Engineeringloaded: VARIABLE GAUGE R&R STUDY

Measurement System Analysis

Chapter 11

Gauge R & R study

Gauge R & R is a means of assessing the Repeatibility and Reproducibility of our measurement systems.

Gauge R & R studies are carried out in order to discover how much of the process variation is due to measurement device and measurement methods.

It can be classified as :

1. Variable Gauge R & R

2. Attribute Gauge R & R

Variable Gauge R & R

Requirements :

A minimum of two operators ( recommend 3 or 4 )
Atleast 10 parts which should be chosen to represent the full range of manufacturing variation ( it may be acceptable to use fewer parts in some special cases. )
Each part should be measured two or three times in a random order.
Operator should not be aware of the previous result when measuring the same part.
There are two methods available :

1. Analysis of Variance ( ANOVA )

2. Xbar and R

The ANOVA method is :

* the recommended approach.

* takes into account any interactive effect between

operator and part.

The interpretation will also depend on the current level of process variation.

ndc is number of distinct categories.
( n >= 5)

" This value represents the number of groups measurement tool can be distinguished from itself.The higher this number the better the tool has in discerning one part from another."

* When number of categories is less than 2,the measurement system is of no value for controlling the process , since one part cannot be distinguished from another.

* When the number of categories is 2, the data can be divided into two groups , say high and low.

* When the number of categories is 3, the data can be divided into 3 groups , say low, middle and high.

* A value of 5 or more denotes an acceptable measurement system.

What Practical action to take if ndc<5 ?

Let's say you do get a value below 5 ? What next ? Well there are two things you can do.

* Analyze more distinct parts that truely represents the entire range of the process.
* Increase precision on your measuring tool.

Calculations related to Variable Gauge R & R Study

* There will be 3 appraiser
* Take 10 parts and each appraiser will take 3 readings of each part.
* Then, average of all 10 parts reading will be calculated for each reading.
* Construct table as shown below :

* Then, from above table calculate Xa bar and Ra bar

Xa bar is average of averages.

Ra bar is average of Ranges.

* Similary ,

for Appraiser 2 and 3 each

Construct table as above and do experiment as above using same 10 parts and find Xb bar and Rb bar.

* After this part average of each part of all 10 parts will be calculated. The 9 Readings ( including reading of appraiser 1 , 2 , and 3 ) will be used to calculate part average as shown in table below.