A powder-scale multi-physics model is developed to investigate the keyhole dynamics and porosity in products fabricated by selective laser melting (SLM) under the sub-atmospheric pressure. The effects of the sub-atmospheric pressure on the plume attenuation of the laser beam, vaporization temperature and vapor recoil pressure are taken into account. The thermo-fluid behaviour in the melt pool under the atmospheric and sub-atmospheric ambient pressure is analysed in the SLM process. The simulation results suggest that the reduction of the sub-atmospheric pressure can increase the melt pool depth, whereas the effects are insignificant under the low sub-atmospheric pressure. As compared with the atmospheric pressure, the sub-atmospheric pressure leads to the decrease of the average temperature and the increase of the average recoil pressure on the keyhole surface, which is in favour of increasing keyhole stability and maintaining keyholes open. Consequently, the sub-atmospheric pressure can help to improve the keyhole stability and thus minimize pore defects in SLM-built products.

建立了粉末级多物理场模型，以研究在低于大气压的条件下通过选择性激光熔化（SLM）制造的产品的锁孔动力学和孔隙率。考虑了低于大气压的压力对激光束羽流衰减，蒸发温度和蒸气反冲压力的影响。在SLM过程中，分析了在大气压和低于大气压的环境压力下熔池中的热流体行为。模拟结果表明，降低低于大气压的压力可以增加熔池深度，而在低低于大气压的压力下，其影响并不明显。与大气压相比 低于大气压会导致钥匙孔表面平均温度降低，平均反冲压力增加，这有利于提高钥匙孔的稳定性并保持钥匙孔的开放。因此，低于大气压的压力可以帮助改善锁孔的稳定性，从而最大程度地减少SLM制造产品中的孔缺陷。