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Search Results: 1 - 10 of 4919 matches for " Américo Scotti "
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Parameter optimization of AC rectangular wave outputs for aluminum cold wire GTAW
Scotti, Américo;Reis, Roberto Aparecido dos;
Journal of the Brazilian Society of Mechanical Sciences , 1999, DOI: 10.1590/S0100-73861999000400009
Abstract: the objective of this work was to optimize the parameter setup for gtaw of aluminum using an ac rectangular wave output and continuous feeding. a series of welds was carried-out in an industrial joint, with variation of the negative and positive current amplitude, the negative and positive duration time, the travel speed and the feeding speed. another series was carried out to investigate the isolate effect of the negative duration time and travel speed. bead geometry aspects were assessed, such as reinforcement, penetration, incomplete fusion and joint wall bridging. the results showed that currents at both polarities are remarkably more significant than the respective duration times. it was also shown that there is a straight relationship between welding speed and feeding speed and this relationship must be followed for obtaining sound beads. a very short positive duration time is enough for arc stability achievement and when the negative duration time is longer than 5 ms its effect on geometry appears. the possibility of optimizing the parameter selection, despite the high inter-correlation amongst them, was demonstrate through a computer program. an approach to reduce the number of variables in this process is also presented.
Análise comparativa da gera??o de fumos entre arames maci?os (GMAW) e tubulares (FCAW)
Garcia, Regina Paula;Scotti, Américo;
Soldagem & Inspe??o , 2010, DOI: 10.1590/S0104-92242010000200004
Abstract: the gmaw (mig /mag) process is widespread in industry. however, it presents limitations regarding metallurgical aspects and geometrical characteristics of the weld bead. the fcaw process, on the other hand, due to presence of fluxes, achieves improvements on these aspects, but the flux might be responsible for larger fume emission. this paper aimed to present a comparative study of fume generation between the gmaw process with short-circuit metal transfer and the gas shielded fcaw process, using wires of same class of resistance (483 mpa of ultimate tension) and application. the experiments were performed in a fume chamber calibrated according to a standard. both wires were evaluated using 100% co2 as the shielding gas and at two current levels. the arc length effect and the use of another shielding gas (25% co2 in argon) were also evaluated. appropriate conditions of contact-tip-to-work-piece distance and arc voltage were selected for each wire-shielding gas combination as a means of making the comparison closer to the reality. the volume of the weld beads per meter was made the same for each level of current, by keeping the same relationship between wire deposition and welding travel speed. the results confirm a higher fume generation rate of the fcaw process (already expected) and that absolute fume generation rate grows as the welding current increases. however, for the gmaw process, analyzed from a relative point of view, it doesn't happen. it was verified that the current effect is more significant on the fcaw process. the increase in the co2 content raised the fume generation rate only for the fcaw process, whilst the arc voltage variation did not demonstrate any effect on it.
Metodologia para parametrizar e avaliar a técnica da ''burn-zinc'' no processo de soldagem a ponto por resistência
Nascimento, Vinicius Castanheira do;Scotti, Américo;
Soldagem & Inspe??o , 2010, DOI: 10.1590/S0104-92242010000100003
Abstract: for minimizing the detrimental effects of zinc during resistance spot welding of galvanized sheets, a technique denominated burn-zinc is usually employed. however, there is no much information and studies available in the current literature about when and how to use this technique. the present work had the objective of assessing and understanding better this technique. for that, a methodology for determination of ideal burn-zing parameters as a function of the sheets was proposed. the evaluation of this methodology was carried out by a series of weldments, by systematically varying current and pressure at compatible levels for zinc burning. high speed filming, synchronized with the electrical signals, was employing for visualizing and results analyses. once the burn-zinc parameters were defined, new weldments were done with and without the burn-zing application. the proposed experimental procedure showed to be efficient for checking and parameterization of the burn-zing technique. however, there were evidences that not always the application of the burn-zing will lead to reduction of the operational time.
