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O fresamento de topo de aços ferramenta, no estado endurecido, pode ser uma alternativa para a fabricação de moldes e matrizes, com alta taxa de remoção. Este trabalho estuda os tipos e mecanismos de desgaste presentes nesta operação de usinagem, bem como o comportamento da emissão acústica. São realizados experimentos com ferramentas de PCBN e Metal Duro usinando os aços H13 (49-51 HRc), VMO (54-57 HRc) e VC131 (57-59 HRc). O desgaste das ferramentas de PCBN é significativamente menor que o desgaste das ferramentas de Metal Duro. O tipo de desgaste predominante é o desgaste de flanco, com indícios de desgastes de cratera. É observada uma combinação entre os mecanismos de desgaste abrasivo e adesivo. Não se observa a formação de trincas abaixo da superfície usinada. Verifica-se que a emissão acústica aumenta com a velocidade de corte e mostra-se também dependente do material da peça e da ferramenta. / The endmilling operation applied to the machining of hardened tool steels, can be seen as an alternative to the conventional sequence of operations used in dies and injection moulds. Normally, eletrodischarge machining, which has a low removal rate, is applied for the finishing operation, just before polishing. The present research work study the types and mechanisms of wear that appear in this machining operation, as well as, the behaviour of Acoustic Emission (EA). Experiments are carried out using PCBN and Carbide tools, machining AISI H13 (49-51 HRc), AISI 6F3 (54-57 HRc) e AISI D6 (57-59 HRc). The wear observed on the PCBN tools was smaller than that on the carbide ones. The type of wear dominating was flank wear, with some presence of crater wear in a few machining conditions. It was also observed a combination between the abrasive and the adhesive mechanisms. It was not noted any cracks on the surface just below the machined surface. The acoustic emission showed to be directly proportional to the cutting speed and also dependent upon the workpiece material and to the tool material.

O fresamento de topo de aços ferramenta, no estado endurecido, pode ser uma alternativa para a fabricação de moldes e matrizes, com alta taxa de remoção. Este trabalho estuda os tipos e mecanismos de desgaste presentes nesta operação de usinagem, bem como o comportamento da emissão acústica. São realizados experimentos com ferramentas de PCBN e Metal Duro usinando os aços H13 (49-51 HRc), VMO (54-57 HRc) e VC131 (57-59 HRc). O desgaste das ferramentas de PCBN é significativamente menor que o desgaste das ferramentas de Metal Duro. O tipo de desgaste predominante é o desgaste de flanco, com indícios de desgastes de cratera. É observada uma combinação entre os mecanismos de desgaste abrasivo e adesivo. Não se observa a formação de trincas abaixo da superfície usinada. Verifica-se que a emissão acústica aumenta com a velocidade de corte e mostra-se também dependente do material da peça e da ferramenta. / The endmilling operation applied to the machining of hardened tool steels, can be seen as an alternative to the conventional sequence of operations used in dies and injection moulds. Normally, eletrodischarge machining, which has a low removal rate, is applied for the finishing operation, just before polishing. The present research work study the types and mechanisms of wear that appear in this machining operation, as well as, the behaviour of Acoustic Emission (EA). Experiments are carried out using PCBN and Carbide tools, machining AISI H13 (49-51 HRc), AISI 6F3 (54-57 HRc) e AISI D6 (57-59 HRc). The wear observed on the PCBN tools was smaller than that on the carbide ones. The type of wear dominating was flank wear, with some presence of crater wear in a few machining conditions. It was also observed a combination between the abrasive and the adhesive mechanisms. It was not noted any cracks on the surface just below the machined surface. The acoustic emission showed to be directly proportional to the cutting speed and also dependent upon the workpiece material and to the tool material.

