- Welding Process Simulationedit
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Because low thermal conductivity and high viscosity are common characteristics of austenitic steel, it is easy to cause a large amount of heat accumulation in the chip area, resulting in tool edge collapse or wear, and the traditional... more
Because low thermal conductivity and high viscosity are common characteristics of austenitic steel, it is easy to cause a large amount of heat accumulation in the chip area, resulting in tool edge collapse or wear, and the traditional preparation method is unsuitable for preparing large and complex austenitic steel components. Wire + arc additive manufacturing (WAAM) provides a great application value for austenitic stainless steel because it can solve this problem. The cold metal transfer (CMT)-WAAM system with good control of heat input was used to fabricate the multi-trace and multilayer stainless steel 321 (SS 321) workpiece in this study. The microstructure and corrosion properties of the SS 321 workpiece were observed and compared with those of an SS 321 sheet. The results showed that the microstructure of the SS 321 workpiece from top to bottom was regularly and periodically repeated from the overlapping remelting zone, inter-layer remelting zone, and primary melting zone. Th...
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In order to achieve high efficiency, energy saving and high quality of welding, it is necessary to carry out research on cable-type wire TIG-MIG hybrid welding. In this study, voltage and current influences on the arc shape in cable-type... more
In order to achieve high efficiency, energy saving and high quality of welding, it is necessary to carry out research on cable-type wire TIG-MIG hybrid welding. In this study, voltage and current influences on the arc shape in cable-type wire TIG-MIG hybrid welding were studied. The results showed that in cable-type wire TIG-MIG hybrid welding, with an increase in the TIG current, the MIG current increased at first and then remained constant, while the MIG basic voltage remained unchanged. With an increase in the MIG voltage, the TIG current produced small changes, but overall, it remained stable. The TIG current of different droplet-transfer modes had different effects.
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Cold cracking susceptibility of the newly developed 9Cr2WVTa steel plate welded with the corresponding gas tungsten arc welding wire has been evaluated using the implant test and the Y-groove cracking test. Measurement of diffusible... more
Cold cracking susceptibility of the newly developed 9Cr2WVTa steel plate welded with the corresponding gas tungsten arc welding wire has been evaluated using the implant test and the Y-groove cracking test. Measurement of diffusible hydrogen content shows that the welding wire is ultra-low welding consumables (0.40 mL/100 g). Results of the implant test show that the fracture critical stress without pre-heating is only 300 MPa and increases up to the yield strength with pre-heating to 150 °C. The fracture critical stress under high heat input decreases to 250 MPa owing to the formation of quenched microstructure. Fractographies show ductile dimple fracture under higher loads and quasi-cleavage fracture under lower loads. Results of Y-groove cracking tests show that the minimum pre-heating temperature is 150 °C and the maximum transverse residual stress is located at the root of the weld metal. Therefore, the heat input should be chosen in a proper range and the pre-heating temperature is no less than 150 °C.
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The stirring effect of a rotating laser on a molten pool can expand the range of the laser heat source and effectively inhibit defects such as pores and improve the quality of the weld joint. Due to laser rotation, the physical... more
The stirring effect of a rotating laser on a molten pool can expand the range of the laser heat source and effectively inhibit defects such as pores and improve the quality of the weld joint. Due to laser rotation, the physical characteristics of the heat source and the dynamic behavior of the keyhole and molten pool are more complicated than those of conventional laser welding. This paper adopts a numerical simulation method. A three-dimensional model is developed, which takes into account the coupling of the keyhole, recoil pressure and molten pool. The model can describe the dynamic behavior characteristics of keyholes and fluid flow and the formation process and mechanism of keyhole-induced pores in welds during rotating laser welding. It can be concluded that in conventional laser welding, the keyhole is deep, narrow and unstable, which usually results in the formation of bubbles. If the bubbles in the molten pool fail to overflow in time, pores are formed. With an increase in ...
