A 3D transient finite element model of Inconel 718 nickel-based superalloy processed by selective laser melting was developed to study the heat flux in the molten pool under the condition of different process parameters and its effect on the temperature field and the shape of molten pool, in which a solid heat transfer module and a laminar flow module in the finite element simulation software COMSOL Multiphysics was applied. In the simulation several special phenomenon characterized with SLM process was considered, such as the interaction between the laser and material with stochastic porosity distribution on powder bed, and the nonlinear change of thermophysical properties due to the state change of material and the influence of the Marangoni effect in the molten pool. The results show that the Marangoni effect caused by the surface tension of molten pool makes the convective heat flux play a leading role in the heat transfer process in the molten pool, and its depth/width ratio is changed by changing the magnitude and direction of the heat flow, what determines the shape of molten pool. The increase in laser power or reduced scanning speed can increase the heat input per unit time, and then lead to a Marangoni convection enhancement within the molten pool, thus enlarge the size of the molten pool. The experimental results are in good agreement with the simulation results.
In the paper, the effects of porosities and average particle sizes of powder layer on light absorption during SLM process were investigated, in which closed-packing models based on Horsfieled’s filling method were established and light absorption was simulated using ray tracing based on laser-material interaction mechanism. The results show the absorption of powder layer of Ti6Al4V alloy is higher than 70%. The decrease of porosity of powder layer benefits to improve the absorption, while the absorption tends to decrease if porosity decreases to a certain value due to the reflection. The decrease of average particle size of powder particles benefits also to improve the absorption. If the light irradiates at positions with different particle arrangements, the absorption behavior changes with irradiation condition whether there occurs the multi-reflection. The above research provides theoretical basis for preparation of new powder materials, their parameter developing for SLM technology and even the properties regulation of SLM fabricated component.