NON-DESTRUCTIVE TESTING


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Smart sensors for NDT of steel


M


aterial defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the


field of quality assurance, intelligent, non-destructive sensor systems play a key role. Experts from the Fraunhofer IZFP in Saarbrücken presented two exhibits at the Blechexpo in Stuttgart in November 2017 that allow fast, reliable and automated characterisation of materials and detection of defects. When quality testing uses time-consuming


destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that testing is restricted to random sampling, faults in processes are often not found until a large amount of scrap has already been produced. Consequently, non-destructive testing methods represent an alternative, and after appropriate adaptation processes, also a replacement for destructive methods for the long run. The steel processing industry needs non-


destructive testing methods in quality assurance. Frequently relevant parameters include hardness, case depth, strength and residual stresses. “An inspection task that is being requested frequently is the monitoring of heavy steel plates, and the related detection of localised increases in surface hardening,” explained Sargon Youssef, researcher and engineer at the Fraunhofer IZFP. A robotics-supported sensor system can rapidly and easily be integrated into production processes. The automated application of intelligent, non- destructive sensor systems not only ensures optimum product quality in production, it is also indispensable for realising current machine learning concepts. The potential use of such systems was demonstrated using an electromagnetic acoustic transducer (EMAT) and a technique known as micromagnetic multiparameter, microstructure and stress analysis (3MA). EMAT allows couplant-free testing of defects in sheet metal, while the parallel application of 3MA makes quantitative material characterisation possible. 3MA determines, in a fraction of a second, different material properties, such as hardness and case hardening depth. In addition, a variety of other magnetic parameters is determined which reflect different material properties (tensile strength, yield strength) and stress states. Using mathematical- statistical techniques such as pattern recognition and


❱ ❱ An engineer performs robotics- supported testing of steel sheets for mechanical properties (residual stresses) using micromagnetic testing (3MA)


regression analysis, the 3MA method determines the relationship between the magnetic characteristics measured and the material properties. Fraunhofer’s 3MA-X8 measuring system is


a variant of 3MA which implements 3MA with particular emphasis on simple calibration, very high measuring speed and variable sensor design. In addition, simultaneous operation of up to eight sensors is possible with a device to cover several measuring positions or accelerate surface scans. The system thus has multi-channel real-time capability. “The combined sensor-based testing process allows early detection of mechanical properties - the residual stress and the hardness of steel, as well as defects like cracks or necking. This will save resources and reduce costs,” explained Frank Leinenbach, development engineer at the Fraunhofer IZFP. In the demonstration, the 3MA-X8 testing technology was shown integrated in a miniaturised rolling line. Here, sheet metal to be tested was measured, detected and sorted. EE


❱ ❱ Schematic layout of a


rolling line for nondestructive


testing of heavy plates


DAQ, Sensors & Instrumentation Vol 1 No. 1 /// 9


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