Molten Metal Flow Research Articles

Influencing of Molten Pool Dynamic Behavior on the Weld Formation during the Laser‐Arc Hybrid Welding of 12 mm Thick Steel

A numerical simulation model is put forward to study the molten pool dynamic behavior and clarify its influencing mechanism on the undercut defects in laser‐arc hybrid welding (LAHW). The undercut defect is a common and challenging problem to address. However, a controversy exists on whether the dynamic process of molten pool can affect undercut defects, and the potential mechanism has been still unclear. The results suggest that profile variation of molten pool surface is driven by surface tension gradient, and the existence of eddy can alter the morphology and surface tension distribution of molten pool, which is the main factor to homogenize the flow field. Compared with the short‐circuit transfer mode, the molten metal flows toward the welds edge at a constant velocity (2.5–3.75 m min−1) in the spray transfer mode, which improves the stability of molten pool flow. It can be observed that the irregular fluctuation of molten metal during the solidification process can directly cause the undercut defects.

Effect of nozzle clogging on vortexing during continuous casting processes: results of an experimental simulation

ABSTRACT Exogenous oxide inclusions in continuously cast steel primarily arise from the entrapment of slag during various stages of steelmaking, including in furnaces, ladles, and molds. To maintain steel cleanliness, operators often pause ladle and tundish processes before ‘slag vortexing’ begins, since this phenomenon (slag vortexing) can adversely affect product quality. Previous studies indicate that sub-entry nozzle clogging can lead to productivity issues and quality defects in cast products. Clogging can cause non-uniform reductions in nozzle diameter along the molten metal flow direction. This study examines the impact of drain port taper (a representation of nozzle clogging) on air core vortex formation during water drainage (simulating molten metal) using a parameter, ‘Characteristic Volume of Air Core.’ Results show that clogged drain ports are prone to vigorous vortexing, significantly affecting efflux velocity and static pressure at drain outlets. The current study also analyzes the dynamic behavior of air core vortexing due to nozzle clogging, revealing that clogging can induce fluctuations in liquid discharge, adversely affecting the casting process. These findings have practical implications for continuous casting processes in steel and other metals.

Design a Gating System for an Aluminum Cast Three-Way Pipe in Sand Casting

The study of aluminum casting work with market demand in the metal casting industry, designing a gating system in aluminum casting using a three-way pipe-shaped sand mold workpiece as a basic shape template in metal casting, namely a flat-face core box with a core. The gating system has a metal inlet with design variables including the pouring height, pouring basin cross-sectional area, rest basin cross-sectional area, running system cross-sectional area and inlet cross-sectional area. From the studying and designing, actual casting experiments were conducted and simulation behavior was analyzed using Cast-Designer software to make decisions and find appropriate design approaches from analyzing simulation results including liquid metal filling time, molten metal flow behavior, metal solidification time and shrinkage porosity formation of the workpiece. The results of the casting experiment and behavior simulation were able to cast the pipe workpiece which is a flat-face core box mold. The analysis results from the software can be used for actual pouring, where the fully cast mold successfully produced a complete workpiece. This can be a guideline for future improvements to reduce the shrinkage of actual cast workpieces.

Numerical simulation of multiphase flow induced by bottom blowing limestone powder in converter steelmaking

A full-scale three-dimensional model of a 120 t steel converter was established to evaluate the effects of bottom-blown limestone particle injection speed, diameter, and nozzle location on the particle distribution and molten metal flow field using numerical simulations. The results indicated that a particle injection speed of 6 m/s, particle diameter of 0.5 mm, and injection nozzle location at 1/2 of the converter bottom radius provided the longest particle residence time and largest quantity of particles in the molten metal. Furthermore, the use of these parameters produced within the molten metal an obvious particle concentration along the centerline of the converter, the fastest average liquid metal–particle flow velocity, and moderate splashing. These optimal injection parameters created favorable kinetic conditions for the dephosphorization reaction essential to steelmaking. This study provide a theoretical basis for realizing the improved efficiency associated with the use limestone instead of lime in practical steel production.

