Conventional Gas Metal Arc Welding Research Articles

Development of hard and wear-resistant SiC-AISI304 stainless steel clad layer on low carbon steel by GMAW process

In the present investigation, a successful attempt has been done to utilize conventional gas metal arc welding (GMAW) setup to develop SiC reinforced AISI 304 stainless steel (ASS) clad layer on low carbon steel (LCS) substrate. The characteristics of the clad bead like bead profile and dilution depend on the GMAW processing parameters like GMAW voltage and consumable wire feed rate (CWFR). The clad deposition at a higher voltage range (30 V) developed a defect-free, uniformly distributed fine SiC-reinforced clad layer with better clad dilution with the substrate. Further, the SiC-reinforced clad layer showed a uniform distribution of fine SiC particles in the steel matrix and also the formation of different hard intermetallics like CrSi2, Mn3Ni2Si, Fe2C, Fe5C2, and Cr7C3 in the clad layer. The SiC-reinforced clad surface showed a significant improvement in Microhardness (up to 504 HV0.5) compared to the steel substrate (180 HV0.5). The clad layer also improved the adhesive wear resistance (upto 8.7 times) and abrasive wear resistance (upto 1.7 times) of low carbon steel substrate.

GMAW hot-wire process with indirect resistive heating of the auxiliary wire

Due to the coupled filler material and energy supply in gas metal arc welding (GMAW) processes, these processes have limited productivity as a result of heat-induced residual stresses and distortion. To increase productivity and decrease heat input, conventional GMAW processes can be combined with an auxiliary hot wire. The disadvantage of hot-wire processes is the small process window due to the required melt pool contact to maintain resistance heating and the magnetic blow effect of the hot-wire current. In this paper, the development of a GMAW hot-wire process with upstream ohmic preheating of the filler wire (between two current nozzles) is presented. Besides an increase of the deposition rate and consequently of the productivity, a decoupling and specific control of the material and energy input depending on the application is aimed at. By reducing the heat input into the base material, the influence on the mechanical-technological properties will be reduced and the development of residual stresses and distortion minimized. Furthermore, by preventing the magnetic arc blow caused by the hot-wire current, the process behavior will be improved, thus increasing its productivity and robustness. The potential of the process is demonstrated using selected welding tests.

Microstructural and wear properties of mild steel cladded with AISI 316L stainless steel using pulsed current gas metal arc welding process

The main objective of this study is to study the microstructure and wear resistance of mild steel (MS) of grade IS 2062 that has had an austenitic stainless steel (AISI 316L) coating applied utilizing the pulsed current gas metal arc welding (PC-GMAW) technique. The PC-GMAW method was used to overcome issues with the conventional gas metal arc welding (CC-GMAW) method used for cladding AISI 316L steel over mild steel, such as a larger heat affected zone (HAZ), coarse-grained deposited weld metal microstructure, less penetration depth and higher dilution and reinforcement height. Optical microscopy (OM) was used to examine the microstructural characteristics of the clad region. Using the pin-on-disc testing machine, the wear rate of cladded specimens was recorded, and scanning electron microscopy (SEM) was used to examine the morphology of wear surfaces. The microhardness distribution of the cladded region was examined, and the wear characteristics of the cladded specimens were correlated. According to the findings, PC-GMAW cladding is harder and more resistant to wear than a mild steel substrate. The PC-GMAW cladding exhibited higher weld metal deposition and lower dilution. Weld overlay hardness was 15.83% higher in the PC-GMAW cladding than in the mild steel substrate. The wear rate was decreased by an average of 20.18% as compared to the mild steel substrate with PC-GMAW cladding.

Development of a low heat-input welding technique for joining thick plates of 250 grade maraging steel to fabricate rocket motor casings

• A low heat-input welding technique for the fabrication of rocket motor casing was devised and implemented. • The novel DP-GMAW reduced heat-input by 67% and RA by 49% compared to conventional GMAW. • DP-GMAW improved weld properties compared to GMAW. Maraging steels are ultra-high strength steels, which are most widely used in different strategic sectors. These steels are well-suited for the fabrication of rocket motor casings, which involves welding as one of the critical manufacturing processes. The major concern regarding welding of maraging steel is the formation of reverted austenite (RA) phase, which deteriorates the mechanical performance of the joints. The conventional arc welding processes involve higher heat-input during welding; the available literature indicates that segregation of alloying elements and the resultant formation of RA are promoted by high heat-input. The present study adopted a novel dual-pulse gas metal arc welding (DP-GMAW) technique, which reduces the heat-input during welding by current pulsing approach. The Dual pulsing approach was capable of 67% reduction of heat-input and 49% reduction of RA when compared to conventional gas metal arc welding (GMAW).

