De uma forma geral, conhecer os limites de estabilidade dinâmica de uma máquinaferramenta durante a usinagem, é um desafio para o fabricante de máquinasferramentas, bem como, para o usuário, que precisa escolher uma máquina que garanta a produtividade desejada. Neste trabalho, um modelo teórico foi utilizado para o desenvolvimento de um método de comparação dos limites de estabilidade dinâmica entre máquinas-ferramentas. Duas ferramentas de corte com seus respectivos sistemas de fixação foram selecionados, uma apropriada às operações de desbaste e outra às operações de acabamento. Utilizando as constantes de corte relacionadas ao material selecionado e a geometria das ferramentas, obteve-se experimentalmente o diagrama de estabilidade para três máquinas sob teste, e utilizando-os, comparou-se os limites de estabilidade para cada máquina, o que ilustra a utilização do método em desenvolvimento. A validação e a precisão dos diagramas foram realizadas por meio de ensaios de usinagem em uma das máquinas sob investigação. Os primeiros resultados demonstram as diferenças entre máquinas-ferramentas usando-se como critério a sua estabilidade dinâmica avaliada pelo diagrama de lóbulos. Os critérios e conceitos aqui discutidos contribuíram para o conhecimento do desempenho e produtividade das máquinas-ferramentas. / Knowing the dynamic stability of a machine tool during the metal cutting process is a challenge to the machine tool builder as well as to the end user, especially when choosing or selecting a machine that achieves the desired productivity and performance. This document proposes and describes a theoretical model to determine a method to compare the dynamic stability limits among several machine tools. Two different tool systems were previously selected and addressed, one of them for roughing and another for finishing operations. Using metal cutting constants related to the selected materials and tool geometry, the stability diagram was obtained experimentally for all the three different machine tools and they were used to compare the dynamic stability limits amongst machines illustrating the application of the developed method. The validation of the proposed method was achieved by machining tests executed in one of the machines under investigation. The first results, based on the practical experiments, show the differences amongst machine tools using as criterion the dynamic stability evaluated by the stability lobe diagram. Such concept has contributed to enhance the knowledge on the machine tool productivity and performance.

Realizou-se um estudo dos efeitos das variáveis de moagem e dos moinhos de alta energia sobre a síntese do composto intermetálico NiAl. A influência do poder de moagem, tamanho de partícula inicial de Ni, agente controlador de processo e dimensões dos corpos moedores durante a síntese do composto NiAl no moinho Spex foi quantificada utilizando-se um planejamento fatorial. Verificou-se uma significativa influência do poder de moagem no tempo de ignição da reação exotérmica de formação do composto NiAl, além da influência da interação entre o poder de moagem, agente controlador de processo e dimensões dos corpos moedores no tamanho médio de partículas dos produtos das moagens. O rendimento no moinho Attritor demonstrou-se dependente do poder de moagem e também da quantidade de agente controlador do processo durante a moagem de misturas de pós de Ni e Al. A síntese por combustão de pós mecanicamente ativados no moinho Attritor levou à formação de NiAl3, Ni2Al3 e NiAl ou somente NiAl, dependendo da temperatura de síntese. Conduziu-se a tentativa de determinação experimental, através da técnica de calorimetria diferencial de varredura, das entalpias de formação dos compostos intermetálicos NiAl3, Ni2Al3, NiAl e Ni3Al; os valores encontrados para Ni2Al3 e Ni3Al foram, respectivamente, 167 kJ/mol e 93 kJ/mol. A formação de NiAl no moinho planetário, ao contrário do verificado nos moinhos Spex e Attritor, ocorreu de maneira gradual e o tempo necessário para a formação do composto foi dependente da quantidade de agente controlador de processo. Para os moinhos planetário e Attritor estimaram-se as respectivas energias de moagens transferidas ao longo do processo e o composto NiAl obtido nestes moinhos foi parcialmente ordenado. O método de Rietveld foi utilizado para a determinação da quantidade de NiAl formado após a moagem nos moinhos planetário e Attritor e também para a estimativa dos tamanhos de cristalitos e da deformação da rede. Amostras particuladas obtidas nos moinhos planetário e Attritor foram consolidadas, sinterizadas a 1300ºC e caracterizadas por ensaios de flexão e microdureza Vickers; as amostras apresentaram um comportamento frágil em flexão e microdureza Vickers inferior em comparação ao valor encontrado na literatura. / A study on the effect of milling variables and high-energy mills on the NiAl intermetallic compound synthesis was