Wire Melting Research Articles

Investigation of formation, microstructure and hardness of Ti-6Al-4V single tracks via Joule-fused filament additive manufacturing

Purpose This paper aims to investigate a novel additive manufacturing (AM) method for titanium alloy using Joule heat as the single heat source to melt TC4 wire, which intends to provide a new low-power, low-cost solution for the processing of titanium alloys. Design/methodology/approach When current flows through the wire and the substrate, Joule heat will be generated to melt the wire and join the wire with the substrate. By stacking the wire layer by layer, finally a part can be formed. The cross-sectional morphology, microstructure and hardness of TC4 single track deposits formed by Joule heat melting wire AM were investigated by various characterization methods. Findings The melting width and melting penetration decreased with the increase of printing speeds. There is no obvious change in single track morphology with the change of printing pressures. The melting width and melting penetration increased with the increase of printing currents. The observation of the internal microstructure of a single track reveals a decrease in grain size as printing speeds increase. The average hardness of the single track was about 363 HV, which is comparable to the hardness of the parts fabricated by selective laser melting process. The printing power is less than 300 W, which is lower than other AM processes. Originality/value This paper provides a novel solution for the processing of titanium alloy parts. Compared with other expensive energy sources, this work only uses an ordinary DC power supply as the energy source. The printing process is simple and the cost is low. The power is much lower than other AM processes.

Investigation on titanium wire melting through high-frequency induction heating for additive manufacturing process

ABSTRACT A high-frequency induction heating (HFIH) system is a novel and clean heat source that can potentially melt high melting point material to develop the wire feed-based additive manufacturing (AM) process. The present study establishes the optimised coil parameters, including coil geometry for melting the titanium wire using induction heating. A fully coupled electromagnetic-thermal-fluid flow model is established to analyse the temperature profile of the wire. The wire feed velocity (0.012 m/s) is incorporated in the coupled model using the deformed mesh method. Optimised wire diameter and coil parameters, such as a three-turn helical coil with a circular cross-section, coil turn spacing of 1.5 mm, and a coupling distance of 4 mm, melt the 3.6 mm titanium wire rapidly and create the molten droplet. The results suggest that the optimised coil parameters improve the magnetic flux density, which enhances joule heating in the wire. However, the conical-spiral coil geometry of the three-turn fails to melt the wire completely. In contrast, the helical coil of the three-turn melts the wire completely. The maximum velocity of the molten metal is found as 0.25 m/s. Effectively, the heat transfer and material flow analysis drives to develop the potential additive manufacturing system.

Technological Features of Filler Wire Melting for Arc Welding and Surfacing with the Introduction of SF6 into Protective Gas Atmosphere

On the basis of the results of experimental studies the paper establishes important patterns of dependence of the frequency of short circuits of the arc gap and the coefficient of loss of electrode metal due to spatter from the voltage on the arc and the feed rate of the filler wire during welding and surfacing with the introduction of gaseous SF6 into the Ar + CO2 protective mixture. It is proposed to introduce fluorine-containing components of SF6 directly into the protective gas mixture of 82 % Ar + 18 % CO2 in quantities not exceeding 2 %. The technology makes it possible to reduce the amount of diffusion hydrogen in the deposited metal, which is an urgent task when welding high-strength steels and materials sensitive to hydrogen embrittlement. Previously, we resolved a number of issues related to the obstacle to increasing the concentration of S in the deposited metal, which made it possible to determine the most effective concentrations of SF6 in the protective gas environment, limited to 1.5 % by volume of the total composition (Ar + CO2) + SF6. At the same time, modification of the protective gas atmosphere with the halide compound SF6 has a significant effect on the melting characteristics of the electrode wire and temperature indicators in the arc combustion zone. This is due to the high ionization potential of fluorine as a product of the high-temperature dissociation reaction of SF6. The results obtained have made it possible to determine the most effective relationships between the values of the mode parameters, as well as to study the specifics of melting the filler wire in a protective atmosphere modified with SF6. Important regularities have been established that reveal the technological features of welding and surfacing with modification of the protective atmosphere with halide compounds.

