Thesis (M.S.)--Oregon Graduate Center, 1986.

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

Made available in DSpace on 2014-06-11T19:28:35Z (GMT). No. of bitstreams: 0 Previous issue date: 2004-04-30Bitstream added on 2014-06-13T19:16:40Z : No. of bitstreams: 1 conz_r_me_guara.pdf: 3551076 bytes, checksum: f033420c8316996c6c21e26fd18ec0d9 (MD5) / O objetivo deste trabalho foi substituir um bloco de grandes dimensões em aço forjado, por chapas finas de aço, laminadas a quente, soldadas pelo processo LASER CO2, destinadas à fabricação de rotores para máquinas elétricas com até 40 MW de potência, para tanto foram utilizadas chapas com 3 mm de espessura, empilhadas, compactadas e fixadas por tirantes. Considerando que a largura das bobinas e blanks disponíveis no mercado nacional não atendem às necessidades dimensionais do produto fez-se necessária a emenda das chapas com grande precisão pelo processo de soldagem Laser CO2. O aço escolhido para tal realização foi um aço de alta resistência e baixa liga (ARBL), com limite de escoamento superior a 550 MPa. O interesse econômico desse estudo está na substituição do material tradicionalmente utilizado, um bloco de grandes dimensões em aço forjado do tipo SAE 4140B por chapas de aço laminadas a quente, a um custo 4 vezes menor. O fator técnico relevante nessa pesquisa foi a preservação das propriedades físicas, químicas e mecânicas por meio de parâmetros controlados de Soldagem Laser CO2. Buscou-se identificar e quantificar a zona termicamente afetada, analisar alterações estruturais, variação de dureza utilizando o método Brinell, e correlacionar estes resultados com a composição química e com a resistência a ruptura, obtida pelo ensaio de tração e pelo método Erichsen de embutimento, determinando a presença, ou não, de microfissuras, poros, inclusões não metálicas ou outras anomalias que pudessem comprometer a junta soldada. Foi considerada ainda a importância da realização dos ensaios para a Qualificação do Procedimento de Soldagem conforme os requisitos do ASME Code Section IX, QW 150 para os ensaios de tração e QW 160 para os ensaios de dobramento, a fim de obter a validação do mesmo... . / The objective of this work was to change a steel forged block with great dimensions by the fine sheet hot laminated steel, welded by Laser CO2, destined to manufacture rotors for electric machines until 40 MW of power, it was used steel sheet with 3 mm of thickness pilled, compacted and fixed by lifter. Considering that the width of the bobbins and blanks available in the national market do not supply the dimensional necessities of the product, it made necessary the joint of plates with great precision, by the Laser process of welding. The steel chosen for such purpose was a high-strength low alloy steel (HSLA) with 550 MPa of Yield strength. The economical interest of this study is the substitution of the traditional material, a block of great dimensions in forged steel type SAE 4140B for hot rolled steel plates, which costs 4 times less. The technical relevant factor in this research was the preservation of physical, chemical and mechanical properties using controlled parameters of Laser cutting and Laser CO2 welding. It searched to identify and quantify the heat affected zone, to analyze structural changes, hardness variation using the Brinell method, and correlate these results with the chemical composition and the rupture resistance by the tensile test and the Erichsen method to determine the presence, or not, of micro tearing, pores, non metallic inclusions or other anomalies that could compromise together the welded joint. It was also considered the importance of the realization of tests for the Qualification of the Welding Procedure in agreement with the requirements of ASME Code Section IX, QW 150 for tensile test and QW 160 for the bend test, in order to get the validation of the procedure. The obtained results indicate that Laser CO2 welding of the HSLA steel is adequate for this construction type.

