Metallic hollow sphere structures (MHSS) are advanced composite materials characterised by a high geometrical reproducibility with relatively constant mechanical and physical properties. The success of such new developed materials depends not only on the production itself. The techniques for further processing and joining are essential. Joining technologies like brazing or gas metal arc welding influence the hollow sphere structures bulk material with a considerable amount of heat. The laser beam welding is a highly efficient technique with a comparatively small heat input. The laser beam ensures only local heat influences and allows individual structures for specific sandwich geometries. The joining of blanks with hollow sphere structures expands the applications and possibilities for them. The challenge of welding hollow sphere structures, for example with blanks to a sandwich structure, lies in the low density of hollow spheres. The surface tension of the molten hollow sphere structures forces the melt to form droplets out of bulk material. The metallic hollow sphere structure vanishes. The missing material can be balanced by feeding massively a wire into the welding bath. However, the additional mass is not suitable for light weight constructions. A joint between the molten feeding wire and a hollow sphere can still not be ensured. Classical joining technologies with a big amount of heat would dissolve the complete hollow sphere structures and are not suitable. In this paper the mechanical properties of laser beam welded hollow sphere structures sandwich structures are presented. The welding was done by a CO 2 -laser with a wave length of 10.6 lm and a maximum power of 1.5 kW. Different geometries of joints have been investigated. The specimens are tested for shear and bending strength. The strength of the weld lines depend on the density of the hollow sphere structures. Higher density raises the strength. Eigenfrequencies have been simulated by modal analysis. Results of simulated and measured values show comparable results, starting by 2 kHz for 1 mm thick blanks and 3 kHz for 2 mm blanks.
Laser drilling is a highly efficient technique to generate holes in almost any material. It offers an alternative manufacturing method to mechanical drilling and water stream cutting. The relatively small amount of heat involved in the process results in a small heat affected zone. This characteristic makes laser processing interesting for several engineering application. Within this chapter the drilling process is applied to cellular materials. A program code was developed and implemented in order to predict the relation between the initial parameters and the final characteristics of the drilling process, such as depth-time behavior for each amount of initial energy. The simulation of the laser drilling process uses the concept of homogenized cellular materials. It is studied the influence of the heat intensity of the laser in the process. Also the influence of material parameters like thermal conductivity, specific heat and enthalpy are studied. The results of the simulations of the drilling process closely match to the experimental results. The thermal conductivity is of paramount importance for the final results of the laser drilling procedures. The program code can be used for example to the optimization of the laser drilling procedures and to determine or confirm the material properties of the materials as well.
Laser beam cutting is a highly efficient technique to cut materials. The relatively small amount of energy being involved during the process results in a small heat affected zone. This characteristic makes laser beam cutting interesting for composite materials. Within this paper the cutting process is applied to metallic hollow sphere structures (MHSS), a relatively new group of advanced composite materials. The metallic hollow sphere structures combine the well-known advantages of cellular metals without major scattering of their material parameters. They are characterised by high geometry reproduction leading to relatively constant mechanical and physical properties. Numerical simulation is used in order to define proper process parameters for a large variety of metallic hollow sphere structures. The finite element method based simulation covers material parameters as well as process parameters like the cutting velocity. Heat conduction, convection and heat radiation is taken into account. The temperature distribution is our fundamental result. It should be mentioned that phase change from solid to liquid state is also included in the computational procedure. Keywords: Laser beam cutting / Cellular Metals / Finite Element Method / Das Laserstrahlschneiden ist ein hocheffizientes Trennverfahren. Der relativ geringe Energieeintrag während des Bearbeitungsprozesses hat eine kleine Wärmeeinflusszone zur Folge. Diese Eigenschaft macht das Laserstrahlschneiden für Verbundwerkstoffe interessant. In diesem Artikel wird das Laserstrahlschneiden auf metallische Hohlkugelstrukturen (MHKS) angewandt, einer neuen Klasse von Verbundwerkstoffen. Die metallischen Hohlkugelstrukturen vereinen die wohlbekannten Vorteile zellulärer Metalle ohne die breite Streuung der makroskopischen Werkstoffeigenschaften. Sie lassen sich durch hohe Reproduzierbarkeit in der Geometrie charakterisieren, die zu relativ konstanten mechanischen und physikalischen Materialeigenschaften führen. Hier wird die numerische Simulation zur Definition von geeigneten Prozessparametern für eine Vielzahl von MHKS herangezogen. Die Finite Elemente Analysen umfasst sowohl Werkstoffparameter als auch Prozessparameter wie beispielsweise die Schnittgeschwindigkeit. Wärmeleitung, Konvektion und Wärmestrahlung wie auch der Phasenübergang beim Schmelzen können im Simulationsmodell berücksichtigt werden. Die Temperaturverteilung ist das wesentliche Ergebnis.
