QMI Brief Newsletter

6/23/2006
Variation Management of Key Characteristics

One of the objectives of the International Aerospace Quality Group (IAQG) is to establish common aerospace industry quality standards and requirements. This goes beyond quality management system standards, and addresses issues that affect product and processes. The IAQG recognized a need for a standard to establish requirements for the variation of key characteristics. The standard, AS9103, requires a thorough assessment of the part production process with the primary goal of controlling and minimizing variation in characteristics produced by production processes.

AS9103 is designed to drive manufacturing process improvement through adequate planning and effective management of key characteristic variation. The key characteristics focus is intended to improve confidence for part features whose variation has a significant influence on end-product form, fit, performance, service life and manufacturability.

What is a key characteristic? For a part, subassembly or system, it is defined as selected geometrical, material properties, functional and/or cosmetic features, which are measurable, whose variation control is necessary in meeting customer requirements and enhancing customer satisfaction. Key characteristics are also selected measurable parameters of a process whose control is essential to manage variation of part or system key characteristics.

How are key characteristics defined? The key characteristics owner normally defines them. The owner is either a person or function that recognizes the reasons for selection of the key characteristic. Typically, these responsibilities are held by internal or external design, quality or manufacturing engineering, and should be identified by a cross-functional team.

AS9103 is comprised of two main sections: General Requirements and Process Model and Outputs. The General Requirements section provides requirements, which must be met regardless of the variation management methodology used. AS9103 requires that variation management activities be formed on identified key characteristics and processes until they are in control, and process capability has been established. Once a process is stable and capable, appropriate monitoring methodologies should be implemented to ensure continued performance.

The producer of the key characteristic is required to maintain appropriate documentation of the characteristic and of manufacturing process elements that influence variation in the key characteristics, as well as their control techniques. If statistical process control is chosen as the method of control, a process capability index shall be calculated only when the process is shown to be stable and in control. AS9103 defines a capable process as one meeting a CpK of 1.33 or greater, or as specified by the customer. Other variation control methods such as tooling, control of process settings, standard processes and mistake proofing may be used to ensure process stability and capability. However, measurable evidence must demonstrate that the controls are effective.

Section 6 of AS9103 addresses Process Models and Outputs. A typical model will consist of several stages beginning with the definition of key characteristics and ending with the monitoring of product manufacturing performance. Once a model is selected, the organization should define the outputs. Examples of outputs in AS9103 are measurement system analysis, ongoing controls for key characteristics, ongoing analysis of business indicators, updated process control documentation and process change documentation.

In summary, many aerospace original equipment manufacturers (OEMs) are beginning to identify key characteristics and will require the use of AS9103 on new programs. Organizations are encouraged to learn variation management methodologies and begin implementing them in order to meet customer requirements and enhance customer satisfaction.

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