Louriel Oliveira Vilarinho

Proposal for a modified fowler-milne method to determine the temperature profile in TIG welding at low currents

It is possible to assess the thermal efficiency of welding shielding gases by means of the arc temperature field analysis. Since this approach opens a remarkable study field to assess different shielding gases, giving support for dealing with advantages and disadvantages of commercial gas mixtures, there is a research line under development, which goal is to find techniques to measure arc temperatures. This work describes a proposed method containing different procedures to quantify plasma jet temperature profiles from experimental data. This method was applied on data taken from TIG welding arc, at low current (40 A). This low current was selected to contrast to and amplify the current literature focus, i.e., high currents. The experiment was conducted using emission spectroscopy, picking punctual luminescence from the plasma through an optic system. The TIG arc was stroked on a water-cooled copper plate and shielded by pure argon. The temperature field was determined through the modified Fowler-Milne method. The introduced modification aimed to overcome the limitation that this method has for low radiation intensity presents in low current arcs: the Fowler-Milne method has an intrinsic threshold of 10,000 - 25,000 K. For a 40-A arc, the lower 10,000-K limiting isotherm is reached close to the cathode, restricting the analysis field, especially for the anode region. The proposed modification suggests a linear distribution of the particle density instead of a Maxwellian one, at temperatures below 12,500 K. The experimental temperature field was compared to a previous publication that deals with numerical simulation and the results were found in good agreement, what indicates the supposition of a linear distribution it is not far from the reality.

Intrinsic errors on cryogenic calorimetry applied to arc welding

This paper discusses the real meaning of the results from cryogenic calorimetry. A new concept of heat input, denominated as effective heat input, is proposed, based on the fact that what is important for welding engineering is the heat that determines the cooling rates and governs the metallurgical transformations. A descriptive model is proposed to explain how heat flows inside a plate to demonstrate that part of the heat leaves the plate before diffusing into it. Experiments using a liquid nitrogen calorimeter, fully automated to minimize intrinsic errors, were carried out to verify the difference in the outcomes when either bead size or plate thickness is a variable in the test. It was concluded that other intrinsic errors persist and the test, as conceived at the moment, can be applied only on comparative manner if all conditions are the same. However, a promising parameter described here as net heat input maybe taken from the test, which would be independent of variables as bead size and plate thickness and more useful for heat flow and metallurgical estimations.

Influência da Tensão de Soldagem e do Gás de Proteção sobre a Correlação entre Indutância e Regularidade da Transferência Metálica na Soldagem MIG/MAG por Curto-Circuito (The Influence of the Welding Voltage and of the Shielding Gas on the Correlation between Inductance and Metal Transfer Regularity in Short-circuiting MIG/MAG Welding)

The MIG/MAG process operating as short-circuiting is widely used when low heat input is a demand. However, in this operating mode, excessive spattering may occur. To mitigate this problem, it is necessary to act on parameter settings. It is known that inductance governs the current increasing/decreasing rate, reflecting on the short-circuiting transfer regularity. However, little is known about the effect of arc voltage and the gas composition on this rate. Thus, in this work it was pursued the influence of the welding voltage and shielding gas composition in the correlation between inductance and metal transfer regularity in short-circuiting MIG/ MAG carbon-steel welding. Weldments were carried out scanning the voltage settings at three different inductance settings and with two differed shielding gases, using the same current level. A quantitative criterion was employed to assess the metal transfer regularity. Metal transfer conditions were visualized by means of synchronized high-speed filming shadowgraphy. The results showed that voltage and shielding gas do not interfere in the up and down current rate for a same inductance setting, but the regularity of the process is dependent of the shielding gas composition and arc voltage.O processo de soldagem MIG/MAG operando no modo de transferencia por curto-circuito e largamente utilizado quando se requer baixo aporte de calor. Porem, operando nesse modo, o processo pode apresentar excessiva geracao de respingos. Para se minimizar este problema, e necessario atuar na regulagem de seus parâmetros. E sabido que a indutância governa a taxa de variacao da corrente, com reflexos sobre a regularidade da transferencia da gota por curto-circuito. Mas pouco se conhece sobre o efeito da regulagem da tensao e do uso de gases sobre essa taxa de variacao. O objetivo deste trabalho foi avaliar a influencia da tensao de soldagem e do gas de protecao na correlacao entre a indutância e a regularidade da transferencia por curto-circuito na soldagem MIG/MAG de aco carbono. Soldagens foram realizadas varrendo-se a regulagem de tensao em tres valores diferentes de regulagem de indutância e com dois gases de protecao, mantendo-se a corrente media constante. Um criterio quantitativo foi utilizado para medicao da regularidade da transferencia. Condicoes de transferencia foram visualizadas por meio de perfilografia sincronizada com filmagem de alta velocidade. Resultados mostraram que a tensao de soldagem e o gas de protecao nao influenciaram as taxas de variacao da corrente para uma mesma regulagem da indutância, mas que mesmo assim a regularidade do processo e dependente do gas de protecao e da tensao de soldagem.

