Orientador: Anselmo Eduardo Diniz / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-23T04:12:20Z (GMT). No. of bitstreams: 1 Carvalho_MartaReginaDelleDonne_M.pdf: 17580883 bytes, checksum: f1ff52988b201685207f750165cbc037 (MD5) Previous issue date: 2013 / Resumo: O resumo poderá ser visualizado no texto completo da tese digital / Abstract: The abstract is available with the full electronic document / Mestrado / Materiais e Processos de Fabricação / Mestra em Engenharia Mecânica

Orientador: Raquel Gonçalves / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agricola / Made available in DSpace on 2018-08-04T02:41:40Z (GMT). No. of bitstreams: 1 Neri_AntonioCarlos_D.pdf: 2011024 bytes, checksum: f186a3983118cb93726e980979e74b80 (MD5) Previous issue date: 2003 / Resumo: As madeiras de reflorestamento têm grande importância na economia nacional, movimentando importantes setores, tais como os de papel e celulose, de recursos energéticos, moveleiros e de construção civil. Embora o Brasil apresente um grande potencial florestal, sendo detentor das maiores reservas florestais tropicais do mundo e possuindo condições de clima e solo favoráveis à implantação de florestas de rápido crescimento, sua participação no comércio internacional de madeiras (2,1%) é, ainda, muito pequena. Em geral, grande parte das indústrias que processam madeiras apresenta baixo rendimento de madeira serrada e qualidade insuficiente do produto final, principalmente devido ao emprego de técnicas de processamento (conhecimento de parâmetros de corte) além de fatores de planejamento da serraria (implantação e Layout) inadequadas. Esse fato revela, portanto, que o setor madeireiro necessita incorporação de inovações tecnológicas. A caracterização de espécies de reflorestamento, no que diz respeito aos parâmetros de usinagem, tais como forças de corte, geometria adequada da ferramenta, espessura de corte, densidade, etc., é imprescindível no processamento da madeira. O objetivo principal deste trabalho foi a determinação dos principais parâmetros de corte (forças de corte, pressão específica de corte e ângulo ideal de saída da ferramenta) para a espécie Pinus taeda, mediante o estudo do comportamento das forças de corte em diferentes posições e regiões de madeira juvenil e adulta do tronco. Além desse objetivo, o trabalho pretendeu, também, avaliar a metodologia de determinação de forças de corte para as espécies de eucalipto (Citriodora, Saligna e Grandis), proposta pelo autor em trabalho anterior. Para alcançar esses objetivos, foram ensaiados 96 corpos-de-prova da espécie Pinus taeda, obtidos de seis árvores provenientes do horto florestal de Manduri, S.P, com um total de 5760 ensaios. Como resultado, para o Pinus taeda foram determinadas as forças em função dos parâmetros espessura de corte e ângulo de saída, bem como foi calculado o ângulo de saída x ideal, que resultou da ordem de 40° para pequenas espessuras de corte e da ordem de 30° para maiores espessuras. Para as espécies de eucalipto (Citriodora, Saligna e Grandis), cujos resultados experimentais foram obtidos pelo autor em trabalho anterior, bem como para o Pinus taeda, foi calculada a pressão específica de corte. Os resultados permitiram, ainda, comprovar que a metodologia avaliada é adequada para utilização na espécie estudada / Abstract: The reforestation wood has great importance in the national economy, running important sectors, such as paper and the cellulose, energy resources, furniture and civil construction. Although Brazil presents a great forest potential, holding the biggest forest reserves of the world and possessing soil and climate conditions favorable to the implantation of forests of fast growth, its participation in the wood international trade (2.1%) is, still, very small. The techniques currently used in processing the wood, usually do not provide good income, neither propitiate good quality in the final product as well. Mainly due to the usage of inadequate parameters of the cutting process, along with inappropriate sawmill planning (implantation and Layout). This fact discloses, therefore, that the lumber sector needs the incorporation of technological innovations. The characterization of kinds of reforestation that respect the cutting parameters, such as, cutting force, adequate geometry of the tool, cutting thickness, density, etc., is essential in the processing of the wood. The main objective of this work was the determination of the main parameters of cutting (cutting force, specific cutting force and ideal exit angle of the tool), for the species of loblolly pine (Pinus taeda L.) by the study of the behavior of the cutting force in different positions of the trunk and in different regions of juvenile and adult of wood. Beyond this objective, the work is intended, also, to evaluate the methodology of determination of cutting force for the wood of eucalyptus, proposed by the author in previously work. To reach these objectives, 96 specimens of the specie Pinus taeda were assayed, taken from 6 trees proceeding from a research forest of Manduri, S.P, resulting in 5760 tests. As a result, the force as function of the evaluated parameters had been determined for Pinus taeda, as well, the ideal cutting angle for specimens thickness environ 0.2 mm was near 40° and for thickness between 0.4 mm and 1.0 mm was near 30°. The specific cutting force was calculated for Pinus taeda, as well as for the Eucaliptus. The former with experimental results obtained in this work and the latter using experimental results obtained in previous work from the author. Finally, the results had proved also that the methodology adopted in this research is appropriated to use in the studied species / Doutorado / Construções Rurais / Doutor em Engenharia Agrícola

