Your supplier tells you a component is within tolerance. Their inspection report says everything is OK. But how confident can you be that the factory’s measurement system is actually giving you reliable results?
This is an easy part of manufacturing quality control to overlook. Different measuring equipment, operators, techniques, environmental conditions, and even the way a component is positioned or handled can produce different measurements. A number recorded on an inspection report should not automatically be treated as the truth.
The consequences can be serious. An unreliable measurement system can cause a manufacturer to reject perfectly good products, accept defective ones, or start adjusting a production process that was not actually the problem.
In this episode of China Manufacturing Decoded, Adrian is joined by Sofeast NPI lead Paul Adams to explain how manufacturers can make measurements more reliable. They discuss calibration, measurement procedures, Gage R&R, Cp and Cpk, Statistical Process Control, and why buyers should focus particular attention on characteristics that are Critical to Quality (CTQ).
What is Gage R&R?
Gage Repeatability and Reproducibility (Gage R&R) is a method used to determine how much variation in a measurement comes from the measurement system itself.
It considers two important questions:
- Repeatability: Can the same person repeatedly measure the same characteristic and get consistent results?
- Reproducibility: Can different people using the same equipment and method obtain consistent results?
If the measurement system itself creates too much variation, manufacturers may be unable to reliably distinguish between good and defective parts.
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Podcast sections
- 00:00:13 – Can you actually trust your factory’s measurements?
- 00:02:29 – Why a measurement result is not automatically the truth
- 00:03:10 – Matching measuring equipment to the tolerance being checked
- 00:05:19 – Why different people can measure the same part differently
- 00:07:09 – How temperature, handling, and the environment affect measurements
- 00:07:41 – Why Paul never relies on a single measurement
- 00:08:10 – Introducing Gage R&R and measurement variability
- 00:09:46 – What makes a measurement system reliable?
- 00:10:20 – Does your measuring equipment have enough resolution?
- 00:10:58 – Calibration and why traceable records matter
- 00:12:51 – The red flag of uncalibrated equipment in a machine shop
- 00:13:42 – Why factories need a defined measurement method
- 00:15:04 – How different operators can create inconsistent inspection results
- 00:16:46 – Why trained inspectors and operators matter
- 00:17:50 – Gage R&R explained: repeatability and reproducibility
- 00:20:14 – How operator technique can introduce measurement variation
- 00:21:05 – Case study: when the test equipment appeared to show product failures
- 00:22:19 – Discovering that the measurement system itself was unreliable
- 00:23:16 – Fixing the test system and identifying genuine product failures
- 00:24:13 – How unreliable measurements lead to bad quality decisions
- 00:25:20 – Why Gage R&R should be done before problems occur
- 00:26:26 – Introducing Cp, Cpk, and Statistical Process Control
- 00:27:17 – How control charts can show a manufacturing process drifting
- 00:28:18 – Finding process problems before parts fall outside tolerance
- 00:32:35 – Do you really need SPC and Gage R&R everywhere?
- 00:33:48 – Focus your effort on Critical to Quality characteristics
- 00:34:53 – What quality data should you ask your manufacturer to provide?
- 00:36:52 – Final takeaway: don’t blindly accept that “all measurements are OK”
You might also like…
- QA/QC Inspection Optimization
- How To Set Up A Process Control Plan [11 Steps]
- How a Supplier’s Quality can be Evaluated and Validated
- What’s A Good QA Auditing & Inspection Program For New Products?
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