Crack Testing and Heat Treat Verification of Gears Using Eddy Current Technology Authors: D. DeVries


While eddy current technology has long been used in the testing of bar, tube, and wire stock, advances in electronics, automation, and coil design have paved the way for a new generation of testers specifically designed for component testing applications. This includes the testing of gears and bearings which go into automotive and industrial applications. These testing systems easily integrate into production processes allowing for in­line testing at production line speeds. In addition to enabling 100% of production components to be inspected, it can help monitor upstream processes notifying operators that something is not functioning correctly. This greatly reduces scrap and warranty costs for gear and bearing manufacturers.
Eddy current crack testing is performed by passing a small pair of coil windings over a section of the component to be tested. These coil windings are small enough to test between gear teeth, and with multi­coil probes can test very complex shapes. Most crack test applications require only one test frequency since most tests require the detection of only surface flaws. Simultaneous testing with multiple frequencies allows for testing of both surface and sub­surface defects when inspecting nonferromagnetic parts.
While not an absolute hardness test like a Rockwell test, eddy current heat treat verification can achieve sorting results on par with Rockwell testing. This has been demonstrated with both forged and powder metal gears. Eddy current heat treat inspection coils come in both standard encircling coil configurations and multi­coil custom configurations. The custom configurations allow for precise location testing verifying that induction heating parameters were correctly applied. Defects to be tested include misplaced case, shallow case, short quench, delayed quench, air cooled, non­heat­treat, and ground out conditions. When performing heat­treat inspection, multiple test frequencies are used to reliably detect these various heat­treat anomalies.
Eddy current testing offers fast, repeatable testing of gears and bearings. Testing data on each component can be stored electronically and re­analyzed off­line at a later date. Eddy current test instruments are designed to integrate with PLC's in material handling stations to set up real­time rejection capabilities. These are all features that complement modern QC requirements.
ISBN: 1-978-61481-053-7 Pages: 9
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