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

Volume 3 ◽  
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.

Validation of evaporation-determined model of arc-cathode coupling in the peak current phase in pulsed GMA welding

2021 ◽  
Author(s):  
Marek Sebastian Simon ◽  
Oleg Mokrov ◽  
Rahul Sharma ◽  
Uwe Reisgen ◽  
Guokai Zhang ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Weld Pool ◽  
Cathode Surface ◽  
Gma Welding ◽  
Gas Metal Arc Welding ◽  
Welding Process ◽  
Qualitative Reasoning ◽  
Current Phase ◽  
Temperature Plasma ◽  
Peak Current

Abstract A first experimental validation of the EDACC (evaporation-determined arc-cathode coupling) model is performend by comparing the experimental and simulated current in the peak current phase of a pulsed GMAW (gas metal arc welding) process. For this, the EDACC model was extended to limit the cathode surface temperature to a realistic value of <2400K. The information on the plasma for the EDACC model was gathered from literature and extrapolated and extended according to qualitative reasoning. The information on the cathode surface of the EDACC model was derived from a steady-state simulation of the weld pool, using an averaging approach over time for the energy and current. The weld pool surface temperature was compared to pyrometric measurements, that were performed for this work, and the agreement was found to be fair. The observed agreement between the modelled and experimentally determined current was within 10%. As strong assumptions were made for the comparison, the validation cannot be considered as final, but the assumptions are thoroughly analyzed and discussed. However the critical link between surface temperature, plasma temperature and total current transmitted could be reconstructed.

Effects of Welding Current on Metal Transfer and Weld Pool Dynamics in Gas Metal Arc Welding

2006 ◽  
Author(s):  
J. Hu ◽  
H. L. Tsai ◽  
P. C. Wang
Keyword(s):  
Weld Pool ◽  
Arc Welding ◽  
Gma Welding ◽  
Gas Metal Arc Welding ◽  
Metal Transfer ◽  
Dominant Factor ◽  
Transient Temperature ◽  
Transfer Mode ◽  
Metal Arc Welding ◽  
Metal Transfer Mode

In gas metal arc welding (GMAW), current is one of the most important factors affecting the mode of metal transfer and subsequently the weld quality. Recently, a new technology using pulsed currents has been employed to achieve the one droplet per pulse (ODPP) metal transfer mode with the advantages of low average currents, a stable and controllable droplet generation, and reduced spatter. In this paper, the comprehensive model recently developed by the authors was used to study the influences of different current profiles on the droplet formation, metal transfer, and weld pool dynamics in GMA, welding. Five types of welding currents were studied, including two constant currents and three waveform currents. In each type, the transient temperature and velocity distributions of the arc plasma and the molten metal, and the shapes of the droplet and the weld pool were calculated. The results showed that a higher electromagnetic force was generated at a higher current and becomes the dominant factor that detaches the droplet from the electrode tip. A smaller droplet size and a higher droplet frequency were obtained for a higher current. The model has demonstrated that a stable ODPP metal transfer mode can be achieved by choosing a current with proper waveform for given welding conditions.

Investigation of Transport Phenomena in Three-Dimensional Gas Metal Arc Welding of Thick Metals

2007 ◽  
Author(s):  
Jun Zhou ◽  
Mohammad S. Davoud ◽  
Hai-Lung Tsai
Keyword(s):  
Base Metal ◽  
Weld Pool ◽  
Arc Welding ◽  
Transport Phenomena ◽  
Gas Metal Arc Welding ◽  
Heat Diffusion ◽  
Liquid Region ◽  
Weld Penetration ◽  
Melt Flow ◽  
Metal Arc Welding

Arc welding is generally used to join thick metals in many engineering applications. However, poor penetration often occurs due to arc heat diffusion into the base metal. Hence, arc welding of thick metals normally requires grooving and/or preheating of the base metal and sometimes requires multiple passes for very thick metals or metals with high conductivity, such as aluminum alloys. In gas metal arc welding of thick metals with grooves and preheating, complicated melt flow and heat transfer are caused by the combined effect of droplet impingement, gravity, electromagnetic force, surface tension, and plasma arc pressure. Understanding these complicated transport phenomena involved in the welding process is critical in improving the penetration depth and weld quality. In this study, mathematical models and associated numerical techniques have been developed to study the effects of grooves and preheating on melt flow, diffusion of species, and weld penetration in gas metal arc welding of thick metals. Complex melt flow, transient weld pool shape and distributions of temperature and species in the weld pool are calculated. The continuum formation is adopted to handle liquid region, mushy zone and solid region. VOF technique is used to handle transient deformed shape of weld pool surface. The preliminary results show both grooves and preheating have important effects on the melt flow in weld pool and the weld penetration. Computer animations showing the evolutions of temperature; melt flow; and the interaction between droplets and weld pool will be presented.

A Study on the Three-Dimensional Analysis of Heat and Fluid Flow in Gas Metal Arc Welding Using Boundary-Fitted Coordinates

1994 ◽  
Vol 116 (1) ◽  
pp. 78-85 ◽  
Author(s):  
J.-W. Kim ◽  
S.-J. Na
Keyword(s):  
Surface Tension ◽  
Fluid Flow ◽  
Weld Pool ◽  
Surface Deformation ◽  
Driving Forces ◽  
Gma Welding ◽  
Gas Metal Arc Welding ◽  
Three Dimensional ◽  
Weld Bead ◽  
Surface Boundary

Computer simulation of three-dimensional heat transfer and fluid flow in gas metal arc (GMA) welding has been studied by considering the three driving forces for weld pool convection, that is the electromagnetic force, the buoyancy force, and the surface tension force at the weld pool surface. Molten surface deformation, particularly in the case of GMA welding, plays a significant part in the actual weld size and should be considered in order to accurately evaluate the weld pool convection. The size and profile of the weld pool are strongly influenced by the volume of molten electrode wire, impinging force of the arc plasma, and surface tension of molten metal. In the numerical simulation, difficulties associated with the irregular shape of the weld bead have been successfully overcome by adopting a boundary-filled coordinate system that eliminates the analytical complexity at the weld pool and bead surface boundary. The method used in this paper has the capacity to determine the weld bead and penetration profile by solving the surface equation and convection equations simultaneously.

Numerical Dynamic Analysis of Moving GTA Weld Pool

1998 ◽  
Vol 120 (1) ◽  
pp. 173-178 ◽  
Author(s):  
Z. N. Cao ◽  
Y. M. Zhang ◽  
R. Kovacevic
Keyword(s):  
Weld Pool ◽  
Plate Thickness ◽  
Three Dimensional ◽  
Calculated Data ◽  
Welding Process ◽  
Welding Current ◽  
Three Dimensional Model ◽  
Full Penetration ◽  
Weld Pools ◽  
Describe Heat Transfer

A three dimensional model with a moving heat source is developed to describe heat transfer and fluid flow in transient weld pools. Full penetration and free top and bottom surfaces are incorporated in the model in order to simulate the welding process more practically. The influence of plate thickness and welding current on the dynamics of weld pools is analyzed using calculated data. It is shown that when the workpiece is nearly penetrated, the depth of weld pool increases quickly. Also, the elevation of the top surface decreases quickly once the full penetration status is established.

scholarly journals Droplet Transfer Induced Keyhole Fluctuation and Its Influence Regulation on Porosity Rate during Hybrid Laser Arc Welding of Aluminum Alloys

Metals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1510
Author(s):  
Leilei Wang ◽  
Yanqiu Zhao ◽  
Yue Li ◽  
Xiaohong Zhan
Keyword(s):  
Aluminum Alloys ◽  
Weld Pool ◽  
Arc Welding ◽  
High Speed ◽  
Welding Current ◽  
Droplet Transfer ◽  
High Speed Imaging ◽  
Hybrid Laser Arc Welding ◽  
Globular Transfer ◽  
Weld Porosity

