MIG Arc Research Articles

Effect of current waveform in MIG arc on weld bead formation in plasma-MIG hybrid welding

Plasma-metal inert gas (MIG) hybrid welding enables to join thick steel plates in single pass. However, arc coupling occurring between the plasma and MIG arcs disturbs its heat source characteristics, lowering the welding quality. This arc coupling phenomenon is not yet understood due to the complexity. This study aims to clarify the effect of current waveform of arc on weld bead formation according to the arc coupling in plasma-MIG hybrid welding. The metal transfer characteristics and bottom side weld pool were observed for direct current (DC) and pulse-MIG current waveforms. In addition, Ni element was used for visualizing the transport process of high-temperature molten metal provided by MIG welding within the weld pool. From these results, the effects of differences in MIG arc current waveforms on heat and mass transport processes within the weld pool and also on weld bead formation on the bottom side through changes in the occurrence of arc coupling were discussed. As a result, it was clarified that the droplets after detachment from the wire were transferred to the weld pool surface under the wire tip for DC MIG current, while those were transferred along the wire axis to the weld pool surface behind the keyhole for pulse-MIG current. When the droplet was transferred to the weld pool region with the forward flow such as the pulse-MIG current case, the heat was transported to the bottom side together with the counter-clockwise eddy behind the keyhole, strongly contributing to increasing the penetration depth. In the case of pulse-MIG current, the plasma arc is oscillated due to the arc coupling. According to this oscillation, the accumulation of molten metal behind the keyhole is prevented to suppress the humping bead formation. Consequently, pulse-MIG current was found to be suitable for increasing the penetration depth and suppressing humping bead formation on the bottom side comparing with DC MIG current.

The Effect of W, Cr, Mo Content on the Microstructure and Mechanical Properties of the Weld Interface of TiC Cermet and Low-Carbon Steel

In this study, the influence of W, Cr, and Mo on the microstructure and mechanical properties of the arc-welded interface of TiC cermet and low-carbon steel was investigated. MIG arc welding was employed to deposit muti-alloyed low-carbon steel flux-cored wire onto the surface of the TiC cermet to create the arc-welded interface. Analysis of the microstructure, phase composition, and shear fracture of the interface were conducted by OM (optical microscopy), SEM (scanning electron microscope), EMPA (Electron Probe X-ray Micro-Analyzer), and XRD (X-ray diffraction) methods. The results indicate that the order of influence on the performance of the welded interface is perceived as Cr > W > Mo. The preferred ratio of element content is W at 1.0 wt.%, Cr at 0.5 wt.%, and Mo at 2.0 wt.%. During the arc-welding process, W and Mo formed a rim structure of TiC particles to inhibit the dissolution of TiC particles, while Cr formed dispersed carbides in the bonding phase. The synergistic impact of these components resulted in the simultaneous enhancement of both the TiC particles and the bonding phase. This led to a significant increase in the shear strength of the TiC cermet welded interface to 787 MPa, marking an 83% improvement compared to the welded interface without reinforcement, which exhibited a shear strength of 430 MPa.

Microstructural evolution and the effect of electron beam melting on the fatigue characteristics of 7075 Al alloy deposited by MIG arc additively manufacturing

Microstructural evolution and the effect of electron beam melting on the fatigue characteristics of 7075 Al alloy deposited by MIG arc additively manufacturing

The influence of different alloyed welding materials on the microstructure and mechanical properties of welded interface in TiC cermet MIG welding bonds

The influence of different alloyed welding materials on the microstructure and mechanical properties of the weld interface in TiC cermet was investigated. MIG arc welding was employed to deposit low carbon steel, austenite stainless steel, and Ni-based filler wire onto the surface of the TiC-based cermet to create the weld interface. SEM, EBSD, XRD, microhardness, and shear testing were conducted for characterization. The results indicate that the joints have a (Heat Affect Zone)HAZ-(Partially Melted Zone)PMZ-UZ(Unmixed Zone) -WM(Welding Metal) structure. During the cooling process, the densely distributed TiC particles in the PMZ act as hard phases, leading to stress concentration and microcracks during solidification of the base metal, which affects the shear strength of the joints.