The efficacy of combined diamond and diamond like carbon coatings, to allow for effective and efficient dry turning of aluminium alloy Al 6082, has been investigated. Optimised diamond and diamond-like carbon (DLC) coatings were combined and deposited onto a WC-Co insert using chemical vapour deposition (CVD) methods. DLC coatings were developed by testing the effects of bias voltage, deposition time and gas pressure. During the development of the DLC layer, the effects of substrate geometry and positioning in the deposition chamber were investigated. It was discovered that coating characteristics could vary significantly across the samples as a result of geometrical effects. This contradicted claims that, as plasma enhanced CVD is a non-line of sight deposition method, any variation in the coating due to geometry would be negligible. SEM analysis revealed coating thickness to increase by over 50%. AFM measurements showed coating roughness to increase by up to 30 times, whilst Raman spectroscopy highlighted a significant decrease in sp3 bonding. This variation in characteristics was seen, through the use of scratch testing, to translate into significantly reduced tribological performance. Friction was increased by 60% and critical load was only half of that of the coating applied to flat surface. The combined coatings were characterised and machining performance was evaluated. Coating characteristics were examined using SEM, AFM and Raman spectroscopy. Cutting trials designed to simulate the expected tool life were conducted. Micro and nano-crystalline diamond coatings, with and without an additional DLC layer were trialled along with a single layer DLC coating. Commercially available uncoated and TiN coating inserts of identical geometry were also trialled as a reference. The results showed that the addition of the DLC layer effectively reduced the roughness of the diamond, however, this did not translate into reduced adhesion of the aluminium to the cutting tip. It has been shown that for this particular machining scenario, a smoother coating effectively increased friction and adhesion of the workpiece material. The investigation has highlighted that due to the complex dynamics of material transfer effects in sliding, it cannot be assumed that a smoother surface layer will lead to improved tribological performance.

