| name | fmea-process |
| description | Process FMEA (PFMEA) — failure mode identification, RPN calculation, severity/occurrence/detection ratings, AIAG-VDA FMEA handbook, control plans, mistake-proofing (poka-yoke), FMEA linkage to design FMEA and control plans. |
| metadata | {"priority":7,"promptSignals":{"phrases":["process FMEA","PFMEA","AIAG FMEA","RPN calculation","failure mode effects analysis","poka yoke"],"minScore":3}} |
Process FMEA (PFMEA) — Complete Skill
PFMEA Overview
Purpose: identify potential process failure modes; assess effects, causes, and controls; prioritize action
Scope: manufacturing and assembly processes; service processes; not product design (that is DFMEA)
Standards: AIAG-VDA FMEA Handbook (2019); IATF 16949 requirement; AS9100 (aerospace); FDA 21 CFR 820 (medical devices)
PFMEA team (cross-functional):
Manufacturing engineer + Quality engineer + Process engineer + Design engineer + Supplier (if applicable)
Facilitator: experienced FMEA practitioner; minimum 4 hours per process step typical
PFMEA Seven-Step Approach (AIAG-VDA 2019)
Step 1: Planning and Preparation
Define scope: boundary diagram (process flow); level of analysis (operation, sub-operation)
PFMEA header: project name, process, FMEA number, responsible engineer, revision date
Step 2: Structure Analysis
Process structure tree:
Process step → Work element → Process characteristics
Example: "Welding station → Arc initiation → Wire feed speed, Arc voltage"
5T Analysis:
Team, Timing, Tasks, Tools, Timing (schedule)
Step 3: Function Analysis
Process function: what the process step is supposed to do
Product characteristic: dimension, surface finish, torque, property the process is intended to achieve
Process characteristic: input variable (wire feed speed, temperature, force) that drives product characteristic
P-diagram (Parameter diagram):
Control factors → [Process] → Product function
Noise factors (uncontrolled: ambient, material variation, machine wear)
Error states (failure modes)
Step 4: Failure Analysis
Failure Mode: how the process could potentially fail to perform its function
- Dimensional: undersize, oversize, out of round
- Surface: scratches, burrs, contamination
- Missing: missing component, missing weld, missing torque
- Wrong: wrong part, wrong orientation, reversed assembly
Effect of Failure (downstream and customer):
Effect on next operation, end customer, vehicle safety
Multiple effects possible (local operation + downstream + end user)
Cause of Failure:
Process input characteristic variation (root cause at process level)
4M analysis: Man, Machine, Material, Method, Measurement, Environment (6M)
Use "Is/Is Not" analysis for each cause
Step 5: Risk Analysis
AIAG-VDA Severity (S) — 1 to 10:
| S | Effect Description |
|---|
| 10 | Affects safe vehicle operation, without warning |
| 9 | Affects safe operation, with warning |
| 8 | Major disruption to downstream production |
| 7 | Minor vehicle performance loss; customer very dissatisfied |
| 6 | Minor vehicle performance; customer dissatisfied |
| 5 | Comfort item degraded; customer somewhat dissatisfied |
| 4 | Customer notices; minor fit/finish/squeak |
| 3 | Customer may notice |
| 2 | Very minor effect; rarely noticed |
| 1 | No effect |
AIAG-VDA Occurrence (O) — 1 to 10:
| O | Probability of Occurrence |
|---|
| 10 | ≥ 1 in 2 (CPKP ≤ 0.33) |
| 8–9 | 1 in 8 to 1 in 20 (CPK = 0.51–0.67) |
| 6–7 | 1 in 80 to 1 in 400 (CPK = 0.83–1.0) |
| 4–5 | 1 in 2,000 to 1 in 15,000 (CPK = 1.17–1.33) |
| 2–3 | 1 in 150,000 to 1 in 1,500,000 (CPK = 1.5–1.67) |
| 1 | < 1 in 1,500,000 (CPK > 1.67) |
AIAG-VDA Detection (D) — 1 to 10:
| D | Detection Ability |
|---|
| 10 | No detection method; defect passes undetected |
| 9 | Visual check only; unreliable |
| 8 | SPC chart; operator check; low effectiveness |
| 6–7 | Attribute gauging; CMM sampling; moderate |
