Recently I got 4 messages from buyers who asked me to clarify what an AQL inspection guarantees and what it doesn’t guarantee.
The problem is, explaining the concept of the AQL (Acceptance Quality Limit) isn’t simple.
Here are two samples of questions (rewritten for clarity and brevity).
Q: We paid a QC firm, they found variety of defects below the AQL limit of 1.5%. Then we found that the proportion of defects was above 1.5%. The QC firm said they’re only liable for the cartons they inspected. Is it normal?
A: No the QC firm shouldn’t say their findings are only applicable to the cartons they inspected. That’s unprofessional. they ought to say it’s perfectly possible that, sometimes, the proportion of defects within the whole batch are going to be above that among the samples they checked.
But in fact , no QC firm will accept liability above 10 or 15 times what they were purchased their service, for a random inspection.
Q: We buy from a Chinese supplier, and that we conduct AQL inspections with a limit at 2.5%. But our customers, in our country, complain as soon as they find a couple of defects. what’s an easy definition of the AQL that I can give to them?
A: The definition of AQL because the “quality level that’s the worst tolerable” comes from the ISO 2859-1 standard.
Here is my simple definition: “I want no quite 1.5% defective items within the whole order quantity, on the average over several production runs of that one product and thereupon one manufacturer” means the AQL is 1.5%.
But, from experience, the AQL may be a concept too time-consuming to elucidate to your customers. Heck, 99% of importers don’t even understand that idea correctly!
You are more happy doing two things:
1.Looking for good manufacturers, and setting the AQL as low as realistically possible. Let’s say 1.0%.
2.Taking a margin of safety: watching the “consumer’s risk quality” table, and supported your usual sample size (let’s say 200 pcs), you’ll only promise to your customers that there’ll be but 4.6% of defects in 90% of cases.
Is that scary? 4.6% of defects, or more, about 10% of the time?
Yes it should be scary. But that’s how the AQL works.
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