Investigation of Properties in Magnesium Alloy Thin Plates after Die Casting Processes

This study systematically analyzed the effect of design conditions on filling behavior and product characteristics when forming thin plates of magnesium alloy (AZ91D) of 0.5 mm or less using the die casting method. As a research method, a casting analysis simulation program was used to predict filling and solidification behavior under various process conditions. The molten metal injection temperature (610~670 °C), mold temperature (160~220 °C), and cooling water temperature (10~55 °C) were selected as key variables, and an analysis was performed for a total of five conditions. A simulation was conducted to analyze the charging speed distribution, location of oxides and bubbles, and solidification pattern. As a result of the study, the flow of molten metal in the low and high-speed sections of the plunger, uniformity of product thickness, and supply conditions of the molten metal were confirmed to be major factors. It is important to manage the molten metal injection temperature at an appropriate level to minimize product defects. Based on these conditions, a prototype was manufactured, the microstructure was observed, and a fine and uniform grain structure was observed in most areas. In mechanical property evaluation, superior physical properties were secured compared to existing bulk materials.

Анализ течений при лазерно-акустической обработке нержавеющей стали AISI 316L

The influence of ultrasonic vibrations on the flow of molten metal during laser processing is investigated. This problem is of interest within the context of modernization of existing technological processes, such as laser welding and cladding, for the production of structures with improved physical and mechanical properties. The introduction of additional ultrasonic energy into the liquid metal bath intensifies the metal flow via forced stirring, which provides its homogenization and leads to an increase in the mechanical properties of the processed material due to the growth of the number of crystallization centers during its solidification. In order to get a better understanding of this combined process and to control it, a method for synthesizing hydrodynamic and strength solvers used in the ANSYS software package is proposed. Setting up the coupling between two corresponding ANSYS Transient Structural and ANSYS CFX modules is executed through the additional ANSYS System Coupling module. Under this numerical implementation of the problem, it is possible to calculate the displacements at the solid metal boundary and their transfer to the liquid metal boundary and vice versa at each moment of time. The impact of laser radiation on the liquid metal is considered taking into account Marangoni convection, and convection and radiation heat transfer. The results of numerical experiments make it possible to conduct a qualitative and quantitative comparison between the liquid AISI 316L stainless steel flows formed without and with ultrasonic vibration. It is shown that the intensification and deceleration of the flows is observed at the average values of the ultrasonic amplitude. This fact correlates with the moments of time at which the deformed surface of the metal in the bath moves down and up. A comparative analysis of the maximum axial velocities inside the liquid metal bath was conducted. The absence of ultrasonic action on the liquid metal motion was observed at the maximum values of the vibration amplitude, which correspond to the maximum displacement and deformation of the surface at the interface between liquid and solid.

Microstructural evolution and mechanical behavior of activated tungsten inert gas welded joint between P91 steel and Incoloy 800HT

This study examines the welded joint between P91 steel and Incoloy 800HT using the activated tungsten inert gas (A-TIG) welding process. The focus is on analyzing the microstructure and evaluating the mechanical properties of joints made with different compositions of activating flux. Owing to the reversal of the Marangoni effect in which the conventional direction of molten metal flow in the weld pool is reversed due to the application of oxide-based fluxes, a complete depth of penetration of 8 mm was successfully achieved. Conducting mechanical tests, such as microhardness, tensile, and Charpy impact toughness tests, elucidates the behavior of the welded specimens under different loading conditions. The findings highlight the effects of grain size, dislocations, and the evolution of fine-sized precipitates in the high-temperature matrix. This study highlights the importance of choosing suitable flux compositions to achieve consistent penetration and dilution in the base metals. Insights into different failure modes and the influence of temperature on the tensile strength were evaluated. Beneficial mechanical properties of the joints (meeting the criteria of ISO and ASTM standards) were found: ultimate tensile strength of 585 ± 5 MPa, elongation 38 ± 2%, impact toughness of 96 ± 5 J, and maximum microhardness of 345 ± 5 HV.

3D Modelling of Layer-by-Layer Heat and Mass Transfer in Wire Arc Additive Manufacturing

A comprehensive three-dimensional transient computational fluid dynamics (CFD) model was developed to analyze the thermophysical phenomena in the arc wire additive manufacturing (WAAM) process. The model includes droplet impact, gravity, heat and mass transfer, molten metal flow, and solid-liquid phase changes. By integrating the mass, energy, momentum, and volume of fluid (VOF) equations, a layer-by-layer additive process was successfully simulated. The accuracy of the model was validated by comparing the simulation results of single-pass single-layer weld beads at three welding positions with experimental data. The established model was utilized to quantitatively investigate the effects of three crucial welding process parameters–welding direction, droplet transfer frequency, and initial temperature–on the multi-layer cladding process. These findings suggest that the use of opposite welding directions in two adjacent layers can result in a well-distributed overall morphology of the weld bead. Moreover, the high initial droplet temperature enhanced the inclination of the weld bead morphology while decreasing the height of each layer. However, the high droplet transfer frequency caused both the height and width of the weld to increase. This research contributes to explaining the formation mechanism of the multi-layer cladding process and offers insights for improving weld bead morphology. This provides valuable theoretical guidance for the process optimization and control of arc additive manufacturing technology.

