Being Smart About Parts

Abstract:This article explains how to effectively deal with some of the time and cost constraints that may be encountered when a measurement system assessment study is conducted. These constraints may restrict the number of parts and repeated measurements that can be used in the study. However, we want as precise an estimate of the true repeatability and reproducibility (R&R) as possible. By incorporating freely available production measurements (baseline data), we can reduce the number of parts in the study to two or three and still obtain a better estimate of the R&R than we would have otherwise. To avoid bias, we must ensure the baseline data reflect the current manufacturing and measurement processes. In the analysis, we assume the process and measurement system is stable for the time interval that covers both the baseline data and the gage R&R study. To address this issue, the article recommends checking for stability in the baseline …

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I believe when calculating the final R&R percentages you should be using variances not standard deviation. In the first example (5 parts/6 repetitions) the % R&R would be 6.95% not 34%. Even without baseline data the GRR results are acceptable I believe.

Richard DeRoeck
--Richard DeRoeck, 04-14-2015

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