Thesis (M. Sc.)(Applied Science)--University of Pretoria, 2006. / Includes summary. Includes bibliographical references. Available on the Internet via the World Wide Web.

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Orientador: Yukio Kobayashi / Banca: Carlos Alberto Soufen / Banca: Juno Gallego / Resumo: O objetivo desse trabalho é analisar cientificamente a realidade encontrada no chão de fábrica de uma empresa fabricante de equipamentos agrícolas comparada aos cuidados teoricamente requeridos na soldagem MAG robotizada e MAG PULSADO de dois aços dissimilares, sendo um aço comum ao carbono, o aço ABNT 6655 LN28, e o outro um aço de baixa liga, o aço SAE 8620. Recomenda-se da literatura que na soldagem do aço SAE 8620 seja utilizado o pré-aquecimento, dessa forma será então analisada a influência da temperatura de pré-aquecimento e do tecimento na microestrutura e na resistência da junta soldada. Para esse objetivo serão soldados vários corpos de prova sob diferentes temperaturas de pré-aquecimento e condições de tecimento. Na análise será considerada a microestrutura resultante na zona termicamente afetada composta pelo material SAE 8620 e a zona fundida, a resistência a tração e ao impacto da junta soldada obtida no processo e a dureza na zona termicamente afetada. Concluiremos que não é recomendável, no chão de fábrica, utilizar-se de pré-aquecimento, corrente pulsada e fazer estudos aprofundados quanto a influência do tecimento levando-se em conta que essas variáveis não afetaram prejudicialmente a microestrutura e resistência da junta e qualquer disposição em contrário encareceria desnecessariamente o processo. / Abstract: The objective of this work is to analyze the reality scientifically found in the ground of factory of a manufacturing company of agricultural equipments compared to the cares theoretically requested in the robotic GMAW e Pulsed of two dissimilar steels, the ABNT LN28 steel and a low alloy steel, the SAE 8620 steel. It is recommended of the literature that in the welding of the steel SAE 8620 the preheating is used, in that way it will be analyzed the influence of the preheating temperature and of the torch weaving movement in the microstructure and in the resistance of the welded joint. For that objective they will be soldiers several test specimens under different preheating temperatures and weaving movements conditions. In the analysis of the resulting microstructure will be considered the heating affected zone composed by the material SAE 8620 and the melted area and the resistance the traction of the welded joint obtained in the process. We will conclude that it is not advisable, in the factory ground, to use of preheating, pulsed current and to do deepened studies as the influence of the torch weaving movement, being considered that those variables didn't affect the microstructure and resistance of the welded joint prejudicially and any disposition in opposite would endear the process unnecessarily. / Mestre

Ph.D. / Materials science / The influence of resonant and sub-resonant frequency vibration on the longitudinal residual stresses in A-36 mild steel weldments has been studied. Residual stress analysis was carried out using sectioning, x-ray and blind-hole-drilling techniques. The hole-drilling method was modified to take into account the effect of local plastic yielding due to stress concentration and the machining stresses, with a resultant accuracy comparable to that obtained by the sectioning method. As a result of the vibratory treatments, residual stress redistribution occurred near the weld; the peak stresses were decreased by up to 30%. The resonant frequency vibration had a more pronounced stress redistribution as compared to the sub-resonant frequency vibration. Transmission electron microscopy studies indicated local plastic deformation as the mechanism by which this stress reduction occurred. Constant amplitude axial fatigue experiments on samples machined from regions adjacent to the weld showed that both the vibratory techniques did not induce any fatigue damage.

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Welding occupies an important place as a major metal fabricating process and steel is the backbone of many an industry. Therefore it is of paramount importance to know the effect of welding on steel.

