In this work, experiments were carried out to determine the welding behaviour of aluminium 1200 based on an increase in the activation time of the positive polarity for tungsten inert gas AC welding of this metal. To achieve this objective, a series of experiments was developed, in such a way that the intensity of the electrical current in the positive and negative polarities was the same; only the duration times in each polarity were modified. During the experiments, the current and voltage signals were acquired. In this way, the arc voltage and potential could be determined for each condition tested. In terms of the fusion behaviour, an increase in penetration and in welded areas was verified to the extent that longer positive polarity times were used. This behaviour is different from that commonly indicated in the literature about welding processes with non-consumable electrodes, which suggests a reduction in penetration with an increase in the positive polarity activation time. However, this trend grows constantly during the experiments from a determined point, where the positive polarity activity times are greater than 4.0 ms in a total period of 20.0 ms. The use of a minimum positive polarity time (1.3 ms) was shown to be effective for cathode cleaning, as it produced welds with satisfactory fusion characteristics and with minimum wear to the tungsten electrode. The good fusion capacity obtained in welds produced with long positive polarity times was attributed to phenomena arising from the emission of electrons due to the field effect that occurs during the positive electrode phases.
Resumo Key-Words: AC-GTAW, cathodic cleaning, thermionic emission, field emission IntroduçãoO processo TIG (Tungsten Inert Gas) se caracteriza por um arco voltaico estabelecido entre um eletrodo de tungstênio, dito não-consumível, e a peça a ser soldada, o que em alguns casos permite a soldagem de chapas metálicas finas (abaixo de 3 mm) sem utilização de metal de adição. Metais ferrosos, tais como o aço inoxidável, são soldados na condição CC-(corrente contínua e eletrodo conectado ao terminal negativo da fonte de soldagem). Nesta condição, a corrente é conduzida através do plasma, parcialmente por íons e principalmente por elétrons que são emitidos a partir do eletrodo de tungstênio (cátodo) [1]. O tungstênio é um metal que pode atingir temperaturas extremamente altas em sua superfície, o que permite que estes elétrons sejam emitidos por efeito termiônico quando a energia acumulada supera um dado valor necessário (relacionada com a função-trabalho do material) [2]. Quando emitindo elétrons
Experiments were carried out to determine the effect of the positive polarity time on cathodic cleaning, arc voltage, arc power and weld bead geometry on AC-GTAW of aluminium. Welding current was kept constant in both positive (EP) and negative polarity. During the experiments current and voltage monitoring was performed to further analysis of arc voltage and arc power. There was an increase in the weld depth and fusion areas when longer EP times were used. This behaviour differs from the traditional literature relating to welding processes with non-consumable electrodes. However, this increase occurs from a certain point, when the EP time is .4?0 ms over a total period of 20?0 ms. The use of a minimum EP time was found to be sufficient to perform the oxide removal, yielding weld beads with satisfactory fusion characteristics and minimum wear of the tungsten electrode.
The use of variants of the GMAW process has become an affordable option in industry. Alternating current Gas Metal Arc Welding (AC-GMAW) arises as one of them, providing additional degrees of freedom for process controllability and versatility. This study focused on the analysis of a complex waveform of the AC-GMAW process for welding stainless steel, employed in modern synergic programs, which has not been widely disseminated in the technical literature and assessed scienti cally. The main objective was to characterize the effects of high intensity pulses in negative polarity over the process and to discuss the potential of this strategy, since it has not been used in conventional AC synergic programs. In order to bring to light information on the phenomena involved, such as the arc climbing on the wire electrode, advanced techniques of high-speed videography were used, synchronized with the acquisition of electrical welding process signals, as well as infrared thermography, to verify the evolution of the cooling of the piece after welding. The results grounded discussions on different AC-GMAW waveforms.The process´s electrical data, along with images of the arc and analysis of the wire melting and workpiece thermal behavior, showed that there was a signi cant visible increase in wire melting during the negative pulse. In addition, it evidenced how the negative electrode increment contributed to the increase in wire melting even at lower power and also showed the thermal effects on the workpiece.
The use of variants of the GMAW process has become an affordable option in industry. Alternating current Gas Metal Arc Welding (AC-GMAW) arises as one of them, providing additional degrees of freedom for process controllability and versatility. This study focused on the analysis of a complex waveform of the AC-GMAW process for welding stainless steel, employed in modern synergic programs, which has not been widely disseminated in the technical literature and assessed scientifically. The main objective was to characterize the effects of high intensity pulses in negative polarity over the process and to discuss the potential of this strategy, since it has not been used in conventional AC synergic programs. In order to bring to light information on the phenomena involved, such as the arc climbing on the wire electrode, advanced techniques of high-speed videography were used, synchronized with the acquisition of electrical welding process signals, as well as infrared thermography, to verify the evolution of the cooling of the piece after welding. The results grounded discussions on different AC-GMAW waveforms. The process´s electrical data, along with images of the arc and analysis of the wire melting and workpiece thermal behavior, showed that there was a significant visible increase in wire melting during the negative pulse. In addition, it evidenced how the negative electrode increment contributed to the increase in wire melting even at lower power and also showed the thermal effects on the workpiece.
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