Induction and conduction thermography: A new surface inspection method suited for the forging industry

Active thermography, using electromagnetic excitation, is a non-contacting, non-destructive evaluation method with a wide range of applications. It allows detecting inhomogenities, like cracks, at or close to the surface of metallic components fast and reliable utilizing infrared imaging. Electric current can be used in two ways for thermography: In induction thermography a current is coupled to the component by passing an AC current through a coil which is in close proximity to the component inspected, while in conduction thermography the current is coupled directly into the component. In this paper we present the basics of this new NDE method, along with several component examples and how to build systems for the inspection. Active thermography using electromagnetic excitation and in particular induction thermography is a method which can be highly automated and is therefore an ideal tool for the inspection of forgings. Examples will be shown for crack testing of various forged steel parts with typical surface defects. The detectability of covered defects will be discussed as well as the reliability of the method and the prospects for automation.