Simulation of dynamic characteristics of powder beds during selective laser melting process

• Main Authors: CHOU, CHING-HSIANG, 周靖翔
• Other Authors: LAI, YI-SHENG
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/549s9x

碩士 === 國立聯合大學 === 材料科學工程學系碩士班 === 107 === In this study, ANSYS fluent software is used to simulate the transient behavior of fluid flow and heat transfer of AM Corrax powders in selective laser melting process. A linear scan is performed on the square, hexagonal, and randomly stacked powder layers with various laser powers. The fluid dynamics can be realized from the temperature and velocity fields of the weld pool. Effects of surface tension on Marangoni convection as well as vaporization on recoil pressure are discussed in relation to the phenomenon of spattering and balling. The surface morphology after solidification is simulated to avoid the use of rough surface for the next powder-spreading step, which may result in additional defects. Therefore, the surface roughness is calculated in this work, and appropriate process parameters are selected to achieve a quality-finished product. Firstly, the Yade code is carried out under the Ubuntu operating system to model simplified paving and scraping processes of SLM. Vibration is applied to compact powders in the space, and then a cumulative size distribution of these powders is generated to match that of AM Corrax ones in three-axis coordinates. Secondly, SolidWorks is implemented to assist in drawing the randomly packing model. The model is then exported to ANSYS fluent software for modeling. In ANSYS, the finite volume method discretizes the integral form of the conservation equations with appropriate integration time. The pressure-based solver uses a solution algorithm to solve pressure and velocity sequentially. Finally, the influence of process parameters and powder packing arrangements on the fluid dynamics are output by CFD-post post-processing software. The results show that the higher the laser power, the stronger the Marangoni convection and recoil pressure. A deep surface depression is observed at high laser power, leading to significant balling and spatter phenomenon, which inevitably increase the surface roughness. On the contrary, the surface roughness tends to be small as the laser power is lowered. Nevertheless, the wetting effect between the powders and the substrate is not good due to insufficient laser melting, and increased volume of pores is generated.