1. Before conducting Process Capability or Machine Capability studies, or implementing Statistical Process Control, to ensure that the measurements used are reliable indicators of the process or machine output.
2. When analyzing control charts, to reduce common causes of variation or investigate potential special causes of variation due to gage error.
3. To compare different measurement equipment and/or fixturing.
4. To qualify operators proficiency on specific measurement equipment.
5. To qualify specific measurement equipment for meeting customer requirements for specific product.
When conducting a Gage R&R Study, it is imperative to use production parts, or parts that are similar to production parts (such as when performing pre-production evaluations). You must not use reference standards, since the ability of the measurement system to precisely measure the standards is not a good indicator of whether the system will precisely measure parts in production. Remember the purposes of the measurement system: to evaluate the suitability of given product for release to (internal or external) customers, and/or to evaluate the stability (i.e. statistical control) and capability of the process producing the parts.
Using production parts allow us to include error associated with measurement fixturing (used to hold the part or gage during measurement), as well as variation within the production pieces themselves. Each of these generally contribute to increased Repeatability errors, since all the operators contend with these problems. However, it might be that select operators have improved techniques for dealing with the poor fixturing or the within-piece variation, so that their Repeatability error is less than the Repeatability from other operators. Recognizing this, when it occurs, can lead to system improvements.
Of course, these techniques are not limited to mechanical inspections, nor to material parts. They can also be applied to optical inspections, chemical analyses, or any other measurement system. In chemical analyses, sample preparation may be a critical component of the measurement. Just as we use production parts above, this preparation should be done using actual product, so that sample preparation is done using ÃƒÂ¢Ã¢â€šÂ¬Ã…â€œreal-worldÃƒÂ¢Ã¢â€šÂ¬Ã‚Â conditions.
Gage R&R Studies are conducted by obtaining a sample of parts, and having representative operators inspect each part (called a piece) multiple times (each inspection is termed a trial). A typical study involves having 3 operators measure 10 pieces 3 trials each. The number of pieces, operators, and trials can vary from case to case, but we need multiple trials to estimate Repeatability and multiple operators to estimate Reproducibility. Multiple parts provide better estimates of Repeatability and Reproducibility, as well as Part Variation.
When we conduct the Gage R&R Study, keep these things in mind:
use production pieces (see above)
randomize the order of the pieces presented to each operator
number each part (example 1-10), but try to keep this hidden from the operator (some operators have astounding memories!)
See also: R&R Studies