Desenvolvimento e avaliação de calorímetros por nitrogênio líquido e fluxo contínuo para medição de aporte térmico

Um dos parâmetros mais influentes no processo de soldagem a nivel industrial e de pesquisa e o calor entregue a chapa (aporte termico) devido a sua direta ligacao com a mudanca das caracteristicas metalurgicas e propriedades mecânicas da junta soldada. Para o estudo e quantificacao do calor aportado na peca de trabalho, tem-se utilizado tanto metodos teoricos (analiticos e numericos), quanto experimentais (calorimetria). Estas tecnicas apresentam ampla dispersao dos resultados obtidos para o rendimento termico. Desta forma, a proposta deste trabalho e apresentar o projeto, construcao e avaliacao de um calorimetro de nitrogenio liquido e fluxo continuo (agua) para a medicao do aporte termico e rendimento termico de processos GTAW e GMAW. Para o processo GTAW, cordoes sobre chapa foram realizados com Ar puro e chapas de aco ao carbono ASTM A36 e variou-se os parâmetros de soldagem como corrente, comprimento do arco, velocidade de soldagem e comprimento do cordao de solda. Foram tambem realizadas soldagens sobre chapa com o processo GMAW em transferencia por curto-circuito e goticular (spray), onde o arame utilizado foi AWS ER70S-6 (1,2 mm de diâmetro)e gas de protecao Ar+25%CO2 (curto-circuito) e Ar+5%O2 (goticular). Para os processos derivativos (STT - Surface Tension Transfer, RMD - Regulated Metal Deposition, CMT - Cold Metal Transfer, GMAW-P - Pulsado e GMAW-PV - Polaridade Variavel) foram tomados como base parâmetro de soldagem encontrados por outros autores no Laprosolda (Centro para Pesquisa e Desenvolvimento de Processos de Soldagem). De modo geral, o calorimetro de nitrogenio liquido apresentou boa repetibilidade com diferenca maxima de 3%. Tambem foi observado que durante os testes realizados no calorimetro de nitrogenio liquido apresentaram resultados coerentes para as diferentes condicoes de soldagem e reportando valores de rendimento termico global de 70,3% para o processo GTAW, 78,6% para GMAW curto-circuito convencional, 73,6% para GMAW goticular e 76,1% para os processos GMAW curto circuito-controlado. Os resultados obtidos com o calorimetro de fluxo continuo (agua) acompanharam a tendencia do calorimetro de nitrogenio liquido, mas com resultados medios 12% abaixo.

Um critério para determinar a regulagem da tensão em soldagem MIG/MAG por curto-circuito

Abstract: This paper presents an exploratory study on a criterion called “Criterion for Stability Laprosolda Transfer in MIG / MAG with short circuit”, which aims at a quantitative analysis of the regularity of metal transfer for setting parameters for MIG / MAG conventional in short circuit. Initially it is stated the foundation for development of this criterion. The evaluation of that was made by welding and comparisons of results with the efficiency of deposition and the geometric characteristics of the weld bead. For this, the test plates with 3.18 mm thick and 1 mm gap between them was welded in the same range of current and feeding speed, using wire AWS ER70S-6 1.2 mm of diameter protected by the mixture 85% Argon - carbon dioxide 15%. To meet the proposed relationship, it was covered up the regulation of welding voltages from very low to very high for what was expected for this condition of welding. The results confirm the effectiveness of the “Index of regularity” as a means of assessing adjustments welding MIG / MAG to minimize spatter and optimize the coating on the weld bead.

Influência da regulagem de parâmetros de soldagem sobre a estabilidade do processo MIG/MAG operando em curto-circuito

Due to the wide applicability of short-circuiting GMA welding, a fully understanding of the parameter settings on the metal transfer stability turn into an important issue. Bead-on-plate welds were carried out for assessing the influence of voltage, CTWD and up and down current rates over the metal transfer regularity, using 3 commercial shielding gas blends. As comparative criterion, the transfer regularity was quantified through an index taken from voltage and current traces. The results shown that, working with short-circuits, the setting voltage has strong influence on the metal transfer stability; there is an optimum range. This range is remarkably influenced by the shielding gas type, current value, CTWD and inductance factor settings. The lower the CO2 content in the blend, the more regular the transfer. The inductance factor effect is dependant of the CO2 content in the blend.Devido ao potencial de aplicabilidade do processo MIG/MAG no modo de transferencia por curto-circuito, torna-se importante o pleno entendimento da regulagem dos parâmetros sobre a estabilidade da transferencia metalica e suas consequencias sobre a geracao de respingos. Soldagens de simples deposicao sobre chapas foram realizadas para verificar a influencia da variacao da tensao, DBCP e das taxas de crescimento e decrescimento da corrente na estabilidade da transferencia por curto-circuito, utilizando-se como gas de protecao 3 misturas largamente utilizadas na pratica. Como criterio de comparacao, foi quantificada a regularidade da transferencia atraves de um indice a partir do comportamento do sinal de tensao de soldagem. Os resultados mostram que, operando em curtocircuito, a tensao regulada tem forte influencia sobre a estabilidade de transferencia, existindo uma faixa otima. Esta faixa e fortemente influenciada pelo tipo de gas, valor da corrente, DBCP e regulagem do fator de inducao. Quanto menor o teor de CO2, mais regular se torna a transferencia. O efeito do fator indutivo depende do teor de CO2 na mistura.

