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1.
This article presents a mathematical model simulating the effects of surface tension (Maragoni effect) on weld pool fluid
flow and weld penetration in spot gas metal arc welding (GMAW). Filler droplets driven by gravity, electromagnetic force,
and plasma arc drag force, carrying mass, thermal energy, and momentum, periodically impinge onto the weld pool. Complicated
fluid flow in the weld pool is influenced by the droplet impinging momentum, electromagnetic force, and natural convection
due to temperature and concentration gradients, and by surface tension, which is a function of both temperature and concentration
of a surface active element (sulfur in the present study). Although the droplet impinging momentum creates a complex fluid
flow near the weld pool surface, the momentum is damped out by an “up-and-down” fluid motion. A numerical study has shown
that, depending upon the droplet’s sulfur content, which is different from that in the base metal, an inward or outward surface
flow of the weld pool may be created, leading to deep or shallow weld penetration. In other words, it is primarily the Marangoni
effect that contributes to weld penetration in spot GMAW. 相似文献
2.
Sung H. Ko Choong D. Yoo Dave F. Farson Sang K. Choi 《Metallurgical and Materials Transactions B》2000,31(6):1465-1473
The dynamic behavior of stationary fully penetrated gas tungsten arc weld pools was investigated through numerical simulation.
The effects of arc pressure, electromagnetic force, and surface tension gradients on surface depression, convection, and temperature
distribution were calculated. The top surfaces of fully penetrated pools were easily depressed since they were only supported
by surface tension. Circulatory convection patterns were generated by electromagnetic forces and surface tension gradients
and were significantly affected by the vertical velocity component produced by pool oscillation. The temperature distribution
in and around the pool was influenced by pool convection. During pool formation and growth, the fully penetrated molten pool
sagged dramatically when the bottom pool diameter approached the top diameter. The sagged pool oscillated with higher magnitude
and lower frequency than partially penetrated or fully penetrated pools before sagging occurred. The dynamic behavior and
the amount of material lost during melt-through were affected by the pool size and the magnitude of arc pressure. 相似文献
3.
P. K. Ghosh S. R. Gupta H. S. Randhawa 《Metallurgical and Materials Transactions A》2000,31(9):2247-2259
The performance of the pulsed-current gas metal arc welding (GMAW) process for vertical-up weld deposition of steel has been
found to be superior over the use of the short-circuiting arc GMAW process with respect to the tensile, impact, and fatigue
properties of the weld joint. The microstructure, weld geometry, and mechanical properties of a pulsed-current weld joint
are largely governed by the pulse parameters, and correlate well to the factor φ, defined as a summarized influence of pulse parameters such as peak current, base current, pulse-off time, and pulse frequency.
The increase of φ has been found favorable to refine the microstructure and enhance the tensile strength, C
v
toughness, and fatigue life of a weld joint. The fatigue life of a short-circuiting arc weld joint has been found to be markedly
reduced due to the presence of an undercut at the weld toe and incomplete side-wall fusion of the base material. 相似文献
4.
Computer simulation of convection in moving arc weld pools 总被引:3,自引:0,他引:3
Computer simulation for three-dimensional convection in moving arc weld pools was described, with three distinct driving forces
for flow considered — the electromagnetic force, the buoyancy force, and the surface tension gradient on the pool surface.
Formulation of the electromagnetic force in the weld pool was presented. The calculated and experimentally observed fusion
boundaries were compared. The arc efficiency and spatial distributions of the current density and power density used in the
calculations were based on experimentally measured results, in order to verify the model. The effects of the electromagnetic
and surface tension forces were discussed. 相似文献
5.
Weld pool fluid flow can affect the penetration of the resultant weld significantly. In this work, the computer simulation
of weld pool fluid flow and its effect on weld penetration was carried out. Steady-state, 2-dimensional heat and fluid flow
in stationary arc welds were computed, with three driving forces for fluid flow being considered: the buoyancy force, the
electromagnetic force, and the surface tension gradient at the weld pool surface. The computer model developed agreed well
with available analytical solutions and was consistent with weld convection phenomena experimentally observed by previous
investigators and the authors. The relative importance of the influence of the three driving forces on fluid flow and weld
penetration was evaluated, and the role of surface active agents was discussed. The effects of the thermal expansion coefficient
of the liquid metal, the current density distribution in the workpiece, and the surface tension temperature coefficient of
the liquid metal on weld pool fluid flow were demonstrated. Meanwhile, a new approach to free boundary problems involving
simultaneous heat and fluid flow was developed, and the effort of computation was reduced significantly. 相似文献
6.
