AQL sampling bags of parts

[AFrazer]

We supply one of our customers with bags of 100 parts. The customers uses a sampling plan of AQL1.5 Inspection Level G2, the only thing is they are sampling by bag but then rejecting the delivery if a single part fails requirements.

So if we supply a delivery of 5,000 parts, they count this as 50 bags, sample 8 bags, and return the batch if 1 part fails.

To my mind, the sampling plan should be by part, so if we deliver 5,000 parts, they sample 200, and reject if 8 parts fail.

Obviously we want to reduce the number of failed parts that we supply and that is our focus, but I'd just like to know what the Elsmar community thinks about the method of sampling used and whether it is right or not?

 

[japayson]

Are you saying you don't think this customer is following their stated sample plan?
Is the sample plan part of the P.O.? That is have customer and supplier agreed upon this inspection plan?
It will be hard to tell the customer they are doing it wrong, regardless of the wisdom of methods involved. Researching this is a start, though.

 

[hogheavenfarm]

So you are saying they sample 800 pieces (8 bags) and reject on 1? With a 1.5% defect level they want no more than 75 defective pieces in 5000 parts. So 50 bags total might see 7 or 8 defectives? Doesn't sound right to me, but I am no sampling expert.

 

[Tagin]

According to this calculator, your expectation (200 sampled, reject on 8+) is correct:
What is the AQL (Acceptance Quality Limit) in QC Inspections?

It sounds more like they are using AOZ (accept on zero), not AQL.

 

[AFrazer]

Are you saying you don't think this customer is following their stated sample plan?
Is the sample plan part of the P.O.? That is have customer and supplier agreed upon this inspection plan?
It will be hard to tell the customer they are doing it wrong, regardless of the wisdom of methods involved. Researching this is a start, though.

You've hit the nail on the head, I don't think the customer is following their stated sample plan, the plan isn't part of the PO, isn't specified on the drawing and there is only vague reference to it in the Supplier Quality Agreement. It's entirely defined in the customers internal inwards goods inspection SOPs which they can change at will without our agreement.

I'm still keen to pursue it (carefully), the defect which they are checking for is low risk (cosmetic, low cost, 100% checked during assembly) and so logically shouldn't be subject to such an inspection regime which fails the batch for a fraction of a % defect rate.

 

[AFrazer]

According to this calculator, your expectation (200 sampled, reject on 8+) is correct:

It sounds more like they are using AOZ (accept on zero), not AQL.

Thanks Tagin, hadn't heard of AOZ before but it sounds exactly like what they are doing, I'll have a go at negotiating a change from AOZ to AQL with the customer, will need a bit of luck though!