Comparative study between TIG-MIG hybrid and MIG welding of 1.4462 duplex steel joints

Duplex steels are used for applications that require high strength and ductility combined with good corrosion resistance. An economical welding technology to handle these steels is achieved by combining the MIG and TIG arc processes. The aim is to improve welding speed and quality by utilizing a TIG-MIG hybrid welding process to join 1.4462 duplex steel with a thickness of 2 mm. The interaction between the two arcs, caused by the blowing effect, is an enormous challenge that can be counteracted with a defined torch position and current modulation. For this purpose, a variation of the MIG (pulsed and AC pulsed arc) and TIG process (AC and pulsed DC) took place. The influence of electrical parameters on process stability and material transfer was investigated. For analysis, an evaluation of high-speed recordings (5000 frames per second) and synchronized measured current/voltage curves (200 kHz) is carried out. Based on a number of selected specimens, a welding procedure test according to ISO 15614-1 is performed to determine the welding seam quality. The test includes the characterization by tensile and hardness testing and macroscopic and microscopic examination. Additionally, the specimens are examined according to ISO 5817.

KTIG–MIG hybrid arc welding process

Metal-inert gas welding is an important welding process but the process instability easily induces spatter and undercut defects. To improve the welding process stability, a new hybrid arc welding process, named KTIG–MIG, was proposed in this paper. Arc characteristics were preliminarily studied. It is found that in KTIG–MIG hybrid welding, MIG arc is stable even it is shielded with pure argon gas; stable spray transfer is easily achieved in a much wider process window, especially the lowest voltage to achieve spray transfer is greatly reduced; KTIG arc voltage decreases than that in single KTIG arc, and MIG arc current is higher than the pre-set value. Cooling state of the KTIG tungsten plays a key role in slowing tungsten erosion.

The Cracking of Al-Mg Alloys Welded by MIG and FSW under Slow Strain Rating.

Al-Mg alloys used in the shipbuilding industry were tested. The most commonly used alloy AW 5083 and alloy AW 5059 with higher strength properties were selected. Both native materials and their joints welded by the traditional MIG arc welding method and the friction stir welding (FSW) method were tested. Both methods are approved by classification societies which allow them to be used in construction by the shipbuilding industry. The research was carried out in two stages. The first study was an "in-situ tensile test in SEM". The surfaces of the deformed specimens' changes were observed in the vacuum chamber of a Philips XL30 scanning electron microscope. During the tests, the force and elongation of the specimen were recorded. In addition, a chemical analysis of selected precipitates was performed by energy dispersive spectrometry (EDS) using the EDAX adapter. Slip lines were observed on the surface of the tested specimens, which are arranged in bands in the native material and in a disordered manner in the joints welded by MIG and FSW methods. Cracking starts mainly through decohesion at the matrix-precipitate interfaces. In the second stage of the research, slow strain rate testing (SSRT) was carried out in accordance with ISO 7539-7:2005. The tests were carried out on a specially designed test stand, where the FT-5307 strain gauge force sensor with a measuring range of 0-16 kN was used to measure the force value. The PSz 20 transducer with a measuring range of 0-20 mm was also used. The test consisted of subjecting the specimen to increasing deformation with the strain rate έ = 1.6 × 10-6 s-1 until destruction. The fracture surfaces of the SSRT specimens were subjected to fractographic analysis using a Philips XL-30 scanning electron microscope. The results of fractographic studies after the SSRT test of the native materials and their joints welded by the MIG and FSW methods indicate that the trans-crystalline cracking mechanism is dominant, characterized by ductile fracture, and cracks are initiated at the interfaces of the precipitates with the matrix. The research results show that the plastic deformation increases and micro-cracks develop and merge into a main crack, which, after reaching the critical dimension, rapidly develops, causing the destruction of the material. The fracture micrographs of the specimens of base metals and their joints welded by FSW and MIG after the SSRT test allow us to conclude that the cracking mechanism was trans-crystalline ductile.

Molten pool behavior and solidification characterization in steady magnetic field assisted laser-MIG hybrid welding of aluminum alloy

Microstructure evolution is highly correlated with the melt flow characterization in welding. In this study, a 3D heat flow model with consideration of magnetic field was constructed to describe the temperature field, the flow and keyhole behaviors in the molten pool during the laser-MIG hybrid welding. The role of magnetic flux density in the molten pool dynamics and microstructure evolution was explored. A moving hybrid heat source model including Gaussian surface heat source model and Gaussian rotary body heat source model as well as double ellipsoidal heat source model was carried out to elucidate the laser and MIG arc energy distribution. Decent agreement is realized between the measured weld geometry and predicted weld pool dimension. Numerical results indicate that an expanded molten pool is clearly observed under magnetic field. As the magnetic flux density increases, the downward flow velocity of the molten pool is enhanced. Moreover, visible difference of oscillation growth period for keyhole depth is produced and this leads to a variation in the time it takes for the molten pool to stabilize. Significant grain refinement appearing in both arc-affected zone at the weld upper part and laser-affected zone at the weld lower part is documented although the refinement degree varies at different zones. This is attributed to the formation of many initial nuclei or crystallites, originated from the enhanced flow of the molten pool with the assistance of magnetic field. This study provides a perspective in understanding the physical phenomena involved in magnetic field assisted laser-MIG hybrid welding and lays the foundation for weld microstructure optimization.