Made available in DSpace on 2015-07-13T12:10:22Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-02-27. Added 1 bitstream(s) on 2015-07-13T12:25:20Z : No. of bitstreams: 1 000836524.pdf: 2928493 bytes, checksum: 9b4c204130ec38c0829711c994ed2731 (MD5) / O estudo do comportamento de materiais, metálicos e não metálicos, sob a ação de desgaste micro abrasivo por esfera rotativa, tem sido reconhecido como um meio viável para avaliação não destrutiva em superfícies com revestimento duro aplicado por soldagem, sendo a soldagem uma forma rápida para recuperação e manutenção de corpos moedores na mineração e na indústria sucro-alcooleira. Com foco neste cenário, o trabalho em questão, tem o objetivo de projetar e construir uma máquina de ensaio micro abrasivo por esfera rotativa fixa em condições de força normal constante e pressão constante. Como corpos-de-prova, foram utilizadas chapas de aço carbono ASTM A36 de 12,5 mm de espessura e eletrodo revestido da liga Fe-Cr-C com Ø4,0 mm aplicando o revestimento em uma, duas e três camadas. Para o processo de desgaste foi inserido entre a esfera de aço AISI 52100 e o corpo de prova uma pasta abrasiva preparada com carbeto de silício preto com tamanho médio de 5 μm por partícula e água destilada. Nos ensaios realizados, em todos os casos, na análise por microscopia óptica das crateras revelaram somente a presença de desgaste abrasivo por riscamento e a diluição mostrou-se influente na formação da microestrutura do revestimento e uma correlação entre a dureza e resistência ao desgaste / The study of the behavior of materials, metallic and non-metallic, under the action of micro abrasive wear by rotating sphere, has been recognized as a viable means for nondestructive evaluation on surfaces with hard coating applied by welding. Welding is a quick way to recovery and maintenance in mining and ethanol industry. Focusing in this scenario, the work in question aims to design and build a micro abrasive testing machine with a fixed rotating sphere in a position to constant normal force and constant pressure. ASTM A36 mild steel with 12.5 mm thick were used as testing specimen materials and coated electrode of Fe- Cr-C alloy with ø4.0 mm applying the coating once, twice three layers. Between the AISI 52100 steel ball and specimen was placed abrasive slurry of silicon carbide with an average size of 5 μm per particle and distilled water. In the tests performed, in all cases, the analysis by optical microscopy of craters only revealed the presence of abrasive wear by grooving abrasion and dilution proved to be influential in the formation of the coating microstructure and a correlation between hardness and wear resistance

The J-laying technique for the construction of offshore pipelines requires a fast welding process that can produce sound welds in the horizontal-vertical position. The suitability of narrow gap gas metal arc welding (NG-GMA W) process for this application was previously demonstrated. The present programme studied the influence of process parameters on the fusion characteristics of NG-GMA welding in a range of different shielding gas compositions and welding positions. Statistical techniques were employed for both designing the experimental programme and to process the data generated. A partial factorial design scheme was used to investigate the influence of input variables and their interaction in determining weld bead shape. Modelling equations were developed by multiple linear regression to represent different characteristics of the weld bead. Transformation of the response variable based on the Cox-Box method was commonly used to simplify the model format. Modelling results were analysed by graphical techniques including surface plots and a multiplot approach was developed in order to graphically assess the influence of up to four input variables on the bead shape. Conditions for acceptable bead formation were determined and the process sensitivity to minor changes in input parameters assessed. Asymmetrical base metal fusion in horizontalvertical welding is discussed and techniques to improve fusion presented. At the same time, the interaction between the power supply output characteristic and the bead geometry was studied for narrow gap joints and the effect of shielding gas composition on both process stability and fusion of the base metal was assessed. An arc instability mode that is strongly influenced by arc length, power supply characteristic and shielding gas composition was demonstrated and its properties investigated. An optimized shielding gas composition for narrow gap process was suggested.

Thesis (MTech (Mechanical Engineering))--Peninsula Technikon, Cape Town, 2001 / Since the discovery of arc welding at the beginning ofthe century, metal transfer has been a topic ofresearch interest. Metal transfer can, in fact be related to weld quality, because it affects the arc stability. Furthermore, it determines the weld spatter, penetration, deposition rate and welding position. Gas Metal Arc Welding (also known as Metal Inert Gas- or MIG welding) is the most co=on method for arc welding steels and aluminurn alloys. Approximately 40% of the production welding in the country is accomplished by this process in which the thermal phenomena and melting ofthe solid electrode are coupled to the plasma arc and the weld pool. Thus the therrno- fluid behaviour of the electrode and detaching drops can have significant effects on the subsequent weld quality and production rate. The knowledge of how metal transfer affects this arc welding process is important for welding control and process automation, as well as in the development of improved welding consumables. Gas metal arc welding has a distinct feature, indicated by the results of Lesnewich [24], [23], that for most gases, there is a discrete metal droplet formation change between low and high current operations. Naturally the droplet size will have a significant influence on the properties ofthe welds. In globular transfer which occurs at low current, the welding electrode melts and produces large droplets (usually larger in diameter than the electrode wire diameter). This mode of transfer is associated with high spatter levels and thus undesirable in terms of welding economics. An increase in welding current will, for most welding! shielding gases, produce metal transfer with smaller droplets, which is termed spray transfer. This mode oftransfer is associated with high voltage and amperage settings, thus producing high deposition rates limited to the flaUhorizontal position.

