🔍 Introduction #
For many quality professionals, understanding the theoretical flow from DFMEA → PFMEA → Control Plan is easy. But when it comes to real-world implementation, things get tricky.
In this article, we walk you through a practical case study from the automotive industry that shows:
- How a design-level failure mode identified in DFMEA leads to process-level risks in PFMEA,
- How those risks are managed through prevention and detection controls,
- And how the Control Plan captures these controls for real-world production monitoring.
Let’s dive into an example: Bracket Weld Assembly for a Car Seat Frame.
🚗 Case Study Context #
Product:
Welded Bracket to join Seat Back Frame and Recliner Mechanism
Project Stage:
Product design complete → Moving into process planning and validation
📌 Step 1: DFMEA – Identifying Design Risk #
Function:
Bracket must maintain structural integrity during rear crash impact.
Design Failure Mode:
Bracket fractures under crash load
Potential Effect:
Seat detachment, passenger injury (Critical)
Severity:
10 (safety risk)
Potential Causes in DFMEA:
- Inadequate bracket thickness
- Weak weld location
- Material selection not meeting tensile requirement
Prevention Controls in DFMEA:
- FEA simulations
- Material spec review
- Weld point optimization in CAD
Recommended Action:
Increase weld length + use high-strength material (HSLA steel)
✅ Design risk identified and mitigated in DFMEA.
🔁 Step 2: Linking to PFMEA – Process-Level Risk #
PFMEA Process Step:
Welding Operation – Robotic MIG welding of bracket to frame
Function:
Securely join bracket to seat frame
Process Failure Mode:
Weak weld joint
Effect:
Bracket fractures under load → same as DFMEA effect
Severity:
10 (carried over from DFMEA due to safety risk)
Process Causes:
- Incorrect welding current
- Poor wire feed rate
- Missing weld due to robot misalignment
Occurrence:
4 (based on past field history)
Prevention Control:
- PLC program to set fixed welding parameters
- Barcode scan to confirm correct weld recipe
Detection Control:
- Visual inspection
- Weld current monitoring
- Sensor-based weld presence check
Recommended Action:
Introduce real-time weld current monitoring via PLC
✅ The process is designed to prevent and detect the design-level risk.
🧾 Step 3: Control Plan – Implementation of Controls #
Now we transfer the controls from PFMEA into the Control Plan.
| Process Step | Characteristic | Control Method | Sample Size | Frequency | Reaction Plan |
|---|---|---|---|---|---|
| Bracket Welding | Weld Current | PLC – Real-time current monitoring | 100% | Continuous | Stop line, check robot program |
| Weld Presence | Weld presence sensor | 100% | Every part | Rework/re-weld, inform maintenance | |
| Weld Visual Appearance | Visual inspection (burn marks, undercut, spatter) | 1 per hour | Operator check | Scrap/rework as per work instruction |
Special Characteristic:
- Weld is marked as Critical Characteristic (●) in both PFMEA and Control Plan
✅ Control Plan translates PFMEA controls into executable process checks.
🔗 The Linkage Map #
Let’s visualize how the risk flows from DFMEA → PFMEA → Control Plan:
DFMEA
└── Function: Bracket integrity under crash
└── Failure Mode: Bracket fracture
└── Cause: Weak weld design
└── Severity: 10
└── Action: Improve weld design
↓
PFMEA
└── Process Step: Bracket Welding
└── Failure Mode: Weak weld
└── Cause: Incorrect weld current
└── S: 10 (from DFMEA), O: 4, D: 5
└── Controls: PLC parameter check, weld sensor
↓
Control Plan
└── Step: Welding
└── Characteristic: Weld current, weld presence
└── Control Method: PLC monitoring, visual check
└── Frequency: Continuous / 100%
└── Reaction: Stop and reprogram
🎯 Why This Linkage Is Important #
| Purpose | How It’s Achieved |
|---|---|
| Traceability | Same failure mode tracked from design to process to shopfloor |
| Risk-Based Thinking | High-severity issues in DFMEA are proactively controlled in PFMEA and Control Plan |
| Audit Compliance (IATF) | Easy to show linkage of product risk to process control during audits |
| Customer Satisfaction | Prevents design risks from turning into field failures |
| Change Management Ready | If weld design changes → All linked docs (DFMEA, PFMEA, Control Plan) are traceable |
✅ Best Practices for Linking DFMEA → PFMEA → Control Plan #
- Start with DFMEA during design reviews (APQP Phase 2)
- Translate failure effects and severity into PFMEA
- Copy over special characteristics from DFMEA to PFMEA
- Use PFMEA output as the input for Control Plan
- Maintain consistent process step numbering
- Keep document references and revision levels traceable
- Train cross-functional teams on how to follow this flow
📘 Summary: A Closed-Loop Example #
| Stage | Key Output |
|---|---|
| DFMEA | Bracket fracture under load → Increase weld area in design |
| PFMEA | Weak weld due to poor current → Add weld parameter controls |
| Control Plan | PLC real-time monitoring + visual inspection for weld quality |
This creates a closed-loop system that starts with risk identification and ends with risk control and monitoring.
📚 Related Guides #
- AIAG-VDA DFMEA 7-Step Approach
- AIAG-VDA PFMEA 7-Step Approach
- Control Plan | Step-by-Step Tutorial
- How FMEA Drives Control Plan
- Special Characteristics in Automotive Manufacturing
👇 Final Thoughts #
If DFMEA is the brain that predicts risk, and PFMEA is the nervous system that analyzes it,
then the Control Plan is the muscle that takes action.
By creating a strong linkage between them, you build a robust, risk-controlled, and audit-ready manufacturing system.
