Predictive analytical and numerical modeling for orthogonal cutting

In this thesis, a predictive analytical and numerical modeling approach for the orthogonal cutting process is proposed to calculate temperature distributions and subsequently, forces and stress distributions. The models proposed include a constitutive model for the material being cut based on the work of Weber, a model for the shear plane based on Merchants model, a model describing the contribution of friction based on Zorev’s approach, a model for the effect of wear on the tool based on the work of Waldorf, and a thermal model based on the works of Komanduri and Hou, with a fraction heat partition for a non-uniform distribution of the heat in the interfaces, but extended to encompass a set of contributions to the global temperature rise of chip, tool and work piece. The models proposed in this work, try to avoid from experimental based values or expressions, and simplifying assumptions or suppositions, as much as possible. On a thermo-physical point of view, the results were affected not only by the mechanical or cutting parameters chosen, but also by their coupling effects, instead of the simplifying way of modeling which is to contemplate only the direct effect of the variation of a parameter. The implementation of these models was performed using the MATLAB environment. Since it was possible to find in the literature all the parameters for AISI 1045 and AISI O2, these materials were used to run the simulations in order to avoid arbitrary assumption.

Contribution to dynamic characteristics of the cutting temperature in the drilling process considering one dimension heat flow

The machining of hardened steels has always been a great challenge in metal cutting, particularly for drilling operations. Generally, drilling is the machining process that is most difficult to cool due to the tool`s geometry. The aim of this work is to determine the heat flux and the coefficient of convection in drilling using the inverse heat conduction method. Temperature was assessed during the drilling of hardened AISI H13 steel using the embedded thermocouple technique. Dry machining and two cooling/lubrication systems were used, and thermocouples were fixed at distances very close to the hole`s wall. Tests were replicated for each condition, and were carried out with new and worn drills. An analytical heat conduction model was used to calculate the temperature at tool-workpiece interface and to define the heat flux and the coefficient of convection. In all tests using new and worn out drills, the lowest temperatures and decrease of heat flux were observed using the flooded system, followed by the MQL, considering the dry condition as reference. The decrease of temperature was directly proportional to the amount of lubricant applied and was significant in the MQL system when compared to dry cutting. (C) 2011 Elsevier Ltd. All rights reserved.

Power cycling lifetime estimation of IGBT power modules based on chip temperature modeling

In this doctoral thesis, methods to estimate the expected power cycling life of power semiconductor modules based on chip temperature modeling are developed. Frequency converters operate under dynamic loads in most electric drives. The varying loads cause thermal expansion and contraction, which stresses the internal boundaries between the material layers in the power module. Eventually, the stress wears out the semiconductor modules. The wear-out cannot be detected by traditional temperature or current measurements inside the frequency converter. Therefore, it is important to develop a method to predict the end of the converter lifetime. The thesis concentrates on power-cycling-related failures of insulated gate bipolar transistors. Two types of power modules are discussed: a direct bonded copper (DBC) sandwich structure with and without a baseplate. Most common failure mechanisms are reviewed, and methods to improve the power cycling lifetime of the power modules are presented. Power cycling curves are determined for a module with a lead-free solder by accelerated power cycling tests. A lifetime model is selected and the parameters are updated based on the power cycling test results. According to the measurements, the factor of improvement in the power cycling lifetime of modern IGBT power modules is greater than 10 during the last decade. Also, it is noticed that a 10 C increase in the chip temperature cycle amplitude decreases the lifetime by 40%. A thermal model for the chip temperature estimation is developed. The model is based on power loss estimation of the chip from the output current of the frequency converter. The model is verified with a purpose-built test equipment, which allows simultaneous measurement and simulation of the chip temperature with an arbitrary load waveform. The measurement system is shown to be convenient for studying the thermal behavior of the chip. It is found that the thermal model has a 5 C accuracy in the temperature estimation. The temperature cycles that the power semiconductor chip has experienced are counted by the rainflow algorithm. The counted cycles are compared with the experimentally verified power cycling curves to estimate the life consumption based on the mission profile of the drive. The methods are validated by the lifetime estimation of a power module in a direct-driven wind turbine. The estimated lifetime of the IGBT power module in a direct-driven wind turbine is 15 000 years, if the turbine is located in south-eastern Finland.

