Os processos de manufatura, bem como os parâmetros de processamento utilizados produzem diferentes resultados com relação à integridade de uma superfície. Estas alterações se refletem em mudança das propriedades da superfície, as quais podem influenciar o desempenho dos componentes. O presente trabalho estuda o efeito da integridade superficial gerada pelos processos de torneamento e retificação na resistência à fadiga de contato do aço ferramenta AISI H13. A influência do processo de usinagem e dos parâmetros de corte no estado da superfície e subsuperfície, e como estas características afetam o desempenho são determinados. Foram geradas quatro condições diferentes para as superfícies torneadas mediante a combinação de parâmetros de corte. As superfícies retificadas foram produzidas empregando as mesmas condições de retificação, com isso, obteve-se a mesma condição para todos os corpos de prova ensaiados. As características medidas da integridade superficial foram: os parâmetros de rugosidade, tensões residuais, microdureza Vickers da seção transversal e ruído magnético de Barkhausen. Foi determinado o desempenho das superfícies por fadiga de contato de rolamento, num equipamento na configuração esfera-plano. Os corpos de prova foram anéis de AISI H13 temperados e revenidos. A totalidade dos ensaios foi realizada até a ocorrência de lascamento (Spalling). Os ensaios foram realizados com lubrificação e com uma máxima pressão de contato de Hertz de 3,6 GPa. Foi observado que dependendo do nível de integridade superficial induzido pelo processo de usinagem e dos parâmetros selecionados, o desempenho da superfície em fadiga de contato de rolamento foi afetado. Contudo, as melhores condições de desempenho foram dos materiais retificados, e para os materiais torneados o melhor desempenho foi obtido com maiores velocidades de corte. / The manufacturing process and the machining parameters selected lead to different integrity of the surface, and these characteristics will influence the functional performance of the components. This study evaluated and analyzed the effect of surface integrity on the contact fatigue resistance of the H13 hot work tool steel. The surfaces were manufactured by hard turning and grinding process. Therefore, the influences of the machining process and the cutting parameters on the surface and on the subsurface layer were studied. Four different turned surfaces were obtained as a combination of cutting parameters selected for the tests. On the other hand, grinding surfaces were generated using the same machining conditions. The characteristics of surface integrity evaluated were: surface roughness parameters, residual stresses, Barkhausen noise, and microhardness of surface and sub-layers in transverse section. It was also evaluated the performance of the samples by rolling contact fatigue tests conducted in a ball on washer machine. The specimens were rings made of AISI H13 steel, which were quenched and tempered. All tests were performed until the occurrence of spalling. The tests were carried out under lubrication and with a maximum Hertz contact pressure of 3.6 GPa. Monitoring and failure detection were carried out by analyzing the changes in the vibration signal of the test machine sensors. It was observed that the performance of the surface in rolling contact fatigue resistance was affected by the level of the surface integrity, related to the machining process and the machining parameters.

