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| Home > Publications database > Untersuchungen zur Spanbildung metallischer Werkstoffe anhand von in situ Röntgenbeugungsexperimenten |
| Dissertation / PhD Thesis | PUBDB-2017-00632 |
;
2016
Universität Berlin
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Please use a persistent id in citations: doi:10.3204/PUBDB-2017-00632
Abstract: For the optimization of machining processes with geometrically defined cutting edge afundamental understanding of the chip formation process is necessary. However it islimited due to the hard metrological detectability of the area of action. Modern sourcesfor high energetic synchrotron radiation and new detectors enable in situ diffractionexperiments during the cutting process within a very small gauge volume.In the present study the method of in situ diffraction with high-energy synchrotronX-radiation was used for the first time for a comprehensive study of the chip formationprocess during orthogonal cutting experiments. Information about the microstructuraldevelopment in terms of local microstrains, domain sizes, stacking fault probabilitiesand preferred crystal orientations as well as the spatially resolved stress states withinthe chip formation zone have been obtained from diffraction data. For the workpiecesteel C45E with bcc structure and the fcc aluminium alloy AlCuMg1 the influenceof the cutting parameters were studied through a variation of the undeformed chipthickness, the cutting edge radius and the rake angle. On the basis of the results frombrass alloys CuZn10, CuZn37 and CuZn40 the influence of the stacking fault energyand the influence of a second phase have been investigated for various rake angles.A significant dependence of the maximum stresses on the rake angles was observed.The maximum stresses increase upon a decreasing rake angle. In contrast, the maximumstresses do not show a significant dependence on the undeformed chip thicknessand the cutting edge radius. However, a significant dependence of the stress gradientswas observed. Stronger stress gradients can be observed with smaller undeformedchip thickness, smaller cutting edge radius and higher rake angles. During chip formationa strong decrease in domain sizes and an increase in microstrains can be observedwhich proves a strong strain hardening within the chip.The microstructural gradients show identical behaviour as the macroscopic stresses,exhibiting a clear relation between the microstructural development and the evolvingstress state.A further strain hardening was proven within the observed built-up edges, due to thedecrease in domain sizes and an increase in microstrains. The strain hardening resultsin an increase in the von Mises stresses and the hydrostatic stresses.For the first time, the results of a cutting simulation could be compared to experimentaldata. It was concluded that the appearing differences between experiment andsimulation are mainly addressed to the disregard of the strong microstructural developmentand the resulting strain hardening of the material. Using the shear angle relationof OPITZ and HUCKS it could be shown that the experimental data on the stress statesin the chip formation zone can be used to verify and extend existing chip formationmodels. It is shown that the assumption of a free chip flow could not be hold. Therefore,a extension of the relation considering the normal stresses in direction of the chipflow is necessary for a correct calculation of the shear angle.
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