Can I reduce the Sample Size? Sampling check of more than 1,000 pieces daily

[YKT]

I've a question on AQL which I'll need help to decipher...

Let say I'm producing FMCG products, where within 1 day, I'll be producing quite a high number of products. Now, if my client imposed an AQL number, which requires me to do a sampling check of more than 1,000 pieces check per day, is there another way out, whereby I do not need to inspect 1000 pieces at one go, but still satisfying the AQL ?

What if I can prove my Cpk is good ? Can I escape from doing 1000 over pieces of inspection ?

My point is, is there a way of 'by-passing' the required number of samples in the sampling plan, for a given AQL ????

[Benjamin28]

Good morning YKT,

In regard to your question, yes there is another way out. When determining sampling size based on a AQL you take into consideration the "levels" of inspection.

"When it is necessary to determine an inspection level, a number of factors must be considered in order to optimize the cost/risk relationship. These are:

1.The operating characteristic (OC) curves to evaluate the technical properties of various plans.
2.The supplier's risk and discrimination afforded by various inspection levels.
3.Knowledge of the production process.
4.Process capability knowledge and past quality performance history.
5.Item complexity.
6.Cost and importance of examination or test, particularly when testing is expensive, time consuming or destructive.
7.Importance of the quality characteristics to be examined, that is, critical, major and so forth.
8.Analysis of consumer's risk."

http://www.sqconline.com/military-st...ansi-z1.4.html

This will let you tinker with the numbers a bit to give you an idea, I'm somewhat strapped for time atm so I will leave you with this for now and you can return with more questions if you need.

Oh I should add this is based on MIL STD 105E which is obsolete, use it only as an example.

[antoine.dias]

Originally Posted by YKT

I've a question on AQL which I'll need help to decipher...

Let say I'm producing FMCG products, where within 1 day, I'll be producing quite a high number of products. Now, if my client imposed an AQL number, which requires me to do a sampling check of more than 1,000 pieces check per day, is there another way out, whereby I do not need to inspect 1000 pieces at one go, but still satisfying the AQL ?

What if I can prove my Cpk is good ? Can I escape from doing 1000 over pieces of inspection ?

My point is, is there a way of 'by-passing' the required number of samples in the sampling plan, for a given AQL ????

On top of the comments from Benjamin :
Maybe you can talk to your client and proof that a sample check of 1000pcs is overkill.
Anyway, If you want to change a customer required item - talk to the customer.

Best regards,

Antoine

[Tim Folkerts]

YTK,

I can think of a few different approaches to your question.

As you say, if you have SPC data showing the process is in control and capable, you may well be able to get the customer to accept that data instead of sampling data. If fact, SPC is in many ways better than sampling.

As Benjamin said, adjusting the "level" is another option. To get a sample size over 1000, it looks like you might be at "Q" on the table - presumably 500,000+ pieces with the typical Level II inspection. If you went down just one step to Level I, the sample size drops from 1250 to 500. If you use one of the "special levels", you might get down under 100 for a sample size.

Another option would be to get the customer to agree to "reduced inspection". This would also drop you from 1250 pieces to 500 pieces for sample size.

One final option I can think of is to go to double or multiple sampling plans. Sticking with the typical "Level 2, normal inspection for 500,000+ parts = Q" plan, the multiple sampling plan lets you start with only 315 pieces. If the sample is good, you can quit there. The downside is you might end up having to check 2200 parts! Multiple sampling is good if the lots tend to be either quite good or quite bad.

Tim F

[Bev D]

are you measuring continuous data or is your inspection criteria categorical (pass / fail)?

is continuous there are many mor eoptions for a reduced sample size.

talking to your customer is always the best first approach....

[YKT]

Originally Posted by Bev D

are you measuring continuous data or is your inspection criteria categorical (pass / fail)?

is continuous there are many mor eoptions for a reduced sample size.

talking to your customer is always the best first approach....

thanks for all the replies. I am measuring variable data, i guess, this is what you call continuous, right ?


Anyway, some customers are still very stubborn, and i believe their understanding of AQL and sampling is quite limited as well. When they look at the MIL-STD sampling plan, and cross check on the lot size and the required AQL, they will be adamant to use the sample size, regardless of the size.

When they come in to audit, and found out we are not doing as per required, (taking let say 2000 samples for every lot), they will make noise and want to issue SCAR ! OMG !

These guys are pretty straight forward and they just follow the table....

How do I convince them ??? MY QC is screaming for doing a high number of sampling !!

[Bev D]

Originally Posted by YKT

thanks for all the replies. I am measuring variable data, i guess, this is what you call continuous, right ?


Anyway, some customers are still very stubborn, and i believe their understanding of AQL and sampling is quite limited as well. When they look at the MIL-STD sampling plan, and cross check on the lot size and the required AQL, they will be adamant to use the sample size, regardless of the size.

If you have "variables" data and your custoemrs are adamant about AQLs direct them to Mil Std 414 (now ANSI Z1.9). this is for variables data and allows for much cmaller sample sizes than Mil Std 105 which is for data that can only be judged as pass/fail. Both satisfy an AQL approach.

The other alternative is to propose a cost change that woudl pay for all of the inspection. Having the data to show that you have a stable capable process backs up why the large sample size pass/fail testing is not needed to ensure that you are meeting the requirements and that in fact the request for a specific type of test is a requiremetn of the contract itself. Money and data talk: the buyer at your customer can be your friend when it comes to unreasonable supplier quality folks...I have resolved many similar situations this way. (when the SQE won't listen to sound quality theory)

[YKT]

if I have a process with a proven consistent Cpk of 1.33 and above for couple of months, how can I related the Cpk reading to AQL ?

Technically Cpk will tell you the process capability, which in turn, if I sue the z-value table, I'll be able to determine the estimated number of product out of specs (or defects per million opportunity -just like in 6-sigma)

AQL is also a concept of giving confidence to the customer, saying that our process is capable of meeting a maximum defect per lot as agreed.

Thus, if I have a good Cpk, (which means I'm confidently churning out good products), technically it will be a good measure to tell them (customer) that they should have more confidence with my products, even without going through a stringent inspection (with a large number of samples !)

Anyway, the question is, how do i link or relate the Cpk data to AQL ?