iSixSigma

25 ppm

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  • #51890

    Rina
    Member

    Dear all,
    Im a QC staff. Our customer has stated they will accept defect max 25 ppm. How can i calculate 25 ppm? What should i do to get 25 ppm? Is there a method (like sampling plan) that would give me 25 ppm?I would appreciate any feedback/help from all.
    Thank you,
    Rina

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    #181552

    Mike Smith
    Participant

    Do what Bill Smith (the founder of six sigma)Β himself suggested :
    Broaden the spec limits !
    It allows you get any level of defects you want !!
    Sounds ridiculous but read Bill Smith’s IEEE paper …

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    #181554

    Scott
    Member

    Customer Issue: Need to achieve 25 ppm defect rate or lot will be rejected
    Terminology:Β  The words specifications and test limits are two different things.Β  In my work, the customer establishes the specifications.Β  From the specifications test limits are established.Β  The test limits are smaller than the specification limits.Β  For example
    Specifications = 10 cm +/- 0.5cmΒ  Γ  This implies that 25 ppm canΒ’t be improved unless the customer agrees to widen the specification limits.
    Test limits = 10 cm +/- 0.4 cm.Β  Γ  This requires an evaluation of risk to widen the test limits.
    Purpose of Test Limits: The purpose of the test limits is to guarantee (used loosely) that the out-going product meets the customerΒ’s specifications.Β 
    What Determines the Test Limits: Here are a few factors which can impact the selection of test limits when extremely small defects are required.Β  (1) Gauge capability, (2) correlation between production tools, (3) correlation between production measurements, and customer measurements, and (4) Cpk. Β 
    Perhaps you can think of other factors.

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    #181557

    jane doe
    Participant

    Your customer requires a level at their facility of 25PPM. This doesn’t mean that it is being achieved at yours. Your process may be, say, 2000 PPM…the customer does not care about this… only that they experience 25PPM max. Therefore, if your process can not be improved (and i gather it can) you are expected to take the alpha risk. The question is: How to protect customer from a process that yields (in this example) 2000PPM? Your organization needs to find those units that the customer is even now experiencing. This is an interesting point. I would start with examining the customers measurement system, and if it is no better than yours (assuming they are acceptable) then perform a ‘gauge agreement’ between the two methods. Then, improve your process via DOE (which I would do anyway). Gauge agreements are simple to perform, but the analysis of the results should be examined closely.A sampling plan won’t get you to 25PPM (at the customer location). Unless you are already there, 100% inspect is what the customer needs until such time where you can meet the expected level. A C=0 sampling plan does no good until lot sizes reach (about) 950 units. Therefore, the old AQL level with r=0 will afford greater protection (when those lot sizes are less than 950ish). What is gained is the reduced amount of units looked at. This will not relieve you of screening 100%, however.PPM is calculated thus:total rejects / total presented * (one million).Hope this helped.

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