Precisão dimensional e qualidade de superfície usinada são fundamentais em componentes de aplicações mecânicas. Dentre as variáveis que exercem influência sobre estes fatores, está a grande quantidade de calor gerado na usinagem, que deve ser reduzida, minimizando seus efeitos na ferramenta e na estrutura superficial e sub-superficial da peça. Reduzir este calor e seus efeitos é uma das funções da lubri-refrigeração, porém, intensificamse as pesquisas com o objetivo de restringir ao máximo o uso destes fluídos. Neste trabalho, analisou-se a eficiência da lubri-refrigeração na qualidade da superfície usinada, no desvio dimensional e na variação microestrutural de amostras do aço AISI 4140 com diferentes microestruturas, usinado pelo processo de torneamento longitudinal. Observou-se que a lubri-refrigeração não teve efeito considerável sobre a qualidade da superfície usinada, não apresentando uma melhora significativa na rugosidade. Na questão dimensional observou-se que, em mais de 60% dos ensaios realizados, os resultados com e sem a presença da lubri-refrigeração mantiveram-se dentro da faixa de tolerância préespecificada, e na avaliação microestrutural, avaliando a deformação plástica, observou-se que houve uma queda na dureza da borda do material, em comparação com regiões mais próximas do centro do corpo-de-prova. / Dimensional deviation and surface quality are fundamental components for mechanical applications. The variables that influence these factors, the quantity of heat generated must be reduced in order to minimize their effects on tool and on the superficial and sub-superficial structure of the piece. Reducing this heat and its effects is one of the cooling functions; however, the researches trying to restrict the use of those fluids. In this work, the cooling efficiency was analyzed on the surface quality, dimensional deviation and microstructural variation of AISI 4140 steel samples machined with different microstructure by longitudinal turning process. As a result, it was found that the cooling is not a significant effect on surface quality, not improving the roughness. In regard to dimensional, it was noticed in more than 60% of tests that the results with and without the presence of cooling kept between the pre-specified tolerance ranges. In the microstructural analysis, analyzing the plastic deformation, it as noticed that the hardness decrease in the edge of the sample, comparing with the center.

The machining of a new alloy often presents a challenge. While useful assumptions can be drawn from materials of similar properties, there will always be unpredictable outcomes. Titanium alloys have been employed in the aerospace industry due to their high mechanical properties and good strength-to-weight ratio. Ti-64 (Ti-6Al-4V) was the standard choice until recently, when Ti-555.3 (Ti-5Al-5V-5Mo-3Cr) began to take its place. Ti-555.3 has improved resistance to fatigue and higher mechanical properties compared to Ti-64 and is able to maintain its strength when exposed to high temperatures, which warrants its acceptance for many applications. However, its chemical reactivity, low thermal conductivity and high mechanical properties are known to cause challenges when cutting this alloy. Making use of both experimental procedures and computational resources, this work presents a comparison between these two aerospace alloys under different process conditions, setting the ground for further academic development and optimization strategies. Determining that these alloys are substantially different from a machinability standpoint (lower tool life, abrasion & chipping as dominant wear mechanisms and nonuniform chip formation for Ti555.3 versus Ti-64). Based on this further investigation should be carried out for optimal tooling selection to improve the machining of Ti555.3. / Thesis / Master of Applied Science (MASc)

Particle-reinforced MMCs (pMMC) such as aluminum alloys reinforced with ceramic silicon carbide particles (AlSiC) require special cutting tools due to the high hardness and abrasive properties of the ceramic particles. Diamond coated cutting tools are ideal for machining this type of pMMC. Previous research studies focus on the machinability of pMMCs with low ceramic content. The aim of this research is to determine the optimal cutting parameters for machining AlSiC material containing high silicon carbide particle reinforcement (>25%). The optimal cutting parameters are determined by investigating the relationship between cutting forces, tool wear, burr formation, surface roughness, and material removal rate (MRR). Experimental milling tests are conducted using CVD diamond coated end mills and non-diamond tungsten carbide end mills. It was found that low tool rotation speeds, feed rates and depths of cut are necessary to achieve smoother surface finishes of R a < 1 μm. A high MRR to low tool wear and surface roughness ratio was obtainable at a tool rotation speed of 6500 r/min, feed rate of 762 mm/min and depth of cut of 3 mm. Results showed that a smooth surface roughness of the workpiece material was achieved with non-diamond tungsten carbide end mills, however, this was at the expense of extreme tool wear and high burr formation. The use of coolant caused a 50% increase in tool wear compared to the dry-cutting experiments which had lower cutting tool forces.

