Orientador: Eduardo Carlos Bianchi / Banca: Luiz Eduardo de Angelo Sanchez / Banca: Gilberto de Magalhães Bento Gonçalves / Banca: Carlos Eiji Hirata Ventura / Banca: Alessandro Roger Rodrigues / Resumo: A presente tese estudou a influência da friabilidade de dois rebolos de CBN (alta friabilidade - HF e baixa friabilidade - LF) na retificação cilíndrica externa de mergulho do aço AISI 4340, temperado e revenido, para vários avanços. Os resultados obtidos demonstraram que, comparativamente, o rebolo de baixa friabilidade (CBN LF) fornece melhor acabamento para a peça em termos de rugosidade e desvios de circularidade, com menor desgaste de rebolo, em todos os avanços. Por outro lado, o consumo de potência e seus sinais de emissão acústica foram sempre mais elevados. Para a tensão residual, a baixa friabilidade auxilia na geração de tensões compressivas na peça. Todavia, mesmo com a alta friabilidade, para condições mais agressivas de corte também é possível obter tensões compressivas elevadas. Nenhuma das condições de usinagem alterou a microestrutura das peças retificadas, com base nos resultados de microdureza Vickers. A elevada friabilidade, de um modo geral, pode promover fratura excessiva dos grãos, que acabam por aumentar o riscamento e deteriorar a qualidade superficial das peças, além de desgastar mais o rebolo, em virtude do predomínio da macrofratura sobre a microfratura. Ao mesmo tempo, contudo, reduz as forças de corte e o consumo de potência. Deve-se levar em conta todos os fatores à disposição para efetuar a melhor escolha de rebolo e sua friabilidade para determinada aplicação. / Abstract: The present thesis aimed to study the influence of friability of two CBN wheels (high friability - HF and low friability - LF) on the external plunge cylindrical grinding of the AISI 4340 steel, quenched and tempered, for different feed rates. The results showed that CBN LF provided better workpiece finishing in terms of surface roughness and roundness deviations, with lower wheel wear, in all feed rates. However, power consumption and acoustic emission signals were always higher than for CBN HF. For residual stresses, low friability contributes to the generation of compressive stresses on the workpiece. For high feed conditions, even CBN HF can provide high compressive stresses. None of the grinding conditions caused alterations on the workpiece microstructure, based on the results for Vickers microhardness. High friability can promote excessive grain fracture, which can increase scratching and deteriorate the surface quality, causing higher wheel wear as well (since macrofracture predominates over microfracture). On the other side, it can reduce cutting forces and power consumption. All factors at disposal must be taken into account in order to conduct the optimal selection of grinding wheel- as well as its adequate friability - for each specific application. / Doutor

Made available in DSpace on 2014-06-11T19:28:21Z (GMT). No. of bitstreams: 0 Previous issue date: 2013Bitstream added on 2014-06-13T20:18:00Z : No. of bitstreams: 1 silva_t_me_bauru.pdf: 5556945 bytes, checksum: bfc0f29139dcb742000855aef9d22106 (MD5) / Uma técnica utilizada para substituir o método de lubri-refrigeração convencional é a mínima quantidade de lubrificante (MQL). Este método utiliza de uma mistura de óleo e ar à elevada pressão, reduzindo a quantidade de fluído de corte necessário para a usinagem. Entretanto, em diversos estudos feitos na área de retificação com MQL, nota-se que há a necessidade de aperfeiçoamento dessa técnica com relação à limpeza da zona de corte do rebolo. Devido à dificuldade do baixo fluxo de fluído, em remover os resíduos superficiais acumulados, cavados aderem à superfície da ferramenta abrasiva, preenchendo os poros do rebolo e prejudicando o processo. Sendo assim este trabalho busca promover uma técnica de limpeza para o rebolo do tipo CBN, na retificação cilíndrica de aço ABNT4340 temperado e revenido, com a utilização de MQL. Através de um dispositivo, foi colocado em contato na superfície periférica do rebolo, bastões retangulares compostos dos materiais: Teflon, Óxido de alumínio e Carbeto de silício. As variáveis de saída do processo analisadas foram o comportamento da força tangencial de corte, rugosidade, emissão acústica, relação G (volume de material removido/volume do rebolo desgastado), fotos em microscópio eletrônico de varredura, microdureza e circularidade. O método MQL com o dispositivo, foi comparado com as seguintes condições de lubri-refrigeração: Convencional; MQL sem limpeza com local de ar. Com base nos resultados obtidos, o método de limpeza utilizando o dispositivo juntamente com o bastão de carbeto de silicone, comprovou em algumas condições a obtenção de melhores resultados e ausência de danos térmicos, se comparado aos outros métodos / A technique used to replace the method of conventional lubrification and cooling is the minimum quantity lubricant (MQL). This method uses a mixture of oil and air to the high pressure, reducing the amount of fluid required for machining. However, in various studies in the field of grinding with MQL, it is noted that there is a need for improvement of this techique with respect to cleaning the cutting zone of the wheel. Due to the difficulty of low fluid flow, to remove the accumulated surface residue, chips adhere to the surface of the abrasive tool, filling the pores of the wheel and impairing the process. Thus, this work seeks to promote a clening technique for the type CBN wheel, the grinding cylindrical AISI 4340 steel hardened and tempered, with the use of MQL. Through a device was placed in contact on the peripheral surface of the grinding wheel, rectangular rods compounds materials: Teflon, aluminum oxide and silicon carbide. The output variables of the process were analyzed the behavior of the tangential cutting force, surface roughness, acoustic emission, G ratio (volume of material removed/volume of wheel worn), in photos scanning electron microscope, hardness and roundness. The method MQL with the device was compared with the followin conditions of lubrication and cooling: Conventional; MQL without cleaning; MQL and cleaning air nozzle. Based on the results obtained, the cleaning method using the device with the bat silicon carbide, proved in some conditions to obtain better results and no thermal damage, compared to other methods

