Untersuchungen zur Spanbildung metallischer Werkstoffe anhand von in situ Röntgenbeugungsexperimenten

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

Untersuchungen zur Spanbildung metallischer Werkstoffe anhand von in situ Röntgenbeugungsexperimenten

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 stresse

In situ high energy X-ray diffraction for analyzing the local stress distribution and microstructure in the chip formation zone during orthogonal cutting of steel C45E

The stress distribution in the chip formation zone during cutting is an asked question in the field of manufacturing technology and is required for a fundamental understanding of the chip formation process. New synchrotron facilities with high photon flux provide the opportunity to measure the local strains with a high spatial resolution. Therefore, the steep stress gradients in the chip formation zone can be analyzed. Performing in situ high energy synchrotron X-ray diffraction during orthogonal cutting at the HEMS beamline (PETRA III/Hamburg), the beam size and therefore the measuring positions could be reduced to 0.02 mm x 0.02 mm. The stress distribution exhibits steep stress gradients and shows significant dependencies on the cutting parameters and a strong change of the microstructure was observed, namely a reduction of domain sizes and the development of a shear texture. The results of these in situ experiments serve to evaluate and extend existing chip formation models and will be used for the optimization of FEM (Finite Element Method) cutting simulations

Stresses during orthogonal cutting of Aluminium Al2017 samples analysed by in situ diffraction

The local stress distribution in the chip formation zone of the aluminium alloy Al2017 was analysed, whereby Al2017 serves as an characteristic example for materials with fcc structure. Therefore, diffraction studies with synchrotron X-radiation during orthogonal cutting of aluminium Al2017 samples were performed at the High Energy Materials Science beamline P07 at the storage ring PETRA III in Hamburg/Germany. Additionally, the measurement provided information about the microstructural development in the chip formation zone by means of the FWHM (full width at half maxima), reflection intensities and texture. The data was recorded by the 2D detector MAR345. The cutting setup was integrated in a tension/compression testing machine, which realized the movement of the workpiece by the movement of the upper die. The beam had a cross section of 20x20 µm. The influence of important cutting parameters such as the rake angle, cutting edge radius and undeformed chip thickness on the stress distribution was proven. Steep stress gradients were observed normal to the shear plane. Compressive stresses are existing in the shear zone for all directions, whereby the highest stresses were found in cutting direction. Tensile stresses were observed behind the cutting edge. The strongly deformed areas in the chip formation zone show a reduction of domain sizes. Also the formation of a texture was observed which is more pronounced for measuring positions with a strong shear deformation. The experimental results will be used to improve FEM (Finite Element Method) simulations and evaluate and extend existing chip formation modells

Stress distribution in the chip formation zone of fcc materials Al2017 and alpha brass analysed by in situ diffraction

The stress distribution in the chip formation zone during cutting is an asked question in the field of manufacturing technology and leads to a fundamental understanding of the chip formation process. The local strains in the chip formation zone were obtained in situ by high energy synchrotron X-ray diffraction during orthogonal cutting at the HEMS beamline (PETRA III/Hamburg).The present study compares the stress states of two fcc materials, namely the aluminium alloy Al2017 and single phase alpha brass

Stress distribution in the chip formation zone of brass alloys with different zinc contents analysed by in situ diffraction

The research of machining processes with geometrically defined cutting edge, such as drilling, milling and turning, plays an important role in the field of production technology, because machining processes are intensely used in industrial manufacturing techniques. In this context, the stress distribution in the chip formation zone during cutting is an asked question and requires a fundamental understanding of the chip formation process.High energy synchrotron X-ray diffraction during orthogonal cutting enables the spatially resolved measurement of the local strains in the chip formation zone [1, 2]. The in situ diffraction experiments were performed at the HEMS beamline (PETRA III/Hamburg) with a beam size of 20 x 20 µm². The experiments were performed in transmission geometry with a 2D-Detector (Fig. 1a). The measuring positions within the chip formation zone are shown in Fig. 1b.The present study compares the stress states of the brass alloys CuZn40, CuZn37 and CuZn10. This selection includes single and two phase alloys as well as alloys with different stacking fault energies due to the variation of the Zn-content, whereby a higher Zn-content results in lower stacking fault energies. The soft material CuZn10 exhibits only small stress gradients whereby an increase in the zinc content leads to higher strength and thus to steeper stress gradients and higher stresses. These differences in the stress distributions lead to different shear angles and therewith have an influence on the chip geometry