performed. The effect of ball-to-powder ratio, Ni particle initial size, the use of process control agent and milling media size on NiAl synthesis in a Spex mill was evaluated using a factorial design. It was shown that ball-to-powder ratio plays an important role in the ignition time of the mechanically induced reaction of NiAl intermetallic formation; moreover, an interaction of ball-to-powder ratio, process control agent and milling media size was found to affect the particle size of milling products. During milling of Ni and Al powder, the yield of an Attritor mill was found dependent on ball-to-powder ratio and the process control agent quantity. After combustion synthesis of powders, which were previously mechanically activated in the Attritor mill, monophasic NiAl or a mixture of NiAl3, Ni2Al3 and NiAl were obtained depending on synthesis temperature; however, swelling of samples was verified in both situations. The enthalpy of formation of Ni2Al3 and Ni3Al was measured using differential scanning calorimetry and the experimental values were, respectively, 167 kJ/mol and 93 kJ/mol. NiAl compound formation occurred through an exothermic reaction in Spex and Attritor mills, on the other hand, this intermetallic was gradually formed during milling in the planetary mill, and, in this milling device, the time for compound formation was dependent on process control agent quantity. Furthermore, the energy transferred to the powder during milling in planetary and Attritor mills was estimated, and the NiAl synthesized in these devices was partially disordered. Also, the Rietveld method was employed to determine the amount of NiAl synthesized in planetary and Attritor mills, and, also, estimate crystallite size and lattice strain of milling products. Finally, milling products of planetary and Attritor mills were consolidated and sintered at 1300ºC so that Vickers microhardness and flexion tests could be performed; these tests indicated a fragile behavior, and hardness lower than the value found on literature.

The prevalence of digital manufacturing in creating increasingly complex products with small batch sizes, requires effective methods for production process planning. Toolpath generation is one of the challenges for manufacturing technologies that function based on the controlled movement of an end effector against a workpiece. The current approaches for determining suitable tool paths are highly dependent on machine structure, manufacturing technology and product geometry. This dependence can be very expensive in a volatile production environment where the products and the resources change quickly. In this research, a novel approach for the flexible generation of toolpaths using a mathematical formulation of the desired objective is proposed. The approach, based on optimisation techniques, is developed by discretising the product space into a number of grid points and determining the optimal sequence of the tool tip visiting these points. To demonstrate the effectiveness of the approach, the context of milling machining has been chosen and a genetic algorithm has been developed to solve the optimisation problem. The results show that with meta-heuristic methods, flexible tool paths can indeed be generated for industrially relevant parts using existing computational power. Future computing platforms, including quantum computers, could extend the applicability of the proposed approach to much more complex domains for instantaneous optimisation of the detailed manufacturing process plan.

The purpose of this thesis is to investigate the correlation between the penetration force of cutting fluids and machining stability. General studies are made to understand the classification of cutting fluids based on their chemical compositions. It is summarized why the proper selection of cutting fluid for different machining processes is important. The role of cutting fluids in machining process is documented as well as other related issues such as delivery methods, storage, recycling, disposal and failure modes. The uniqueness of this thesis is that it constructs a new mathematical model that would help to explain and quantify the influence of the penetration force of cutting fluid on machining stability. The basic principles of milling process, especially for thin wall machining are reviewed for building the mathematical model. The governing equations of the mathematical model are derived and solved analytically. The derived solutions are used to construct the stability charts. The results show that there is a direct correlation between the machining stability and the changes of the penetration force of the cutting fluid. It is shown that the machining stability region is narrowed as the penetration force of the cutting fluid increases while other machining variables are assumed to be constant. This narrowness of the stability region is more obvious at spindle speed over 6000 rpm.