Automobile and aero industries have an increasing interestin materials with improved mechanical properties. However, manyof these new materials are classified as difficult-to-cut withconventional tools. It is obvious that tools, cutting processesand cutting models has to be devel-oped parallel to materialsscience. In this thesis rotary cutting tools are tested as analternative toexpensive diamond or cubic bore nitridetools. Metal matrix composites mostly consist of a light metalalloy (such as aluminium or titanium) reinforced with hard andabrasive ceramic parti-cles or fibres. On machining, thereinforcement results in a high rate of tool wear. This is themain problem for the machining of MMCs. Many factors affect thelife length of a tool, i.e. matrix alloy, type, size andfraction of the reinforcement, heat treatment, cuttingconditions and tool properties. In tests, the Al-SiC MMC formed a deformation layer duringmilling, probably affected by lack of cooling. The dominatingfactor for tool life was the cutting speed. Water jet or CO2cooling of turning did not provide dramatic increase in toollife. With PCD, cutting speeds up to 2000 m/min were usedwithout machining problems and BUE formation. Tool flank wearwas abrasive and crater wear created an "orange-peel type" wearsurface. PCD inserts did not show the typical increase in flankwear rate at the end of its lifetime. The use of self-propelled rotary tools seems to be apromising way to increase tool life. No BUE was formed on therotary tool at high cutting data. The measurements indicatethat the rotary tool creates twice as good surface as PCDtools. The longest tool life was gained with an inclinationangle of 10 degrees. Tool costs per component will beapproximately the same, but rotary cutting tool allows higherfeeds and therefore a higher production rate and thus a lowerproduction cost. The rotary cutting operation might have a potential toincrease productiv-ity in bar peeling. The lack of BUE withrotary cutting gives hope on higher tool life. The test resultsshow that tool wear was 27% lower with rotary cutting tools.Increase of cutting speed from 22 to 44 m/min did not affectcutting forces. This indicates that the cutting speed canincrease without significant change in tool wear rate. Issues related to rotary cutting like cutting models,cutting processes, standards, tools and models have beendiscussed. A tool wear model with kinetic energy has beendiscussed. KEYWORDS:Difficult-to-Cut material, Metal MatrixComposite (MMC), Machining, Machinability, Rotary Cutting Tool,Acoustic Emission / <p>QCR 20161026</p>

A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Masters of Science in Engineering, 2016 / This research is focused on optimizing the surface integrity of Ti-6Al-4V using advanced carbide inserts and minimum quantity lubrication (MQL). Experiments were designed to machine twenty Ti-6Al-4V blocks under dry and MQL lubricating conditions using innovative cemented carbide inserts produced by Liquid Phase Sintering (LPS) and Spark Plasma Sintering (SPS). The cutting speed, feed rate, and depth of cut, were considered as machining parameters, while the cutting force, temperature, tool wear, surface roughness and residual stress were considered as performance characteristics. The results obtained for surface roughness and residual stress measurements were used to analyze the surface integrity of the machined Ti-6Al-4V samples. The influence of sintering techniques and milling parameters on performance characteristics and surface integrity were investigated from experimental results obtained. Discrepancy in behavioral trends with respect to lubricating conditions was also investigated. The analyses of milling results showed that cutting speed played a major role in the optimization of surface integrity of the Ti-6Al-4V work pieces followed by the depth of cut. The results also showed that the LPS inserts performed better than the SPS inserts due to their better mechanical properties (higher fracture toughness (KIC) and transverse rupture strength). The application of MQL was also observed to significantly reduce milling temperatures resulting in better surface integrity. However, an optimized surface integrity of the Ti-6Al-4V samples was achieved during MQL milling with the 10Co-L insert at a low finishing speed of 75m/minute and a reduced depth of cut of 0.5mm.

