Search

Abstract: The systematic interaction of sedimentation and electrical field in electrophoretic deposition allows the tailoring of specific properties of deposited green bodies. This technique permits a selective deposition of the nanosized fraction of conventional powders with broad or non-monomodal particle size distribution, thus making preceding classification obsolete. Potential applications are coatings with a very smooth surface or the replication of microstructures or moulds which are filled with nanosized particles and subsequently with coarser particles as support in one process step. Also, graded structures can be fabricated with regard to particle size distribution, porosity and composition (e.g. zirconia toughened alumina). In this paper, the interaction of sedimentation and electrical field in electrophoretic deposition is described. In addition the effectiveness of the combined process will be shown. [Copyright &y& Elsevier]

Abstract: Electrophoretic deposition (EPD) is mostly used for producing moulds and layers. The present work shows the fabrication of ceramic microparts by the use of structured electrodes. As electrode structures euro coins and spinning nozzles were used. Additionally a cost effective and simple method was developed, which allows preserving the original master mould by using microstructured silicone moulds as substrate. This was enabled by coating the silicone moulds with graphite to obtain an electrically conductive surface, required for electrophoretic deposition. [Copyright &y& Elsevier]

Based on previous work, the material properties of zirconium disilicide containing net-shape ceramic compositions are adjusted to minimize the edge flaking that occurs during micromilling of the green bodies. The material compositions (besides ZrSi2, also containing ZrO2, Al2O3, MgO, SiO2, and a polysorbate) are granulated and axially dry pressed to pellets, which are wet milled with a 0.5-mm-diameter tool. The structure's edge flaking is quantitatively determined and compared with previous results. The mechanical properties of the green and sintered bodies are also characterized. The strengths of the green bodies depend on their composition and treatment. Additionally, a correlation between the Weibull moduli of the green compacts and the moduli of the sintered parts is shown. For the sintered ceramics, Weibull strengths of up to 344 MPa can be achieved. It is also shown that the dimensional accuracy of the net-shape material is maintained. [ABSTRACT FROM AUTHOR]

Two-component micropowder injection molding allows two different materials and, hence, two different functions to be integrated in one microdevice. This requires both components to be matched precisely. Therefore, high dimensional accuracy is essential in the successful development of a two-component micropart. This paper is about studies of the accuracy of the diameters of the inner hole of a gear wheel to be used as the first component of a shaft-to-collar connection. Diameters were measured in two defined directions, oriented 90° relative to each other. Items discussed are the size accuracy of green bodies and sintered specimens as well as the effects of different gating concepts. Sometimes, the inner hole is eccentric, depending on the gating concept employed. It was shown that a point-shaped gate can exert pressure on the feedstock nearby, thus causing deformation and reducing the diameter in these areas compared to the diameter in areas far from the gating system. The results also show that the eccentricity of the inner hole after sintering differs from that measured on green bodies, which is an indication of anisotropy in sintering. Moreover, the types of powder were seen to have an effect. [ABSTRACT FROM AUTHOR]

Abstract: At Karlsruhe Institute of Technology (KIT), a He-cooled divertor design for future fusion power plants has been developed. This concept is based on the use of modular cooling fingers made from tungsten and tungsten alloy, which are presently considered the most promising divertor materials to withstand the specific heat load of 10MW/m2. Since a large number of the finger modules (n >250,000) are needed for the whole reactor, developing a mass-oriented manufacturing method is indispensable. In this regard, an innovative manufacturing technology, Powder Injection Molding (PIM), has been adapted to W processing at KIT since a couple of years. This production method is deemed promising in view of large-scale production of tungsten parts with high near-net-shape precision, hence, offering an advantage of cost-saving process compared to conventional machining. The complete technological PIM process for tungsten materials and its application on manufacturing of real divertor components, including the design of a new PIM tool is outlined and, results of the examination of the finished product after heat-treatment are discussed. A binary tungsten powder feedstock with a solid load of 50vol.% was developed and successfully tested in molding experiments. After design, simulation and manufacturing of a new PIM tool, real divertor parts are produced. After heat-treatment (pre-sintering and HIP) the successful finished samples showed a sintered density of approximately 99%, a hardness of 457 HV0.1, a grain size of approximately 5μm and a microstructure without cracks and porosity. [Copyright &y& Elsevier]

Two-component micro powder injection moulding experienced significant progress in the recent past. Starting as a manufacturing method for integrating two different plastics, the extension of two-component injection moulding (2C-IM) from pure plastics to more resistant materials like ceramics or metals (2C-PIM) provided sophisticated and challenging applications. With the transfer of 2C-PIM to micro systems, two-component micro powder injection moulding (2C-MicroPIM) was established. Up to a certain extend sinter joining is an alternative to 2C-PIM. It allows for component assemblies to be moulded as separate low-complexity parts which are then joined into complex assemblies. This procedure considerably reduces the time and cost required to manufacture the injection moulding tools. This article gives an overview of the development of 2C-MicroPIM-from two component plastic devices to the production of complex two-component micro assemblies made of two ceramic or metallic materials and the state-of-the-art of science and technology of sinter joining. [ABSTRACT FROM AUTHOR]