The potential of Additive Manufacturing (AM) for microwave and mm-wave applications is increasingly being revealed thanks to recent advancements in research. AM empowers engineers with new capabilities to manufacture complex conformal geometries quicker and at lower costs. It allows, for instance, the embedding of RF front ends into functional structures. In this dissertation, two aspects of AM are explored: (a) The development and characterization of techniques that improve the performance of AM microwave circuits and antennas, and (b) study of complex geometries, such as meshed structures, as an alternative to reduce material usage, cost, and weight of the components. Micro-dispensing of silver paste (CB028) is extensively used in this work as a viable approach for manufacturing microwave planar transmission lines. However, the performance and upper-frequency range of these lines are limited by the cross-sectional shape and electrical conductivity of the printed paste, as well as the achievable minimum feature size which is typically around 100 μm. In this work a picosecond Nd:YAG laser is used to machine slots in a 20-25 μm-thick layer of silver paste (Dupont CB028) that is micro-dispensed on a Rogers RT5870 substrate, producing coplanar waveguide transmission lines with 16-20 μm-wide slots. It is shown that the laser solidifies 2 μm wide region along the edges of the slots, thus significantly increasing the effective conductivity of the film and improving the attenuation constant of the lines. The extracted attenuation constant at 20 GHz for laser machined CB028 is 0.74 dB/cm. CPW resonators and filters show that the effective conductivity is in the range from 10 MS/m to 30 MS/m, which represents a 100x improvement when compared to the values obtained with the exclusive use of micro-dispensing. Another main aspect of this dissertation is the study of meshed structures in coplanar waveguides. For most AM processes the materials utilized for the conductive layer are the most expensive ones; hence, there is value in minimizing the conductor surface area used in a circuit. In this work, the approach of meshed ground coplanar waveguide (MGCPW) is analyzed by simulating, fabricating and measuring a broad set of meshed ground geometry sizes. Furthermore, a physical-mathematical model is presented, which predicts the characteristic impedance and the capacitance per unit length of MGCPW with less than 5.4% error compared to simulated data. A set of filters is designed and fabricated in order to demonstrate the approach. The main parameter affected by meshing the ground plane is the attenuation constant of the waveguide. It is shown that 50% mesh density in the ground plane of a MGCPW line can be used with less than 25% increase in the loss. In contrast, the loss of finite ground coplanar waveguide (FGCPW) can increase by as much as 108% when the ground size is reduced by the same factor (50%). Both 3D printing (micro-dispensing) and traditional printed circuit board manufacturing are used in this work, and most of the propagation characterization is performed at 4 GHz. A meshing technique is also applied to rectangular waveguides, and its effects are studied. It is presented as an option for high power, low loss, but also reduced weight applications. A set of meshed Ku-band waveguides was fabricated using binder jetting 3D printing technology showing that the weight can be reduced by 22% with an increase in loss of only 5%, from 0.019 dB/cm for the solid part to 0.020 dB/cm average across the band with the meshed design. Further weight reduction is possible if higher loss is allowed. To demonstrate the concept, a comparison is made between non-meshed and meshed waveguide 4 pole Chebyshev filters. Finally, the BJ technology is characterized for Ku-Band rectangular waveguide and reflector antenna applications. This technology is characterized using electron beam microscopy (SEM) and energy dispersive spectroscopy (EDS). The RF performance of the 3D printed circuits is benchmarked with Ka-band cavity resonators, waveguide sections, and a filter. An unloaded resonator Q of 616 is achieved, and the average attenuation of the WR-28 waveguide section is 4.3 dB/m. The BJ technology is tested with a meshed parabolic reflector antenna, where the illuminating horn, waveguide feed, and a filter are printed in a single piece. The antenna shows a peak gain of 24.56 dBi at 35 GHz.

Doctor of Philosophy / Department of Industrial & Manufacturing Systems Engineering / Zhijian Pei / Grinding is one of the important operations employed in modern manufacturing industry to remove materials and achieve desired geometry and surface finish. Simultaneous double side grinding (SDSG) and ultrasonic vibration assisted grinding (UVAG) are two typical cost-effective grinding processes which are utilized to grind semiconductor materials and high performance ceramic materials, respectively. The objectives of this research are to investigate several technical issues in modern grinding processes by using theoretical, numerical, and experimental research approaches. Those technical issues are related to SDSG and UVAG, which have been chosen as two typical grinding processes for this research. This thesis reviews the literature on SDSG (covering process applications, modeling of grinding marks, and modeling of wafer shapes) and UVAG (covering process applications, edge chipping, and coolant effects, etc). The theoretical research work of this thesis is conducted by developing mathematical models for grinding marks and wafers shapes in SDSG of silicon wafers. These developed models are then used to study the effects of SDSG parameters on the curvature of the grinding marks, the distance between adjacent grinding marks, and the wafer shapes. The numerical research work of this thesis is done by conducting a three dimensional (3-D) finite element analysis (FEA) of UVAG process. A 3-D FEA model is developed to study the edge chipping commonly observed in UVAG of ceramics. Edge chippings not only compromises geometric accuracy but also possibly causes an increase in machining cost. A solution to reduce the edge chipping is proposed based upon the FEA simulations and validated by pilot experiments. Several experimental studies are conducted to provide new knowledge for the UVAG process. Firstly, a novel coolant delivery system is explored for UVAG machine system. Secondly, UVAG is introduced into machining of fiber-reinforced ceramic matrix composites (CMC). Results of a feasibility study and a designed experimental investigation show that UVAG is a promising process for CMC machining. Finally, an experimental study on cutting forces during UVAG of zirconia/alumina composites is conducted. The feasibility to machine different zirconia/alumina composites using UVAG is also investigated and discussed. The findings in this thesis will provide theoretical and practical guidance for modern grinding processes especially for SDSG and UVAG.