Les technologies de fabrication additive(FA) basées sur la technique de fusion laser sur lit de poudres, telles que les procédés de fusion sélective laser (Selective Laser Melting ‘SLM’) et de fusion par faisceau d'électrons (Electron Beam Melting ‘EBM’), ne cessent de se développer afin de produire des pièces fonctionnelles principalement dans les domaines aérospatial et médical. Le procédé de fabrication additive offre de nombreux avantages, tels que la liberté de conception, la réduction des étapes de fabrication, la réduction de la matière utilisée, et la réduction de l'empreinte carbone lors de la fabrication d'un composant. Néanmoins, les pièces obtenues nécessitent une opération d’usinage de finition afin de satisfaire les tolérances dimensionnelles et l’état de surface. / Additive Manufacturing (AM) techniques based on powder bed fusion like Selective Laser Melting(SLM) and Electron Beam Melting processes(EBM) are being developed to make fully functional parts mainly in aerospace and medical sectors. There are several advantages of using AM processes like design freedom, reduced process steps, minimal material usage and reduced carbon footprint while producing a component. Nevertheless, the parts are built with near net shape and then finish machined to meet the demands of surface quality and dimensional tolerance.

Este trabalho apresenta estudos de usinabilidade de chapas MDF (Medium Density Fiberboard), tendo por objetivo principal efetuar uma análise do desempenho de corte em relação à qualidade da superfície usinada e à força específica de corte paralela necessária, a fim de se verificar a influência dos parâmetros estudados para operações de usinagem de acabamento e desbaste, respectivamente. No estudo para operação de acabamento verificou-se a influência da espessura de corte,velocidade de avanço e sentido de corte, em operação de fresamento cilíndrico periférico, sobre a rugosidade superficial da borda das chapas MDF. Uma fresadora vertical foi utilizada para gerar as superfícies, cuja rugosidade superficial foi medida por um perfilômetro de apalpamento. No estudo para operação de desbaste, a força específica de corte paralela foi avaliada em função da variação do ângulo de saída, da espessura de corte e da profundidade de corte, em operação de corte ortogonal. Para tanto, foram empregadas uma plaina limadora e uma célula de carga de extensômetros resistivos, conectada a um programa de aquisição e análise de dados. A partir da análise dos resultados obtidos, foi possível identificar a influência de cada parâmetro de corte empregado. / This work presents a MDF (Medium Density Fiberboard) machinability study aiming to carry out a cutting performance analysis regarding to surface quality and parallel specific cutting force, in order to verify the cutting parameters effect on the finishing and roughing machining operations, respectively. In the finishing study, it was verified the effect of the cutting thickness, cutting speed and direction of cutterhead rotation with relation to feed direction, in peripheral milling, on the MDF edges surface roughness. The surfaces were developed by a moulder, which roughness were measured by a stylus perfilometer. In the roughing study, the parallel specific cutting force was assessed in relation to the variation of the rake angle, cutting thickness and depth of cut, for the orthogonal cut. For this, it was used a planing machine and a resistance dynamometer, coupled in a data acquisition and analysis system. From the analysis of the obtained results, it was possible to identify the influence of each cutting parameter considered.

