The AIAG-VDA 7-Step FMEA approach recommends starting with a structure analysis that breaks down a system into system → subsystem → component levels.
To make this concept practical, let’s consider an electric motor and analyze its breakdown into stator and winding, which are critical for motor function and reliability.
👉 This example shows how Structure Analysis forms the foundation for later steps like Function Analysis (Step 3) and Failure Analysis (Step 4).
Step 1: Define the System #
- System: Electric Motor Assembly
- Purpose: Convert electrical energy into mechanical rotation to power applications (e.g., vehicle propulsion, industrial equipment).
Step 2: Identify Subsystems #
Within the electric motor, major subsystems include:
- Rotor (rotating part)
- Stator (stationary part with windings)
- Housing (protective casing)
- Bearings (support rotation)
For this example, we focus on the Stator Subsystem.
Step 3: Break Down the Subsystem (Stator) #
The stator is the heart of the motor. It includes:
- Core (Laminations): Provides magnetic path.
- Windings (Coils): Carry current to generate magnetic field.
- Insulation: Prevents short-circuits.
- Slots & End Turns: Define winding placement and strength.
Step 4: Component Level – Winding #
The winding is a critical component because it directly enables electromagnetic conversion.
- Function: Carry current and generate rotating magnetic field.
- Requirements:
- Resistivity within design limits.
- Thermal endurance (e.g., withstand 150°C).
- Insulation strength to prevent shorting.
- Potential Failures:
- Short circuit due to insulation breakdown.
- Open circuit due to wire breakage.
- Overheating due to excess current or poor cooling.
👉 By analyzing down to the winding level, the team ensures critical risks are captured early.
Example Structure Tree – Motor → Stator → Winding #
Electric Motor (System)
│
├── Rotor (Subsystem)
│ ├── Shaft
│ ├── Magnets
│ └── Laminations
│
├── Stator (Subsystem)
│ ├── Core (Laminations)
│ ├── Windings (Component)
│ ├── Insulation
│ └── Slots
│
├── Housing (Subsystem)
│ ├── Covers
│ └── Seals
│
└── Bearings (Subsystem)
├── Inner Ring
├── Outer Ring
└── Lubrication
📌 The breakdown helps identify interfaces (e.g., winding ↔ insulation, stator ↔ rotor) where many failures occur.
Why This Example is Important in FMEA #
- Provides clarity on what is being analyzed (avoids confusion).
- Ensures critical components like winding are not overlooked.
- Builds traceability from system to component level.
- Creates a logical flow for moving into Function Analysis.
Case Study – DFMEA for Electric Motor Winding #
- Function: Generate electromagnetic field.
- Requirement: Current capacity up to 20A, insulation withstand 150°C.
- Failure Mode: Short circuit in winding.
- Failure Effect: Motor fails, vehicle will not start.
- Severity: 9 (High).
👉 This shows how starting from structure analysis leads directly into function, failure, and risk analysis.
Common Mistakes to Avoid #
- Stopping at the system level → missing critical component risks.
- Over-detailing → listing every screw or washer unnecessarily.
- Ignoring interfaces (e.g., rotor ↔ stator gap).
- Treating structure analysis as paperwork instead of a thinking process.
Key Takeaways #
- Structure Analysis requires breaking down system → subsystem → component.
- In this example: Motor → Stator → Winding forms a clear traceable structure.
- Detailed breakdown helps ensure critical risks (like winding failure) are captured.
- This analysis feeds directly into Function Analysis (Step 3).
Next Lesson #
👉 Continue with Lesson 3.4: Step 3 – Function Analysis
