No abstract

ZusammenfassungDie Vermessung von Spänen, welche bei einem Drehprozess entstehen, ist insbesondere bei einer helixartigen Form eine große Herausforderung. Die Analyse lässt sich nur in den Randbereichen durchführen, da die inneren Bereiche durch den Span selbst verdeckt werden. Außerdem lassen sich Späne, die aus sprödem Material bestehen, nicht zerstörungsfrei analysieren. Da sich metallisches Material sehr genau durch einen Computertomographen vermessen lässt, wurde eine Methode entwickelt, mit welcher sich das 3D-Bild eines Spanes virtuell zu einem geradlinigen Span transformieren lässt. Im Anschluss liegt der Fokus auf der Extrahierung des Segmentspanabstandes, welcher über einen Stauchungsfaktor mit der Segmentspanbildungsfrequenz zusammenhängt. Zuletzt wird die Methode mit einer manuellen Untersuchung der Späne unter einem konfokalen Mikroskop verglichen, wobei gezeigt werden kann, dass der Vorteil der CT-Analyse darin liegt, dass sie auch in der Analyse helixförmiger Späne zu einem Ergebnis kommt.

This work investigates the relationship between acoustic emission and chip segmentation frequency of Ti-6Al-4V at the external longitudinal turning process. Therefore, several sensors like structure borne sensors, microphones and a force dynamometer have been installed in a vertical turning machine. To induce a change of the segmentation frequency, several experiments with different feed rates have been carried out. From each experiment the acoustic emissions have been recorded and the generated chips have been analyzed. Since the chips get stretched or compressed during the chip formation the change in the length is calculated to get an estimation of the segmentation frequency. The comparison of the spectral analysis of the acoustic emission signals and the chip analysis has shown that both methods show the same tendency. The segmentation frequency decreases with increasing feed.

A key element in robust transit-time ultrasonic flow measurement is the accurate estimation of the transit-time difference. Conventional methods, such as cross-correlation or the estimation in the phase domain, are limited in their robustness against signal distortions, interfering signals or noise. In this work, we present a novel method to estimate the transit-time difference through the fusion of selected analytic wavelet packet coefficients. The combination of the complex coefficients, which represent a projection of the signal on analytic wavelets, with a configurable time-frequency resolution allows a sub-sample estimation at the frequency of interest. After giving an introduction into the fundamentals of analytic wavelet packets based on multi-scale filtering, we introduce two features that correlate strongly with the transit-time difference. The selection and fusion of these features is done by using correlation coefficients with a calibration set and principal component analysis. Finally, using a clamp-on flow measurement system, the robustness against temperature variation and measurement noise is shown and compared with conventional methods.