Abstract:In this article, the camera settings for high-speed imaging of the arc, metal transfer, and weld pool in gas metal arc welding (GMAW) are investigated. The results show that by only changing camera exposure times and the selection of narrow bandpass filters, images that reveal features of the arc such as the iron vapor-dominated region, metal transfer and weld pool behavior can be produced without the need for external light sources. Using the images acquired, the arc length was measured and the relationship between arc length and arc voltage is discussed. The results show that for low values of current, the measured welding voltage increases with increasing arc length; however, for high current values, the arc voltage increases even though the measured arc length becomes shorter. It is suggested that the increase in arc voltage for high values of welding current is due to the increased evaporation of the wire electrode which decreases the plasma temperature and consequently the arc plasma electrical conductivity.
A novel process of welding GMAW-CW (Gas Metal Arc Welding-Cold Wire) had been developed with it resemblance to the GMAW (Gas Metal Arc Welding), the GMAW-CW has an additional wire fed into de weld pool, allowing better deposition rates, while maintaining weld characteristics. However, there is a more complex situation related to the HAZ (Heat Affected Zone) and weld geometry prediction than the GMAW conventional. The welding energy is a high metallurgical important parameter because together with the geometric characteristics of the gasket and the preheat level is decisive in thermal cycles imposed to the material, and therefore in the possible microstructural transformations and behavior of the joint. The behavior of representative curves of thermal cycling reflects important aspects regarding the conditions used in welding. Usually such factors as the type of process, use or non- pre or post- heating, heat input, multipass welding, are able to establish differences in the form of a heat cycle curve. In this work, it was applied the dual ellipsoidal model of heat input, adapted to the GMAW-CW and compared to the same model over the GMAW, using existing experimental data and predicting the HAZ dimensions in function of weld and welding parameters. The results found had less than 10% error from experimental data in a more refined version of the model, whereas the difficulties to predict cold wire addition influences were not trivial.
RESUMOO monitoramento contínuo da qualidade da energia elétrica (QEE)é essencial para fornecedores e consumidores de energia elétrica.Dentre as métricas avaliadas, as distorções harmônicas são distúrbiosem frequência indesejados nos sistemas elétricos e, por isso,são importantes parâmetros de QEE. O cálculo da Transformada Rápidade Fourier (FFT) é uma das maneiras de estimar as harmônicase pode exigir um hardware relativamente sofisticado quando implementadoem tempo real e com número de pontos relativamentealto. Buscando equipamentos de relativo baixo custo, este artigoapresenta estratégias de processamento de sinais e de implementaçãodo cálculo de uma FFT de 1600 pontos para estimativa dasdistorções harmônicas. O algoritmo desenvolvido foi embarcado emum equipamento para monitorar sistemas de alimentação elétricade corrente alternada trifásicos, que deve ser de classe S e atenderàs normas IEC 61000-4-7 e IEC 61000-4-30. Serão mostradas, emdiferentes implementações, quais foram as otimizações realizadasem software e hardware para a realização do cálculo desta FFT,utilizando um microcontrolador ARM Cortex-M7. Foram avaliadosas quantidades de memória flash e RAM requeridas, o númerode operações complexas realizadas e o tempo necessário para aexecução da transformada, levando em consideração a utilizaçãoou não das memórias cache e da TCM (Memória Altamente Acoplada)presentes no microcontrolador empregado no projeto. Osresultados mostraram uma diminuição significativa do custo computacional,especialmente quando se utilizou as memórias cache eimplementou-se a FFT com decimação no tempo.
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