Tool cutting force modeling and wear estimation of micro -end-milling operations

The applications of micro-end-milling operations have increased recently. A Micro-End-Milling Operation Guide and Research Tool (MOGART) package has been developed for the study and monitoring of micro-end-milling operations. It includes an analytical cutting force model, neural network based data mapping and forecasting processes, and genetic algorithms based optimization routines. MOGART uses neural networks to estimate tool machinability and forecast tool wear from the experimental cutting force data, and genetic algorithms with the analytical model to monitor tool wear, breakage, run-out, cutting conditions from the cutting force profiles. ^ The performance of MOGART has been tested on the experimental data of over 800 experimental cases and very good agreement has been observed between the theoretical and experimental results. The MOGART package has been applied to the micro-end-milling operation study of Engineering Prototype Center of Radio Technology Division of Motorola Inc. ^

Tool cutting force modeling and wear estimation of micro-end-milling operations

The applications of micro-end-milling operations have increased recently. A Micro-End-Milling Operation Guide and Research Tool (MOGART) package has been developed for the study and monitoring of micro-end-milling operations. It includes an analytical cutting force model, neural network based data mapping and forecasting processes, and genetic algorithms based optimization routines. MOGART uses neural networks to estimate tool machinability and forecast tool wear from the experimental cutting force data, and genetic algorithms with the analytical model to monitor tool wear, breakage, run-out, cutting conditions from the cutting force profiles. The performance of MOGART has been tested on the experimental data of over 800 experimental cases and very good agreement has been observed between the theoretical and experimental results. The MOGART package has been applied to the micro-end-milling operation study of Engineering Prototype Center of Radio Technology Division of Motorola Inc.

An investigation of the relationship between temperature, forces and tool wear in turning and drilling

Developing a means of predicting tool life has been and continues to be a focus of much research effort. A common experience in attempting to replicate such efforts is an inability to achieve the levels of agreement between theory and practice of the original researcher or to extrapolate the work to different materials or cutting conditions to those originally used. This thesis sets out to examine why most equations or models when replicated do not give good agreements. One reason which was found is that researchers in wear prediction, their predictions are limited because they generally fail to properly identify the nature of wear mechanisms operative in their study. Also they fail to identify or recognise factors having a significant influence on wear such as bar diameter. Also in this research the similarities and differences between the two processes of single point turning and drilling are examined through a series of tests. A literature survey was undertaken in wear and wear prediction. As a result it was found that there was a paucity in information and research in the work of drilling as compared to the turning operation. This was extended to the lack of standards that exist for the drilling operation. One reason for this scarcity in information on drilling is due to the complexity of the drilling and the tool geometry of the drill. In the comparative drilling and turning tests performed in this work, the same tool material; HSS, and similar work material was used in order to eliminate the differences which may occur due to this factor. Results of the tests were evaluated and compared for the two operations and SEM photographs were taken for the chips produced. Specific test results were obtained for the cutting temperatures and forces of the tool. It was found that cutting temperature is influenced by various factors like tool geometry and cutting speed, and the temperature itself influenced the tool wear and wear mechanisms that act on the tool. It was found and proven that bar diameter influences the temperature, a factor not considered previously.

Growth and Development of Purple Nutsedge Based on Days or Thermal Units

This work was carried out with the objective of elaborating mathematical models to predict growth and development of purple nutsedge (Cyperus rotundus) based on days or accumulated thermal units (growing degree days). Thus, two independent trials were developed, the first with a decreasing photoperiod (March to July) and the second with an increasing photoperiod (August to November). In each trial, ten assessments of plant growth and development were performed, quantifying total dry matter and the species phenology. After that, phenology was fit to first degree equations, considering individual trials or their grouping. In the same way, the total dry matter was fit to logistic-type models. In all regressions four temporal scales possibilities were assessed for the x axis: accumulated days or growing degree days (GDD) with base temperatures (Tb) of 10, 12 and 15 oC. For both photoperiod conditions, growth and development of purple nutsedge were adequately fit to prediction mathematical models based on accumulated thermal units, highlighting Tb = 12 oC. Considering GDD calculated with Tb = 12 oC, purple nutsedge phenology may be predicted by y = 0.113x, while species growth may be predicted by y = 37.678/(1+(x/509.353)-7.047).

