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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
51

Contribuição para os usuários de sistemas CAD/CAM/CNC em operação de fresamento de topo em aço para moldes e matrizes / Contribution to the users of systems CAD/CAM/CNC in end milling operation in steel for molds and dies

Costa, Gustavo Guilherme dos Santos 16 June 2011 (has links)
The increased in the demand for plastic products and the need for reduction manufacturing times, and the growing dependence of man on the computer in present day, especially in manufacturing activities, has resulted in constant research of technological developments in order to supply these needs. In dies and molds manufacturing industry for plastic injection requiring machining operations such as (milling, drilling and polishing, among others), is increasing dependence by computer systems, such as CAD/CAM. This technology helps in the manufacturing steps, provides fast and high accuracy in the manufacturing of complex geometries. Therefore, to understand and to use efficiently these resources that aided in manufacturing are of enormous importance for the optimization of a production process. In this context, this work presents a study on the use of resources programming CAD/CAM in milling operation of cavities steel VP50 with inserts cemented carbide with ball nose. The influence of two types of interpolation (linear and circular) and tolerances bands (0.05 mm and 0.1 mm) that define the tool path for machining of a cavity that has a similar form the a mold of a battery cover cell phone. As output variables evaluated were machining time, the number of lines of the program, the parameters of surface roughness (Ra, Rq, Rz) of parts, the radius of curvature, form deviation of any line profile and the tool wear. The results showed that, from the statistical point of view (ANOVA), none of the conditions of interpolation and tolerance employed significantly influenced the values of surface roughness in form deviation of any line and tool wear. Linear interpolation with tolerance of 0.1 mm was most viable for the production of such cavity in the conditions investigated because the produced good finish, low tool wear and machining time is shorter. / O aumento pela demanda por produtos plásticos e a necessidade de redução nos tempos de fabricação, além da crescente dependência do homem pelo computador em dias atuais, especialmente nas atividades de fabricação, tem implicado na busca por constantes desenvolvimentos tecnológicos a fim de suprir estas necessidades. Na indústria de fabricação de matrizes como também de moldes para injeção de plásticos (que necessitam de operações de usinagem tais como fresamento, furação e polimento, dentre outros), é cada vez maior a dependência pelos sistemas computacionais, como o sistema CAD/CAM. Essa tecnologia auxilia nas etapas de fabricação, oferece rapidez e alta exatidão na fabricação de geometrias complexas. Portanto, entender e saber utilizar de forma eficiente estes recursos que auxiliam na manufatura são de enorme importância para a otimização de um processo produtivo. Neste contexto, este trabalho apresenta um estudo sobre a utilização de recursos de programação CAD/CAM em fresamento de cavidades de aço VP50 com insertos de metal duro ponta de esférica. Foi investigada a influência de dois tipos de interpolações (linear e circular) e tolerâncias (0,05mm e 0,1 mm) que definem o percurso da ferramenta na usinagem de uma cavidade que possui forma semelhante a um molde da tampa da bateria do aparelho celular. Como variáveis de saída foram avaliadas o tempo de usinagem, o número de linhas do programa, os parâmetros de rugosidade superficial (Ra, Rq, Rz) das cavidades, o raio de curvatura, o desvio de forma de uma linha qualquer e o desgaste das ferramentas. Dos resultados obtidos, constatou-se que, sob o ponto de vista estatístico (ANOVA), nenhuma das condições de interpolação e tolerância empregadas influenciou significativamente nos valores de rugosidade da superfície, no desvio de forma de uma linha qualquer e desgaste das ferramentas. A interpolação linear com tolerância de 0,1mm mostrou-se a mais viável para a produção de tal cavidade nas condições investigadas devido a bom acabamento produzido, pequeno desgaste e tempo de usinagem mais curto. / Mestre em Engenharia Mecânica
52

Hodnota firmy Modos spol. s r. o. / The valuation of the company Modos spol. s r.o.

Šindlerová, Veronika January 2008 (has links)
The aim of this thesis is to find out the financial gain of the integrated system of management quality, human safety and environment by the valuation of the company. My thesis includes the evaluation of the efficiency of integrated system of management quality, human safety and environment and after that there is included the valuation of the company in two versions. The first version reflects the real situation, the company has implemented the integrated system of management quality, human safety and environment. The second version reflects the hypothetical situation, in this settings the company wouldn't have the integrated system. The difference between these two valuation is the financial gain of this system.
53

Concentrator photovoltaics combined with reverse osmosis and membrane distillation for high-efficiency desalination and electricity production / Koncentrerade solceller i kombination med omvänd osmos och membrandestillation för högeffektiv avsaltning och elproduktion