Uma metodologia para parametriza o do processo MIG/MAG CA A methodology for parameterization of the AC MIG/MAG process
Américo Scotti,Lindbergh Souza Monteiro
Soldagem & Inspe??o , 2012, DOI: 10.1590/s0104-92242012000300011
Abstract: O processo MIG/MAG CA tem um potencial muito grande de aplica o, por permitir unir as características da soldagem MIG/MAG convencional (corrente contínua, com o eletrodo no positivo) com as de se usar corrente negativa na soldagem MIG/MAG. Entretanto, o formato de onda de corrente (alternada, pulsada no positivo e constante no negativo) demanda uma sele o criteriosa de seus inúmeros parametros de regulagem, o que vem limitando o estudo e aplica o desta vers o de processo MIG/MAG. O objetivo deste trabalho foi propor e avaliar uma metodologia capaz de estimar os parametros de regulagem do processo MIG/MAG CA, de tal forma a se obter soldas com estabilidade de comprimento de arco e cord es com geometria adequada. é feita uma descri o passo a passo da defini o dos parametros de entrada e da forma de se obter experimentalmente alguns valores de parametros necessários para estima o de outros valores de regulagem. As equa es de estima o s o apresentadas e discutidas. é feita uma demonstra o da aplica o da metodologia, com a valida o dos resultados pela compara o entre valores estimados e reais. The AC MIG/MAG process presents remarkable application potential, since it allows join the characteristics of the conventional MIG/MAG process (direct current, electrode positive) with the ones obtained when negative current is applied in MIG/MAG welding. However, the current wave shape (alternate, pulsed in positive and constant in negative polarities) demands a criterions selection of its innumerous setting parameters, fact that limits the development and application of this process version. The objective of this work was to propose and assess a methodology able to estimate the setting parameters of the CA MIG/MAG welding process, in such a way to result in welds with arc length stability and adequate bead geometry. A step-a-step description of the input parameter definitions and of the way to experimentally obtain some parameter values needed to estimate other setting parameters. The estimation equations are presented and discussed. A demonstration of the methodology application is carried out, with validation through actual welds.
Parameter optimization of AC rectangular wave outputs for aluminum cold wire GTAW
Scotti Américo,Reis Roberto Aparecido dos
Journal of the Brazilian Society of Mechanical Sciences , 1999,
Abstract: The objective of this work was to optimize the parameter setup for GTAW of aluminum using an AC rectangular wave output and continuous feeding. A series of welds was carried-out in an industrial joint, with variation of the negative and positive current amplitude, the negative and positive duration time, the travel speed and the feeding speed. Another series was carried out to investigate the isolate effect of the negative duration time and travel speed. Bead geometry aspects were assessed, such as reinforcement, penetration, incomplete fusion and joint wall bridging. The results showed that currents at both polarities are remarkably more significant than the respective duration times. It was also shown that there is a straight relationship between welding speed and feeding speed and this relationship must be followed for obtaining sound beads. A very short positive duration time is enough for arc stability achievement and when the negative duration time is longer than 5 ms its effect on geometry appears. The possibility of optimizing the parameter selection, despite the high inter-correlation amongst them, was demonstrate through a computer program. An approach to reduce the number of variables in this process is also presented.
A quality and cost approach for welding process selection
Silva, César Rezende;Ferraresi, Valtair Antonio;Scotti, Américo;
Journal of the Brazilian Society of Mechanical Sciences , 2000, DOI: 10.1590/S0100-73862000000300002
Abstract: the aim of this work was to propose, apply and evaluate a methodical approach to select welding processes in a productive environment based on market requirements of quality and costs. a case study was used. the welds were carried out in laboratory, simulating the joint conditions of a manufacturer and using several welding processes: smaw, gtaw, pulsed gtaw, gmaw with co2 and ar based shielding gases and pulsed gmaw. for quality analysis geometrical aspects of the beads were considered and for cost analysis, welding parameters and consumable prices. quantitative indices were proposed and evaluated. after that, evaluation of both quality and costs was done, showing to be possible to select the most suitable welding process to a specific application, taking into account the market conditions of a company.