Pitfalls in the assessment of murine atherosclerosis

This review provides examples of the fact that different procedures for the measurement of atherosclerosis in mice may lead to interpretation of the extent of atherosclerosis having markedly different biological and clinical significance for humans: 1) aortic cholesterol measurement is highly sensitive for the detection of early and advanced atherosclerosis lesions, but misses the identification of the location and complexity of these lesions that are so critical for humans; 2) the histological analysis of the aortic root lesions in simvastatin-treated and control mice reveals similar lesion morphology in spite of the remarkable simvastatin-induced reduction of the aortic cholesteryl ester content; 3) in histological analyses, chemical fixation and inclusion may extract the tissue fat and also shrink and distort tissue structures. Thus, the method may be less sensitive for the detection of slight differences among the experimental groups, unless a more suitable procedure employing physical fixation with histological sample freezing using optimal cutting temperature and liquid nitrogen is employed. Thus, when measuring experimental atherosclerosis in mice, investigators should be aware of several previously unreported pitfalls regarding the extent, location and complexity of the arterial lesion that may not be suitable for extrapolation to human pathology.

Análise do processo de torneamento a quente auxiliado por resistência elétrica de quartzo

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

A influência da aplicação de fluído de corte no torneamento da liga de aluminio AA 7075

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Energia específica de corte e integridade superficial no microfresamento do ABNT 1045

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudo da geometria da aresta de corte de ferramentas aplicadas ao torneamento de superligas à base de níquel com alta velocidade de corte

Pesquisadores e indústrias de todo o mundo estão firmemente comprometidos com o propósito de fazer o processo de usinagem ser precisamente veloz e produtivo. A forte concorrência mundial gerou a procura por processos de usinagem econômicos, com grande capacidade de produção de cavacos e que produzam peças com elevada qualidade. Dentre as novas tecnologias que começaram a ser empregadas, e deve tornar-se o caminho certo a ser trilhado na busca da competitividade em curto espaço de tempo, está a tecnologia de usinagem com altas velocidades (HSM de High Speed Machining). A tecnologia HSM surge como componente essencial na otimização dos esforços para manutenção e aumento da competitividade global das empresas. Durante os últimos anos a usinagem com alta velocidade tem ganhado grande importância, sendo dada uma maior atenção ao desenvolvimento e à disponibilização no mercado de máquinas-ferramentas com rotações muito elevadas (20.000 - 100.000 rpm). O processo de usinagem com alta velocidade está sendo usado não apenas para ligas de alumínio e cobre, mas também para materiais de difícil usinabilidade, como os aços temperados e superligas à base de níquel. Porém, quando se trata de materiais de difícil corte, têm-se observado poucas publicações, principalmente no processo de torneamento. Mas, antes que a tecnologia HSM possa ser empregada de uma forma econômica, todos os componentes envolvidos no processo de usinagem, incluindo a máquina, o eixo-árvore, a ferramenta e o pessoal, precisam estar afinados com as peculiaridades deste novo processo. No que diz respeito às máquinas-ferramenta, isto significa que elas têm que satisfazer requisitos particulares de segurança. As ferramentas, devido à otimização de suas geometrias, substratos e revestimentos, contribuem para o sucesso deste processo. O presente trabalho objetiva estudar o comportamento de diversas geometrias ) de insertos de cerâmica (Al2O3 + SiCw e Al2O3 + TIC) e PCBN com duas concentrações de CBN na forma padrão, assim como modificações na geometria das arestas de corte empregadas em torneamento com alta velocidade em superligas à base de níquel (Inconel 718 e Waspaloy). Os materiais foram tratados termicamente para dureza de 44 e 40 HRC respectivamente, e usinados sob condição de corte a seco e com utilização da técnica de mínima quantidade de lubrificante (minimal quantity lubricant - MQL) visando atender requisitos ambientais. As superligas à base de níquel são conhecidas como materiais de difícil usinabilidade devido à alta dureza, alta resistência mecânica em alta temperatura, afinidade para reagir com materiais da ferramenta e baixa condutividade térmica. A usinagem de superligas afeta negativamente a integridade da peça. Por essa razão, cuidados especiais devem ser tomados para assegurar a vida da ferramenta e a integridade superficial de componentes usinados por intermédio de controle dos principais parâmetros de usinagem. Experimentos foram realizados sob diversas condições de corte e geometrias de ferramentas para avaliação dos parâmetros: força de corte, temperatura, emissão acústica e integridade superficial (rugosidade superficial, tensão residual, microdureza e microestrutura) e mecanismos de desgaste. Mediante os resultados apresentados, recomenda-se à geometria de melhor desempenho nos parâmetros citados e confirma-se a eficiência da técnica MQL. Dentre as ferramentas e geometrias testadas, a que apresentou melhor desempenho foi a ferramenta cerâmica CC650 seguida da ferramenta cerâmica CC670 ambas com formato redondo e geometria 2 (chanfro em T de 0,15 x 15º com raio de aresta de 0,03 mm).

