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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