Hou, Novalie, Jiang, Sofie January 2020 (has links)
This project is a bachelor thesis and aims to study the integration of concentrator photovoltaics (CPV), reverse osmosis (RO) and membrane distillation (MD) for water desalination and purification. In this report, an introduction of the need for efficient water desalination is presented. Following the introduction, relevant literature has been reviewed to build up the fundamental understanding of CPV, RO and MD. A general classification of CPV subsequently introduced. In order to acquire a more comprehensive understanding of CPVs, two case studies were performed with two different types of CPV/T. The cost efficiency of each type of CPV was analysed when integrated with RO and MD systems. The result turns out to be that it was not economically beneficial to have MD in the integrated system. The reason behind is the extensive thermal energy demand of MD. Other affecting parameters, such as location and system types were also discussed. Lastly, improvements and suggestions for further studies were considered. / Detta projekt är en kandidatuppsats och syftar till att studera ett integrerande system bestående av koncentrerade solceller (CPV), omvänd osmos (RO) och membrandestillation (MD) för vattenavsaltning och rening. Rapporten börjar med en introduktion om behovet av effektiv avsaltning av vatten. Relevant litteratur har granskats för att bygga upp den grundläggande förståelsen för CPV, RO och MD. Därefter gjordes en klassificering av CPV. För att få en mer omfattande förståelse av CPV valdes två olika typer av CPV /T för en djupare undersökning. Kostnadseffektiviteten för varje CPV analyserades, när dessa var integrerade med RO- och MD-system. Resultatet visar sig att det tyvärr inte var ekonomiskt fördelaktigt att ha med MD i det integrerade systemet. Anledningen bakom detta var det omfattande termiska energibehovet för MD. Andra avgörande faktorer, såsom plats och systemtyp diskuterades tillika. Slutligen avslutades rapporten med förslag på förbättringar och områden för vidare studier.
54

Towards an Integrated Water Quality Monitoring System Using Low Cost Electrochemical Sensors

Alam, Arif Ul January 2019 (has links)
The monitoring of pharmaceuticals, heavy metal, pH and free chlorine concentration in drinking water is important for public health and the environment. However, conventional laboratory-based analytical methods are labor-intensive, expensive, and time consuming. This thesis focuses on developing an integrated, highly sensitive, easy-to-use, and low-cost pharmaceuticals, heavy metal, pH and free chlorine sensing system for drinking water quality monitoring. A low-temperature, solution-processed modification of multi-walled carbon nanotubes (MWCNT) with β-cyclodextrin (βCD) on glassy carbon electrode is developed for detecting low levels of acetaminophen. The adsorption properties of βCD are combined with the high surface area of carbon nanotubes towards enhanced electrochemical sensing of acetaminophen with a limit of detection of 11 nM and linear range from 0.05-300 μM. Also, a systematic investigation is carried out using four types of modified MWCNT-βCD. A novel, one-step approach called Steglich esterification modified MWCNT-βCD results in large effective surface area, and fast electron transfer towards sensitive detection of acetaminophen and 17β-estradiol (E2, primary female sex hormone) in the range of 0.005–20 and 0.01–15 μM, with low detection limits of 3.3 and 2.5 nM, respectively. The similar MWCNT-βCD modified electrodes can also detect heavy metal ion (lead, Pb2+) with a limit of detection of <10 ppb. Low frequency noise behavior of these sensors are studied. A spin-coated Pd/PdO based pH sensor, and amine-modified carbon electrode-based free chlorine sensor are fabricated on a common substrate together with the pharmaceuticals and heavy metal sensors. A Wheatstone-bridge temperature sensor is fabricated based on silicon and PEDOT:PSS on another substrate. All the sensors are connected to an Arduino microcontroller based data acquisition system with a smartphone application interface. The integrated sensing system is easy-to-use, low-cost, and can provide accurate monitoring data with real drinking water samples. / Dissertation / Doctor of Philosophy (PhD) / Low-cost, easy-to-use, and sensitive monitoring system for pharmaceuticals, heavy metal, pH and free chlorine in drinking water is crucial for public health safety. In this thesis, we develop solution-based synthesis of multi-walled carbon nanotubes modified by β-cyclodextrin for electrochemical sensing of pharmaceuticals and heavy metal. The modification approaches are compared and characterized to analyze their electrochemical behavior and sensing performances. The developed sensors are highly sensitive toward the detection of acetaminophen (a widely used pain-killer) and estrogen hormone in drinking water. We also develop a modified spin-coating technique to deposit palladium/palladium oxide films for potentiometric pH sensor, a calibration-free free chlorine sensor based on modified carbon electrode, and a resistive temperature sensor. The developed pH, free chlorine and temperature sensors are highly sensitive, and stable with fast response time. All the sensors are integrated and interfaced with a custom-made and smartphone-controlled electronic readout system for accurate and on-site drinking water quality monitoring at low cost.

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