Molten Metal Flow Research Articles

Modelling Die Filling in Ultra-Thin Aluminium Castings

This work aims to develop flow and thermal control methods for the high pressure die casting (HPDC) of very thin-walled aluminium components where thicknesses are predominantly less than 1 mm. One specific aim includes developing advanced modelling capability using CFD software to predict the complex structure of the metal flow in the die and the casting solidification. The modelling based on FLOW-3D started initially with a fluidity die study to establish several key parameters in HPDC modelling through experimental validation. A new test casting geometry has been designed in the form of a shallow tray with other features such as changes in curvature, fins and bosses. The casting thickness can be made variable in the die. The experimental work was conducted on a 250-tonne HPDC machine. Initial models of molten metal flow in the die cavity based on a runner design for casting thicknesses between 1.5 mm and 1 mm are presented. The detailed model required a very large mesh of very small elements, and more accurate physical parameters which may not have been previously available.

Lorentz Force Flowmeter for Liquid Aluminum: Laboratory Experiments and Plant Tests

This article aims to demonstrate that molten metal flow at a high temperature can be measured effectively in a contactless manner by using external direct current magnetic fields. The device applied in the present work is termed Lorentz force flowmeter (LFF) and is based on exposing the flow to a magnet system and measuring the drag force acting on it. Two series of measurements are reported. In the first series, we perform a model experiment in the laboratory using the eutectic alloy GaInSn, which is liquid at room temperature. The second series of measurements is devoted to two plant tests on flow measurement of a liquid aluminum alloy. In both tests, the force acting on the magnet system is measured that is equal to the Lorentz force acting on the flow. To generalize our results, we also derive the scaling law that relates the force acting on a localized magnet system to the flow rate of a fluid with arbitrary electrical conductivity. This law shows that LFF, if properly designed, has a wide range of potential applications in ferrous and nonferrous metallurgy.

Numerical Simulation of Casting Process for Gray Iron Butterfly Valve

During casting process design, CAD/CAE technology can play important role to avoid macroscopic irregularity, internal defect and assure casting performance. Based on the casting process analysis and gating system design, the numerical simulation of gray iron butterfly valve was done by hydrodynamic software Flow-3D to obtain its optimal process scheme. According to the simulation results including flow field, temperature field and defect distribution, the merits and faults of designed schemes were investigated and then the feasible gating system was proposed. The results showed that, compared with top or intermediate casting, when adopting bottom casting, steady flow of molten metal and reasonable temperature distribution could be achieved. And workpiece defects mainly distributed in riser. The predicted results are in good agreement with practical ones.

Numerical Study on Laser Cladding Process of Magnesium Alloys

In this paper, a three-dimensional simulation model for laser-cladding processes of magnesium alloys is proposed. The applied loading is a moving heat source that depends on process parameters such as power density, laser beam diameter and scanning speed. The effects of process parameters on the melt pool are quantitatively discussed by numerical analysis. In these parameters, Marangoni force is the most important in affecting the molten metal flow and the contour of the melt pool. Both the length and depth of the melt pool vary sharply with temperature dependence of surface tension when the absolute value of this temperature dependence is at lower value.

The Multicell Volume of Fluid (MC-VOF) Method for the Free Surface Simulation of MFD Flows. Part I: Mathematical Model

This paper is the first part of a two-part paper which presents a simulation algorithm of unsteady, electromagnetically driven molten metal flows with free surfaces. At the free boundary, the variable space-distribution of the normal Lorentz forces is taken into account by proper computation of the electromagnetic field and pressure. For each calculation time step, a transport equation of the melt's volume is solved for multicell blocks and subsequently, the free surface is reconstructed by an inward gathering of the melt volume. Therefore, the free surface can be more accurately simulated with the following improvements:(1) Consideration of the normal electromagnetic force densities exerted on the melt surface.(2) Strictly volume conserving displacement of the free surface.(3) Absence of numerically created holes in the melt or of separated fluid droplets, respectively.Comparisons between computational and experimental results to verify the validity of the mathematical model will be presented in the second part of the paper.