Orientador: Vicente Afonso Ventrella / Co-orientador: Juno Gallego / Banca: Aparecido Carlos Gonçalves / Banca: Ricardo Cury Ibrahim / Resumo: O estudo do comportamento de materiais, metálicos e não metálicos, sob a ação de desgaste micro abrasivo por esfera rotativa, tem sido reconhecido como um meio viável para avaliação não destrutiva em superfícies com revestimento duro aplicado por soldagem, sendo a soldagem uma forma rápida para recuperação e manutenção de corpos moedores na mineração e na indústria sucro-alcooleira. Com foco neste cenário, o trabalho em questão, tem o objetivo de projetar e construir uma máquina de ensaio micro abrasivo por esfera rotativa fixa em condições de "força normal constante" e "pressão constante". Como corpos-de-prova, foram utilizadas chapas de aço carbono ASTM A36 de 12,5 mm de espessura e eletrodo revestido da liga Fe-Cr-C com Ø4,0 mm aplicando o revestimento em uma, duas e três camadas. Para o processo de desgaste foi inserido entre a esfera de aço AISI 52100 e o corpo de prova uma pasta abrasiva preparada com carbeto de silício preto com tamanho médio de 5 μm por partícula e água destilada. Nos ensaios realizados, em todos os casos, na análise por microscopia óptica das crateras revelaram somente a presença de desgaste abrasivo por "riscamento" e a diluição mostrou-se influente na formação da microestrutura do revestimento e uma correlação entre a dureza e resistência ao desgaste / Abstract: The study of the behavior of materials, metallic and non-metallic, under the action of micro abrasive wear by rotating sphere, has been recognized as a viable means for nondestructive evaluation on surfaces with hard coating applied by welding. Welding is a quick way to recovery and maintenance in mining and ethanol industry. Focusing in this scenario, the work in question aims to design and build a micro abrasive testing machine with a fixed rotating sphere in a position to "constant normal force" and "constant pressure". ASTM A36 mild steel with 12.5 mm thick were used as testing specimen materials and coated electrode of Fe- Cr-C alloy with ø4.0 mm applying the coating once, twice three layers. Between the AISI 52100 steel ball and specimen was placed abrasive slurry of silicon carbide with an average size of 5 μm per particle and distilled water. In the tests performed, in all cases, the analysis by optical microscopy of craters only revealed the presence of abrasive wear by "grooving abrasion " and dilution proved to be influential in the formation of the coating microstructure and a correlation between hardness and wear resistance / Mestre

The study was aimed at controlling the weld geometry of thin-plate titanium and one of its alloys (Ti-6Al-4V) by ultrasonic means and qualiFying the metals in the as-welded condition in terms of their grain sizes and mechanical properties. The alignment and symmetry of the weld pools were successfully tested by using ultrasonic shear waves. The grain sizes at the weld fusion zone were found to be related to their ultrasonic attenuation by a mathematical relationship. The temperature effect in locating weld pool radii in titanium was found at temperatures up to 600 °C. The ultrasonic velocity decreased as the temperature increased and the square of temperature affected the rate of change of the ultrasonic velocity. After compensation for the temperature effect, the maximum location error of the weld pool radius was 17 % which was comparable to previous measurement using different techniques.A positive relationship was seen between weld geometry (penetration depth and weld width) and heat input. A welding spectrum for titanium and its alloys of different thicknesses was obtained. Back shielding gas was beneficial in obtaining good welds. Both heat input rate and cooling rate were found to affect the grain size of the weld, with the cooling rate being the dominant factor. The grain size exhibited a Hall-Petch effect on mechanical properties, such as the tensile properties and fracture toughness of the weld. The phase transformation positively contributed to better mechanical properties in most cases, whilst the presence of interstitials worsened tensile properties. A system was developed in this study to utilise the above information and data for possible real-time and closed-loop control of the TIG welding process to give a desirable weld. Specifically, a process control data base was built up using software and a knowledge-based system for acceptable welding parameters, which were determined by acceptable penetration depth, grain size and mechanical properties. An algorithm was successfully written which relates the ultrasonic signal to the penetration depth of the weld. A hardware control circuit was built which took in the ultrasonic signal and converted it to a driving signal to change the welding speed and thereby change cooling rate.

Friction Stir Processing (FSP) of aluminium alloys has been used to modify and improve the microstructure and relevant properties of fusion welded aluminium alloys. The effect of FSP on MIG-Laser Hybrid (MLH) welded aluminium alloy 6082-T6 mechanical and microstructural properties has been studied in this research. The FSP process was used on 6mm thick aluminium alloy plates and a tool was designed specifically for FSP, and the effect of varying speeds was analysed before the final FSP welds were made. The effect of FSP was analysed by optical microscopy, tensile, microhardness and fatigue testing. The aim of the study was to determine whether the FSP process has a beneficial influence on the mechanical properties and metallurgical integrity of MIG-Laser Hybrid welded 6082-T6 aluminium alloy with varying gap tolerances. Three welding processes were compared, namely combined Friction Stir Processing on MIG-Laser hybrid process (FSP-MLH), MLH and Friction Stir Welding (FSW) as part of the analysis. (FSP was carried out on MLH components when it was found that FSP is not an entirely complete welding process but rather a finishing process per se.) The aim of this dissertation is to investigate the effects of the FSP process on the weld quality of MLH welded joints and also to compare this to individual processes like FSW and MLH. This investigation was undertaken in order to gain an understanding of the effect of these processes on fatigue performance and microhardness distribution on aluminium alloy 6082-T6 weld joints.

M.Ing. (Electrical And Electronic) / Please refer to full text to view abstract