Fluid flow and weld penetration in stationary arc welds 总被引:1,自引:0,他引:1
Weld pool fluid flow can affect the penetration of the resultant weld significantly. In this work, the computer simulation
of weld pool fluid flow and its effect on weld penetration was carried out. Steady-state, 2-dimensional heat and fluid flow
in stationary arc welds were computed, with three driving forces for fluid flow being considered: the buoyancy force, the
electromagnetic force, and the surface tension gradient at the weld pool surface. The computer model developed agreed well
with available analytical solutions and was consistent with weld convection phenomena experimentally observed by previous
investigators and the authors. The relative importance of the influence of the three driving forces on fluid flow and weld
penetration was evaluated, and the role of surface active agents was discussed. The effects of the thermal expansion coefficient
of the liquid metal, the current density distribution in the workpiece, and the surface tension temperature coefficient of
the liquid metal on weld pool fluid flow were demonstrated. Meanwhile, a new approach to free boundary problems involving
simultaneous heat and fluid flow was developed, and the effort of computation was reduced significantly. 相似文献
7.
A mathematical model is developed to describe the globular transfer in gas metal arc welding (GMAW). This work is both theoretical
and experimental. Using the volume-of-fluid (VOF) method, the fluid-flow and heat-transfer phenomena are dynamically studied
during the following processes: droplet formation and detachment, impingement of a droplet on a solid substrate, impingement
of multiple droplets on the molten pool, and solidification after the arc extinguishes. A He-Ne laser, in conjunction with
the shadow graphing technique, is used to observe the metal transfer processes. Theoretical predictions and experimental results
are in close agreement, suggesting that the theoretical treatment of the model is good. 相似文献
8.
《Canadian Metallurgical Quarterly》1998,37(3-4):265-273
Heat and momentum transfer in a submerged electric smelting furnace were investigated in a physical model, using oil and an aqueous calcium chloride solution to simulate the slag and matte phases, respectively. Gas evolution at the electrode was simulated by the injection of gas through the electrode in the model. A mathematical model for fluid flow and heat transfer in the model was also developed. The measured temperature distributions near the oil⧹solution interface could only be reproduced in the mathematical model by the imposition of a no-slip boundary condition at the interface. This condition impedes the transfer of heat and momentum into the lower phase; the implications for smelting are discussed. 相似文献
9.
A mathematical model of gas tungsten arc welding considering the cathode and the free surface of the weld pool 总被引:4,自引:0,他引:4
A two-dimensional axisymmetric numerical model, including the influence of the cathode and the free surface of the weld pool,
is developed to describe the heat transfer and fluid flow in gas tungsten arc (GTA) welding. In the model, a boundary-fitted
coordinate system is adopted to precisely describe the cathode shape and deformed weld-pool surface. The current continuity
equation has been solved with the combined arc plasma-cathode system, independent of the assumption of current density distribution
on the cathode surface, which was essential in the previous studies of arc plasma. It has been shown that the temperature
profile, the current, and the heat flux to the anode show good agreement with the experimental data. Moreover, the current
and the heat-flux distributions may be affected by the shape of the cathode and the free surface of the weld pool. 相似文献
10.
《钢铁冶炼》2013,40(1):75-80
AbstractTwin roll strip casting is regarded as a prospective technology offering many economic benefits. The control of fluid flow in the pool is, however, particularly difficult due to the high casting speed and small pool volume. In the present study, a three-dimensional mathematical model has been developed for the coupled analysis of fluid flow, heat transfer and solidification in the pool using the finite difference method. The characteristics of transport phenomena in the pool of a twin roll strip caster using a wedge type melt delivery system were analysed by numerical simulation. The results show that it is desirable for the wedge melt delivery system to provide the uniformity of flow and temperature in the pool to maintain the casting process and improve the strip quality. 相似文献
11.
