Thickness Measurements in Industrial Environment

Jens Klier, Stefan Weber, Daniel Molter, Shiva Mohammadzadeh, Andreas. Keil, Fabian Friederich, Georg von Freymann, and Joachim Jonuscheit

Fraunhofer ITWM, Fraunhofer-Platz 1, 67663 Kaiserslautern, Germany

Terahertz measurement technology enables non-contact and non-destructive coating thickness measurement using time-of-flight analysis. Terahertz technology has proven in numerous laboratory tests that it is a suitable technique for measuring coatings in the technically interesting thickness range of 10 – 3,000 μm [1]. In this presentation, various applications in the industrial environment will be presented:

End-of-line control of car coating
The car bodies are coated in multiple layers for protection or finishing. A measuring system is required here that can determine the individual layer thicknesses within a multi-layer system. For integration into the production process, it must be demonstrated that the sensor can be positioned using a robot. Furthermore, there are always position tolerances in the continuous production process, so the sample is not always in the same position for measurement. Due to the large number of machines in a production hall, there are always vibrations that interfere with the measuring process. A measuring system must be able to deal with these disturbance variables. Its suitability for use has been successfully demonstrated in several field tests in production facilities in the automotive industry.

Wall thickness measurement of tubes after extrusion
To minimize the amount of material used in the production of tubes, the wall thickness of tubes must be measured and controlled early on in the process, ideally directly after the extruder. The established ultrasonic measurement technology cannot be used as the tubes are still warm and the speed of sound is highly temperature-dependent. Each temperature change automatically leads to incorrect measurements. In the terahertz range, the material parameters are largely temperature-independent, and therefore the wall thickness can be measured at an early stage.

Inline-coating measurement of battery foils
The established terahertz TDS technology is used to test the coating of cathode foil in the battery manufacturing process. The newly developed photonic FMCW radar enables coating thickness measurement on the cathode and anode foil for the first time. In addition to this property, this measurement technology is scalable, which makes its use significantly more economical. Systems with 8 parallel measuring channels have already been realized.

References
[1] Ellrich, F., Bauer, M., Schreiner, N. et al. “Terahertz Quality Inspection for Automotive and Aviation Industries,” J. Infrared Milli. Terahz. Waves 41, 470–489 (2020); https://doi.org/10.1007/s10762-019-00639-4