Arc Mode Research Articles

Exploring the cutting edge: Recent trends in cold metal transfer welding

Cold metal transfer welding is known for its automated welding process, which is equipped with shortcircuit-based deposition of filler wire, which allows it to control its heat input parameter properly along with a wire feed rate. Cold metal transfer’s main characteristic, which greatly affected the manufacturing industries, is joining thin, similar, or dissimilar metal sheets as the processing heat input is minimal. This review paper (covering 104 studies) examines how joining different metals with varying welding parameters affects their weld appearance, microstructure, tensile strength, and the formation of joint failure. The main focus was on what additional methods, like hardfacing or post-heat treatment of material, must be adopted to enhance the joint's weld quality and appearance. The paper starts with the investigation of numerous dissimilar weld joints formed by the cold metal transfer technique, along with the effect of varying welding parameters and ultrasonic-assisted cold metal transfer hybrid welding on the weld quality and post–pre-weld heat treatment of materials. A comparison of different cold metal transfer arc modes employed in wire-arc additive manufacturing has also been discussed briefly. At the end of the analysis, it was noted that some metal joints had a positive impact, and some gained a negative effect while increasing the heat input. The research articles studied in this paper indicate that not every material would exhibit the same welding property when subjected to a specific set of varying welding parameters.

Wire-arc directed energy deposition of high performance heat treatment free Al-6Mg-0.3Sc alloy

The release of residual stress during heat treatment of additively manufactured components could lead to significant deformation, particularly for those with thin-wall features and variable cross-sections. In this study, high performance heat treatment free Al-6Mg-0.3Sc alloy components were fabricated using the wire-arc directed energy deposition (DED) technique, achieving a yield strength of 223.0 ± 0.9 MPa, tensile strength of 408.5 ± 3.2 MPa, and elongation of 20.6 ± 1.7 %. The results indicate that compared to the CMT arc mode, the CMT + PA arc mode leads to a more pronounced bimodal microstructure, resulting in improved elongation. The mechanical property enhancement mechanism relies more on solid solution strengthening and grain boundary strengthening than on precipitation strengthening. Additionally, this study establishes for the first time a correlation between droplet transition and microstructure evolution. The research presented herein lays a theoretical foundation for wire-arc DED in the direct manufacturing of large thin-walled components without the need for heat treatment.

Analyses of nonequilibrium transport in atmospheric-pressure direct-current argon discharge under different modes

Abstract The key plasma parameters under different discharge modes, such as heavy-particle and electron temperatures, electron number density, and nonequilibrium volume of plasmas, play important roles in various applications of gas discharge plasmas. In this study, a self-consistent two-dimensional nonequilibrium fluid model coupled with an external circuit model is established to reveal the mechanisms related to the discharge modes, including the normal glow, abnormal glow, arc, and glow-to-arc transition modes, with an atmospheric-pressure direct-current (DC) argon discharge as a model plasma system. The modeling results show that, under different discharge modes, the most significant difference between the preceding four discharge modes lies in the current and energy transfer processes on the cathode side. On one hand, the current to the cathode surface is mainly delivered by the ions coming from the plasma column under the glow discharge mode due to the low temperature of the solid cathode, whereas the thermionic and secondary electrons emitted from the hot cathode surface play a very important role under the arc mode with a higher cathode surface temperature and higher ion flux toward the cathode. On the other hand, the energy transfer channel on the cathode side changes from mainly heating the solid cathode under the glow mode to simultaneously heating both the solid cathode and plasma column under the arc mode with an increase in the discharge current. Consequently, the power density in the cathode sheath (P c) was used as a key parameter for judging different discharge modes, and the range of (0.28–1.2) × 1012 W m−3 was determined as a critical window of P c corresponding to the glow-to-arc-mode transition for the atmospheric-pressure DC argon discharge, which was also verified by comparison with the experimental results in this study and the data in the previous literature.

Mechanical characterization and microstructural evolution of Inconel 718 and SS316L TIG weldments at high temperatures

This study examines the impact of both constant and pulsed current on the tensile characteristics, micro-hardness of weld surface, and metallurgical properties of the Inconel 718 and SS316L weldments. The Tungsten Inert Gas (TIG) welding process utilized two distinct arc modes to combine incompatible metals. The pulse frequency was systematically adjusted within the range of 2 Hz–6 Hz in order to investigate its impact on the welding parameters. A tensile test was performed using a universal testing equipment under various temperature conditions, including room temperature and an elevated temperature of 350 °C. When the samples were welded at a frequency of 4 Hz, both the Ultimate Tensile Strength (UTS) and Yield Strength (YS) were greater compared to when the samples were welded at 2 Hz, 6 Hz, or a continuous arc mode. Furthermore, it was noted that the YS-to-UTS ratio was higher for the weldments produced at 4 Hz pulse frequency. The UTS of current and pulsed (4 Hz) modes at a temperature of 350 °C were determined to be 505 and 524 MPa, respectively. Pulse welding demonstrated a higher hardness number compared to steady welding due to the regulated rate of heat. The TIG weldments of Inconel 718 and SS316L demonstrated superior mechanical and metallurgical qualities when exposed to elevated temperatures. The practical implications of these findings are relevant to the fabrication of turbine discs and shafts.

Моделювання електродугового режиму електропечі і аналіз її функціонування у реальному часі

Моделювання електродугового режиму електропечі і аналіз її функціонування у реальному часі

Simulation of electric arc mode of electric furnace and analysis of its operation in real time

Simulation of electric arc mode of electric furnace and analysis of its operation in real time

Investigating the Forming Characteristics of 316 Stainless Steel Fabricated through Cold Metal Transfer (CMT) Wire and Arc Additive Manufacturing.

Wire and arc additive manufacturing (WAAM), recognized for its capability to fabricate large-scale, complex parts, stands out due to its significant deposition rates and cost-effectiveness, positioning it as a forward-looking manufacturing method. In this research, we employed two welding currents to produce samples of 316 austenitic stainless steel utilizing the Cold Metal Transfer wire arc additive manufacturing process (CMT-WAAM). This study initially evaluated the maximum allowable arc travel speed (MAWFS) and the formation characteristics of the deposition bead, considering deposition currents that vary between 100 A and175 A in both CMT and CMT pulse(CMT+P) modes. Thereafter, the effect of the CMT+P mode arc on the microstructure evolution was analyzed using the EBSD technique. The findings indicate that the arc travel speed and deposition current significantly affect the deposition bead's dimensions. Specifically, an increase in travel speed or a reduction in current results in reduced bead width and height. Moreover, the employment of the CMT+P arc mode led to a reduction in the average grain size in the mid-section of the sample fabricated by CMT arc and wire additive manufacturing, from 13.426 μm to 9.429 μm. Therefore, the components of 316 stainless steel produced through the CMT+P-WAAM method are considered fit for industrial applications.

A comparative study on microstructure and mechanical properties of wire-arc directed energy deposited Al–Zn–Mg–Cu alloy based on the cold metal transfer technology

Wire-arc directed energy deposition (DED) of Al–Zn–Mg–Cu alloy faced a tough challenge because of the occurrence of crack and pore defects caused by the high content of alloying elements. Three cold metal transfer (CMT) arc modes were studied to fabricate Al–Zn–Mg–Cu alloy components via the wire-arc DED process, with the aim of optimizing the deposition process and revealing the action mechanism of arc mode on the microstructure and mechanical properties. The effect of the CMT arc mode on the forming accuracy and arc/droplet behaviors was investigated with the assistance of the microscope and high-speed camera. The characteristics of grain morphology, crystallographic texture, and precipitated phase were quantitatively analyzed. The results show that the forming accuracies of deposited samples degenerate when using CMT and CMT pulse modes due to abnormal electrical waveforms and overflow/curve phenomenon. The finest grain size is realized under CMT advance mode because of its induced stirring effect on the molten pool, expanded constitutional supercooling zones, and extremely low heat input. The continuous and coarse precipitated phases in CMT and CMT pulse modes are transferred into dispersive ones in CMT advance mode. Moreover, the quantity and size of pores are also reduced in CMT advance mode. The combined action of microstructure optimization and defect reduction is conducive to improving the mechanical properties. Finally, the preferable ultimate tensile strength (∼278.15 MPa) and top elongation (∼6.50 %) of as-deposited Al–Zn–Mg–Cu alloy are achieved.

The effect of direct energy deposition arc mode on the porosity of AA5087 aluminum alloy

The paper evaluates the effect of the welding mode of the CMT-based direct energy deposition arc (DED-Arc) process on the porosity of AA5087 aluminum alloy walls. Three welding modes were used to produce the walls: cold metal transfer (CMT), CMT-Pulse (CMT-P), and CMT Cycle-Step (CMT-CS) with heat inputs of 128.5 J/mm, 150.4 J/mm, and 152 J/mm, respectively. Porosity was assessed with a light microscopy (LM) and computer tomography (CT). The wall produced with the lowest heat input had the lowest average porosity of 0.641 % compared to CMT-P (0.799 %) and CMT-CS (0.766 %). CT results followed the same trend with porosity of 0.21 %, 0.32 %, and 0.27 % for CMT, CMT-P, and CMT-CS, respectively. The porosity level strongly correlates with the hydrogen content. The lowest porosity (CMT) at the lowest hydrogen content (5.29 ppm) is associated with lower hydrogen solubility in a molten pool at lower heat inputs. Most of the detected pores in all modes ranged from 51 to 100 μm in size.

Effect of welding mode on selected properties of additively manufactured AA5087 aluminium alloy parts

Wire and arc additive manufacturing (WAAM) is a popular direct energy deposition (DED) method for producing large-scale metallic components. The main advantages of the technique are a high deposition rate and low cost. Furthermore, the utilization of the WAAM is prevalent in the aerospace industry. The AA5087 aluminium alloy with 4.5 wt.% of magnesium has been investigated because of its excellent properties. The present research deals with the study of thermal cycles and fields developed in the alloy during additive manufacturing with two different Cold metal transfer (CMT) modes, namely conventional (CMT) and cycle-step (CMT-CS). The welding system was equipped with a Fronius TransPulse Synergic 3200 CMT power source, a Fanuc Arc Mate 1000iC 6-axes robot with an R 30iA control unit, a welding torch, and a 1-axis positioner. The AA5087 aluminium alloy welding wire with a diameter of 1.2 mm was deposited onto the AA5083 aluminium alloy plate with dimensions of 70 mm x 200 mm x 3 mm during the experiment. The thermal cycles were documented using an Ahlborn Almemo 5690-2 measuring station equipped with K-type thermocouples. The thermal fields were monitored with a FLIR E95 thermography camera. The results showed the evident influence of arc mode on the temperatures developed in manufactured aluminium alloy parts during the process of WAAM.

Modulation of characteristic zones in NiTi alloys fabricated via wire arc additive manufacturing

The application of additive manufacturing (AM) is gradually extending to different industrial sectors. Most additively manufactured metallic components typically exhibit an inherent columnar grain structure, the control of which has been a challenging issue. In this study, the microstructures of the characteristic zones (heat-affected zone and transition zone) were controlled by adjusting the deposition strategy and arc mode during wire arc additive manufacturing (WAAM) of NiTi alloy. Compared to the sample fabricated by cold metal transfer (CMT) mode, the oscillating (O) sample shows a higher tensile strength of 793.6 MPa, while the pulsed (P) sample shows a better elongation of 5.8%. The high strength of the O samples is mainly due to the significantly lower aspect ratio of its columnar grains, while fine equiaxed grain structure in the transition zone of the P samples is responsible for the better plasticity. Different microstructures in the characteristic zones can be tailored by combining the forced melt flow, pulse frequency and undercooling, which provides vast freedom for the associated mechanical properties control. Our work provides a new strategy to regulate the microstructure and thus mechanical properties of additively manufactured NiTi alloys.

Effect of Filler Wires on Welding Strength and Microstructural Changes of Inconel 718 and AISI 316L Dissimilar Weldments

In this research, the effect of fillers wires on weldability, welding strength and structural changes of dissimilar welds of Inconel 718 and AISI 316L are studied. Pulse arc mode in TIG welding with multiple passes were used to join V-groove configuration with 1.6 mm filler diameter. Constant welding parameters were used for both the weldments to study the effect of alloying elements of filler wires. Tensile properties were evaluated by conducting tensile test on universal testing machine as per ASTM E/8 standards. To reveal the structural changes at various zones of weldment, optical microscope was utilized. The dissimilar metals were joined successfully using two-filler wires without any internal defects. The highest tensile strength of 553 MPa was observed in Hastelloy filler weldment when compared with ERNiCrMo-4 filler weldment (530 MPa). Also, the better yield strength properties were observed in Hastelloy filler weldment. Well defined with clear grain boundaries were observed in both the filler weldments. Due to the pulsed arc mode, segregation of alloying elements was reduced.

Effect of arc mode on laser-arc hybrid additive manufacturing of Al–Cu alloy: Pore defects, microstructure and mechanical properties

Laser-arc hybrid additive manufacturing (LAHAM) of Al–Cu alloy was carried out to investigate the effects of different arc modes on pore formation, microstructure characteristics, and tensile properties. The introduction of high-frequency pulse current and cyclic polarity reversal in the CMT-PADV mode was found to be beneficial for reducing pores. Compared with CMT and CMT-P modes, the CMT-PADV mode exhibited a transformation from columnar grains to equiaxed grains, with the smallest grain size of 26.6 μm, the highest fraction of high-angle grain boundaries of 84.2 %, and the longest length of grain boundaries reaching 14.9 cm. Moreover, the eutectic structure along the grain boundaries was observed in the samples fabricated by CMT and CMT-P modes, while it appeared disrupted and intermittently distributed in the CMT-PADV mode. In this case, the excellent mechanical properties were obtained for CMT-PADV mode, with tensile strength and elongation 276.6 MPa and 23.82 % in horizontal directions, 262.9 MPa and 20.9 % in vertical directions, respectively.

Metallurgical, mechanical and corrosion behavior of Interpulse and pulsed current TIG dissimilar welds of Monel 400 and AISI 316L

This research work explores the weldability, structural integrity, mechanical properties, and corrosion behavior of dissimilar welds of Monel 400 and AISI 316L developed by using Interpulse and pulse arc current modes in TIG welding process. ERNiCrMo-3 filler of 1.6 mm was used to fill the V-groove configuration of 5 mm thick plates in multiple passes. Metallurgical changes were observed in both Interpulse and pulsed current dissimilar weldments using optical and scanning electron microscope techniques. Mechanical properties of the joined structures were evaluated by performing tensile tests on UTM and hardness measurements on weld surfaces using Vickers hardness tester. The resistance against the corrosion especially at the weld area of both welded structures was measured using a cyclic sweep test. From the XRT and visual inspection analyses, the joined structures were free from defects and also seen the uniformity of the filler distribution toward the base metals. The grain structure with well-defined grain structures were identified in PC-TIG weldments whereas fine grains with clear distribution of filler alloying elements were seen in Interpulse-TIG weldments. Interpulse-TIG weldments exhibited with better mechanical and corrosion resistance properties than the PC-TIG weldments vowing to constricted arc mode during the welding process.

Radiotherapy of prostate and head-and-neck tumour: An optimal treatment planning comparison for intensity modulated radiotherapy and volumetric modulated arctherapy techniques.

To evaluate and compare merits between intensity modulated radiotherapy and volumetric modulated arc-therapy radiotherapy techniques to determine which technique can achieve better treatment plan quality and efficient delivery. The retrospective study was conducted at the Radiation Oncology Department of SanBorotlo Hospital, Vicenza, Italy, in 2019, and comprised data from Jan 2019 to Dec 2019 related to prostate and head-and-neck patients in whom Pinnacle³ treatment planning system was used for optimisation with different prescribed doses and target geometries for intensity modulated radiotherapy and volumetric modulated arc-therapy techniques. Treatment plans were simulated using 6MV photon beam of SynergyS® Linac (Linear accelerator). The plan quality was evaluated using dose-volume indices for planning target-volume and organs-at-risk. ArcCHECK™ phantom was used for dose agreement verification between planed and delivered doses. Data of 8 patients was analysed. Intensity modulated radiotherapy and volumetric modulated arc-therapy treatment plan quality for prostate was found to be similar, but volumetric modulated arc-therapy had significant results for maximum dose (p=0.005). Intensity modulated radiotherapy and volumetric modulated arc-therapy plans for head-and-neck achieved adequate target coverage and sparing of organs at risk, and produced clinically acceptable treatment plans. The percentage of target coverage (p=0.001), dose maximum (p=0.013) and conformity index (p=0.000) were significant. A significant gain for all planning target volume dose-volume indices was noted (p<0.05). Volumetric modulated arc-therapy obtained better plan with significant values and improved sparing of organs at risk compared to intensity modulated radiotherapy for both prostate and head-and-neck treatments while maintaining doses to the organs at risk (p<0.05). Dynamic arc mode of beam delivery provided increased degrees of freedom of volumetric modulated arc-therapy beam intensity modulation, depicting superior dose distribution than intensity modulated radiotherapy.

Investigation of the influence of opening speed on vacuum arc under transverse magnetic field

The objective of this paper is to investigate the vacuum arc characteristics on transverse magnetic field (TMF) contacts at different opening speeds. Experiments are carried out at different opening speeds. The experimental current ranges from 7 to 16 kA (peak current) at approximately 50 Hz. The contact material is CuCr30. The results show that increasing the opening speed increases the expansion speed of the arc after ignition. A higher opening speed increases the gap distance at which an anode spot occurs and reduces the duration of the instability stage, and it also reduces the duration of the motion stage. The arc motion can be optimized by adjusting the opening speed. The moment of contacts separation has no obvious influence on the gap distance at the transition of the arc mode. When the arc ignites between the arms, it expands slowly. This phenomenon is analyzed by a finite element method. The simulation results show that the ignition position influences the current direction, which influences electromagnetic force of the arc. The radial electromagnetic force is smaller when the arc ignites between the arms, causing a stagnation of the arc.

P6322-type SrNiIO6: An ideal half-metallic candidate with a fully spin-polarized Weyl complex

Researchers are interested in magnetic topological materials because they can integrate magnetic and topological properties. Using the first-principles calculations, we identify the P6322-type SrNiIO6 as a dynamically stable half-metallic candidate with a completely spin-polarized Weyl complex formed by two hourglass charge-3 and six charge-1 Weyl points. Furthermore, distinct surface arcs linked the projections of two spin-polarized charge-3 Weyl points and six spin-polarized charge-1 Weyl points, resulting in a fully spin-polarized sextuple-helicoid surface arc mode on the (001) surface of P6322-type SrNiIO6. P6322-type SrNiIO6 with fully spin-polarized charge-3 and charge-1 Weyl points and a fully spin-polarized sextuple-helicoid surface arc mode is, without a doubt, a promising candidate for applications in spintronic and topological physics.

2-D Dynamic Excitation Temperature of Cu+ Under Diffuse Mode in Vacuum Arc

Cu I (Cu neutrals) excitation temperature is usually measured by researchers while analyzing vacuum arcs (ignited by CuCr electrodes). Since ions may have information that neutrals do not have, measuring Cu II (Cu <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{+})$</tex-math> </inline-formula> might reveal some new features of the vacuum arc. In this article, Cu II excitation temperature is measured by observing seven Cu II lines. Measurement results show the existence or not of a Cr component in a vacuum arc can greatly change the 2-D distribution pattern of Cu II excitation temperature (researchers suggest no influence on Cu I); from a “flat” shape changes to a “columnar” or a “bowl” shape (related to gap length). However, the Cr ratio in CuCr electrodes does not cause a noticeable difference both in Cu II excitation temperature value and in 2-D distribution shape. In the case of CuCr electrodes, before the arc mode change to anode spot mode, a new phenomenon occurs under diffuse mode; as the arc current grows higher than a critical value under a certain length of the gap, the temperature starts to drop in the area near the anode surface, forming a temperature valley. This temperature valley can be interpreted as a local increase in Cu II density. The local ion eruption caused by the Cr component might be a trigger or a pre-process for arc mode changing to anode spot mode.

Quenched and Tempered Steels Welded Structures: Modified Gas Metal Arc Welding-Pulse vs. Shielded Metal Arc Welding

Quench and tempered (Q&amp;T) steels are widely used for a diverse range of applications, particularly in the mining and defence industry, where wear and unconventional loading are common. Furthermore, they are particularly prone to hydrogen assisted cold cracking (HACC), imposing a more careful selection of consumables and requiring a comparably higher welder skill level to fabricate defect-free structures. Therefore, the cost of fabrication of welded structures is higher when the more preferred welding technique of shielded metal arc welding, SMAW, is employed. The introduction of the modified pulsed arc mode of depositions, a variation to pulsed arc deposition, has improved the productivity rates and can be utilised by welders with a greater skill variations. In this study, full-strength butt welds of Q&amp;T steel (AS/NZS 3597 Grade 700), with the thickness of 20 mm, are fabricated under a high level of restraint using both conventional SMAW and modified pulse gas metal welding (GMAW-P). The study investigated the economic feasibility of the two deposition modes and the propensity to cracking for the welded joints under high restraint conditions. Utilising the modified GMAW-P resulted in 63% and 88% reduction in the ‘Arc-On’ time and the total normalised fabrication time, respectively. However, strict controls must be implemented, due to the increased propensity to lack of fusion-type defects, to optimise the welding procedure and mediate for such defects if GMAW-P is to provide a techno-economically beneficial alternative to conventional SMAW when welding Q&amp;T steels.

Metallurgical, mechanical and corrosion behaviour of pulsed and constant current TIG dissimilar welds of AISI 430 and Inconel 718

This research work explore the weldability, structural integrity, mechanical properties and corrosion behaviour of dissimilar welds of Inconel 718 and AISI 430 developed by using constant and pulse arccurrent modes in TIG welding process. The welded structures defects for inspected by employing X-ray radiography images as well as macrostructures. Metallurgical changes were observed using optical & scanning electron microscope techniques. Mechanical properties of the joined structures were evaluated by performing tensile test on UTM and hardness measurements on weld surfaces using Vickers hardness tester. The resistance against the corrosion especially at the weld area of both welded structures was measured. The joined structures were free from flaws and also seen the uniformity of the filler distribution towards the base metals. The grain coursing with well-defined grain structures were identified in CC-TIG weldmentswhereas fine grains with clear distribution of filler alloying elements were seen in PC-TIG weldments. PC-TIG weldments exhibited with better mechanical and corrosion resistance properties than the CC-TIG weldments vowing to pulse arc mode during welding process. The aerospace and nuclear industries will benefit from the study's findings especially turbine disc and shaft assembly.