Le broyage est une opération couramment réalisée dans de nombreux secteurs industriels. Malgré son apparente simplicité, le broyage met en jeu des phénomènes de fragmentation complexes dépendant à la fois des propriétés de la matière, des sollicitations mécaniques dans le broyeur, et de la dynamique des poudres au sein de celui-ci. Aujourd'hui l'évolution des technologies de broyage repose essentiellement sur un savoir-faire empirique et de nombreux efforts sont encore à déployer pour améliorer leur efficacité énergétique. Cette optimisation ne pourra être réalisé qu'en s'appuyant sur une connaissance fine des phénomènes mis en jeux à plusieurs échelles (échelle sub-particulaire, échelle de la particule, du lit de poudre et du procédé). L'objectif de ces travaux de thèse est de mettre en évidence les paramètres clés influençant les mécanismes de comminution et l'efficacité énergétique du broyage. Un modèle numérique de rupture de particules présentant des défauts sous forme de clivage a été mis en œuvre. Il a permis notamment d'analyser l'influence de la distribution spatiale des fissures sur la statistique des seuils de rupture en lien avec les chemins de fissures et la taille des fragments. A l'échelle du procédé, une étude expérimentale, réalisée au sein d'un broyeur de laboratoire, a permis de proposer un modèle énergétique s'inspirant de celui de Rittinger mais tenant compte des phénomènes d'agglomération. Ce modèle a ensuite été généralisé à différentes technologies de broyage à media broyant pour comparer leur efficacité énergétique lors du broyage de matières minérales, végétale ainsi qu'en condition de cobroyage. / Although grinding is a widespread operation in industrial processes, it remains poorly understood. The difficulty to model grinding not only lies in the complexity of the fragmentation, which depends on material properties and loading dynamics, but also on the stress transmission from the grinder to the particles. The development of grinding technologies has led to an empirical know-how, and much more effort is still needed to understand the the mechanisms of the comminution of particles. This objective can be achieved only by increasing knowledge on the phenomena involved at different scales (sub-particle heterogeneities, particle, powder bed and boundary conditions of the process).In this PhD work, we investigate the key parameters influencing comminution mechanisms and the energetic efficiency of grinding. A numerical model of particle breakage including a subparticle distribution of cleavages was developed. This model allowed us to analyze the cracks patterns, fragment sizes and probability distribution of failure. At the scale of the process, an extensive experimental study of comminution was carried out using a laboratory mill. An energy evolution inspired by Rittinger model but taking into account the agglomeration phenomena was proposed. This model was then extended to other grinding technologies to compare the energy efficiency for grinding minerals, vegetal particles and their comilling.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Esta tese tem por objetivo estudar a precisão de uma nova estrutura robótica para operações de fresamento, em substituição às convencionais maquinas-ferramentas seriais, especialmente as fresadoras e os centros de usinagem CNC. A estrutura proposta está baseada no conceito da cinemática paralela, tendo a análise da precisão sido realizada em função do mapeamento dos erros de posicionamento da ferramenta de corte dentro do espaço de trabalho disponível, durante operação de fresamento de acabamento, aplicando modelagem matemática. A motivação está na busca por altos desempenhos e as estruturas robóticas paralelas possuem diversas vantagens perante as estruturas seriais: construção modular, massa reduzida, altas velocidades/acelerações. Por outro lado, há ainda problemas a serem solucionados, como: garantia da precisão, otimização do espaço de trabalho e redução/eliminação de singularidades. A metodologia aplicada no desenvolvimento deste trabalho compreende quatro etapas: a proposta de uma nova estrutura robótica desenvolvida a partir de métodos de síntese existentes; o desenvolvimento de modelos matemáticos para caracterizar o seu comportamento cinemático; a identificação das fontes de erro que influenciam no desvio de posição da ferramenta; a elaboração de modelos matemáticos e algorítmos computacionais para analisar o grau de influência de cada fonte de erro identificada. Desenvolvemos uma estrutura robótica de topologia assimétrica 2UPS+PRP, com as seguintes características: mobilidade 3 com três translações no espaço, reduzido número de componentes e movimento na direção z independente dos movimentos nas direções x e y. Apresentamos os algoritmos computacionais para mapear os erros cinemáticos, geométricos e elásticos através da discretização do espaço de trabalho disponível, baseado nas matrizes Jacobianas e no princípio do trabalho virtual. Com relação aos mapeamentos dos desvios de posição da ferramenta obtidos, chegamos a algumas conclusões. Os maiores erros cinemáticos ocorreram quando as imprecisões impostas aos dois membros motores laterais tinham sinais contrários. Os erros geométricos com tolerâncias dimensionais na classe de trabalho IT5, foram os mais relevantes dentre os erros considerados. Os erros elásticos, considerando forças de usinagem de acabamento, foram os menos relevantes entre os erros considerados, sendo expressiva a influência da rigidez das juntas universais e esféricas. A utilização do princípio do trabalho virtual, com parâmetros de rigidez concentrados, mostrou ser eficaz e eficiente, comparado ao SMA (análise da matriz estrutural) e ao FEM (método dos elementos finitos), devido ao menor trabalho para o desenvolvimento da sua formulação e ao tempo computacional reduzido para o seu processamento. / This thesis has the purpose to study the precision of a new robotic structure for milling operations, in substitution to the conventional serial machine-tools, specialy the CNC milling machines and cutting centers. The proposed structure is based on the parallel