Dynamic keyhole behaviors and element mixing in paraxial hybrid plasma-MIG welding with a gap

A paraxial hybrid plasma-MIG welding process is developed to join middle-thick high strength steel plates with a butting gap. The arc and metal vapor characteristics are investigated by an advanced three-dimensional spectroscope measurement system. The dynamic keyhole behaviors and element mixing are studied by a three-dimensional numerical model. The numerical and experimental results show that the Fe vapor ejected from the wire surface, other than the plasma keyhole, has a great influence on arc characteristics. The butting gap affects the keyhole stability and molten metal flow, as well as the element mixing. With a gap, the keyhole opens and closes periodically. The opposing flows at the front and rear keyhole bottom walls, and the pressure imbalance in the keyhole bottom contribute to the keyhole collapse. The gap promotes the downward flow below the MIG arc center, which helps to transport the Ni element from the top surface of the MIG pool region to the bottom. The “Pull-Push” molten metal flows in the top molten pool suppress the Ni element to flow from the MIG pool region to the plasma pool region. As a result, the Ni content is inhomogeneous in the hybrid pool, and higher in the bottom of the MIG pool region.

Influence of Energy Ratio of Hybrid Heat Source on Residual Stress Distribution of 7A52 Aluminum Alloy VPPA-MIG Hybrid Welding

Variable Polarity Plasma Arc-Metal Inert Gas (VPPA-MIG) welding process is a new hybrid welding process with broad application prospects for aluminum alloy structure in the fields of aerospace manufacturing, transportation and others. The heat source of the hybrid welding process is composed of VPPA heat source and MIG heat source. When the total input energy of VPPA-MIG hybrid heat source is constant, the different energy ratio of VPPA arc and MIG arc affects not only the forming effect of hybrid weld, but also the stress distribution of hybrid welding joint. Hole-drilling method was used to analyze the influence of the ratio of VPPA and MIG arc energy on the distribution of welding residual stress in the process of 10 mm 7A52 aluminum alloy VPPA-MIG hybrid welding. The results show that the peak magnitude of hybrid welding residual stress increases with the increase of the ratio of VPPA arc energy. Considering the appearance of weld forming, VPPA-MIG hybrid welding parameters of 7A52 aluminum alloy are optimized on the basis of the distribution characteristic of residual stress. When the ratio of VPPA arc energy is selected between 35% and 40%, the peak magnitude of transverse residual stress is (in the direction vertical to the weld) no more than 92.0 MPa, and the peak magnitude of longitudinal residual stress(in the direction parallel to the weld) is no more than 234.3 MPa. It shows that the VPPA-MIG hybrid welding with optimized parameters can not only produce weld joint with satisfied macroscopic appearance, but also avoid high peak magnitude of residual stress.

Elucidation of arc coupling mechanism in plasma-MIG hybrid welding process through spectroscopic measurement of 3D distributions of plasma temperature and iron vapor concentration

This study aims to clarify the mechanism of arc coupling phenomenon in plasma-MIG hybrid welding through the tomographically spectroscopic measurement of 3D distributions of plasma temperature and iron vapor concentration. The arc coupling strongly depends on arc current waveforms, so both the cases using DC MIG current and pulse MIG current were performed for the comparison. As a result, in the case using DC MIG current, two arcs were regularly connected, because the high temperature region between two arcs with an enough electrical conductivity was widely formed, retaining the current conduction between arcs. In the case using pulse MIG current, the two arcs were strongly connected only in the upslope duration of pulse MIG current. Both arcs were weakly connected or disconnected in other durations. The arc connection is thought to be governed by the balance between the stiffness and deflection of both arcs. In the case using pulse MIG current, two arcs were not connected in the downslope duration of pulse MIG current, although the pulse MIG current was similar with that in the upslope duration. In the upslope duration, the MIG arc is thought to be constricted because of the thermal pinch effect to increase the current density, which enhances the stiffness of MIG arc to prompt the arc connection. In contrast, the pulse MIG current density becomes lower in the downslope duration, which deflects the MIG arc backward to disconnect the arcs. The plasma current increased by 35 A during the arc connection, which increased the plasma arc temperature below the nozzle by 1000 K. The result implies that the arc coupling affects the distributions of the arc pressure and shear force by plasma arc acting on the keyhole inner wall, governing the keyhole stability as well as the weld pool formation process.