Powder metals are becoming a popular choice in the automotive and other manufacturing industries because of their ability to meet wide ranging product functional requirements without compromising the performance of the product. They offer various advantages, including weight reduction, near net-shape processing capability, and their ability to be sintered to achieve desired properties in the end-product. However, in order to satisfy the product design requirements during manufacturing, they need to be machined to the required tolerances. Machining of powder metals is quite different to machining of traditional metals because of their specific properties, including porosity. This thesis work deals with the finish machining of powder metal steels in automotive applications, for increased tool-life/reduced tool-wear. Tool-life is affected by a variety of factors such as tool grade selection, tool coating, cutting conditions and tool geometry including cutting edge geometry. This work involves optimization of cutting conditions for plunge cutting and boring operations of automotive powder metal components using PCBN and carbide tools. The cycle time of the process introduces an additional constraint for the optimization model along with the tool-wear criterion. Optimized cutting conditions are achieved for maximum tool-life.

This licentiate thesis has the main focus on evaluation of the wear of coated and uncoated polycrystalline cubic boron nitride cutting tool used in cutting operations against hardened steel. And to exam the surface finish and integrity of the work material used. Harder work material, higher cutting speed and cost reductions result in the development of harder and more wear resistance cutting tools. Although PCBN cutting tools have been used in over 30 years, little work have been done on PVD coated PCBN cutting tools. Therefore hard turning and hard milling experiments with PVD coated and uncoated cutting tools have been performed and evaluated. The coatings used in the present study are TiSiN and TiAlN. The wear scar and surface integrity have been examined with help of several different characterization techniques, for example scanning electron microscopy and Auger electron spectroscopy.   The results showed that the PCBN cutting tools used displayed crater wear, flank wear and edge micro chipping. While the influence of the coating on the crater and flank wear was very small and the coating showed a high tendency to spalling. Scratch testing of coated PCBN showed that, the TiAlN coating resulted in major adhesive fractures. This displays the importance of understanding the effect of different types of lapping/grinding processes in the pre-treatment of hard and super hard substrate materials and the amount and type of damage that they can create. For the cutting tools used in turning, patches of a adhered layer, mainly consisting of FexOy were shown at both the crater and flank. And for the cutting tools used in milling a tribofilm consisting of SixOy covered the crater. A combination of tribochemical reactions, adhesive wear and mild abrasive wear is believed to control the flank and crater wear of the PCBN cutting tools. On a microscopic scale the difference phases of the PCBN cutting tool used in turning showed different wear characteristics. The machined surface of the work material showed a smooth surface with a Ra-value in the range of 100-200 nm for the turned surface and 100-150 nm for the milled surface. With increasing crater and flank wear in combination with edge chipping the machined surface becomes rougher and showed a higher Ra-value. For the cutting tools used in milling the tendency to micro edge chipping was significant higher when milling the tools steels showing a higher hard phase content and a lower heat conductivity resulting in higher mechanical and thermal stresses at the cutting edge.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Hardened steel is usually machined under dry condition. Application of an overhead flood cooling generally leads to premature tool failure because the heat generated that helps the shearing process needed to form the chips is reduced by its cooling action. This work proposes to study the application of MQF (Minimum Quantity of Cutting Fluid) when turning the heat treated hardened AISI D6 steel with PCBN (Polycrystalline Cubic Boron Nitride) tools and compare with the dry machining. The spray of a vegetable based cutting fluid was applied between the workpiece and the flank face of the tool. Overhead direction of the MQF and between the secondary flank face of the tool and the workpiece were also tested. Tool wear (VB), surface roughness (Ra, Rz e Rq) and cutting forces (Fx, Fy e Fz) were considered the output variables and the results were compared to those obtained when cutting in dry condition. The influence of the input parameters: cutting speed and feed rate, as well as their interactions were statistically analyzed. Considering the tool wear and the surface roughness, the application of the cutting fluid by the MQF technique in the direction between the flank face and the workpiece showed better results than the dry condition when employing the lowest feed rate of 0.05 mm/rev, regardless the cutting speed used. This cutting fluid application technique also presented good results when the cutting speed of 310 m/min was tested, regardless the feed rate employed. Therefore, this cutting speed should be recommended for high production in turning of AISI D6 steel with the MQF technique. The application of MQF through other directions (overhead and between the secondary flank face and the workpiece) also showed competitive results. / Aços temperados são geralmente usinados na condição a seco. A aplicação de uma refrigeração geralmente conduz a uma falha prematura da ferramenta porque o calor gerado durante o processo, que ajuda o cisalhamento, é reduzido pela ação refrigerante do fluido de corte. Este trabalho propõe estudar a aplicação do método de MQF (Minima Quantidade de Fluido) ao tornear o aço tratado termicamente, classe AISI D6, utilizando ferramenta de PCBN (Nitreto Cúbico de Boro Policristalino) e comparar com a condição a seco. A pulverização de um fluido de corte de base vegetal foi aplicada entre a peça de trabalho e a superfície de folga da ferramenta. A direção sobre-cabeça e entre a superfície de folga secundária e a peça também foram testadas em algumas condições de corte. O desgaste da ferramenta (VB), a rugosidade superficial (Ra, Rz e Rq) e as forças de usinagem (Fx, Fy e Fz) foram utilizadas como parâmetros de saída e seus resultados foram comparados com os resultados obtidos nos testes na condição a seco. As influências dos parâmetros de entrada: velocidade de corte e avanço, bem como suas interações, nas variáveis de saída (desgaste da ferramenta, rugosidade superficial e forças de usinagem) foram analisados através de métodos estatísticos. Considerando o desgaste da ferramenta e a rugosidade superficial da peça, a aplicação do fluido de corte pela técnica MQF na direção da superfície de folga principal apresentou melhores resultados que a condição a seco, quando se utilizou o menor avanço testado de 0,05 mm/rev, independente da velocidade de corte. Esta técnica também apresentou bons resultados quando a velocidade de corte de 310 m/min foi testada, independente do avanço. Assim, esta velocidade de corte deve ser recomendada para uma boa produção no torneamento do Aço AISI D6 com a técnica MQF. A aplicação do MQF nas outras direções (sobrecabeça e na superfície de folga secundária) também mostrou resultados competitivos. / Mestre em Engenharia Mecânica

