【文章內(nèi)容簡介】 mall and plex shaped parts especially made of ceramics since handling expenses for ceramic parts can reach up to 80% of the overall costs [5]. For MicroPIM of real structures with a large surface to volume ratio, however, additional process variations are required arising from the high content of inanic powder in the feedstock and the physical properties like high thermal conductivity and density gradients: ? To replicate micro features the powder particle size bees significant because features are in the range of the surface roughness for normal PIM applications. By using coarse powders no good profile quality could be obtained. For micro features the average particle size should be one to two magnitudes smaller than the structural details. Sometimes very fine powders in the submicron range are required [6]. ? The strength of the feedstock is mainly controlled by the interfacial strength of the inanic particles and the binder matrix. For demolding microparts without flaws, the feedstock has to have a sufficient strength. ? MicroPIM of plex microponents has to be carried out at elevated tool temperatures to prevent freezing of the feedstock before filling all details of the mold. The tool temperature has to be in the range of the glass transition temperatures or the crystallite melting point depending on the type of thermoplastics used as a binder in the feedstocks. Prior to demolding, the injection molding tool has to be cooled down to a demolding temperature determined by the material and the specific microstructures. This tempering cycle leads to relatively long cycle times in micro injection molding and has to be pensated by ., increasing the number of microstructured mold cavities [7, 8]. ? Micro structures represent “blind holes” which are filled from the face of the mold insert. Normally the trapped air in the mold can escape through the dividing plane when injecting. For MicroPIM, however, any gap must be avoided because it would be filled by the feedstock. Therefore, the tool has to have a sealing and the machine periphery must be equipped with a vacuum unit to be able to evacuate the mold prior to injection molding to avoid the socalled Dieseleffect [7, 8]. ? Using conventional injection machines for micro parts the predominant amount of feedstock is needed for the runner system and supporting structures. Additionally, the residence time of the thermoplastic material is increased leading to degradation and reduced properties of the parts [9]. Sometimes the micro parts cannot be molded separately but are placed on a base plate. The costly rework for isolating should be avoided using smaller injection molding machines especially adapted to micro injection molding. This article describes the development of MicroCIM for the fabrication of isolated microparts for a micro annular gear pump. The microparts were made of zirconia with a desired thickness of 500 μm by MicroCIM. New methods for the finishing of ceramic microparts with very tight tolerances as well as the assembling of ponents of a micro annular gear pump had to be developed and are reported. 2. Design and preparation Fig. 2 shows an exploded viewof the micro annular gear pump. The diameter of the housing parts is mm. The housing parts should be fixed using pins. More dimensions of microponents are given in Fig. 3. A minimal wall thickness of approximately 80 μm at the rotors arises. Because the power loss of the micro annular gear pump increases with the second order of the gaps between moving parts, the tolerance between moving parts has to be as small as possible. The gaps between external and internal rotors, as well as between external rotor and rotor housing were defined to be less than 3 μm. Note that both rotors also have to be less than 3 μmthinner than the rotor housing to prevent jamming. To guarantee the adjustability of two tolerances between three parts, only one dimension per part can be varied. Since the available space for microparts on a LIGAmold insert is limited to 20 mm times 60 mm only small parts can be varied. Hence, both the outlines of the internal as well as the external rotor were changed. Variations were made by equidistant offsets of the shape in steps of 1 μm resulting in diameter variations of 2 μm for each part. For the internal rotor seven variations were made。 for the external rotor, however, only four variations were made for reasons of limited space. The principle of adjusting the tolerances is displayed in Fig. 4 by picking the appropriate internal rotors to adjust the gap to the external rotor and picking the appr