Chapter on "Statistical Process Control and Variation Management"

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Statistical Process Control and Variation Management to Satisfy As9103

REQUIREMENTS

Statistical process control and variation management to satisfy AS9103 requirements

To assure customer satisfaction, Space, Aviation and Defense industry must produce a safe, improved and reliable products that meet applicable and customer requirements. However, the globalization and diversity of national and regional requirements have complicated these objectives. Organizations are facing challenges to purchase products globally and at all level of supply chain. Moreover, suppliers are facing challenges in delivering varying products to multiple customers at varying expectations. To address these challenges, the Aerospace industry has established the IAQG (International Aerospace Quality Group) to enhance a significant improvement in quality during the production process. Part of the strategy to enhance quality management is the application of AS9100 that specifies the international standard for the product.

i: AS9100 -- Society of Automotive Engineers (SAE), Quality Management

The international standard specifies quality management systems to produce quality products that meet customer requirements and statutory regulations. AS9100 is a widely adopted standardized quality management system to enhance quality production in the aerospace industry. The AS9100 was released in October 1999 with the collaboration of the SAE (Society of Automotive Engineers) and the European Association of Aerospace Industries. The AS9100 replaces the AS900 and incorporates the current version of ISO900. Major aerospace suppliers and manufacturers are required to comply with the AS9100 as requirements of doing business. Typically, the AS9100 is to improve the effectiveness of quality management system to meet the customer requirements and satisfaction. Apart from AS9100, the aerospace organizations are also required to meet AS9103 requirements.

ii. AS9103 - Society of Automotive Engineers, Quality Management Systems - Variation

Management of Key Characteristics

One of the major objectives of the International Aerospace Quality Group is to establish common industry quality and requirements in the Aerospace industry. The primary objective of KC (Key Characteristics) in AS9103-Variation Management is to provide a common standard and expectation to be met within the aerospace industry. Typically, the Key Characteristics focus on the method to establish common requirements at all level of supply chain in order to improve safety and quality as well as enhancing cost reduction. The standard laid down by the AS9103 is to provide a uniform process for the documentation, control, identification and guidance within the Space, Aviation, and Defense industry.

The purpose of AS9103 is to enhance aerospace standard and driving improvement in the production and manufacturing process through effective management of Key Characteristics. The scope of the AS9103 shall be applicable to all production process in the aerospace industry and influence the variation of KC. Typically, AS9103 are designed for the following stakeholders:

Producers: Organizations that perform the process affecting manufacturing of the part.

Customers: Organizations that provides Part via purchase order, contract, engineering drawings, and specifications.

Process Control Document (PCD): This is a written document describing a manufacturing plan to control variation in the Key Characteristics.

1. Meeting the requirements of AS9103

The requirements of AS9103 are as follows:

Variation management activities should be performed on KC's.

Appropriate monitoring methodology shall be used to enhance continued performance,

Identification of lower level of KC's where necessary to control variation of KCs higher level,

Creating and maintaining appropriate documentation,

To establish process capability when KC is in-control.

iii. Statistical Process Control and Variation Management

Statistical Process Control (SPC) is a statistical technique used to enhance quality control of products to make products conform to the required standards.

"Statistical process control (SPC) involves inspecting a random sample of the output from a process and deciding whether the process is producing products with characteristics that fall within a predetermined range. SPC answers the question of whether the process is functioning properly or not." (Wiley 2009 P. 173).

In the aerospace industry, the SPC is an effective tool to control the KC. The following requirements shall be met by using the SPC:

1. The process capability index (e.g., Cpk and Cp) will be calculated only when the process is in standard control and shown to be stable using an appropriate control charts or statistical methods.

2. The process shall be specified by the customer and be capable when Cpk > 1.33). A Key Characteristic is considered capable, if its Cpk is equal or exceeds 1.33,

3. The characteristics shall be traceable to the specific product or part and have similar variability when similar key characteristics from different products are combined on the same control chart,

The statistical methods are used to justify reduced frequency of inspection. (Crossley, 2008).

In the manufacturing process, the attributes of data are collected as they are being produced, and by establishing upper and lower control limits, it will be possible to control the variations before parts' production leads to a defective production.

b. Background

i. Evolution of SPC

Walter a. Shewhart was the first scientist who pioneered the SPC at Bell Laboratories in 1920s. However, at&T along Harry Romig and Harold Dodge formed a team to develop a sampling inspection based on rational statistical basis. In 1934, the SPC was applied in the Army for the manufacturing of ammunition and control charts, and successful application of SPC made Army Ordnance to engage George Edwards to consult for the use of the SPC (statistical process control) in the Army departments.

Since 1970s, SPC has been applicable in the manufacturing industry to enhance quality of finished product. SPC uses statistical tools to identify the performances of production process in order to predict significant variations that may results in the production of sub-standard product. The SPC is also applicable to the post-manufacturing inspection, and each product is accepted or rejected based on how it meets design specifications. (Fontanares, 1997).

1.Key tools in SPC

The SPC has various tools in its application. Control chart is one of the tools that SPC uses to measure data.

a.Control charts

The control chart is a statistical control tool to determine if a business or manufacturing process is in a state of statistical control. The control chart involves measuring variations in the production process and control chart can differentiate common sources from "assignable" ("special") sources. Typically, common sources are part of the process, however, they are less applicable in the manufacturing than special sources. A control chart will indicate a process is under control if the process is stable.

b. Process Control Index

Process Control Index is the strategy to compare two or more process. The common index in the process control is as follows:

Pp = a simple and indicator of process performance,

Ppk = Process Performance Index,

Cp = Process Capability,

Cpk = Process Capability Index,

In the control chart, if the data is within the control limits, this shows that production process is operating as expected and any process falling below control limit will render the product non-standard.

c. And charts

Variable data control charts are used to monitor the mean, the process target and the process variation. Typically, the x-bar and R-chart are the common type of control charts, and the control centerline, and the standard deviation are the tools used establish x-bar and R-chart. The product standard should be within the centerline in order not violating the rules of control chart. (Yang, 2011).

ii. Variation Management

1.AS9103

AS9103 is a variation management that integrates the statistical process control in the KC. The AS9103 stipulates that the process is capable if Process Capability Index (Cpk) > 1.33 or as specified by the customer. Typically, AKC is considered capable in the production process if Cpk exceeds or meets 1.33. Moreover, the AS9103 integrates the control chart in the production process to reduce the occurrence of defective product.

The clause of AS9103 describes a "model that may be used in fulfilling the requirements of this standard and is presented for illustration and clarity. The model consists of several stages, starting with the definition of product/process related KCs and/or identification of CIs, whose control is achieved through KCs variation management, and ending with the monitoring of product manufacturing or maintenance process performance." (SAE Aerospace 2012 P. 8).

iii. Necessity of AS9100

In the aerospace industry, AS9100 has become a necessity for doing business because reliability is very critical in the aerospace industry. Minor mistakes in the production of goods and services could be fatal to the industry. Thus, quality management plays a critical role in the overall supply chain. AS9100 is an international accepted quality standard for suppliers and producers, and AS9100 has become a contractual quality standard for aerospace suppliers and manufactures. (International Organization for Standards, 2008).

ISO 9001 is also an international standard for quality management and provides organizations set of principles to ensure a common approach to quality management to achieve a customer satisfaction. Despite the benefits of ISO 9001 in enhancing quality performance in the production process, the ISO 9001 does not mandate statistical control process in the manufacturing process. However, the SPC has become a critical tool in the aerospace production to eliminate the variations that could lead to the production of a defective… READ MORE

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