NUMERICAL STUDY FOR GTA WELD SHAPE VARIATION BY COUPLING WELDING ARC AND WELD POOL

A numerical modeling of the welding arc and weld pool is studied for moving GTA welding to investigate the effect of the surface active element oxygen and the plasma drag force on the weld shape. Based on the 2D axisymmetric numerical modeling of the argon arc, the heat flux, current density and plasma drag force are obtained under different welding currents. Numerical calculations to the weld pool development are carried out for moving GTA welding on SUS304 stainless steel with different oxygen contents 30 ppm and 220 ppm, respectively. The results show that the plasma drag force is another dominating driving force affecting the liquid pool flow pattern, except for the Marangoni force. The different welding currents will change the temperature distribution and plasma drag force on the pool surface, and affect the strength of Marangoni convection and the weld shape. The weld D/W ratio initially increases, followed by a constant value around 0.5 with the increasing welding current under high oxygen content. The weld D/W ratio under the low oxygen content slightly decreases with the increasing welding current. The predicted weld shape by simulation agrees well with experimental results.

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Transport Phenomena and Their Effect on Weld Quality in GMA Welding of Aluminum Alloys

Volume 3 ◽

10.1115/ht-fed2004-56733 ◽

2004 ◽

Author(s):

H. Guo ◽

H. L. Tsai ◽

P. C. Wang

Keyword(s):

Aluminum Alloys ◽

Weld Pool ◽

Gma Welding ◽

Gas Metal Arc Welding ◽

Welding Current ◽

Weld Penetration ◽

Three Dimensional Model ◽

End Effects ◽

Welding Arc ◽

Micro Cracks

Gas metal arc welding (GMAW) of aluminum alloys has recently become popular in the auto industry to increase fuel efficiency of a vehicle. In many situations, the weld is short (say, less than two inches) and the “end effects” become very critical in determining the strength of the weld. At the beginning stage of the welding, when the metal is still “cold”, which is frequently called cold weld, limited weld penetration occurs. On the other hand, at the ending stage of the welding, a “crater” is formed involving micro-cracks and micro-pores. Both the cold weld and the crater can significantly decrease the strength of the weld and are more severe for aluminum alloys as compared to steels. Hence, there are strong needs to improve the GMAW process in order to reduce or eliminate the aforementioned end effects. In this paper, both mathematical modeling and experiments have been conducted to study the beginning stage, ending stage, as well as the quasi-steady-state stage of GMA welding of aluminum alloys. In the modeling, a three-dimensional model using the volume-of-fluid (VOF) method is employed to handle the free surfaces associated with the impingement of droplets into the weld pool and the weld pool dynamics. Transient weld pool shapes and the distributions of temperature and velocity in the weld pool are calculated. The predicted solidified weld bead shapes, including weld penetration and/or reinforcement, are in agreement with experimental results for welds in the aforementioned three stages. It was found that the thickness of the molten weld pool is smaller and there is no vortex developed, as compared to steel welding. The lack of penetration in cold weld is due to the lack of pre-heating by the welding arc. Three techniques are proposed and validated numerically to improve weld penetration by increasing the energy input at the beginning stage of the welding. The crater formation is caused by rapid solidification of the weld pool when the welding arc is terminated. By reducing welding current and reversing the welding direction before terminating the arc, the weld pool is maintained “hot” for a longer time allowing melt flow to fill-up the crater. This method is validated experimentally and numerically to be able to eliminate the formation of the crater and the associated micro-cracks.

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Experimental study and numerical modeling of arc and weld pool in stationary GTA welding of pure aluminum

The International Journal of Advanced Manufacturing Technology ◽

10.1007/s00170-014-5651-8 ◽

2014 ◽

Vol 71 (9-12) ◽

pp. 2059-2071 ◽

Cited By ~ 12

Author(s):

Amir Hossein Faraji ◽

Massoud Goodarzi ◽

Seyed Hossein Seyedein ◽

Mohammad Hasan Zamani

Keyword(s):

Experimental Study ◽

Numerical Modeling ◽

Weld Pool ◽

Pure Aluminum ◽

Gta Welding

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Role of Welding Parameters in Determining the Geometrical Appearance of Weld Pool

Journal of Engineering Materials and Technology ◽

10.1115/1.2805961 ◽

1996 ◽

Vol 118 (4) ◽

pp. 589-596 ◽

Cited By ~ 17

Author(s):

R. Kovacevic ◽

Z. N. Cao ◽

Y. M. Zhang

Keyword(s):

