Tag: inspection

Which AQL do you choose?

One of the most frequent questions we receive regarding on-site quality inspections relates to selecting AQLs, or Acceptable Quality Levels.  AQLs represent the maximum percent defective that you consider acceptable.

Pro QC’s Assistant Operations Manager in China, Cesar Marsical, address the question below:

The selection of AQLs and sampling plan for a given lot size depends on too many factors to permit the issuance of a “pre-selected” standard set of plans for specified lots. Each user should select AQLs and sampling plans that are tailored to best meet their needs.  Pro QC can assist with this process.

Some of the factors that must be considered prior to selecting the AQLs are:

1) Classifications or categories of defects such as Critical, Major and Minor – Critical defects would generally require zero defects, which means the highest AQL value should be imposed.  Major defects would generally require a lower AQL than those for minor defects.

2) Process capabilities under good commercial practice with respect to the defects in question – For example, if under normal production process, the defect levels cannot be kept below 2.0 percent defective, the selection of an AQL of 0.15 percent defective, although desirable for the defects in question, may not be practical.

3) Consumer preferences – These may require higher AQL’s or permit lower AQL’s than process capabilities would indicate.

4) Time and cost required to sample and inspect a lot under various AQLs – The smaller the AQL, the more time and cost of inspection.

Some of the factors that may be considered prior to selecting the sampling plans for a given lot size includes:

1) The applicable AQLs – The AQL dictates, among other things, the smallest sample size that can be used and the size of the “jumps” from one sample size to the next larger one.

2) The relative ability of the plans to discriminate between “good” and “bad” lots. – Although several plans in these standards have the same AQL, they differ in their ability to reject lots worse than the AQL’s. The OC (Operating Characteristics) curve in the standards of this subpart provides the basis for determining the discriminating ability of each plan.

3) The amount, time, and cost of sampling required.

4) The size and value of the lots relative to the producer and consumer protection a sampling plan affords.  One may be willing to take larger risks of passing “bad” lots that are small or of lesser value than they would for larger more valuable lots.

5) The knowledge about the lot(s) to be submitted for inspection – Lots consisting of product produced under essentially the same conditions may require smaller sample size than those consisting of product produced by different shifts and different raw stocks for example.

6) The record of the quality level of previously submitted lots – The sample size can be smaller for lots submitted from a supplier with a consistent record of quality levels significantly better than the specified AQL(s) than sample sizes for the supplier whose records shows considerable variability in quality, “borderline” supplies or products worse than the AQL.

Based on the above, decide what quality levels you are willing to live with and what quality level that you are not willing to live with.

Contact us for more info, or assistance with this process.

 

Why inspect? What are the benefits?

This is one of the most frequent questions we receive, and it’s often a hot debate at quality industry events as well.

At the end of the day, inspecting product for quality prior to shipment does the following things:

  • Verifies that product specifications are being met and avoids unnecessary reengineering work later
  • Confirms important quantity verification
  • Checks packaging integrity to avoid costly damage during transit
  • Reduces overall quality risks and cost

I am unable to recall a client where the total cost of inspections wasn’t covered by one or more quality issues preventatively called out prior to shipment.  The benefits exceed the investment and are a valuable component to the overall quality assurance process.

For more information regarding Pro QC’s inspection services, visit our website.

Evaluating inspection reports

Many companies anxiously await product quality inspection results and focus on the “accept” or “reject” status alone.  However, it is important to note that useful information exists within the details that are worth examining.  Here are a few things that should be considered:

Defect Trends – An accepted inspection doesn’t mean that no defects were noted.  It just means they fell within the AQL (Acceptable Quality Limit).  Maintaining a spreadsheet of defect data can help identify trends and areas of improvement.  Using the idea of 80/20 (Pareto), continuous improvement efforts can be targeted at defects contributing 20% of the total, with the expectation that an 80% overall improvement will result.

Packaging Variance – If packaging details are not provided in the product specification, the inspector will report the findings and use the package integrity testing (ISTA drop-test) to determine if there are any issues.  However, it is useful to note variations in packaging when they exist.  Digital photos and metric information is included within the reports.

Product Specification Revision – As inspection reports are issued and findings evaluated, changes to the product specification should be made as a continuous improvement effort.

For additional information regarding understanding the inspection process, click here.

 

Your quality questions answered

We’ve  answered many of our most commonly asked quality questions in our newsletter.  As a recap, here are the most popular:

What happens during a pre-shipment inspection?

What is a “drop test”?

How do you address the issue of a supplier that has the desired capabilities but is inconsistent in quality performance?

What is root cause analysis?

What is life cycle testing and how is it performed?

What is the difference between a continuity test and a hipot test?

Visit the Pro QC website to subscribe to the quarterly newsletter. And, let us know if there are any questions you would like to see us include!

Classifying defects… Is it major, minor or critical?

One of the most common questions we receive regarding inspections is how defects are classified.

The most important component of product quality is knowing your product.  And, that requires detailed product specifications that identify exactly how the item(s) should turn out.  Product specifications should also include defect details with classifications that later link to accept/reject determinations during QC checks.  Defects can be anticipated, but the list should evolve through observation and consumer feedback.  Metrics, as always, are incredibly useful here where continuous improvement is concerned.

Each defect is generally classified as either major, minor or critical.  At Pro QC, we use the following general descriptions:

Critical – Any condition found which poses the possibility of causing injury or harm to, or otherwise endangering the life or safety of, the end user of the product or others in the immediate vicinity of its use.

An example of a critical defect might be a sharp plastic bur that has potential to scratch or otherwise harm people.  The AQL (acceptable quality level) is generally 0.10 here so any critical defects noted would result in a rejected inspection.

Major – Any condition found adversely affecting the product’s marketability and sale-ability or adversely affecting its required form, fit or function and which is likely to result in the end user returning it to the source from which is was purchased for replacement or refund.

An example of a major defect might be a large (1.5″ or larger) scratch on the exterior front of the product.  The AQL is generally tighter for major defects noted, so less is acceptable in a general sample size to achieve a passing result.

Minor – Any condition found which while possibly less than desirable to the end user of the product, does not adversely affect its required marketability, sale-ability, form, fit or function and is unlikely to result in its return to the source from which it was purchased.

An example of a minor defect might be a small (up to 1.5″) scratch on the bottom of the product. 

Pro tip: The more specific the product criteria is, the less subjective the nature of the defects.  Providing photos as examples is particularly useful.  Tracking defects and noting areas for improvement when trends are identified helps improve the overall manufacturing process and end-use value to the consumer.