SPC vs. 100% Inspection - Is SPC still value-added when 100% inspection is in place?

[brahmaiah]

Originally Posted by howste

That's an interesting rule you've made up. I disagree. 100% inspection is justifiable in any industry based on risk and cost.

I have also said 100% inspection is justifiable in high risk industries like Aerospace and health.By advocating 100% inspection Are we not negating the teachings of (American)quality gurus who taught SPC to the world.
Every one knows Inspection is a non-value added process.
V.J.Brahmaiah

[Jim Wynne]

Originally Posted by brahmaiah

I have also said 100% inspection is justifiable in high risk industries like Aerospace and health.By advocating 100% inspection Are we not negating the teachings of (American)quality gurus who taught SPC to the world.
Every one knows Inspection is a non-value added process.
V.J.Brahmaiah

No, everyone does not know that. One of the things that grates on me is the old "100% inspection is only 80% effective" bromide. There's no empirical basis for it--it's just something that people regurgitate in order to avoid thinking about what they're doing.

SPC is about the economic control of processes. That's why Walter Shewhart's landmark book was called Economic Control of Quality of Manufactured Product. His idea, carried forward by Deming, was to (as Deming put it) "eliminate the need for mass inspection." Note that it doesn't say "eliminate the need for inspection." SPC isn't intended to try to make things perfect, or to eliminate all defects, which just isn't possible in the vast majority of cases. The need for inspection (100% or otherwise) should be reduced as far as possible, but to think that it's never necessary or that it's inherently undesirable in all cases is just wrong.

[Vicman]

I agree on Jim post, and I will add some information to that:

SPC, 100% inspection, and sample plans are some of the tools that are available to us, we have to decide which one to use and fit the best to our purpose of CONTROL.
There is always variation present in all kind of processes. In some cases we need to performance a hundred percent inspection or use SPC techniques, you know all depends.

For example:
“We cannot perform a 100% inspection in destructive or fatigue tests of products such as brakes or wheels” in this case we may use a Weibull distribution curve, as our statistical tool in order to estimate the possibility of a failure to occur.

“A crew from a commercial airline needs to go through a complete characteristic and parameters check list prior to take off” this is a valuable tool also.

Both methods are good is us to decide which one to use.

[mbehmazia]

Just adding my two cents. Unless I am missing something, let's take a step back here. With a question such as SPC vs 100% inspection, with that thought process in mind, let's just make 50% of our production all scrap! Don't laugh, why not? Heck, we are sorting it 100% right? Can you imagine such a thing? Always reduction in variation and prevention will win the day vs. detection imho. 100% sorting will not save lost resources such as time, money, material, etc. I am extremely curious on why such a question would even be asked unless you are in between stages meaning the cost of even sending one bad part to your customer could mean lost contracts, etc. !00% is great for a stop-gap measure however, imho, not the norm you want your organization to get use to and comfortable with.

[bobdoering]

Originally Posted by mbehmazia

Just adding my two cents. Unless I am missing something, let's take a step back here. With a question such as SPC vs 100% inspection, with that thought process in mind, let's just make 50% of our production all scrap! Don't laugh, why not? Heck, we are sorting it 100% right? Can you imagine such a thing?

The question was not 100% inspection OR SPC, it was if you are already doing 100% inspection, is it value added to do SPC, and we showed how yes, that is the case. SPC may take the 50% scrap situation - if that was the current capability - and reduce it if the technology was available.

Originally Posted by mbehmazia

Always reduction in variation and prevention will win the day vs. detection imho. 100% sorting will not save lost resources such as time, money, material, etc. I am extremely curious on why such a question would even be asked unless you are in between stages meaning the cost of even sending one bad part to your customer could mean lost contracts, etc. 100% is great for a stop-gap measure however, imho, not the norm you want your organization to get use to and comfortable with.

Yes, reducing variation - which SPC can do if performed correctly - is a good thing. But, it is physically impossible for SPC to assure 100% good product on its own. There are 2 reasons for this: 1) SPC is sampling, and 2) there are such things called "special causes". SPC attempts to control common cause variation. It has no control of special causes, and if they occur intermittently, the sampling will not catch them. If your customer has 0 defect requirements (and many do), SPC will NOT ensure 100% good product. Sorry...it is physically impossible. So, yes, an organization may have to get comfortable with it to meet customer requirements. Hopefully, it was built into the costing.

[mbehmazia]

Yes, mostly American manufacturers imho. If you have to "get use" to 100% inspection as a norm, again, imho, you should not be in that particular commodity in the first place. I am 100% American, born and raised in Michigan actually. "Getting use to"...100% inspection tells me about an organization's top management support. A cop out imho. Also, "vs" imho does mean one or the other. Of course all of us Quality professionals would never dream (or would hope not) only utilizing only one or the other Quality problem solving tool for any given scenario. My extensive travels have showed me one thing, among many, I would never hear such a thing in some other countries, meaning SPC vs. 100% inspection...all catching up with us now.

[Jim Wynne]

Originally Posted by mbehmazia

Yes, mostly American manufacturers imho. If you have to "get use" to 100% inspection as a norm, again, imho, you should not be in that particular commodity in the first place. I am 100% American, born and raised in Michigan actually. "Getting use to"...100% inspection tells me about an organization's top management support. A cop out imho. Also, "vs" imho does mean one or the other. Of course all of us Quality professionals would never dream (or would hope not) only utilizing only one or the other Quality problem solving tool for any given scenario. My extensive travels have showed me one thing, among many, I would never hear such a thing in some other countries, meaning SPC vs. 100% inspection...all catching up with us now.

Once again, the OP said he's already doing 100% inspection, and wanted to know if it would be useful to do SPC in addition to it, not in place of it. Unfortunately I'm not in a position of omniscience and can't see the OP's process and can't offer an opinion as to whether the 100% inspection he's doing is needed or not. There are times--all over the world and in many types of businesses--when 100% inspection is necessary and can't be responsibly done away with and this is despite mindless platitudes about 100% inspection being evil in every case.

[bobdoering]

Originally Posted by mbehmazia

Yes, mostly American manufacturers imho. If you have to "get use" to 100% inspection as a norm, again, imho, you should not be in that particular commodity in the first place. I am 100% American, born and raised in Michigan actually. "Getting use to"...100% inspection tells me about an organization's top management support. A cop out imho... I would never hear such a thing in some other countries, meaning SPC vs. 100% inspection...all catching up with us now.

I guess you missed the point about SPC not capable of ensuring 100% good product, didn't you? I guess "other countries" must be able to tolerate a quality level worse than 0 defects to never perform 100% inspection, or your experience is still too limited to have come across those industries that demand 0 defects elsewhere in the world. I know our suppliers from elsewhere in the world do 100% inspection, so I think your sampling holds some error...as sampling tends to do.

"Getting use to"...100% inspection has no relationship to lack of an organization's top management support. It has to do with the recognition that any sampling methodology can not assure 0 defects, and the organization is willing to protect their customer from defects. It can also be a fail-safe redundancy. With international shipments, it is generally cheaper to ensure with absolute certainty that parts leaving the firm are good before starting their journey on a boat. In that respect, it shows a significant top management support, willing to spend the time and effort to ensure quality product to their customer.

There may be things that are "catching up with us now", but 100% inspection is not it.