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).

The Reality Check: If a process step or inspection is not in the Control Plan, it does not officially exist. An operator performing an "informal check" is uncontrolled variance.

The Golden Thread: Lineage of Logic

A Control Plan 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.

Anatomy of a Control Line Item

Ambiguity in the Control Plan causes operator error. Each entry must define five specific parameters.

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 specific Gauge ID).
Validation: The Gauge listed must have a passing Gage R&R (MSA) study.

4. Frequency (The Rhythm)

Frequency is a function of Process Capability (Cpk), not "standard practice."

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

5. Reaction Plan (The Consequence)

This tells the operator exactly what to do when the check fails.

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

The Reaction Plan: The "OCAP"

The Reaction Plan is the Out of Control Action Plan. It is not a suggestion; it is an algorithm for the operator.

The "Stop-Call-Wait" Syndrome:

Do not write "Call Quality Engineer" as the primary reaction. The line will stop for hours waiting for you. The Reaction Plan must empower the operator to Contain and Correct autonomously where possible.

Reaction Logic Levels:

Level 1 (Operator): Re-measure to confirm. If confirmed fail -> Stop Machine -> Tag Part "Reject".
Level 2 (Setter/Lead): Adjust process parameters (within Control Plan limits). Change tool. Re-verify first piece.
Level 3 (Escalation): If Level 2 fails to fix the issue -> Call Engineering. Initiate Non-Conformance Report (NCR).

Stop / Contain / Release Rules

You must define the strict criteria for stopping the line and, more importantly, the criteria for restarting it.

1. Stop Rules (When to Halt)

Safety Breach: Any failure of a safety curtain, interlock, or E-stop. Immediate Hard Stop.
Consecutive Rejects: Three (3) consecutive parts failing the same parameter.
Setup Verification Fail: First Article Inspection (FAI) failure.
Trend Violation (SPC): Seven points on one side of the mean (Shift) or points outside Control Limits.

2. Containment Rules (The "Bucket" Protocol)

When a defect is found, you must assume all parts produced since the last "Good" check are suspect.

Traceback: Identify the time of the last successful inspection.
Quarantine: Isolate 100% of WIP (Work in Progress) produced between "Last Good Check" and "Now."
Screening: You must inspect every single unit in the suspect window for the specific defect.
Clean Point: Establish a "Clean Point" (Serial Number or Time Stamp) where known good production resumes.

3. Release Rules (Restart Criteria)

You cannot just turn the machine back on. The process is "Guilty until proven Innocent."

Correction Verified: The root cause (broken tool, wrong setting) must be physically corrected.
Setup Verification: Run a new First Piece. It must measure nominal (centered in spec), not just "in spec."
Sign-Off: For Safety or Critical Characteristic failures, the Quality Manager or Process Engineer must physically sign the "Restart Authorization."

The Three Phases of Control

The Control Plan evolves as process maturity increases.

Prototype Control Plan:

Method: 100% Inspection. Manual data logging.
Goal: Validate the design intent.

Pre-Launch (Safe Launch) Plan:

Method: Increased Frequency (e.g., 200% of normal sampling).
Goal: Contain "Infant Mortality" issues. Exit criteria = 3000 defect-free units.

Production Control Plan:

Method: Statistical Sampling based on Cpk.
Goal: Monitor process drift.

Final Checklist

Control Point	Critical Requirement
Traceability	High RPN features in PFMEA must have a specific check in the Control Plan.
Spec Alignment	Control Plan Specs must match the Engineering Drawing 1:1.
Reaction Plan	Must explicitly state: Stop, Contain, and Correct actions.
Containment	"suspect window" = All parts since the Last Good Check.
Restart Authority	Define who authorizes restart after a Critical Failure (e.g., QE Sign-off).
Safe Launch	New lines must run Pre-Launch (High Frequency) controls before full release.
Gauge Validity	Every tool listed must have a valid Calibration Sticker and MSA Study.