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Importance of Performing Gage Repeatability and Reproducibility (GR&R) before actual quality data collection Part 2

In measurement system analysis (MSA), we would like to accomplish accuracy and precision of the ,measurement data.   Accuracy can be achieved through performing calibration on the measuring device for variable GR&R and clear operational definition for attribute GR&R.  Precision can only be achieved through GR&R studies followed by improvement of the measuring process if the GR&R does meet the required standard.   Calibration and GR&R studies are completely different.  Some manufacturers tend to  mix up both calibration and GR&R studies.  There was once an established supplier show me a calibration record when I ask for GR&R studies report????!!!!




GR&R studies need to have a lot of data collection,  very often most suppliers or manufacturers choose to ignore conducting GR&R studies unless it is requested by customer.  After working with over 100 electronic parts suppliers,  most of them will jump straight  into actual data collection without bothering about accuracy and precision of their measurement system.  They did not realize that without GR&R studies there is no way to know if the data they are collecting is reflecting the actual process variation.  GR&R study is a must for new measuring device or after the device had undergo major repair or move to another location.   In some industries GR&R study is required in new product qualification where GR&R report should be included in First Article Inspection (FAI) Report.

Although measurement process is one of 6 process input (5Ms and 1E),  however it is NOT the actual variation from process input. The variation in measure comes from measurement process and not the product itself.  We would like to reduce variation contributed from measurement process to be a small as possible so that our observed data will show more actual process variation.  Ideally in variable GR&R we only want < 20% of total process variation come from measurement input per item 5.  Therefore if GR&R value is above the acceptable level then we must improve the measurement process. 




The correct method to conduct GR&R is also very important right from operational definition to selecting sample to interpreting the results.  For those who had already attended my training class before would know the proper steps to obtain accurate GR&R value.

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Without GR&R study we will never know if the data collected show is the actual process variation or measurement process variation.  There are cases where measurement process variation contributed more than 50% of the total process variation. In this case we will only need to improve the measurement process rather than the actual process improvement!  If the measurement data is not accurate and/or precise, it will lead us to the wrong action and conclusion.  We could do a lot process improvement to man, machine, method or material and yet the data does not reflect the improvement we made due poor measurement process. 

In summary we have to conduct GR&R studies with the purpose
  • Quantify the precision of the Measurement System
  • Check for measurement system integrity
  • Ensure our data from measurement data does NOT have error which cause us to make wrong decision

Therefore I hope that after reading this article,  my reader will make some effort to conduct GR&R studies before any process improvement initiatives to ensure that process variation is NOT contributed from measurement process. 

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