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Plasma arc welding (PAW)-cable-type seven-wire GMAW (gas metal arc welding) hybrid welding is known as a high-efficiency welding combining plasma arc, GMAW arc and cable-type welding wire. In this study, numerical simulation via Fluent of... more
Plasma arc welding (PAW)-cable-type seven-wire GMAW (gas metal arc welding) hybrid welding is known as a high-efficiency welding combining plasma arc, GMAW arc and cable-type welding wire. In this study, numerical simulation via Fluent of the molten pool temperature field and flow field and experimental verification were conducted on Q235 thin plate hybrid welding with cable-type wire to explore molten pool fluid behavior. The simulation results show that keyholes form in the molten pool due to the strong penetration ability of a plasma arc and then the evolved pores by the surface tension float out of the molten pool. When the GMAW welding current increases, both the length and width of the weld pool enlarge, the weld reinforcement increases and the flow rate of molten metal in the weld pool also speeds up. While the PAW current increases, the weld pool length also increases and the molten metal in the weld pool significantly flows faster, but the weld reinforcement decreases. When...
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A three-dimensional numerical model is used to simulate heat transfer and fluid flow phenomena in fiber laser + gas metal arc welding (GMAW) hybrid welding of an aluminum alloy, which incorporates three-phase coupling and is able to... more
A three-dimensional numerical model is used to simulate heat transfer and fluid flow phenomena in fiber laser + gas metal arc welding (GMAW) hybrid welding of an aluminum alloy, which incorporates three-phase coupling and is able to depict the keyhole dynamic behavior and formation process of the keyhole-induced porosity. The temperature profiles and fluid flow fields for different arc powers are calculated and the percent porosities of weld beads were also examined under different conditions by X-ray non-destructive testing (NDT). The results showed that the computed results were in agreement with the experimental data. For hybrid welding, with raising arc power, the keyhole-induced porosity was reduced. Besides the solidification rate of the molten pool, the melt flow was also closely related to weld porosity. A relatively steady anti-clockwise vortex caused by arc forces tended to force the bubble to float upwards at the high temperature region close to the welding heat source, w...
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Abstract The present study aims to develop a unified three dimensional numerical model for fiber laser+GMAW hybrid welding, which is used to study the fluid flow phenomena in hybrid welding of aluminum alloy and the influence of laser... more
Abstract The present study aims to develop a unified three dimensional numerical model for fiber laser+GMAW hybrid welding, which is used to study the fluid flow phenomena in hybrid welding of aluminum alloy and the influence of laser power on weld pool dynamic behavior. This model takes into account the coupling of gas, liquid and metal phases. Laser heat input is described using a cone heat source model with changing peak power density, its height being determined based on the keyhole size. Arc heat input is modeled as a double ellipsoid heat source. The arc plasma flow and droplet transfer are simulated through the two simplified models. The temperature and velocity fields for different laser powers are calculated. The computed results are in general agreement with the experimental data. Both the peak and average values of fluid flow velocity during hybrid welding are much higher than those of GMAW. At a low level of laser power, both the arc force and droplet impingement force play a relatively large role on fluid flow in the hybrid welding. Keyhole depth always oscillates within a range. With an increase in laser power, the weld pool behavior becomes more complex. An anti-clockwise vortex is generated and the stability of keyhole depth is improved. Besides, the effects of laser power on different driving forces of fluid flow in weld pool are also discussed.
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As a high-efficiency and high-quality welding process, hybrid laser-arc welding (HLAW) has significant potential of application in welding thick plate. Understanding the features of welding residual stress benefits the optimization of... more
As a high-efficiency and high-quality welding process, hybrid laser-arc welding (HLAW) has significant potential of application in welding thick plate. Understanding the features of welding residual stress benefits the optimization of HLAW process. In the present study, based on thermal elastic–plastic theory, a three-dimensional finite element model is developed to predict the residual stress and distortion in HLAW for butt joint of 12-mm-thick steel plate. GMAW heat input and laser energy are modeled as one double-ellipsoid body heat source and one cone body heat source with enhanced peak density along the central axis, respectively. Residual stresses and distortions are calculated for single-pass and multi-pass hybrid welding processes. The results show that the distribution features of longitudinal and von Mises equivalent residual stresses in single-pass hybrid welding are similar to that in multi-pass hybrid welding. A large tensile stress is generated at the weld zone and its vicinity. Compared with GMAW, the zone with high residual stress in hybrid welding is decreased largely, but there is no improvement in peak residual stress. Among three cases, the distortion in single-pass hybrid welding has the lowest value.
