6SQ ToolsWhat Is a Control Plan and How Do You Build One in APQP?
In any manufacturing or assembly process, consistency is the foundation of quality. But how do you ensure that every part, every shift, and every operator produces the same result? The answer lies in a simple yet powerful document: the Control Plan. If you are working under IATF 16949 or following the AIAG Advanced Product Quality Planning (APQP) methodology, the Control Plan is not optional—it is a mandatory deliverable that links your process design to daily production control.
What It Is
A Control Plan is a structured, living document that describes the actions required to maintain a process within defined specifications. It identifies the key product and process characteristics, the measurement methods used to monitor them, and the reaction plan if something goes out of control. As defined in the AIAG APQP manual (and now formalized under the Customer-Specific/CTS Control Plan requirements in the IATF 16949 context), the Control Plan is the written summary of the process control strategy.
It is not a list of inspection steps. Instead, it is a proactive plan that answers three questions for each operation:
The Control Plan is created during the APQP Phase 3 (Process Design and Development) and is updated after production trials and continuous improvement activities. It covers all phases of product life: prototype, pre-launch, and production.
How It Works: The Core Columns and Steps
The Control Plan is typically a table. While formats vary by customer, the AIAG framework defines a standard set of columns that you must complete. Here is the logical sequence to build one:
Important note from the AIAG framework: The Control Plan must reference the Process FMEA. Every high-risk failure mode from the FMEA should have a corresponding control in the plan. If the FMEA says "prevent," the Control Plan must show the prevention method; if it says "detect," the plan must show the detection method.
A Worked Illustrative Example
Example data (illustrative only) — This is a simplified example for a machining station, not real factory data.
Process Step | Product Char. | Spec | Method | Sample Size / Freq. | Control Method | Reaction Plan
In this example, the plan tells the operator exactly what to measure, how often, and what to do if the reading is abnormal. It also tells the auditor that the process is under statistical control (SPC) for the critical diameter, not just "inspected."
Common Pitfalls to Avoid
Closing
A well-built Control Plan is the bridge between your engineering intent and the shop floor reality. It tells every operator, every shift, and every auditor exactly how the process is kept in control. If you are starting from scratch or need a structured template that follows the AIAG/CTS framework, you can use the free Control Plan tool at 6SQ: https://www.6sq.com/tools/control_plan/. Build it once, update it often, and let it guide your daily quality decisions.
What It Is
A Control Plan is a structured, living document that describes the actions required to maintain a process within defined specifications. It identifies the key product and process characteristics, the measurement methods used to monitor them, and the reaction plan if something goes out of control. As defined in the AIAG APQP manual (and now formalized under the Customer-Specific/CTS Control Plan requirements in the IATF 16949 context), the Control Plan is the written summary of the process control strategy.
It is not a list of inspection steps. Instead, it is a proactive plan that answers three questions for each operation:
- What could go wrong
- How do we detect it
- What do we do if it happens
The Control Plan is created during the APQP Phase 3 (Process Design and Development) and is updated after production trials and continuous improvement activities. It covers all phases of product life: prototype, pre-launch, and production.
How It Works: The Core Columns and Steps
The Control Plan is typically a table. While formats vary by customer, the AIAG framework defines a standard set of columns that you must complete. Here is the logical sequence to build one:
- Identify the process step or station. List each operation in sequence, from receiving to shipping.
- Define the characteristic. For each step, list the product characteristic (e.g., diameter, hardness) and the process characteristic (e.g., temperature, pressure) that must be controlled.
- Set the specification. Write the nominal value and tolerance or the reference to the engineering drawing/spec.
- Choose the measurement method. Specify the gauge, test, or sensor used (e.g., caliper, CMM, visual check).
- Determine the sample size and frequency. How many pieces and how often (e.g., 5 pieces every 2 hours).
- Define the control method. This is the heart of the plan. It can be an SPC chart, a checklist, a poke-yoke device, or a supervisory review.
- Document the reaction plan. What does the operator do when a part is out of spec or the process is unstable (e.g., stop, notify supervisor, quarantine last 50 parts).
Important note from the AIAG framework: The Control Plan must reference the Process FMEA. Every high-risk failure mode from the FMEA should have a corresponding control in the plan. If the FMEA says "prevent," the Control Plan must show the prevention method; if it says "detect," the plan must show the detection method.
A Worked Illustrative Example
Example data (illustrative only) — This is a simplified example for a machining station, not real factory data.
Process Step | Product Char. | Spec | Method | Sample Size / Freq. | Control Method | Reaction Plan
- Op 20: CNC Turning | Outer Diameter | 25.00 ± 0.05 mm | Digital micrometer | 5 pcs / every 2 hrs | X-bar & R chart | Stop, inspect last 50 pcs, notify supervisor
- Op 20: CNC Turning | Surface Finish (Ra) | ≤ 1.6 µm | Surface tester | 1 pc / per batch | Operator check | Adjust tool insert, re-run first-off
- Op 30: Deburring | Edge condition | No burrs | Visual (standard photo) | 100% | Poke-yoke / visual audit | Segregate, rework, retrain operator
In this example, the plan tells the operator exactly what to measure, how often, and what to do if the reading is abnormal. It also tells the auditor that the process is under statistical control (SPC) for the critical diameter, not just "inspected."
Common Pitfalls to Avoid
- Writing the plan after production starts. The Control Plan must be drafted before tooling and gauging are finalized; otherwise, it becomes a history report, not a control strategy.
- Copying the inspection plan. A Control Plan is not a QC checklist. It must include process parameters and operator self-checks, not just final inspection.
- Ignoring the FMEA link. If the FMEA identifies a high severity risk, the Control Plan must have a corresponding control. A missing link is a common audit finding.
- Leaving reaction plans vague. "Contact supervisor" is not a reaction plan. Specify what to do with the suspect product (quarantine, sort, rework) and how many pieces to review.
- Forgetting to update. The plan is a living document. Every engineering change, new failure mode, or CAPA must trigger a review of the Control Plan.
Closing
A well-built Control Plan is the bridge between your engineering intent and the shop floor reality. It tells every operator, every shift, and every auditor exactly how the process is kept in control. If you are starting from scratch or need a structured template that follows the AIAG/CTS framework, you can use the free Control Plan tool at 6SQ: https://www.6sq.com/tools/control_plan/. Build it once, update it often, and let it guide your daily quality decisions.
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