Optimization of Multi-Gate System in Casting Process Based on Experimental Study

Abstract: This paper proposes a gating system design for casting process using an experimental study. The principle behind multi-gate system optimization is to eliminate defects such as compression gas inclusions, cold shorts and mixing etc. Industrial and research experience shows that the flow of molten metal in the gating system before entering the extraction cavity significantly influences the quality of the casting. In general, slow filling causes defects like cold shirt and mixing while fast filling causes inclusion of sand and causes defects like holes. A gating system consists of runners, sprue gates and filters. The position, number, size, and shape of these elements play an important role. A systematic methodology for gating design optimization considering filling rate maximization has been developed based on limiting constraints. These include pouring time, gating ratio, modulus of ingate, mold erosion, Reynolds number at ingate section and filling rate of molten metal. Molten metal kinematics viscosity similar to that of liquid water can be used to determine the fillings and flowrate of the molten metal in the mold cavity. Aluminum generally has the same kinematics as water. Thus the water flow can be studied by adding the necessary design improvements to the multi-gate system, from which it will be easier to detect defects and will be easier to detect defects and will greatly improve the overall casting quality

Analysis of the Effect of Feeder Volume on Shrinkage Porosity Defects in Piston Products through the Gravity Die Casting Process

To achieve defect-free casting (soundness casting) with a minimal amount of shrinkage porosity, refinement during the casting process is necessary. In the gravity die casting process, there are parameters that lead to product defects, especially in the casting design, focusing on the gating system and feeder system as pathways for the flow of molten metal to supply the molten metal into the mold cavity. This research was conducted to examine the effect of adding feeder dimensions on shrinkage porosity, specifically on Al-Si piston products with a Silicon content of 12-13%. Feeder dimensions were varied in nine variations by adding height and width to the feeder gate, initially measuring 90mm in height and 32mm in width, along with the addition of insulation to the feeder to retain the heat of the casting process. Cooling used water and argon, with water placed at the center core and pin core and argon placed on the outer mold, with a solidification time of 150 seconds and pouring time of 3 seconds considered constant. This study used a Computer Aided Engineering (CAE) approach, namely MagmaSoft or the application of software to model the gravity casting system process. The results showed the lowest percentage of shrinkage at feeder dimensions of 114mm in height and 45mm in width with a mold temperature of 220°C was 0.76% of the product

Microscopic mechanisms for initiation and evolution of femtosecond laser-induced columnar structures above the surface level of aluminum.

A better understanding of the formation of femtosecond (fs) laser-induced surface structures is key to the control of their morphological profiles for desired surface functionalities on metals. In this work, with fs laser pulse irradiation, the two stages of formation mechanisms of the columnar structures (CSs) grown above the surface level are investigated on pure Al plates in ambient air. Here, we find that the redeposition of ablated microscale clusters following fs laser pulses of irradiation acts as the nucleation sites of CS formation, which strongly affects their location and density within the laser spot. Furthermore, we suggest their structural growths and morphological shape changes are directly associated with the competition among four laser-impact hydrodynamical phenomena: laser ablation, subsequent molten metal flow, particles' redeposition, and metal vapor condensation with continued pulse irradiation.

Stabilizing Flow of Molten Steel in Mold during Slab Continuous Casting through Electromagnetic Swirling Flow in Nozzle

Bias flow of molten metal in slab mold caused by unstable flow from submerged entry nozzle can deteriorate the slab quality during continuous casting. In this study, a novel electromagnetic swirling flow in nozzle (EMSFN) technique, which utilizes electromagnetic force to stabilize the flow in the nozzle and subsequently control the flow in the mold, is proposed. The mechanism for controlling unstable flow through EMSFN is explored through numerical simulation and water model experiments. In the results, it is shown that the molten steel is rotated under the effect of magnetic field and flows into the mold along the upper edge of the nozzle outlet, which weakens the impact of molten steel on the bottom of nozzle and stabilizes the outflow from nozzle. The flow field is consistently symmetrical on both sides of the nozzle. The impact depth of molten steel flowing down along the narrow sides of the mold on both sides is greatly reduced. The surface velocity on both sides of the nozzle changes uniformly. The range of surface velocity variation with EMSFN is only 10% of that with a conventional nozzle. The EMSFN technique can help prevent slag entrapment and improve the flotation of inclusions and bubbles.