Les travaux présentés dans cette thèse s'inscrivent dans le cadre du projet européen ACCENT sur la maitrise de l'intégrité de surface par la surveillance lors de l'usinage des pièces critiques aéronautiques. Des études antérieures ont montrées que des anomalies générées lors de l'usinage peuvent induire un abattement sur la tenue en fatigue des pièces. Dans ce contexte, l'objectif de ces travaux est de modéliser la relation entre l'intégrité de surface et les signaux enregistrés lors du perçage de l'Udimet®720. A partir d'une démarche expérimentale basée sur le Couple-Outil-Matière et les plans d'expériences, une caractérisation de l'usure de l'outil, de l'intégrité de surface et des signaux enregistrés a été effectuées en fonction des conditions d‘usinage et du contexte de l'opération (lubrifiant, dureté matière). Cette caractérisation à permis d'établir des corrélations entre les caractéristiques de l'intégrité de surface et celles des signaux. Ces corrélations ont été modélisées par des méthodes directes et statistiques, afin de mettre en avant la pertinence des capteurs de puissance, d'efforts et d'accélération par rapport aux anomalies d'usinage. Ainsi les capteurs permettent la prédiction de la couche de matière affectée par l'opération quelque soit le contexte d'usinage. / The works presented in this thesis join within the framework of the European project ACCENT on surface integrity control by process monitoring during the manufacturing of aeronautical critical parts.Previous studies showed that anomalies generated during the manufacturing process can reduce the fatigue lifecycle. In this context, the objective of this work is to model the relation between the surface integrity and the signals recorded during the drilling of Udimet®720. From an experimental approach based on Couple-Tool-Material and design of experiments, a characterization of tool wear, surface integrity and recorded signals was made according to the cutting conditions and manufacturing disturbances (lubricant, material hardness).This characterization establishes correlations between the characteristics of surface integrity and those of signals. These correlations were modeled by direct and statistical methods, to advance the relevance of sensors (power, efforts and acceleration) with regard to manufacturing disturbances. So the sensors allow the prediction of the thermo-mechanically affected layer generated by the operation in most of manufacturing conditions.

Neste trabalho, estudou-se a integridade superficial durante o torneamento de um ferro fundido nodular com carbonetos, considerando a heterogeneidade microestrutural (fração volumétrica, tamanho e morfologia de grafita e dos carbonetos) e os efeitos dos parâmetros de corte (avanço, velocidade de corte e profundidade de corte), baseados num planejamento fatorial fracionário 24-1. Este texto apresenta, numa primeira parte, uma revisão baseada em referências bibliográficas clássicas da engenharia de superfícies, na tentativa de definir os conceitos que compõem a integridade da superfície. Posteriormente, descrevem-se os resultados de ensaios preliminares, realizados com a finalidade avaliar os níveis do processo e os efeitos desses parâmetros na integridade da superfície. Finalmente, realizaram-se os ensaios de usinagem em corpos-de-prova de ferro fundido nodular com carboneto, nos diâmetros de 80 mm e 140mm. Durante os ensaios de torneamento empregaram-se duas velocidades de corte (60 m/min e 180 m/min), dois avanços (0,1 mm/rev e 0,3 mm/rev) e duas profundidades de corte (0,2 mm e 0,3 mm). Após os ensaios de usinagem, foram realizadas: a avaliação das propriedades do material usinado (dureza e microestrutura), a análise de topografia da superfície usinada mediante avaliação da rugosidade, e a avaliação da influência dos parâmetros de usinagem na rugosidade. Encontrou-se uma dependência estatisticamente significativa da variação nas propriedades mecânicas dos corpos-de-prova em função da microestrutura, e mostraram-se os efeitos dessas variações em termos da integridade da superfície usinada. / In this work, the surface integrity of a ductile cast iron with carbides was studied during turning operations, considering the microstructural heterogeneity (volume fraction, size and morphology of the graphite and carbides) and the effect of the machining parameters (feed, cutting speed and depth of cut), based on a fractional factorial design 24-1. This work presents, initially, a literature review based on classic works on surface engineering, as an attempt to define the main concepts of surface integrity. Later, the results of preliminary test are described, which were conducted in order to define the process levels and the effects of these levels on the surface integrity. Finally, turning tests were conducted on specimens of ductile iron with carbides, at diameters of 80 and 140 mm. Two cutting speeds (60 m/min and 180 m/min), two feeds (0,1 mm/rev and 0,3 mm/rev) and two depths of cut (0,2 mm and 0,3 mm) were selected during the tests. Machined specimens were analyzed in terms of the properties of the machined material (hardness and microstructure) and of the roughness of the machined surface. The effect of the machining parameters on the roughness was also studied. A statistically significant dependence was observed for the properties of the machined specimens as a function of the microstructure and the effect of these properties on the surface integrity is presented.