Mechanical properties and microstructural characteristics of wire arc additive manufactured 308 L stainless steel cylindrical components made by gas metal arc and cold metal transfer arc welding processes

Wire arc additive manufacturing (WAAM) is suitable for manufacturing large-scale complex parts due to many advantages, including high disposition rate and low cost and thus become a viable advanced manufacturing technique. In the present study, two different arc welding processes were used to fabricate 308 L austenitic stainless steel (SS) cylindrical components. The mechanism and impact of the processes on the microstructure and mechanical characteristics were analysed. The results indicated that the component produced by the cold metal transfer (CMT) arc welding process exhibits finer grains and higher amount of ferrite than conventional gas metal arc welding (GMAW) process. Furthermore, the percentage of anisotropy in tensile strength was reduced from 8.07% to 6.21% for cylinders built by the GMAW process to the CMT process. In addition, the average ultimate tensile strength (UTS), elongation (EL) and hardness of the CMT cylinder are 5.17–7.0%, 4.029–7.80% and 4.02–5.88% higher than the GMAW cylinder, irrespective of orientations. The tensile properties are higher than those of the 308 L welding wire and other arc-welding based additively manufactured 308 L stainless steel parts. The produced WAAM 308 L SS cylinders exhibited superior performance than the stainless steel made by industrial forging standards. Therefore, the 308 L SS cylindrical components made by WAAM technique are found to be suitable for industrial application.

Effect of thermal history on microstructure evolution and mechanical properties in wire arc additive manufacturing of HSLA steel functionally graded components

In this study the microstructure evolution during wire arc additive manufacturing (WAAM) with high strength low-alloy (HSLA) steel was studied to employ this knowledge in the WAAM parts microstructure control, which was demonstrated by the functionally graded specimen manufacturing with only ER110S-G grade wire. The experiment design was based on the application of two WAAM modes: the cold metal transfer (CMT) and a conventional self-regulated gas metal arc welding (C-GMAW) mode. Material thermal history was estimated with the use of finite element modeling and the microstructure transformations were assessed using the calculated continuous cooling transformation (CCT) diagram. The microstructure was investigated with the use of optical and scanning electron microscopy. Mechanical properties were determined by tensile and microhardness tests, digital image correlation analysis was applied to detect the deformation zones during tensile tests of the functionally graded specimen. The results of the study showed a strong correlation between cooling rate, tempering time and microstructure and hence mechanical properties: depending on the thermal history the microhardness varied from 283 to 411 HV. Both C-GMAW and CMT modes resulted in the formation of two main zones: the no-diffusion upper zone and the diffusion lower zone. In the upper zone the microstructure is determined by cooling rate from 800 °C down to 500 °C. The upper zone consists of martensite, bainite, a mixture of martensite and bainite, martensite-austenite phase (MA) and retained austenite (RA). In the lower zone the microstructure is determined by the tempering time in the range 700–200 °C. The lower zone consists of a tempered martensite, troostite, sorbite, alpha ferrite, MA-phase and carbites. Both C-GMAW and CMT modes resulted in the relatively high ultimate tensile strength (UTS): 807 MPa for CMT and 759 MPa for C-GMAW. CMT and C-GMAW resulted in the different elongation in the horizontal and vertical directions, it ranged from 5 to 10%. Cooling rate and tempering time regulation allowed to manufacture the functionally graded specimen with the relatively high strength and with the predetermined fracture localization.

