Defining Scope, Boundaries & Assumptions in FMEA

Before jumping into failure modes, effects, and action priorities, there’s one crucial step you cannot skip in FMEA:
Defining the Scope, Boundaries, and Assumptions.

This step is important for:

• Accurate and focused risk analysis
• Better team alignment
• Avoiding duplication or gaps
• Better traceability and audit readiness

Without a well-defined scope and clear assumptions, your FMEA can be:

• Too broad or too narrow for use and action point of view
• Misalignment with other engineering documents (DVP&R, Control Plan, etc.)

In the AIAG-VDA 7-Step FMEA approach, this activity to be done in Step 1: Planning and Preparation.

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Concept Explained – What Are Scope, Boundaries & Assumptions? #

Scope – What is included in this FMEA?

Scope defines the focus and purpose of the FMEA. 

It clarify that:

• Which system, subsystem, or process is being analyzed
• The objectives of the FMEA (e.g., safety, compliance, quality)
• Which customer requirements or functions are considered

DFMEA (Design FMEA): The scope is usually a product, subsystem, or component.

PFMEA (Process FMEA): The scope is a process, line, or operation step.

FMEA-MSR: The scope is a system that must monitor itself during customer use.

Example – Defining Scope

• DFMEA: Electric motor [scope = stator design.]
• PFMEA: Welding process [scope = spot-weld operation in chassis assembly.]
• FMEA-MSR: ABS braking system [scope = sensor monitoring & response system.]

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Boundaries – What’s in, and what’s out?

Boundaries define what is included and excluded in FMEA analysis. They also describe the interfaces with other systems or processes.

Therefore, the based document you should refer here is boundary diagram. This clearly mention what we should include in our study for technical risk analysis (FMEA).

Why Boundary definition important?

• It prevents the team from going into unnecessary detail.
• Helps focus only on responsibility areas.
• Avoids duplication when multiple FMEAs exist for the same product.

Example – Defining Boundaries

PFMEA (Welding Process):

• Included: Welding electrode wear, welding current, weld time.
• Excluded: Raw material steel sheet quality (covered by supplier FMEA).
• Interfaces: Fixture alignment with stamping process.

DFMEA (Electric Motor):

• Included: Stator winding design, insulation.
• Excluded: Vehicle wiring harness (covered in system-level FMEA).
• Interfaces: ECU and power supply.

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Assumptions – What do we assume to be true?

Assumptions are conditions or inputs the team agrees and accept that it is correct, even if not verified in this FMEA.

Why Assumptions Are Important

• FMEAs cannot analyze every possible condition therefore assumptions helps to narrow focus.
• It make sure all team members have a common understanding.
• Helps auditors and customers understand the limits of analysis.

Example of FMEA Assumptions

• Operating temperature range = -20°C to +50°C.
• Nominal torque requirement = 200 Nm.
• Operator is trained to perform this step..
• Preventive maintenance of equipment will be performed as per plan.

Note: Assumptions must be reviewed and documented. If they change, the FMEA must be updated, so that future teams or auditors know what conditions were considered.

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Where This Fits in the 7-Step FMEA Process #

Now defining scope, boundaries, and assumptions is a core part of Step 1: Planning & Preparation in the AIAG-VDA 7-Step Method.

Step 1 also use for:

• Clarification of customer and legal requirements
• Defining 5Ts: InTent, Timing, Team, Task, Tools
• Understanding lessons learned and special characteristics

So, a clear scope make sure that all subsequent steps, like structure analysis, function analysis, failure modes are well aligned and your FMEA is effective.

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Real-World Examples (DFMEA + PFMEA) #

DFMEA – Electric Drive Unit (EDU)

Element	Description
Scope	Analyze the EDU mechanical subassembly for failure risks related to torque transmission and noise
Boundaries	Exclude inverter and battery interface (analyzed in HV system FMEA)
Assumptions	Shaft hardness is validated; system operates between -40°C to +125°C

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PFMEA – Robotic Spot Welding Process

Element	Description
Scope	Analyze robot-assisted spot welding of side-body panel
Boundaries	Exclude body-in-white framing and handling robots
Assumptions	Weld tip alignment is calibrated daily; input panels meet GD&T specs

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Common Mistakes & How to Avoid Them #

Mistake	How to Fix It
No formal scope statement	Use a standard format to define what’s in/out
Team unclear on assumptions	Document them in the header or a separate FMEA planning sheet
Overlapping boundaries with other FMEAs	Use a boundary diagram or system breakdown for understanding
Updating structure without updating scope	Always revise the scope when new subsystems or steps are added

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Best Practices & Expert Tips #

• Link the scope to customer-specific requirements and interface matrices
• Document boundaries in the FMEA header or planning sheet
• Update scope whenever design/process changes affect the analysis range
• Use a boundary diagram for complex systems (e.g., ECU, hybrid system, ADAS)
• Review assumptions during cross-functional reviews or audits.

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FMEA Planning Sheet Template – Include These Fields #

Use this format during FMEA Step 1 planning:

Field	Description
FMEA Type	DFMEA / PFMEA / MSR
System / Process	e.g., EPS motor, Spot Welding
Scope	Clear statement of what’s analyzed
Boundaries	What is included and excluded
Assumptions	Agreed-upon inputs and external validations
Team	Names and departments
Timing	Project milestone for FMEA completion

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Summary #

• Scope, boundaries, and assumptions are important for an effective FMEA.
• They define what you’re analyzing, what you’re not, and under what conditions.
• Clear definitions prevent wasted effort, confusion, and audit findings.
• This activity is part of Step 1 – Planning & Preparation in the AIAG-VDA 7-Step Method.
  

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