Short-circuit Transfer Mode Research Articles

Key mechanism of metal transfer and characteristic of cavity evolution during SAW using in-situ X-ray imaging method

The metal distribution and transfer during submerged arc welding (SAW) were investigated using in situ X-ray high-speed imaging method. The flux-wall droplet transfer mode was observed for the first time in SAW using a 1.6 mm diameter 308 L wire and the repelled droplet transfer mode and short circuit droplet transfer mode are also confirmed as the three fundamental modes. As the unique forces in the SAW, the supporting force and viscous resistance by the flux wall to the droplet affect the droplet geometry feature and transfer mode. These two forces are determined by the geometrical morphology of the cavity. As the welding speed increases from 1.5 mm/s to 4 mm/s, the proportion of short circuit transfer mode decreased from 70.69% to 3.64% while the repelled droplet transfer mode increased from 3.45% to 96.36% due to the reduction of cavity volume. The proportion of flux-wall transfer mode initially increased and then decreased. It reached the highest as the vertical cavity formed at the welding speed of 2 mm/s. Once the welding speed exceeds 4 mm/s, the flux-cored droplet transfer mode disappeared. The proportion of the other two tends to be stable because of an almost unchanged cavity volume.

Deepening the understanding of arc characteristics and metal properties in GMAW-based WAAM with wire retraction via a multi-physics model

Wire retraction is used in the short-circuit droplet transfer mode of gas metal arc welding (GMAW) to improve the stability of transfer, reduce heat input and decrease spatter. The significant effects of wire retraction on the arc plasma characteristics and the thermal properties of the metal are not well understood. In this paper, we develop a three-dimensional, transient, multi-physics coupled GMAW model with wire retraction and apply it to wire arc additive manufacturing (WAAM) of an aluminum alloy. The model takes into account the wire's downward and upward motion, droplet growth and detachment, arc plasma heating, metal vaporization, melting and solidification of the molten pool, and the relative motion of the wire and substrate. The model is used to simulate the deposition of a single layer, and the evolution of the arc characteristics and the metal thermal and flow behavior are analyzed. The results demonstrate that during a wire motion period, the arc characteristics are determined by both the transient welding current and the distance between the welding wire and the molten pool. The arc plasma has a significant influence on the temperature and flow of the droplet and the molten pool metal when the wire is well separated from the melt pool and the welding current is in its peak phase. The energy and momentum of the metal in the molten pool are primarily influenced by the metal transfer, and the maximum flow velocity and maximum temperature occur at the time of the short-circuit contact. The results demonstrate the advantages of using a low welding current during droplet transfer, which is made possible by wire retraction. The model is validated by comparing the predicted morphology of the deposited layer and the shape of the arc during a wire motion period with experimental results, with reasonable agreement found.

A novel high-efficient welding technology with rotating arc assisted by laser and its application for cryogenic steels

To obtain high efficiency and good weld quality for medium thick steel plates, a novel welding technology of hybrid arc laser welding was proposed through rotating arc assisted by laser. Rotating arc provides heat to melt feeding wire and groove for high deposition and good fusion. Laser is helpful not only to arc rotating, but also to molten pool mixing. The proposed welding technology was used in the application of 9% Ni steel with medium thickness in the field of LNG storage tanks. The 21 mm thick steel plates were successfully achieved with only 2 welding passes. The weld formation was well-qualified, and no defects can be observed. The droplet transfer, keyhole and molten pool flow were investigated with high-speed camera and electric signal analysis. Experimental results showed that the droplet transferred in periodic alternation pattern of rotating spray transfer mode and short-circuit transfer mode. The laser keyhole kept stable during the droplet transfer process. The molten pool was fully mixed under the coupling effect of the arc, droplet and laser beam. The weld metal was in homogenous composition. Low temperature (−196 °C) impact energy of weld metal center and fusion line were much higher than related requirements. Obvious dimples on the fracture surface indicated that the fracture mechanism was in ductile fracture mode. Research results provided a theoretical basis for efficient construction and safe service of LNG containers made by cryogenic Ni steel.