An Approach to Assessing S960QL Steel Welded Joints Using EBW and GMAW

In recent years, ultra-high-strength structural (UHSS) steel in quenched and tempered (Q+T) conditions, for example, S960QL has been found in wider application areas such as structures, cranes, and trucks due to its extraordinary material properties and acceptable weldability. The motivation of the study is to investigate the unique capabilities of electron beam welding (EBW) compared to conventional gas metal arc welding (GMAW) for a deep, narrow weld with a small heat-affected zone (HAZ) and minimum thermal distortion of the welded joint without significantly affecting the mechanical properties. In this study, S960QL base material (BM) specimens with a thickness of 15 mm were butt-welded without filler material at a welding speed of 10 mm/s using the high-vacuum (2 × 10−4 mbar) EBW process. Microstructural characteristics were analyzed using an optical microscope (OM), a scanning electron microscope (SEM), fractography, and an electron backscatter diffraction (EBSD) analysis. The macro hardness, tensile strength, and instrumented Charpy-V impact test were performed to evaluate the mechanical properties. Further, the results of these tests of the EBW joints were compared with the GMAW joints of the same steel grade and thickness. Higher hardness is observed in the fusion zone (FZ) and the HAZ compared to the BM but under the limit of qualifying the hardness value (450 HV10) of Q+T steels according to the ISO 15614-11 specifications. The tensile strength of the EBW-welded joint (1044 MPa) reached the level of the BM as the specimens fractured in the BM. The FZ microstructure consists of fine dendritic martensite and the HAZ predominantly consists of martensite. Instrumented impact testing was performed on Charpy-V specimens at −40 °C, which showed the brittle behavior of both the FZ and HAZ but to a significantly lower extent compared to GMAW. The measured average impact toughness of the BM is 162 J and the average impact toughness value of the HAZ and FZ are 45 ± 11 J and 44 ± 20 J, respectively.

Experimental study on application of gas metal arc welding based regulated metal deposition technique for low alloy steel

ABSTRACT In this work, a modified and advanced welding technique named regulated metal deposition (RMD) has been implemented for joining ASTM A387-11-2 low alloy steel plates. Mechanical behavior and microstructure of welded joints have been experimentally investigated after the recommended heat-treatment process. The microstructures of welded joints were examined using optical and scanning electron microscopes. Optical microscopy indicated the existence of bainitic and martensitic phases in the base material and weld zone, respectively. Scanning electron microscopy combined with energy dispersive x-ray analysis displayed the presence of martensitic colonies as well as deposits of carbide precipitates in both weldments. The mechanical properties of these weldments, namely micro-hardness, tensile strength, and impact strength were also investigated. A comparative study has also been carried out for the same material using the conventional gas metal arc welding, in which the microstructure and mechanical behavior of regulated metal deposition weldments have been compared to those of gas metal arc weldments. Regulated metal deposition weldments showed better mechanical behavior than the gas metal arc weldments for low alloy steel.

Comparison of welding residual stress and deformation induced by local vacuum electron beam welding and metal active gas arc welding in a stainless steel thick-plate joint

Local vacuum electron beam welding (LVEBW) breaks through the limit of vacuum chamber and can be flexibly proceeded in more working conditions. Using LVEBW to substitute conventional gas metal arc welding will greatly improve production efficiency. In view of the severe effect of welding residual stress (WRS) on product safety, the WRS induced by two methods should be comprehensively evaluated, thus for providing the designer and engineer with a theoretical basis and guidance to control the WRS in thick-plate joint. This paper investigated the WRS and deformation induced by LVEBW and metal active gas arc welding (MAG) in SUS310S thick-plate joint via numerical simulation and experiment. Based the simulation and experiment results, the WRS and deformation induced by the LVEBW and MAG were compared quantitatively. Results show that the distribution of WRS induced by two methods are significantly different. The high longitudinal residual stress (RS) region in LVEBW joint is much narrower than that in MAG joint and the maximum transverse RS in LVEBW joint is smaller than that in MAG joint. Both the transverse shrinkage and out-of-plane deformation induced by LVEBW is far less than that induced by MAG. Meanwhile, LVEBW has a great efficiency advantage over MAG.

First assessment on the microstructure and mechanical properties of gtaw-gmaw hybrid welding of 6061-t6 AA

Abstract Plates of 6061-T6 aluminum alloy of 6.35 mm thick were welded by using the hybrid gas tungsten arc - gas metal arc welding process (GTAW-GMAW) and compare with the conventional gas metal arc welding (GMAW). An ER-5356 filler wire of 1.2 mm in diameter and argon of high purity as protective gas were used in both processes. The aim of the experiments was to assess the effects that yield the GTAW-GMAW welding process on the microstructure and the mechanical properties of the welded joints in the as weld and after artificial aging condition. Heat inputs were set up between ∼ 0.9 kJ/mm and ∼ 1.1 kJ/mm. Plots of the grain size and porosity ratio showed that GTAW-GMAW promoted a grain structure refinement and a reduction of porosity in weld metal. In addition, GTAW-GMAW indicate a reduction on the degradation in the heat affected zone in the as weld condition and a 40 % increase in welding speed. There was observed a major losing of magnesium in weld metal in the conventional GMAW process, this effect reflects on the final mechanical strength and microhardness of weld metal after artificial aging, as less Mg is available to get in solid solution.