Alloys from Anau: The Manipulation of Metallic Properties in 3rdMillennium B.C. Southern Central Asia

ABSTRACTMetallography, chemical analysis, and microhardness testing of copper-alloy objects from Anau, Turkmenistan (c. 3000-2400 B.C.), were undertaken to determine how technological choices influenced the properties of the finished objects. Additionally, this analytical program assessed the position of the Anau metals in the development of metallurgy in southern Central Asia. Metallographic analysis of three bladed objects, all copper-arsenic alloys with 1% to 5% arsenic, showed that their edges had been cold-worked to a greater or lesser degree to create a blade that maintained a sharp edge, but also had flexibility to withstand impacts. Microhardness testing confirmed that the blade edges had a higher hardness than the interior metal. One of the objects had sulfur-rich inclusions in the metal matrix, suggesting the original charge had at least some sulfide ore. Conversely, a curved rod, made from a copper-lead-tin alloy, was cast to shape and showed no additional working of the metal. Lead, visible as black particles in the microstructure, was likely added to make the molten metal flow more easily. The metallographic and chemical analyses showed that the Anau objects fit into the tradition of Southern Central Asian metallurgy, though the presence of tin in objects of this period is more rare here than in later periods. Anau smiths displayed an ability to manipulate both physical and chemical properties of metal in order to produce functional objects with optimal characteristics.

The Multicell Volume of Fluid (MC-VOF) Method for the Free Surface Simulation of MFD Flows. Part II: Experimental Verifications and Results

This second part of a two-part paper presents the experimental verifications of the Multicell Volume of Fluid method developed in the first part. The calculated results are compared with measurements performed for a medium frequency of about 0.4 kHz in an induction crucible furnace, at the low industrial frequency 50 Hz in an inductive rotational stirrer and at higher frequencies of about 30 kHz in an electromagnetic levitation device. Thus, the verifications were realized in these three laboratory setups for different values of the penetration depth of the electromagnetic field and also for different turbulent molten metal flows with one or two free surfaces. The computational results show a good agreement with the experimental data.The established Multicell Volume of Fluid method, characterized by a strictly volume conserving displacement of the free surface, a precisely defined contour of the calculated free surface without the numerical creation of unphysical holes and separated droplets and by calculation stability, will be further extended to the simulation of the more complex flows and free surface profiles resulted by using a new method of electromagnetic levitation melting in two-frequency magnetic fields.

Aluminum Car Wheel Molding Methods and Numerical Simulation of Forming Process

Weight reduction at wheels is important due to its unsprung mass and the associated reduction of fuel consumption and the better ride-and-handling comfort. Especially in the front of the car, a weight reduction is necessary to ease the critical mass distribution at the front axle and therefore increase driving safety. The casting defects that are caused by molten metal were cold shut formation, entrapment of air, gas, and inclusion. But the control of casting defects has been based on the experience of the foundry engineers. In this paper, computer simulations have been carried out to analyze the flow of molten metal. Using Anycasting software to numerical simulating the process of car wheel molding filling and solidification, materials selecting and casting process characteristics and defects of the parts are studied, the causes of casting defects are analyzed.

Numerical Simulation and analysis of molten flow in the shot sleeve of die casting process

AbstractThis work presents a numerical study of the flow of molten metal in the shot sleeve of horizontal high‐pressure die casting machine during the injection process. The analysis of the wave of the molten metal created by plunger motion can be of help in reducing porosity in manufactured parts caused by air entrapment. The used numerical model, which considers the problem as two‐dimensional, is based on the conservation equations of mass and momentum. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Features in the simulation of electromagnetic flowmeters of molten metals

Methods for simulation of electromagnetic flowmeters that expand the capabilities of experimental studies of the devices by means of non-spill methods as well as under the conditions that are typical of their use in a flow of molten metal are considered.

Developing a new 2D model for heat transfer and foam degradation in EPS lost foam casting (LFC) process

In this study, a 2D model is developed for heat transfer, foam degradation and gas diffusion at the interfaces of the liquid metal, foam pattern and gaseous gap in between, for EPS lost foam casting process. In this model based on mass and energy balance between gas and molten metal, radiation and conduction between foam and molten metal and convection between gas and molten metal are considered, both metal and foam surfaces are tracked and gap volume and pressure are calculated. A combination of energy balance and geometric correlations is used to define receding foam surface during mold filling. Gas flow in the gap is considered as wedge flow and Nusselt number for a laminar incompressible wedge flow is used for it. To apply our model to an example case, SOLA-VOF algorithm was used to simulate the flow of molten metal with free boundaries. Model results are compared with some data reported in the literature which show acceptable agreement. It is found that besides radiation in the gaseous area between foam and molten metal, conduction also plays an important role in foam degradation and control of molten metal velocity. This model can acceptably predict the effect of some parameters like foam density, coating permeability and foam degradation temperature.