Modelo descritivo do fluxo de calor em soldagem a arco visando o conceito de calor imposto efetivo
Scotti, Américo;Reis, Ruham Pablo;Liskevych, Olga;
Soldagem & Inspe??o , 2012, DOI: 10.1590/S0104-92242012000200010
Abstract: the objective of the present paper is to propose a global model for describing heat flow in arc welding, aiming the understanding of the phenomena involved. the attempt is to fill out a gap of knowledge which has been generated between the application of simplified analytical models (not totally realistic) and numerical models (that disguises the physics of the phenomena). initially, a physic-oriented description of the reasons for welding arc voltage drop is presented. this description is based on the heat generation and its losses to maintain the balance between deionization and reionization, in contrast to the approach that the arc is comparable to an electrical resistor. following, a descriptive model of the thermal subsistence of the arc is proposed to describe the heat transference from the arc to the plate. then, a second descriptive model is proposed to explain how the heat enters, diffuses and leaves the workpiece during welding. sequentially, it is discussed how the application of these two models in a global way allows to understand that not all the heat flow from the arc to the plate will affect the cooling rate of the heated parts. a proposal for applying the term effective heat input to mean the heat parameter which is important to be determined in welding is put forward.
Um modelo qualitativo para explicar a influência da polaridade na taxa de fus?o no processo MIG/MAG
Souza, Daniel;Resende, André Alves de;Scotti, Américo;
Soldagem & Inspe??o , 2009, DOI: 10.1590/S0104-92242009000300002
Abstract: one of the main advantages of the mig/mag process is its high productivity. usually, the positive polarity is employed, due to a higher arc stability, less spattering and adequate bead profiles. however, a higher production capacity than observed in the conventional mig/mag process has been demanded for some applications. in the current literature related to mig/mag, it is mentioned that the negative polarity provides a higher fusion rate than the positive one, despite of leading to higher spattering and bead misshapen. unfortunately, there is no much information available about the effects of process variables in this polarity, as much as concerning justifications. thus, in this work was attempted to understand the reasons for a higher fusion rate at cc-, as well as the respective effect on the bead geometry. for that, mig/mag comparative welds were carried out at both polarities, using two shielding gas blends and two current values. the transfer mode and arc behavior were assessed by synchronized shadowgrafy technique. the bead geometry was evaluated through metallographic procedures. from the results, which does not agree entirely with the current literature, it was observed that as much the transfer mode as the bead morphology and finish depend on the shielding gas composition. to explain the phenomena inherent to a higher fusion rate at cc-, it is claimed that the fact of the arc to climb the wire surface at this polarity is the governing factor.
Determination of the momentum of droplets impinging on the pool during aluminium GMAW
Scotti, Américo;Rodrigues, Carlos Eduardo Aguiar Lima;
Soldagem & Inspe??o , 2009, DOI: 10.1590/S0104-92242009000400008
Abstract: the purpose of this work was to raise the kinematics and dynamics characteristics of the droplets under transference during aluminium gma welding and quantify the partial effect of the momentum on the weld bead formation. it is initially claimed that a better way of quantifying this effect would be through the mass flow rate of the droplets reaching the weld pool; calculated parameter denominated here as effective momentum. bead-on-plate gmaw, shielded with ar, was carried out using an aluminium alloy wire. three levels of current and two levels of arc length were employed in the experimental design. high-speed filming shadowgraphy, synchronized with the electrical signals, was used as measuring tool. dedicated computational programs were employed to quantify arc lengths and size, frequency, acceleration and speed of the droplets. it was confirmed that in spite of the low values of the effective momentum for aluminium gmaw, the momentum is one of the governing factor in developing bead penetration. the interaction between effective momentum and welding current and its effect on the aluminium gmaw bead geometry is discussed.
A quality and cost approach for welding process selection
Silva César Rezende,Ferraresi Valtair Antonio,Scotti Américo
Journal of the Brazilian Society of Mechanical Sciences , 2000,
Abstract: The aim of this work was to propose, apply and evaluate a methodical approach to select welding processes in a productive environment based on market requirements of Quality and Costs. A case study was used. The welds were carried out in laboratory, simulating the joint conditions of a manufacturer and using several welding processes: SMAW, GTAW, pulsed GTAW, GMAW with CO2 and Ar based shielding gases and pulsed GMAW. For Quality analysis geometrical aspects of the beads were considered and for Cost analysis, welding parameters and consumable prices. Quantitative indices were proposed and evaluated. After that, evaluation of both Quality and Costs was done, showing to be possible to select the most suitable welding process to a specific application, taking into account the market conditions of a company.
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