Gauge R&R (non destructive)

Gauge R&R (Gauge Repeatability and Reproducibility) is a measurement system analysis. It analysis the amount of measurement variation introduced by a measurement system, which consists of the measuring instrument it self and the operators using the instrument.

The variation in a measurement system analysis.

1. Repeatability: variation from the measurement instrument
2. Reproducibility: variation from the operators using the instrument
3. Overall Gage R&R, which is the combined effect of 1 and 2
   

Type of Gauge R&R

This document is about crossed Gauge R&R and is used when the measurement is non destructive. When using a test that is destructive Use the Nested Gauge R&R.

Crossed (non destructive)	Nested (destructive)

Usage

1. Select GRR in the statistical mode drop-down menu
   
2. De-select destructive Gauge R&R
   
3. Generate the measurement GRR => Generate GRR array
   
   • The amount of operators, parts and replicates must be bigger than 2
4. Organize Gauge R&R
   • Select parts that represents the process variation (if you take 3 parts take one from the low, middle and the high part of the variation.
   • Select operators preferable operators that are normally doing this measurements.
   • Use one Gauge (machine, production line).
5. Conduct the Gauge R&R
6. Min p: above this value the interaction between part and operator is taken out (standard 0.05).
7. Sigma: is used in the %Gauge R&R tolerance (standard 6 sigma).

Interpretation

• For a GRR % Var and %Tolerance the thumb rule is:
  • Less than 10% Good
  • Between 10% and 30% The measurement system is acceptable but this depends on the application. Cost of improving measurement system, yield, cost of repair, etc.
  • Above 30% the measurement system is not acceptable should bee improved.
• If there is a big variation due to the operators, train the the operators to improve the measurement.
• Gage R&R and measure accuracy are two different things!

Formula

Anova according Anova DOE.

Repeatability

If the interaction is not significant.


If the interaction is significant.

Reproducibility

If the interaction is not significant.


If the interaction is significant.

Part to part

If the interaction is not significant.


If the interaction is significant.

Gauge R&R

Total

Example

Looking to this example the Gauge R&R is sufficient 9.37% this is smaller than 10% for a good Gauge R&R. In the example there are tolerance borders (-10...90) so the %Tol is leading.
There is a significant difference between the different parts, and not between the operators. Looking to the graph this is also visible. The interaction is not significant.

If there are no tolerance borders then the Gauge R&R was just good but it is wise to improve the measurement method so that the %Tol Gauge R&R is below 10%.

Data file

How to improve the Gauge R&R value

Anova

Operator: if Operators is significant it is wise to improve the measurement instructions and train the operators.
Interaction: if interaction is significant it is wise to improve the measurement instructions and train the operators. Due to not additive relation between operators and parts. This can be caused by a operator that has higher measurement error at low or high values.

Gauge R&R

Reproducibility: If the influence of the Reproducibility is high it is wise to review the measurement instruction and training of the operators.
Repeatability: If the influence of the repeatability is high it is wise review how the measurement is done.

Links

• http://www.itl.nist.gov/div898/handbook/mpc/section4/mpc4.htm
• http://en.wikipedia.org/wiki/ANOVA_gauge_R%26R