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FMEA (Failure Mode and Effects Analysis)

FMEA（失效模式与影响分析）

Overview

概述

FMEA systematically identifies potential failure modes, their effects, causes, and current controls. Each failure is scored on Severity (S), Occurrence (O), and Detection (D) on 1-10 scales. RPN = S × O × D prioritizes which risks to address first. AIAG-VDA FMEA (2019) replaces RPN with Action Priority (AP) matrix.

FMEA系统性地识别潜在失效模式、其影响、原因及现有控制措施。每项失效都会按照严重度（S）、发生度（O）和探测度（D）以1-10分进行评分。RPN = S × O × D用于确定优先处理的风险。AIAG-VDA FMEA（2019版）用行动优先级（AP）矩阵替代了RPN。

When to Use

使用场景

Trigger conditions:

Designing new products/processes and identifying risks proactively
Systematically evaluating existing failure modes for prioritization
Meeting automotive (IATF 16949) or medical device (ISO 13485) quality requirements

When NOT to use:

For root cause analysis of a known problem (use fishbone/5-why)
For statistical analysis of defect data (use SPC or Pareto)

触发条件：

设计新产品/流程并主动识别风险
系统性评估现有失效模式以确定优先级
满足汽车行业（IATF 16949）或医疗器械行业（ISO 13485）的质量要求

不适用场景：

已知问题的根本原因分析（使用鱼骨图/5Why法）
缺陷数据的统计分析（使用SPC或帕累托图）

Algorithm

算法流程

IRON LAW: Severity Can NEVER Be Reduced by Design Changes
Severity is determined by the EFFECT on the customer. A brake failure
is always severity 10, regardless of how unlikely or detectable it is.
FMEA reduces risk by: lowering Occurrence (better design/process) or
improving Detection (better testing/inspection). NEVER inflate
Detection scores to lower RPN artificially.

IRON LAW: Severity Can NEVER Be Reduced by Design Changes
Severity is determined by the EFFECT on the customer. A brake failure
is always severity 10, regardless of how unlikely or detectable it is.
FMEA reduces risk by: lowering Occurrence (better design/process) or
improving Detection (better testing/inspection). NEVER inflate
Detection scores to lower RPN artificially.

Phase 1: Input Validation

阶段1：输入验证

Define scope: Design FMEA (DFMEA) or Process FMEA (PFMEA). Assemble cross-functional team. Prepare: process flow diagram or system block diagram. Gate: Scope defined, team assembled, reference diagrams available.

定义范围：设计FMEA（DFMEA）或流程FMEA（PFMEA）。组建跨职能团队。准备：流程图或系统框图。 验收节点： 已定义范围、组建跨职能团队、准备好参考图表。

Phase 2: Core Algorithm

阶段2：核心算法

List all potential failure modes for each function/process step
For each failure mode, identify: effect on customer, root cause(s), current prevention controls, current detection controls
Score: Severity (1-10), Occurrence (1-10), Detection (1-10)
Classic RPN: RPN = S × O × D. Prioritize high RPNs.
AIAG-VDA AP: Use the S-O-D combination matrix to assign Action Priority: High, Medium, Low.
Define recommended actions for High-priority items with responsibility and target dates

列出每个功能/流程步骤的所有潜在失效模式
针对每个失效模式，识别：对客户的影响、根本原因、现有预防控制措施、现有探测控制措施
评分：严重度（1-10）、发生度（1-10）、探测度（1-10）
经典RPN计算： RPN = S × O × D。优先处理高RPN项。
AIAG-VDA行动优先级： 使用S-O-D组合矩阵分配行动优先级：高、中、低。
为高优先级项定义建议措施，明确责任人与目标日期

Phase 3: Verification

阶段3：验证

Review: are all functions/steps covered? Do severity scores match actual customer impact? Are detection scores realistic (not overly optimistic)? Gate: Complete coverage, realistic scoring, actions assigned for high-priority items.

审核：是否覆盖所有功能/步骤？严重度评分是否匹配实际客户影响？探测度评分是否符合实际（不过于乐观）？ 验收节点： 覆盖完整、评分符合实际、已为高优先级项分配措施。

Phase 4: Output

阶段4：输出

Return FMEA register with prioritized actions.

