Metal Transfer Mode Research Articles

Effects of Active Gases on Droplet Transfer and Weld Morphology in Pulsed-Current NG-GMAW of Mild Steel

The current research of narrow-gap gas metal arc welding (NG-GMAW) primarily focuses on improving the sidewall fusion and avoiding the lack-of-fusion defect. However, the high cost and operation difficulty of the methods limit the industrial application. In this study, small amount of active gases CO2 and O2 were added into pure argon inert shielding gas to improve the weld formation of pulsed-current narrow-gap gas metal arc welding (NG-GMAW) of mild steel. Their effects on droplet transfer and arc behavior were investigated. A high-speed visual sensing system was utilized to observe the metal transfer process and arc morphology. When the proportion of CO2, being added into the pure argon shielding gas, changes from 5% to 25%, the metal transfer mode changes from pulsed spray streaming transfer to pulsed projected spray transfer, while it remains the pulsed spray streaming transfer when 2% to 10% O2 is added. Both CO2 and O2 are favorable to stabilizing arc and welding process. O2 is even more effective than CO2. However, O2 is more likely to cause slags on the weld surface, while CO2 can improve the weld appearance in some sense. The weld surface concavity in NG-GMAW is greatly influenced by the addition of active gas, but the weld width and weld penetration almost keep constant. This study proposes a new method which is beneficial to improving the weld bead formation and welding process stability.

Classification of transfer modes in gas metal arc welding using acoustic signal analysis

Gas metal arc welding (GMAW) is a welding process in which an electric arc is formed between a wire electrode and a metal workpiece alongside a shielding gas to protect the arc from contaminants. There are several ways in which the molten electrode droplet can be transferred to the weld pool known as metal transfer modes. Identifying the metal transfer mode automatically is essential to monitor and control the welding process, especially in automated processes employed in modern Industry 4.0 manufacturing lines. However, limited research on this topic has been found in literature. This paper explores the automatic classification of metal transfer modes in GMAW based on machine learning techniques with various signals from the welding process, including acoustics, current, voltage and gas flow rate signals. Time and frequency domain features are first extracted from these signals and are used in a support vector machine classifier to detect the metal transfer modes. A feature selection algorithm is proposed to improve the prediction rate from 80 to 99% when all four signals are utilised. When only the non-intrusive acoustic signal is used, the prediction rates with and without the proposed feature selection algorithm are approximately 96% and 81%, respectively. The high prediction rate demonstrates the feasibility and promising accuracy of the acoustic signal–based classification method for future smart welding technology with real-time adaptive feedback control of the welding process.

Gas Metal Arc Welding Modes in Wire Arc Additive Manufacturing of Ti-6Al-4V.

In wire arc additive manufacturing of Ti-alloy parts (Ti-WAAM) gas metal arc welding (GMAW) can be applied for complex parts printing. However, due to the specific properties of Ti, GMAW of Ti-alloys is complicated. In this work, three different types of metal transfer modes during Ti-WAAM were investigated: Cold Metal Transfer, controlled short circuiting metal transfer, and self-regulated metal transfer at a direct current with a negative electrode. Metal transfer modes were studied using captured waveform and high-speed video analysis. Using these modes, three walls were manufactured; the geometry preservation stability was estimated and compared using effective wall width calculation, the microstructure was analyzed using optical microscopy. Transfer process data showed that arc wandering depends not only on cathode spot instabilities, but also on anode processing properties. Microstructure analysis showed that each produced wall consists of phases and structures inherent for Ti-WAAM. α-basketweave in the center of and α-colony on the grain boundary of epitaxially grown β-grains were found with heat affected zone bands along the height of the walls, so that the microstructure did not depend on metal transfer dramatically. However, the geometry preservation stability was higher in the wall, produced with controlled short circuiting metal transfer.

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

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

Effect of Filler Metal Type on Microstructure and Mechanical Properties of Fabricated NiAl Bronze Alloy Using Wire Arc Additive Manufacturing System

This study observed the effect of filler metal type on mechanical properties of NAB (NiAl-bronze) material fabricated using wire arc additive manufacturing (WAAM) technology. The selection of filler metal type is must consider the field condition, mechanical properties required by customers, and economics. This study analyzed the bead shape for representative two kind of filler metal types use to maintenance and fabricated a two-dimensional bulk NAB material. The cold metal transfer (CMT) mode of gas metal arc welding (GMAW) was used. For a comparison of mechanical properties, the study obtained three specimens per welding direction from the fabricated bulk NAB material. In the tensile test, the NAB material deposited using filler metal wire A showed higher tensile strength and lower elongation (approx. +71 MPa yield strength, +107.1 MPa ultimate tensile strength, −12.4% elongation) than that deposited with filler metal wire B. The reason is that, a mixture of tangled fine α platelets and dense lamellar eutectoid α + κIII structure with β′ phases was observed in the wall made with filler metal wire A. On the other hand, the wall made with filler metal wire B was dominated by coarse α phases and lamellar eutectoid α + κIII structure in between.

Metal Transfer Mapping for Flux-Cored Arc Welding Process by Using Near-Infrared Filming

In the flux-cored arc welding (FCAW) process, the transfer of filler metal to the base material to accomplish the weld bead, determines the weld quality. It must be pointed out that the radiation emitted from the weld arc, fumes and particles (spattering) in this process represent a barrier for these studies based on the process visualization. The objective of this study is to assess metal transfer during the FCAW process of ASTM 1020 steel by filming the phenomena with assistant of near-infrared visualization, contributing to a better understanding of this process and to evaluate characteristics of metal transfer. It can clearly be seen that how the droplet is created and transferred in this process and also identify the different modes of metal transfer by changing the parameters of voltage and wire feed speed in metal transfer maps. Finally, having achieved the metal transfer maps, the suitable condition and approach for developing arc control strategies for the FCAW process were introduced.

Effect of wire feeder force control on laser metal deposition process using coaxial laser head

Laser based Direct Energy Deposition (DED), also called Laser Metal Deposition (LMD), is a process that is widely used for cladding and repair applications and increasingly for additive manufacturing processes [Chen Hong, Dongdong Gu, Donghua Dai, Andres Gasser, Andreas Weisheit, Ingomar Kelbassa, Minlin Zhong, and Reinhart Poprawe, Opt. Laser Technol. 54, 98–109 (2013)]. Its controlled energy input and its ability to control the dilution allow the use of less material and the production of thin and precise layers increasing productivity and reducing costs [Erwin Werner Teichmann, “Analysis of welding process variants aiming cladding with Inconel 625 of API X46 steel pipes,” Ph.D. thesis in Mechanical Engineering, Post-Graduation Program in Mechanical Engineering, Federal University of Santa Catarina—UFSC, Florianópolis, 2016, p. 213, see https://repositorio.ufsc.br/handle/123456789/17223 (accessed 12 May 2020); Thomas Schopphoven, Andres Gasser, and Gerhard Backes, “EHLA: Extreme high-speed laser material deposition,” Laser Tech. J. 14, 26–29 (2017)]. Associated with those characteristics is the ability to operate using both powder and wire additives. The last one presents a series of advantages, as lower price per kilogram, lower porosity on the deposited material, and lower health risks for users. The use of a coaxial wire feeding laser head allows an omnidirectional operation for the laser head, presenting a great advantage when compared to lateral feeding systems. For soldering applications, some suppliers offer wire feeding systems that allow one to control the force applied by the wire on the substrate. This system measures the contact between the wire and the bottom of the melt pool, enabling a bridge metal transfer mode. The bridge transfer mode is essential, since the surface tension plays the main influence and, on the other hand, gravity plays only a minor role in the metal transfer. The results of using a force control system with different settings and a comparison between samples produced with and without this control are discussed. The material for both, samples and wire, is the stainless steel 316L. To assist the analysis, high-speed videos, process data acquisition, and macrographs are made.

Construction of metal transfer modes maps for an ER4130 filler metal in GMAW process

Metal transfer modes (MTMs) maps were constructed for GMAW process using ER4130 and 98%Ar-2%O2 shielding gas. There is no available MTMs maps for this filler metal which is used to obtain matching strength in welds of AISI 4130/4140 steels. These maps serve as tools to establish the MTM given a welding current and voltage, which is useful when an engineer is trying to qualify welding procedures according to construction codes. The maps were built analyzing current and voltage signals recorded at 5000 samples/second during bead-on-plate welds. The main advantage of this methodology is its simplicity of instrumentation without expensive cameras, but has low resolution and it is difficult to identify finer characteristics of MTMs, such as subgroups (repelled globular, streaming, rotational spray), drop diameter, explosive transfer, etc. Several MTMs were identified in the signal analysis and grouped into natural MTMs (short circuit, globular and spray) and interchangeable modes (short-circuit-globular, globular-spray and short-circuit-globular-spray).

Effects of Filler Wire Intervention on Gas Tungsten Arc: Part II - Dynamic Behaviors of Liquid Droplets

In gas tungsten arc welding (GTAW), the filler wire in-creases the deposition efficiency and influences the welding stability. Its interactions with the gas tungsten arc (GTA) are significant to better understand the welding process and to monitor and control weld quality. In view of this, the first part of the work, Effects of Filler Wire Intervention on Gas Tungsten Arc: Part I — Mechanism, explained the inter-action mechanisms between the filler wire and the gas tungsten arc based on the proposed arc-sensing method of detecting probe voltage (i.e., the voltage signal between the filler wire and the tungsten electrode/workpiece). In this second part of the work, experiments were designed to make the filler wire melt in different areas of the arc to study the dynamic behaviors of the droplet and its effect on the arc. Typical metal transfer modes are discussed, and droplet oscillation is geometrically characterized through image processing and then analyzed in the time domain and time-frequency domain. The results show that the liquid droplet affects the arc through its transfer to the weld pool, its oscillation, and occupying the arc space. Information about these dynamic behaviors can be easily reflected in the probe voltage, which would be a valuable signal to monitor the process stability in GTAW with filler wire. This work shows the potential of the proposed sensing method for monitoring and controlling weld quality in all welding positions, GTA-based additive manufacturing, etc.

Effects of cold metal transfer mode on the reaction layer of wire and arc additive-manufactured Ti-6Al-4V/Al-6.25Cu dissimilar alloys

Components of Ti and Al dissimilar alloys were obtained by wire and arc additive manufacturing using two cold metal transfer (CMT) modes. Direct current CMT (DC-CMT) mode was used for Ti alloy deposition, and DC-CMT or CMT plus pulse (CMT + P) mode was used for the Al alloy deposition. During deposition of the first Al alloy layer, little and a significant amount of Ti alloy were melted using DC-CMT and CMT + P mode, respectively. TiAl3 formed in the reaction layer when DC-CMT mode was used, while TiAl3, TiAl, and Ti3Al formed in the reaction layer when CMT + P mode was used. Compared to using DC-CMT mode, more cracks occurred when using CMT + P. The nanohardness of the reaction layer was between that of the Al and Ti alloys, irrespective of the CMT modes. The average tensile strengths of the samples using DC-CMT and CMT + P mode were 108 MPa and 24 MPa, respectively. DC-CMT mode was more suitable for the wire and arc additive manufacturing of Ti/Al dissimilar alloys.

Analysis of metal transfer and weld geometry in hot-wire GTAW with indirect resistive heating

In this publication, the different metal transfer modes of a hot-wire GTAW process with indirect resistive preheating of the wire are presented. The hot-wire GTAW process is characterized by an additional preheating unit that is used to heat the wire before it reaches the melt pool. Thus, to preheat the wire, the contact between the melt pool and the wire is not necessary. In order to examine the metal transfer of the wire, deposition welds are analysed using a high-speed camera with a laser light source as well as a data acquisition unit. The presented results comprise the impact analysis of the GTAW current, the hot-wire current, the wire feeding rate, the wire feeding angle as well as the wire feeding direction. The observed metal transfer modes can be characterized as either a constant melting bridge (cmb) between the wire and the melt pool or a recurring melting bridge (rmb). The analysis also reveals that the influence of the process parameters and thus the metal transfer mode on the bead properties is only marginal.

Expert System Analysis of TIG Molten Weld Metal Fluidity Using the Bond Dimensionless Number

The different modes of molten metal transfer makes up a critical aspect of welding behavior which significantly affects weld quality, so having basic understanding of the fluidity behavior of the molten weld metal will help Fabrication experts to produce weld structures with optimal strength and quality. In this present work, the Expert analysis of TIG molten weld metal fluidity using the Bond dimensionless Number was achieved. An expert experimental design was done generating 30 sets of experimental runs considering current voltage wire diameter and wire feed rate and the bond dimensionless number as response. The second order quadratic model was developed employing the response surface methodology. A model having 89% coefficient of determination and p-value of < 0.0001. The result obtained showed that current has a very significant effect on the bond number indicating that a higher current will minimize the bond which translates into an improved fluidity of the TIG molten weld metal.

The effect of wire size on high deposition rate wire and plasma arc additive manufacture of Ti-6Al-4V

Wire + arc additive manufacture (WAAM) is suitable for building large-scale components with high deposition rate. However, in order to further increase the deposition rate of Ti-6Al-4V to improve productivity and reduce manufacture costs without significantly compromising the quality, some fundamental process characteristics need to be investigated. In this paper, the effect of wire size on the limitation of deposition rate and bead shape in plasma arc additive manufacture was studied along with the process tolerance and melting characteristics, such as the effect of current and nozzle size on keyhole behaviour and the effect of wire feeding position on deposition process. The results show that with the same heat input the deposition rate increases linearly with the wire size due to the increasing melting efficiency. The bead geometry obtained with a thinner wire has a higher aspect ratio, which can be attributed to the difference in the distribution of the energy between wire and workpiece. The likelihood of keyhole increases with increasing current and decreasing nozzle size, and it can be mitigated by using thicker wires. The wire feeding position plays a significant role in determining the metal transfer mode, which has a great impact on the bead shape and process stability. Also, as the deposition rate changes thin wire is more sensitive to wire feeding position than thick wire in terms of metal transfer behaviour.

Uncertainty analysis of a water flow calorimeter while welding in short-circuit and spray transfer regimes

The thermal efficiency of arc welding influences the cooling rate, peak temperature, and microstructures of a weld, which affects the material properties of the welded joint. This work quantifies the uncertainty of thermal efficiency measurements on gas metal arc welds using low (2.5 kW) and high (9.5 kW) arc powers. In order to understand the effect of calorimeter parameters on the measured efficiency, a two-factor, two-level full factorial design was carried out for each arc power condition. In this study, the factors are flow rate (2 l/min and 5 l/min) and plate thickness (0.25 in. [6.35 mm] and 0.375 in. [9.53 mm]). The results show that the uncertainty in the thermal efficiency measurements increases when both higher flow rates and plate thickness are used. Moreover, the use of a thick plate causes the heat transfer regime to change, increasing the cooling rate and decreasing the observed thermal efficiency. Uncertainty is also influenced by the metal transfer mode during welding.

Wire and arc additive manufacturing of 4043 Al alloy using a cold metal transfer method

Cold metal transfer plus pulse (C + P) arc was applied in the additive manufacturing of 4043 Al alloy parts. Parameters in the manufacturing of the parts were investigated. The properties and microstructure of the parts were also characterized. Experimental results showed that welding at a speed of 8 mm/s and a wire feeding speed of 4.0 m/min was suitable to manufacture thin-walled parts, and the reciprocating scanning method could be adopted to manufacture thick-walled parts. The thin-walled parts of the C + P mode had fewer pores than those of the cold metal transfer (CMT) mode. The thin- and thick-walled parts of the C + P mode showed maximum tensile strengths of 172 and 178 MPa, respectively. Hardness decreased at the interface and in the coarse dendrite and increased in the refined grain area.

The effect of metal transfer modes on mechanical properties of 3CR12 stainless steel

The effect of metal transfer modes on mechanical properties of welded 3CR12 stainless steel was investigated. This was achieved by butt welding 10 mm thick plates of 3CR12. The effect of the metal transfer modes on the microstructure and the mechanical properties of the 3CR12 steel was then investigated as it was hypothesized that the change in welding positions will affect the transfer modes partly because of gravity. The microscopic examination revealed that the substrate was characterized by dual phase microstructure. Using the spectroscopic examination results, the ferritic factor calculation had shown that the microstructure was expected to be ferritic–martensitic during air cooling process. The tensile strength and Charpy impact energy were measured to be 498 MPa and 102 J, respectively. The heat input in the material was observed to be greater than 1 kJ/mm, which is the limiting factor for grain growth. Grain growths were observed in the heat affected zone of the welded materials. Ferritic–martensitic microstructure was observed in the microstructure. The grain growth altered the mechanical properties of the test material. Globular down hand had higher mechanical properties than spray down hand. Globular vertical up had better mechanical properties than globular vertical down.

Interactive Phenomena in Hybrid KPAW–GMAW-P

A hybrid welding technique formed by combining keyhole plasma arc welding (KPAW) and pulsed gas metal arc welding (GMAW-P) is characterized by the complex interactions of the arc, droplet, keyhole, and weld pool. With the help of a high-speed video camera, zirconia particles, and a thermal camera, the complex interactive phenomena of the hybrid KPAW–GMAW-P process was analyzed. Owing to the formation of a direct-current path between the KPAW cathode (tungsten electrode) and the GMAW anode (welding wire), the ionized plasma arc was extended to the GMA side, causing an expansion of the GMA. The current at the GMAW droplet was diverged; thus, the Lorentz force promoted a more stable one pulse one droplet metal transfer mode compared with that of GMAW-P. The strong backward flow from the keyhole was suppressed because of the pull-push flow pattern on the top surface of the weld pool be-tween the two arcs. As the heat and molten metal in the weld pool were transported from the region near the GMA (high temperature) to the region near the plasma arc (low temperature), the weld pool temperature decreased.

Underwater Pulse-Current FCAW - Part 1: Waveform and Process Features

The typical metal transfer mode in conventional underwater wet flux cored arc welding (FCAW) delivers large droplet repulsive transfer with low frequency. The process stability and the weld quality are seriously deteriorated with significant spatter and frequent arc extinctions. It is thought the repulsive forces applied on droplets can be reduced by rapidly decreasing the welding current, making the droplets sag and oscillate. A novel underwater pulsecurrent FCAW was proposed to periodically regulate the forces applied on droplets. The experimental system was developed with specially designed pulse current and reliable arc length control. Visual and electrical signals were collected simultaneously to study the process features. It was found that the maximum droplet diameter decreased to less than 5 mm; the temporary arc-extinguishing frequency decreased significantly; there was almost no short-circuit transfer and surface-tension transfer; and the stability of the welding process was significantly improved.

Effect of welding parameters on weld formation quality and tensile-shear property of laser welded SUS301L stainless steel lap filet weld

Laser welding of lap-filet joints SUS301L austenitic stainless steel plates were carried out with filler wire. Results showed that the weld zone was composed of columnar austenite and a small amount of δ-ferrite. The effect of feed direction, wire distance (H), laser incident position (L) and laser incident angle on the wire melting mechanism, weld pool geometry, metal transfer modes and heat distribution were studied with the assistance of the high speed camera recording the welding process. Better weld quality was obtained under the circumstances of leading direction, wire distance 0.5mm, laser incident position 0.5mm, and laser incident angle 0̊. The fracture was always located in the weld where the thickness of it was the smallest. There was a linear relationship between the weld width and the smallest weld thickness. The maximum tensile-shear force was 24.46kN. The fracture mode was ductile fracture with fracture surface dimples.

Fabrication of metallic parts with overhanging structures using the robotic wire arc additive manufacturing

Abstract Robotic wire arc additive manufacturing (WAAM) technology has been widely employed to fabricate medium to large scale metallic components. It has the advantages of high deposition rates and low cost. Ideally, the deposition process is carried out in a flat position. The build direction is vertically upward and perpendicular to a horizontal worktable. However, it would be difficult to directly deposit complex parts with near horizontal ‘overhangs’, and temporary supports may be required. Thus, it is necessary to find an alternative approach for the deposition of ‘overhangs’ without extra support in order to simplify the deposition set-up. This paper proposed a fabrication method of producing metallic parts with overhanging structures using the multi-directional wire arc additive manufacturing. Firstly, based on the metal droplet kinetics and weld bead geometry, two different Gas Metal Arc Welding (GMAW) metal transfer modes, namely short circuit transfer and free flight transfer, were evaluated for the multi-directional wire arc additive manufacturing. Subsequently, the effects of process parameters, including wire feed speed (WFS), torch travel speed (TS), nozzle to work distance (NTWD) and torch angle, on the stability of positional deposition were investigated. Finally, the effectiveness of the proposed strategy was verified by fabricating three complex samples with overhangs.