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Not all DPMO the same

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  • #45762

    Sorour
    Participant

    Is there a standard for DPMO calculations on a manufacturing line?  I’m seeing differences on how people report defects and opportunities.
    For Example; a phone is made from a PCB and a housing.  The PCB of the phone has 100 components and has 350 joints.  The PCB is tested at an ICT machine.  The PCB is then assembled into a housing for the phone using 4 screws.  The phone is then functional tested using 20 different tests.  How do you calculate the entire process’s DPMO?
    Thanks,
    Paul.

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    #150255

    Iain Hastings
    Participant

    Paul,
    You’ve posed several questions here which I will try to answer in turn, however, it is not entirely clear to me what you are using DPMO for.
    First question: Is there a standard for DPMO calculations on a manufacturing line? The short answer is “No”. When DPMO is used, companies usually develop their own guidelines and then rigidly adhere to those guidelines. There are different philosophies as to what actually constitutes an opportunity. One school includes all “active” opportunities – things that are measured, another philosophy is to consider parts and connections only. Of course, how this is defined within different industries varies – for example stuffing a PCB with a 32-pin part might be considerd 32 opportunities whereas in a transactional process each data entry field may be considered an opportunity. As DPMO is often used as a measure of complexity and thus used to compare different processes/products it gets back to the point about consistency. Basically DPMO is dpu normalized for complexity.
    With respect to how you calculate the entire process DPMO:
    First, determine what constitutes an opportunity – remember you are not looking to create an opportunity for the sake of it but to use it for comparison purposes only.
    Second, map the process and determine the defect opportunities at each stage.
    Third, count the number of units through each stage and the number of defects.
    Fourth, calculate dpu at each stage and sum these dpu’s to get the total for the process. Similarly sum the total number of opportunities /unit for the process (simply the sum of the ops/unit at each stage
    Fifth, convert to DPMO by dividing the sum of the dpu by the sum of the opportunities per unit and multiplying by 1 million.
    Getting back to my original point though, unless you are using DPMO to compare items of different complexity it is not clear to me why you would go through the pain of developing guidelines. Knowing the yield at each stage of the process may be sufficient.

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    #150256

    Savage
    Participant

    IPC has two standards related to DPMO calculations:
    7912A & 9261A
    http://www.ipc.org
    Good luck.

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    #150263

    Airedale
    Participant

    Paul,

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    #150268

    Xao Ping
    Member

    DPMO is meaningless jargon.  It can mean anything you want.
    For example, how many opportunities are there for posting on this forum in a day ?
     

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