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Made available in DSpace on 2014-06-11T19:24:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-08-08Bitstream added on 2014-06-13T19:11:30Z : No. of bitstreams: 1 miyahara_vtp_me_bauru.pdf: 2291410 bytes, checksum: 78394af51024880d944d61b992b06ad2 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O objetivo desse trabalho é analisar cientificamente a realidade encontrada no chão de fábrica de uma empresa fabricante de equipamentos agrícolas comparada aos cuidados teoricamente requeridos na soldagem MAG robotizada e MAG PULSADO de dois aços dissimilares, sendo um aço comum ao carbono, o aço ABNT 6655 LN28, e o outro um aço de baixa liga, o aço SAE 8620. Recomenda-se da literatura que na soldagem do aço SAE 8620 seja utilizado o pré-aquecimento, dessa forma será então analisada a influência da temperatura de pré-aquecimento e do tecimento na microestrutura e na resistência da junta soldada. Para esse objetivo serão soldados vários corpos de prova sob diferentes temperaturas de pré-aquecimento e condições de tecimento. Na análise será considerada a microestrutura resultante na zona termicamente afetada composta pelo material SAE 8620 e a zona fundida, a resistência a tração e ao impacto da junta soldada obtida no processo e a dureza na zona termicamente afetada. Concluiremos que não é recomendável, no chão de fábrica, utilizar-se de pré-aquecimento, corrente pulsada e fazer estudos aprofundados quanto a influência do tecimento levando-se em conta que essas variáveis não afetaram prejudicialmente a microestrutura e resistência da junta e qualquer disposição em contrário encareceria desnecessariamente o processo. / The objective of this work is to analyze the reality scientifically found in the ground of factory of a manufacturing company of agricultural equipments compared to the cares theoretically requested in the robotic GMAW e Pulsed of two dissimilar steels, the ABNT LN28 steel and a low alloy steel, the SAE 8620 steel. It is recommended of the literature that in the welding of the steel SAE 8620 the preheating is used, in that way it will be analyzed the influence of the preheating temperature and of the torch weaving movement in the microstructure and in the resistance of the welded joint. For that objective they will be soldiers several test specimens under different preheating temperatures and weaving movements conditions. In the analysis of the resulting microstructure will be considered the heating affected zone composed by the material SAE 8620 and the melted area and the resistance the traction of the welded joint obtained in the process. We will conclude that it is not advisable, in the factory ground, to use of preheating, pulsed current and to do deepened studies as the influence of the torch weaving movement, being considered that those variables didn't affect the microstructure and resistance of the welded joint prejudicially and any disposition in opposite would endear the process unnecessarily.

M.Ing. (Mechanical Engineering) / The use of longitudinally welded tube are limited in certain sectors of industry due to the belief that seamless tubes are superior. The main objective of this study was to try and prove that sufficient resistance to internal pressure could be achieved by longitudinally welded type 304L stainless steel tubes, while subjected to various external forces. A knowledge of plasticity theory and failure criteria provides the basis of the different mechanisms of tube failure. Four different tests were performed using different external forces, while internal pressure was increased until failure occurred. It was found that test specimens failed after reaching acceptable pressures, irrespective of the external loading conditions.

The primary objectives of this thesis investigation were: 1. To establish the maxima and minima values, within limits of the welding machine parameters: current and time, for 28 gauge, 24 gauge, 20 gauge, 18 gauge, and 16 gauge of SAE CR 1010 steel. 2. To implement and calibrate the instrumentation necessary to determine accurate values, within limits, of the variables under investigation. Also, to devise suitable controls for those fixed variables not investigated. 3. To correlate values of welding current and time with resulting tensile-shear strengths of the lapped welding joints. 4. To establish the combination of welding current and weld time which gives a maximum value of tensile strength for the metal gauges under investigation. A brief review of the more important literature on resistance spot welding variables was presented. The calibration process of determining voltage, resistance, and current was described. The mathematical prediction models (relationship between weld strength and weld time) were established for each heat control setting for different thicknesses under investigation, based on non-linear regression techniques. From the prediction models and the use of Calculus, the maximum tensile-shear strengths and corresponding maximum weld cycles were computed. The minimum weld strengths and weld cycles were determined by the welding conditions that just produced a weld of measurable strength. / Master of Science