Evolving Quality Levels - Expectations for Lowered Defect Levels

Golfman25

Trusted Information Resource
#11
99.8% has been the required quality target for our biggest customer for years. Below that, you get lots of “help” from the customer and less new business. It is darn hard to meet, and it has taken lots of different tools for us to get there.

Part of the answer is forming good relationships with the customer’s QE’s that I have to deal with. With targets like this, every little bit helps, and if you are able to form a good relationship and are proven to be an honest and trustworthy person, sometimes you get the benefit of the doubt when the cause is in that grey area between “their fault” or “our fault” or “purge stock” or “no need”.

Also, just like your sampling plan, the customer will usually not detect every nonconforming part. If it is something minor like the flange on a part is .003” OOT but it still fits when the mechanic grabs the part to bolt it on, no one knows. Does that mean you can or should “slip in” those bad parts and try to sneek them past your customer? No! But in reality, no matter what way you measure quality, you are not likely catching every defect, and neither are the customers. What you measure is best-case.

And of course it takes good old fashioned, best-effort based on what you can afford to do and still stay in business, QA and QC practices. Take PA and CA seriously. Hire good people. Treat them well. Walk the talk.
If it is .003 OOT but stil works is it a defect? To me the biggest thing is over dimensioned parts.
 
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Bev D

Heretical Statistician
Staff member
Super Moderator
#12
If it is .003 OOT but stil works is it a defect? To me the biggest thing is over dimensioned parts.
An alternative perspective is that this is a 'fit' interaction. A part might be slightly out of spec on the large side and still fit IF the mating part is on the accomodating side of it's tolerance...

Of course, it could be a specification that is too tight

And I've seen specifications set too generously. I actually encounter this condition more frequently the other two above. The part causes failures in the end system, but is completely in tolerance.
 

Ninja

Looking for Reality
Staff member
Super Moderator
#13
<snip>.... The part causes failures in the end system, but is completely in tolerance.
I work in the multilayer electronics industry.

If a single plant going from raw ceramic powder, through forming, punching, shaping, printing metallization, stacking, lamination, singulation, firing, reduction, deburring, termination, buffing, testing, lead attach or pre-plating, to the end product...it is simply not possible to spec 100% output.

It is totally possible to have all steps "in tolerance" and have 0% yield.
The process, by nature, relies on one off-mean step to be balanced by a subsequent process off-mean the other way.

The best quality increase IMO was the automation of high speed 100% test.

It some days amazes me that product is ever made in spec....but it is, and a whole lot of it. The deeper you look into each of the process dependencies, the more awed (or terrified) you can become.

Zero defect without high speed 100% test is simply a ridiculous concept in this industry. (though folks still ask for it)
:2cents:
 
P

PaulJSmith

#14
Up until recently, I've worked nearly my entire career in electronics, Ninja. So, I completely understand the "awe" of things that probably shouldn't work ... yet they do ... somehow.

Zero defects is everyone's goal, of course. However, there are many situations where it's simply not reasonable to expect it 100% of the time.
 

Golfman25

Trusted Information Resource
#16
By the ISO definitions, no. But it IS nonconforming. Nonconforming product doesn't meet specifications. Defective product doesn't work as intended.
Fair enough. So if we are looking for zero defects = as long as it works?

Problem is many rejections are for non-conforming product not defective. Seems like a waste of resources to chase non-conformances for product which otherwise works fine. IDK?
 

howste

Thaumaturge
Super Moderator
#17
Fair enough. So if we are looking for zero defects = as long as it works?

Problem is many rejections are for non-conforming product not defective. Seems like a waste of resources to chase non-conformances for product which otherwise works fine. IDK?
That's why when your car has a problem you take it in for repair and not rework. All you care about is if it works. Rework is often more expensive.

ISO 9000:2015 said:
repair
action on a nonconforming product or service to make it acceptable for the intended use
ISO 9000:2015 said:
rework
action on a nonconforming product or service to make it conform to the requirements
If a design-responsible organization is proactive about saving money they should look at rejects and relax specifications where a part is just as functional with wider tolerances. However, there may be cases where a nonconforming part is functional, but with a reduced level of performance, so watch out...
 

normzone

Trusted Information Resource
#18
I work in the multilayer electronics industry.
It some days amazes me that product is ever made in spec....but it is, and a whole lot of it. The deeper you look into each of the process dependencies, the more awed (or terrified) you can become.

Zero defect without high speed 100% test is simply a ridiculous concept in this industry. (though folks still ask for it)
:2cents:
We're the folks that put your products in assemblies, and we do 100% burn-in and test, via combined manual and automated, and we still have component failures at this stage. Fortunately, assembly return rate for in warranty component failures runs under 0.5% for us.
 
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Bev D

Heretical Statistician
Staff member
Super Moderator
#19
Problem is many rejections are for non-conforming product not defective. Seems like a waste of resources to chase non-conformances for product which otherwise works fine. IDK?
Yes if the specifications are truly too tight, they should be changed rather than simply rejecting good parts.

However, in the case of mating parts the interaction of the part dimensions is what counts. the match up is typically random such that an out of tolerance part might fit fine with one part but not with another part...this is the dilemma of tolerancing mating parts.

Also as Howste alluded to, mating parts have an additional requirement regarding wear. they may fit today, but will wear and break tomorrow. this was the exact point of the famous ford-mazda transmission study and the original purpose of Cpk. (not the current abomination that tries to equate continuous data distributions to number of out of tolerance parts.

As miner said (in another post thread?) this line of discussion points out the real need to have better designs and more collaborative robust causal analysis when failures inevitably occur.
 

normzone

Trusted Information Resource
#20
Yes if the specifications are truly too tight, they should be changed rather than simply rejecting good parts. ... this line of discussion points out the real need to have better designs and more collaborative robust causal analysis when failures inevitably occur.
I wish everybody I worked with thought this way ...

:bonk:
 
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