Setting customer product specifications

Six Sigma – iSixSigma Forums Old Forums Finance Setting customer product specifications

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    I would appreciate your comments regarding your ways to set process specifications. It is often driven by customer requirements. However in my case our customer is asking us to give them some initial specifications as a starting point. 
    This is a new product that we have only 2 dataset available (~1000 data points total). My approach has been
    1. Analysed the data on a XmR chart. Deduced standard deviation from it (using XmR method not the pooled standard deviation since the capability analysis will be using the XmR method)
    2. Since this is a short data run, to get the likely long tern standard deviation I have timed it by 1.5 (used by many industries to estimate the long term stdev.)
    3. To get a capable process I would need a Cpk of minimum 1.33 using the long term standard deviation as point 2. 1/2 range will then be 1.5 x initial stdev x 1.33.
    4. After 30 runs to review the data. Analyse the 30 print runs on a XmR chart taking into account the large subgroup, review and validate the specifications and long term capability that way.
    Note: If I was to take the pooled standard deviation, times it by 1.5. Get 1/2 the range by timing it by 1.33 the specifications range would be significantly greater and way beyond what the customer is likely to accept. Would you still analysed the data using the XmR method? From our point of view that would be better, greater range, better capability. Any ideas?
    Your comments would be greatly appreciated.
    Many thanks



    If you would like, send me the 1000 data point as a single column, or the two groups of data separately, and I will propose specifications for you and tell you how I did it. Send it to me at [email protected].

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