Ensuring Precision in Quality Control: Attribute Gauge R&R for Eddy Current Testing of Tap Hole Minor Diameter

Introduction

In high-precision manufacturing, inspection reliability is critical. This post explains an Attribute Gauge Repeatability and Reproducibility (R&R) study for an Eddy Current Test (ECT) system used to evaluate tap hole minor diameter. The study confirms the system’s suitability for production quality control.

Why Attribute Gauge R&R Matters

Attribute Gauge R&R assesses:

• Repeatability: Does the same inspector give consistent results?
• Reproducibility: Do different inspectors agree with each other and the standard?
• Reliability: Can we trust the inspection process for OK/NG decisions?

Study Overview

• Inspection Method: Eddy Current Testing (ECT)
• Feature: Tap Hole Minor Diameter (M8 × P1.25, tolerance class 6H)
• Samples: 22 parts (OK and NG)
• Appraisers: 3 inspectors (A, B, C)
• Trials: Each appraiser inspected all samples twice.

Key Findings

1. Internal Consistency

All appraisers showed 100% repeatability within their own evaluations.

2. Agreement with Standard

• Appraisers A and B: 100% accuracy
• Appraiser C: 95.45% accuracy (one misclassification)

3. Statistical Indicators

• Overall Agreement: 95.45%
• Fleiss’ Kappa: 0.97 → Near-perfect agreement
• p-value: 0.0000 → Statistically significant

Correlation Analysis

The study also examined the relationship between minor diameter and ECT value:

• Pearson Correlation: -0.981 → Almost perfect negative correlation
• Regression Model:
  ECT Value=1870−187.8×Minor Diameter
• R²: 96.17% → Extremely strong linear relationship

Practical Implications

• Inspection Reliability: ECT system validated as highly accurate.
• Process Control: Maintain minor diameter within tolerance for desired ECT performance.
• Predictive Modeling: Use regression for quality forecasting.

Conclusion

The Attribute Gauge R&R study confirms excellent reliability of the ECT system for tap hole inspection. Combined with strong correlation analysis, manufacturers can confidently use ECT for real-time quality control.

Next Steps

• Schedule calibration and GRR checks every 6 months.
• Train appraisers on borderline cases.
• Apply regression model for predictive quality monitoring.

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KIMEC|Expert Group

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