Journal of the Brazilian Society of Mechanical Sciences and Engineering, 2021
Power is an indirect measurand, determined by processing voltage and current analogue signals thr... more Power is an indirect measurand, determined by processing voltage and current analogue signals through calculations. Using arc welding as a case study, the objective of this work was to bring up subsidies for power calculation. Based on the definitions of correlation and covariance in statistics, a mathematical demonstration was developed to point out the difference between the product of two averages (e.g. P = $$\overline{U} x \overline{I}$$ U ¯ x I ¯ ) and the average of the products (e.g. P = ($$\overline{UxI}$$ UxI ¯ ). Complementarily, a brief on U and I waveform distortion sources were discussed, emphasising the difference between signal standard deviations and measurement errors. It was demonstrated that the product of two averages is not the same as the average of the products, unless in specific conditions (when the variables are fully correlated). It was concluded that the statistical correlation can easily flag the interrelation, but if assisted by covariance, these statis...
Atmospheric pressure argon arcs were investigated by emission spectroscopy and electric explorati... more Atmospheric pressure argon arcs were investigated by emission spectroscopy and electric exploration techniques in the range of 50-200 A. The first technique gives temperature maps for arc currents in good agreement with previously published data. An extensive study on Langmuir probes in arcs was performed and a multi-wire apparatus was constructed. Because the probe characteristic curve is distorted at high pressure, only the ion saturation part of this curve is available under these conditions and temperatures are obtained from the inversion of the ion saturation current. However, the values obtained are systematically lower than the optical spectroscopy determinations. This is attributed to the recombination between ions and electrons, reducing the particle number. Since the temperature is proportional to the particle density, recombination lowers the temperature.
To overcome a shortage of flexible and low-cost solutions for wire arc additive manufacturing (WA... more To overcome a shortage of flexible and low-cost solutions for wire arc additive manufacturing (WAAM) preprocessing, this work’s objective was to develop and validate an in-house computational programme in an open-source environment for WAAM preprocessing planning. Algorithms for reading STL (stereolithography) files and implementing rotation, slicing, trajectory planning, and machine code generation were elaborated and implemented in the Scilab environment (free and open-source). A graphical interface was developed to facilitate user interaction, with 5 options for path planning. The functionality of each work step is detailed. For validation of the software, single and multiple-layer prints, with different geometrical complexity and printing challenges, were built in a CNC table geared by the generated machine code. The validation criteria were deposition imperfection, morphological, and dimensional tolerances. The outputs showed that the parts were successfully printed. Therefore,...
Resumen Se evaluo el comportamiento de electrodos revestidos AWS E 7018, en funcion del contenido... more Resumen Se evaluo el comportamiento de electrodos revestidos AWS E 7018, en funcion del contenido de los componentes en el revestimiento periferico aplicado, con el objetivo de mejorar su desempeno. Las proporciones en las mezclas para los revestimientos se establecieron con base en un diseno experimental de tipo Mc Lean Anderson, donde las variables de entrada son: X1- la pirolusita, X2- la caliza+fluorita (para relacion caliza: fluorita=1) y X3- el FeCrMn. Las mezclas homogenizadas fueron aglomeradas con silicato de sodio y agua para conformar las pastas que se aplicaron por inmersion sobre el revestimiento basico de los electrodos de 3,2 mm de diametro del nucleo metalico. Para evaluar los electrodos fueron obtenidas las isolineas de comportamiento de las tasas de fusion y deposicion, de la eficiencia de deposicion y de la geometria de los cordones. Se concluye que la composicion del revestimiento de mejor desempeno condiciona cambios favorables frente al electrodo sin revestimie...
The aim of this work was to evaluate the use of negative polarity in the trail wire in double-wir... more The aim of this work was to evaluate the use of negative polarity in the trail wire in double-wire MIG/MAG-welding filling passes. A comparative study of the conventional technique (two wires working with pulsed DCEP) and the proposed combinations of pulsed DCEP in the lead wire with pulsed DCEN in the trail wire and pulsed DCEP in the lead wire with controlled short-circuit CSC(-) in the trail wire was carried out. The mean current in each wire and the ratio of travel speed to wire feed rate (for the same bead volume per unit weld length), as well as wire type and size, shielding gas composition and joint type (a butt joint in a flat position), were kept constant. Bead surface finish and geometry, deposition efficiency and maximum travel speed for each combination were evaluated. In conclusion, the use of negative polarity in the trail wire increased the deposition rate (higher travel speeds for the same bead) compared with the use of pulsed DCEP in both wires but at the cost of re...
