The air conditioning unit (AC unit) is one of the major sound sources for exterior and interior noise of a railway vehicle. The design of such devices is a compromise between main functions like efficiency, fluid mech...
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In the majority of cases, aluminium matrix composites (AMCs) consist of a relatively ductile matrix and hard ceramic particles embedded therein. In addition to an increased tool wear, machining of these materials invo...
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ISBN:
(纸本)9780956679024
In the majority of cases, aluminium matrix composites (AMCs) consist of a relatively ductile matrix and hard ceramic particles embedded therein. In addition to an increased tool wear, machining of these materials involves surface imperfections like voids and scaling. An approach to reduce the generation of suchlike imperfections is a modification of the cutting edge geometry. Turning tests have shown that smooth surfaces can be generated by using natural diamond tipped tools with a very small clearance angle of approximately 0.5 and a minor feed of 0.05 mm.
This contribution presents current results on ultra-precision grinding and polishing of silicon carbide for mirrors, which has been investigated within the research project MirrorFab. The effects of different grinding...
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ISBN:
(纸本)9780956679024
This contribution presents current results on ultra-precision grinding and polishing of silicon carbide for mirrors, which has been investigated within the research project MirrorFab. The effects of different grinding wheels and process parameters on the shape accuracy, surface roughness and the grinding forces are discussed. It turned out, that surface qualities in the range of 10 nm Rms can be achieved with appropriate parameters. In polishing, the focus is set to the investigation of the effects of various polishing pads and slurries on the material removal rate and surface roughness. Two combinations (polishing pad and slurry) are recommended, one features a high material removal rate for fast removal of grinding marks and the other one a low surface roughness for final smoothing. The presented results enable a systematic adaption of the grinding and polishing processes to the varying requirements in manufacturing silicon carbide mirrors.
In the described investigations, nano-impact tests were conducted on PVD film surfaces previously subjected to micro-blasting at different pressures for constant duration. Micro-blasting improves the film mechanical p...
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ISBN:
(纸本)9789608810433
In the described investigations, nano-impact tests were conducted on PVD film surfaces previously subjected to micro-blasting at different pressures for constant duration. Micro-blasting improves the film mechanical properties due to the induced residual compressive stresses into the coating structure. The film mechanical properties as well as the ratio of the film yield to rupture stress (SY/SM) grow up to a certain micro-blasting pressure. The augmentation of SY/SM ratio increases simultaneously the film brittleness. For analyzing the effect of the SY/SM ratio on the film brittleness, a multi-layer 3D-FEM model simulating the nano-impact test was developed, employing the LS-DYNA software package. The FEM calculated results converge sufficiently with the attained experimental ones. Based on these results, the film's failure initiation and evolution can be predicted depending on the SY/SM ratio of the individual film layers.
Simulation is established within the development process in order to validate technical systems at an early stage. Nonetheless, the required level of detail and the late availability of simulation models limit an econ...
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Simulation is established within the development process in order to validate technical systems at an early stage. Nonetheless, the required level of detail and the late availability of simulation models limit an economic application. This paper describes a novel approach for an interactive and mechatronic design of technical alternatives at early stages of development and in this regard the evaluation with physically based simulation models.
Currently grinding is commonly used as the finishing operation to manufacture seal mating surfaces and bearing surfaces, especially in the automotive industry. It would lead to more resource-efficient production if th...
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Currently grinding is commonly used as the finishing operation to manufacture seal mating surfaces and bearing surfaces, especially in the automotive industry. It would lead to more resource-efficient production if the cost- and energy-intensive grinding process could be replaced by machining with geometrically defined cutting edges, such as hard turning [1] , [2] . However, turning operations usually cause a twist structure on the surface, which can convey lubricants like a pump. Several methods exist to overcome this problem, for example, tangential turning, rotation turning and turn broaching, etc. Due to the high costs of tools and special machines required by these methods, the industrial application is still limited. This paper describes a more efficient approach by applying a modified feed kinematic. When using this approach, hard turning produces twist-free surfaces. The results of the latest twist test methods have confirmed that the surfaces are free of twist, hence free of conveying effect of lubricant and that they are suitable for application in manufacturing of seal mating surfaces and bearing surfaces. Furthermore, this method requires only minimal investment in any turning machine.
Micro-EDM is a well-known process for precision micro machining of difficult to cut materials. It is especially beneficial when machining complex micro structures such as deep bores, grooves or undercuts in highly wea...
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Micro-EDM is a well-known process for precision micro machining of difficult to cut materials. It is especially beneficial when machining complex micro structures such as deep bores, grooves or undercuts in highly wear resistant materials. One constraint is its limitation to electrically conductive materials. Advanced materials such as high-temperature resistant engineered ceramics are gaining more and more importance, nonetheless due to their manifold applications in transport, energy and also biomedical areas. An adaption of micro-EDM to nonconducting ceramics could bring together the design freedom implemented in the EDM process and the beneficial material properties of engineered ceramics. In the last years, research has successfully applied the assisting electrode method to zirconia material, allowing for the micro-EDM to proceed notwithstanding the electrically nonconducting properties. Using suitable dielectric and process parameters, the machining continues even after the electrically conducting starting layer has been removed. Within this study the micro-EDM milling of zirconia is investigated in order to further understand the mechanisms of ceramics machining. Roughness and surface characteristics are analyzed and compared to the equivalent metal parts. The voltage and current signals are recorded using high speed deep memory A/D converters to allow for an insight into the process. With the findings the process can be improved in terms of speed, accuracy and achievable structures.
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