返回带有优先级措施的FMEA登记册。

Output Format

输出格式

json

{
  "fmea_items": [{"failure_mode": "seal leak", "effect": "water damage", "cause": "material degradation", "severity": 8, "occurrence": 4, "detection": 6, "rpn": 192, "ap": "high", "action": "add pressure test at final inspection"}],
  "summary": {"total_modes": 45, "high_priority": 8, "medium": 15, "low": 22},
  "metadata": {"type": "PFMEA", "scope": "assembly line 3"}
}

json

{
  "fmea_items": [{"failure_mode": "seal leak", "effect": "water damage", "cause": "material degradation", "severity": 8, "occurrence": 4, "detection": 6, "rpn": 192, "ap": "high", "action": "add pressure test at final inspection"}],
  "summary": {"total_modes": 45, "high_priority": 8, "medium": 15, "low": 22},
  "metadata": {"type": "PFMEA", "scope": "assembly line 3"}
}

Examples

示例

Sample I/O

输入输出样例

Input: Coffee machine brewing module, function: "heat water to 93°C" Expected: Failure modes: overheating (S=7, O=3, D=4, RPN=84), under-heating (S=5, O=4, D=3, RPN=60), no heating (S=8, O=2, D=2, RPN=32).

输入： 咖啡机冲泡模块，功能：“将水加热至93°C” 预期输出： 失效模式：过热（S=7, O=3, D=4, RPN=84）、加热不足（S=5, O=4, D=3, RPN=60）、无法加热（S=8, O=2, D=2, RPN=32）。

Edge Cases

边缘案例

Input	Expected	Why
S=10, any O and D	Always high priority	Safety-critical failures require action regardless of RPN
RPN=100 (S=10,O=1,D=10) vs (S=1,O=10,D=10)	Same RPN, very different risk	This is why AIAG-VDA AP replaces pure RPN
No current controls	D=10 (no detection)	Honest assessment drives improvement

输入	预期结果	原因
S=10，任意O和D	始终为高优先级	安全关键型失效无论RPN如何都需采取措施
RPN=100（S=10,O=1,D=10） vs（S=1,O=10,D=10）	RPN相同，但风险差异极大	这正是AIAG-VDA AP矩阵替代纯RPN的原因
无现有控制措施	D=10（无法探测）	如实评估才能推动改进

Gotchas

注意事项

RPN is misleading: RPN=100 from S=10,O=1,D=10 (catastrophic but rare, undetectable) is very different from S=1,O=10,D=10 (trivial but frequent). AIAG-VDA AP matrix addresses this flaw.
Scoring consistency: Without calibration, different team members score differently. Use scoring rubrics with examples and calibrate as a team.
Detection ≠ prevention: A low Detection score (good detection) doesn't prevent the failure — it only catches it. Prioritize Occurrence reduction over Detection improvement.
Living document: FMEA must be updated when design/process changes, new failure data appears, or corrective actions are implemented. A static FMEA provides diminishing value.
Scope creep: An FMEA that tries to cover everything becomes unmanageable. Focus on the critical functions or highest-risk areas first.

RPN存在误导性：由S=10,O=1,D=10（灾难性但罕见、无法探测）得出的RPN=100，与S=1,O=10,D=10（轻微但频繁）得出的RPN=100风险差异极大。AIAG-VDA AP矩阵解决了这一缺陷。
评分一致性：若未校准，不同团队成员的评分会存在差异。使用带示例的评分准则并开展团队校准。
探测≠预防：低探测度评分（探测效果好）无法防止失效——只能发现失效。优先降低发生度而非提升探测度。
动态文档：当设计/流程变更、出现新失效数据或实施纠正措施时，必须更新FMEA。静态FMEA的价值会逐渐降低。
范围蔓延：试图覆盖所有内容的FMEA会变得难以管理。首先聚焦关键功能或最高风险领域。

References

参考资料

For AIAG-VDA AP matrix and scoring tables, see
```
references/aiag-vda-ap.md
```
For S/O/D scoring rubrics, see
```
references/scoring-rubrics.md
```

关于AIAG-VDA AP矩阵和评分表，请查看
```
references/aiag-vda-ap.md
```
关于S/O/D评分准则，请查看
```
references/scoring-rubrics.md
```