No description available.

A theory of the sub-ambient fluid pressure phenomenon observed during the wet sliding of a disk on a polymeric pad is presented. Two-dimensional fluid pressure mapping using membrane pressure sensors reveals a large, asymmetrical sub-ambient pressure region occupying about 70 percent of the disk-pad contact area. At the same time, a small positive pressure region exists near the trailing edge of the disk. This phenomenon is believed to be present during chemical mechanical polishing (CMP) and can contribute to the contact pressure, affecting the material removal rate and removal uniformity. Depending on the load and pad speed, the real contact pressure can be more than 2 times the nominal contact pressure due to the applied load. Tilt measurements of the disk carried out by a capacitive sensing technique indicate that the disk is tilted towards the leading edge and pad center when the pad is rotating. In addition, wafer bow is found to be less than 2 m and wafer tilt with respect to the wafer carrier is 5 to 7 m in the CMP configuration. A two-dimensional mixed-lubrication model based on the Reynolds equation is developed and solved using a finite differencing scheme. The pad is modeled as two layers: a top asperity layer described by the Greenwood and Williamson equation, and the bulk pad as linearly elastic. The orientation of the disk is determined by balancing the fluid and solid forces acting on it and solving using a modified Newtons method. It is found that the tilt of the disk and the pad topography play important roles in the distribution of fluid pressure through affecting the film thickness distribution. For a pad with severe topography, minimum and maximum fluid pressures of -90 kPa and +51 kPa respectively are detected. The model is able to recreate the experimental pressure maps. A material removal rate model based on mechanical abrasion and statistics has also been developed. Comparisons of model predictions and silicon oxide polishing results show agreement.

This study aims to develop a precision polishing system with high machining rate efficiency. The system is mainly composed of a loading mechanism, a work piece and a polishing pad with belt-shape. The loading mechanism is to generate a specific pressure distribution between the pad and the work surface.¡@Such a pressure distribution is to render the machining rate distribution, along the contact zone between pad and work surface, capable of compensating the work surface error.¡@With the capability of accurately removing the work surface error left by the previous machining method, this polishing system can improve the form precision of work and become an effective high precision machining tool. In this thesis, the relation between the applied loadings and the pressure distribution were established by the finite element method.¡@A linear model described this relation with the applied loading as the input and the desired pressure distribution as the output. The unknown coefficients of the model were then derived from the simulation data by the finite element method. When a desired pressure distribution was given, the applied loadings could be solved from the model by either the simultaneous equation method or the least squared error method.¡@A main issue to investigate in the study was to examine whether a pressure distribution with an arbitrary wavelength spectrum could be obtained by the proposed scheme. A detailed analysis about the effect of wavelength in pressure distribution on the precision of loading estimation was done. Four conclusions could be made from the study. 1.The proposed polishing system can be applied to a free surface with either concave or convex geometrical features 2.The proposed linear model can suggest proper loadings to generate desired pressure distribution with good precision if the wavelength of pressure distribution is large enough. 3.The Shannon sampling theorem can be used to give a qualitative description of the properness of the model in generating a desired pressure distribution. 4.The proposed polishing method has a high machining repeatability when the operating condition is well controlled.