A principal motivação deste trabalho foi a procura da resposta para o dilema entre que as maiores... more A principal motivação deste trabalho foi a procura da resposta para o dilema entre que as maiores taxas de produção de eletrodos revestidos com pó de ferro se devem às suas capacidade de trabalhar com maior corrente ou à uma maior eficiência de fusão metálica do ferro adicionado na forma de pó. Um estudo neste sentido foi feito utilizando-se três eletrodos comerciais, cuja principal distinção referia-se ao teor de pó de ferro no revestimento. Os eletrodos foram caracterizados em relação às suas dimensões, densidade e composição (via MEV-EDS) do revestimento. Utilizando-se dois níveis de corrente, foram avaliadas as taxas de fusão e deposição e a geometria do cordão na confecção de filetes na posição plana (junta em ângulo). Pelos resultados, verificou-se que, independentemente da intensidade da corrente, as taxas de fusão e deposição são maiores no sentido crescente da maior concentração de pó de ferro no revestimento. Ficou demonstrado que o mecanismo gerador de maiores taxas de de...
Resumo Uma das novas abordagens em soldagem é a aplicação de técnicas de alimentação pulsada do a... more Resumo Uma das novas abordagens em soldagem é a aplicação de técnicas de alimentação pulsada do arame de adição para TIG e MIG/MAG. Entretanto, tais técnicas necessitam de alimentadores de arame e/ou tochas específicos, o que acaba limitando sua implementação pelo custo destes equipamentos. Assim, o presente trabalho tem como objetivo introduzir e avaliar de forma exploratória técnicas para pulsar a alimentação do arame aplicadas de forma independentemente de alimentadores e/ou tochas especiais. São apresentadas uma técnica com acionamento eletromecânico e outra com eletromagnético. Foram avaliados os efeitos da amplitude e frequência da alimentação pulsada sobre a formação de cordões de solda sobre chapa e sobre os sinais elétricos correspondentes. Para TIG, percebeu-se que a pulsação da alimentação tem potencial para modificar o cordão e tornar mais regular a transferência de material para a poça. Já para MIG/MAG, verificou-se que a pulsação da alimentação pode interferir no proce...
The alloying system and thermal history of the hot rolling process applied to highstrength low-al... more The alloying system and thermal history of the hot rolling process applied to highstrength low-alloy steels (HSLA) leads to a very particular behavior of these materials under welding thermal cycles. In this work, microstructures and hardness of a graincoarsened heat-affected zone (HAZ) were analyzed from API 5L X80 Nb microalloyed steel specimens after undergoing simulated thermal cycles to represent both first and tempering passes. The first thermal cycle for each sample reached the peak temperature of 1350°C, while the second was of 950°C. Using the different cooling curves imposed by the simulator, a continuous cooling transformation (CCT) diagram was raised for both conditions. The predominant microstructure for the first thermal cycle was granular bainitic ferrite at low cooling rates, but it changed into bainitic ferrite as cooling rate increases, reaching some presence of martensite at the highest cooling rates. The microstructure in the second thermal cycle is quasi-polygon...
Resumen Se aborda la obtención de un fundente para recargue duro por Soldadura con Arco Sumergido... more Resumen Se aborda la obtención de un fundente para recargue duro por Soldadura con Arco Sumergido (SAW), empleando ferrocromo-manganeso y escoria obtenidos de la reducción carbotérmica simultánea de cromita y pirolusita. El ferrocromo-manganeso y la escoria fueron obtenidos, concibiendo que ambos productos satisfagan los requisitos de los componentes (sistema de aleación y matriz) de un fundente aglomerado para el recargue. El proceso de fusión-reducción para la obtención de la aleación y la escoria fue realizado en horno de arco eléctrico de corriente continua. El vertido fue realizado en agua para facilitar la separación y molienda de los productos de colada. Fue elaborado un fundente experimental, empleando la aleación y escoria obtenida. Fueron obtenidos depósitos por SAW, los cuales fueron caracterizados en cuanto a: composición química, microestructura y dureza. Se concluyó que el fundente obtenido a partir de ferrocromo-manganeso y escoria de la reducción carbotérmica simultá...
Out-of-phase current pulsing has been commercially claimed to be indispensable for minimizing mag... more Out-of-phase current pulsing has been commercially claimed to be indispensable for minimizing magnetic interaction between arcs in the twin-wire gas metal arc welding (GMAW) process and reaching stable operations. This paper presents an investigation about the use of out-of-phase current pulse technology as applied to the twin-wire GMAW process. High-speed digital images were recorded with the objective of evaluating the metal transfer and the behavior of the voltaic arcs under the influence of out-of-phase current pulsing at different current levels. Conditions of in-phase and out-of-phase pulsing were evaluated and compared to no pulsed settings. A relationship between pulsing and pool oscillation was investigated, but it seems the natural frequency of the pool is the governing phenomena. Weldments were deposited on overlap joints in the flat position in order to study the resulting geometric characteristics. The results showed no evidence that out-of-phase current pulses can impo...
