Heat Source Characteristics of Ternary-Gas-Shielded Tandem Narrow-Gap GMAW

Residual stresses can affect both the static strength and the fatigue endurance of welded joints. Residual stresses can be assessed by numerical simulation; however, the simulation of the welding process is a complex task that requires knowledge of several parameters, many of which can only be estimated with some uncertainty. The reduction in the number of these parameters can lead to a more feasible and efficient study. In this work, the finite element method is used to assess the capability of different thermal methods used to simulate a single pass of the gas metal arc welding process in reproducing the temperature distribution around the weld. Results of the simulations are compared to experimental measurements of the surface temperature close to the welding area. The thermal techniques analyzed adopt different levels of complexity, from the basic implementation of a constant initial temperature assigned to a given material volume, to the more comprehensive and widespread Goldak's double-ellipsoid model. The study shows that, close to the weld seam, very similar thermal behaviors can be achieved by employing each one of the analyzed methods. Secondly, considering the constant initial temperature method, the comparison between experimental measurements and numerical simulations showed a fairly good agreement, suggesting that a relatively simple method (i.e., requiring the setting of only one parameter) can be used to efficiently reproduce the thermal history of a welding process.

Section: Numerical Resultsmentioning

confidence: 99%

Evaluation of Heat Sources for the Simulation of the Temperature Distribution in Gas Metal Arc Welded Joints

Chiocca

Frendo

Bertini

2019

“…Wei et al [7] developed non-axisymmetric tungsten narrow gap tungsten arc welding, in which the heating of the rotating arc and the stirring action of the molten pool make a good shape weld. Cai et al [8,9] combined the tandem technology to the narrow gap welding; a uniform fusion weld was obtained under appropriate welding parameters. In the above solutions, the motion path of the welding arc is changed mechanically, so the welding arc can heat the side wall directly, and the side wall penetration is increased significantly.…”

Section: Introductionmentioning

confidence: 99%

Influence of the Longitudinal Magnetic Field on the Formation of the Bead in Narrow Gap Gas Tungsten Arc Welding

Jian

2020

The oscillation arc assisted by an extra alternating longitudinal magnetic field (LMF) in narrow gap tungsten arc welding is proved to be effective in avoiding welding defects due to insufficient fusion at the side walls in joining thick wall plates. The behavior of the welding arc and molten pool under the LMF is simulated to reveal the influence of the LMF on the formation of a uniform penetration weld bead. A unified mathematical model was developed for the narrow gap tungsten arc welding including the plasma arc, molten pool, electrode, and their interactions. Under the LMF, the whole welding arc is deflected and oscillates between the two side walls. When the magnetic-field strength is larger than 6 mT, the axis of the arc deflects to the side wall; the maximum value of heat flux at the bottom decreases by one-half, and the maximum value at the side wall is increased by a factor of ten. On the other hand, under the LMF, the forces acting on the molten pool are changed; the fluid flow pattern is helpful to increase the heat transferred to the side walls. The model is validated by experimental results. Both the percentage deviations of the simulation weld penetration at the side wall and at the bottom from the experimental results are lower than 10%.

“…In the past decades, the increasingly fierce competition of the commercial industry has put much emphasis on efficiency, which gives impetus to the development of manufacturing automation. Gas metal arc weld (GMAW), a method in which liquid metal droplets are formed and detached from the electrode wire, is widely used in automatic manufacturing and robot welding because of high productivity and reliable usability [1,2].…”

Section: Introductionmentioning

confidence: 99%

Comparative Study of Droplet Transfer Modes on Appearance, Microstructure, and Mechanical Properties of Weld during Pulsed GMAW

Zhai

Xue

Wang

et al. 2020

Droplet transfer plays a crucial role in welding stability and quality of pulsed gas metal arc weld (GMAW), referring to the process of heat and mass transition. In this work, the appearance, microstructure, microhardness, tensile properties, and impact toughness with three typical modes of droplet transfer in pulsed GMAW (ODMP: one drop per multiple pulses; ODPP: one drop per pulse; MDPP: multiple drops per pulse) were studied and compared. The results showed that the better welding appearance, the deeper penetration, and the less fume covered on the steel plate could be found during the ODPP welding process. At the same wire feeding speed and arc length, the average current was similar in ODPP and MDPP conditions. However, the average current in the ODMP condition was about 15 A larger than the other two, contributing to the higher heat input. Compared with MDPP and ODMP, the longest elongation and impact energy of the welded joint were found in the ODPP condition. Furthermore, the decrease of elongation and impact toughness in the ODMP condition might result from the higher heat input and the coarsen microstructure, like the proeutectoid ferrite and ferrite side plate.