Shanping Lu Hidetoshi Fujii Kiyoshi Nogi 《Metallurgical and Materials Transactions A》2004,35(9):2861-2867
Small CO2 additions of 0.092 to 10 vol pct to the Ar shielding gas dramatically change the weld shape and penetration from a shallow
flat-bottomed shape, to a deep cylindrical shape, to a shallow concave-bottomed shape, and back to the shallow flat-bottomed
shape again with increasing CO2 additions in gas thermal arc (GTA) welding of a SUS304 plate. Oxygen from the decomposition of CO2 transfers and becomes an active solute element in the weld pool and reverses the Marangoni convection mode. An inward Marangoni
convection in the weld pool occurs when the oxygen content in the weld pool is over 80 ppm. Lower than 80 ppm, flow will change
to the outward direction. An oxide layer forms on the weld pool in the welding process. The heavy oxide layer on the liquid-pool
surface will inhibit the inward fluid flow under it and also affects the oxygen transfer to the liquid pool. A model is proposed
to illustrate the interaction between the CO2 gas and the molten pool in the welding process. 相似文献
12.
《Baosteel Technical Research》2010,(Z1):92
In twin-roll strip casting process,transport phenomena of fluid in the molten pool directly affect the process stability and the quality of products.In order to elucidate the fundamental transport phenomena in twin-roll casting,a commercial software called ProCAST was employed to simulate the transient fluid flow and level profile behaviors during the early stage of the process in this study.The coupled set of governing differential equations for mass,momentum and energy balance were solved with the finite element method and the transient free surface problem was treated with a volume of fluids(VOF) approach.The effect of different delivery systems configuration on flow pattern,level profile in the pool was studied and analyzed in this paper. The new wedge metal delivery systems have been optimized for the twin-roll strip caster.It was shown that new type metal delivery systems had a preferable effect on the uniform distribution of fluid and level fluctuation in the pool.The simulation results also provide a valuable basis for the optimization of delivery system and process parameters during the initial pouring stage. 相似文献
13.
Greg D. Rigby Les Strezov Chris D. Rielly Scott D. Sciffer John A. Lucas Geoffrey M. Evans 《Metallurgical and Materials Transactions B》2000,31(5):1117-1123
An experimental and numerical study has been conducted to investigate the flow field in the vicinity of a moving solid boundary
that passes through a free surface into a liquid phase. Through the use of particle image velocimetry (PIV) techniques, the
variation in the liquid velocity field in the vicinity of the three-phase contact line has been quantified for solid boundary
velocities ranging between 0.12 and 1.01 m s−1. The experimental measurements provide good verification for a preliminary numerical model that predicts the bulk-bath flow
patterns and boundary layer thickness.
This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney,
Australia, under the joint sponsorship of ISS and TMS. 相似文献
14.
Physical vapor deposition (PVD) assisted by an electron beam is one of several methods currently used to apply thermal barrier
coatings (TBCs) to aircraft components subjected to high-temperature environments. The molten pool of source material inherent
in this process shall be the subject of analysis in this investigation. A model of the melt pool and the ingot below shall
be generated in an effort to study the fluid flow and heat transfer within the pool. This model shall incorporate all of the
following mechanisms for heat transfer into and out of the melt pool/ingot system: electron-beam impingement upon the melt
pool surface, absorption of latent heat of evaporation at the melt pool surface, radiation from the melt pool surface, loss
of sensible heat carried off with the vapor, and cooling by the crucible containing the melt pool/ingot. Fluid flow within
the melt pool model shall be driven by both natural convection and by surface tension gradients on the melt pool surface.
Due to the complexity of the differential equations and boundary equations governing the model, this detailed study shall
be performed through a finite element analysis. Reduced order models of the system will be generated from this investigation.
An analysis will also be performed to ascertain the error introduced into these models by uncertainty in the thermophysical
property data used to generate them. 相似文献
15.
《钢铁冶炼》2013,40(3):209-213
AbstractThe interaction of liquid steel and an inclined impinging oxygen jet in an electric arc furnace (EAF) is of interest both commercially and scientifically. The bath activity in the EAF may vary from a surface splash ejected to high elevation to intense subsurface mixing. The system is appropriately modelled using water and nitrogen with scaled flowrates. In previous work, the gas/liquid contact was investigated by use of a geometrically similar 1/3rd scale three-dimensional water model. The cavity formed by the jet contacting the liquid surface was characterised by four modal regimes. These regimes were seen to depend on the lance angle, the height of the lance and the jet flowrate. To investigate the evolutionary mechanisms of the cavity regimes, a two-dimensional water model study was undertaken. The two-dimensional water model was a rectangular viewing tank with an inner movable glass wall that allowed a very thin slice of the system to be obtained. The shape of the cavity formed on the water surface was seen clearly along with the expected cavity oscillations. High speed video footage of the two-dimensional system allowed the cavity oscillation to be directly observed. The gas-liquid interaction produced a wave that travelled along the surface of the cavity until it reached the cavity crest where it was torn from the liquid surface and dispersed in a splash. It is the regular progression of the wave's nodes and antinodes along the cavity surface that makes the cavity appear to oscillate. When the wave reaches the crest of the cavity, it will either fall back into the path of the gas jet or be projected as a splash depending on the verticality of the cavity surface. The two-dimensional work, along with the initial three-dimensional investigation, has shown that the troublesome splash in the EAF is caused by how the lance is positioned directionally or azimuthally. By changing the lance angle or height the deleterious splashing of molten metal may be prevented, ameliorated or controlled. The frequency of the wave production was determined from the high speed video footage. The cavity oscillation was found to be a function of the size of the cavity, the inclined height of the lance and the modal regime being produced. Alterations to the flow through the lance had only a moderate effect on the frequency of oscillation indicating that velocity was not the major influential factor. 相似文献
16.
Numerical analysis of metal transfer in gas metal arc welding 总被引:1,自引:0,他引:1
The present article describes a numerical procedure to simulate metal transfer and the model will be used to analyze the transport
processes involved in gas metal arc welding (GMAW). Advanced Computational fluid dynamics (CFD) techniques used in this model
include a two-step projection method for solving the incompressible fluid flow; a volume of fluid (VOF) method for capturing
free surface; and a continuum surface force (CSF) model for calculating surface tension. The electromagnetic force due to
the welding current is estimated by assuming several different types of current density distribution on the free surface of
the drop. The simulations based on the assumption of Gaussian current density distribution show that the transition from globular
to spray transfer mode occurs over a narrow current range and the size of detached drops is nonuniform in this transition
zone. The analysis of the calculation results gives a better understanding of this physical procedure. Comparisons between
calculated results and experimental results are presented. It is found that the results computed from the Gaussian assumption
agree well with those observed in experiments. 相似文献
17.
18.
Flow driven by a combination of thermocapillary, Lorentz, and buoyant forces has been investigated in an axisymmetric and
stationary weld pool numerically. By assuming a small value for the capillary number, the top and bottom boundaries can be
taken to be flat, and the surface deflections can be calculateda posteriori as a domain perturbation. Owing to thin boundary layers that exist at the top free surface and next to the vertical wall,
very fine grids are required in these regions in order to obtain an accurate solution to the Boussinesq form of the Navier-Stokes
equations. This was done by solving the governing equations by multigrid methods to which a local grid refinement technique
was added. Welding of both aluminum and steel were considered. The essential difference between these two materials for this
analysis is that the Prandtl number of aluminum is an order of magnitude smaller than that of steel. Through a parametric
study, the thermocapillary forces and Lorentz forces were found to dominate buoyancy forces in a typical welding situation.
Although the flows in weld pools include a pronounced recirculating region near the top surface, isotherms could be determined
in the case of aluminum to a good approximation by a conduction analysis, owing to the smallness of its Prandtl number and
the relative thinness of the welded plate considered. For steel, the isotherms deflect considerably for high current inputs.
Formerly with the Department of Mechanical Engineering, The Ohio State University. 相似文献
19.
A mathematical representation is developed for describing the flow field in liquids or melts, agitated by a symmetrically placed impinging gas jet. The problem is formulated by the statement of the axi-symmetrical turbulent fluid flow equations using the Prandtl-Komogorov model for the eddy viscosity. The resultant differential equations are solved numerically and the computed results are shown to be in reasonable agreement with experimental data reported in the literature. This problem is thought to be relevant to various metals refining operations and the results should also be helpful for the interpretation of laboratory scale studies in which molten metals are contacted with impinging gas jets. 相似文献
20.
Modeling of fluid flow and heat transfer in the plasma region of the dc electric arc furnace 总被引:2,自引:0,他引:2
A mathematical model describing the transport processes in the plasma arc in dc electric arc furnaces has been developed.
The equations of conservation of mass, momentum, and energy are solved numerically in conjunction with Maxwell's equations
of the electromagnetic field to calculate the velocity and temperature distributions in the plasma region. The heat transfer
from the arc to a rigid anode surface is calculated. The model is applied to obtain quantitative results on the relative importance
of the various modes of heat transfer from the electric arc to the anode surface. Computational results were obtained for
varying arc current magnitudes and anode-cathode distances. The model predicts higher arc jet velocity and a broader arc core
at higher arc current. The shorter arc length is more efficient for transferring heat to the anode. 相似文献