Additive manufacturing of quartz glass using coaxial wire feeding technology

This study explores the process of coaxial wire feeding and melting for quartz additive manufacturing using Direct Energy Deposition (DED). Quartz glass, valued for its excellent mechanical, optical, and thermal properties, is widely used in semiconductor, aerospace, and optical communication industries. Additive manufacturing offers advantages such as cost-effective materials, rapid formation, and customization of structures. However, current methods for additive manufacturing of quartz glass often result in low quality or require complex post-processing, particularly for optical components. In optics, there is a demand for high-quality, straightforward processes, and custom-shaped quartz glass. This article presents a coaxial wire feeding mechanism wherein quartz wire is fed vertically downward along the optical axis into the melting zone created by a CO2 laser, facilitating smooth material deposition onto the molten zone’s surface. Laser power, wire feeding speed, substrate movement speed, and defocusing distance are key factors influencing the quality of single-layer quartz glass formation. Positive defocusing was found to have a beneficial impact on single-layer quartz glass additive manufacturing. Subsequently, optimized process parameters enabled the production of uniformly cross-sectional single-layer quartz glass. Microscopic morphology analysis and temperature field simulation were conducted on the experimental results before and after optimization. Finally, complex quartz glass structures were additively manufactured using the optimized experimental parameters. Results demonstrate that coaxial wire feeding technology has significant potential for achieving uniform dimensions and complex structures in quartz glass additive manufacturing.

Study on droplet transfer behavior and spattering mechanism in Mg-Gd-Y-Zr alloy regulated short circuit (Fronius CMT) welding

The quality, performance, and morphology of Mg-Gd-Y-Zr alloy regulated short circuit (Fronius CMT) welding components is directly depend on whether the droplet transfer process is stable. However, due to the inherent properties of the material, Mg-Gd-Y-Zr alloy is highly sensitive to heat input, and prone to spattering in the process of droplet transfer. In this work, three types of spattering were observed through high-speed cameras, which are caused by internal burst of droplet, wire withdrawal, and repelled transfer. Causal relationship of spattering mechanism and process parameter was explored especially in the stage of wire melting and droplet growth, and a simplified numerical model was used as an auxiliary means to further reveal the spattering of repelled transfer. The result indicated that the recoil pressure of metal vapor is the vital factor which destabilize the shape and motion trajectory of droplet and eventually caused spattering. The range of the process parameter for achieving a stable droplet transfer and well-formed weld bead is relative narrow which the peak current is recommended between 150 A to 170 A, and peak duration around 7 ms.

Understanding the formation of laser-induced melt pools with both wire and powder feeding in directed energy deposition

Wire-powder fed directed energy deposition (WP-DED) has been applied to produce high-performance metal parts. Compared to DED with the feed of a single filler (either powder or wire), simultaneous WP-DED exhibits more complex interactions between fillers and laser-induced melt pools, such as additional powder collisions by wire, different filler properties, intricated heat transfer paths, etc. At present, there is little mechanistic understanding of the interactions among wire, powder particles, and laser-generated melt pools in the WP-DED. In this work, we discovered the filler-melt pool interactions in a coaxial wire-powder fed DED (CWP-DED) process by in situ experimental characterizations. In particular, we investigated the wire-influenced particle dynamics before entering the melt pool. When in-flight particles interact with the melt pool, the temporal-varied melt pool geometry as well as melt flow dynamics were characterized. The bubble formation and evolution in CWP-DED were also revealed. We found that the extruded wire would affect the trajectory of in-flight particles and reduce their velocity before the entry of melt pool due to the inelastic collision. The melt pool size decreased with powder feed rate; however, the powder feed rate had limited influences on the melt pool oscillation. Four modes of fluid flow were observed in the melt pool, including backward flow, upwards flow to the wire-melt pool interface, rebounded flow, and clockwise flow. At a high powder feed rate, more gas-induced bubbles occurred along the melt pool boundary and wire-melt pool interfaces. This study provides a fundamental understanding of filler-melt pool interactions during the CWP-DED process to advance the development of next-generation, fast-rate additive manufacturing technology.

Underwater wet welding of high-strength low-alloy steel using self-shielded flux-cored wire with highly exothermic Al/CuO mixture

Underwater wet welding processes with minimal energy consumption and high efficiency is the future goal for researchers in the field. Al/CuO exothermic mixtures in consumables for land welding process can improve welding process stability and decrease the electrical dependence of the welding process. To confirm the beneficial effects of Al/CuO thermite and gain a better understanding of metallurgical properties of the thermite welds in underwater environment, this study investigated underwater wet self-shielded flux-cored arc welding (FCAW-S) of high-strength low-alloy steel with highly exothermic Al/CuO mixture. The effects of Al/CuO thermite on arc stability, weld metallurgical behavior and melting characteristics of flux-cored wire were clarified. The ratio of chemical heat in the flux to the heat required to melt welding wire increased from 4.7% to 38.4% with the addition of Al/CuO, potentially accelerating the melting of flux-cored wires. The arc stability with thermite addition was superior to that without the addition of thermite. The presence of copper as a result of metallurgical reactions had a substantial impact on metallurgical behavior of underwater wet welds. The ferrite weld was a non-equilibrium Cu supersaturated solid solution, which increased the microhardness and tensile strength of wet welds. The measured cooling time proved that the incorporation of Al/CuO had the capacity to reduce cooling rate. The incorporation of 50 wt% thermite yielded a 7.8% increase in welding process efficiency compared to the base formulation. Current work provided an important direction for the development of a chemically self-heating flux-cored wire.

Experimental Study on Wire Melting Control Ability of Twin-Body Plasma Arc

The twin-body plasma arc has the decoupling control ability of heat transfer and mass transfer, which is beneficial to shape and property control in wire arc additive manufacturing. In this paper, with the wire feeding speed as a characteristic quantity, the wire melting control ability of twin-body plasma arc was studied by adjusting the current separation ratio (under the condition of a constant total current), the wire current/main current and the position of the wire in the arc axial direction. The results showed that under the premise that the total current remains unchanged (100 A), as the current separation ratio increased, the middle and minimum melting amounts increased approximately synchronously under the effect of anode effect power, the first melting mass range remained constant; the maximum melting amount increased twice as fast as the middle melting amount under the effect of the wire feeding speed, and the second melting mass range was expanded. When the wire current increased, the anode effect power and the plasma arc power were both factors causing the increase in the wire melting amount; however, when the main current increased, the plasma arc power was the only factor causing the increase in the wire melting amount. The average wire melting increment caused by the anode effect power was approximately 2.7 times that caused by the plasma arc power. The minimum melting amount was not affected by the wire-torch distance under any current separation ratio tested. When the current separation ratio increased and reached a threshold, the middle melting amount remained constant with increasing wire-torch distance. When the current separation ratio continued to increase and reached the next threshold, the maximum melting amount remained constant with the increasing wire-torch distance. The effect of the wire-torch distance on the wire melting amount reduced with the increase in the current separation ratio. Through this study, the decoupling mechanism and ability of this innovative arc heat source is more clearly.

Control of meltpool shape in laser welding

In laser welding, the achievement of high productivity and precision is a relatively easy task; however, it is not always obvious how to achieve sound welds without defects. The localised laser energy promotes narrow meltpools with steep thermal gradients, additionally agitated by the vapour plume, which can potentially lead to many instabilities and defects. In the past years, there have been many techniques demonstrated on how to improve the quality and tolerance of laser welding, such as wobble welding or hybrid processes, but to utilise the full potential of lasers, we need to understand how to tailor the laser energy to meet the process and material requirements. Understanding and controlling the melt flow is one of the most important aspects in laser welding. In this work, the outcome of an extensive research programme focused on the understanding of meltpool dynamics and control of bead shape in laser welding is discussed. The results of instrumented experimentation, supported by computational fluid dynamic modelling, give insight into the fundamental aspects of meltpool formation, flow direction, feedstock melting and the likelihood of defect formation in the material upon laser interaction. The work contributes to a better understanding of the existing processes, as well as the development of a new range of process regimes with higher process stability, improved efficiency and higher productivity than standard laser welding. Several examples including ultra-stable keyhole welding and wobble welding and a highly efficient laser wire melting are demonstrated. In addition, the authors present a new welding process, derived from a new concept of the meltpool flow and shape control by dynamic beam shaping. The new process has proven to have many potential advantages in welding, cladding and repair applications.

Lattice Boltzmann modeling of convective heat and solute transfer in additive manufacturing of multi-component alloys

Additive manufacturing (AM) is a remarkable breakthrough technology, allowing for the direct fabrication of three-dimensional components through the layer-by-layer stacking of materials. A novel free Surface lattice Boltzmann (LB) model is developed to simulate the heat and solute transfer in AM of multi-component alloys. The behavior liquid phase is described by using the free surface LB model, and the phase transitions between solid and liquid are modeled by using the LB-enthalpy method. A LB equation is directly constructed, which accounts for solute transfer in a certain multi-component alloys system. The thermodynamic information used in the calculation of phase transitions are determined by an extensive thermodynamic database. The model is validated via several benchmark examples of fluid flow and heat transfer. The characteristics of convective heat and solute transfer within various AM are investigated. Finally, the non-equilibrium convective heat transfer, phase transitions, and macroscopic segregation are discussed within the AM melt pools. The melt pool expands and convective heat transfer is enhanced by the Marangoni effect. Thus there is a consistent decrease in solute segregation. The solute segregation is more severe near the surface of the deposit layer. Additionally, the thermal convection experiences cyclic intensification attributed to the successive impact of multiple droplets in wire feeding and melting AM. This continuous impact serves to diminish the solute segregation. The results underscore the significant potential and advantages of LB method in accurately simulating the AM, which provides valuable insights for understanding the underlying mechanism of heat and solute transfer in materials and manufacturing.

Study of an additive manufacturing technology using pulsed inductive wire melting

Additive manufacturing is becoming increasingly widespread and has developed very dynamically in recent years. For the processing of metals, powder or wire is usually used as the feedstock. The energy source used in wire-based processes is usually electric arcs or lasers. In this contribution, a technological approach for additive manufacturing of metal structures by induction melting with pulsed generator power is used. Therefore, the principle of oscillating Lorentz forces is utilized in this approach and analytically investigated with the aid of a FE simulation model. In the experiments, a continuously fed steel wire is inductively melted and deposited dropwise onto a substrate heated to different preheating temperatures without the use of a nozzle or crucible.

Improved strength in nickel‑aluminum bronze/steel bimetallic component fabricated using arcing-wire arc additive manufacturing with alternating deposition strategy

To enhance microstructure and mechanical properties, arcing-wire arc additive manufacturing (AWAAM) with alternating deposition strategy was firstly employed to produce nickel‑aluminum bronze (NAB)-steel components. The implementation of alternating deposition strategy fostered the creation of interlocked microstructures, establishing robust bonds at the interface. Moreover, the convection within the melt pool during alternating deposition induced the formation of numerous precipitates, serving as a precipitation reinforcement. Simultaneously, these precipitates served as heterogeneous nucleation sites, facilitating the formation of substantial fine equiaxed crystals, resulting in grain boundary strengthening. A comprehensive examination of microstructure and mechanical properties was conducted using a variety of microscopy techniques and mechanical testing for components with and without arcing-wire. After applying arcing-wire, precise control was exerted over the melting of both matrix and wire, effectively preventing interface cracking caused by excessive melting. Moreover, with the arc heat input diminished, the temperature gradient in the melt pool decreased, leading to grain and precipitate refinement, consequently enhancing their strength. Owing to microstructural modifications, AWAAM demonstrated enhancements in ultimate tensile strength and yield strength by up to 20.1 % and 21.1 %, respectively, when compared to WAAM.

An operando synchrotron study on the effect of wire melting state on solidification microstructures of Inconel 718 in wire-laser directed energy deposition

Directed energy deposition (DED) with a coaxial wire-laser configuration has gained significant attention in recent years for the production of large-scale metallic components because of its low directional dependence, fast deposition rate, high feedstock efficiency, and low manufacturing costs. This work studies the coaxial wire-laser DED process of Inconel 718 alloy under a stable deposition condition with a relatively low input volumetric energy density (55.5 J/mm3). Post characterization reveals a cluster of refined grains at the center-bottom region of the as-printed track. Operando high-energy synchrotron X-ray experiments and multi-physics modeling are applied innovatively to study the fundamental mechanism responsible for the formation of this microstructure. The X-ray diffraction experiment provides direct evidence, which is supported by the simulation, that the feeding wire can reach the melt pool bottom and release solid particles (primarily carbides) near the mushy zone owing to insufficient melting. Consequently, these sub-micron sized particles suppress the growth of large columnar grains and cause the formation of unique microstructural heterogeneity. This discovery offers new opportunities for tailoring the solidification microstructure by controlling the melting state of the feedstock wire in DED process, in addition to commonly known factors such as the thermal gradient and solidification velocity.

Thermo-capillary-gravity bidirectional modelling for evaluation and design of wire-based directed energy deposition additive manufacturing

Wire-based directed energy deposition (w-DED) is an additive manufacturing process well-suited for building large-scale structural components. Deposit bead geometry and its relation to process parameters is a vital aspect of a w-DED process, which is crucial for preventing defects and minimising material waste. In this study, a thermo-capillary-gravity bidirectional analytical model is developed based on the fundamental governing physics, enabling fast predictions of both w-DED bead geometries and process parameters. A novel method is also proposed to determine the power transfer efficiency and wire melting efficiency defined in the model. In the forward modelling, deposit bead geometries, such as layer height and width, can be predicted for given process parameters and material properties. In the reverse modelling, the outputs of the model are process parameters, including heat source power and travel speed, to achieve the deposit bead geometries as required for a given application. This bidirectional modelling approach is applicable to different w-DED processes, and it has been validated for the deposition of steel walls using plasma transferred arc and cold wire gas metal arc processes. The developed bidirectional analytical model could be used as an efficient and reliable tool for w-DED process evaluation and design.

Thermal fluid dynamics of the effect of filler wire on deposition rate and bead formation intending plasma arc-based DED

The influence of filler wire configuration, such as size and geometry, on the deposition rate (DR) and bead formation, has been studied in wire arc-based directed energy deposition (WADED), but the fundamental physics underlying its effect on wire melting and melt pool dynamics remains unclear. In this paper, a series of plasma arc-based DED (plasma-DED) experiments were conducted to investigate the impact of five different filler wire configurations on DR and bead dimensions. The coupling behaviours of wire melting, metal transfer and melt pool dynamics under the five filler wire configurations were also simulated numerically using the authors' recently developed wire-feeding model. The calculated wire melting and bead cross-sections are consistent with the experimental images and measurements. The results demonstrate that the filler wire significantly affects the highest DR by altering wire melting and metal transfer behaviours through changes in arc energy absorption. The filler wire with a rhombus geometry which is closer to a Gaussian-like arc distribution than the flat wire was shown to get higher DR and more stable metal transfer. Furthermore, different filler wire configurations lead to distinct melt pool behaviours, including temperature distribution and flow velocity, due to various metal transfer behaviours and arc shading effects. This study sheds light on the fundamental physics underlying the impact of filler wire on wire melting and bead formation for the first time. The methods and findings can guide improving DR and controlling bead shape in the plasma-DED process.

Observation of Arc and Metal Transfer Behavior according to Shielding Gas in the WAAM of Ti–6Al–4V Alloy Using the Pulsed Gas Metal Arc Process

In arc welding and wire arc additive manufacturing (WAAM) of Ti alloys, pulsed gas metal arc (GMA) processes have a higher deposition than shortcircuiting GMA mode processes, such as cold metal transfer, surface tension transfer, and controlled short-circuit processes. In this study, pulsed GMA WAAM of Ti–6Al–4V alloy was conducted under Ar, Ar50%/He50% mixed, and He shielding gases. Owing to the thermionic emission of electrons from the Ti substrate, cathode jets were emitted from the high-temperature region of the weld pool, which interfered with droplet transfer into the weld pool. The arc shape surrounding the droplet varied according to the shielding gas, and the arc was established at the bottom of the hanging droplet under the He shielding gas, which disturbed droplet detachment. Two spatter generation modes of droplet ejection from the weld pool surface and inflight droplet repelling were observed, and droplet ejection was the most frequent spatter generation mechanism. The mixed shielding gas showed the best performance in terms of arc stability, wire melting, droplet transfer, and spatter suppression. The arc, cathode, and metal transfer characteristics were elucidated in this study, and a suitable gas composition for pulsed GMA WAAM of Ti alloys was proposed.