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A three-dimensional numerical model of double-arc in tandem gas metal arc welding (GMAW) was established based on the theory of arc physics, momentum equation, energy equation, continuous equation and Maxwell equations. The effects of... more
A three-dimensional numerical model of double-arc in tandem gas metal arc welding (GMAW) was established based on the theory of arc physics, momentum equation, energy equation, continuous equation and Maxwell equations. The effects of different welding current on temperature field, velocity field and pressure field on the surface of workpieces were investigated. The results showed that the maximum values of arc temperature, arc plasma velocity and arc pressure on workpieces surface were increased with the increasing welding current. These maximum values occurred at the tip of double-wire. The current density and axial deflection angle of coupling arc were increased following the increasing welding current.
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The high manganese steel surfacing layer was deposited on Q235 steel by flux-cored wire gas shielded welding. The as-welded surfacing layer was heated at 1050[Formula: see text]C and quenched in the water, then was tempered at... more
The high manganese steel surfacing layer was deposited on Q235 steel by flux-cored wire gas shielded welding. The as-welded surfacing layer was heated at 1050[Formula: see text]C and quenched in the water, then was tempered at 300[Formula: see text]C. The microstructure, hardness and wear resistance of as-welded surfacing layer and that after heat treatment were comparatively analyzed. The results showed that compared with the as-welded surfacing layer, a large number of fine carbides dispersed in the austenite matrix for the surfacing layer after heat treatment. Meanwhile, the hardness and wear resistance of surfacing layer were slightly improved. The furrow in the abrasive wear for surfacing layer was shallower. Under the action of work hardening, the hardness of high manganese steel surfacing layer gradually increased while the loss weight decreased with the wear time less than 30 min. The hardness of surfacing layer reached the maximum and the loss weight of wear remained unchan...
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Without any presupposed mechanism, a unified three-dimensional model is developed to predict the formation of humping bead in high speed gas metal arc welding, which considers the three phase coupling of solid, liquid and gas and the... more
Without any presupposed mechanism, a unified three-dimensional model is developed to predict the formation of humping bead in high speed gas metal arc welding, which considers the three phase coupling of solid, liquid and gas and the effect of shear stress exerting on weld pool surface caused by arc plasma. A strong backward fluid flow in weld pool is identified as the major factor for bead hump formation. The generation of thin liquid transition zone and its premature solidification are two conditions responsible for the occurrence of humped weld. In case of low inner contact angle between the liquid metal and workpiece surface, the bead hump is still generated. With increasing welding current, the bead hump can be suppressed.
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Abstract Arc shape, droplet transfer, weld pool behavior and temperature fields were studied to investigate the influence of low current auxiliary TIG arc on weld formation and microstructure in TIG-MIG hybrid welding and compared with... more
Abstract Arc shape, droplet transfer, weld pool behavior and temperature fields were studied to investigate the influence of low current auxiliary TIG arc on weld formation and microstructure in TIG-MIG hybrid welding and compared with conventional MIG welding. Results indicated that the MIG arc is stabilized by a leading TIG arc while it is destabilized by a trailing TIG arc. Regardless of the TIG arc leading or trailing, it decentralized the MIG arc force and reduced the impingement of droplet. The backward fluid flow in the hybrid welding was decelerated relative to the conventional MIG welding. The slower backward fluid flow in hybrid welding impeded the accumulation of high temperature filler metal in the tail of weld pool and provided the molten metal more time to fill the weld toe which resulted in suppression of the undercut defect. The top surface temperature gradient at the middle and tail of the hybrid weld pool was lower than that in the MIG weld pool, albeit the welding heat input was increased. Microstructure analysis showed evidence of prominent dendrite formation at higher welding speeds with no obvious grain coarsening in the weld zone of TIG-MIG hybrid weld joint while its HAZ became narrower.
