DEVELOPMENT OF LOW-MELTING GLASSCERAMIC BONDS FOR HIGH RESOURCE DIAMOND-ABRASIVE TOOLS

Research is aimed at creating high-resource diamond-abrasive tools with a large-pore structure of the working layer, the use of which reduces the occurrence of grinding defects when processing materials sensitive to overheating. The formation of an open structure of the working layer ensures effective chip removal, which excludes a decrease in the сutting ability of the tool due to contamination with grinding sludge and creates favorable conditions for intensifying the processing of materials when using high-speed cutting modes. As part of the research, low-melting glass-ceramic binders for diamond-abrasive tools have been developed, which make it possible to increase the tool service life due to the prevention of diamond grains premature destruction and the creation of a large-pore open structure of the working layer. Using a set of calculated data about the main characteristics of glass compositions by factor planning means, the dependences «composition - properties» were determined and the area of optimal compositions of glass-ceramic bonds was established, which ensure sintering of a diamond-containing composite at a temperature of 550–650 °C. The efficiency of the use of alumino-silicate microspheres of technogenic origin as a structure-forming filler providing the formation of a large-pore structure is shown. The features of the chemical and phase composition of the technogenic spheres recovered from the fly ash of the Krivoy Rog TPP have been determined. It has been established that when the diamond-bearing layer of the tool is sintered in the shell of the ash spheres, crystalline new formations with high hardness (hercynite, mullite, maghemite, spinel) are formed. Using ash spheres and developed low-melting binders, which include up to 30 mass. % of glass waste, the laboratory samples of diamond-containing composites with open porosity of 45-50% were made. Studies of their microstructure and morphological features made it possible to determine the pore size (130-200 μm) and establish that during grinding, partial destruction of ash spheres occurs with the formation of additional cutting elements, which increases the tool cutting ability. The research results indicate the advisability of using the proposed approach for selection of the diamond-ceramic composite components and the modes of heat treatment of the diamond-bearing layer when creating a tool. This approach will significantly expand the possibilities of manufacturing large-pore diamond-abrasive tools with a high service life at minimal material costs and will improve the processing of parts made of difficult-to-machine materials.

Influence of gas permeability of abrasive tools on their structural and mechanical parameters

Quality assurance and processing capacity are essential performance parameters of abrasive tools. It is of prime importance for grinding wheels operating at a speed of 35–60 m/s. In this case, the opportunities to increase the high-rate grinding efficiency without burns are associated with using high-porosity and low-hardness wheels. Artificial pore-forming agents are used to manufacture tools. Introduction of pore-forming agents decreases grinding forces and increases the maximum grinding depth without burns. The porosity of filled compound materials can be attributed to the conception of gas permeability. The gas permeability parameter describes the openness degree of such structures and the velocity of the air volumes passing through porous materials. The porosity and gas-permeability degrees of the material of high-porous ceramic-bond abrasive tools with various parameters, depending on the abrasive material type, porogen grain size and content, and the composite structure number have been studied. It appeared that the porosity degree of high-porous abrasive tools, made both of fused alumina and silicon carbide increases as the structure number, grain size, and content of burning porogens increases. Besides, the increase degree of fused alumina is a little higher than that of silicon carbide. The gas permeability degree depends on the factors mentioned above in nearly the same way. Compared to porosity, the effect of gas permeability increases due to an altered structure, grain size, and content of porogens is much higher, up to 6 times. In this case, the gas permeability value is primarily characteristic of the pore size; in other words, the speed and volume of the air or lubrication and cooling fluid penetrating the material structure increase correspondingly at nearly the same increase of the pore size by several times and at the same volume porosity degree. The gas permeability degree can be used for quantitative and qualitative description of the material structure of high-porous abrasive tools, as well as their structural and mechanical parameters. The operating parameters of tools can depend on the gas permeability level of their materials. Thus, the results of abrasive processing can be foreseen.

