Numerical investigation of droplet impact on the welding pool in gas metal arc welding

Abstract

A transient three-dimensional model that describes physical phenomena inside a welding pool during gas-metal arc welding process is presented. The model considers such phenomena as heat-mass transfer, electromagnetics, hydrodynamic processes and deformation of the weld pool free surface. The fluid flow in the weld pool is induced due to the presence of the mechanical impact of the droplets, thermo-capillary surface tension, thermal buoyancy and electromagnetic forces. The weld pool surface deformation is calculated by considering arc pressure and droplet impact force. A comparative analysis of the impact of the electric current of the welding arc and different force factors causing the motion of liquid metal in the weld pool on the shape of the welded seam was carried out and discussed. Keywords: Arc welding / numerical simulation / hydrodynamics / welded seam formation / droplet impact Es wird ein transientes, dreidimensionales Modell vorgestellt, das die physikalischen Phä nomene in einem Schmelzbad beim Metallschutzgasschweißen beschreibt. Das Modell berü cksichtigt solche Phä nomene wie Wä rme-und Massenü bertragung, elektromagnetische Phä nomene, hydrodynamische Prozesse und die Deformierung der freien Schmelzbadoberflä che. Die Strö mungen im Schmelzbad werden hervorgerufen durch den mechanischen Aufprall der Tropfen, die thermokapillare Oberflä chenspannung, den thermischen Auftrieb und elektromagnetische Krä fte. Bei der Berechnung der Deformation der Schmelzbadoberflä che werden der Lichtbogendruck und die Kraft der auftreffenden Tropfen berü cksichtigt. Eine vergleichende Analyse des Einflusses des elektrischen Stromes des Schweißlichtbogens und der verschiedenen Krä fte, die die Bewegung des flü ssigen Metalls im Schmelzbad verursachen, auf die Form der Schweißnaht wurde durchgefü hrt und diskutiert. Schlü sselwö rter: Lichtbogenschweißen / numerische Simulation / Strö mungen / Schweißnahtbildung / Tropfenwirkung

Simplified surface heat source distribution for GMAW process simulation based on the EDACC principle

“…Another argument in favor of the EDACC model in terms of physical consistency is that when applying the Gaussian heat source, the forces due to the Marangoni effect are often overestimated due to the much larger surface temperatures and resulting temperature gradients, as well as uncertainties on the value of the surface tension which is very sensitive to the chemical composition (see [16]). With the EDACC model and this presented simple formulation, this overestimation is not necessary, because it shows that the current approaches for modeling the weld pool formation (for example, see [17] and [18]) are based on assumptions and parameters, which are adjusted to give the desired result, but which are in principle unphysical or unjustified. Therefore, it should be noted that while it is possible to achieve simulation results that closely resemble real welding experiments that as long as the individual phenomena and their resulting interaction are still insufficiently taken into account, a quantitative validation in terms of a weld pool formation comparison seems to be unreasonable.…”

“…Finally, the resulting distributions for heat flux and current density can be normalized and multiplied with more empirical values for the arc power P Arc and the arc current I Arc (see Eq. (17) and Eq. (19)).…”

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

“…For this, the mean power in the process was multiplied by the arc efficiency η = 0.8 to account for losses by radiation from the arc and resistance heating in the wires. The power that was necessary to heat the droplets to an assumed droplet temperature of T droplet = 2500 [K] was subtracted from the total power as well, in order to receive an approximation for the mean power to the cathode P Arc , cf [17].…”

Arc-cathode attachment in GMA welding

“…The model for the weld pool was based on a model of weld pool calculation presented in [20] and implemented in ANSYS CFX in reduced form (without the calculation of the free surface) to speed up calculation. In this work, it serves to show the plausibility of the model for cathode-arc attachment.…”