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In this work, an Inconel 625 thin-wall structure was fabricated by the gas tungsten arc welding (GTAW) hot-wire arc additive manufacturing process. The microstructure and mechanical properties of the Inconel 625 samples, extracted from... more
In this work, an Inconel 625 thin-wall structure was fabricated by the gas tungsten arc welding (GTAW) hot-wire arc additive manufacturing process. The microstructure and mechanical properties of the Inconel 625 samples, extracted from different orientations and locations of the thin-wall structure, were investigated and compared. The results showed that the additively manufactured Inconel 625 component, made by hot-wire GTAW, had good quality. Its microstructure consisted of dendrites, equiaxial crystals, and cellular crystals. The average hardness from the bottom to the top was similar, indicating that the thin wall had good consistency. The plasticity in the deposition direction was better than those in the other three regions, which was related to the dendritic structure in the sedimentary direction.
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The microstructure and corrosion resistance of samples fabricated by Q345 and 308 bimetallic feedings using two kinds of processes of wire-arc additive manufacturing (WAAM) was observed and compared with that of sample manufactured by a... more
The microstructure and corrosion resistance of samples fabricated by Q345 and 308 bimetallic feedings using two kinds of processes of wire-arc additive manufacturing (WAAM) was observed and compared with that of sample manufactured by a single feeding wire of Q345 or 308. The results show that the interface between the Q345 and 308 had no defects and metallurgical bonding. The hardness of bimetal Q345/308 additive manufacturing samples was higher than that of Q345 or 308 single wire additive manufacturing. The sample made of Q345 single wire had serious electrochemical corrosion, while the sample made of 308 single wire had pitting corrosion. The pitting corrosion of the sample reinforced by bimetal Q345/308 feeding wires was improved.
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The keyhole plasma arc welding (K-PAW) is widely applied in engineering project now as a high energy beam welding with its advantages of low-cost and easy operation. However, the arc instability may arise and welding defects will be... more
The keyhole plasma arc welding (K-PAW) is widely applied in engineering project now as a high energy beam welding with its advantages of low-cost and easy operation. However, the arc instability may arise and welding defects will be produced in K-PAW due to the high current and strong plasma penetrating force when medium thickness plates are welded, finally weakening the efficiency of K-PAW. Furthermore, it is found that the flow field of liquid metal in the molten pool and the stability of keyhole have a critical influence on welding quality. Therefore, modeling and simulating molten pool, keyhole and flow field in the K-PAW quasi steady process except for arc starting and ending phases are helpful to understand the welding process theory completely and promote its application further. But to date, there is little study on the coupled analysis of molten pool and keyhole in the quasi steady welding process due to the difficulty to make keyhole stable. In this work, based on the prin...
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CoCrFeNiSiMoW medium-entropy alloy coatings (MEACs) were fabricated by plasma-arc surfacing welding on Q235 steel. The microstructures and mechanical properties of CoCrFeNiSiMoW MEACs were studied. CoCrFeNiSiMoW MEACs are made from a... more
CoCrFeNiSiMoW medium-entropy alloy coatings (MEACs) were fabricated by plasma-arc surfacing welding on Q235 steel. The microstructures and mechanical properties of CoCrFeNiSiMoW MEACs were studied. CoCrFeNiSiMoW MEACs are made from a mixture of NiCrCoMo cubic (FCC) solid solution phase, (Fe, Ni), Mo1.24Ni0.76, and CoCx phases by XRD analysis. The average hardness values of the one- and two-layer CoCrFeNiSiMoW MEACs obtained were 186 ± 1.56 and 198 ± 1.78 HV, respectively. Compared with the one-layer CoCrFeNiSiMoW coating, the two-layer coating has a better wear performance due to its higher hardness. Its corrosion resistance is better because of its higher Ni content.
