AQL Sampling



Quality professionals use AQL sampling to determine the acceptance or rejection of inspection material. Inspection material can be raw goods, purchased parts, inprocess production, final goods and services, pre and post shipment parts, etc. Inspectors depend on AQL plans to determine the amount of parts to inspect.

AQL stands for “Acceptable Quality Level”. AQL is the poorest level of quality for the process that you would consider acceptable.

Stages of AQL Sampling

  1. First select the appropriate industrial sampling plan.
  2. Determine the AQL %
  3. Decide the sampling plans parameters
  4. Establish the sample size, accept and reject criteria
  5. Randomly select the parts.
  6. Inspect each part for the given feature(s)
  7. Accept or Reject the remaining parts.

Snap Sampling Plans!

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Do you...

  • Inspect parts, items, material?
  • Need an AQL sampling method that supports your inspection activities?
  • Want to quickly apply the correct sampling method based on your production methods?
  • Want to swiftly determine the correct sample size, accept and reject criteria for your inspection?
  • Think statistical sampling plans are difficult, confusing or complicated?
  • Need to check your company's sampling plans for the correct application?
  • Make up your own sampling plans?
  • Need to learn about a specific sampling plan because of your customer requirements?
  • Want to improve your Quality Systems?

If you answer yes to any of the above questions then you need Snap Sampling Plans!

Videos and pictures of Snap Sampling Plans!

Many companies use the wrong inspection AQL sampling plan because managers, engineers, supervisors and inspectors have not been trained in statistical sampling. Because of this, they may create their own deficient sampling plan. Or they may use a known industry standard plan without fully understanding that standard’s purpose or methods. When this occurs, they put their business and their customers at risk. In addition they waste valuable inspection time and inspection cost. Don't let this happen to your business.

Snap Sampling Plans! software combines all the key industry standard attribute sampling plans into one place. Because there are over 10,000 sampling possibilities, you need this software to eliminate the confusion. Snap Sampling Plans! guides you in selecting the correct AQL sampling plan.

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Snap Sampling Plans lets you eliminate the confusion between

  • Continuous Production vs. Lot Inspection
  • Zero Acceptance vs. Standard Acceptance Inspection
  • Critical vs. Major vs. Minor Inspection
  • Receiving vs In-Process vs. Final Inspection sampling
  • Defect History vs. No Defect History Inspection
  • Destructive Testing vs. Non Destructive Testing
  • Different Inspection Levels
  • Different Inspection Types

With Snap Sampling Plans!, you answer a few yes / no questions and then you provide your desired AQL and lot size. As you answer the questions, the software details advantages and disadvantages to your choices. Snap Sampling Plans! then produces one specific sampling plan that matches your specific needs.

For intermediate users, you can easily select your desired industry standard. Input your desired AQL and lot size. Instantly you have your sampling plan report with sample size, accept and reject criteria.

If you’re an advance user, you can compare the AQL sampling plans. Input your AQL and lot size, Snap Sampling Plans! provides the possible sampling plans from all of the included industry standards. This valuable tool lets you research, compare and select a plan that works best. With this tool you may decide to change your production method or inspection method to a better fit. With this info you can save your company significant money because it helps you design lean inspection and production.

Snap Sampling Plans! incorporates the attribute sampling standards from Mil Std 105 / Ansi Z1.4, Dodge Romig, Mil Std 1235, Schilling Zero Acceptance, and Squeglia Zero Acceptance Plans.

As a bonus, with purchase of the software, you will receive copies of the non copyrighted standards for your review. Linked instructions for purchasing the copyrighted standards are also included.

Your Satisfaction is Guaranteed.

Within 30 days, if you are not satisfied with Snap Sampling Plans!, I will refund your money.

Snap Sampling Plans! is only $49

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(Created by Quality Assurance Solutions)


Selecting the Sampling Plan.

Probably the most difficult step of the sampling stages because selecting the correct AQL sampling plan depends on your situation. Are you inspecting parts for receiving inspection? Are you monitoring production? Do you know the history of defects for the material? Are inspecting for safety issues? Do you allow for defects during sampling?

There are many statistical AQL sampling plans. Authors established these plans based on different situations. Some plans were written for lot inspection, while some for production inspection. Some plans focus on safety related issues, while some cover major and minor features. Some plans allow for reduction of inspection when defect levels decrease, some don’t. Some plans allow for defects (or inspection mistakes), some don’t.

Because of the complexity, there are college level courses that cover sampling theory. These courses detail the major plans and elaborate on the AQL tables.

Fortunately, you don’t have to take a college course to learn this material. Snap Sampling Plans! quickly lets you select and apply the correct AQL sampling plan.


Determine the AQL %

AQL stands for “Acceptable Quality Level”. AQL is the poorest level of quality for the process that you would consider acceptable.

You establish the AQL % depending on the feature that under inspection. If the feature has high importance, you will select a lower AQL. AQL percentage can be as low as .01% and the highest AQL can be 10%. You select a number in between these two.

In many cases, your customer already determined the AQL. To find this information, check the customer drawing or contract.

Sampling plans provide tables with multiple AQLs. In general, each plan has a given limit of AQLs. The AQL table shows one column with the AQL percentage and another column with a code letter that represents the lot size. In some cases these can be hard to interpret because you may need to refer to multiple tables to actually find the exact sample size.


Sampling Plans Parameters

Since the authors wrote each AQL sampling plan to cover a given inspection situation, each plan has different parameters. Two of the common parameters for each plan is AQL percentage and lot size. Other parameters include defect percentage, sampling level, inspection level, and inspection type.

Without reading the standards or receiving training, the parameters can be confusing. Again Snap Sampling Plans! simplifies the selections for the users.

Within the standards, for each different parameter, there are different tables. When changing the parameters, you increase the time to find your inspection sampling plan. Open the standard, review table A which takes you to table C which takes you to Table D. Find your inspection criteria on Table D. Changing parameters is very time consuming. Snap Sampling Plans! software fixes this.


Establish the Sample Size, Accept and Reject Criteria

The main reason that the authors wrote each plan was to determine the sample size, accept and reject criteria. After finding this you are done with the standards until the next inspection.

The sample size number tells you how many parts to pull from the lot.

The accept number tells you the maximum allow number of rejects within that sample to accept the lot.

The reject number tells you the minimum number of defects within the sample to reject the lot.


Randomly Select the Parts

Select the parts randomly from the lot is critical to making a sound decision on the lot. If you pull the parts off the top of the pile for the inspection sample, this is not random inspection. In this case you are pulling parts from one moment of production time and that moment does not represent the entire production. Random means that the sample comes from an unknown origin. There are many tools that generate random numbers. Many calculators have this built in feature.


Inspect Each Part

After you select the inspection sample you then inspect the parts. As you inspect the parts, you separate the good parts from the bad parts.

You record the number of good parts and the number of rejects.

You may be inspecting multiple features or characteristics on the parts. Depending on the feature importance, you may have different AQLs or Inspection parameters for each feature. This is difficult to master if you are relying on reviewing the industry standard for each feature. If you’re doing this, try using Snap Sampling Plans! which makes multi-feature inspection easier.


Accept or Reject the Remaining Parts

Based on your accept / reject number and the end results from the sample inspection, you decide whether or not to accept the material.

If the number of defects is less then or equal to the accept number you accept the parts. Move the parts to the next step.

If the number of defects is greater or equal to the reject number you reject the parts. Segregate the lot and issue corrective action.


After reviewing this page on AQL sampling plans see this for more info on the sample size calculator



Quality Assurance Solutions
Robert Broughton
(805) 419-3344
USA
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