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  • #43852

    ian Lock
    Participant

    Can anyone help me. I am recording the number of blow holes in an automated weld process. There are 4 idnetical machines so I have a measure of number of blow holes per machine  / shift. I have constructed box plots to look at the spread but am a little stuck as to where we go next. Which hypothesis method should i be using.

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    #139660

    BTDT
    Participant

    Ian:We had a similar welding project and found that we had to be really clear on the operational definition of a ‘defect’. Once you have tackled that, then make sure that the number of defects is gathered in a standardized way that means something. In other words, take into account differing amounts of downtime and feed rates for each machine otherwise I could decrease the number of blow holes by shutting the machine down for an hour or so.In order to show the significance of the differences, you can do a Chi-square/proportion test on the number of defects per unit whatever.You will likely get a number of posts suggesting control charting the process. Depending on whether the feedrates are constant and identical, you should consider one of the four types of attribute control charts to monitor the process.Cheers, BTDT

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    #139793

    k.bhadrayya
    Participant

    Dear Ian
    First be clear about the purpose of measuring the number of blow holes / machine /shift of 4 identical machines. Is the purpose is to find out the best performing machine out of  4 mchines ? or the purpose is to reduce the number of blow holes for a better weld. with out clear objective application of hypothesis does not yield any thing. Based on the objective the techinique can be decided.
     
    K.Bhadrayya
    [email protected]

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