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A novel laser percussion drilling technology assisted by an electric field with lateral air blowing is reported. The lateral air blowing is first proposed for assisting the E-field assisted laser drilling for improving hole-drilling... more
A novel laser percussion drilling technology assisted by an electric field with lateral air blowing is reported. The lateral air blowing is first proposed for assisting the E-field assisted laser drilling for improving hole-drilling performance, quality and efficiency by blowing away the vapor plume and cooling the target workpiece. A high-speed camera is first used for observing and characterizing the transient laser percussion drilling process with and without an electric field and/or a lateral airflow. It was indicated that the transverse electric force and/or the side air blowing expedited the spatial motion with dispersion and density reduction of the vapor-plasma plume for enhancing laser drilling efficiency via weakening the plume-induced shield effect. The recast layer was reduced by using the transverse E-field assistance with and without lateral air blowing, and the combined assistance of a transverse E-field together with a lateral airflow was more effective for reducing ...
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Considering the coupling of a droplet, keyhole, and molten pool, a three-dimensional transient model for the full penetration laser + metal inert gas (MIG) hybrid welding of thin copper alloy plate was established, which is able to... more
Considering the coupling of a droplet, keyhole, and molten pool, a three-dimensional transient model for the full penetration laser + metal inert gas (MIG) hybrid welding of thin copper alloy plate was established, which is able to simulate the temperature and velocity fields, keyhole behavior, and generation of the welding defect. Based on the experimental and simulation results, the weld formation mechanism for the hybrid butt welding of a 2 mm-thick copper alloy plate was comparatively studied in terms of the fluid dynamic feature of the melt pool. For single laser welding, the dynamic behavior of liquid metal near the rear keyhole wall is complex, and the keyhole has a relatively drastic fluctuation. An obvious spattering phenomenon occurs at the workpiece backside. Meanwhile, the underfill (or undercut) defect is formed at both the top and bottom surfaces of the final weld bead, and the recoil pressure is identified as the main factor. In hybrid welding, a downward fluid flow i...
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In this study, CoCrFeMnNiW medium-entropy alloy coating on Q235 was fabricated by plasma surfacing technology. The wear performance of the prepared one-layer coating and the two-layer coating was studied by a friction and abrasion tester.... more
In this study, CoCrFeMnNiW medium-entropy alloy coating on Q235 was fabricated by plasma surfacing technology. The wear performance of the prepared one-layer coating and the two-layer coating was studied by a friction and abrasion tester. The microstructure and performance of the CoCrFeMnNiW coating were researched by optical microscope, a nano-indentation test, SEM, and hardness tester. The results show that the microstructure of the coating is made up of a fusion zone, equiaxed dendrites near the fusion zone, coarse columnar crystals, and near-surface with a certain direction between the near-fusion zone and near-surface fine equiaxed grains. The wear mechanism of one layer coating was abrasive with wear and fatigue wear. The wear mechanism of the two-layer coating was adhesive with wear and fatigue wear. For CoCrFeMnNiW MEA coating, the main factors determining their wear resistance were the value of its depth recovery ratio (ηh) and EIT.
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In this paper, ER50-6 steel was fabricated by wire arc additive manufacturing (WAAM) with an A-W GTAW system. The microstructure, mechanical properties, and corrosion behaviors of ER50-6 steel by WAAM were studied. The results showed... more
In this paper, ER50-6 steel was fabricated by wire arc additive manufacturing (WAAM) with an A-W GTAW system. The microstructure, mechanical properties, and corrosion behaviors of ER50-6 steel by WAAM were studied. The results showed that, with the GMAW current increased, from the bottom to the top of the sample, the microstructure was fine ferrite and granular pearlite, ferrite equiaxed grains with fine grains at grain boundaries, and columnar ferrite, respectively. The average hardness in the vertical direction of samples 1# and 2# was 146 and 153 HV, respectively. The hardness of sample 2# increased because of the refinement of grain. The pores in the sample increased as the bypass current increased. The higher bypass current also has a deterioration effect on the corrosion behavior of ER50-6 steel.
