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# Understanding Gage R&R Analysis

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The presentation explains the fundamentals of Measurement System Analysis (MSA) also known as Gage R&R Analysis.

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### Understanding Gage R&R Analysis

1. 1. Rajiv Iyer Understanding Measurement System Analysis (MSA) also known as Gage R&R Analysis
2. 2. 2 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?
3. 3. 3 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
4. 4. 4 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.
5. 5. 5 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.
6. 6. 6 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 Response Ref Ref + 0.05 × Tol Ref - 0.05 × Tol Run Chart - Sample Type 1 Gage Study - Sample Report
7. 7. 7 For more information on Gage R&R and how it relates to Instron systems, read the whitepaper For any other inquiries, contact us or visit our blog