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Cp and Cpk values

floydl

#23600

Cp and Cpk values | 3 March, 2003

With regard to measuring dot diameter on my dispensers, is there an easier way to calculate the Cp and Cpk values? This manual data crunching is for the birds!

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#23610

Cp and Cpk values | 3 March, 2003

Hi floydl, I completely understand when it comes to data crunching after long hours of performing measurements, it's the last and most important arduous task in obtaining performance data. If a measurement and evaluation process that traditionally took from 4-6 hours can be reduced to less than one hour, would you consider it? You're probably using Excel's statistical function formulas to organize, massage and calculate the data to determine Cp and Cpk performance values. Most coordinate measurement machines can easily measure X/Y dot position but require more sophisticated software upgrades with algorithms that measure diameter. A system in use called the CmController makes X/Y and diameter measurements all in one field of view (FOV) and reports each dots deviation from its set point value across the entire glass plate for quick analysis of dispense parameters and positioning system accuracy and repeatability. The CmController software automatically calculates the statistical attributes of standard deviation, mean value and relates the values to the specification of the machine. The result is Cp and Cpk values that either meet or fail the machines intended operation specifications. Machines operating outside of specification limits can be expected to yield poor quality performance with potential defects such as oversized dots causing subsequent reflow defects, and missing dots causing missing component defects. Let me know if you require additional assistance. Thanks!

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EW

#23642

Cp and Cpk values | 4 March, 2003

I'm not sure to what degree you are manually crunching this data.....If you can set up the data manually, or parse the data from a recording function, to allow it to import into a database with a formula for Cpk, and everything else you could ever invent. This is easy, and it can handle large volumes of site specific measurements. The table data can be isolated and ordered if there is a sequence to be analyzed in a control chart.

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#23650

Cp and Cpk values | 4 March, 2003

Hello EW, thanks for your input, the data collection for measurements such as these can get confusing because you're calculating deviations from set point location to actual placement location and then analyzing the full result. Then there are many other influences that must be factored into the calculations such as how well does the resulting data fit the specification of the machine. Then, if we do our job well, we need to look at each opportunity that can effect a machines accuracy and repeatability. It becomes a lengthy process. I agree with you on importing and auto-calculating based on a formula, that certainly would save time. Let me know if you require additional assistance. Thanks!

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