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### Six Sigma Quality Engineering

Week 5

Chapters 5 (Measure Phase)

Variable Gauge R&R

“Data is only as good as the system that measures it. If you can’t measure it, you can’t manage it.”

The Science of Measurement

“I often say that when you measure what you are speaking about and express it in numbers, you know something about it.”

LORD KELVIN, 1891

He clearly stressed that little progress is possible in any field of investigation without the ability to measure. The progress of measurement is, in fact, the progress of science.

Objectives

- Measurement Systems Analysis
- Key Terminology
- Variable Gauge R&R
- A tool for estimating measurement system error
- How to conduct a gauge R&R
- Minitab Output
- Gauge R & R Study Exercise

Definitions

- Variable Data
- Continuous measurements such as length, voltage, viscosity
- Repeatability
- Variation in measurements obtained with one gage when used several times by one appraiser.
- Reproducibility
- Variation in the average of the measurements made by different appraisers using the same measurement system.

What is GR&R?

Measurement Systems Analysis

How good is our measurement system?

2T = 2p + 2m

2T = Total Variance

2p = Process Variance

2m = Measurement Variance

GRRRRRRR!!!

Actual Process Variation

Measurement Variation

Long-term Process Variation

Short-term Process Variation

Variation within

a Sample

Variation

due to

Gage

Variation

due to Operators

Repeatability

Reproducibility

Linearity

Accuracy

Stability

Possible Source of VariationHow to set up a Variable GRR Study

- Preparation & Planning
- 1 Gauge
- 3 Operators (Appraisers)
- 10 Parts
- 3 Trials
- Randomize the readings
- Code the parts (blind study) if possible
- 3 Ops x 10 parts x 3 trails = 90 Data Points
- 4 Ops x 10 parts x 3 trails = 120 Data Points

Minitab Gage R&R Graphical Output

The number of distinct categories of parts that the process is currently able to distinguish (Must distinguish at least 5 types of parts)

Acceptability Criteria

- R&R Indices
- 10% Acceptable Measurement System
- 10% - 30% May be acceptable based upon application, cost of measurement device, cost of repair, etc.
- 30%Not acceptable. Measurement system needs improvement.
- Number of Distinct Categories Index
- 1 Unacceptable. One part cannot be distinguished form another.
- 2 -4 Generally unacceptable
- 5 Recommended

Module 0025

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