Induction thermography is a non-destructive and contact-free procedure for the detection of surface cracks on conductive materials. The presence of surface cracks leads to local distortions of eddy currents produced by an induction coil. Accordingly, temperature surges occur in the corresponding positions. This allows reveal defects using a thermal imaging camera.
This automatable method is suitable for the examination of semi-finished products as well as complexly shaped components. The system is comprised of one or more infrared cameras, an induction coil and a high-frequency generator which heats the test parts continuously or in pulses.
Thermography: A proven method
DEFECTOVISION IR makes defects on the material surface visible to the eye and provides information on the size and depth of defects via thermal images. This minimizes expensive reworking of the test parts. The testing method of inductive thermography covers nearly 100% of the material surface and works without contact.
In testing with DEFECTOVISION IR, the part to be tested goes through an induction coil and is heated on the surface at the same time. Four infrared cameras detect the resulting temperature distribution of the material. At exposed defects, a local temperature increase occurs with an amplitude that depends on the size of the material defect. The digital data is evaluated by the test electronics, which determines the precise position and category of the defects fully automatically.
Since the measured temperature distribution of the material surface also depends on its condition, the test part is slightly wet with water before heating. This guarantees a high uniformity and an increase in the emission degree that is important for the temperature measurement, and it ensures reproducible test results.
With the newly developed and patented evaluation principle from FOERSTER, each surface point is scanned several times. This makes it possible to decide finally whether the test signal indicates a real material defect or whether it is an error.
Parts with complex geometries are difficult or impossible to examine in some regions with eddy current testing. Often only magnetic particle testing or penetrant testing remain for the examination of such part. These methods cannot be conveniently automated. With DEFECTOVISION CT, the flexible induction thermography for components FOERSTER now offers a new solution to examine complex parts for defects.
A typical system consists of a thermal imaging camera and an induction coil with a generator. An induction pulse generates heat sources in the location of surface defects on the part. The thermal recordings are analyzed with video and image processing algorithms. This allows to automate the testing. Typical components often have special structural properties, such as threading, gearing, blades or profiles. Often such parts are forged, sintered, produced in additive manufacturing or sometimes formed. Pores and cracks in welding seams can also be detected efficiently.
Examples for thermography applications on components include:
- Gears, pinions
- Transmission components
- Forged parts (bevel gears, tulips, shaft forks)
- Profile sheets
- Welding seams (laser, SAW)
- Turbine components (blades)