Numerical and experimental study of arc and weld pool behaviour for pulsed current GTA welding

Extending the weldability of novel materials, and improving the weld quality by tailoring weld microstructures are key factors to obtain the welding techniques demanded in the modern manufacturing industries. This can be done, for example, by feeding chemical elements from a consumable wire into the weld pool during welding. The mixing of chemical components in the weld pool and the resulting post-solidification weld microstructures are influenced by weld pool hydrodynamics. Weld pool hydrodynamics is known to be primarily driven by Marangoni forces acting at the free liquid surface, i.e by tangential gradients in surface tension along the liquid surface due to pronounced lateral gradients in temperature and surface active element concentration. In this research, we develop a Computational Fluid Dynamics model to study steel weld pool hydrodynamics during conduction mode laser spot welding. It is concluded that free surface deformations and instabilities have a strong impact on the fluid flow and heat transfer in weld pools, and should therefore be accounted for in weld pool simulations. With increasing the surface active element concentration and laser power, the weld pool flow becomes highly unstable and can no longer be accurately modeled with a flat surface assumption. More accurate predictions of weld pool physics can be made if the free surface, solidification stage, and three-dimensionality are taken into account. This reduces the need for the use of unphysical parameter fittings widely reported in literature.

Marangoni driven free surface flows in liquid weld pools

Effect of enhanced heat and mass transport and flow reversal during cool down on weld pool shapes in laser spot welding of steel

Optimization of gas tungsten arc welding process by response surface methodology

This work reports a theoretical and numerical study of the parameters related to the process of laser powder deposition through a lateral nozzle. For this purpose, a 3D quasi-stationary finite element model was developed analytically and implemented numerically. The proposed model estimates the shape of the melt pool depending on the process parameters including scanning speed, powder mass flow, laser power, and physical properties. Also, phase transformations and physical properties (density, thermal conductivity, and specific heat) vary as function of temperature. In addition, thermo-capillary forces and their effect on fluid flow inside the melt pool are considered. The obtained set of equations coupled through the temperature variable was solved using COMSOL Multiphysics. The results are presented and compared with previously obtained experimental data, in which chromium powder was deposited, allowing validation of the model. Finally, variations at the melt pool geometry in terms of the operational parameters are analyzed. This model aims at estimation of melt pool geometry during laser powder deposition in time reasonably short to allow for predictable process control.

F. Roger

Papers

Optimal parameters for pulsed gas tungsten arc welding in partially and fully penetrated weld pools