Journal of the Brazilian Society of Mechanical Sciences and Engineering, 2021
Power is an indirect measurand, determined by processing voltage and current analogue signals thr... more Power is an indirect measurand, determined by processing voltage and current analogue signals through calculations. Using arc welding as a case study, the objective of this work was to bring up subsidies for power calculation. Based on the definitions of correlation and covariance in statistics, a mathematical demonstration was developed to point out the difference between the product of two averages (e.g. P = $$\overline{U} x \overline{I}$$ U ¯ x I ¯ ) and the average of the products (e.g. P = ($$\overline{UxI}$$ UxI ¯ ). Complementarily, a brief on U and I waveform distortion sources were discussed, emphasising the difference between signal standard deviations and measurement errors. It was demonstrated that the product of two averages is not the same as the average of the products, unless in specific conditions (when the variables are fully correlated). It was concluded that the statistical correlation can easily flag the interrelation, but if assisted by covariance, these statis...
Atmospheric pressure argon arcs were investigated by emission spectroscopy and electric explorati... more Atmospheric pressure argon arcs were investigated by emission spectroscopy and electric exploration techniques in the range of 50-200 A. The first technique gives temperature maps for arc currents in good agreement with previously published data. An extensive study on Langmuir probes in arcs was performed and a multi-wire apparatus was constructed. Because the probe characteristic curve is distorted at high pressure, only the ion saturation part of this curve is available under these conditions and temperatures are obtained from the inversion of the ion saturation current. However, the values obtained are systematically lower than the optical spectroscopy determinations. This is attributed to the recombination between ions and electrons, reducing the particle number. Since the temperature is proportional to the particle density, recombination lowers the temperature.
To overcome a shortage of flexible and low-cost solutions for wire arc additive manufacturing (WA... more To overcome a shortage of flexible and low-cost solutions for wire arc additive manufacturing (WAAM) preprocessing, this work’s objective was to develop and validate an in-house computational programme in an open-source environment for WAAM preprocessing planning. Algorithms for reading STL (stereolithography) files and implementing rotation, slicing, trajectory planning, and machine code generation were elaborated and implemented in the Scilab environment (free and open-source). A graphical interface was developed to facilitate user interaction, with 5 options for path planning. The functionality of each work step is detailed. For validation of the software, single and multiple-layer prints, with different geometrical complexity and printing challenges, were built in a CNC table geared by the generated machine code. The validation criteria were deposition imperfection, morphological, and dimensional tolerances. The outputs showed that the parts were successfully printed. Therefore,...
Resumen Se evaluo el comportamiento de electrodos revestidos AWS E 7018, en funcion del contenido... more Resumen Se evaluo el comportamiento de electrodos revestidos AWS E 7018, en funcion del contenido de los componentes en el revestimiento periferico aplicado, con el objetivo de mejorar su desempeno. Las proporciones en las mezclas para los revestimientos se establecieron con base en un diseno experimental de tipo Mc Lean Anderson, donde las variables de entrada son: X1- la pirolusita, X2- la caliza+fluorita (para relacion caliza: fluorita=1) y X3- el FeCrMn. Las mezclas homogenizadas fueron aglomeradas con silicato de sodio y agua para conformar las pastas que se aplicaron por inmersion sobre el revestimiento basico de los electrodos de 3,2 mm de diametro del nucleo metalico. Para evaluar los electrodos fueron obtenidas las isolineas de comportamiento de las tasas de fusion y deposicion, de la eficiencia de deposicion y de la geometria de los cordones. Se concluye que la composicion del revestimiento de mejor desempeno condiciona cambios favorables frente al electrodo sin revestimie...
The aim of this work was to evaluate the use of negative polarity in the trail wire in double-wir... more The aim of this work was to evaluate the use of negative polarity in the trail wire in double-wire MIG/MAG-welding filling passes. A comparative study of the conventional technique (two wires working with pulsed DCEP) and the proposed combinations of pulsed DCEP in the lead wire with pulsed DCEN in the trail wire and pulsed DCEP in the lead wire with controlled short-circuit CSC(-) in the trail wire was carried out. The mean current in each wire and the ratio of travel speed to wire feed rate (for the same bead volume per unit weld length), as well as wire type and size, shielding gas composition and joint type (a butt joint in a flat position), were kept constant. Bead surface finish and geometry, deposition efficiency and maximum travel speed for each combination were evaluated. In conclusion, the use of negative polarity in the trail wire increased the deposition rate (higher travel speeds for the same bead) compared with the use of pulsed DCEP in both wires but at the cost of re...