Selective laser melting has shown incredible growth as a metallic additive manufacturing process in recent years. While it does provide many solutions and new ways to approach challenges, it does not come without issues of its own, namely, surface roughness. In the as-printed state, the surface roughness of selectively laser melted parts is unacceptable for use in engineering applications. Additionally, selective laser melting is used to produce complex geometries with hard to reach features, preventing conventional mechanical polishing from being successful. Therefore, it is necessary to evaluate non-mechanical polishing processes as treatments for surface roughness. In this study, electrochemical and laser polishing were investigated as potential start-to-finish treatments for the surface roughness of selectively laser melted parts. Following this preliminary study, a follow-up study investigating the effect on the mechanical strength of a lattice design that electropolishing would have. Electropolishing was found to significantly reduce the surface roughness of the as-printed part, but not to a usable value. Additionally, electropolishing was found to be unacceptable for use on lattice parts. Laser polishing was found to significantly reduce the surface roughness of the part but had feature size issues preventing a perfectly smooth surface.

published_or_final_version / abstract / Industrial and Manufacturing Systems Engineering / Master / Master of Philosophy

published_or_final_version / abstract / Industrial and Manufacturing Systems Engineering / Master / Master of Philosophy

Este trabalho apresenta uma contribuição experimental cujo objetivo é fornecer elementos para o aprimoramento tecnológico das etapas de polimento de rochas ornamentais. Alguns aspectos da tribologia, ramo do conhecimento amplamente utilizado nas engenharias mecânica e de materiais, foram transferidos para o estudo do polimento de rochas ornamentais e subsidiaram a investigação da interação do tribossistema composto pela rocha, pelo abrasivo e por condições operacionais. Foi desenvolvido um equipamento em laboratório que possibilitou a simulação do processo de polimento, em diversas condições operacionais, considerando as variáveis tempo, velocidade de rotação e intensidade das cargas aplicadas. Foram comparados polimentos, em condições industrial e laboratorial de rochas graníticas, visando estabelecer as influências das suas características composicionais, texturais e estruturais no processo. Os resultados permitiram definir as condições ideais para a obtenção de melhor qualidade no brilho das rochas e representa uma contribuição tanto para o entendimento do processo de polimento propriamente dito como também para a otimização do processo industrial. / This work shows an experimental contribution which goal is to provide elements to the technological improvement of each step of dimension stones polishing. Some aspects of tribology, a discipline of mechanical and material engineering, has been used on the research of dimension stones polishing and has supported the investigation of the interaction of the tribosystem composed of rock, abrasive and operational conditions. For this research, a device was developed in the lab in order to make possible the simulation of the polishing process at different operational conditions, considering the variables time, rotation speed, and intensity of the loads applied. The polishing of granite rocks at industrial and lab conditions has been compared, aiming at determining the influence of each rock characteristics such as mineral composition, texture and structure during the process. The results allowed for the definition of the ideal conditions to obtain the best quality of rock brightness and they represent a contribution to the understanding of the polishing process itself as well as provide an optimization of the industrial process.

O aspecto técnico das rochas de revestimento é o primeiro condicionante para o seu uso nas edificações, seguido das suas características tecnológicas, da tipologia do jazimento e dos possíveis defeitos decorrentes das etapas de extração e beneficiamento. O presente trabalho aborda os mecanismos que influenciam no processo de polimento, lembrando que a indústria ainda se baseia no empirismo, com generalizações não condizentes que aumentam o custo de produção das placas. Foram escolhidos três tipos de rochas \"graníticas\": Sienogranito (Vermelho Brasília), Migmatito (Jacarandá Rosado) e Monzogranito (Cinza Andorinha), por serem de alta comercialização e consideradas no processamento industrial como \"dura\", \"média\" e \"mole\", respectivamente. Foram ensaiadas no simulador de polimento de rochas (SPR), utilizando o abrasivo magnesiano e antes de iniciar o processo foi determinada a rugosidade superficial de cada amostra. Variando-se a carga aplicada na politriz, a velocidade, o tempo e monitorando a perda de massa associada ao brilho, foi possível estabelecer as condições ideais para os tipos de rochas estudadas. / Dimension stones aesthetics are the main factor considered in their use for buildings, followed by technological characteristics, deposit\'s typology and possible extraction and beneficiacion effects. This paper approaches the influential mechanisms on polishing process, considering that industry still bases itself on empiricisms, with incoherent generalizations that increase production slabs cost. Three types of granite rocks were evaluated: Sienogranite (Vermelho Brasília), Migmatite (Jacarandá Rosado) and Monzogranite (Cinza Andorinha), due to their highly commercialization. The rocks are classified at the industrial process as hard, medium and soft (respectively). They were tested with a polishing rock simulator through the use of magnesium abrasives and had the surface roughness pre-determined for each sample. By altering the polishing machine applied load, as well as speed and time, and having the brightness associated weight loss monitored, it was possible to stabilish ideal conditions for the studied rock types.