A review of electromagnetic stirring on solidification characteristics of molten metal in continuous casting

The solidification of molten metal represents a pivotal phase in the preparation and shaping of metallic materials. Continuous casting, as a crucial juncture in the solidification of molten metal, occupies a position of paramount significance. Nevertheless, during the process of continuous casting, challenges emerge, including uneven temperature field distribution, non-uniform solidification microstructures, and the presence of impurities, leading to defects such as segregation and shrinkage in the castings. Researchers have devoted decades to addressing these issues, culminating in the discovery that the application of electromagnetic stirring during continuous casting can expedite the flow of molten metal, enhance solute diffusion, thereby achieving uniform temperature and flow field distributions, refining solidification microstructures, and ameliorating macrosegregation, among other benefits. This article provides an overview of the recent research achievements and advancements in the utilization of electromagnetic stirring during the continuous casting process. It primarily elucidates various stirring devices commonly employed in continuous casting and expounds upon the influence of electromagnetic stirring on solidification characteristics. And the current problems and future development trends in the application of electromagnetic stirring were discussed.

Effect of Superheat on Microstructure and Mechanical Properties of Al-7Si-2Fe Alloy

Recycling of aluminum (Al) alloys is critical to meet the demands of global net zero emission targets. The major challenge in the recycling of Al alloys is the presence of a higher content of iron as an impurity in Al alloy scraps, which deteriorates the mechanical properties of recycled alloys. In the present work, Al-7%Si alloys and Al-7%Si-2Fe alloys were cast at three different superheat temperatures to study the effect of superheat on the formation of iron intermetallic particles in these alloys. Microstructure–mechanical properties correlations were carried out using SEM-EDS and tensile testing of the alloys. 3D x-ray computed tomography (XCT) results show that the β-phase intermetallic particles were observed to be large and platelet-shaped in the Al-7Si-2Fe alloy cast at 700°C, while these particles appeared to be finer and uniformly distributed throughout the sample in the alloy cast at 900°C. XCT results show the presence of large shrinkage porosity in the Al-7Si-2Fe alloy cast at 700°C, due to the presence of large intermetallic particles which hinder the flow of molten metal during solidification of the alloys. Tensile test results show that the addition of 2% iron resulted in a significant reduction in the elongation of the alloy at all superheat temperatures.

Dynamic evolution of keyhole and weld pool throughout the thickness during keyhole plasma arc welding

Keyhole plasma arc welding (K-PAW) of medium-thick plates often faces instability in the initial keyhole penetration stage, so a thorough investigation of the keyhole and weld pool behavior in this stage is needed. In this paper, a special "sandwich visual sensing structure" was adopted to obtain images of weld pool and keyhole of the SUS304 stainless-steel plate during the plasma arc welding. This method allows direct observation of keyhole growth and weld pool flow throughout the thickness of the workpiece under different welding conditions. When the welding current is reduced, the plasma arc cannot melt through the metal, and the arc sweeps through the keyhole bottom like a “roller coaster”. The trends of keyhole dimensions along different directions during various welding processes were quantitatively investigated. As the weld proceeds to half of the plate thickness, the mutation zone of the rear keyhole wall becomes very common, and the rear keyhole wall's morphology frequently transforms between type I and type II. Weld pool flow characteristics during constant-speed welding were classified into four types. Last, the molten metal flow cycle and the molten metal cloud cluster have been observed by the new visual sensing method. This paper provides the industry with a more intuitive way to study the keyhole and the weld pool for K-PAW, as well as offers important guidance for the first normal penetration in the medium-thickness plate K-PAW process.

Multi-physical field simulation to yield defect-free IN718 alloy fabricated by laser powder bed fusion

In this study, we used a model that combines thermal, mechanical, and fluid dynamics principles to analyze the melting and solidification process in laser powder bed fusion (LPBF). To ensure accurate simulation results, our computational fluid dynamics model takes into account various factors, such as heat transfer, radiation, molten metal flow, phase change, and the interaction between the laser and the material. We found that the combined effects of recoil pressure, Marangoni convection, and surface tension play a crucial role in the evolution of the melted IN 718 alloy. Excessive recoil force can cause powder spatters and keyholes, while inefficient Marangoni effect leads to non-uniform melting. Through our simulation-experimental investigation, we were able to achieve a high-density (99.96 %) IN 718 alloy at a scanning speed of 700 mm/s. This research demonstrates the ability of a multi-physical model to accurately predict the quality of melted materials and contribute to the development of new materials, not limited to nickel-based alloys in LPBF.

