How to develop a Control Plan

First, it is useful to understand what a Control Plan is and when it is used.

A Control Plan is a documented description of the controls applied to a process and its products. It summarizes the system used to minimize process and product variation. Sketches may be attached where needed to illustrate the controls. However, a Control Plan does not replace the information contained in detailed operating instructions.

In practice, the Control Plan describes the actions required at each stage of a process, from receiving materials to delivery. During normal production, it specifies the monitoring and control methods used for product and process characteristics. As production processes are continually improved and updated to meet new needs, the Control Plan reflects these changes in process conditions. It helps maintain quality by establishing a basis for quality checks and process monitoring.

The Control Plan is maintained and used throughout the product life cycle. At the beginning, it records the initial plan for controlling the process. It then guides process control and product quality assurance. A single Control Plan may cover a group or family of products manufactured using the same process flow.

The Control Plan must remain a living document, reflecting the current control methods and measurement systems. It is updated as those methods and systems are evaluated and improved.

IATF 16949 requires the Control Plan to include the controls used in manufacturing, including job set-up verification, first-off/last-off part validation, monitoring methods for special characteristics, customer-required information where applicable, and reaction plans for detected nonconformities or processes that become statistically unstable or incapable.

The specific requirements are set out in Annex A of IATF 16949.

Control Plans generally address three separate phases:

• Prototype: describe the dimensional measurements and material and performance or functional tests to be performed during prototype manufacture. The organization may develop a Control Plan for this phase when required by the customer.
• Pre-launch: before production begins, prepare a Control Plan describing the process controls, dimensional measurements, and material and performance or functional tests to be performed. Production and inspection data are collected for the PPAP submission used to obtain customer approval for serial production.
• Production: before serial production begins, prepare a Control Plan describing product and process characteristics, process controls, tests and measurement systems used in serial production.

The standard requires the organization to review its Control Plan in the following circumstances:

• When the organization determines that nonconforming product has been shipped to a customer;
• When any change occurs that affects the product or process;
• Following a customer complaint and the implementation of related corrective actions;
• At a defined frequency established through risk analysis.

In some cases, customer approval is required following a review or revision of the Control Plan.

Developing a Control Plan requires a multidisciplinary team drawn from different departments and the use of available information to understand the process, including:

• The process flow diagram (PFD);
• FMEA
• Lessons learned from the development of similar products;
• A team with in-depth knowledge of the manufacturing and inspection processes;
• Information from design reviews;
• Optimization methods.

Annex A of the standard also defines minimum Control Plan content. The information is grouped as follows:

• General data;
• Product control information;
• Process control information;
• Methods to be used;
• Reaction plans for nonconformities or process variation.

During internal, second-party or third-party audits, the following 12 common Control Plan issues are frequently identified:

• The wrong Control Plan phase is selected — for example, “Prototype” is checked even though the plan is used for serial production.
• The Control Plan is not updated following defects, 4M changes, engineering change orders or other relevant changes.
• The operations do not match the established process flow diagram (PFD), for example because they are out of sequence or an operation is missing.
• Key equipment required for an operation is omitted.
• Product characteristics are missing or incorrectly identified.
• Process characteristics are missing or incorrectly identified.
• Special characteristics (SC) or critical-to-quality characteristics (CTQ) are not marked.
• Tolerances for process or product characteristics do not match the drawing requirements.
• Evaluation or measurement techniques do not reflect actual practice.
• Sampling frequency or sample size does not match actual practice or other company requirements.
• The current control method is incorrect or inconsistent with actual practice or other company requirements. In particular, statistical methods for special characteristics are not clearly specified.
• Reaction plans for nonconformities and process variation are ineffective. General instructions such as “stop, call and wait” or “inform a supervisor” do not specify responses for particular situations. A situation requiring the planned response may have occurred, yet there are no records or other evidence that the Control Plan was followed.