Materials and Technologies

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Authors: R. Ivănuş
Abstract: The powder metallurgy technique was adopted to prepare SiCp copper alloy matrix composites. The mechanical properties of the composites were measured to investigate the influence of processing parameters, SiC particle characteristics and metallic coating (copper) of the SiC particles. It was found that the mechanical properties of the composites prepared by pressing, sintering, re-pressing, and resintering are superior to those of composites prepared by the pressing and sintering route, and that sintering temperature was an important factor in controlling composite properties. Changes in hardness, theoretical density, ultimate tensile strength, and wear resistance of composites containing SiC of varying silicon carbide content were observed. In all cases, composites made from copper coated SiCp exhibited better properties than those from uncoated particles.
143
Authors: Manuela Covaciu, Traian Canta, Elena Gordo
Abstract: The paper presents studies about reducing the sintering temperature of PM High-Speed Steel obtained by water atomization. The powder was characterized to proceed with compaction and sintering at different temperatures between 1140-1220°C in different atmospheres: nitrogen (N2), nitrogen-hydrogen-methane (N2/H2/CH4) and vacuum. It is described the experiment in able to increase hardness by a quenching and tempering heat treatment that was carried out on sintered samples at 1140°C in vacuum atmosphere at 1200°C in N2/H2/CH4.
147
Authors: Traian Canta, Dan Frunză, Manuela Covaciu
Abstract: The present paper presents experimental results on Al foam produced by powder metallurgy method. Their lightweight property makes them attractive for the cores of structural sandwich panel in products ranging from sport equipment to lightweight building panels. The process of metallic foam manufacture as well as the testing methods used for the characterization of their physical, mechanical and chemical properties will be exposed.
153
Authors: Lorenzo Donati, Luca Tomesani, Lorella Ceschini, Iuri Boromei
Abstract: An original inverse extrusion test was developed in order to study the microstructural evolution in the plastic deformation of 6060 and 6082 aluminium alloys. Sample billets were extracted from commercial logs and subjected to plastic deformation in an inverse extrusion process, particularly aimed at producing different strain and strain rate conditions at representative positions within the billet section. Different experiments were performed at various temperatures and strain rates. The particular thermo-mechanical history of each point in different experiments was then reconstructed by FEM analysis. The cups were sectioned and the microstructure was analysed at some representative locations, to relate it to the FEM simulation results.
157
Authors: I.I. Zaharia, Virgil Geamăn
Abstract: The paper presents some experimental data about the thixoforming process applied to different aluminum alloys very used in the Romanian machine building industry. From many procedures for obtaining the semisolid slurry described in the paper, based on specialized literature [2, 3, 4] in particular, the accent is given to choose the mechanical mixture in the overheated mould until it reached the liquid alloy temperature. The main results are based on reducing of stirring time for increasing the benefits of the new technology. All procedures and results are described in the paper and also some specific conclusions are given. The experimental data of the research, were obtained in the specific testing laboratory from Transilvania University of Brasov.
161
Authors: W. Presz, M. Kaczorowski
Abstract: In metal forming processes in the tool-workpiece contact area occur high pressure, surface expansion and elevated temperature. It makes ideal circumstances for braking of the lubricant film that causes a direct contact between metallic surfaces. Such a contact usually leads to buildups creation on the tool surface. These phenomena mainly result product surface damage. Damages can also refer to tool surface since the hardness of buildups can be comparable with the tool hardness. The cause of this investigation was finding the answer of the question what was the reason of extreme hardness of buildups created during bulk metal forming processes of 1H18N9T austenitic stainless steel. The studies were conducted using transmission electron microscopy (TEM). On the basis of analysis structural and electron diffraction pattern it was suggested that simultaneously to very well known strengthening mechanism like grain refinement, the additional mechanism can not be excluded. Based mostly on the electron diffraction pattern (appearance of forbidden reflexes for FCC) it is suggested that this additional mechanism could be the marthensitic transformation caused by very high plastic deformation.
165
Authors: Khalil Khalili, Seyed Yousef Ahmadi-Brooghani, M. Rakhshkhorshid
Abstract: 3D Scanners are used in industrial applications such as reverse engineering and inspection. Customization of existing CAD systems is one of rapid ways to supplying a 3D Scanning software. In this paper, using AutoLisp and Visual Basic programming languages, AutoCAD has been customized. Also facilities of automatic scanning of physical parts, in the domain of free form surfaces, have been provided. Furthermore, possibilities such as, control of scanner automotive system, representation of registered point clouds, generation of polygon and /or NURBS model from primary or modified point clouds, have been prepared. Triangulation and image processing techniques along with a new fuzzy logic algorithm have been used to extract the depth information more accurate. These, accompanying with AutoCAD capabilities have provided acceptable facilities for 3D scanning.
169
Authors: Liviu Nistor, M. Tintelecan
Abstract: The most important activity of wire drawing technology is the correct design of stages geometry. The wire drawing within a roller die is described by an irregular deformation on wire width, strongly connected by the gauge shape between the rollers and cross section wire surface. Free lateral wire surface that has no contact with the roller on the deformation zone obstructs the wire elongation. There is a biunique correspondence between the shape and dimension of wire that enters between the rollers, and the free space between the rollers, corresponding to a specific stage of drawing. This has a great effect on dimensional accuracy of final wire. A drawing zone feature based model, allowed the examination of interaction evolution between wire and rolls geometry. This analysis helps the user of this technology to make a proper change in the arrangement and position of wire entering between rolls, or in the rolls configuration.
173
Authors: Monica Sas-Boca
Abstract: Friction between powder and tools plays a major role during cold compaction of PM components with results on the inhomogeneous densification. The present work deals with a new method of compaction for PM components by using the friction force between die and compacts as an active pressing force in order to reduce the density gradient. The proposal technique consists in moving the container of the die, during pressing stage to the punch direction with a well determined speed. As a result, the friction force acts in the same sense as the pressing load with better distribution of powder flow during compaction. The experimental results of compaction parameters versus density have proved the decreasing of the density gradient by increasing die/punch speed rate. A sharp density gradient on the specimen height moving container contrarily to the punch.
177
Authors: Nicolae Ghiban
Abstract: Present paper presents the results concerning the modeling process of extrusion of a profile type “Yalle body”. COSMOS soft was used in order to simulate the extrusion process. 3D model contains elements type SOLID, witch simulates the nonlinear behavior in the field of elasticplastic domain. The constitutive equation of Iliusin and Dracker-Prager relation and Von Misses criterion were used in simulation. The three dimensions model contains 1504 nods and 1750 elements in two different position of the die (optimum position and “out of optimum position”). For both of die positions were presented variation of equivalent total stresses, tangential stresses in different steps (1st step, critical step, and 20th step, by dividing the whole extrusion process in equal steps).
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