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A three-dimensional numerical model of arc in gas metal arc welding (GMAW) with single cable-typed wire was established based on the theory of arc physics. The influences of different shielding gas flow rates on the features of... more
A three-dimensional numerical model of arc in gas metal arc welding (GMAW) with single cable-typed wire was established based on the theory of arc physics. The influences of different shielding gas flow rates on the features of temperature field, velocity field and pressure field were investigated. The results showed that the maximum velocity of arc plasma along radial direction and the arc pressure on the surface of workpieces were increased obviously with the increase of the shielding gas flow rate, while the arc temperature was changed little. This phenomenon was mainly attributed to the increasing collisions between arc plasmas and the self-rotation action of cable-typed wires. The arc temperature at the tip of the cable-typed wire reached the maximum. The maximum flow velocity of arc plasma was located at the tip of wire (2–8 mm). The arc pressures in the central axis reached the maximum pressure. The simulation results were in agreement with the experimental results.
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A three-dimensional transient model is proposed to investigate the weld pool dynamic behavior in laser + metal inert gas (MIG) hybrid fillet welding of aluminum alloy in the horizontal position, which allows for the joint configuration... more
A three-dimensional transient model is proposed to investigate the weld pool dynamic behavior in laser + metal inert gas (MIG) hybrid fillet welding of aluminum alloy in the horizontal position, which allows for the joint configuration and coupling of the keyhole, droplet and weld pool as well as the heat and mass exchange between gas and liquid phases and is able to simulate the temperature distribution, fluid flow and formation process of a keyhole-induced pore in hybrid welding with a horizontal fillet joint. The weld porosity is also measured using x-ray nondestructive testing technology. Keyhole behavior and the formation mechanism of keyhole-induced porosity were analyzed. The calculated results are in generally good agreement with the experimental ones. A clockwise vortex always exists at the middle part of the weld pool. The formation and growth of the molten metal bulge on the keyhole wall are responsible for the occurrence of a gas bubble, which has a variation in size and shape and can be split during welding. The keyhole collapses easily at its middle or upper part in horizontal fillet welding, and the capture of the bubble by the upper molten pool boundary enhances the possibility of porosity formation to some degree. The keyhole-induced pore is mainly formed at the regions near the keyhole bottom and the upper fusion line of the weld pool.
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Abstract The keyhole induced porosity in laser-MIG hybrid fillet welding of aluminum alloy in the horizontal position was investigated with simulation and experimental methods. A three dimensional model is developed, which takes into... more
Abstract The keyhole induced porosity in laser-MIG hybrid fillet welding of aluminum alloy in the horizontal position was investigated with simulation and experimental methods. A three dimensional model is developed, which takes into account geometric feature of horizontal filled joint and the coupling of keyhole, droplet and molten pool. Meanwhile, the major forces are also incorporated in the model. The inclination of heat source is dealt with through rotation of coordinate system. This model is able to calculate the keyhole dynamic behavior and the formation process of gas bubble as well as keyhole induced porosity directly. Also, it can describe the merging and disappearing of bubbles. The weld porosity was examined by the X-ray non-destructive testing. Large weld pool size provides more time for bubble to escape from the molten pool, which is the major factor responsible for the reduction in hybrid welding. Besides, the forward flow caused by the clockwise vortex is weakened, which also plays a positive role in improving the stability of back keyhole wall. The keyhole collapses at the middle part easily in horizontal fillet welding, raising the possibility of forming large pore. Bubble is easy to be captured by the upper weld pool boundary when floating up. With enhancing the welding current, the stability of keyhole is enhanced to some extent and the keyhole induced porosity is reduced.
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A cable-type welding wire (CWW) gas metal arc welding (GMAW) method was proposed as a novel approach, using CWW for the consumable electrode. Droplet transfer influences the welding process, and the forces on the droplet were analyzed to... more
A cable-type welding wire (CWW) gas metal arc welding (GMAW) method was proposed as a novel approach, using CWW for the consumable electrode. Droplet transfer influences the welding process, and the forces on the droplet were analyzed to elucidate the metal transfer phenomenon observed during the welding process. The effects of the arc pressure, rotating force, and welding parameters were analyzed to understand the metal transfer. The special structure of the CWW affected the arc characteristics and forces during metal transfer as part of the welding process. The droplet formed by droplets from each thin wire, the arc, and electromagnetic forces on droplet formation and the coupling process were analyzed. The arc pressure and rotating forces are beneficial to metal transfer and increase the droplet transfer frequency. The droplet size decreases with increasing welding parameters.