Orientador: Marcos Valério Ribeiro / Banca: Manoel Cleber de Sampaio Alves / Banca: Amauri Hassui / Resumo: A utilização de ensaios de avaliação da usinabilidade dos materiais pode ser um fator determinante na viabilidade de processos de fabricação, contribuindo no planejamento dos custos, prazos e na busca pela qualidade do produto através de desenvolvimentos de estratégias e tecnologias de usinagem. Quando o produto usinado é um cilindro, que faz o papel de ferramenta no processo de laminação, a necessidade de tal desenvolvimento fica clara quando se analisa os requisitos para alta performance de cilindros de laminação e se identifica que eles são os mesmos requisitos para alta performance de insertos de usinagem: resistência ao desgaste, tenacidade e dureza. Assim esse trabalho propõe um ensaio de usinabilidade em laboratório para a avaliação de dois materiais de cilindros de laminação: o ferro fundido indefinido e o ferro fundido indefinido microligado. O ensaio foi executado através do fresamento com três arestas de metal duro em um centro de usinagem e a análise de usinabilidade foi feita pelo critério de fim de vida da ferramenta de usinagem. Foi constatado que a adição de elementos de liga na composição química dos cilindros influenciou diretamente na usinabilidade do ferro fundido indefinido microligado, pois a fração volumétrica de carbonetos VC aumentou em quase três vezes nesse material resultando em um desgaste abrasivo nas arestas das ferramentas de corte / Abstract: The use of tests to evaluate the machinability of the material may be a determining factor in the viability of manufacturing processes, and contribute to planning the cost, time and in the search for the quality of the product through development of strategies and machining technologies. When the machined product is rolling mill roll, who played as a tool in the milling process the need for such development becomes clear when is examined the requirements for high performance rolling mill roll and identifies that they are the same requirements for high performance machining tools: wear resistance, toughness and hardness. So, this work proposes a machinability test in laboratory seeking the evaluation of two materials for rolling mill rolls: an indefinite chilled double poured cast iron and a microalloyed indefinite chilled double poured cast iron. The test was performed by milling with three edges of carbide on a machining center and the machinability analysis of this work was done by the criterion of end of life of the machining tool. The work found that the addition of alloying elements on the chemical composition of the rolling mill rolls directly influenced the machinability of microalloyed indefinite chilled double poured cast iron, because the volume fraction of carbides VC increased by almost three times in this material resulting in an abrasive wear on the edges of cutting tools / Mestre

<p>U radu je izvršeno eksperimentalno istraživanje procesa obrade struganjem u cilju saznanja o obradivosti termički obrađenog čelika Izvršeno je modeliranje funkcija obradivosti preko izmerenih karakteristika stanja procesa: sila rezanja, hrapavosti obrađene površine, temperature u procesu rezanja i habanja alata. Modeliranje funkcija obradljivosti je izvršeno pomoću faktornog plana eksperimenta, kao i primenom veštačkih neuronskih mreža. Analiziran je uticaj režima rezanja, geometrije alata, vrste materijala alata i habanja alata na pomenute izlazne parametre procesa.</p> / <p>The experimental study of the process of turning is carried out in order to learn about the machinability of thermally treated steel. The modeling of the machinability functions through the measured characteristics of the process state is carried out: the cutting force, the roughness of the machined surface, the temperature in the cutting process and tool wear. The modeling of the machinability functions was done using the experimental factor design, as well as the application of artificial neural networks. Tool geometry, tool material and wear influence on output parameters was analised</p>

<p>Large improvements in cutting tool design and technology, including the application of advanced surface engineering treatments on the cemented carbide insert, have been achieved in the last decades to enhance tool performance. However, the problem of improving the tool body material is not adequately studied.</p><p>Fatigue is the most common failure mechanism in cutting tool bodies. Rotating tools, tool going in and out of cutting engagement, impose dynamic stresses and require adequate fatigue strength of the tool. Working temperatures of milling cutter bodies in the insert pocket can reach up to 600°C depending on the cutting conditions and material of the workpiece. As a result, steel for this application shall have good hot properties such as high temper resistance and high hot hardness values to avoid plastic deformation in the insert pocket of the cutting tool. Machinability of the steel is also essential, as machining of steel represents a large fraction of the production cost of a milling cutter.</p><p>This thesis focus on the improvement of the cutting tool performance by the use of steel grades for tool bodies with optimized combination of fatigue strength, machinability and properties at elevated temperatures.</p><p>The first step was to indentify the certain limit of the sulphur addition for improved machinability which is allowable without reducing the fatigue strength of the milling cutter body below an acceptable level. The combined effect of inclusions, surface condition and geometrical stress concentrator on the fatigue life of the tool steel in smooth specimens and in tool components were studied in bending fatigue.</p><p>As the fatigue performance of the tools to a large extent depends on the stress relaxation resistance at elevated temperature use, the second step in this research was to investigate the stress relaxation of the commonly used milling cutter body materials and a newly steel developed within the project. Compressive residual stresses were induced by shot peening and their response to mechanical and thermal loading as well as the material substructures and their dislocation characteristics were studied using X-ray diffraction.</p><p>Softening resistance of two hot work tool steels and a newly developed steel was investigated during high temperature hold times and isothermal fatigue and discussed of with respect to their microstructure. Carbide morphology and precipitation as well as dislocation structure were determined using transmission electron microscopy and X-ray line broadening analysis.</p>