M.Ing. (Mechanical Engineering) / Titanium and its alloys have the potential to serve as a strategic economic driver of the South African economy. The manufacture and use of high strength, lightweight materials such as titanium alloys have become of great importance in the aerospace and biomedical industries over the past few decades. The manufacturing costs of titanium alloy components however, are considered high due to the poor machinability of the material. Furthermore, as with all metals during machining, surface residual stresses are induced into the material. These are of particular interest in the aerospace industry as they can be either detrimental or beneficial to the performance and fatigue life of materials. The aim of this investigation is therefore to examine the effect that machining parameters have on the magnitude, sign and distribution of residual stresses induced in Grade 4 and 5 titanium alloys during high performance machining (turning). The effect of these machining parameters is investigated by residual stress measurements conducted with X-ray diffraction and grain structure analysis of the machined surfaces by optical microscopy. Results show that cutting speed and depth of cut have a significant effect on the residual stresses. At low cutting speeds, the surface residual stresses are largely compressive, becoming more tensile with an increase in cutting speed. An increase in depth of cut also introduces more compressive residual stresses into the material. The microstructural analysis of the alloys shows that grain deformation decreases with an increase in cutting speed and cutting depth.

M.Ing. (Mechanical Engineering) / High strength alloys such as titanium are widely used within applications that require specific material properties. These include high strength, high temperature as well as low weight applications. Thus a need arises to investigate the fundamental to understand the mechanics of how these materials are machined. Titanium alloys are known for the difficulties that arise during the machining thereof. Complexities arise due to its inherent material properties, the most important property being the retention of strength at high temperatures. In addition to maintaining its strength, it becomes highly chemically reactive with other materials at increased temperatures. All these factors contribute to extreme temperatures at the tool chip interface contributing to increased tool wear and shortened tool life. The aim of the research is to investigate the effect of machining on various cutting process parameters including cutting force, temperature, tool wear and surface finish for grade 2 and grade 5 titanium alloys during high speed turning. Grade 2 titanium is a commercially grade with lower mechanical properties, while Grade 5 is titanium alloy with substantially higher mechanical properties and is the most widely used titanium alloy. In addition an experimental setup was developed and verified to conduct fundamental research on the high speed machining of titanium alloys. A literature review was concluded with focus on the machining of titanium alloys. This was followed by the development of the experimental setup, measurement and compilation of data. The data was compiled into graphs and compared with the current research available. The research found that for the cuts performed, that cutting forces are independent of cooling applied and that no substantial variation was noted between the two grades. When temperatures were evaluated, dramatic drops in temperature were noted when coolant was applied. As temperatures increased, specifically during un-cooled cutting, the inserts deteriorated having an effect on the quality of the surfaces obtained. When coolant was applied, substantial temperature drops were achieved, improving tool life and directly improving surface finishes. The best surface finish was achieved for higher cutting speeds as and lower feed rates. This phenomenon was found for both grades of titanium evaluated. The largest amount of tool wear was noted for the highest cutting speeds, with increased values noted for Grade 5 in comparison with Grade 2. This phenomenon is noted for crater as well as flank wear.

Parallel manipulators have many advantages over traditional serial manipulators. These advantages include high accuracy, high stiffness and high load-to-weight ratio, which make parallel manipulators ideal for machining operations where a high accuracy is required to meet the requirements that modern standards demand. A number of previous workers have determined the stiffness of parallel platforms using the duality between instantaneous kinematics and statics in parallel mechanisms. For the aforementioned analysis, compliance is introduced in the actuators, resulting in a platform stiffness matrix. This methods furthermore predicts when the platform approaches a singular or ill-conditioned configuration. However, this idealized estimate of the stiffness is not accurate enough to determine how an actual platform assembly will react to an externally applied force. For a planar parallel platform, the out of plane stiffness is not included in the resulting stiffness matrix since the kinematics equations are derived only in the plane in which the platform operates. Recently, the finite element method (FEM) has been used by some workers to determine the stiffness of spatial manipulators. These models are mainly used to verify stiffness predicted using kinematic equations, and are restricted to relatively simple truss-like models. In this study, state-of-the-art finite elements are used to determine the out of plane stiffness for parallel manipulators. Beam elements that make use of Timoshenko beam theory and flat shell elements with drilling degrees of freedom are used to model the platform assembly. The main objective of this study is to quantify the stiffness, particularly the out of plane stiffness, of a planar parallel platform to be used for machining operations. The aim is to suggest a design that is able to carry out machining operations to an accuracy of 10 µm for a given tool force. Reducing the weight of a parallel manipulator used in machining applications has many advantages, e.g. increased maneuverability, resulting in faster material removal rates. Therefore the resulting proposed design is optimized with respect to weight, subject to displace¬ment and stress constraints to ensure feasible stiffness and structural integrity. This optimization is carried out with both gradient-based methods and a genetic algorithm (GA). The gradient-based methods include LFOPC and Dynamic-Q. A binary GA, imple¬mented as both a micro GA and full GA, is used to provide for the future inclusion of discrete design variables. Stiffness maps, as proposed by Gosselin, are drawn for the optimal design. These stiffness maps can aid in determining the best toolpath inside a feasible workspace. It is envisaged that this work, together with current work at the University of Pretoria, will result in a feasible design for a planar parallel platform to be used in industry. An application of such a planar parallel platform lies in retro-fitting existing, relatively inexpensive 3-axis milling equipment. This increases their capability at a lower cost than the of the alternative of purchasing a traditional 5-axis milling center. / Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2006. / Mechanical and Aeronautical Engineering / unrestricted