A principal motivação deste trabalho foi a procura da resposta para o dilema entre que as maiores... more A principal motivação deste trabalho foi a procura da resposta para o dilema entre que as maiores taxas de produção de eletrodos revestidos com pó de ferro se devem às suas capacidade de trabalhar com maior corrente ou à uma maior eficiência de fusão metálica do ferro adicionado na forma de pó. Um estudo neste sentido foi feito utilizando-se três eletrodos comerciais, cuja principal distinção referia-se ao teor de pó de ferro no revestimento. Os eletrodos foram caracterizados em relação às suas dimensões, densidade e composição (via MEV-EDS) do revestimento. Utilizando-se dois níveis de corrente, foram avaliadas as taxas de fusão e deposição e a geometria do cordão na confecção de filetes na posição plana (junta em ângulo). Pelos resultados, verificou-se que, independentemente da intensidade da corrente, as taxas de fusão e deposição são maiores no sentido crescente da maior concentração de pó de ferro no revestimento. Ficou demonstrado que o mecanismo gerador de maiores taxas de de...
Resumo Uma das novas abordagens em soldagem é a aplicação de técnicas de alimentação pulsada do a... more Resumo Uma das novas abordagens em soldagem é a aplicação de técnicas de alimentação pulsada do arame de adição para TIG e MIG/MAG. Entretanto, tais técnicas necessitam de alimentadores de arame e/ou tochas específicos, o que acaba limitando sua implementação pelo custo destes equipamentos. Assim, o presente trabalho tem como objetivo introduzir e avaliar de forma exploratória técnicas para pulsar a alimentação do arame aplicadas de forma independentemente de alimentadores e/ou tochas especiais. São apresentadas uma técnica com acionamento eletromecânico e outra com eletromagnético. Foram avaliados os efeitos da amplitude e frequência da alimentação pulsada sobre a formação de cordões de solda sobre chapa e sobre os sinais elétricos correspondentes. Para TIG, percebeu-se que a pulsação da alimentação tem potencial para modificar o cordão e tornar mais regular a transferência de material para a poça. Já para MIG/MAG, verificou-se que a pulsação da alimentação pode interferir no proce...
The alloying system and thermal history of the hot rolling process applied to highstrength low-al... more The alloying system and thermal history of the hot rolling process applied to highstrength low-alloy steels (HSLA) leads to a very particular behavior of these materials under welding thermal cycles. In this work, microstructures and hardness of a graincoarsened heat-affected zone (HAZ) were analyzed from API 5L X80 Nb microalloyed steel specimens after undergoing simulated thermal cycles to represent both first and tempering passes. The first thermal cycle for each sample reached the peak temperature of 1350°C, while the second was of 950°C. Using the different cooling curves imposed by the simulator, a continuous cooling transformation (CCT) diagram was raised for both conditions. The predominant microstructure for the first thermal cycle was granular bainitic ferrite at low cooling rates, but it changed into bainitic ferrite as cooling rate increases, reaching some presence of martensite at the highest cooling rates. The microstructure in the second thermal cycle is quasi-polygon...
Resumen Se aborda la obtención de un fundente para recargue duro por Soldadura con Arco Sumergido... more Resumen Se aborda la obtención de un fundente para recargue duro por Soldadura con Arco Sumergido (SAW), empleando ferrocromo-manganeso y escoria obtenidos de la reducción carbotérmica simultánea de cromita y pirolusita. El ferrocromo-manganeso y la escoria fueron obtenidos, concibiendo que ambos productos satisfagan los requisitos de los componentes (sistema de aleación y matriz) de un fundente aglomerado para el recargue. El proceso de fusión-reducción para la obtención de la aleación y la escoria fue realizado en horno de arco eléctrico de corriente continua. El vertido fue realizado en agua para facilitar la separación y molienda de los productos de colada. Fue elaborado un fundente experimental, empleando la aleación y escoria obtenida. Fueron obtenidos depósitos por SAW, los cuales fueron caracterizados en cuanto a: composición química, microestructura y dureza. Se concluyó que el fundente obtenido a partir de ferrocromo-manganeso y escoria de la reducción carbotérmica simultá...
Out-of-phase current pulsing has been commercially claimed to be indispensable for minimizing mag... more Out-of-phase current pulsing has been commercially claimed to be indispensable for minimizing magnetic interaction between arcs in the twin-wire gas metal arc welding (GMAW) process and reaching stable operations. This paper presents an investigation about the use of out-of-phase current pulse technology as applied to the twin-wire GMAW process. High-speed digital images were recorded with the objective of evaluating the metal transfer and the behavior of the voltaic arcs under the influence of out-of-phase current pulsing at different current levels. Conditions of in-phase and out-of-phase pulsing were evaluated and compared to no pulsed settings. A relationship between pulsing and pool oscillation was investigated, but it seems the natural frequency of the pool is the governing phenomena. Weldments were deposited on overlap joints in the flat position in order to study the resulting geometric characteristics. The results showed no evidence that out-of-phase current pulses can impo...
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