Introduction to Gage R&R Studies

1. Introduction to Gage R&R Studies Rahul Iyer, ASQ-CQE Mesa AZ April 2015

2. Overview • What Is A Gage R&R • Definition Of Certain Terms • Who Does It • What Must A Person Know • Setting Up The Study • Data Collection • Calculation Methods • Evaluation Of Results

3. What Is Gage R&R • Gage Repeatability and Reproducibility (Gage R & R) • A statistical tool that measures the amount of variation in the measurement system arising from the measurement device and the people taking the measurement • Every manufacturing company that is audited is required to do Gage R&R studies

4. Definitions • Repeatability • Variation that is observed when one or more operators repeat the same measurement, on the same part and characteristic, using the same gauge • not always influenced by human (operator) variation • Reproducibility • Variation that is observed when multiple operators are unable to reproduce the same test-group average within limits predicted by repeatability

5. Who Does It • Production / Manufacturing • At Least Three People Who Normally Do Measurement In Production • Quality Inspectors / Technicians • Lab Technicians • Production People • It does not matter who collects the data • NOTE: A Calibration Technician Would Be A Good Choice

6. What Must A Person Know • Must know how to measure the feature using the prescribed measuring tool • Need To Make Sure Which Part They Are Measuring • Sample of parts need to be numbered in a way that the person doing the measurement does not know • Sample of parts need to be numbered in a way that the person recording the data knows which part it is

7. What Must A Person Know • Must know how to measure the feature using the proscribed measuring tool • Need To Make Sure Which Part They Are Measuring • Sample of parts need to be numbered a way that the person doing the measurement does not know • Sample of parts need to be numbered a way that the person recording the data knows which part it is

8. Setting Up The Study • Normal Sample Is: • 10 Parts • 3 Operators • 3 Trials • Total of 90 measurements taken • Smaller sizes may be used if there is a specific reason: • Cost • Requirements • Time

9. Data Collection • Parts Should Be Presented To The Person Doing The Measurement In A Random Order • Person Recording The Data Should Be Able To Track Each Measurement By Sample The Part Quantity Number Assigned • Typical Matrix for Data Collection Shown On Next Slide

10. Matrix Showing Recorded Data For Gage R&R

11. Calculation Methods • Average & Range (“Long AIAG”) • assumes that an error term called “appraiser × part interaction” equals zero • intended for spreadsheets or pocket calculators • Range (“Short AIAG) • reserved for special situations • ANOVA

12. G R&R Calculations Constants are as follows: n = 3, D4* = 2.58, D3* = 0, K1 = 3.05, K2 = 2.70, K3 = 1.62

13. G R&R Calculations

14. G R&R Calculations

15. Evaluation of Results • % of Tol column evaluates the measurement process in terms of capability to determine whether parts meet tolerance • % of TV column evaluates the measurement process in terms of capability to detect changes in total variation (TV, an estimate of process variation)

16. Evaluation of Results • GRR% of Tol = 13.5% is “fairly good” • The combined uncertainty (i.e., variation) including repeatability on production parts, reproducibility and appraiser × part interaction • summed by a method called RSS (root sum square) • GRR% of TV = 32.2%, is not acceptable • if we need a gauge to use for experiments to reduce process variation, we should choose a different gauge for that purpose • If we need a gauge only to determine whether parts meet tolerance, this gauge will likely be adequate

17. Conclusion • What Is A Gage R&R • Definition Of Certain Terms • Who Does It • What Must A Person Know • Setting Up The Study • Data Collection • Calculation Methods • Evaluation Of Results