Influencing Microstructure of Vanadium Carbide Reinforced FeCrVC Hardfacing during Gas Metal Arc Welding

Vanadium carbide (VC) reinforced FeCrVC hardfacings have become important to improve the lifetime of tools suffering abrasive and impact loads. This is because the microstructural properties of such hardfacings enable the primary VCs to act as obstacles against the penetrating abrasive. Because dilution is supposed to be the key issue influencing the precipitation behaviour of primary carbides during surfacing, the development of deposit welding processes exhibiting a reduced thermal impact, and hence lower dilution to the base material, is the primary focus of the current research. By inserting an additional hot wire in the melt, an approach was developed to separate the material and energy input during gas metal arc welding (GMAW), and hence realised low dilution claddings. The carbide content could be increased, and a grain refinement was observed compared with conventional GMAW. These effects could be attributed to both the reduced dilution and heterogeneous nucleation.

Effect of GTAW remelting on the corrosion performance of AISI 316L cladding

AbstractGas tungsten arc welding (GTAW) process was used for remelting of the top clad layers of austenitic stainless steel 316L deposited on low‐carbon steel using gas metal arc welding (GMAW) process. Different electrochemical techniques were used for assessing and comparing sensitization and pitting corrosion performance of these clads (both in the as‐welded as well as aged condition), besides comparing their passive film characteristics. Top clad layer remelting was influential upto a penetration depth of around 2.34 mm. Aging of clads at 750°C/24 hr accelerated the precipitation of carbides, which suppressed partially due to their remelting as indicated by electron probe microanalysis studies. Due to this GTAW remelted clads exhibited a relatively lesser degree of sensitization and higher pitting corrosion resistance as compared to the conventional GMAW clads. X‐ray photoelectron spectroscopy studies revealed a relatively higher concentration of O, Cr, Ni, and Mo in the passive film of remelted clad surfaces than the conventional ones, which accounted for enhanced protectiveness of passive film on remelted surfaces as indicated by electrochemical impedance spectroscopy studies.

Influence of rotation frequency and rotation diameter on mechanical properties and microstructure of weld metal produced by MCAW-RE

The MCAW process with rotating electrode (MCAW-RE) is a variation of the conventional gas metal arc welding process, which a metal-cored wire is submitted to a rotational movement along a pre-established diameter. This process enhances narrow gap welding, since the rotational motion of the electrode allows the electric arc to reach peripheral regions of the groove, preventing lack of fusion on the sidewall. As a result, reduced costs and superior productivity compared with the conventional GMAW process are obtained. The limited literature about this process is focused on the operational characteristics, and works studying the mechanical properties are not available. Thus, this work evaluates the mechanical and microstructural properties of weld metals obtained by the MCAW-RE process in order to allow a decision about its technical feasibility to replace the GMAW process in industry. Initially, beads on plate weld tests were performed with varying rotation frequency and rotation diameter, in order to determine the parameters to be used in welded joints. High-strength steel weld metals were obtained by welding performed in steel plates with dimensions of 500 × 300 × 10 mm. Mechanical tests and metallographic examination were carried out in samples removed transversally to the weld bead. The results showed that the impact toughness of the weld metals can achieve the requirements for several industrial applications. The results showed that the GMAW process with rotating electrode-cored wire has a high potential for replacement of the GMAW in industrial applications.

Mechanical and Microstructural Characteristics of Conventional and Robotic Gas Metal Arc Welded Low Carbon Steel Joints: A Comparative Study

In the recent automobile era, SAE 1022, low carbon manganese steel is widely used in structural members of automobiles. These steels possess good weldability and need proper heating treatment conditions when high thickness sections are being used in the structural application. Mostly, gas metal arc welding (GMAW) is preferred in automobile industries to have which produces better penetration with some minor defects like improper fusion of sidewall, etc. The increasing demand in the field of the automobile led to the attention over automated GMAW is being preferred to reach better productivity with zero defects. The samples were welded by the conventional GMAW method and automated through a robot. From the experimental test results, welding current of 450A, welding speed of 350 mm/min and a land height of 4 mm yielded a maximum tensile strength of 647 MPa and hardness of 275 HV in the coarse-grained heat-affected zone region with a robotic mode of GMAW. The comparative study proved that automated process produced better mechanical properties and improved efficiency.