Numerical simulation of heat transfer and fluid flow of molten metal in MMA–St copolymer lost foam casting process

In this study, a computational fluid dynamics (CFD) code was developed to calculate the filling pattern using volume of fluid (VOF) algorithm with donor–acceptor method for free surface simulation. This algorithm has been modified to include the pressure of the gas produced from foam degradation. For this purpose a heat transfer model and 2D foam degradation model were developed. In heat transfer model, radiation and conduction between foam and molten metal; and convection between gas and molten metal were considered. In order to evaluate the results of simulation, a bench scale casting apparatus was assembled and the casting was conducted in a transparent mold. The effect of several parameters such as coating thickness, foam density and vacuum level on the gap temperature, gap pressure and filling speed was studied with the developed software. It was found that the simulated results are in good agreement with experimental results.

Numerical study of alloying element distribution in CO 2 laser–GMA hybrid welding

This article addresses the physical assumptions and mathematical models required to precisely predict molten metal flow in CO 2 laser–GMA hybrid welding and assesses that welding phenomena can be explained by the consequent simulation results. To this end, three-dimensional transient simulations of CO 2 laser–GMA hybrid welding for the laser trailing the arc are conducted by combining the arc welding model and the laser welding model without any interactive effect between the two. Additionally, based on the hypothesis that fluid flow inside a molten pool might affect the alloying element distributions, an additional conservation equation is newly suggested and united with the aforementioned models to examine the hypothesis and the validity of the models. It is found that similar fusion zones and alloying element distributions are predicted by numerical simulations, although for a laser- and material-dependant quantity ε, which is the function of material properties and laser wavelength and decides the reflectivity together with incident angle in the simplified Fresnel’s reflection model, the theoretical value of 0.08 rather than the compensated value of 0.2 is used in the simplified Fresnel’s reflection model for steel and CO 2 laser. It is thought that these are not only strongly affected by molten metal flow but also the assumptions and models used in the flow calculation are appropriate. However, in spite of the good prediction results, it is deemed that many effects overlooked in this study should be investigated in further studies.

Direct numerical simulations of magnetic field effects on turbulent flow in a square duct

Magnetic fields are crucial in controlling flows in various physical processes of industrial significance. One such process is the continuous casting of steel, where different magnetic field configurations are used to control the turbulent flow of steel in the mold in order to minimize defects in the cast steel. The present study has been undertaken to understand the effects of a magnetic field on mean velocities and turbulence parameters in turbulent molten metal flow through a square duct. The coupled Navier–Stokes magnetohydrodynamic equations have been solved using a three-dimensional fractional-step numerical procedure. The Reynolds number was kept low in order to resolve all the scales in the flow without using a subgrid scale turbulence model. Computations were performed with three different grid resolutions, the finest grid having 8.4×106 cells. Because liquid metals have low magnetic Reynolds number, the induced magnetic field has been considered negligible and the electric potential method for magnetic field-flow coupling has been implemented. After validation of the computer code, computations of turbulent flow in a square duct with different Hartmann numbers were performed until complete laminarization of the flow. The time-dependent and time-averaged nature of the flow has been examined through distribution of mean velocities, turbulent fluctuations, vorticity, and turbulent kinetic energy budgets.

Improving the Temporal Resolution of Magnetic Induction Tomography for Molten Metal Flow Visualization

Magnetic induction tomography (MIT) is a nondestructive monitoring technique for imaging the electromagnetic properties of an object by mutual induction data of pairs of excitation and sensing coils. MIT has potential application in monitoring of molten metal flow in continuous casting. The main advantage of the MIT for this application is the contactless nature of the measurement process and its potential to generate images with high temporal resolution. Traditionally, the MIT image is formed using one frame of measured data that includes data from all excitation coils. In this paper, we study the improvement of the temporal resolution by reconstructing MIT images using data from one excitation at a time and using the Kalman-filtering approach. The images are presented using experimental data of the MIT system tested in a continuous casting unit. The MIT system used in this study can produce images 8 times faster than before by using new dynamical image reconstruction technique.