Two-component micro powder injection moulding (2C-MicroPIM) is a special variant of micro injection moulding. It enables the integration of two different functions in one micro assembly due to the combination of different materials. By 2C-MicroPIM it is possible to realise fixed and movable connections. For both applications, the two components have to be adapted well to each other. The adaptation has to cover the materials as well as the processes. In this context, especially the sintering process is of importance since the degree of shrinkage and physiochemical processes at the interface between both components determine either the formation of a fixed junction between the components or the formation of a gap. Both processes are temperature-dependent. Therefore, it can be assumed that by a certain temperature these processes can affect the interface in such a way that it may get in conflict with the formation of movable connections, i.e., there is a limiting temperature at which the components are not joined together. Above this temperature joining of the components occurs at least partially. For this study, shaft-to-collar connections were produced by 2C-MicroPIM. They consist of a gear wheel made of zirconia feedstock and an axle made of alumina feedstock. The 2C-MicroPIM process has influence on the characteristics of the micro parts, like functionality, density and mechanical properties. This work focuses on movability of the shaft-to-collar connection as the most important function. The sintering temperature required for movable connections constitutes important limits for the overall process. The aim of our presented work is to determine the limit temperature or temperature range at which movable connections cannot be formed due to the mentioned processes. Furthermore it was analysed if there is a smooth transition from movable connections to unmovable connections with increasing temperature or if this transition takes place within a small temperature range. Within a given temperature interval the portion of movable connections out of all sintered samples were counted for each peak temperature. The results showed that the number of movable connections decreases with increasing peak sintering temperature. Hence, production of movable connections has a limit with respect to sintering temperature. This temperature limit was found to be sharply defined at around 1,460-1,470°C. [ABSTRACT FROM AUTHOR]

The increasing importance of two-component microinjection molding is due to the potential to integrate different functionalities in one assembly without applying additional procedures. Furthermore, it enables a mass production technique of assemblies made up of two or more components. For mechanical advantages like toughness, hardness, or sufficient tribological behavior, metal or ceramic materials have to be used; the resulting process type is known as two-component micropowder injection molding (2C-MicroPIM). As this technology permits, in principle, the realization of fixed as well as movable junctions, a variety of new applications will be available. However, the two crucial aspects of 2C-MicroPIM research are the selection of adequate materials and an optimized process development. This article describes the challenges and approaches of the process development. The feasibility of ceramic 2C-MicroPIM assemblies has been demonstrated by a shaft-to-collar connection, which is composed by a zirconia gear wheel and a shaft made of alumina. [ABSTRACT FROM AUTHOR]

The progress in microinjection molding has paved the way for the fabrication of complex components. Particularly, the integration of different functionalities made possible by two-component injection molding is a challenging facet of this technology. For the production of robust microdevices consisting of two different metals or ceramics a special variant of this technology has to be implemented: two-component micropowder injection molding (2C MicroPIM). The study presents the materials and powder combinations suitable for 2C MicroPIM. The investigations included considerations on materials behavior during feedstock compounding, injection molding, debinding, and sintering of the assemblies. As a result of dilatometric measurements and on the basis of theoretical considerations and characterization of a 2C MicroPIM part at the phase boundary the requirements beneficial for either a fixed or a movable junction were defined. A shaft-to-collar connection was used to demonstrate the applicability of the selected materials. The investigated ceramic powders and the organic components for the feedstock development for the realization of a shaft-to-collar connection with 2C MicroPIM are clearly applicable when a dispersant like stearic acid is added. [ABSTRACT FROM AUTHOR]

Two-component micro powder injection moulding (2C-MicroPIM) broadens the scope of possible microsystem applications since it facilitates the integration of two different materials and, hence, also two different functions in one micro assembly. As shown recently, not only two-component micro parts with fixed junctions can be produced, but, in principle, also parts with movable connections. This paper describes the difficulties associated with the realisation of shaft-to-collar connections with a movable junction. As an approach the gating concept of the injection moulding tool was changed. With the modified injection moulding tool, movable connections were obtained after sintering the micro parts to a maximum temperature of 1,450°C. Thus, the production of sintered movable connections does no longer require additional steps. [ABSTRACT FROM AUTHOR]

Powder injection molding is a preferred technology for the production of micro parts or microstructured parts. Derived from the well known thermoplastic injection molding technique it is suitable for a large-scale production of ceramic and metallic parts without final machining. To achieve good surface quality and control the part size and distortions is an important goal to allow mass production. This means that all process steps like part design adjusted for MIM/CIM-technology, appropriate choice of powder and binder components and injection molding simulation to design the sprue are required. Concerning the injection molding itself high quality mold inserts, high-precision injection molding with suitable molding machines like Battenfeld Microsystem50 or standard machine with special equipment like variotherm or evacuation of the molding tool and an adjusted debinding and sintering process have to be available. Results of producing micro parts by powder injection molding of ceramic feedstock will be presented. [ABSTRACT FROM AUTHOR]

Multi-component injection molding combined with electroplating, the so-called MSG process, represents a promising process chain to replicate metallic microstructures. MSG is the German acronym of ‘Mehrkomponenten-Spritzgießen und Galvanoformung’, in English ‘Multi-component Injection Molding and Electroplating’. The process is based on the highly accurate reproduction of surface details through injection molding to build a microstructure into a two-component template and electrodeposition of e.g. nickel into this cavity. This electroplated micropart is the replication of the former structure. To study the influence of the mold insert on the accuracy of the molded part and the produced microparts, a test specimen was fabricated and analyzed using a milled mold insert. On the mold insert, three microcoil parts, the components of a microgripper, were micromilled. The effect of the individual process steps on the surface quality and dimensional changes of the final microcoil will be presented. It will also be shown how the quality of the injection molding insert influences the dimensional accuracy of the produced microparts. Finally, potential process improvements will be outlined. [ABSTRACT FROM AUTHOR]

Abstract: The combustion synthesis in “Ti–TiO2” and “Ti–Al” powdery mixtures in air under atmospheric pressure has been studied. The results of X-ray diffraction analysis showed TiN and AlN as prevalent phases in the combustion products. Hence, the deep interaction with atmospheric nitrogen during metals combustion in air occurs. The mechanism of TiN and AlN formation instead of thermodynamically stable TiO2 and Al2O3 formation by burning in air is proposed on the basis of XRD and SEM data. [Copyright &y& Elsevier]