DFMEA Structure Analysis

In DFMEA, Structure Analysis is Step 2 of the AIAG-VDA 7-Step Approach and acts as the blueprint for the entire analysis.

After defining the scope and boundaries in Step 1, the next move is to visualize and break down the product into its:

• Systems → Subsystems → Components
• Internal & external interfaces
• Flow of energy, materials, and signals

This step is crucial because you cannot analyze risk without clearly understanding the structure.

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🎯 Objective of Step 2 #

“Define and visualize the product architecture using a structure tree and function block diagram to support downstream failure and risk analysis.”

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🚗 DFMEA Structure Analysis – Case: 12V Electric Water Pump (EWP) #

We will now perform structure analysis for our case study product — a 12V Electric Water Pump, used in ICE and hybrid vehicles for coolant flow regulation.

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📊 1. Design Structure Tree (System → Subsystem → Component) #

The structure tree organizes the system hierarchy from top-level system down to its parts. It helps link functions, failures, and causes at each level.

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🔧 Structure Tree for EWP

Electric Water Pump (System)
│
├── Mechanical Assembly (Subsystem)
│   ├── Pump Housing
│   ├── Impeller
│   ├── Shaft
│   ├── Bearings
│   └── Mechanical Seal
│
├── Electrical Drive (Subsystem)
│   ├── Rotor
│   ├── Stator
│   ├── PCB (Controller Board)
│   ├── Hall Sensor
│   └── Power MOSFETs
│
├── Interfaces (External)
│   ├── Electrical Connector (PWM, 12V, GND)
│   └── Coolant Inlet & Outlet
│
└── Mounting System
    ├── Bracket
    └── Rubber Isolators

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🎯 Why This Matters?

Each element in the structure:

• Will have its own function (Step 3),
• Can potentially fail (Step 4),
• Will be analyzed for risk (Steps 5–7).

This tree allows mapping of effects and causes in a top-down and bottom-up way.

✅ TIP: This structure tree will be mirrored in the DFMEA form’s column “Next Higher Level” and “Next Lower Level.”

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🔄 2. Functional Block Diagram (FBD) #

The Functional Block Diagram (FBD) shows how different parts of the EWP interact and how signals, energy, and materials flow.

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🧩 FBD for Electric Water Pump

           +----------------------+
           |   ECU (Vehicle)      |
           |  [PWM Signal]        |
           +----------+-----------+
                      |
                      v
             +--------+--------+                 +----------------+
             |  Electrical PCB  |    Signal      |  Ground Return |
             |  (Controller)    +---------------->     Path       |
             +--------+--------+                 +----------------+
                      |
               Motor Control (3-Phase Signal)
                      |
                      v
             +--------+--------+
             |   BLDC Motor     |       Energy Transfer
             | (Rotor & Stator) +-----------------------------+
             +--------+--------+                             |
                      |                                     v
              Mechanical Rotation                    +------|-------+
                      |                               |   Impeller   |
                      v                               |(Coolant Flow)|
             +--------+--------+                      +--------------+
             |     Shaft        |
             +--------+--------+
                      |
                      v
             +--------+--------+
             |  Mechanical Seal | ← Coolant sealing
             +--------+--------+
                      |
                      v
             +------------------+
             | Pump Housing     | ← Coolant Interface to System
             +------------------+

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🔌 Interfaces Identified in FBD

Interface Type	Element	Description
Electrical	Connector ↔ ECU	Power, Ground, PWM
Signal	ECU ↔ PCB ↔ Motor	Signal processing
Mechanical	Shaft ↔ Impeller	Torque transfer
Sealing	Shaft ↔ Seal ↔ Housing	Prevent leakage
Thermal	PCB ↔ Housing	Heat dissipation
Material	Coolant ↔ Impeller/Housing	Chemical compatibility

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🧠 Additional Visual: Interface Matrix (for Later Reuse) #

To support failure analysis, we’ll also prepare an Interface Matrix in the next steps (used in Step 4 and 5). But here’s a preview:

From	To	Interface Type	Critical?
ECU	EWP PCB	PWM Signal	Yes
PCB	Motor	Electrical (3-Phase)	Yes
Rotor	Shaft	Mechanical	Yes
Shaft	Impeller	Mechanical	Yes
Coolant	Seal	Environmental	Yes
PCB	Housing	Thermal	Medium
Housing	Bracket	Mounting	Low

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📑 Template: Structure Analysis Worksheet (Excerpt) #

Level	Element	Next Higher	Next Lower	Function
System	EWP	Vehicle Thermal System	Subsystems	Regulate coolant flow
Subsystem	PCB	EWP	MOSFETs, Controller	Control motor signal
Component	Impeller	Mechanical Assy	None	Move coolant
Component	Seal	Mechanical Assy	Shaft	Prevent leakage
Interface	Connector	EWP	ECU, GND	Electrical input

📥 Download full editable Structure Tree & FBD template (Excel + PPT)

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✅ Outputs of Step 2 #

By completing this step, you will have:

• ✅ A clear Structure Tree (system → component breakdown)
• ✅ A Functional Block Diagram (FBD) that traces all flows
• ✅ Identified key interfaces (internal & external)
• ✅ Built the base for Steps 3–7 (function → failure → risk analysis)

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🔗 Internal Linking Suggestions #

• Step 3: Function Analysis – Defining Functions and Requirements
• Download: DFMEA Structure Tree Template (Excel)
• Download: FBD Template (PPT/Visio)

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🧠 Pro Tip #

“If your structure isn’t clear, your DFMEA will be messy. A strong Structure Tree ensures you identify every element that might fail — and nothing gets missed.”

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🏁 Conclusion #

Structure Analysis is like drawing the map before starting the journey. It aligns your entire DFMEA team on what you’re analyzing, how it’s built, and what connects to what.

With this foundation, you’re now ready for Step 3: Function Analysis, where we define the intended performance of each element and how it interacts.