This licentiate thesis has the main focus on evaluation of the wear of coated and uncoated polycrystalline cubic boron nitride cutting tool used in cutting operations against hardened steel. And to exam the surface finish and integrity of the work material used. Harder work material, higher cutting speed and cost reductions result in the development of harder and more wear resistance cutting tools. Although PCBN cutting tools have been used in over 30 years, little work have been done on PVD coated PCBN cutting tools. Therefore hard turning and hard milling experiments with PVD coated and uncoated cutting tools have been performed and evaluated. The coatings used in the present study are TiSiN and TiAlN. The wear scar and surface integrity have been examined with help of several different characterization techniques, for example scanning electron microscopy and Auger electron spectroscopy.   The results showed that the PCBN cutting tools used displayed crater wear, flank wear and edge micro chipping. While the influence of the coating on the crater and flank wear was very small and the coating showed a high tendency to spalling. Scratch testing of coated PCBN showed that, the TiAlN coating resulted in major adhesive fractures. This displays the importance of understanding the effect of different types of lapping/grinding processes in the pre-treatment of hard and super hard substrate materials and the amount and type of damage that they can create. For the cutting tools used in turning, patches of a adhered layer, mainly consisting of FexOy were shown at both the crater and flank. And for the cutting tools used in milling a tribofilm consisting of SixOy covered the crater. A combination of tribochemical reactions, adhesive wear and mild abrasive wear is believed to control the flank and crater wear of the PCBN cutting tools. On a microscopic scale the difference phases of the PCBN cutting tool used in turning showed different wear characteristics. The machined surface of the work material showed a smooth surface with a Ra-value in the range of 100-200 nm for the turned surface and 100-150 nm for the milled surface. With increasing crater and flank wear in combination with edge chipping the machined surface becomes rougher and showed a higher Ra-value. For the cutting tools used in milling the tendency to micro edge chipping was significant higher when milling the tools steels showing a higher hard phase content and a lower heat conductivity resulting in higher mechanical and thermal stresses at the cutting edge.