Neste trabalho, estudou-se a integridade superficial durante o torneamento de um ferro fundido nodular com carbonetos, considerando a heterogeneidade microestrutural (fração volumétrica, tamanho e morfologia de grafita e dos carbonetos) e os efeitos dos parâmetros de corte (avanço, velocidade de corte e profundidade de corte), baseados num planejamento fatorial fracionário 24-1. Este texto apresenta, numa primeira parte, uma revisão baseada em referências bibliográficas clássicas da engenharia de superfícies, na tentativa de definir os conceitos que compõem a integridade da superfície. Posteriormente, descrevem-se os resultados de ensaios preliminares, realizados com a finalidade avaliar os níveis do processo e os efeitos desses parâmetros na integridade da superfície. Finalmente, realizaram-se os ensaios de usinagem em corpos-de-prova de ferro fundido nodular com carboneto, nos diâmetros de 80 mm e 140mm. Durante os ensaios de torneamento empregaram-se duas velocidades de corte (60 m/min e 180 m/min), dois avanços (0,1 mm/rev e 0,3 mm/rev) e duas profundidades de corte (0,2 mm e 0,3 mm). Após os ensaios de usinagem, foram realizadas: a avaliação das propriedades do material usinado (dureza e microestrutura), a análise de topografia da superfície usinada mediante avaliação da rugosidade, e a avaliação da influência dos parâmetros de usinagem na rugosidade. Encontrou-se uma dependência estatisticamente significativa da variação nas propriedades mecânicas dos corpos-de-prova em função da microestrutura, e mostraram-se os efeitos dessas variações em termos da integridade da superfície usinada. / In this work, the surface integrity of a ductile cast iron with carbides was studied during turning operations, considering the microstructural heterogeneity (volume fraction, size and morphology of the graphite and carbides) and the effect of the machining parameters (feed, cutting speed and depth of cut), based on a fractional factorial design 24-1. This work presents, initially, a literature review based on classic works on surface engineering, as an attempt to define the main concepts of surface integrity. Later, the results of preliminary test are described, which were conducted in order to define the process levels and the effects of these levels on the surface integrity. Finally, turning tests were conducted on specimens of ductile iron with carbides, at diameters of 80 and 140 mm. Two cutting speeds (60 m/min and 180 m/min), two feeds (0,1 mm/rev and 0,3 mm/rev) and two depths of cut (0,2 mm and 0,3 mm) were selected during the tests. Machined specimens were analyzed in terms of the properties of the machined material (hardness and microstructure) and of the roughness of the machined surface. The effect of the machining parameters on the roughness was also studied. A statistically significant dependence was observed for the properties of the machined specimens as a function of the microstructure and the effect of these properties on the surface integrity is presented.

NiTi alloys have been the focus of Shape Memory Alloys (SMA) research and applications due their excellent ductility and shape memory properties, and these alloys have been extensively used in automotive, aerospace, and in biomedical applications. The effects of machining on the surface integrity and the corresponding material and mechanical properties of alloys can be best studied by utilizing NiTi alloys as workpiece material since their physical and mechanical properties are highly microstructure dependent. However, due to very poor machining performance of NiTi shape memory alloys, no comprehensive or systematic investigation on this topic has been conducted by researchers as yet. The current study makes a substantial and unique contribution to this area by making the first and significant contribution to studies on machining performance of NiTi shape memory alloys, and by achieving improved surface integrity and machining performance using cryogenic applications, which give significant reductions of tool-wear, cutting forces, and surface roughness. The influence of machining process conditions, including dry, MQL, preheated, cryogenic machining, and the effects of prefroze cryo machining on surface integrity characteristics such as microhardness, phase transformation, phase transformation temperature, depth of plastically deformed layer have been examined extensively, and unique findings have been obtained. The effects of machining process conditions, in particular preheated and cryogenic machining conditions, on thermo-mechanical and shape memory characteristics were identified through thermal cycling and stress-strain tests. For the first time, orthogonal cutting of NiTi shape memory alloys has been carried out in this study to investigate surface integrity comprehensively. Surface integrity and machining performance are compared for dry and prefroze cryogenic cooling conditions under a wide range of cutting speeds. Stress-induced martensitic phase transformation and deformation twinning were found in prefroze cryogenic and dry cutting conditions respectively. The existing microstructure-based constitutive models were used and modified to predict machining-induced phase transformation and resulting volume fraction. The modified model was implemented in commercial FEM software (DEFORM-2D) as a customized user subroutine. The obtained results from simulation and orthogonal cutting tests were compared considering martensitic volume fraction during cutting with various cutting speeds. The model captured the experimental trend of volume fraction induced by various cutting speeds and process variables. Overall, FEM simulation of cutting process of NiTi was successfully presented.

