M
MSA studies results in a %GRR value plus a bias-estimate etc. This can be translated into: The measurement process uses a percentage of the total tolerance you are verifying. The amount used by the measurement process is often denoted "U" when normal spread has been calculated .
Therefore you should only approve the part you are measuring if the result falls inside the specification limits minus "U" on each side of the interval (if bias is also considered, you could add this to the GRR or correct your measurement results systematically....).
This leads to questions like:
If the product has been produced for years before the MSA-study was done, we have actually approved parts measuring: tolerance+ (2x"U"), so should we then increase our tolerance limit with 2 x "U" (a "U" at LCL and UCL), and proceed approving parts inside "old" tolerance limits (new tol.-2x"U")?
Or should we only approve parts within: tol.-(2 x "U") and then exspect higher rejection rates?
If it is a new product and say the %GRR = 20 for a tolerance interval 10-20, could we then approve parts that measures 12-18 (having subtracted 20% of 10 from each side of the interval, not considering bias etc.)?
Have you any inputs on this?
How do you handle the measurement uncertainty in practice with regards to verification of parts?
It is mainly the "political" issues regarding introduction of MSA-studies and there results in a product verification process and in running production, that concerns me.
Therefore you should only approve the part you are measuring if the result falls inside the specification limits minus "U" on each side of the interval (if bias is also considered, you could add this to the GRR or correct your measurement results systematically....).
This leads to questions like:
If the product has been produced for years before the MSA-study was done, we have actually approved parts measuring: tolerance+ (2x"U"), so should we then increase our tolerance limit with 2 x "U" (a "U" at LCL and UCL), and proceed approving parts inside "old" tolerance limits (new tol.-2x"U")?
Or should we only approve parts within: tol.-(2 x "U") and then exspect higher rejection rates?
If it is a new product and say the %GRR = 20 for a tolerance interval 10-20, could we then approve parts that measures 12-18 (having subtracted 20% of 10 from each side of the interval, not considering bias etc.)?
Have you any inputs on this?
How do you handle the measurement uncertainty in practice with regards to verification of parts?
It is mainly the "political" issues regarding introduction of MSA-studies and there results in a product verification process and in running production, that concerns me.