Rajiv Iyer

Understanding Measurement System Analysis (MSA)

also known as Gage R&R Analysis

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Gage R&R Analysis – Fundamental Concepts

• Critical tool in

understanding capabilities

of any system used by

different operators for

measuring a part

• “R&R” stands for

Repeatability and

Reproducibility

• Core question to answer:

Is the gage/instrument

capable of distinguishing

between good and bad

units?

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Gage R&R Analysis - Methods

• Analysis of Variance (ANOVA) Method

• Estimates variability of each factor to understand effect of each factor on the response from the experiment

• Extended to gage R&R to identify if parts, operators, or both have any effect or not

• Total %R&R estimated – to understand contribution of each factor for variability

• x̄ & R Method

• Alternate method to conduct gage R&R analysis

• For use when less trials are run, compared to ANOVA

• Uses the average and range of the data to estimate the %R&R value

• Does not provide details on factor significance to the measurement like ANOVA method

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Gage R&R Analysis – Guidelines

*Guidelines recommended by AIAG in 1990s

GRR Decision Comments

Under 10%

Generally considered to be an

acceptable measurement

system.

Recommended, especially useful when trying to sort or

classify parts or when tightened process control is required.

10% to 30%May be acceptable for some

applications.

Decision should be based upon, for example, importance of

application measurement, cost of measurement device, and

cost of rework or repair. Should be approved by the customer.

Over 30% Considered to be unacceptable.

Every effort should be made to improve the measurement

system. This condition may be addressed by the use of an

appropriate measurement strategy; for example, using the

average result of several reading of the same part

characteristic in order to reduce final measurement variation.

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How Does Gage R&R Apply to Instron?

• Instron products – Used for running

destructive and non-destructive

materials testing

• Gage R&R can be classified into

two types: destructive gage R&R

and non-destructive gage R&R

• Non-destructive gage R&R

example: compression and stiffness

measurements of springs with

widely different stiffness.

• Destructive gage R&R example:

tension of different plastic

specimens (rigid, semi-rigid and

soft).

Note: It is highly recommended to choose parts or specimens that closely reflect the system’s

intended application.

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Type I Gage Study – P/T Ratio

• Used to investigate precision and accuracy of a measurement system without considering other sources of variations (operators, parts)

• Simpler study used for verification of pre-installed or old systems

• P/T Ratio – The precision-to-tolerance ratio estimates how precise the data is to the defined tolerance or specification limits

• Highly valuable in production and QC environments

• Guidelines for P/T ratio are the same as the table on slide # 4 defined by AIAG

Reference 0.4268

Mean 0.42686167

StDev 0.000202571

6 × StDev (SV) 0.001215427

Tolerance (Tol) 0.017071

Basic Statistics

Bias 0.00006167

T 1.667376123

PValue 0.106

(Test Bias = 0)

Bias

Cg 1.40

Cgk 1.30

Capability

%Var(Repeatability) 7.12%

%Var(Repeatability and Bias) 7.67%

Gage name: Sample GRR

Date of study: Sample

Reported by: Rajiv Iyer

Tolerance: Sample

Misc: Sample

28252219161310741

0.4276

0.4272

0.4268

0.4264

0.4260

Observation

Re

sp

on

se

Ref

Ref + 0.05 × Tol

Ref - 0.05 × Tol

Run Chart - Sample

Type 1 Gage Study - Sample Report

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For more information on Gage R&R

and how it relates to Instron systems,

read the whitepaper

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