Particleboard (PB) is a widely used panel material because of its physical properties and low cost. Unfortunately, cutting can degrade its surface creating rejects and increasing manufacturing costs. A major challenge is PB’s internal variability. Different particle and glue bond strength combinations can sometimes create high quality surfaces in one area and defects such as edge chipping in nearby areas. This research examines methods of improving surface quality by examining PB characteristics and their interactions with the cutting tool. It also develops an analytical model and software tool that allows the effects of these factors to be simulated, thereby giving practical guidance and reducing the need for costly experiments. When PB is cut and the glue bond strength is weaker than the particle strength, particles are pulled out, leading to surface defects. When instead the glue bond strength is stronger than the particle strength, particles are smoothly cut, leading to a high quality surface. PB is modeled as a matrix of particles each with stochastically assigned material and glue bond strengths. The PB model is layered allowing particles to be misaligned. Voids are modeled as missing particles. PB cutting is modeled in three zones. In the finished material and tool tip zones, particles are compressed elastically and then crushed at constant stress. After failure, chip formation occurs in the chip formation zone. At large rake angles, the chip is modeled as a transversely loaded beam that can fail by cleavage at its base or tensile failure on its surface. At small rake angles, the chip is modeled as the resultant force acting on the plane from the tool tip through to the panel surface. Experimental and simulation results show that cutting forces increase with depth of cut, glue content and particle strength. They decrease with rake angle. Glue bond strength can be increased to the equivalent particle strength through the selection of particle geometry and the subsequent increased glue bond efficiency, which increases the cut surface quality without the need for additional glue. Minimizing the size and frequency of voids and using larger rake angles can also increase surface quality. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

This thesis presents models and algorithms necessary to simulate the five-axis flank milling of jet-engine impellers in a virtual environment. The impellers are used in the compression stage of the engine and are costly, difficult to machine, and time-consuming to manufacture. To improve the productivity of the flank milling operations, a procedure to predict and optimize the cutting process is proposed. The contributions of the thesis include a novel cutter-workpiece engagement calculation algorithm, a five-axis flank milling cutting mechanics model, two methods of optimizing feed rates for impeller machining tool paths and a new five-axis chatter stability algorithm. A semi-discrete, solid-modeling-based method of obtaining cutter-workpiece engagement (CWE) maps for five-axis flank milling with tapered ball-end mills is developed. It is compared against a benchmark z-buffer CWE calculation method, and is found to generate more accurate maps. A cutting force prediction model for five-axis flank milling is developed. This model is able to incorporate five-axis motion, serrated, variable-pitch, tapered, helical ball-end mills and irregular cutter-workpiece engagement maps. Simulated cutting forces are compared against experimental data collected with a rotating dynamometer. Predicted X and Y forces and cutting torque are found to have a reasonable agreement with the measured values. Two offline methods of optimizing the linear and angular feeds for the five-axis flank milling of impellers are developed. Both offer a systematic means of finding the highest feed possible, while respecting multiple constraints on the process outputs. In the thesis, application of these algorithms is shown to reduce the machining time for an impeller roughing tool path. Finally, a chatter stability algorithm is introduced that can be used to predict the stability of five-axis flank milling operations with general cutter geometry and irregular cutter-workpiece engagement maps. Currently, the new algorithm gives chatter stability predictions suitable for high speed five-axis flank milling. However, for low-speed impeller machining, these predictions are not accurate, due to the process damping that occurs in the physical system. At the time, this effect is difficult to model and is beyond the scope of the thesis. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate