Melt Pool Flow Research Articles

Numerical and Analytical Modeling of Free-Jet Melt Spinning for Fe75−Si10−B15 (at. %) Metallic Glasses

Amorphous fiber, ribbon, or film is produced through melt spinning. In this manufacturing process, a continuous delivery of amorphous material is simultaneously dependent on the wheel spinning rate, metallic liquid viscosity, surface tension force, heat transfer inside the melt pool and along the substrate, and other parameters. An analysis of a free-jet melt spinning for fiber manufacture has been performed to relate the process control parameters with amorphous formation. We present a numerical simulation of transient impingement of a free melt jet with a rapidly rotating wheel, along with theoretical estimates of melt ribbon thickness, to investigate dynamical characteristics of the flow in melt pool. The nucleation temperature and the critical cooling rate are predicted in the paper for alloy Fe75–Si10–B15 (at. %). Thermal conduction is found to dominate undercooling in melt spinning by comparing the temperature and velocity measurements with our numerical simulation and the analytical solutions.

A procedure to fully control and trace the weld quality for laser-arc hybrid welding under production conditions

Hybrid welding combining a laser beam with a MIG/MAG-arc has high potential to fill joint gaps and to shape the weld surface. The geometrical variations and the oxidation of the joint edges can have significant influence on the resulting weld surface shape and on fatigue life. In the presented study, edge tolerances such as edge mismatch were measured. By consequent scanning of the tolerances, high speed imaging of the melt pool flow dynamics and scanning of the resulting weld surface profile, a systematic identification and explanation of the weld quality on the joint edge conditions can be achieved, even for complex products in rough industrial environment. A corresponding general procedure is presented. From a case study, the limits of quality aspects such as undercuts were quantitatively identified and qualitatively explained.

Melt Pool Flow and Surface Evolution During Pulsed Laser Micro Polishing of Ti6Al4V

Extensive experimental work has shown that pulsed laser micro polishing (PLμP) is effective for polishing micro metallic parts. However, the process physics have not been fully understood yet, especially with respect to the melt pool flow. A reliable physical model can be of significant assistance in understanding the fluid flow in the melt pool and its effect on PLμP. In this paper, a two-dimensional axisymmetric transient model that couples heat transfer and fluid flow is described that was constructed using the finite element method. The model not only provided the solutions to the temperature and velocity fields but also predicted the surface profile evolution on a free deformable surface. The simulated melt depth and resolidified surface profiles matched those obtained from optical images of PLμPed Ti6Al4V sample cross-sections. The model was also used to study the effect of laser pulse duration on the melt pool flow. The study suggests that longer pulses produce more significant fluid flows. The cut-off pulse duration between capillary and thermocapillary regimes, below which minimal Maragoni flow should be expected, was estimated to be 0.66 μs for Ti6Al4V, which also matched well with the experimental results. It is evident that the coupled model offers reliable predictions and thus can be extended for a more complex parametric study to provide further insights for PLμP.

Analysis of the Rapid Central Melt Pool Flow in Hybrid Laser-Arc Welding

Hybrid laser arc welding creates a long weld pool tail. By high speed imaging the melt velocity behind the keyhole was measured to be very high, of the order of meters per second. Fluid dynamics simulation was carried out locally in the central axial plane of the pool tail. The high speed melt layer redistributes its momentum to slow movement of the deeper bulk. The consequences of initially high melt speed and its mass flow redistribution on the formation of the central reinforcement peak are discussed.

Modeling of laser cladding with powder injection

Laser cladding is one of the material additive manufacturing processes used to produce a metallurgically bonded deposition layer. To obtain a high-quality resulting part, a deep understanding of the underlying mechanisms is required. In this article, a mathematical model is developed to simulate the coaxial laser-cladding process with powder injection, which includes laser- substrate, laser-powder, and powder-substrate interactions. The model considers most of the associated phenomena, such as melting, solidification, evaporation, evolution of the free surface, and powder injection. The fluid flow in the melt pool, which is mainly driven by Marangoni shear stress as well as particle impinging, together with the energy balances at the liquid-vapor and the solid-liquid interfaces, are investigated. Powder heating and laser power attenuation due to the powder cloud are incorporated into the model in the calculation of the temperature distribution. The influences of the powder injection on the melt pool shape, penetration, and flow pattern are predicted through the comparison for the cases with powder injection and without powder injection. Dynamic behavior of the melt pool and the formation of the clad are simulated. The effects of the process parameters on the melt pool dimension and peak temperature are further investigated based on the validated model.

The development of temperature fields and powder flow during laser direct metal deposition wall growth

The additive manufacturing technique of laser direct metal deposition (DMD) has had an impact in rapid prototyping, tooling and small-volume manufacturing applications. Components are built from metallic materials that are deposited by the continuous injection of powder into a moving melt pool, created by a defocused laser beam. The size of the melt pool, the temperature distributions around it and the powder flux are critical in determining process characteristics such as deposition rate. In this paper, the effects that changes in the distance between the laser deposition head and the melt pool have on these factors as a part is built using a coaxial powder feeding system are considered via a two-part analytical model. A heat flow model considers three-dimensional temperature distributions due to a moving Gaussian heat source in a finite volume and a simple mass-flow model considers changes in powder concentration with distance from the deposition head. The model demonstrates the effect of adjusting the melt pool standoff in different ways on melt pool and powder flow characteristics as a DMD structure is built, and hence allows the effect on build rate to be predicted. Its validity is verified by comparison with a series of 316L stainless steel walls, built using different standoff adjustment methods. The model is found to be able to explain the dimensional characteristics found.