This is perhaps one of the most useful CM4D graphs during an investigation or development phase, yet it is one of the most simple.Each feature on a component is individually evaluated and compared to the 6S standard of Ppk > 1.66. The graph shows the mean and plus/minus 3S as a blue bar with the existing main tolerance behind. It is therefore very easy to determine if the problem is an offset, (small blue bar that is high or low) or a process control problem (Large blue bar). The direction of error is clearly marked as Hi/Low or In/Out etc. So that adjustment can be made in the correct direction. The graph will calculate the tolerance band needed to achieve Ppk = 1.66 and show the values. The graph also evaluates the ”Normality” of the data and it’s correlation coefficient to a normal distribution (Abnormal data should not be used for offset calculation without further investigation as a few “outliers” could be causing the problem and these might be not representative of normal production).
Finally Each graph is colour coded. Green Graphs have already achieved the desired level of Ppk and no action is required. Red graphs have low Pp and low Ppk and have process variation issues in-depth investigation of the process is recommended. Light green graphs have good repeatability, but low Ppk. They also have data that shows as normally distributed. These features are candidates for simple tooling adjustment of maybe a tolerance offset. Orange graphs are similar to light green and might be candidates for offset, however the data shows as “abnormal” so further investigation of the data to identify and eliminate unusual measurements is recommended.
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Please contact us if you wish to try ATS CM4D in your plant.