Eddy Current TestingEddy current testing is an approved, non-destructive inspection method that utilizes electromagnetic signals to examine the structure of a metallic object. In a typical scenario, a small coil of wire is excited by an alternating current (AC) signal and held in close proximity to the metallic object. The magnetic field generated by the coil of wire enters the metallic object and causes a small electrical current to flow inside the metal. These are called eddy currents. The eddy currents flowing in the metal will change their flow depending on the “material structure” of the metal. The presence of cracks or flaws will influence how the signals flow, as will differing heat treat conditions, case depth, alloy content, and physical properties. Comparing the eddy current flow in a metallic object “under test” to “known good” object will indicate whether there are flaws or a different material structure in the component. Testing at multiple frequencies facilitates the finding of structural defects. Eddy current testing offers a clean, fast, non-contact examination which makes it well suited for use in testing of newly manufactured components. In most instances, the tests can integrated into a production line allowing the manufacturer to test 100% of their products at line speed, with integrated material handling systems able to reject out-of-tolerance components. Eddy current probes containing multiple miniature coils can be positioned to test very specific areas such as wear surfaces, bearing surfaces, and areas susceptible to cracking or manufacturing defects. Eddy current testing helps manufacturers cut down on scrap and warranty costs by identifying manufacturing issues right on the assembly line. Eddy current testing also reduces or eliminates the need to sample test with dye penetrant or magnetic particle inspection for flaw detection, and cutting and etching to determine proper heat treat and case depth patterns. As manufacturers increase the use of induction heating techniques, determination of shallow case, misplaced case, short quench, and other heat treat processing errors is a critical requirement that can be met with eddy current testing. Eddy current testing is used on forged, powder metal, and machined components, as well as on bar, tube, and wire stock. Typical components tested include gears, bearings, and shafts. Bar, tube and wire applications include testing of welding wire, railroad rails, and hypodermic needles.
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