Numerical Analysis of Metal Transfer Process in Plasma MIG Welding

In plasma MIG welding, inert gas introduced from the torch nozzle is ionized in the upstream region of the MIG arc, which is termed “plasma”. This study aims to clarify the effect of the plasma on the metal-transfer process in the plasma MIG welding through numerical analysis. As a result, the plasma with a temperature of approximately 10,000 K was found to be formed around the wire tip. The MIG arc temperature around the wire tip was 11,000 K at the maximum, which was lower than that of the conventional MIG welding by approximately 1000 K. This difference was caused by the decreased current density around the wire tip due to the influence of the plasma. The droplet temperature was also decreased by 400 K due to this lower current density. The amount of the metal vapor evaporated from the droplet was decreased compared to that of the conventional MIG welding due to the lower droplet temperature. This might lead to a decrease in fume formation generally known in the plasma MIG welding. In the conventional MIG welding, the arc attachment was concentrated around the wire tip, leading to a higher current density. However, in the plasma MIG welding, the plasma transported to the surrounding of the wire tip increases the electric conductivity in that region, due to the influence of the metal vapor mixture. This leads to the dispersion of the arc attachment toward the wire root. Consequently, the current density in the plasma MIG welding was found to decrease compared with that of the conventional MIG welding. The lower current density in plasma MIG welding decreases the Lorenz force acting on the wire neck, thus delaying droplet detachment to make the droplet diameter larger and the metal transfer frequency smaller. The latter was about 20% of that in the conventional MIG welding.

Research on the performance of laser-MIG arc tandem welding of CP-Ti/304 stainless steel bimetallic sheets

In this study, CP-Ti/304 stainless steel (SS) bimetallic sheets were prepared without the formation of Ti-Fe intermetallics in the joint. This required preparing a groove in the flyer and parent layer, and melting S211 wire using laser-MIG arc welding in tandem. The laser was used for the parent layer metal (CP-Ti) and the MIG arc was used for melting the S211 wire and filling the flyer layer groove. As the melting points of the parent layer metal CP-Ti (1660 °C) and the flyer layer metal 304 SS (1454 °C) were higher than the fill wire S211 (965–1035 °C), the parent and flyer layer metals were joined without melting. Liquid mixing of dissimilar metals was avoided and Ti-Fe intermetallics were not formed. The joint was observed to fracture at the laser weld zone and the right side of MIG arc weld zone, with a maximum tensile strength of approximately 680 MPa.

Numerical Analysis of Stress Evolution in MIG Arc Brazing-fusion Welding of Al Alloy to Galvanized Steel Plate

Numerical Analysis of Stress Evolution in MIG Arc Brazing-fusion Welding of Al Alloy to Galvanized Steel Plate

Observation of Arc Behaviour in TIG/MIG Hybrid Welding Process

In this project, the influence of TIG currents’s variation on arc stability of TIG/MIG hybrid welding was studied by comparing with MIG welding process. The welding current-voltage waveform was analyzed to characterize the arc stability of the MIG arc. From the observations, the introduction of TIG arc as low as 60 A of current significantly change the MIG arc stability in TIG/MIG hybrid welding. The length of MIG arc in TIG/MIG welding increased with the introduction of the TIG arc as compared with MIG welding. The increase of arc length was due to the arc interaction between the TIG arc and MIG arc, which is affecting the wire melting rate. At the maximum TIG current, the diameter of the molten droplet decreased with the increment of droplet transfer frequency.

MIG Arc Effects on Root Penetration of Laser Hybrid Welded T-Joints

MIG Arc Effects on Root Penetration of Laser Hybrid Welded T-Joints

Research on weld formation mechanism of laser-MIG arc hybrid welding with butt gap

