Gage R & R study is part of measurement system analysis. (MSA – six-sigma concept), The meaning of gage r & r is gage Repeatability & Reproducibility. During the gauge r & r study, one thing you need to keep in mind is that the gauge r & r study does not give an idea about products or parts quality, it defined how the measurement system works accurately.
In this article you learn what is gage r & r, what is the purpose of conducting a gage r & r study, when we use gage r & r study & learn two different examples with a downloadable Excel – data template to conduct the study & downloadable excel – master template to calculate gage repeatability & reproducibility.
Now a day to manufacture critical parts, maintaining the accuracy, precision & reliability of measurement systems is a very important aspect. Generally, most of the industry’s routine practice do calibration of instruments for reliability on measurement system but calibration is not only one aspect with measurement system variations, there are several key areas affecting the measurement system, in this article, we understand how gage r & r study used to know measurement system is perfect or not.
What is the purpose to gage r & r study?
- To know the reliability of the measurement system.
- If certain industries followed the IATF standard then, IATF 16949 clause 7.1 5.1.1 requires gage repeatability & reproducibility study. (MSA)
- The customer requirement is to identify measurement system accuracy with a gage R & R study.
Usage of gage repeatability & reproducibility.
- Gage r & r study use only when the measuring system is manual or measurement system with human involvement.
- When the measurement system is automatic without human intervention in the case gage r & r study is not used.
Now, it is time to understand what gage repeatability is & gage reproducibility.
Definition of gage R & R
Gage r & r is a statistical tool to measure variation in the measurement system. In short gauge r & r method is used to identify errors with measurement systems or errors with equipment & appraiser. (appraiser means a person or human who is associated with measuring activity)
After, a basic understanding definition & important aspects of gage r & r, individually understand what is repeatability & reproducibility.
Gage repeatability
Gage repeatability is a process to measure gauge variation or measuring instrument accuracy.
Gage repeatability is generally used to identify variation within the system, within the part, within the instrument, within the appraiser & within the environment.
Gage reproducibility
Gage reproducibility is a process to measure appraiser variation or accuracy of measuring a person.
Gage reproducibility is generally used to identify variation between systems, between parts, between instruments, between appraisers & between environments.
Before reviewing the attached example we need to understand certain characteristics as per listed below.
Equipment Variation
Equipment variation known as one-appraiser measures the same part dimensions with the same gage more than one time with the same characteristics.
Appraiser Variation
Appraiser variation is defined as more than one appraiser measuring the same part dimensions with the same gauge & same characteristics.
Part Variation
Part variation basically measures dimensions with more than one appraiser, more than one part with the same gage & same characteristics, and in short part, variation measures ranges between different parts.
Gage R & R
Gage R & R provides information on the combined approach, equipment variation as well as appraiser variation.
Acceptance criteria of gage r & r
- If % GRR < 10% – the measurement system is acceptable.
- If 10% < % GRR < 30% – the measurement system is conditionally accepted.
- If % GRR > 30% – the measurement system is not acceptable.
Total Variation
Total variation provides information on a combined approach for identifying variations of the part to part, equipment to equipment & appraiser to appraiser.
Number of distinct categories (NDC)
NDC provides information on sample part variations against equipment & appraiser variations.
Acceptance criteria – greater than or equal to 5.
Example: – 1
One of the small-scale spring manufacturing Industry’s requirements is to conduct a gage r & r study at the workplace, basically, they plan to pick one product & conduct a study, reviewing important information given below to perform a gage r & r study.
10 manufactured parts to be measured.
- 3 appraisers to measure parts.
- A Digital Vernier caliper is used to measure parts.
- Measuring data to be stored on the datasheet.
The review process of study.
Measurement starts with the first appraiser & measures each part on a random basis out of 10 parts, not sequentially followed by data sheet sr. no. for measuring parts but follow random sr. no. & record data in Excel template.
Each appraiser measures 3 times each part on a random basis. – for clear understanding follow the Excel template for data capturing. (For ex. One appraiser stated measurement then complete all the 10 parts on a random basis & then repeat the same practice two times simultaneously, repeating data capturing for better accuracy as per shown in the datasheet & then the same practice was followed by the other two appraisers.)
Review the below-listed data table for 10 parts of measurement with three appraisers.
After reviewing the above data calculate the below-listed activities.
- Equipment variation (%)
- Appraiser variation (%)
- Gage Repeatability & Reproducibility (%)
- Part variation (%)
- No. of distinct categories.
Solution: –
Please review the attached Excel sheet for Example – 1.
Example – 2
Please review below-attached data table & calculate the listed activities.
- Equipment variation (%)
- Appraiser variation (%)
- Gage Repeatability & Reproducibility (%)
- Part variation (%)
- No. of distinct categories.
Solution: –
Please review the attached Excel sheet for Example – 2.