kinematics concept and the precision analysis was realized, applying mathematical models, to obtain the positioning errors mapping of the cutting tool in the available workspace, during finishing milling operations. The motivation is on the search higher performances and the parallel robotic structures have several advantages to the serial structures: modular construction, lightness, high velocities/acelerations. Otherwise, there are still problems to be solved, like: guaranty of precision, workspace optimization and reduction/elimination of singularities. The methodology applied for the development of this work involves four steps: the proposal of a new robotic structure developed using existing synthesis methods; the development of mathematical models to characterize its kinematic behavior; the error sources identification that influences the deviation of the tool position; the elaboration of mathematical models and computer algorithms to analyse the influence level of each identified error source. We developed one assymmetric robotic structure 2UPS+PRP, with the following characteristics: mobility 3 with three translations in the space, reduced number of componentes and displacement in z direction independent from the displacents in the x and y directions. We presented the computer algorithms to map the kinematic, geometric and elastic errors, throw the discretization of the available workspace, based on the Jacobian matrices and the virtual work principle. With regard to the tool position deviation mappings obtained, we reach to some conclusions. The major kinematic errors occurred when the imprecisions imposed to the two lateral actuatores had opposed signals. The geometric errors with dimensional tolerances in the IT5 work class, were the more relevant among the considered errors. The elastic errors, considering finishing manufacturing forces, were the less relevent among the considered errors, being expressive the influence of the rigidity of the universal and spherical jounts. The utilization of the virtual work principle and concentrated rigidity parameters, showed to be efficacious and efficient, compared to the SMA (astructural matrice analisis) and the FEM (finite elements methode), because of the minor work to develop its formulations end the reduced computer time to its prosecution.

Os mecanismos amplamente utilizados em aplicações industriais são de tipo serial, porém há algum tempo vem sendo desenvolvidos estudos sobre as vantagens que os mecanismos de arquitetura paralela oferecem em contraposição com os seriais. Rigidez, precisão, altas frequências naturais e velocidade são algumas características que os mecanismos paralelos atribuem a máquinas já consolidadas na indústria, destinadas principalmente nas operações de manipulação (pick and place). Nesse sentido, é relevante o estudo sobre a funcionalidade em outros tipos de operação como a usinagem e, particularmente o fresamento. Para isto, devem-se ainda explorar e desenvolver as capacidades dos mecanismos paralelos em relação à rigidez e à precisão nas operações mencionadas. Foi desenvolvido previamente o projeto e montagem do protótipo de uma máquina fresadora de arquitetura paralela. Também aracterizado pela redundância na atuação para o posicionamento da ferramenta. Com este intuito, pretende-se no trabalho atual, avaliar o erro estático de posicionamento da ferramenta por métodos experimentais, quantificar os deslocamentos, realizar um mapeamento experimental em diversas configurações dos membros. Por outro lado, pretende-se adaptar um modelo numérico simplificado que possa prever as deformações elásticas em diversas configurações, que contemple o efeito de juntas lineares flexíveis e que de alguma forma ajude a identificar as principais fontes de erro. Para tal, foram elaboradas rotinas de programação que através da cinemática inversa e o uso do método dos elementos finitos tentem prever o que de fato acontece nos experimentos. Foi proposta também uma implementação alternativa para o controle do mecanismo através de um software CNC e a conversão de coordenadas cartesianas em coordenadas dos atuadores, isto ajudaria na geração do código G. Finalmente, foram elaboradas algumas trajetórias que tentam avaliar a exatidão e repetitividade do mecanismo além de descrever outras trajetórias livres. / Serial mechanisms have been widely used in industrial applications, on the other hand some studies related to advantages of parallel kinematics and its benefits have been developed in the last decades. Stiffness, accuracy, high natural frequencies and velocities are some characteristics that this kind of kinematic architecture attribute to some industrial machines specially used in \"pick and place\" operations. However, it remains relevant to study the functionality that parallel mechanisms could offer in other kind of applications such as milling. In order to achieve this, it is important to evaluate and explore the capabilities and performance characteristics when precision and stiffness are involved. A milling machine with parallel architecture prototype has been designed and constructed in previous works. The tool positioning is characterized by redundant actuation. The present work aims to evaluate the static error of the tool positioning mechanism by experimental procedures, in order to quantify the tool displacements under some established loads and to elaborate an experimental map for static error in different mechanism configurations. On the other hand, it is intended to adapt a simplified numerical model that could predict the stiffness behavior along the workspace including the effect of flexible linear actuators. For this purpose, a finite element method script was developed to solve all the structure displacements. In addition, it was proposed an alternative control implementation that works through an open source CNC software and its appropriate kinematic conversion for the mechanism characteristics and the generation of G Code scripts. Finally, some trajectories were planned in order to evaluate accuracy and repeatability in two proposed paths besides some other free operations.

