Gage Repeatability & Reproducibility forContinuous Data

Instructor’s Name

Introductions

Your Name Your Position What type of measurements you take in a

given day

Agenda

Introduction…………………..…..……(30 minutes) Theory of gage R & R……..…..……..(50 minutes) How to plan and execute a gage R & R study ...

………………………………………..(20 minutes)--- Break ---

How to calculate the total gage R & R for a measurement system…………...……(75 minutes)

--- Break ---

How to improve a gage R & R result ……………………………………...…..(60 minutes)

--- Break ---

Conclusion & Wrap-Up………...….…(20 minutes)

Theory of Gage Repeatability & Reproducibility

What do we expect from data?

Accuracy– Calibration

Precision– Repeatability (Equipment)– Reproducibility (Operator)

Accurate, but not precise

Precise, but not accurate

Accuracy AND Precision

A good measurement system must provide data that is BOTH accurate and precise.

How do we know?

By conducting a GAGE REPEATABILITY GAGE REPEATABILITY AND REPRODUCIBILITY STUDYAND REPRODUCIBILITY STUDY

Measurement vs Measurement System

Measurement - value or data Measurement System - everything

involved in performing the measurement– measurement tool– part or sample– operator– procedure– environment

Gage R & R takes into account the entire Gage R & R takes into account the entire measurement system, not just the measurement.measurement system, not just the measurement.

Measurement Resolution

The resolution of a gage is the smallest unit of measure the gage is able to read.

A gage should have a resolution of less than 10% of the total specification tolerance.

Example: Specification: +/- 0.050

Q: What is the maximum gage resolution?Total tolerance: 0.050 + 0.050 = 0.100

10% of total tolerance: 0.100 * 0.10 = 0.010

A: The gage should have a resolution of 0.010 or less.

Measurement Variation

Total Variation =

Actual Part-to-Part Variation +

Measurement Variation Variation can come from anywhere within

the measurement system:MMan (operator)

MMethod

MMaterial (part)

MMeasurement

MMachine (tool)

MMother Nature (environment)

Exercise 1: Length of a Pen

Group Size: 3 - 4 participants Materials: 6” plastic ruler, Exercise 1 in

Student Manual Task: Record all possible sources of

measurement variation if your group was asked to measure the length of pen.

Duration: 10 minutes

Total Gage R & R

The total gage R & R of a measurement system is the final number calculated from a gage R & R study.

Total gage R & R has two parts:– Repeatability or Equipment Variation (E.V.)– Reproducibility or Appraiser Variation (A.V.)

Total Gage R & R = E.V.2 + A.V.2

Judging the Total Gage R & R

If Total Gage R & R is:

– < 20%: ACCEPTABLEACCEPTABLE

– Between 20% and 30%: CONDITIONALCONDITIONAL

– > 30%: UNACCEPTABLEUNACCEPTABLE

How to Plan and Execute a Gage R & R Study

Planning

The typical gage R & R study uses– 2 or 3 operators– 10 parts

Each operator will measure each part two or three times.

In general, more data is better.

Selecting Parts

Do NOT just select 10 parts at random! Samples should cover the full range of the

specification and beyond.

Example: Specification: 1.000 +/- 0.025Q: What should be the range of the samples?

Full specification range: 0.975 - 1.025A: The samples should cover the full specification range and beyond, so they should cover approximately 0.950 to 1.050.

Bonus Q: What should the gage resolution be for this case?

Tips for Data Gathering

Stay as close to the existing process as possible.

Use a scribe to record data. Identify samples. Randomize the order of the samples for

measurement. Do not round the data.

Time to take a…

BREAK!

How to Calculate a the Total Gage R & R for a Measurement System

Tips on the Gage R & R Worksheet

Be able to perform all calculations by hand (a computer is not always available).

Save a master copy of the blank spreadsheet (Read-Only).

Shaded cells contain formulas. Enter data in white cells only.

Record all background information at the top of first page of the worksheet.

Three Ways to Calculate

Measurement Unit Analysis– Raw calculation of the data.

Percent Tolerance Analysis– Relates measurement variation to the

specification.– Product Acceptance

Percent Study Analysis– Relates measurement variation to the total

process variation.– Process Control

Special Cases

Discrete data (go/no go, count, categorical)– Checks for percent agreement among all

operators.– Goal: 100% agreement

Destructive testing (torque, tensile strength)– Instead of repeated measurements, subgroups of

sequentially processed parts are used.– Part variation within the subgroup should be

minimized.

Exercise 2: Dowel Stick Gage R & R

Group Size: 3 - 4 participants Materials: Participant Kit, Student Manual Task: Conduct a gage R & R on the

measurement system for one dimension of the dowel stick. The dimension to be measured will be assigned by the instructor.

Duration: 45 minutes

Time to take a…

BREAK!

How to Improve a Gage R & R Result

Recall from earlier...

Repeatability - Equipment Variation Reproducibility - Appraiser Variation Tolerance Analysis - Product Acceptance Study Analysis - Process Control

Improving a System

High percent repeatability?– Operator judgment / opinion– Awkward sample– Gage calibration– Specification

High percent reproducibility?– Operator training– Sample state or position– Specification

Exercise 3: Dowel Stick Gage R & R (2)

Group Size: 3 - 4 participants Materials: Participant Kit, Student Manual Task: Discuss how to improve the

measurement system as it was used in Exercise 2. Confirm those improvements by performing a Gage R & R study on the new measurement system.

Duration: 55 minutes (10 for discussion, 45 for Gage R & R)

Exercise 3: Dowel Stick Gage R & R (2)

Percent Improvement =

[(Exercise 2 Result) - (Exercise 3 Result)]

(Exercise 2 Result)

Time to take a…

BREAK!

Conclusion & Wrap-Up

Review

The theory behind gage R & R studies How to plan and execute a gage R & R

study How to calculate the total gage R & R How to improve the result of a gage R & R

study.

Exam

There is an exam associated with this course!

Date: x Month yyyy Duration: 90 minutes Passing Score: 80%

Evaluations

Anonymous Please be candid!

Thank you!!