Carbon Fiber Reinforced Polymers (CFRP) are a class of advanced materials widely used in versatile applications including aerospace and automotive industries due to their exceptional physical and mechanical properties. Owing to the heterogenous nature of the composites, it is often a challenging task to machine them unlike metals. Drilling in particular, the most commonly used process for component assembly is critical especially in the aerospace sector which demands parts of highest quality and surface integrity. Conventionally, all composites are machined under dry conditions. While there are drawbacks related to dry drilling, for example, poor surface roughness, there is a need to develop processes which yield good quality parts. This thesis investigates the machining performance when drilling CFRP under cryogenic, MQL and hybrid (CryoMQL) modes and comparing with dry drilling in terms of the machining forces, delamination, diameter error and surface integrity assessment including surface roughness, hardness and sub-surface damage analysis. Additionally, the effect of varying the feed rate on the machining performance is examined. From the study, it is concluded that drilling using coolant/ lubricant outperforms dry drilling by producing better quality parts. Also, varying the feed rate proved to be advantageous over drilling at constant feed.

Porous tungsten is used to manufacture dispenser cathodes due to it refractory properties. Surface porosity is critical to functional performance of dispenser cathodes because it allows for an impregnated ceramic compound to migrate to the emitting surface, lowering its work function. Likewise, surface roughness is important because it is necessary to ensure uniform wetting of the molten impregnate during high temperature service. Current industry practice to achieve surface roughness and surface porosity requirements involves the use of a plastic infiltrant during machining. After machining, the infiltrant is baked and the cathode pellet is impregnated. In this context, cryogenic machining is investigated as a substitutionary process for the current plastic infiltration process. Along with significant reductions in cycle time and resource use, surface quality of cryogenically machined un-infiltrated (as-sintered) porous tungsten has been shown to significantly outperform dry machining. The present study is focused on examining the relationship between machining parameters and cooling condition on the as-machined surface integrity of porous tungsten. The effects of cryogenic pre-cooling, rake angle, cutting speed, depth of cut and feed are all taken into consideration with respect to machining-induced surface morphology. Cermet and Polycrystalline diamond (PCD) cutting tools are used to develop high performance cryogenic machining of porous tungsten. Dry and pre-heated machining were investigated as a means to allow for ductile mode machining, yet severe tool-wear and undesirable smearing limited the feasibility of these approaches. By using modified PCD cutting tools, high speed machining of porous tungsten at cutting speeds up to 400 m/min is achieved for the first time. Beyond a critical speed, brittle fracture and built-up edge are eliminated as the result of a brittle to ductile transition. A model of critical chip thickness (hc) effects based on cutting force, temperature and surface roughness data is developed and used to study the deformation mechanisms of porous tungsten under different machining conditions. It is found that when hmax = hc, ductile mode machining of otherwise highly brittle porous tungsten is possible. The value of hc is approximately the same as the average ligament size of the 80% density porous tungsten workpiece.

