iSixSigma

C = 0

This topic contains 6 replies, has 3 voices, and was last updated by  Cone 18 years, 6 months ago.

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  • #27132

    Cone
    Participant

    All of you posting questions about sampling plans ever stop to ask yourself if this fits with a Six Sigma mentality? Where are you using these sampling plans anyway?

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    #66046

    Joe Perito
    Participant

    C=0 fits nicely with the six sigma mentality. Statistics is the mathematical science of making predictions for the future, or, decisions in the present, based on historical data…. all of which is a “sample” of the “universe”. At no time can a company or service afford the cost of waiting until the horse race is over to place their bet. They must sample the field and make probability calls based on the data that they have available. At no time has anyone infered that they have developed a six sigma process by having actually tested the entire population.

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    #66052

    Cone
    Participant

    uh duh

    C=0 refers to acceptance sampling (you know like incoming inspection where we know we are better able to quantify quality than the guys we pay as experts to produce parts for us — also known as suppiers)

    The kind of sampling you are referring to called inferential statistics and no one is questioning the need for that.

    I go back to the original question.

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    #66054

    Ken Myers
    Participant

    Joe,

    I have to second Gary’s comment…

    Acceptance sampling is a REACTIVE way of CONTROLLING quality to the customer. While it has it’s place in the old Quality Control scheme it serves at best to complement Six Sigma methodology. There are some doubts today whether that statement is reasonable.

    Six Sigma methodology is a PREVENTION based approach of IMPROVING quality within the plant. Obviously, the customer gains in this action, but the supplier gains in addition.

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    #66064

    Joe Perito
    Participant

    Guys, where did I say that I advocate a sampling plan over quality planning? There are “always” suppliers that you must protect yourself against. And, there are numerous customers, that “dictate” that you must have a receiving inspection program with some rhyme or reason to the sampling you do. Sections 4.10.1 and 4.10.2 of the QS-9000 Standard “dictates” the use of a “Zero Defects Sampling Plan” and use of “incoming inspection”… and you “will” be audited on these requirements to maintain your certification. As long as you “have to”, the Zero Defects Sampling Plan is the best to use. If you need an economic explanation and/ or a statistical explanation of the C=0 sampling plan, just ask. I’ll be factual and polite.

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    #66066

    Ken Myers
    Participant

    Joe,

    With all due respect, in my experience of over 20 years working with suppliers the best protection is to work with the suppliers. I mean get out there and show them how to improve their processes so they can build better products for you and their other customers. In addition I also do one more thing, I provide compelling reasons why they should take ownership of their quality. For instance, if they don’t I will go somewhere else to buy my products. This is no different an action than if you were buying the products personally. You know, I’ve found this approach works! Long before there was a Six Sigma method I was developing good relationships with my suppliers to help them build better products for me. Again, with respect, just because something is stated in a standard doesn’t make it correct. While you may have to follow the standard for contractual obligations you don’t have accept it as gospel.

    On a side note, C=0 sampling plans are only economic to use when the average process defective rate is about 1/10 that of the AQL.

    Regards,

    Ken

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    #66070

    Cone
    Participant

    Joe,

    QS9000 does not require incoming inspection, it requires proof of quality.

    C=0 is eyewash, the probability of accepting a very high defect rate is huge because the OC curve are almost flat.

    Work with your suppiers to have assurance of quality. Work with your customers that would dictate incoming inspection to show them in is not necessary and to show them the huge economic impact and the detrimential impact on quality.

    Oh, by the way do the car companies expect to have to do incoming inspection on your parts? Or do they expect to take frequent deliveries and go straight to the production floor with them?

    Gary

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