At present, there are few researches on laser -MIG arc hybrid welding with a large butt gap. In this paper, laser-MIG arc hybrid welding is used to weld low-alloy high-strength steel with a thickness of 3 mm, and a laser-MIG arc hybrid welding process under large gap conditions is developed. This paper studies the effects of arc voltage, laser-wire distance, and wire feed speed on the gap bridging capability of hybrid welding under different butting gaps. Under the condition of the 1 mm butt gap, the influence mechanism of laser-wire distance on weld the weld formation of hybrid welding is analyzed by combining high-speed photography, welding current and voltage waveform, the macroscopic and microscopic morphology of the weld. The results show that there are optimal process parameter values for the effects of arc voltage and laser-wire distance on the gap bridging capability of hybrid welding. Adjusting the laser-wire distance can optimize the energy distribution of laser on the welding wire and weld pool, thus controlling the arc current, voltage, and droplet transition mode, and finally affecting the weld penetration and forming. When the laser-wire distance is 0 mm, the droplet transition frequency is the fastest, and the droplet transition is a mixture of short circuit transition and liquid bridge transition. At this point, the welding rate is the fastest and the welding process is the most stable. However, by comprehensively integrating factors such as the gap bridging capability and the weld penetration, the optimal processing parameters are obtained when the laser-wire distance is 0.5 mm.

A comparison of TIG-MIG hybrid welding with conventional MIG welding in the behaviors of arc, droplet and weld pool

The influence of electrode relative position and TIG current variation on arc stability and weld formation of TIG-MIG hybrid welding were studied comparing with that of conventional MIG welding. The welding current-voltage waveform was analyzed to characterize the arc stability. When TIG arc was leading, the hybrid arc was more stable than conventional MIG welding even when the TIG current was as low as 50 A, while the TIG current should be higher than 100 A to avoid spatters when TIG arc was trailing. The arc shape and droplet transfer were investigated to describe the heat and force distribution in weld pool. When TIG arc was leading, the backward arc force and droplet impingement could not decrease the backward flow of molten metal. The increment of MIG arc length dispersed MIG arc heat and resulted in narrower weld width, compared with conventional MIG welding, which was the main factor to suppress undercut defect. When TIG arc was trailing, the forward arc force and droplet impingement significantly decreased the backward flow velocity and gave molten metal more time to spread transversely to suppress undercut defect. Regardless the relative position of TIG and MIG arcs, the hybrid welding speed could reach up to at least 1.5 m/min.

Microstructure and mechanical properties of Ti/Al dissimilar joints produced by laser-MIG welding–brazing

We butt-welded AA6061 aluminum alloy to Ti6Al4V titanium alloy, dissimilar light metals, by using laser-MIG hybrid welding–brazing without grooves. The parameters of the laser and arc were optimized to produce sound joints with good formation and mechanical properties. The microstructure of the layer of intermetallic compounds (IMCs) was investigated by scanning electron microscopy and energy dispersive spectroscopy. We also tested the tensile strength of the joints with and without reinforcement. The morphology and thickness of the IMCs varied throughout the joints. A continuous thin layer of TiAl3 appeared on the top surface of the Ti6Al4V, on which some rod-like IMCs grew toward the fusion zone. In the upper region of the butt plane, because more heat accumulated there from the high-power laser coupled with the MIG arc, double-layer IMCs with a thickness of [Formula: see text]10.0 [Formula: see text]m formed, composed of TiAl (near the Ti alloy) and TiAl3 (near the fusion zone). In the lower region of the butt plane, the double-layer IMCs became continuous and uniform, the serrated morphology disappeared, and the thickness of the IMC layer decreased to 4.0 [Formula: see text]m. On the backside of the joint, the thickness of the compound layer (TiAl3) was about 1.0 [Formula: see text]m. The average tensile strengths of the reinforced and unreinforced joints were 226 MPa and 210 MPa, respectively, which are up to 88% and 81% of the AA6061 tensile strength, respectively.

Challenges and Opportunities in Remote Laser Welding of Steel to Aluminium

In the last two decades, the automotive industry has been facing demands to reduce fuel consumption and to meet CO2 emissions through applications of lightweight materials. Therefore, aluminium alloys have replaced substantial amounts of steel; and they are receiving significant attention to achieve greenhouse emission targets. However, a critical factor in applications of advanced aluminium in automotive Body in White (BIW) designs depends on availability of cost effective and high performance joining processes. Currently, a Self-Pierce Riveting (SPR) process is extensively used for aluminium BIW sheet metal parts joining which is expensive, additionally increase the weight of the vehicle and cause inefficiency in manufacturing operations. As aluminium alloys are difficult to weld by conventional technologies such as electrical resistance spot welding, MIG arc welding etc., various joining technologies had proposed to weld aluminium alloys and dissimilar alloys over the years. Often, these technologies restrict design flexibility and are expensive for mass production. In this context, Remote Laser Welding (RLW) has gained popularity because of its distinct advantages such as design flexibility, production speed, material and cost savings. This paper provides a critical review of challenges and opportunities for application of RLW to dissimilar metal welding of steel to aluminium. Next steps of research and development are also highlighted.