The objective of this study is to model material removal with cutting tool in the case of the machining of Titanium alloy (Ti-6Al-4V) and to bring a multi-physic comprehension of chip formation and the tool/workpiece interaction by adopting finite element approaches and methodologies. For that, the present contribution begins by a macroscopic modeling of the orthogonal cutting process. The cut material behavior considered is supposed based on JC law. Moreover, in order to simulate properly the chip genesis, the material fracture energy concept is adopted for controlling the material damage evolution. This allows capturing the shear strain localization and consequently the chip segmentation for a given set of cutting parameters. The frictional contact model considers the influence of temperature on the limiting shear stress at the tool/chip interface. As a result, this reliable model has the capability to simulate the cutting process even with high coefficient of friction and with large cutting edge radius. The parametric study carried out by referring to this model shows a very interesting corroboration with experimental results. In a second step, the present research work presents a material microstructure-level cutting model (MML cutting model) for cutting simulation. The crystal plasticity theory is adopted for modeling the cutting of the Titanium alloy Ti-6Al-4V in orthogonal case. In this model, the grains of the studied material are explicitly considered, and their orientation angles and slip system strength anisotropy are considered as the main source of the microstructure heterogeneity in the cutting material. To simulate the material degradation process, the continuum intra-granular damage and discrete cohesive zone inter-granular damage models are developed, wherein the zero thickness cohesive elements are implemented to simulate the bond between grain interfaces. The material model is validated by a comparison of compression tests from literature. Finally, simulation results demonstrate the possibility to capture the influence of the microstructure on the material removal in terms of chip formation. It is demonstrated that the grain orientation angle plays an important role for the chip segmentation and its periodicity during the cutting process. This certainly can affect the evolution of the cutting force. Additionally, the surface integrity is discussed based on the MML cutting model for different cutting speeds and feed rates. Indeed, a parametric study shows that the surface integrity is seriously affected by the machining parameters, and the affected region is limited within three layer grains for the present MML cutting model.

Made available in DSpace on 2014-06-11T19:24:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-01-21Bitstream added on 2014-06-13T19:11:29Z : No. of bitstreams: 1 fusse_ry_me_bauru.pdf: 1253289 bytes, checksum: 13ba46e6c0ba064145f2121824fa4865 (MD5) / A utilização dos fluidos de corte exige certos cuidados, pois os convencionais atualmente empregados, apresentam em sua composição química produtos que podem gerar doenças aos operadores e trazer prejuízos ao meio ambiente. A manutenção e o descarte dos fluidos apresentam custos elevados. O presente trabalho utilizou um tipo de fluido de corte de origem vegetal isento de substâncias tóxicas, e visa utilizar uma nova técnica de aplicação de fluido de corte, a Mínima Quantidade de Lubrificação (MQL) na retificação cilíndrica externa de mergulho de um aço ABNT 4340 temperado e revenido, utilizado comercialmente na fabricação de eixos, virabrequins e engrenagens cujas solicitações mecânicas são elevadas. A MQL é um método que utiliza uma quantidade menor de fluido de corte com relação aos métodos convencionais e já vem sendo pesquisada em outras operações de usinagem como o fresamento e torneamento. A otimização da aplicação do fluido de corte exigiu a confecção de um bocal especial que permitiu a mistura de fluido com ar comprimido, formando assim uma névoa. Utilizou-se dois tipos de aplicação de fluido de corte (MQL e convencional) e dois rebolos (CBN e Al2O3), obtendo-se como parâmetros de saída a força tangencial de corte, energia específica e a integridade superficial do material retificado. Com relação à integridade superficial analisou-se a rugosidade, a circularidade, a microdureza, a tensão residual e a microscopia eletrônica de varredura (MEV). Os resultados alcançados com a MQL mostraram-se promissores na retificação com os parâmetros utilizados. / The use of cutting fluids demands certain cares, because some of then can contain in their chemical composition products that cause illnesses to the operators and bring damages to the environment. The maintenance and the discarding of this kind of fluids generates high costs. The present work used a type of vegetal cutting fluid free from toxic substances, and aims at to apply a new technique of cutting fluid application, the Minimum Quantity of Lubrification (MQL) in the external cylindrical plunge grinding of a tempered and annealed ABNT 4340 steel, used commercially in the manufacturing of shafts, crankshafts and gears with high mechanical loads. The MQL is a method that uses a lesser amount of cutting fluid than the conventional methods. A special nozzle was made to allow the mixture of the cutting fluid with the compressed air forming a misty. This work used a CBN and Al2O3 wheel and two types of fluid application (MQL and conventional). It was observed the influence of the MQL and conventional methods in the tangential cutting force, specific energy and superficial integrity of the ground material (roughness, roundness, residual stress and SEM). The results demonstrated the effectiveness of the MQL method for the input parameters used in this study.

