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Gage Repeatability & Reproducibility for Continuous Data

Gage Repeatability & Reproducibility for Continuous 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)

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Gage Repeatability & Reproducibility for Continuous Data

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  1. Gage Repeatability & Reproducibility forContinuous Data Instructor’s Name

  2. Introductions • Your Name • Your Position • What type of measurements you take in a given day

  3. 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)

  4. Theory of Gage Repeatability & Reproducibility

  5. What do we expect from data? • Accuracy • Calibration • Precision • Repeatability (Equipment) • Reproducibility (Operator) Accurate, but not precise Precise, but not accurate

  6. 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 AND REPRODUCIBILITY STUDY

  7. 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 measurement system, not just the measurement.

  8. 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.

  9. Measurement Variation • Total Variation = Actual Part-to-Part Variation + Measurement Variation • Variation can come from anywhere within the measurement system: Man (operator) Method Material (part) Measurement Machine (tool) Mother Nature (environment)

  10. 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

  11. 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

  12. Judging the Total Gage R & R • If Total Gage R & R is: • < 20%: ACCEPTABLE • Between 20% and 30%: CONDITIONAL • > 30%: UNACCEPTABLE

  13. How to Plan and Execute a Gage R & R Study

  14. 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.

  15. 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 +/- 0.025 • Q: What should be the range of the samples? • Full specification range: 0.975 - 1.025 • A: 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?

  16. 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.

  17. Time to take a… BREAK!

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

  19. 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.

  20. 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

  21. 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.

  22. 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

  23. Time to take a… BREAK!

  24. How to Improve a Gage R & R Result

  25. Recall from earlier... • Repeatability - Equipment Variation • Reproducibility - Appraiser Variation • Tolerance Analysis - Product Acceptance • Study Analysis - Process Control

  26. Improving a System • High percent repeatability? • Operator judgment / opinion • Awkward sample • Gage calibration • Specification • High percent reproducibility? • Operator training • Sample state or position • Specification

  27. 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)

  28. Exercise 3: Dowel Stick Gage R & R (2) Percent Improvement = [(Exercise 2 Result) - (Exercise 3 Result)] (Exercise 2 Result)

  29. Time to take a… BREAK!

  30. Conclusion & Wrap-Up

  31. 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.

  32. Exam • There is an exam associated with this course! • Date: x Month yyyy • Duration: 90 minutes • Passing Score: 80%

  33. Evaluations • Anonymous • Please be candid! Thank you!!

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