## What is a Gauge R&R study in MSA? | GRR Study | Variable MSA Study

### 1) What is a Gauge R&R study in MSA?

→**Gauge R&R**study or “Gauge Repeatability and Reproducibility Study (GRR Study)” is a term which is commonly used in MSA.

#### → To calculate the GR&R %, following five contributors are to be calculated:

- Equipment Variation (EV)
- Appraiser Variation (AV)
- Gauge Repeatability & Reproducibility (
**GRR**) - Part Variation (PV)
- Total Variation (TV)

#### ➤ [1] Equipment Variation (EV) in GRR study in MSA:

➧ This is the "within appraiser" variation.
➧ It measures the variation one appraiser has when measuring the same part

(and the same characteristic) using the same gauge more than one time.

➧ The calculation is given below.

⇒ Where K1 is a constant that depends on the number of trials.

⇒ For 2 trials, K1 is 0.8862.

⇒ For 3 trials, K1 is 0.5908.

#### ➤ [2] Appraiser Variation (AV) in GRR study in MSA:

➧ This is the "between appraisers" variation.

➧ It is the variation in the average of the measurements made by the different appraisers when measuring the same characteristic on the same part.

➧ The calculation is given below.

⇒ Where K2 is a constant that depends on the number of appraisers.

⇒ For 2 appraisers, K2 is 0.7071.

⇒ For 3 appraisers, K2 is 0.5231

#### ➤ [3] Gauge Repeatability & Reproducibility (GRR) in GRR study in MSA:

#### ➤ [4] Part Variation (PV) :

➧ The part variation is determined by multiplying the range of the part averages (Rp) by a constant K3.

➧ K3 depends on the number of parts.

#### ➤ [5] Total Variation (TV) :

### 2) Steps for Gauge Repeatability and Reproducibility (GR&R) Study in MSA:

- Select 10 parts that represent the full range of long-term process variation.
- Identify the appraisers (inspectors or part checker).
- If appropriate, calibrate the gauge or verify that the last calibration date is valid.
- Open the
**Gauge R&R**worksheet to record data. - Have each appraiser assess each part 3 times (trials – first in order, second in reverse order, third random).
- Input data into the
**Gauge R&R**worksheet. - Enter the number of operators, trials, samples and specification limits
- Analyze data in the
**Gauge R&R**worksheet. - Assess MSA trust level.
- Take actions for improvement if necessary.

####
➤ Step 1: Determine the number of parts, the number of appraisers to use and **the number of trials - GRR study in MSA**

➧ There are several issues that must be considered when planning a **gauge R&R**study.

➧ The first is the number of appraisers and the number of parts to use.

➧ The number of parts (n) must be greater than or equal to 5.

➧ The number of appraisers (k) must be greater than 2.

➧ The number of trials (r) must be greater than or equal to two.

➧ This represents how often each appraiser will measure a part.

➧ In addition, the n*k should be greater than 15.

➧ This gives more confidence in the results.

➧ If possible, include all the appraisers who operate the gauge in the study.

####
**➤ Step 2: **Select the parts for the study - GRR study in MSA

➧ The next step is selecting the parts to include in the study.➧ The parts should be selected to reflect the range of variation in the process.

➧ In other words, don't just take 10 parts off the line right in a row.

➧ You need to select the parts so they reflect the variation seen in

the manufacturing process.

####
**➤ Step 3: **Label the parts from 1 to n and designate the appraisers A, B, etc. - GRR study in MSA

####
**➤ Step 4: **Conduct the Measurements - GRR study in MSA

➧ The parts must be run in random order. ➧ Start with appraiser A. Appraiser A measures the parts in random order.

➧ The results are recorded.

➧ This process continues for each appraiser without the appraisers being able to see

the results from other appraisers.

➧ This cycle is continued until you have completed all trials.

➧ Be sure that an appraiser cannot see his/her results from previous trials.

####
➤ **Step 5: Analyzing the Results** - GRR study in MSA

➧ You select five parts that represent typical variation in the length output.

➧ You have each appraiser measure each part three times.

➧ The measurement results are given below.

👉 Click here: GRR Study Excel Template Download

➧ You use the above results to perform the

➧ You start by determining the following:**gauge R&R**calculations.➧ The average for each trial for each appraiser

➧ The average and range for each part for each appraiser

➧ The overall average and average range for each appraiser

➧ The overall average and the average range for the part

➧

**These calculations are shown in the table below.**
👉 Click here: GRR Study Excel Template Download

**→ Determine the average range for the three appraisers.**

**→ Then, determine the difference between the maximum appraiser average and**

**the minimum appraiser average.**

➧ Thus, the difference is

**(3.157) - (2.695) = 0.462****Next, determine the range of the part averages (Rp).**

➧ The smallest part average is for Part 5 (1.94).

➧ So, Rp = (4.10) - (1.94) = 2.16

**→ Putting up these values for all the 5 contributors:**

####
➤ **Step 6: Interpreting the results** - GRR study in MSA

➧ Remember, a **gauge R&R**study is a study in variation.

➧ You must have variation in the parts and in the appraisers to calculate

the above numbers.

➧ To determine if the measurement system is adequate, you must compare

the results to Total Variation (TV).

➧ The number that most people focus on first is the %

**GRR**.
➧ The following guidelines can be used to determine if the measurement system

is acceptable, conditionally acceptable or not acceptable.

➧

**Green: < 10%****of TV****(****Measurement system is acceptable****)**
➧

**Yellow: 10-30%****of TV****(****Measurement system may be acceptable****based on the application**

**)**

➧

**Red: > 30%****of TV****(****Measurement system needs improvement****)**%

**GRR**is greater than 30%.

➧ Sometimes you can look at the %AV and %EV to get insights into where to start

improving the measurement system.

➧ But the study indicates that the measurement system must be improved.

#### ➤ You can also determine the number of distinct categories (ndc) in Gauge R&R Study.

➧ It is similar to looking at how many possible values there are on a range control chart.

➧ The calculation is:

ndc = 1.41(PV/

**GRR**) = 1.41(0.872/0.319) = 3.8

➧ The integer value of

**ndc should be greater than or equal to 5.**

➧ In this case, it is 3.

➧ Again, this is an indication that the measurement system needs improvement.

#### ➤ If repeatability is large compared to reproducibility, then the reasons may be:

1. The instrument needs maintenance;

2. Other reason may be the gauge should be redesigned to be more rigid;

3. The clamping or location for gauging needs to be improved;

4. There is excessive part variation.

2. Other reason may be the gauge should be redesigned to be more rigid;

3. The clamping or location for gauging needs to be improved;

4. There is excessive part variation.

#### ➤ If reproducibility is large compared to repeatability, then possible causes may be:

1. The appraiser needs to be better trained in how to use and read the gauge instrument.

2. Calibrations on the gauge dial are not clear

3. A fixture of some sort may be needed to help the appraiser use the gauge more consistently.

2. Calibrations on the gauge dial are not clear

3. A fixture of some sort may be needed to help the appraiser use the gauge more consistently.

####
**➤ Some improvement points in Gauge R&R study in MSA**

➧ Brainstorm with the team for improvement solutions.➧ Determine the best “practical solution” (may require some experimentation).

➧ Pilot the best solution

➧ Implement the best solution – train employees.

➧ Re-run the study to verify the improvement.

👉 For a regular update :

## 2 Comments

Thank you for the explanation.

ReplyDeleteThank you for your feedback

Delete