Assessment of thermal cycles by combining thermo-fluid dynamics and heat conduction in keyhole mode welding processes

Abstract

A numerical framework for simulation of the steady-state thermal behaviour in keyhole mode welding has been developed. It is based on the equivalent heat source concept and consists of two parts: computational thermo-fluid dynamics and heat conduction. The solution of the thermo-fluid dynamics problem by the finite element method for a bounded domain results in a weld pool interface geometry being the input data for a subsequent heat conduction problem solved for a workpiece by a proposed boundary element method. The main physical phenomena, such as keyhole shape, thermo-capillary and natural convection and temperature-dependent material properties are taken into consideration. The developed technique is applied to complete-penetration keyhole laser beam welding of a 15 mm thick low-alloyed steel plate at a welding speed of 33 mm s −1 and a laser power of 18 kW. The fluid flow of the molten metal has a strong influence on the weld pool geometry. The thermo-capillary convection is responsible for an increase of the weld pool size near the plate surfaces and a bulge formation near the plate middle plane. The numerical and experimental molten pools, crosssectional weld dimensions and thermal cycles of the heat affected zone are in close agreement.

High-power laser beam welding for thick section steels – new perspectives using electromagnetic systems

“…Nonetheless, they are useful even for more specific cases, e.g. in simulations considering equivalent heat source concepts coupling a stationary fluid flow simulation with a transient heat conduction model in autogenous laser beam welding [30, 31], or for the elucidation of the relationship between flow phenomena in the weld pool, the resulting weld geometry and the final mechanical resistance of the weld [32, 33]. Similar simplified models are in the same way well suited if one is interested in evaluating the resulting pressure differences in the weld bead during the application of electromagnetic fields as an inductive weld support system for a given magnetic flux density applied or to limit the parameter window for such application.…”