Droplet transfer behavior and weld formation of gas metal arc welding for high nitrogen austenitic stainless steel

Abstract High nitrogen austenitic stainless steel (HNASS) wire with 0.78 wt.% nitrogen content was used for gas metal arc welding (GMAW) test. The characteristics of droplet transfer and weld formation in different welding parameters were investigated. There were three typical metal transfer modes in GMAW of HNASS, namely in terms of stable short circuit transfer, unstable short circuit transfer and spray transfer. With wire feed speed (WFS) of 3 m/min∼8 m/min and moderate arc voltage, the droplet transfer was stable short-circuiting transition mode. The transfer period and waveform of electrical parameters were regular and the weld formation was satisfactory with few spatters. With the increasing of arc voltage or WFS, the droplet grew up to abnormal large size due to the expansion of supersaturated nitrogen. The electric parameters were more disordered and the metal transfer became unstable with spatter. When wire feed speed was over 10 m/min with high arc voltage, the droplet transfer became spray transfer accompanied by numerous welding fumes. The weld formation of HNASS for unstable short circuit and spray transfer mode was inferior with serious spatters.

Complex Behavior of Droplet Transfer and Spreading in Cold Metal Transfer

In intelligent manufacturing, an intelligent control method of welding process is an important process of intelligent welding manufacturing technology (IWMT). Metal transfer is a key factor to control the welding process. Metal transfer and droplet spreading are of vital importance for welding formation. A new theoretical model of cold metal transfer (CMT) in short-circuit transfer mode is proposed in this paper. In this model, the CMT welding process is regarded as a continuous process of arc heating, mass transfer, short-circuit, and spreading, and the relations between these processes are analyzed. The calculation equations used by the model can analyze the welding formation clearly and simplify the complex welding process into continuous physical behavior. The predicted welding width shows good agreement with the measurement results. The mechanism of increased welding width is also comprehensively analyzed. Results have a certain guiding effect on aluminum alloy welding process control.

Double-sided pulsed laser driven metal transfer in GMAW

Current-independent metal transfer, in free-flight or short-circuiting mode, was previously achieved by utilizing single-side pulsed laser irradiation on the droplet. However, the droplet was always detached with a deflection approximately along the laser incident direction, but not in the wire axial way as generally expected. The droplet deflection also acts as a cushion to the laser impulse. Hence, the double-sided pulsed-laser-driven metal transfer is studied by comparing it with that of non-laser and single laser enhanced metal transfer in this paper. The results demonstrate that double-sided laser irradiation leads to a significant increase in the transfer frequency and process stability. Differing from the way of droplet deflection driven by single laser irradiation, double-sided symmetrical laser irradiation with the same laser pulse parameters results in wire-axial metal transfer of higher frequency, either in drop spray or short-circuiting transfer mode, depending on the arc length. Moreover, the dual laser irradiation contributes considerably to melt the wire when the current is ultra-low. The wire tip was even shaped to a pencil-like profile by the lasers, similar to that of traditional stream spray transfer in high-current GMAW, which facilitates the co-axial metal transfer. The transfer frequency of short-circuiting transfer and drop spray transfer under 80A current is up to100 Hz and 150 Hz (0.8 mm wire diameter, pure argon shielding gas), respectively. Even the current is as low as 40 A, the drop spray transfer frequency can still be up to 100 Hz.

Arc characteristics and metal transfer behavior of CMT+P process for Q235 steel of titanium-steel composite plate

The cold metal transfer (CMT) with addition of pulses (CMT[Formula: see text]P) process is a new CMT welding method. This paper uses a high-speed camera and electrical signal synchronization acquisition system to perform a CMT[Formula: see text]P welding test on a 10 mm thick Q235 steel plate, and performs arc characteristic and droplet transfer behavior in the welding process. It has been founded that under relatively small currents and voltages, the CMT[Formula: see text]P transfer mode is a combination of a projected transfer mode with one droplet in the pulse period and a short circuit transfer mode during the CMT period. The process is stable with little spatter; at relatively large currents and voltages, the transition mode is the combination of pulse transfer, spray transfer and short circuit transfer. It results in one or more droplets that enter the pool both in pulse transfer in the spray transfer mode during the pulse period and in the short circuit transfer mode during the CMT period in a weld cycle.

