Revealing internal flow behaviour in arc welding and additive manufacturing of metals

Abstract

Internal flow behaviour during melt-pool-based metal manufacturing remains unclear and hinders progression to process optimisation. In this contribution, we present direct time-resolved imaging of melt pool flow dynamics from a high-energy synchrotron radiation experiment. We track internal flow streams during arc welding of steel and measure instantaneous flow velocities ranging from 0.1 m s−1 to 0.5 m s−1. When the temperature-dependent surface tension coefficient is negative, bulk turbulence is the main flow mechanism and the critical velocity for surface turbulence is below the limits identified in previous theoretical studies. When the alloy exhibits a positive temperature-dependent surface tension coefficient, surface turbulence occurs and derisory oxides can be entrapped within the subsequent solid as result of higher flow velocities. The widely used arc welding and the emerging arc additive manufacturing routes can be optimised by controlling internal melt flow through adjusting surface active elements.

State of the Art in Directed Energy Deposition: From Additive Manufacturing to Materials Design

“…The surface tension and therefore the internal melt pool flow could be controlled, to a certain extent, using surface active elements. For example, in an Fe system, changes in the concentration of the surface-active elements, like sulphur and oxygen, were shown to modify the internal melt pool flow [72,73]. Besides the Marangoni flow force, other forces, like aerodynamic drag (outward drag forces caused by the plume formed above the melt pool), buoyancy (upward movements of the melt pool due to density changes caused by thermal gradients inside the melt pool), electromagnetic, and Lorentz forces (forces due to electric and magnetic fields generated by the source), may also be present during the DED process [72].…”

The Influence of Surface Deformation on Thermocapillary Flow Instabilities in Low Prandtl Melting Pools with Surfactants

“…Melt pool formation, the internal molten-metal flow behaviour and the subsequent re-solidification affect the quality of the products manufactured using advanced fusion-based processes such as additive manufacturing and fusion welding [1]. During these processes, a localised energy flux is often employed that melts the material, forms a melt pool and induces large temperature gradients over the melt pool surface.…”

“…Transport phenomena in liquid metal melt pools during laser melting encompass solidification and melting, various types of heat transfer (radiation, convection and conduction), laser-material interactions, surface tension effects, and intensive fluid flow that interact each other and respond nonlinearly to the applied boundary conditions [9]. Real-time experimental measurement of heat and fluid flow in low-Prandtl melting pools (Pr = O(10 −1 )) is challenging due to the opacity, high temperature and rapid changes in the system [10] and are mainly limited to two-dimensional interpretations [1]. Thus, numerical simulations with sufficient accuracy are needed to gain a better understanding of the transient heat and fluid flow in low Prandtl melting pools.…”

Laser-arc hybrid welding of 12- and 15-mm thick structural steel

“…To study melt flow under such conditions is very complicated requiring X-ray filmography and tracking particles (such as tungsten). Moreover, it requires advanced equipment for analysis [54]. Evidently, with an increase of plate thickness from 12 to 15 mm, the frequency of humping occurrence is higher due to an increased molten mass of the weld pool.…”