FMEA – Framework Thinking

FMEA

Failure Mode and Effects Analysis

1. Overview of FMEA: A Reliability Analysis Technique That Preempts Failure via RPN

    flowchart LR
    A["Reactive response<br/>after failure occurs<br/>cost & quality loss"] --"Identify and evaluate<br/>potential failure modes in advance"--> B["Prioritize risk<br/>based on RPN"] --"Proactive improvement<br/>of high-risk factors"--> C["Prevent failure<br/>ensure reliability & safety"]

    style A fill:#FFEBEE,stroke:#D32F2F,color:#000
    style B fill:#E3F2FD,stroke:#1976D2,color:#000
    style C fill:#E8F5E9,stroke:#388E3C,color:#000

Definition: A quality/reliability analysis technique that identifies potential failure modes in advance and quantifies risk using RPN (S×O×D) to establish proactive preventive measures.

Scope of analysis: applied across product design, manufacturing processes, systems, and software
Core output: RPN = Severity (S) × Occurrence (O) × Detection (D) → prioritize improvement of high-risk items
Timing: the earlier it is performed in the design/development stage, the lower the correction cost (the 1:10:100 rule)

Characteristics: (Proactive) Removes risk factors at the design/process stage before a failure occurs, minimizing correction cost. (Quantitative prioritization) Uses RPN = S × O × D to numerically objectify the importance of risk factors for prioritizing improvement. (Multi-domain application) Applicable across product design (Design FMEA), manufacturing processes (Process FMEA), and systems (System FMEA).

2. Core Structure of FMEA

a. The 5-Step FMEA Analysis Procedure

    flowchart LR
    S1["1. Define scope<br/>Scope, function, boundary<br/>form the analysis team"]
    S2["2. Identify failure modes<br/>Enumerate<br/>all possible failures"]
    S3["3. Analyze effects & causes<br/>Determine failure impact<br/>derive root causes"]
    S4["4. Calculate RPN<br/>S × O × D<br/>determine risk priority"]
    S5["5. Corrective action<br/>For high-RPN items<br/>establish, execute, verify countermeasures"]

    S1 --> S2 --> S3 --> S4 --> S5
    S5 -->|"Recalculate RPN<br/>verify effect"| S4

    style S1 fill:#E3F2FD,stroke:#1976D2,color:#000
    style S2 fill:#F3E5F5,stroke:#7B1FA2,color:#000
    style S3 fill:#FFF3E0,stroke:#F57C00,color:#000
    style S4 fill:#FFEBEE,stroke:#D32F2F,color:#000
    style S5 fill:#E8F5E9,stroke:#388E3C,color:#000

Step	Key Activities	Output
1. Define scope	Set product/process scope, create functional block diagram	Scope definition document, function list
2. Identify failure modes	Enumerate all potential failure modes for each function	Failure mode list
3. Analyze effects & causes	Analyze the effect of failure on system/users, root cause analysis	Effect/cause analysis table
4. Calculate RPN	Score S, O, D each on a 1–10 scale, calculate RPN, set thresholds	FMEA worksheet
5. Corrective action	Establish, execute, and reassess improvement plans for high-risk items	Corrective action plan

b. RPN Calculation and Risk Management

    flowchart TD
    subgraph R1[""]
        direction LR
        SE["Severity<br/>Magnitude of impact<br/>on the user/system<br/>1 (minor) ~ 10 (critical)"]
        OC["Occurrence<br/>Likelihood/frequency<br/>of the failure mode<br/>1 (rare) ~ 10 (high)"]
    end
    subgraph R2[""]
        direction LR
        DT["Detection<br/>Ability to detect<br/>the failure before shipment<br/>1 (easily detected) ~ 10 (undetectable)"]
        RPN["RPN<br/>Risk Priority Number<br/>= S × O × D<br/>the higher, the more urgent the fix"]
    end

    style SE  fill:#E3F2FD,stroke:#1976D2,color:#000
    style OC  fill:#F3E5F5,stroke:#7B1FA2,color:#000
    style DT  fill:#FFF3E0,stroke:#F57C00,color:#000
    style RPN fill:#1E3A5F,stroke:#1E3A5F,color:#fff
    style R1 fill:none,stroke:none
    style R2 fill:none,stroke:none

Action Criteria Based on RPN Thresholds

RPN Range	Risk Level	Recommended Action
200+	Very high	Immediate design/process change required
100–199	High	Establish and execute a short-term improvement plan
50–99	Medium	Review improvement options, strengthen monitoring
Below 50	Low	Maintain current level, periodic review

Application by FMEA Type

Type	Timing	Scope of Analysis	Key Use
System FMEA	Concept design stage	Overall system structure	Analyze inter-system interface risk
Design FMEA	Detailed design stage	Parts/component design	Proactively remove design weaknesses
Process FMEA	Manufacturing/service process	Process/procedure steps	Prevent process defects and variation causes
Software FMEA	SW design/development stage	Modules, functions, interfaces	Prevent software defects and failures

3. Expected Benefits and Application of FMEA

Category	Expected Benefits	Application and Practical Use
Proactive quality management	Removes failures early in design/development, minimizing correction cost (the 1:10:100 rule)	Proactively remove high-risk design elements with Design FMEA before product launch
Reliability & safety	Focuses management on causes of critical failure through RPN-based prioritization	Meets certification requirements for safety-critical systems such as medical devices, automotive, and aviation
Process improvement	Systematically manages sources of variation in manufacturing/service processes with Process FMEA	Analyzes architecture and interface risk with SW FMEA before sprint kickoff
Cost reduction	Reduces warranty, recall, and rework costs and preempts customer claims	Combined with the Analyze phase of Six Sigma DMAIC for root-cause improvement

FTA (Fault Tree Analysis)GQM