Tag: aql

What types of defects occur most often during inspections?

Over the last three decades, we have inspected an innumerable amount of orders for clients looking to mitigate sourcing risk and uncertainty. As a result, one question we receive often regards identifying trends or commonalties among defects noted.

We asked two of our key team members in Ningbo, China what the most commonly noted issues during inspections include:

“Workmanship is the most common issue due to the variation.”  ~Cynthia Liu (Business Team Manager)

“Inconsistency in production.” ~Nick Chen (Technical Supervisor)

Although each product is unique, we are able to classify our observations by general industry. During inspections, defects are generally classified as major, minor or critical.  More on classifying defects here.

Common defects noted by industry includes:

3 Ways to Use Defect Data to Drive Improvement

Our quality engineers collect data from supplier locations all over the world, and we encourage our clients to get as much value as possible from our reporting to drive overall improvements and support successful supplier partnerships.

Consider the simplified example of conducting weekly pre-shipment inspections of one product at a single supplier site.  The information provided in the product specification determines the defects and whether they are major, minor or critical, which the quality engineer checks for on-site when evaluating the random samples.  An accept, reject or on-hold determination is made for each inspection based on the AQLs and other factors, but defect data can be tracked over time to add value over just the individual shipment result alone.

Here are three ways to get more from defect data:

1) Evaluate a check sheet or other data chart over a period of time such as the basic information below.

CheckSheetExample_Defects

DefectPercents

2) Visualize the information to observe and compare trends over any determined period of time.

Monthly_DefectData

3) Incorporate multiple suppliers to target improvement efforts at each location.  For example, is one supplier exceeding at meeting expectations in one or more areas where others are not?  Why? Use quality tools to further examine root causes and generate corrective actions.

SupplierComparisonThese examples only scratch the surface of what can be captured from quality inspection reports.  Each organization is unique and can determine how to select the data most relevant to goals and objectives.

The sampling app you’ve always wanted… ANSI Z1.4 2003 made easy

ansi_samplingPro QC’s team of technical engineers has developed an Android and iOS application that takes the guesswork out of the accept or reject determination of an on-site quality inspection depending on customizable major and minor AQLs (Acceptable Quality Limits). This application has been incredibly useful for our team on-site, in addition to many of our clients. For convenience, we also have a web-based application.

More on defect classifications here.

To learn more about ANSI Z1.4 2003 sampling, a previous article discusses the topic in more detail.

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.

 

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.