Oscillator-based approach for modeling process dynamics in NC milling with position- and time-dependent modal parameters

Oscillator models provide an efficient approach for simulating the dynamic behaviour of the machine, tool, or workpiece. In their application, however, these models are usually limited to describing the vibration behaviour at one specific position since they do not contain any information about the structure of the machine tool or the workpiece. Additionally, the variation in time dependent parameters caused by the material removal process is not taken into account. In this paper, an adapted model, which takes the position- and time-dependent modal parameters during NC milling into account, is presented and its experimental validation with respect to the machining of thin-walled components is discussed.     

Microstructure and Local Strain Fields in a High‐Alloyed Austenitic Cast Steel and a Steel‐Matrix Composite Material after in situ Tensile and Cyclic Deformation

The tensile and cyclic deformation behaviour of a new metastable austenitic stainless cast TRIP (TRansformation Induced Plasticity) steel and a composite material consisting of austenitic steel matrix (AISI 304) with 5% MgO partially stabilized ZrO₂ (MgO‐PSZ) was studied in‐situ in a scanning electron microscope (SEM). In‐situ tests in the SEM show the evolution of the microstructure with the strain for uniaxial deformation and the number of cycles during fatigue, respectively. Initially, deformation bands develop. In these bands, the face‐centred cubic austenite transforms into the hexagonal ε‐martensite and subsequently to the body‐centred cubic α'‐ martensite. This evolution was studied by different SEM techniques. Electron backscatter diffraction (EBSD) was applied for phase and orientation identification. The dislocation arrangement was investigated applying the electron channelling contrast imaging (ECCI) technique to different deformation stages. The studies are completed with measurements of local displacement fields using digital image correlation (DIC).     

环锭纱与转杯纱的结构差异及其对织物的影响

通过显微镜可以观察到：环锭纱的结构与转杯纱完全不同。表现在纤维被束缚进入纱体的方式各异且各纤维的取向和顺直度不同。这些结构上的差异是由不同的环锭和气流纺纱工艺特点所造成的，但也会由纺织品应用时对纱线的误解所形成。     

Microstructure and mechanical properties of fine grained carbon-bonded Al2O3–C materials

Fine grained carbon-bonded Al₂O₃–C materials as used in ceramic filters have been manufactured by uniaxial and isostatic pressing, respectively. The variation in the microstructure over the cross section of the samples which in particular depends on the shaping technique plays an important role in the wetting of the material by liquid steel. Moreover, the amount and grain size of the binder has a decisive influence on the porosity and bulk density and therefore on the mechanical properties. For this, two different grain size distributions of Carbores^® P binder were used, and in addition the fraction of binder was varied from 5–30 wt%. Tests of the cold crushing strength and of the cold modulus of rupture were performed at room temperature. The adjusted bulk density, open porosity and shrinkage of the samples were determined and the microstructure was analyzed by means of scanning electron microscopy. For control of a homogeneous distribution of carbon in the samples, the residual carbon content was measured also within individual samples at different positions.     

Virtual process systems for part machining operations

This paper presents an overview of recent developments in simulating machining and grinding processes along the NC tool path in virtual environments. The evaluations of cutter–part-geometry intersection algorithms are reviewed, and are used to predict cutting forces, torque, power, and the possibility of having chatter and other machining process states along the tool path. The trajectory generation of CNC systems is included in predicting the effective feeds. The NC program is automatically optimized by respecting the physical limits of the machine tool and cutting operation. Samples of industrial turning, milling and grinding applications are presented. The paper concludes with the present and future challenges to achieving a more accurate and efficient virtual machining process simulation and optimization system.     

Direct free-form deformation of NC programs for surface reconstruction and form-error compensation

In this paper a new approach for manufacturing modified workpieces by milling is presented. In course of product development, several optimization iterations are often required, in which the shape of the workpiece is modified. Conventional method for manufacturing modified workpieces includes a time-consuming and error-prone step of reverse engineering, where the new CAD/CAM data is generated with respect to the measurement data of the manufactured workpiece. The new approach generates a continuous deformation function in order to approximate the discrete displacement vectors between the initial and the modified shapes, and applies this function on the original NC programs of the workpiece. Hence, it is possible to directly manufacture the modified shape. The process of reverse engineering can be eliminated so that manufacturing costs and the time from workpiece design to the production decrease significantly.     

Epitaxial Bragg mirrors for the mid-infrared and their applications

Bragg interference mirrors consisting of stacks of dielectric layers with an optical thickness of a quarter wavelength are of great importance for optoelectronic device applications. For the mid-infrared spectral range mirrors with high reflectivity stop bands are fabricated from combinations of Pb_1−xEu_xTe/EuTe materials by molecular beam epitaxy on BaF₂ substrates. These mirrors designed by the transfer matrix method exhibit reflectivities in excess of 99% by only 3 Bragg mirror layer pairs and very wide stop band regions, reaching a width of up to 60% of the target wavelength. Based on these very efficient mirrors, planar microcavities are demonstrated with an ultra-high effective finesse of up to 1700. Stimulated emission between 3 and 6 μm is obtained by optically pumping a vertical-cavity surface-emitting laser containing PbTe quantum wells with Pb_1−xEu_xTe barriers as active medium embedded between two dielectric Bragg mirrors. Depending on the design of the resonator, pulsed laser operation is observed up to 65°C. The enhancement of light absorption in the cavity is used to study the absorption of superlattices containing correlated self-organized PbSe quantum dots.     

Betriebserfahrungen mit dem Vollgatter und ihre Auswertung

Zusammenfassung Das Bestreben, die Zerspanungsverluste beim Rundholzeinschnitt auf dem Vollgatter zu vermindern, führt zur Feststellung, da? haupts?chlich Unvollkommenheiten in der S?genspannung den Einsatz dicker S?gen mit gro?er Eigensteifigkeit erfordern. Es werden Anregungen gegeben, wie diese M?ngel zu beheben und beachtliche volkswirtschaftliche Vorteile durch Holzersparnis zu erzielen sind.