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

MasterBB

Involved In Discussions
#1
Is SPC still a value-added when 100% inpection are in place. 100% inspection may not catch or detect that the process in control. And also, the related discussion related to assignable causes etc.

I am looking for some feedback, discussion regarding the above.

Thanks in advance.
 
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bobdoering

Stop X-bar/R Madness!!
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#2
Re: SPC vs. 100 % Inspection.

Is SPC still a value-added when 100% inspection are in place. 100% inspection may not catch or detect that the process in control. And also, the related discussion related to assignable causes etc.

I am looking for some feedback, discussion regarding the above.

Thanks in advance.
As usual, the answer is "it depends."

If you can identify significant variables that - when controlled - will provide assurance of a stable process and - in some cases - assure process capability. You may catch bad parts with 100% inspection, but you may be able to prevent them with statistical process control. The value added, then, may be less scrap but - more intangibly but equally important - process knowledge.
 

Jim Wynne

Staff member
Admin
#3
Re: SPC vs. 100 % Inspection.

As usual, the answer is "it depends."

If you can identify significant variables that - when controlled - will provide assurance of a stable process and - in some cases - assure process capability. You may catch bad parts with 100% inspection, but you may be able to prevent them with statistical process control. The value added, then, may be less scrap but - more intangibly but equally important - process knowledge.
It does indeed depend. Use of any statistical tool proceeds with the idea that you're trying to understand the variation in the process and use the understanding to make predictions. If, for whatever reasons, you're not interested in that, then it makes no sense to do SPC.
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#4
Re: SPC vs. 100% Inspection - Is SPC still value-added when 100% inspection is in pla

another clarifying point to the aforementioned "depends": if you have SPC on the INPUTS, you have a much better chance of preventing those pesky failures. This will save time, money and productivity.
 
V

Vicman

#5
Re: SPC vs. 100% Inspection - Is SPC still value-added when 100% inspection is in pla

Hello MasterBB, analyzing your question I will try to understand first..

If I need to do a 100 % inspection that means that an operation or operations are having too much variability and there is a need to catch the parts that fail to meet the customer specs/requirements.
And if my actual controls are not enough to eliminate it, I need to use another tool, a SPC techniques besides my actual inspection sounds good.

But, in order to establish a SPC graph I need to bring the process under control first and eliminate the causes of variation.
This will add value to my process.

Note. - I was a supplier for GM several years ago, and our process team which I was part, got into the same question "100% inspection vs SPC",
That question arises when we were making the process control plan, so we start working in our process and learn from it and then improve it.
Meanwhile we kept the 100% inspection, until we were confident with our process. "We didn't want to ship bad parts in the mean time".
It was not an easy task but our final result was amazing.:)


I hope this will help (Sorry for any English error)
 
P

prototyper

#6
Re: SPC vs. 100% Inspection - Is SPC still value-added when 100% inspection is in pla

Is SPC still a value-added when 100% inpection are in place. 100% inspection may not catch or detect that the process in control. And also, the related discussion related to assignable causes etc.

I am looking for some feedback, discussion regarding the above.

Thanks in advance.
100% inspection is costly and is not 100% effective! The question is, understanding this fact, are you happy to continue indefinitely with 100% inspection? If so, why bother with SPC.

Alternatively, you can measure and improve your process. It may be that you need to review which features or parameters of your process you apply SPC to, if you are just measuring finished product the factors responsible for variation may be clouded among many others.

Analyse the potential causes of variation in your process and be selective about what you measure and where in the process. Use this information to drive improvement. As you start to control each causal factor you may find you can reduce or eliminate final inspection.
 
B

brahmaiah

#7
Re: SPC vs. 100% Inspection - Is SPC still value-added when 100% inspection is in pla

Is SPC still a value-added when 100% inpection are in place. 100% inspection may not catch or detect that the process in control. And also, the related discussion related to assignable causes etc.

I am looking for some feedback, discussion regarding the above.

Thanks in advance.
SPC is a tool in the hands of the operator and not the inspector.People should be properly trained to use it to conrol the process.In mass production industries like bearing and fastener industries SPC is most suitable.All most all quality gurus have endorsed SPC.
100 % inspection is sign of process incapability.The only way to win in the competetive market is to learn to use SPC.We have to learn from the japanese in this matter.
The doubts abovt the powers of SPC are mainly due to poor understanding of the basic principles of SPC and the technics of implementing SPC on the shop floor.
V.J.Brahmaiah
 
Last edited by a moderator:
V

Vicman

#8
Re: SPC vs. 100% Inspection - Is SPC still value-added when 100% inspection is in pla

First at all, you must ask yourself “Is my customer happy” with my actual controls or he is worry about receiving bad parts.
In order to use SPC, as I wrote before you must maintain your 100% inspection and work in your process as well.
I will suggest putting a team together with extensive process knowledge and work to improve this situation. You don’t need to go after every parameter in your process, if you use a good problem solving technique such as: 8 D’s, PDCA, etc. You team certainly will find the root cause(s). And then you can keep an eye on that parameter that drives your improvement by using SPC
 

DanteCaspian

Quite Involved in Discussions
#9
Re: SPC vs. 100% Inspection - Is SPC still value-added when 100% inspection is in pla

I am anti-100% inspection, well nearly. Fast pace automation with inspection with laser, camera, CMM, vision coordinate are essential at times.
In other cases, if I was a customer or the producer, or like in most cases, the consultant, my question is why is there so much effort on inspection? I am led to believe there is high variation an inadequate controls for producing a good part. In nearly every time I have consulted or observed 100% inspection, there is little QC inline and upfront, out side of the inspection. Inspection is not quality control, it is just inspection.
100% is less effective and efficient then the alternative of SPC with better processes. Better processes = better parts = less wasted labour = more time and energy to spend improving the processes.

Find your industries specific stats, your in-house specifics, and challenges; then attack with a well thought out SPC. You can start aggressive for frequency and then back off when all is proven with preventative measures in place. Use the PDCA cycle. That, in my experience has always been a winner and brought true quality control to processes-- with evidence.
Do that, and Juran would be proud.
Such an approach is bigger in scope, but far more rewarding.
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#10
Re: SPC vs. 100% Inspection - Is SPC still value-added when 100% inspection is in pla

Don't forget, you have special causes that can happen between sampling - and sampling may not catch it if it is intermittent. SPC is sampling - and has its limitations. So, even though your process is in control...100% inspection may be needed for certified output.

Doesn't say I like it...just a warning.

Also, you may need 100% inspection if you are using the wrong SPC - like X-bar-R for precision machining.
 
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