Eddy Current Testing
What defects does eddy current testing detect best?
Surface and near-surface cracks, pits, corrosion, and discontinuities in conductive materials; it can also detect certain material-property and thickness variations depending on probe design and setup.
Why is ECT valuable in CNC manufacturing?
It provides fast, non-contact, non-destructive inspection of machined conductive parts, allowing critical components to be screened inline without destroying parts or waiting for lab analysis.
What is the core physical principle behind ECT?
An alternating current in the probe coil generates an oscillating magnetic field, which induces eddy currents in the part; flaws distort those currents, changing the measured electrical impedance.
Eddy current testing (ECT) is a non-destructive testing method that uses electromagnetic induction to generate circulating currents in conductive parts and detects their disruption to reveal surface and near-surface discontinuities. It is commonly applied to machined metal components for crack detection, conductivity sorting, and coating or thin-section thickness measurement.
On a CNC shop floor, eddy current testing is typically run after critical machining, heat treatment, plating, or forming operations to catch tiny cracks, pits, or property shifts before a part moves to final assembly. A probe with an AC-driven coil creates an alternating magnetic field; when it nears a conductive workpiece, eddy currents form in the material, and any flaw distorts that flow, changing the probe impedance and producing a signal. Because the method is non-contact and non-destructive, it fits well into inline automated inspection, giving rapid pass/fail results on machined metal parts, bar stock, tubing, and sheet. It is also used for conductivity sorting and thickness measurement on thin sections or coatings, making it a practical high-speed screening tool for production cells that need to protect finished components without sending every piece to the lab.
Nonconductive workpieces: Eddy current testing requires electrically conductive material, so plastics and composites produce no valid signal. Running ECT on the wrong substrate wastes time and gives false confidence in inspection.
Unstable probe lift-off: Small variations in probe spacing, surface scale, or misalignment swamp the faint signal from a tight crack. Rough machined surfaces demand consistent contact and clean setup to avoid missing defects.
Signal confusion from material changes: Conductivity, permeability, or heat-treatment differences alter eddy-current response and can mimic cracks. Without proper calibration and frequency selection, operators may reject good parts or ship flawed ones.