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

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

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

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

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

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

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

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

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

Matrix Showing Recorded Data For Gage R&R NO. Appr A Oper A Appr B Oper B Appr C Oper C

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

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

G R&R Calculations

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) STD DEV % Contribut ion % TV% TOL Repeatability (EV) %32.2%13.5%R-Bar Reproducibil ity (AV) % UCL-R Appraiser X Part (INT) % Study Variation GRR %32.2%13.5% Total Variation (TV) Part To Part (PV) %94.7%99.1% Tolerance (Tol) Number of Distinct Categories

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

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