Quality Control in Aluminium Profiles : Non-destructive Methods using Non-linear Ultrasonic

Sammanfattning: When aluminium profiles are manufactured, defects may arise, especially when theprofiles are manufactured through extrusion. During the extrusion process, thesedefects occur on parts of the extruded material because of contaminates that needto be found.The goal of the project is to examine two different types of methods that aresuited for aluminium profiles in the category of non-destructive testing (NDT). Thetwo different methods are non-linear ultrasonic methods called Higher Harmonicsand Non-linear Wave Modulation Spectroscopy. The method that works should thenalso be implemented in a fixture. Of these two methods Higher Harmonics showedthe most promising results by identifying which profile has defects and this methodwas also more appropriate to implement in a fixture.The Higher Harmonics method utilizes two transducers, one as an emitter to thesystem and another as a receiver. When the signal from the emitter passes throughthe non-linearities, which are the defects, and propagates to the receiver the signalcan be inspected on an oscilloscope. The received signal is then transformed to thefrequency domain and if there were defects harmonics should be generated. If thereare many harmonics and the magnitude is high, defects are present.A fixture was also designed to work with the Higher Harmonics method usingprofile struts that are easy to connect to a framework. The fixture worked by raisingand lowering the two transducers which have been built into a probe. The emittingprobe was connected to a signal generator and the receiving probe was connected toan oscilloscope. This measuring station did the measurement more consistent andaccurate than before. The most interesting result that was found in the experimentswas that localization of defects could be found.