Comparative study on the microstructures and properties of wire+arc additively manufactured 5356 aluminium alloy with argon and nitrogen as the shielding gas

This research explored the influences of shielding gases on the appearance of weld beads and the microstructures and mechanical properties of thin-wall samples using conventional gas metal arc welding as the heat source by using 5356 aluminium alloy welding wire as the raw materials and nitrogen (N2) and argon (Ar) as the shielding gases. The results showed that under the same parameters and after mono-layer single-bead welding was performed using N2 as the shielding gas, the bead height was higher, the bead width was narrower, and the penetration depth was shallower. The grain size of the thin-wall sample protected by N2 was 43.5–47.8 % smaller than that obtained under Ar protection. However, the sample protected by N2 contained many flaky nitrides, whose presence improved the microhardness but reduced the ultimate tensile strength (UTS) and plasticity. The average UTS of the thin-wall sample protected by N2 in the horizontal direction was 82.5 % of the UTS of the samples shielded using Ar. However, the average elongation in the horizontal direction of the samples protected by N2 was 18.6 % of that of the samples shielded by Ar. The mechanical properties of the sample protected by argon were more excellent.

Interactions of the process parameters and mechanical properties of laser butt welds in thin high strength low alloy steel plates

High strength low alloy steels subjected to the thermomechanical control process present excellent strength–toughness combination, high strength/weight ratio, and weldability. Therefore, they are widely used in structural components, such as pressure vessels, oil/gas transportation pipes, lifting equipment, vehicles, shipbuilding and offshore industries, and in the automotive industry where low thickness (0.8–3 mm thickness) is of great importance. Usually, these steels are welded by conventional gas metal arc welding, which creates wide heat-affected zones, large residual stresses, and distortion in the welded parts. Laser welding is nowadays an alternative process to weld high strength low alloy steel parts due to its advantages. The aim of this work is to understand the effect of process parameters on defects, weld bead geometry, microstructure, and mechanical properties, namely hardness and tensile strength. We identify the main laser welding parameters and their influence on the weld bead geometry and defects, for a 3 mm thick high strength low alloy steel welded under a maximum power of 2 kW. A cross section of the weld seam was optimized achieving a good geometry without porosity. The threshold value of the heat input to achieve complete penetration was determined for different focus diameters. The microstructure, size, and hardness of the heat-affected zone and of the fusion zone are strongly influenced by the heat input. The values of the tensile strength achieved in butt welds were close to the base metal by an appropriate selection of the laser welding parameters and the heat input.

Laser-Driven Programmable Metal Transfer in GMAW

Conventional pulsed laser-enhanced gas metal arc weld-ing (GMAW) employs a single fiber laser focused and aimed on the droplet neck position to produce a laser recoil force and thus ensure the droplet detachment despite the am-perage of the welding current. One drop per laser pulse metal transfer is obtained, and the droplet deflects away from the wire axis along the laser incident direction. This implies that the droplet trajectory may also be controlled if the direction of the laser recoil force can be adjusted. Such a controllability is expected to bring an entirely new capa-bility to the GMAW process: active control on the weld beam geometry. To this end, double-sided, laser-enhanced GMAW was proposed and experimentally verified in this pa-per. The two lasers were symmetrically positioned, and both aimed at the droplet neck. The laser pulse peak power, du-ration, and pulse phase of the two lasers can all be programmed to regulate the laser recoil forces. The metal transfer under twin laser irradiations (same laser pulses and phases) was first verified. Then the effectiveness on controlling the droplet trajectory of three proposed control strategies — peak power matching, peak width matching, and phase matching of the two lasers — were evaluated. The results showed laser peak power matching is optimal for obtaining desired droplet trajectory. Since the laser can be easily controlled in real time, the transfer frequency, droplet size, and trajectory can all be adjusted in real time, and the metal transfer evolves into programmable transfer.