Influence of rotational speed of centrifugal casting process on appearance, microstructure, and sliding wear behaviour of Al-2Si cast alloy

Although the manner in which the molten metal flows plays a major role in the formation of the uniform cylinder in centrifugal casting, not much information is available on this topic. The flow in the molten metal differs at various rotational speeds, which in turn affects the final casting. In this paper, the influence of the flow of molten metal of hyper eutectic Al-2Si alloys at various rotational speeds is discussed. At an optimum speed of 800 rpm, a uniform cylinder was formed. For the rotational speeds below and above these speeds, an irregular shaped casting was formed, which is mainly due to the influence of melt. Primary a-Al particles were formed in the tube periphery at low rotational speed, and their sizes and shapes were altered with changes in rotational speeds. The wear test for the inner surface of the casting showed better wear properties for the casting prepared at the optimum speed of rotation.

English

The research on a number of welding problems, for instance microstructural evolution, weld induced distortion and welding residual stresses, necessitates comprehensive information about the thermal history of the weldment and welded structures. In the present work, an efficient thermal model using finite element method (FEM) is developed for linear fiber laser welding process on 316 stainless steel of 3mm thick plate. In this modeling approach, the thermal conductivity of molten material is increased artificially for several folds to account the enhanced heat transfer due to high convective flow of liquid molten metal within the weld pool. In order to validate the developed FE model, a series of welding experiments are carried out using highly focused fiber laserwith 800 W - 1000 W laser power and 13.33 mm/s - 18.33 mm/s laser scanning speed. The computed weld pool shapes and dimensions are compared with the experimental results at similar welding conditions. Relatively fair agreement between the numerical simulation and experimental results designates the robustness of the modeling approach followed here.

Modeling of electromagnetic separation of inclusions from molten metals

The presence of inclusions greatly influences the mechanical and the corrosion resistance of metallic alloys. These influential effects become more crucial when using metallic scrap, due to the high levels of inclusions and other contaminants such as non-metallic and oxides particles. Metal cleanliness requirements are becoming more striking, enforcing higher demands on the efficiency and flexibility of refining methods. Recently electromagnetic separation technique has been considered as a new method for the production of metals free from inclusions. In this study, a mathematical model has been developed to simulate the flow of molten metal through a channel in the presence of electromagnetic force field generated by interaction between a stationary electromagnetic field and DC current passing through the melt. A generalized model based on Newton's second law of motion was developed for the motion of inclusions in the melt flowing through the channel of separator by considering different forces acting on particle including electromagnetic force. A physical model was designed and constructed to visualize the inclusion separation phenomena and to verify the mathematical model. The predicted particle trajectories and separation in the physical model were compared with those obtained from experiments which showed reasonably good agreement. Parametric studies were performed using the mathematical model to evaluate the effects of various parameters, such as electromagnetic force strength, particle size and melt inlet velocity on the inclusion removal efficiency.

Analysis of Fin-Tube Joints in a Compact Heat Exchanger

This article deals with an analysis of fin-tube joints as functions of topological alterations of the joint fillet size. Based on numerical predictions of a joint topology formed by the surface tension driven reactive flow of molten metal, and subsequently verified by empirical evidence gathered through both laboratory and industrial testing, the topology alterations were identified for thermal integrity studies. Subsequently, thermal characteristics of corresponding fin-tube joints were determined in terms of two models of the thermal contact resistance. Model predictions of the fin efficiency with an altered topology of the joint zone were compared with the simulation results from a computational fluid dynamics study, and the results fit well. Numerical predictions of joint topology were devised using an in-house-developed finite-element code, and verified by the Surface Evolver code. Such prediction provided quantitative joint topology information that was needed in assessments of the joint thermal performance. Experimental data were obtained using a computer-controlled transparent hot zone with an ultra-high-purity nitrogen background atmosphere under tightly controlled conditions, and also by an analysis of the state-of-the-art manufacturing process data obtained from an industrial setting. It is demonstrated that a value of fin efficiency, assumed as recommended by traditional sizing design procedures, may drastically differ from actual values.

Influence of welding parameters on distribution of wire feeding elements in CO2 laser GMA hybrid welding

The effect of welding parameters on the distribution of wire feeding elements has been investigated during CO2 laser and pulsed gas metal arc hybrid welding process. The molten metal flow on the pool surface and inside of the samples was observed by a high speed video camera and an in situ X-ray transmission imaging system respectively. The results indicate that the fluid flow towards the inside of keyhole, namely inward flow, improves the homogeneity of weld metal. The distribution of alloying elements is more homogeneous in leading laser compared with leading arc, since both of the drag force of the plasma jet and momentum of droplet promote the inward flow in leading laser. Almost homogeneous distribution of alloying elements can be attained if the oxygen content in the shielding gas is more than 2%, since the Marangoni flow direction changes from outward to inward with increasing the oxygen content.