Methodology for determination of parameters for welding MIG with variable polarity1

The development of electronic power sources for welding has allowed the study of innovative processes, generally with the objective of improving the capacity of production linked to low levels of thermal support. The existing processes are based on the metal transfer mode and on the development of wave forms that improve control of the process. The metal inert gas-variable polarity pulsed process is a derivative of the conventional metal inert gas process that combines the advantages of the use of positive polarity, such as good arc stability and cathode cleaning, with those given by negative polarity, principally the high fusion rate of the electrode and low thermal support to the base metal. However, this process has only found limited use due to the scarcity of technical and scientific publications. As a result, this work sets out a proposal for a methodology to determine welding parameters in four different wave formats and varying the negative electrode rate across three levels in a way that provided arc and metal transfer stability, the evaluation of the process was carried out by filming the arc and analysing the geometric characteristics of the weld bead. The method was shown to be sufficiently efficient with satisfactory stability results.

O arco TIG a 100 A e argônio puro é um arco especial

By stating that an improved understanding of the physical mechanisms controlling process performance can usually be translated into higher levels of consistency and productivity for that process, it is expected to investigate these mechanisms. Among the various approaches for process physical characterisation, the electric-arc study unveils the process stability from the related phenomena. Specifically for arc welding, which high quality levels are required, the TIG process outstands. Further looking into this process, a parameter set calls the attention: 100-A current and pure argon as shielding gas. These values attribute to the arc special transitional characteristics, such as static characteristic, laminar-turbulent regime, arc dimensions and anode voltage fall. These characteristics are presented and discussed. From this discussion, a challenging for the Revista Soldagem & Inspecao readers is brought out. The idea is gathering their point of view and contributions with the objective of consolidating the knowledge on the electric arc in non-consumable process and, eventually, leading to technological results for a better process application.

Estudo da emissão de raios infravermelho próximo em processos de soldagem a arco

O estudo de boa parte dos fenomenos envolvidos no processo de soldagem necessita de auxilio visual e a luminosidade emitida pelo arco pode representar uma grande barreira. Uma das formas utilizadas atualmente para se obter a visualizacao do processo, sem a interferencia do arco, consiste em iluminar o processo com o infravermelho proximo e utilizar filtros durante a aquisicao das imagens. Assim, e importante investigar o comportamento do arco de soldagem em relacao a sua emissao luminosa no espectro infravermelho. Desta forma, a proposta deste trabalho foi a realizacao de um estudo comparativo entre a emissao do arco de soldagem de radiacao infravermelha proxima em dois processos largamente utilizados, TIG e MIG/MAG, focando tambem sua influencia por parâmetros como a corrente de soldagem e a protecao gasosa utilizada. Com o uso de um sensor de luminosidade e a utilizacao de um sistema de lentes opticas, foram realizados experimentos, adquirindo o espectro luminoso emitido pelo arco voltaico. Atraves dos resultados obtidos, ou seja, do valor numerico de energia luminosa do arco de soldagem (integracao do espectro) e possivel se obter, com a utilizacao desta mesma metodologia, a energia luminosa no infravermelho proximo e, consequentemente, a intensidade luminosa, necessaria para a sobreposicao do arco durante a aquisicao de imagens.

Sistema embarcado para monitoramento sem fio de sinais em soldagem a arco elétrico com abordagem tecnológica

Industrially, arc welding process is the most important in equipment production and repair, and being a special manufacturing process, which cannot be completely inspected for flaws only after its completion, production monitoring is necessary. This monitoring is technologically required by ISO 3834:2005 and ISO 17662:2005, which say that the manufacturer must take measures to guarantee necessary quality, and also specify data to be monitored and equipment and measurement systems correct calibration. It, therefore, can be used to ensure process documentation and corrective actions taken. There are monitoring systems that perform satisfactorily, but the use of cable communication and/or dedicated computer restrict their industrial applications. Then, an independent embedded system, capable of monitoring different welding process signals and that communicates in a robust and flexible way to different devices is crucial for the industry. It must be a user-friendly system and use the state-of-the-art in communication technology. Because of this need, a system for wireless arc welding signals monitoring, called Moso WiFi, was then designed and built. Three acquisition channels are available (voltage, current and wire feed speed), and validated by instrumentation in TIG and MIG/MAG welding (short circuit, spray and pulsed), demonstrating wide applicability and robustness at a hardware low cost.