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Fluorescence laser scanner for in-line inspection of functional coatings in metal processing industries

: Holz, Philipp; Brandenburg, Albrecht

Postprint urn:nbn:de:0011-n-5491315 (1.9 MByte PDF)
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Created on: 4.7.2019

Lehmann, Peter (Hrsg.) ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Optical Measurement Systems for Industrial Inspection XI : 24-27 June 2019, Munich, Germany
Bellingham, WA: SPIE, 2019 (Proceedings of SPIE 11056)
Paper 110561X, 13 pp.
Conference "Optical Measurement Systems for Industrial Inspection" <11, 2019, Munich>
Bundesministerium fur Wirtschaft und Energie BMWi (Deutschland)
ZF4036504 PO6
Conference Paper, Electronic Publication
Fraunhofer IPM ()
corrosion protection; lubrication; fluorescence laser scanner; fluorescence measurement; fluorescence imaging

Metal processing industries utilize two types of functional coatings. Conversion coatings, based on Zirconium and/or Titanium, generate corrosion resistance and paint adhesion for aluminum surfaces. Another type of functional coatings are lubricants based on mineral oil, which act as corrosion protection as well as drawing and punching oil. Efficient process development and control requires the monitoring of the thickness of these functional coatings. In this article, we present a new optical setup, which uses a rotating polygon-scanning mirror in combination with laserinduced fluorescence to monitor the spatial distribution of lubricants and conversion coatings on metal sheets. In the presented setup, the beam of a 405 nm diode laser excites auto-fluorescence of the organic molecules inside the functional coatings. By using a fast rotating scanner mirror combined with a fast analogue digital conversion, the presented setup reaches data rates of 400 lines/s consisting of 1000 data points each. Installing the scanner system at a distance of 1200 mm above the metal sheets, realizes a field of view of 2200 mm. At strip speeds of 2 m/s, the distance between two scanner lines on the surface to be investigated is 5 mm. In addition to the description of the optical system, we present different approaches for the calibration of systems for inline fluorescence measurements. For the calibration of lubricant layers in the range down to one micrometer, the reference samples are weighted. To evaluate the limit of detection of the system we use a multiphase carbon analyzer. We show the calibration results for different lubricants and metal materials with different surface textures typically used in car body manufacturing.