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AS9100 and Sampling - ANSI ASQ Z1.4 C=0 Conflict

WCHorn

Rubber, Too Glamorous?
Trusted Information Resource
#1
Per AS9100C 8.2.4, ?When the organization uses sampling inspection as a means of product acceptance, the sampling plan shall be justified on the basis of recognized statistical principles and appropriate for use (i.e., matching the sampling plan to the criticality of the product and to process capability).?

Some SAE parts standards and material specifications used to call out MIL-STD-105, 1.5AQL, Level II, Normal sampling for acceptance. They adopted ANSI ASQ 1.4Z as its replacement. All?s well and good up to there. The groups that controlled the standards and specs then changed them expediently by just continuing to use the sample size from that standard but change the acceptance number (C) to zero. This is by far a more stringent requirement and I think not well thought out.

I have argued that that change created a conflict with AS9100C because it?s not justified on the basis of recognized statistical principles. For example, sometimes a 2.5 AQL will be more stringent than a 1.5 AQL because the sample size will be bigger.

What do you think? Conforms to AS9100C, or not?
 
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Michael_M

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#2
Re: AS9100 and Sampling - ANSI ASQ 1.4Z C=0 Conflict

As I understand it, when using sample inspection C=0 means that if you find a single defect then you must test 100% for that defect.

For example: An outside diameter of a shaft 1.000 +/-.005. As you are measuring your sample, if any one part within the sample measures (for example) .994 then the 1.000 diameter must be measured 100% on all parts before acceptance.

If I am not correct on this, please enlighten me.
 

WCHorn

Rubber, Too Glamorous?
Trusted Information Resource
#3
Re: AS9100 and Sampling - ANSI ASQ 1.4Z C=0 Conflict

As I understand it, when using sample inspection C=0 means that if you find a single defect then you must test 100% for that defect.

For example: An outside diameter of a shaft 1.000 +/-.005. As you are measuring your sample, if any one part within the sample measures (for example) .994 then the 1.000 diameter must be measured 100% on all parts before acceptance.

If I am not correct on this, please enlighten me.
You are correct; I don't see how that's germane to my question, though.
 
P

PeterWang

#4
Re: AS9100 and Sampling - ANSI ASQ 1.4Z C=0 Conflict

Hi WCHorn , I think you are right.In Automotive industry i meet the same problem.Actualy, i think the C=0 sampling plan is an idiomatic usage comes from OEM customer.The right C=0 plan should be MIL-STD-1916
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#5
Re: AS9100 and Sampling - ANSI ASQ 1.4Z C=0 Conflict

Mandating c=0 plans in general is not statistically rational
Some c=0 plans are statistically valid
Many are not. What you describe is not rational or statistically justifiable.

They certainly do not stem from 'recognized statistical principles'. They are mostly an ill-conceived slogan that panders to a well intentioned yet uninformed belief concerning the existance of a defect in a sample and the defect rate in the lot. This makes them popular and 'politically correct'.

Does it conform to AS? depends on your quality rep and auditor...and how much they buy into the mythology.

a fun read on the subject:
"Acceptance Sampling? The Enterprise Strikes Back! AS9100 c =0 Plans; when Slogans Supplant Science" by Joe Maciulla, Quality Engineering, Vol. 18, No. 2. (June 2006), pp. 237-266
 

Michael_M

Trusted Information Resource
#6
Re: AS9100 and Sampling - ANSI ASQ 1.4Z C=0 Conflict

You are correct; I don't see how that's germane to my question, though.
Sorry, I should have put in a :topic:or said something to the fact that I am asking an additional question. When I read your post, I must have mis-read or mis-understood. I thought you were asking something different and then I started questioning my own mind.
 
D

danielleecm

#7
hi, not sure if i am right here. AS9100 is probably a guide on the sampling requirements and its quite up to the QA in question to determine the criticality of the product inspected and its conformance to customer requirements.
Likewise, if the parts inspected is critical to the customer in terms of performance, C=0 should be reasonable.
By the way, why change from MIL-STD 105 1.5AQL to ANSI ASQ 1.4Z ? Can advise?
 
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