Tree, Block Diagram, Process Flow Diagram.
• Essential for both DFMEA and PFMEA as the foundation for next steps.
• Clear structure = fewer gaps, better risk prevention.

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Next Lesson #

👉 Continue with Lesson 3.3.1: System, Subsystem, and Component Breakdown