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Weight Error (Shortage) added in to PPM

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  • #27674

    Murali Manoharan
    Participant

    We are an automotive ancillary unit specializing in precision turned parts. Our products goes through a number of stages. During each stage, we give an allowance (-1%) due to weighment error. Should this 1% be added in the PPM calculation because it is a loss to the company or can it be ignored for this calculation as it is not something due to process inefficiency?

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    #68099

    Niraj Goyal
    Participant

    Hi,
     
    The important point in your case is that it is a loss to the company. This “buffer” is kept because of the quality variability you think or have measured that you have.
     
    I think it will help your company to put this as  defective quality – the cost will then drive you to cut variability, saving money and improving quality simultaneously.
     
    Niraj
     

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    #68116

    Dewayne
    Participant

     Murali, I would not add this amount to the PPM, as it is a management decision to compensate and not a measure of nonconformity. The decision to make “extra” parts may be based upon potential variance of normal conditions, and such compensation may be wise. The weight count variation factor may be due to the effect of normal variances, material weight variation, or weight scale variation, and ending up with additional inventory may not be a problem at all, whereas having to make one additional unexpected part might easily result in non-profitable production versus profitable. If “extras” end up in stock, maybe the compensation factor can be eliminated, even though this is not the desirable position that you want to be in.. 
     
    The correct answer is to have sufficient control within each process that the  compensation is not needed, and that should be your primary objective in eliminating the need for the adjustment factor, but until you can get there, the decision for the extra part may be necessary, and is more likely to be a result of inadequate management than a reflection of nonconformity.  – Dewayne   

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    #68127

    b.balagopal
    Participant

    Any error is a loss? Instead of declaring a flat 1% one needs to look scientifically as to what are the weighment systems you are having. Then go through the catalogue of these instruments to see to what accuracy the system can measure.Calibrate the instruments and set to get the designed accuracy of the system. If you do not get the designed accuacy then the gap can be termed as a loss and improvement efforts needs to focus on it.Now in case it meets designed accuracy one needs to work out the cost benefit analysis of more accurate system to prevent the intrinsic loss due to design. There is a thing called drift as far as instruments are concerned. If you calibrate at a reasonably close frequency one can calculate loss due to drift and plug loss by setting weighing system more frequently

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