Numerical assessment and experimental verification of the influence of the Hartmann effect in laser beam welding processes by steady magnetic fields

Abstract

Controlling the dynamics in the weld pool is a highly demanding challenge in deep-penetration laser beam welding with modern high power laser systems in the multi kilowatt range. An approach to insert braking forces in the melt which is successfully used in large-scaled industrial applications like casting is the so-called Hartmann effect due to externally applied magnetic fields. Therefore, this study deals with its adaptation to a laser beam welding process of much smaller geometric and time scale. In this paper, the contactless mitigation of fluid dynamic processes in the melt by steady magnetic fields was investigated by numerical simulation for partial penetration welding of aluminium. Three-dimensional heat transfer, fluid dynamics including phase transition and electromagnetic field partial differential equations were solved based on temperature-dependent material properties up to evaporation temperature for two different penetration depths of the laser beam. The Marangoni convection in the surface region of the weld pool and the natural convection due to the gravitational forces were identified as main driving forces in the weld pool. Furthermore, the latent heat of solid-liquid phase transition was taken into account and the solidification was modelled by the Carman-Kozeny equation for porous medium morphology. The results show that a characteristic change of the flow pattern in the melt can be achieved by the applied steady magnetic fields depending on the ratio of magnetic induced and viscous drag. Consequently, the weld bead geometry was significantly influenced by the developing Lorentz forces. Welding experiments with a 16 kW disc laser with an applied magnetic flux density of around 500 mT support the numerical results by showing a dissipating effect on the weld pool dynamics.

Thermal Marangoni Flow Past a Permeable Stretching/Shrinking Sheet in a Hybrid Cu-Al2O3/Water Nanofluid

“…Nadeem et al (2018) explored the stagnation point flow of hybrid Cu-Al 2 O 3 / water nanofluid on a circular cylinder while Rostami et al (2018) Marangoni convection is generated due to the variations of surface tension gradients, either in the temperature, concentration or both gradients. Marangoni convection is extensively applied in welding (Bachmann et al 2016;Cui et al 2018;Kidess et al 2016), crystal growth (Minakuchi et al 2017;Timoveef et al 2015) and soap film stabilisation (Bournival et al 2017;Raza et al 2016). A brief explanation of the theory of Marangoni convection flow was discussed by Arifin et al (2011).…”

Thermophysical Phenomena in Metal Additive Manufacturing by Selective Laser Melting: Fundamentals, Modeling, Simulation, and Experimentation

“…be found in the fields of laser and electron beam welding (see e.g. [9,23,45,47,86,85,103,127,135]). Future SLM simulation models could strongly benefit from these works.…”

Numerical and experimental investigation of magnesium/aluminum laser welding with magnetic field

“…Bachmann et al [18] simulated the effect of a stable transverse magnetic field in high power laser beam processing of Al alloy and they believed the magnetic field altered the temperature distribution and eliminated the influence of thermo-capillary flow. Bachmann et al [19] subsequently investigated the of the Hartmann effect on the model of magnetic field assisted laser jointing of Al alloy and they thought that it is advantageous for the uniform distribution of mechanical stress by reducing the influence of Marangoni effect. Rong et al [20] built a model of magnetic field supported laser welding of 316L steel and they suggested that magnetic field was helpful for reducing the welding deformation based on the calculated results.…”