Effect of metal transfer mode on spatter and arc stability in underwater flux-cored wire wet welding

The effect of metal transfer mode on spatter and arc stability during underwater flux-cored wire wet welding at different process parameters are investigated adopting the synchronous acquisition system of X-ray image and electric signal. Two spatter modes i.e. the local droplet repelled spatter and the droplet explosion spatter were observed for the first time. The generation of the local droplet repelled spatter is attributed to the excessive and unstable repulsive forces, while the droplet explosion spatter is caused by the unstable repulsive forces and gas dynamic force. Welding spatters and arc stability depend on the metal transfer mode. During wide-angle globular repelled transfer mode, the droplet repelled spatter mode is observed and the forming frequencies of the local droplet repelled spatter and droplet explosion spatter are higher than other transfer modes. The short-circuit explosions are observed in short-circuit explosive transfer mode, causing numerous short-circuit explosive spatters. With the increase of arc voltage, both the spatter loss coefficient and voltage variation coefficient decrease firstly to the minimum at the arc voltage of 32 V and then increases gradually, attributed to the type and proportion of metal transfer mode.

A contribution to the study of negative polarity in GMA welding

Gas metal arc welding (GMAW) using the electrode with negative polarity (DCEN) has been frequently suggested as a potential means of increasing production capacity. The objective of this work was to further study the performance of negative polarity in GMAW of carbon steels. In this project phase, bead-on-plate welds were carried out in flat position to assess the effect of different potential shielding gas compositions on bead geometry, finishing and spattering. The characteristics were compared with DCEP at the same current, but depositing the same volume of material per unit of length (more industrial related comparison). The arc length was kept the same by adjusting voltage to reach shortest arcs, yet with suitable non short-circuiting metal transfer mode. An approach to measure bead convexity was also proposed and assessed. The results showed that DCEN is feasible as a means of increasing GMAW production capacity. However, to become DCEN applicable with GMAW, the results suggest an Ar-based blend with around 6.5% of O2 is the most appropriate shielding gas, as much as that there is a demand for a standard electronic controlled power source able to work in constant current mode.

Joining of aluminum alloys to galvanized mild steel by the pulsed DE-GMAW with the alternation of droplet transfer

In this study, the welding-brazing process of pulsed double electrode gas metal arc welding (pulsed DE-GMAW) provides a potential method to join dissimilar metals (i.e., joining of aluminum alloys to galvanized mild steel). In order to evaluate the stability of welding process, a mathematical model of the alternation of droplet transfer for the pulsed DE-GMAW is established based on the spring-mass-damper model. The droplet alternative transfer is a free flight with short circuiting transfer mode, which is analyzed and detected during the welding process with double pulsed current. Meanwhile, the pulsed DE-GMAW technology is found to be feasible to join the aluminum alloys to the galvanized mild steel. The variable weldability process of aluminum-galvanized steel could be obtained with a wire by optimizing welding parameters. Microstructures of the intermetallic reaction layer and bonding mechanism of optimized weld-brazed specimens with aluminum ER4043 and ER5356 wires are analyzed and conducted by SEM and tensile test.

Effects of welding velocity on metal transfer mode and weld morphology in underwater flux-cored wire welding

Metal transfer process in underwater flux-cored welding are investigated by X-ray transmission method for welding velocity from 0.5mm/s to 9.5mm/s. The metal transfer mode of underwater flux-cored wire welding is the mixed transfer mode mainly composed of four fundamental transfer modes i.e. wide-angle globular repelled transfer mode, small-angle globular repelled transfer mode, surface tension transfer mode and short-circuit transfer mode. The category and proportion of fundamental modes constituting the mixed mode depend strongly on the welding velocity owing to the variation of force condition on droplet. With increasing welding velocity, the proportion of the wide-angle globular repelled transfer mode increases continually while that of the surface tension transfer mode and short-circuit transfer mode decreases, and the proportion of the small-angle globular repelled transfer increases firstly and then decreases gradually. The welding appearance and cross-sectional macrostructure of weld specimens at different welding velocities are also investigated. When the welding velocity increases from 0.5mm/s to 3.5mm/s, the weld width decreases from 20mm to 12mm and the weld penetration increases rapidly from 0.8mm to 3.7mm, completely different from in-air welding.