Self-healing of cracks during ductile regime machining of silicon: Insights from molecular dynamics simulation

During nanoindentation and ductile-regime machining of silicon, a phenomenon known as “self-healing” takes place in that the microcracks, microfractures, and small spallings generated during the machining are filled by the plastically flowing ductile phase of silicon. However, this phenomenon has not been observed in simulation studies. In this work, using a long-range potential function, molecular dynamics simulation was used to provide an improved explanation of this mechanism. A unique phenomenon of brittle cracking was discovered, typically inclined at an angle of 45° to 55° to the cut surface, leading to the formation of periodic arrays of nanogrooves being filled by plastically flowing silicon during cutting. This observation is supported by the direct imaging. The simulated X-ray diffraction analysis proves that in contrast to experiments, Si-I to Si-II (beta tin) transformation during ductile-regime cutting is highly unlikely and solid-state amorphisation of silicon caused solely by the machining stress rather than the cutting temperature is the key to its brittle-ductile transition observed during the MD simulations

New Possibilities for Geophysical Parameter Retrievals Opened by GCOM-W1 AMSR2

A new approach to retrieve sea surface wind speed (SWS) in tropical cyclones (TCs) from the Advanced Microwave Scanning Radiometer 2 (AMSR2) data is presented. Analysis of all six AMSR2 C- and X-band channel measurements over TCs is shown to efficiently help to separate the rain contribution. Corrected measurements at 6.9 and 10.65 GHz are then used to retrieve the SWS. Spatial and temporal collocation of AMSR2 and tropical rain measurement mission (TRMM) microwave instrument (TMI) data is then further used to empirically relate TMI rain rate (RR) product to RR estimates from AMSR2 in hurricanes. SWS estimates are validated with measurements from the stepped frequency microwave radiometer (SFMR). As further tested, more than 100 North Atlantic and North Pacific TCs are analyzed for the 2012–2014 period. Despite few particular cases, most SWS fields are in a very good agreement with TC center data on maximum wind speeds, radii of storm, and hurricane winds. As also compared, very high consistency between AMSR2 and L-band SMOS wind speed estimates are obtained, especially for the super typhoon Haiyan, to prove the high potential of AMSR2 measurements in TCs.

Modeling The Effects Of Temperature And Ph On The Resistance Of Alicyclobacillus Acidoterrestris In Conventional Heat-treated Fruit Beverages Through A Meta-analysis Approach.

In this work, all publicly-accessible published findings on Alicyclobacillus acidoterrestris heat resistance in fruit beverages as affected by temperature and pH were compiled. Then, study characteristics (protocols, fruit and variety, °Brix, pH, temperature, heating medium, culture medium, inactivation method, strains, etc.) were extracted from the primary studies, and some of them incorporated to a meta-analysis mixed-effects linear model based on the basic Bigelow equation describing the heat resistance parameters of this bacterium. The model estimated mean D* values (time needed for one log reduction at a temperature of 95 °C and a pH of 3.5) of Alicyclobacillus in beverages of different fruits, two different concentration types, with and without bacteriocins, and with and without clarification. The zT (temperature change needed to cause one log reduction in D-values) estimated by the meta-analysis model were compared to those ('observed' zT values) reported in the primary studies, and in all cases they were within the confidence intervals of the model. The model was capable of predicting the heat resistance parameters of Alicyclobacillus in fruit beverages beyond the types available in the meta-analytical data. It is expected that the compilation of the thermal resistance of Alicyclobacillus in fruit beverages, carried out in this study, will be of utility to food quality managers in the determination or validation of the lethality of their current heat treatment processes.