| 4–5 | Error proofing; 100% inspection |
| 2–3 | Error proofing (poka-yoke) + 100% gauge check |
| 1 | Error proofing prevents failure entirely |
Risk Priority Number (RPN — Legacy Method)
RPN = S × O × D [range: 1 to 1000]
Legacy threshold: RPN ≥ 100 → mandatory action
Limitation: RPN non-unique (5×5×5 = 125 = 1×5×25); doesn't distinguish high-severity low-RPN cases
AIAG-VDA Action Priority (AP — 2019 Replacement)
Action Priority (AP) table replaces RPN threshold:
AP = H (High), M (Medium), L (Low) based on S, O, D combination
Key rule: S = 9 or 10 → mandatory action regardless of O and D
High (H): must take action to reduce risk
Medium (M): action strongly recommended
Low (L): action at team discretion
Step 6: Optimization
Recommended actions:
Reduce O: change process, add error proofing, improve process controls
Reduce D: improve detection method, add verification step, 100% inspection
Reduce S: requires design change (DFMEA involvement)
Poka-Yoke (Error Proofing):
Level 1 — Prevention: physically prevents wrong action (guide pins, asymmetric slots, foolproofing jigs)
Level 2 — Detection: detects error before it becomes defect (limit switches, sensors, camera inspection)
Level 3 — Warning: signals operator of potential error (light curtains, alarms)
Level 4 — Correction: automatically corrects error (adaptive feedback, servo control)
Action responsibility: assign responsible person + target completion date for each recommended action
Step 7: Results Documentation
Control plan linkage:
PFMEA → Control plan (reaction plan for each control characteristic)
Control plan columns: part number, operation, control characteristic, spec/tolerance, measurement method, sample size/frequency, reaction plan
PFMEA linkage to DFMEA:
DFMEA: failure mode at product level → PFMEA failure mode at process level
Special characteristics (SC): DFMEA identifies SC → PFMEA shows how process controls SC
Special Characteristics
Significant characteristics (SC): diamond symbol; require statistical control
Critical characteristics (CC): star symbol; affect safety or regulatory compliance; require 100% verification or error proofing (D ≤ 3)
Key characteristics: significant impact on customer satisfaction; require special process control
PPAP (Production Part Approval Process): PFMEA required in PPAP submission package (AIAG PPAP 4th Edition Level 3+)
PFMEA for Non-Automotive Industries
Medical devices (FDA 21 CFR 820 + ISO 13485):
Risk management: ISO 14971; PFMEA is primary risk tool
Severity linked to patient harm: S=10 → death; residual risk (after controls) must meet acceptable risk limit
Aerospace (AS9100 + SAE ARP4761):
Systems FMEA + PFMEA; safety assessment process (SAP)
Catastrophic effect: probability ≤ 10⁻⁹ per flight hour (FAR 25.1309)
Process pharma (21 CFR Part 211 cGMP):
PFMEA for manufacturing process qualification; process characterization → FMEA → design space
Standards
| Standard | Scope |
|---|
| AIAG-VDA FMEA Handbook (2019) | Automotive PFMEA — current standard |
| IATF 16949:2016 | Automotive QMS — FMEA required |
| SAE J1739 | Potential failure mode and effects analysis |
| IEC 60812 | FMEA general standard |
| ISO 14971 | Risk management for medical devices |
| AS9100 Rev D | Aerospace QMS — FMEA requirements |
Output
Provide: process name and step analyzed, team members, top 5 failure modes by AP (High priority first), for each: failure mode description, effect (S rating), cause (O rating), current controls and detection method (D rating), AP (H/M/L) or legacy RPN, recommended action (reduce O/D/S), poka-yoke level (1–4) if applicable, responsible person and target date, revised AP/RPN after action, special characteristic designation (SC/CC), control plan linkage (measurement method, frequency, reaction plan), and applicable standard (AIAG-VDA 2019, IATF 16949).