Study on quantitative metallographic analysis method of copper wire melt trace under short-circuit and fire conditions

Study on quantitative metallographic analysis method of copper wire melt trace under short-circuit and fire conditions

Effect of SAW electrode wire preheating current on its melting rate and weldment properties of HSLA steel joint

ABSTRACT Weld strength and quality are mostly affected by process parameters, which, in turn, influence the mechanical properties of weld metal and heat affected zone. In this research work, effect of electrode wire preheating on different responses including electrode wire melting rate, wire and plate melting efficiency, width of heat affected zone, microhardness, and corrosion rate of weld metal was studied. The experiments were carried out to accumulate the response data using the optimisation techniques. Then, the quadratic mathematical models were developed and checked the significance using the tests such as ANOVA, F-test and lack of fit. The preheat current is found to be the most contributing parameter, which efficiently enhanced the wire melting rate, wire melting efficiency and microhardness of weld metal whereas reduced the plate melting efficiency, heat affected zone (HAZ) width and corrosion rate. In addition, micrographs and micro-hardness results also confirmed the significant influence of preheat current.

Development of swing arc narrow gap GMAW process assisted by swaying wire

In order to further raise narrow gap welding efficiency while improving weld formation, a swing arc narrow gap GMAW process assisted by swaying wire is developed. This process swings the arc to increase groove sidewall penetration, and simultaneously adds a swaying wire to raise the welding deposition rate as well as modify the weld shape. The present work realizes a digital synchronous swaying control between the swing arc and the additional wire on the basis of kinematic modeling, and analyzes the characteristics of arc linear energy distribution in the groove. Arc behaviors, weld formation, and additional wire melting rate are then investigated for the cold wire assisted process. The reduction rates of weld layer number and welding time are also particularly proposed to evaluate the welding efficiency. Experimental results show that the developed process stabilizes the swing arc by attracting the arc to heat the additional wire in synchronous swaying, and yields good welds of sufficient penetrations and indistinctively-changed thickness even at fast feeding rates of the cold wire. Furthermore, the weld layer number and the welding time decrease respectively by ∼26% and ∼54% at most due to a 120% increase in the deposition rate, achieving a high-efficiency and high-quality narrow gap arc welding.

Heat and mass transfer in electron beam additive manufacturing

The electron beam wire-feed additive manufacturing (EBAM) technology utilizes a high-energy electron beam as a heat source to bombard a metal wire in the vacuum environment to form a molten pool. The stability and quality of the deposition mainly depend on the transition behavior of the droplet. To conduct this research, a high-fidelity thermo-fluid dynamic simulation model based on the local reconstruction of the 3D model was developed and verified. The model used the Monte-Carlo algorithm to update the scattering trajectories and residual energies of high-energy electrons on the irradiated surface of the wire and molten pool at each time step in the numerical calculation. Quantitatively analyzed the “electron-wire” instantaneous energy coupling mechanism in the droplet transition mode, insertion transition mode, and liquid bridge transition mode, and finally established an energy-matching criterion for maintaining a stable deposited track morphology. The results show that during the initial stage of wire melting, the droplet will climb along the wire feeding direction, grow under gravity, and eventually drop under the combined effects of gravity and recoil pressure. Different forms of molten droplets will form various solidification morphology, with the liquid bridge transition mode being the most desirable. To maintain a stable liquid bridge transition, it is necessary to control the droplet generation height within the range of 0–2.7 mm. The collapse of the deposited track, caused by heat accumulation during the multilayer deposition, would also alter the droplet generation height. Therefore, to maintain the liquid bridge transition mode in the multilayer multi-channel forming process, it is also necessary to ensure that the energy density of the deposited track is slightly greater than 1.16×1010 J/m3 and the energy density of the wire is slightly greater than 2.63×1010 J/m3.