Introduction to Gage R&R Studies

Rahul Iyer, ASQ-CQE

Mesa AZApril 2015

OverviewWhat 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

DefinitionsRepeatability

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 KnowMust 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 KnowMust 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 StudyNormal 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

10.5295 0.5295 0.5295 0.5295 0.5295 0.529 0.529 0.5295 0.5295

20.5285 0.528 0.5285 0.5285 0.5285 0.528 0.5285 0.529 0.5285

30.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53

40.529 0.5295 0.5295 0.529 0.5295 0.5295 0.5295 0.5295 0.5295

50.5305 0.5305 0.53 0.53 0.5305 0.5305 0.53 0.5305 0.5305

60.5285 0.5285 0.5285 0.5285 0.5285 0.528 0.5285 0.5285 0.528

70.5305 0.53 0.53 0.53 0.5305 0.5305 0.5305 0.5305 0.53

80.5295 0.5295 0.5295 0.529 0.5295 0.53 0.5295 0.5295 0.5295

90.529 0.529 0.529 0.529 0.529 0.5295 0.5295 0.529 0.529

100.5295 0.5295 0.529 0.5295 0.5295 0.529 0.5295 0.5295 0.5295

Calculation MethodsAverage & 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

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)

0.00023 10.37% 32.2% 13.5% R-Bar 0.00038

Reproducibility

(AV)

0.00000 0.00% 0.00% 0.00% UCL-R 0.00099

Appraiser X Part (INT)

0.00000 0.00% 0.00% 0.00% Study Variation

0.0007

GRR 0.00023 10.37% 32.2% 13.5% Total Variation

(TV)0.00070

Part To Part (PV)

0.00066 89.63% 94.7% 99.1% Tolerance(Tol) 0.00167

Number of Distinct Categories 4.1 10.3

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

ConclusionWhat 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