Orientador: Alessandro Roger Rodrigues / Banca: Hidekasu Matsumoto / Banca: Otávio Villar da Silva Neto / Resumo: Este trabalho apresenta um estudo sobre a influência das condições de fresamento na formação de cavaco, microestrutura, dureza e rugosidade da peça. Foi ensaiado um aço baixo carbono 0,15%C com dois tamanhos de grão distintos. Para ambos os materiais da peça, empregou-se 8 condições de usinagem variando a velocidade de corte, o avanço da ferramenta e a profundidade de usinagem visando à aplicação da Análise de Variância (ANOVA), dando-se destaque à usinagem considerada como alta velocidade de corte e convencional. Os ensaios de fresamento de topo concordante a seco foram conduzidos em um centro de usinagem CNC de 11 kW de potência e rotação do eixo-árvore de 7.500 rpm. Utilizou-se ferramenta de diâmetro 25 mm com dois insertos de metal duro revestidos com Al2O3. Os resultados apontam para uma influência dos parâmetros de corte sobre todas as variáveis de resposta, exceto a macrodureza. Velocidades de corte e profundidades de usinagem maiores causaram deformação da microestrutura do material "como recebido" próxima à superfície fresada. Os mesmos parâmetros governaram o aumento da microdureza superficial e da profundidade da camada endurecida. O material com grãos ultrafinos não apresentou deformação da microestrutura próxima à superfície fresada nem aumento de microdureza superficial. A velocidade de corte influiu apenas na profundidade da camada endurecida. A rugosidade foi inversa e diretamente influenciada pela velocidade de corte e avanço da ferramenta, respectivamente, sendo dependente também do tamanho de grão do material da peça. Os mesmos parâmetros de corte influíram de forma significativa no ângulo de deformação da microestrutura dos cavacos, cuja classificação foi dependente do material e das condições de usinagem. / Abstract: This work deals with the influence of milling conditions on chip formation, microstructure, hardness and roughness of workpiece. A 0.15%C low carbon steel with two different grain sizes was milled. For both workpiece materials eight milling conditions were employed where cutting speed, tool feed and depth of cut varied and combined aiming at Analysis of Variance application. The machining conditions considered as High-Speed Cutting (HSC) and Conventional were focused. The milling tests considering down-milling and dry conditions were carried out in a CNC machining center with 11 kW power and 7,500 rpm spindle rotation. A 25 mm diameter endmill with two inserts coated of Al2O3 was used. The results indicated the cutting parameters influenced on all output variables except the macrohardness. Greater cutting speed and depth of cut caused deformation of workpiece microstructure with 10.8 um grain size near milled surface. The same parameters governed the increase of surface microhardness and hardened layer depth. Refined grain material did neither present deformation of microstructure near milled surface nor increase of microhardness. The cutting speed influenced only on depth of hardened layer. Roughness was inverse and directly influenced by cutting speed and tool feed, respectively, and dependent on grain size of workpiece material. These parameters also influenced on deformation angle of chip microstructure which were classified as continuous for 10.8 um grain size and segmented for the ultrafine grain, in this case just for some milling conditions. / Mestre