Hybrid laser arc welding (HLAW) features advantages such as higher welding speed and gap tolerance as well as smaller welding deformation and heat-affected zone than arc welding. Porosity in hybrid laser arc weld due to keyhole fluctuation tends to be the initial source of crack propagation, which will significantly diminish the weld performance. A high-speed imaging technique was adopted to record and analyze the droplet transfer and keyhole fluctuation behavior during hybrid laser arc welding of aluminum alloys. A heat transfer and fluid flow model of HLAW was established and validated for a perspective of the evolution process of droplet transfer and keyhole fluctuation. The relationship between keyhole fluctuation and weld porosity was also revealed. During the droplet transfer stage, liquid metal on the top surface of the weld pool flows toward the keyhole originated by globular transfer, and the keyhole fluctuates and decreases significantly, which has a higher tendency to form a bubble in the weld pool. The bubble evolves into porosity once trapped in the mush-zone near the trailing edge of the weld pool. Therefore, globular transfer during HLAW is the principal origin of keyhole fluctuation and weld porosity. Welding current has a significant influence on keyhole fluctuation and weld porosity rate. Droplet transfer frequency, keyhole fluctuation, and porosity rate increase with higher welding current under the globular transfer mode. The porosity rate shows a nearly positive correlation with the standard deviation of keyhole fluctuation.

A Study on Experimental Design Methods for the Automatic GMA Welding Process

2019 ◽  
Vol 294 ◽  
pp. 119-123
Author(s):  
Zong Liang Liang ◽  
Tae Jong Yun ◽  
Won Bin Oh ◽  
Bo Ram Lee ◽  
Ill Soo Kim
Keyword(s):  
Experimental Design ◽  
Taguchi Method ◽  
Arc Welding ◽  
Gma Welding ◽  
Gas Metal Arc Welding ◽  
Welding Process ◽  
Welding Current ◽  
Welding Parameters ◽  
Bead Width ◽  
Arc Welding Process

Generally, the welding parameters directly affect the weld forming and the joint performance. Because many parameters are involved in the automatic arc welding process, it is not realistic to use traditional experimental methods, such as full factorial design. Therefore, it is important to find out the good experimental design method to determine the welding parameters for optimal joint quality with a minimal number of experiments. Therefore, this study is aimed at investigating the effect of DOE (Design of Experiment) methods on bead width of mild steel parts welded by the automatic GMA (Gas Metal Arc) welding process. In this work, Taguchi method was used for studying the effect of the welding parameters on optimization of bead width, while Box-Behnken method was utilized to develop a mathematical model relating the bead width to welding parameters such as welding voltage, arc current, welding speed and CTWD (Contact Tip to Work Distance). The S/N (Signal-to-Noise) ratio and the ANOVA (Analysis of Variance) were employed to find the optimal bead width. Confirmation tests were carried out to validate the effectiveness of the Taguchi method. The experimental results show that welding current mainly affected the bead width. The predicted bead width of 3.12mm was in good agreement with the confirmation tests. With the regression coefficient analysis in the Box-Behnken design, a relationship between bead width and four significant welding parameters was obtained. A second-order model has also been established between the welding parameters and the bead width as welding quality. The developed model is adequate to navigate the design space.

Three-Dimensional Modeling of Plasma Arc in Arc Welding

2006 ◽  
Author(s):  
G. Xu ◽  
H. L. Tsai
Keyword(s):  
Magnetic Field ◽  
Weld Pool ◽  
Arc Welding ◽  
Gas Metal Arc Welding ◽  
Three Dimensional ◽  
Plasma Arc ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Three Dimensional Modeling ◽  
Dimensional Modeling

Most previous three-dimensional modeling work in gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) focuses on the weld pool. Almost all three-dimensional weld pool models are based on the two-dimensional axisymmetric Gaussian assumption of plasma arc pressure and heat flux. In this paper the three-dimensional plasma arc is modeled and results are presented. The velocity, pressure, temperature, current density, and magnetic field of the plasma arc are computed by solving the conservation equations of mass, momentum, and energy, as well as part of Maxwell's equations. This three-dimensional model allows one to study the non-axisymmetric plasma arc caused by external perturbations such as the external magnetic field. It also provides more accurate boundary conditions when modeling the welding pool. The future work is to unify it with the weld pool model and accomplish a complete three-dimensional model of GTAW and GMAW.

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