Application of large-area electron beam irradiation to micro-edge filleting

Efficient micro-edge filleting with curvature radius from 10 to 100 μm for industrial products is required, since a demand for industrial components with precise and complex shape has been increasing recently. In large-area electron beam (EB) irradiation method, wide area of metal surface can be melted instantly and uniformly. Therefore, highly efficient surface finishing of metal can be performed. In addition, edge of convex part rounds since material removal and/or melting of the edge is preferentially done there due to difficulty of heat diffusion at the edge and concentration of EB. In this study, possibility of micro-edge filleting for workpiece with sharp edge by large-area EB irradiation was investigated. Experimental results show that micro-edge filleting without remarkable shape change of side surface near the edge can be performed under appropriate EB conditions. The curvature radius of edge can be controlled from sharp edge to rounded edge, and ideal curvature radius is obtained. Furthermore, thermo-fluid analysis with considering the concentration of EB to the edge was performed to clarify flow of molten metal and mechanism of edge shape change in the EB irradiation. Edge shape change can be simulated by the thermo-fluid analysis. It was made clear that surface tension is main driving force for edge shape change in large-area EB irradiation.

Cross-scale process quality control of variable polarity plasma arc welding based on predefined temperature field

This study investigates the underlying causes of Variable Polarity Plasma Arc Welding (VPPAW) spatial positional instability and its adverse impact on weld seam quality. Microstructural analysis reveals that the primary cause of poor transverse mechanical properties is the asymmetric distribution of grains. Through the study of heat and mass transfer in the molten pool, it was found that the asymmetric flow of molten metal under the influence of gravity is the main factor leading to uneven temperature distribution and asymmetric grain distribution in the weld pool. A novel approach based on a predefined temperature field is proposed to regulate the weld pool's stability and welding quality. The implementation of the predefined temperature field effectively improves VPPAW weld pool flow, leading to enhanced temperature distribution and grain size and distribution. These findings provide a theoretical foundation and valuable engineering recommendations for achieving high-quality spatial position welding in VPPAW.

The characteristics of dynamic stability in aluminium alloy keyhole weld pool flow

The keyhole welding process in Variable Polarity Plasma Arc Welding enhances weld quality significantly, yet it introduces pool instability. Dynamic stability is pursued by investigating molten metal flowing within keyholes and their characteristics. Weld pool flow patterns are obtained via particle tracking, while instability characteristics are captured employing a high-speed camera. Analysing directional molten metal flow unveils Convergence and Separation Points in weld pool flow. The latter’s displacement induces weld pool instability, resulting in an increase in keyhole area and a reduction in the pinch angle. The keyhole area signifies pool instability, while the rear wall angle reflects the welding state. These findings provide a theoretical basis for weld control and advance vision-based intelligent manufacturing welding techniques.

Laser butt welding of thin stainless steel 316L sheets in asymmetric configurations: A numerical study

Laser butt welding of thin metal sheets is a widely used fusion-based joining technique in industrial manufacturing. A comprehensive understanding of the complex transport phenomena during the welding process is essential for achieving high-quality welds. In the present work, high-fidelity numerical simulations are employed to investigate the influence of various symmetric and asymmetric welding configurations on the melt-pool behaviour in conduction-mode laser butt welding of stainless steel sheets. The analysis focuses on the effects of laser power density, heat source misplacement and different welding scenarios, including plates with a root gap, high-low mismatches, and dissimilar thicknesses, on the molten metal flow and heat transfer. The results show that advection is the dominant mechanism for energy transfer in the melt pool, and its contribution increases with higher laser power. The non-uniform temperature distribution over the melt-pool surface induces Marangoni shear forces, driving the flow of molten metal and leading to the formation of vortices and periodic flow oscillations within the pool. The effects of various types of asymmetries on the thermal and molten metal flow fields, as well as the process stability, are thoroughly examined and compared with symmetrical welding configurations. These comprehensive simulations provide valuable insights into the fluid flow dynamics and thermal field evolution during laser butt welding of thin metal sheets. The knowledge gained from this study can facilitate process optimisation and guide the improvement of weld quality in practical applications.