Quantitative understanding of frictional phenomena between the tool and the workpiece is essential for accurate modeling of the Friction Stir Welding (FSW) process. Two methods of measuring the tool-workpiece interface are proposed that allow frictional measurements to be made under extreme conditions. The first method uses a cylindrically curved surface in contact with a flat plate. The ranges of temperature, velocity, and normal force used in this method are 100–600°C, 0.38–2.0 m/s (75–400) surface feet per minute (SFM)), and 450–2700 N (100–600 lbf), respectively. Data are gathered at different parameter level combinations to provide enough data to create an empirical model representing the data. Two friction modes with distinct characteristics are observed. One mode, Coulomb-Amonton's friction, has frictional force proportional to normal force, while the other mode, plastic shear deformation friction, has frictional force independent of normal force. A linear statistical model has been developed to characterize each of the frictional modes for the polycrystalline cubic boron nitride (PCBN) tool and 1018 steel work piece interface as functions of temperature, velocity, and normal force. Two linear models were chosen. A statistical method called membership function regression was used to determine the coefficients of these two models. The resulting model has a correlation of (Predicted Force) = 1.0445(Measured Force) with an R^2 value of 0.83. The second method was an attempt to measure friction with a measurable contact area at a range of temperatures, velocities, and normal pressures. This method rubs the end of a cylindrical rod with a concentric cylindrical pocket against a flat plate. This method caused precessions of the tool on the workpiece. As a result of this precession, plastic shear deformation friction measurements are invalid. However, Coulomb-Amonton's friction is still valid. The experiments of the PCBN-stainless steel interface found that Coulomb-Amonton's friction did not depend on temperature and velocity. In addition, no plastic shear deformation friction was identified using this method and this interface combination.

In this study, friction spot welding was used to join DP980 steel sheet. Four different ultra-hard tool materials were used with the objective of determining which tool material produced the highest number of acceptable-strength welds. Three of the tools were composed of various mixtures of polycrystalline cubic Boron Nitride (PCBN), Tungsten, and Rhenium. These materials are referred to herein as Q60, Q70, and Q80, the "Qxx" designation denoting the percentage of the volume of the tool material composed of PCBN. The fourth tool tested was composed entirely of PCBN. The Q70 tool produced approximately 1100 welds of acceptable strength before average weld strength decreased below the acceptable value, and the Q60 tool produced approximately 600 welds of acceptable strength. The Q80 material did not produce any welds with strengths above the acceptable value. However, Q80 produced the greatest number of welds of consistent strength. The PCBN tool, being the hardest, also did not produce any welds of acceptable strength, and failed at 257 welds. This failure is presumed to be a result of a tool/parameter mismatch which caused excessive loads on the tool. This research revealed that the weld parameters and tool materials used in this study will not generally provide for feasibility of implementation in industry. Further advances in weld parameter selection, tool geometry, and tool materials will be necessary in order to make friction spot joining of high strength steels an economically viable option.

This thesis covers some aspects of hard part turning of carburised steels using a poly‑crystalline cubic boron nitride (PCBN) cutting tool during fine machining. The emphasis is on the influence of the steel cleanliness and the characteristics of non‑metallic inclusions in the workpiece on the active wear mechanisms of the cutting tool. Four carburising steel grades suitable for automotive applications were included, including one that was Ca‑treated. A superior tool life was obtained when turning the Ca-treated steel. The superior machinability is associated with the deposition of lubricating (Mn,Ca)S and (CaO)x-Al2O3-S slag layers, which are formed on the rake face of the cutting tool during machining. Moreover, the transfer of work material to the rake face crater is characteristic in hard part turning of clean steels. It can be because of the lack of sulfides that protect the cutting edge when turning machinability treated steels. This corresponds to the more pronounced crater wear caused by the low‑sulfur steels than that of the steels with higher sulfur contents. It was also concluded that the composition of the non‑metallic inclusions in the Ca‑treated steel is a more important factor than the inclusion number and size, in hard part turning using a PCBN cutting tool. Also, a 3D analysis after electrolytic extraction was found to give a more precise characterisation of non‑metallic inclusions than the conventional 2D analysis by SEM‑EDS. In turn, better correlations to machinability and mechanical properties can be obtained. Hence, the use of this technique is beneficial for future material development. Finally, the challenge for future metallurgy is to manufacture high‑performance steels with improved combined properties of mechanical strength and machinability. / <p>QC 20150422</p>