AQL Process (Acceptable Quality Level) Issues And Resolution

The commonly used AQL process (Acceptable Quality Level) approach to test incoming lots for quality has fundamental issues. The shortcomings of AQL need to be understood by those setting up the AQL product test requirements and those applying the results from incoming parts lots testing.

AQL Process Issues And Resolution

The PDF article below provides background information about AQL testing, its issues and resolution.

Near the end of the article it is stated: 

When we are examining an AQL process sample lot of parts, population statements are being made about each lot. However, in most situations, a lot could be considered a time series sample of parts produced from the process.

With this type of thinking, our sampling can lead to a statement about the process that produces the lots of parts. With this approach, our sample size is effectively larger since we would be including data in our decision making process from previous sampled lots. Scoping the situation using this frame of reference has another advantage. If a process non-conformance rate is unsatisfactory, the statement is made about the process, not about an individual lot.

The customer can then state to its supplier that the process needs to be improved, which can lead to specific actions that result in improved future product quality.

This does not typically occur with AQL process testing since focus in lot sampling is given to what it would take to get the current lot to pass the test. For this situation, it might end up being, without the customer knowing it, a re-sample of the same lot. This second sample of the same lot could pass because of the test uncertainty, as described earlier (in the article).

For the complete article text download the PDF through the link below

How to Resolve AQL Process Issues

The article discusses the need for assessing process stability and then reporting how the process (that produces the product) is performing.

A 30,000-foot-level report statistically assesses a process for stability (from a high level point of view) and then, for a stable process, report how the process is performing relative to its specifications. A 30,000-foot-level report-out provides an alternative sample reporting approach that addresses AQL process statistical testing issues.

In the 30,000-foot-level chart shown below, the process response “viscosity” is considered stable (left individuals chart has no point beyond upper or lower control limits). The probability plot (right chart) considers the data from the individuals chart as a “random data sample of the future” to provide the non-conformance estimate statement at the bottom of the chart.


AQL alternative report-out


With 30,000-foot-level charting as an alternative to AQL process testing, an organization can have its supplier electronically provide a 30,000-foot-level chart(s) of the output of a process that is producing its product. With process metric evaluations like the one above, the organization can then require that their supplier reduce the frequency of non-conformance from the process (if needed) via a process improvement project.

“Proof” that improvement was made from any process enhancement efforts is that the individuals chart (left chart above) transitions to an enhanced level of performance. To see an illustration of  this “process improvement demonstration” CLICK HERE.

Additional information about 30,000-foot-level charting is found in Chapters 12 and 13 of Integrated Enterprise Excellence Volume III.  How-to improve a process and control the process to maintain its gain is found in other chapters.


AQL issues resolution book


The concepts above can also be expanded to the overall business via an Integrated Enterprise Excellence (IEE) Business Management System.  IEE addresses the business scorecard and improvement issues described in a 1-minute video:


AQL video


Automatic 30,000-foot-level reporting is available through the Enterprise Performance Reporting System (EPRS) software.  This software could be used as a communication tool between supplier and customer relative to the output quality of processes that are producing their products; i.e, the processes’ 30,000-foot-level metrics.


Contact Us to set up a time to discuss with Forrest Breyfogle how your organization might gain much from an Integrated Enterprise Excellence (IEE) Business Process Management System and its enhancement to traditional AQL process testing.


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