Fluid Flow ◽

Weld Pool ◽

Numerical Models ◽

Three Dimensional ◽

Welding Current ◽

Gta Welding ◽

Welding Parameters ◽

Geometrical Shape ◽

Arc Length ◽

Weld Pools

A three-dimensional numerical model is developed to describe the fluid flow and heat transfer in weld pools. Both full penetration and free deformation of the top and bottom weld pool surfaces are considered. Temperature distribution and fluid flow field are obtained. In order to analyze the influence of welding parameters on the geometrical appearance of weld pools, a normalized model is developed to characterize the geometrical appearance of weld pools. It is found that welding current can significantly affect the geometrical shape. When welding current increases, the curvature of the pool boundary at the trailing end increases. The effect of the welding speed on the geometrical appearance is slight, although its influence on the pool size is great. In the interest range of arc length (from 1 mm to 4 mm), the arc length can affect both the size and the shape of the weld pool. However, compared with the welding current and speed, its influences are much weaker. GTA welding experiments are performed to verify the validity of the numerical models. The appearance of weld pools was obtained by using machine vision and a high-shutter speed camera. It is found that the calculated results have a good agreement with the experimental ones.

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A Study on Parameter Optimization for Circumferential Gas Tungsten Arc (GTA) Welding of Small Pipes considering Backing Gas Pressure: Part 1: Analysis of Weld Pool Surface Profile

Proceedings of the Institution of Mechanical Engineers Part B Journal of Engineering Manufacture ◽

10.1243/pime_proc_1996_210_088_02 ◽

1996 ◽

Vol 210 (1) ◽

pp. 77-85 ◽

Cited By ~ 1

Author(s):

S-J Na ◽

T-J Lho

Keyword(s):

Temperature Distribution ◽

Finite Difference ◽

Weld Pool ◽

Surface Profile ◽

Welding Current ◽

Gta Welding ◽

Welding Parameters ◽

Difference Model ◽

Gas Tungsten Arc ◽

Pool Surface

It is well known that the weld bead becomes wider and the weld pool hangs down as the circumferential welding of small-diameter pipes progresses, if constant welding conditions are maintained over the entire joint length and/or no appropriate backing gas is supplied into the pipe. In order to obtain a weld bead which is uniform in width and does not hang down over the whole circumference of the pipe, the welding parameters such as welding current, welding velocity and backing gas pressure should be optimized as the welding progresses. In order to optimize the welding parameters, a mathematical model for determining the temperature distribution in the pipe workpiece and the surface profile of the resultant weld pool is indispensable. An efficient finite difference model was adopted for calculating the three-dimensional transient temperature distribution in circumferential gas tungsten arc (GTA) welding of pipes. Its solution was obtained by employing the alternating direction implicit (ADI) finite difference method, in which a periodic boundary condition and a periodic cubic spline function were used. For calculating the weld pool surface profiles in full penetration circumferential welding of pipes, a governing equation was derived in the cylindrical coordinate and solved using a simple finite difference model with the ADI scheme. In Part 2 of this paper, an efficient parameter optimization method is used to evaluate the optimal welding current for a required bead width when the welding velocity is given.

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Modeling of the Weld Shape Development During the Autogenous Welding Process by Coupling Welding Arc with Weld Pool

Journal of Materials Engineering and Performance ◽

10.1007/s11665-009-9570-z ◽

2009 ◽

Vol 19 (7) ◽

pp. 942-950 ◽

Cited By ~ 10

Author(s):

Wenchao Dong ◽

Shanping Lu ◽

Dianzhong Li ◽

Yiyi Li

Keyword(s):

Weld Pool ◽

Welding Process ◽

Weld Shape ◽

Welding Arc

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Electrodynamics of a magnet moving through a conducting pipe

Canadian Journal of Physics ◽

10.1139/p06-065 ◽

2006 ◽

Vol 84 (4) ◽

pp. 253-271 ◽

Cited By ~ 16

Author(s):

M Hossein Partovi ◽

Eliza J Morris

Keyword(s):

Drag Force ◽

Eddy Currents ◽

Numerical Study ◽

Full Range ◽

Magnetic Behavior ◽

Integral Form ◽

Asymptotic Formulas ◽

Pipe Material ◽

Point Dipole ◽

Axially Symmetric

The popular demonstration involving a permanent magnet falling through a conducting pipe is treated as an axially symmetric boundary-value problem. Specifically, Maxwell's equations are solved for an axially symmetric magnet moving coaxially inside an infinitely long, conducting cylindrical shell of arbitrary thickness at nonrelativistic speeds. Analytic solutions for the fields are developed and used to derive the resulting drag force acting on the magnet in integral form. This treatment represents a significant improvement over existing models, which idealize the problem as a point dipole moving slowly inside a pipe of negligible thickness. It also provides a rigorous study of eddy currents under a broad range of conditions, and can be used for magnetic braking applications. The case of a uniformly magnetized cylindrical magnet is considered in detail, and a comprehensive analytical and numerical study of the properties of the drag force is presented for this geometry. Various limiting cases of interest involving the shape and speed of the magnet and the full range of conductivity and magnetic behavior of the pipe material are investigated and corresponding asymptotic formulas are developed.PACS Nos.: 81.70.Ex, 41.20.–q, 41.20.Gz

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