2.4 Control Plan + Reaction Plan (Stop/Contain/Release Rules)

The Control Plan (CP) is the operational constitution of the manufacturing floor. While the PFMEA predicts theoretical risk, the Control Plan prescribes the actual policing of that risk. It is the single source of truth that translates engineering intent (GD&T, Specs) into operator reality (Gauges, Checks, Reaction). If a process step or inspection is not in the Control Plan, it does not officially exist.

The Golden Thread: Lineage of Logic

A Control Plan does not appear in a vacuum. It is the final link in the data chain. You must demonstrate direct traceability.

• DFMEA (Design Risk) defines Key Product Characteristics (KPCs).
  • Example: "Shaft Diameter" is critical for bearing fit.
• PFMEA (Process Risk) defines Key Process Characteristics (KCCs).
  • Example: "Machine Spindle Speed" controls the Shaft Diameter.
• Control Plan defines How we check the KCC to protect the KPC.
  • Action: Measure Spindle Speed every hour; Measure Shaft Diameter every 5 parts.

The Rule: Every High RPN (Risk Priority Number) in the PFMEA must have a corresponding detection or prevention line item in the Control Plan. No orphans.

The Three Phases of Control

The Control Plan evolves as process maturity increases. Do not copy-paste the Production Plan into the Prototype phase.

1. Prototype Control Plan

• Objective: Validation of Design.
• Method: 100% inspection, typically manual data logging.
• Focus: Dimensional verification and material testing.

2. Pre-Launch (Safe Launch) Plan

• Objective: Validation of Process Stability (Early Production Containment).
• Method: Increased frequency (e.g., 200% of normal sampling).
• Focus: Catching "Infant Mortality" issues and debugging the line.
• Exit Criteria: Defined number of defect-free runs (e.g., 3000 units or 3 shifts).

3. Production Control Plan

• Objective: Statistical Control.
• Method: Sampling based on Capability (Cpk).
• Focus: Monitoring process drift.

Anatomy of a Control Line Item

A valid Control Plan entry requires five specific definitions. Ambiguity here causes operator error.

1. Characteristics (What)

Distinguish between Product (The Output) and Process (The Input).

• Bad: "Check Solder."
• Good: "Solder Paste Height (Process)" and "Fillet Wetting Angle (Product)."

2. Specification / Tolerance (The Standard)

Must match the print exactly.

• If the print says 10.0 ± 0.1 mm, Then the CP lists 9.9 – 10.1 mm.
• Pro-Tip: Do not use "Visual OK" as a spec. Use "No burrs visible at 4x magnification" or reference a specific Limit Sample ID.

3. Evaluation Technique (The Tool)

Define the Measurement System.

• Hardware: Caliper, CMM, Go/No-Go Fixture (Quote the Gauge ID).
• Software: Vision System, ICT.
• Requirement: The Gauge listed must have a valid Gage R&R (MSA) study.

4. Sample Size & Frequency (The Rhythm)

This is a function of Process Capability (Cpk) and Risk.

• If Cpk < 1.33 (Unstable) -> 100% Inspection.
• If Cpk > 1.67 (Capable) -> Sample 1 piece every 4 hours.
• If Safety Critical -> Mistake Proofing (Poka-Yoke) or 100% Auto-Check required.

5. Reaction Plan (The Consequence)

This is the most critical and often neglected column. It tells the operator exactly what to do when the check fails.

• Bad: "Notify Supervisor." (Too vague, slow).
• Good: "Stop Line. Segregate last 2 hours of production. Adjust Tool Offset +0.02mm. Re-measure."

Dynamic Management (Living Document)

The Control Plan is not a static artifact. It drives the feedback loop.

• Scenario: Customer Complaint (Field Failure)
  • Action: Review the CP. Was the defect characteristic listed?
    • If Yes: The method/freq was insufficient. Update CP to tighten inspection.
    • If No: The CP was incomplete. Add the characteristic immediately.
• Scenario: Process Change (ECO)
  • Action: If the tool, material, or machine changes, the CP must be re-revised and re-approved before production resumes.

Final Checklist

Control Point	Requirement / Threshold	Non-Negotiable Rule
Traceability	1:1 Link to PFMEA	Every high-risk failure mode must have a Control Plan check.
Reaction Plan	Specific Instructions	Must define Stop, Contain, and Correct actions. No generic "Notify."
Tolerances	Matches Print	Specs in CP must equate to Engineering Drawings.
Frequency	Based on Cpk	Low Cpk (< 1.33) requires 100% inspection or Poka-Yoke.
Phasing	Safe Launch	New products must use "Pre-Launch" criteria (Higher Sampling) initially.
Evaluation	Valid MSA	Listed gauges must have passed Gage R&R (< 10% or < 30% conditional).