ANALYTICAL DETERMINATION OF THE MICRORELIEF PARAMETERS FORMED AS A RESULT OF CENTERLESS GRINDING OF THE FULL SPHERE

При технологической подготовке операций чистовой и отделочной обработки деталей абразивными инструментами очень важными задачами являются прогнозирование ее результатов в зависимости от назначенных режимов и назначение режимов в зависимости от требуемого качества обработанных поверхностей. Имеющиеся многочисленные справочные материалы такого характера получены в лабораторных условиях, носят дискретный характер, не учитывают специфическую топографию поверхностей абразивных инструментов и множества других условий и поэтому недостаточно достоверны. На их основе возможно планировать технологический процесс только предварительно, а затем неизбежно требуется уточнять его параметры экспериментальным путем, что приводит к значительному удорожанию процесса подготовки производства. Наличие достоверной аналитической методики позволяет кратно снизить эти затраты, и поэтому она настоятельно необходима не только и даже не столько при выполнении научных исследований, сколько в реальном производстве. В статье аналитически определены параметры микрорельефа, образующегося в результате бесцентрового шлифования полной сферы. Уточнено влияние процесса выхаживания на формирование шероховатости сферы. Приведена методика расчета среднеарифметического отклонения микропрофиля сферической поверхности In the technological preparation of the operations of finishing processing of parts with abrasive tools, it is very important to predict its results depending on the assigned modes and the purpose of modes depending on the required quality of the processed surfaces. The available numerous reference materials of this nature were obtained in laboratory conditions, are discrete in nature, do not take into account the specific topography of the surfaces of abrasive tools and many other conditions, and therefore are not reliable enough. On their basis, it is possible to plan the technological process only in advance, and then inevitably it is necessary to refine its parameters experimentally, which leads to a significant increase in the cost of the production preparation process. The availability of a reliable analytical method allows you to multiply these costs, and therefore it is urgently needed not only and even not so much when performing scientific research, but in real production. In the article, we analytically determine the parameters of the microrelief formed as a result of centerless grinding of a full sphere. We determined the influence of the nursing process on the formation of the sphere roughness. We present a method for calculating the arithmetic mean deviation of the micro-profile of a spherical surface

Impregnation of the surface of niobium alloy when grinding with corundum and silicon carbide wheels

The features of the formation of a relief after grinding a niobium alloy with abrasive tools made of corundum and silicon carbide on a ceramic bond are considered. The treated surface is studied with a scanning two-beam electron microscope. Keywords: niobium, grinding, corundum, silicon carbide, material transfer, impregnation, micro-X-ray pattern. [email protected]

Research on The Bonding Properties of Vitrified Bonds With Porous Diamonds and The Grinding Performance of Porous Diamond Abrasive Tools

Ordinary diamond presents the disadvantages of poor self-sharpening and concentrated grinding stress when it is used as an abrasive. Moreover, this kind of diamond cannot be well wetted by the vitrified bond, resulting in a lower holding force of the binder to the abrasives (i.e., the diamond is easy to detach from the binder matrix during grinding). These comprehensive factors not only reduce the surface quality of the processed workpiece, but also hinder the processing efficiency. In order to solve these problems, a new type of porous diamond with high self-sharpening properties was prepared using a thermochemical corrosion method in this study. Our results showed a great improvement in pore volume and specific surface area of the porous diamond compared with ordinary diamond abrasive particles, and the holding force and wettability of vitrified bond to the porous diamond abrasive particles were also improved. Compared with ordinary diamond abrasive tools, porous diamond abrasive tools showed a 29.6% increase in grinding efficiency, a 15.5% decreased in grinding ratio, a 27.5% reduction in workpiece surface roughness, and the scratches on the silicon wafer surface were reduced and refined.

Edge finishing of large turbine casings using defined multi-edge and abrasive tools in automated cells

Automate finishing processes is a global challenge in several industrial sectors. Concretely, when dealing with aero-engine components, only simple finishing processes are automated nowadays. Most of the high-added value components manufactured are finished hand working, using deburring and polishing manual techniques. The driver of the proposed work is to achieve the necessary knowledge to introduce in a production line a complete finishing process for automated robotic deburring applications with low machinability materials (Inconel 718 in this case-study) on aero-engine casings with complex geometries: extruded casting bosses, internal features, etc. For this purpose, a three-step methodology is presented and analysed, providing a feasible workflow combining visual inspection for part positioning and edge location, with multi-edge solid tools and flexible abrasive tools to automate finishing operations, taking into account all process singularities. Results show that, using correct techniques, processes and parameters, an automated finishing process reducing operating time can be implemented in production lines.