Arc characteristics and metal transfer behavior of CMT + P welding process

The cold metal transfer (CMT) with addition of pulses (CMT+P) process is a new CMT welding method. The CMT+P transfer mode is a combination of a projected transfer mode with one droplet per pulse and a short circuit transfer mode during the cold metal transfer period. The results indicate that the current and voltage waveforms of the CMT+P welding process were quite different from those of the traditional CMT process. The appearance of the high initial arcing current and the current pulse steps as well as the low current for the pulse time phase for the first CMT period indicate a stable, smooth CMT+P transfer process. The high pulse current of the CMT+P process results in a higher heat input compared to the CMT process. A greater penetration and contact angle of the weld bead can be obtained by increasing the pulse number.

Simulation of Dynamic Behavior and Prediction of Optimal Welding Current for Short-Circuiting Transfer Mode in GMAW

An improved “mass–spring” model to analyze the entire short-circuiting transfer (SCT) dynamic process based on the association between the arcing and circuiting phases has been proposed. This paper analyses the basic characteristics of displacement of the droplet mass center and oscillation velocity of droplet variation. In addition, the effect of welding current on the short-circuiting frequency is studied. The results of the simulations conducted agree well with the experimental results obtained. An analysis method for optimal welding current during SCT is also proposed, and the droplet transport stability is discussed. Simulation results demonstrate that the relative displacement of the droplet mass center and the average equivalent diameter of the transfer droplets are at a minimum under the optimal welding current condition. This research provides a reference for further simulation of the SCT process and useful guidance for the selection of optimum technics parameters.

Comparação da Estabilidade do Arco e da Variabilidade da Geometria de Soldas obtidas pelos Processos MIG/MAG e Arame Tubular

ResumoApesar da similaridade, os processos MIG/MAG e Eletrodo Tubular apresentam particularidades quanto à estabilidade do arco e variabilidade nas características dos cordões. Assim, a escolha de um dos processos, para aplicação específica deveria considerar como tais particularidades afetam a qualidade destas soldas. Para subsidiar esta escolha, o presente estudo teve como objetivo investigar como a mudança na corrente média afeta a estabilidade e a regularidade das transferências de metal em soldas realizadas com tensão constante e corrente pulsada e comparar a variabilidade da geometria e da diluição destas soldas. Para atingir estes objetivos foram realizadas soldas automatizadas, tendo como metal de base o aço ABNT 1020 e como metais de adição o arame AWS ER70S-6 e AWS E71T-1. Além das soldas com variação da corrente média, os testes envolveram a determinação dos parâmetros para a ocorrência de transferência estável por curto-circuito, goticular e pulsado. Os resultados mostraram que a tensão que determina a maior estabilidade na transferência pelo modo curto-circuito, independe da velocidade de soldagem e aumenta com a velocidade do arame, mostraram também que as soldas com arame tubular apresentaram maiores variabilidades comparadas ao arame maciço.

Effect of boric acid on metal transfer mode of underwater flux-cored wire wet welding

For obtaining high quality of underwater welding repairing for nuclear power equipments, the influence of boric acid on metal transfer process of underwater flux-cored wire wet welding in boric acid solution is explored by an X-ray transmission system. The research results show that the mixed repelled globular transfer and solid short circuit transfer mode and the mixed repelled globular transfer and surface tension transfer mode are two kinds of main metal transfer modes during underwater welding in boric acid solution. The proportion of the mixed repelled globular transfer and surface tension transfer mode is increasing with the increasing of concentration of boric acid solution, which is caused by the difference of force condition of the droplet.

Metal transfer in underwater flux-cored wire wet welding at shallow water depth

The metal transfer process of underwater flux-cored wire wet welding is successfully observed by an X-ray transmission method. The relatively large retention forces acting on the droplet induced by the electromagnetic force, vaporization force, surface tension resultant force and gas flow drag force make the transfer mode as a combination of globular repelled transfer mode and short circuit transfer mode with the average transfer frequency of 4.3Hz with arc voltage of 24V and welding current of 240A.

