Two-dimensional heat transfer and melt flow in the laser-impact zone at selective laser melting of thin walls -- II: Modeling

TL;DR

This paper develops and validates a CFD model of heat transfer and melt flow in laser melting, revealing vortex formation, flow dynamics, and providing an analytical model for melt pool depth estimation to optimize the process.

Contribution

It introduces a novel CFD model with an original Riemann solver for simulating melt flow and heat transfer in SLM, and proposes an analytical model for melt pool depth estimation.

Findings

Formation of outward vortices in the melt pool.

Flow velocities are insufficient for complete homogenization.

Melt pool depth is proportional to linear energy density.

Abstract

Part II of the present work concerns modeling and analyzing the experimental data obtained in Part I. A computational fluid dynamics (CFD) model of two-dimensional conductive heat transfer and thermocapillary-driven convection is developed. The conservation laws for mass, momentum, and energy are numerically solved by a second-order Godunov finite-volume method using an original Riemann solver developed for the applied equation of state. The CFD model is validated by comparison with the experiments. Formation of two outward vortices in the melt pool is revealed. Surface-active impurities can make the surface tension-temperature function non-monotonous giving raise additional vortices with the opposite inward flow direction. The influence of melt convection on the melt pool size is not considerable in the conditions of selective laser melting (SLM). The flow velocity in the melt pool is around or less than the laser scanning speed. This means insufficient mixing in the melt pool. One cannot expect a complete homogenization of chemical composition when using powder blends in SLM. The correlation between the error of the Rosenthal model and the latent heat of fusion is carefully studied resulting an analytical model for estimating the melt pool depth. In the studied SLM cases, the accuracy of the developed analytical model is within 10% relative the CFD model. The obtained experimental and theoretical results indicate that the melt depth is approximately proportional to linear energy density LED in the typical conditions of SLM. This can be useful when optimizing the SLM process.