Effect of post-weld heat treatment on microstructure and mechanical properties of DP800 and DP1200 high-strength steel butt-welded joints using diode laser beam welding

Among the available high-strength steels, there is growing demand for dual phase (DP) steels for wide application in the automotive industry owing to their good combination of high strength, ductility and formability. Also, the use of innovative welding technologies like laser beam welding (LBW) has growing importance in the field of high-strength steel because of its excellence in providing high-quality welds, high welding speed, high power density, low heat input, a narrow heat-affected zone and low heat distortions as compared to the conventional gas metal arc welding process. However, the hardening and softening in the heat-affected zone is a major issue when welding high-strength steel, i.e. DP steel grades, greatly affecting the strength, formability and plasticity of the whole-welded joint and thus affecting service performance and reliability. Based on preliminary experiments, the optimal welding condition was a nominal laser power of 1.0 kW and a welding speed of 8 mm/s. The aim of this work is to analyse and compare the weld and heat-affected zone characteristics, microstructure and mechanical properties of DP steels with 1-mm thick butt joints of DP800 and DP1200 high-strength steel (HSS) by diode laser beam welding. The effects of post-weld heat treatment (PWHT) on the strengthening of the laser-welded joints were evaluated by microstructural examinations under optical microscope and scanning electron microscope, and mechanical properties were examined by microhardness test, three-point bending tests and tensile tests.

A preliminary study on gas metal arc welding-based additive manufacturing of metal parts

Introduction: In the past three decades, additive manufacturing (AM), also known as 3D printing, has emerged as a promising technology, which allows the manufacture of complex parts by adding material layer upon layer. In comparison, with other metal-based AM technologies, gas metal arc welding-based additive manufacturing (GMAW-based AM) presents a high deposition rate and has the potential for producing medium and large metal components. To validate the technological performance of such a manufacturing process, the internal quality of manufactured parts needs to be analyzed, particularly in the cases of manufacturing the parts working in a critical load-bearing condition. Therefore, this paper aims at investigating the internal quality (i.e., and mechanical properties) of components manufactured by the GMAW-based AM technology.
 Method: A gas metal arc welding robot was used to build a thin-walled component made of mild steel on a low-carbon substrate according to the AM principle. Thereafter, the specimens for observing and mechanical properties were extracted from the built thin-walled component. The of the specimen were observed by an optical microscope; the hardness was measured by a digital tester, and the tensile tests were carried out on a tensile test machine.
 Results: The results show that the GMAW-based AM-built thin-walled components possess an adequate that varies from the top to the bottom of the built component: structures with primary dendrites in the upper zone; granular structure of with small regions of at grain boundaries in the middle zone, and grains of in the lower zone. The hardness (ranged between 164±3.46 HV to 192±3.81 HV), yield strength (YS offset of 0.2% ranged from 340±2 to 349.67±1.53 ), and ultimate tensile strength (UTS ranged from 429±1 to 477±2 ) of the GMAW-based AM-built components were comparable to those of wrought mild steel.
 Conclusions: The results obtained in this study demonstrate that the GMAW-based AM-built components possess adequate and good mechanical properties for real applications. This allows us to confirm the feasibility of using a conventional gas metal arc welding robot for additive manufacturing or repairing/re-manufacturing of metal components.

Numerical study on arc-droplet coupled behavior in magnetic field controlled GMAW process

The metal transfer behavior is one of the most pivotal links of gas metal arc welding (GMAW) for improving the welding quality. Arc impacts the current path and heat input on the droplet surface, in reverse, the metal droplet detachment makes the arc to flicker. It is hard to make the metal transfer process clear with only experimental methods since the limited measuring space and high temperature in the welding region. In this work, with the help of computational fluid dynamics software ANSYS FLUENT, a magnetohydrodynamic model including argon arc plasma and steel wire and the droplet is constructed by using two independent governing equations of gas and metal phase for the mass, momentum, and energy balance. Comparing the magnetic field controlled GMAW with conventional GMAW, the temperature field, current density distribution, electric potential field, static pressure field and also metal vapor mass fraction distribution are highlighted. It is shown that the metal transfer frequency decreases and droplet diameter increases with 180 A welding current when applying an external constant axial magnetic field 0.002 T. So, the arc length decreases before the detaching moment, the current density expands in the arc region and the voltage decreases. The centrifugal movement impedes the downward flow and transfers heat from the droplet center to the outside region.