Influência dos procedimentos e modos de transferência no processo MAG na redução de deformações em painéis de estruturas navais

Juntamente com o crescimento da indústria naval brasileira surgiram problemas provenientes dos processos de produção na forma de distorções e tensões residuais. Neste trabalho foi estudada a influência de procedimentos de soldagem (sequência e direção de soldagem e uso do passe reverso) e modos de transferência (MAG-CC, MAG-STT e MAG-CW) sobre os valores de distorções. Todas as soldagens foram realizadas com o arame ER70S-6 e gás de proteção CO2 puro no modo curto-circuito. Ao final das soldagens, observou-se que a variável mais importante foi a mudança de direção de soldagem, que está ligada diretamente aos níveis de restrição do painel teste. As sequências utilizadas surtiram pouco efeito nos valores de distorção. O passe reverso obteve valores baixos de distorção, contudo, mostrou-se improdutivo. Observou-se que os valores de distorção para os processos e MAG-STT resultaram em valores de distorção semelhantes. Os painéis soldados pelo processo MAG-CW obtiveram os menores valores de distorção mensurados.

The controlled short circuit GMAW process: A tutorial

The paper reviews the principles, benefits and limitations of the conventional short circuit transfer mode in GMA welding before describing the development and benefits of the controlled short circuit approach. Various options are described and an attempt is made to categorize the current commercial systems.

Análise comparativa dos processos de soldagem GMAW e FCAW com transferência metálica por curto-circuito na posição horizontal

Os processos de soldagem com arame maciço (GMAW) e arame tubular (FCAW), que competem entre si em termos de qualidade, produtividade e operacionalidade, requerem do usuário informações seguras de suas principais características e aplicações para determinar as condições mais adequadas de soldagem. Desta forma, o objetivo deste trabalho é comparar a potencialidade de cada processo na soldagem horizontal de aço carbono ABNT 1020, variando o tipo de gás de proteção, a corrente e tensão de soldagem, mantendo constante a taxa de fusão por unidade de comprimento. Para a realização deste estudo foram utilizados os arames AWS E71T-1 e ER 70S-6 sob as proteções gasosas 100%CO2 e Ar+25%CO2 em dois níveis de corrente e quatro níveis de tensão. As características avaliadas foram a regularidade de transferência metálica no modo curto-circuito, a capacidade produtiva através da taxa e rendimento de deposição e o escorrimento do cordão de solda dentro do chanfro. De maneira geral, os dois processos apresentaram semelhança na capacidade produtiva, mostrando certa dependência do valor da tensão de soldagem. Também se observou que, na mesma faixa de corrente e com a elevação da tensão, houve mudanças nas características de transferência metálica nos dois processos. Em relação ao escorrimento dos cordões de solda, o processo GMAW apresentou melhores cordões em menores tensões. Para o processo FCAW os valores dos escorrimentos não apresentaram grandes variações, tendo uma condição melhor que o GMAW para maiores valores de tensão de soldagem (região de predominância de transferência metálica conduzida pelo fluxo sem curto-circuito). O gás de proteção 100%CO2, para ambos os processos, foi o que proporcionou melhor rendimento de depósito com predominância de transferência metálica por curto-circuito.

Spatter reduction in GMAW of stainless steel sheets using CBT process

In non-pulsed gas metal arc welding (GMAW), spatter can be reduced by lowering the short-circuit current to a low level just before the re-arcing. The controlled bridge transfer (CBT) process, which optimizes accuracy of predicting the re-arcing in real time in response to the molten metal transfer, realizes stable, low spatter level. In this paper, the methods for controlling short-circuit transfers to minimize spatter and to realize stable arcs in GMAW of stainless sheet using argon-rich shielded gases are investigated. The new CBT process has been developed by applying the specific arc length control that is not affected by abnormal rise in arc voltage in argon-rich shielded gas welding. This process can suppress the spatter generation caused by fluctuation in the vibratory motion of the weld pool or inaccurate prediction of the re-arcing in the succeeding short-circuit/re-arcing cycle, and thereby spatter-free GMAW in the short-circuit transfer mode can be carried out even on stainless steels.