In manufacturing engineering, especially in machining process, the definition of a reference plane is the first essential step within the overall process. After the reference plane is applied at the component all other features are processed with reference to this basic plane. During any process the component has to be clamped in order to resist the processing forces. There are several clamping systems available, such as pneumatic, magnetic systems or magneto-rheological (MR) systems. Depending on its stiffness the component is deformed due to the clamping forces, stresses are introduced. This effect can be neglected for components with a high stiffness and nearly rigid body behaviour. However, the deformation of low stiff components under clamping forces, e.g. sheet metals, is relatively large and is in the same range as the addressed accuracy of machining process. Due to the introduced elastic clamping stresses the component will reconfigure after clamping, this phenomenon is known as springback.The focus of this work is the design of a clamping system for flexible bodies in order to reduce the springback and to enable high precision processing. This clamping system consists in a set of supports, which adjust to the surface of the body without introducing stresses and causing no springback after the machining process. The number and the arrangement of the supports are optimized as a function of the intensity and position of the milling force and the geometrical and mechanical properties of the body as well. The functional unit of the clamping system is a cylindrical bodysliding nearly frictionless within a pipe. Numerical simulation is used for configuration and optimization. The developed clamping systems can also be used to process freeform shaped bodies. In der spanenden Bearbeitung ist die Schaffung einer Referenzfläche, an der sich alle weiteren Bearbeitungen orientieren, der erste wesentliche Schritt. Zur Aufnahme der Bearbeitungskräfte werden Werkstücke üblicherweise gespannt, beispielsweise über pneumatische, magnetische oder magnetorheologische Systeme. Je nach Steifigkeit erfährt das Werkstück dadurch Deformationen, die wiederum Spannungen hervorrufen. Während dieser Effekt für Werkstücke mit hoher Steifigkeit vernachlässigt wird, können die Deformationen bei weniger steifen Werkstü-cken, wie beispielsweise bei Blechen, in der gleichen Größenordnung wie die geforderte Bearbeitungsgenauigkeit liegen. Die nach der Bearbeitung auftretende Rück-federung macht die angestrebte Bearbeitungsgenauigkeit zunichte.Corresponding author: C. Janousch, Aalen University, Beethovenstraße 1, 73430 Aalen, Germany, E-Mail: Christoph.Janousch@hs-aalen.de 1 Aalen University, Beethovenstraße 1, 73430 Aalen, Germany 2 KMS-Metall, Gottlieb Daimlerstraße 3, 73460 Hüttlin-gen, Germany Mat.-wiss. u. Werkstofftech. 2015, 46, No. 4-5 DOI 10.
Heat conductivity is a well-known energy transfer method and it is here applied to the study of metal foams and laser processing. Metallic hollow sphere structures (MHSS), a relatively new group of advanced composite materials, combine the advantages of cellular metals without major scattering of their material parameters. They are characterised by high geometry reproduction leading to relatively constant mechanical and physical properties.The laser processing technology provides not only a laser cutting but also a laser soldering procedure. Within this work a laser cutting process is applied to MHSS. Laser beam cutting is a highly efficient technique to cut materials, because the relatively small amount of heat affects only a small heating zone.Numerical simulation is used in order to define proper process parameters for a large variety of MHSS. The finite element method based simulation covers material parameters as well as process parameters like the cutting velocity. Heat conduction and convection are taken into account and the phase change from solid to liquid state as well. Within the simulations the concept of representative volume element (RVE) is applied. The temperature distribution is the fundamental result.
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