introduction to gage r&r
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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
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