De uma forma geral, conhecer os limites de estabilidade dinâmica de uma máquinaferramenta durante a usinagem, é um desafio para o fabricante de máquinasferramentas, bem como, para o usuário, que precisa escolher uma máquina que garanta a produtividade desejada. Neste trabalho, um modelo teórico foi utilizado para o desenvolvimento de um método de comparação dos limites de estabilidade dinâmica entre máquinas-ferramentas. Duas ferramentas de corte com seus respectivos sistemas de fixação foram selecionados, uma apropriada às operações de desbaste e outra às operações de acabamento. Utilizando as constantes de corte relacionadas ao material selecionado e a geometria das ferramentas, obteve-se experimentalmente o diagrama de estabilidade para três máquinas sob teste, e utilizando-os, comparou-se os limites de estabilidade para cada máquina, o que ilustra a utilização do método em desenvolvimento. A validação e a precisão dos diagramas foram realizadas por meio de ensaios de usinagem em uma das máquinas sob investigação. Os primeiros resultados demonstram as diferenças entre máquinas-ferramentas usando-se como critério a sua estabilidade dinâmica avaliada pelo diagrama de lóbulos. Os critérios e conceitos aqui discutidos contribuíram para o conhecimento do desempenho e produtividade das máquinas-ferramentas. / Knowing the dynamic stability of a machine tool during the metal cutting process is a challenge to the machine tool builder as well as to the end user, especially when choosing or selecting a machine that achieves the desired productivity and performance. This document proposes and describes a theoretical model to determine a method to compare the dynamic stability limits among several machine tools. Two different tool systems were previously selected and addressed, one of them for roughing and another for finishing operations. Using metal cutting constants related to the selected materials and tool geometry, the stability diagram was obtained experimentally for all the three different machine tools and they were used to compare the dynamic stability limits amongst machines illustrating the application of the developed method. The validation of the proposed method was achieved by machining tests executed in one of the machines under investigation. The first results, based on the practical experiments, show the differences amongst machine tools using as criterion the dynamic stability evaluated by the stability lobe diagram. Such concept has contributed to enhance the knowledge on the machine tool productivity and performance.

IsaMill is a stirred type mill used in mineral industry for fine and ultra-fine grinding. The difficulty in obtaining the internal flow information in the mill by experimental techniques has prevented the development of the fundamental understanding of the flow and generating general methods for reliable scale-up and optimized design and control parameters. This difficulty can be effectively overcome by numerical simulation based on discrete element method (DEM). In this work a DEM model was developed to study particle flow in a simplified IsaMill. The DEM model was validated by comparing the simulated results of the flow pattern, mixing pattern and power draw with those measured from a same scale lab mill. Spatial distributions of microdynamic variables related to flow and force structure such as local porosity, particle interaction forces, collision velocity and collision frequency have been analyzed. Among the materials properties of particles, it is shown that by decreasing particle/particle sliding friction coefficient, the particle flow becomes more vigorous which is useful to grinding performance. Restitution coefficient does not affect the particle flow significantly. A too low or too high particle density could decrease grinding efficiency. Although grinding medium size affects the flow, its selection may depend on the particle size of the products. Among the operational variables considered, the results show that fill volume and mill speed proved to be important factors in IsaMil process. Increase of fill volume or mill speed increases the interaction between particles and agitating discs which results in a more vigorous motion of the particles. Among the mill properties, particle/stirrer sliding friction plays a major role in energy transfer from stirrer to particles. Although there exists a minimum collision energy as particle/stirrer sliding friction increases, large particle/stirrer sliding friction may improve grinding performance as it has both large collision frequency and collision energy. However, that improvement is only up to a critical particle/disc sliding friction beyond which only input energy increases with little improvement on collision frequency and collision energy. Reducing the distance between stirrers or increasing the size of disc holes improves high energy transfer from discs to particles, leading to high collision frequency and collision energy. Among the different stirrer types, the energy transfer is more effective when disc holes are present. Pin stirrer shows increased collision energy and collision frequency which also result in a high power draw. Using the DEM results, a wear model has been developed to predict the wear pattern of the discs. This model can be used to predict the evolution of the disc wear with the time. It is shown that energy transfer from discs to particles are increased when discs are worn out. An attempt has also been made to analyze the microdynamic properties of the mill for different sizes. It is shown that specific power consumption and impact energy are correlated regardless of the mill size and mill speed.