为获得高致密及高精度金属零件,有必要消除选区激光熔化快速成型过程的球化现象.文中从理论上分析了金属熔池球化的演变机制以及消除球化的方法,发现改变激光功率、扫描速度、铺粉厚度等成型参数可以弱化球化现象的原因,在于能对上一层基础有足够的熔化量：如对上一层基础有熔化量,则熔池分为熔化粉末所形成的上部熔池以及熔化基础形成的下部熔池;上部熔池受气液界面张力的作用,总有发生球化的趋势;但下部熔池不会发生球化,且对上部熔池的球化趋势起阻碍作用,当下部熔池熔液充分多时,会完全消除上部熔池的球化现象.采用平均粒径为75μm的铜基合金粉末,在150及80W激光功率下改变扫描速度及铺粉厚度进行的成型实验证实了上述分析.

In order to obtain metal parts with high density and accuracy,the balling phenomenon in selective laser melting（SLM） process should be eliminated.In this paper,the evolution mechanism and weakening method of balling are theoretically analyzed,finding that the change of processing parameters,such as laser power,scan speed and powder layer thickness can effectively weaken the balling because there is sufficient melting amount of the substrate.When the substrate is melted to a certain degree,the fresh molten pool is divided into an upper pool formed by metal powders and a lower one formed by a part of substrate.The former always has a tendency of balling due to the liquid-gas interfacial tension,while the latter without balling can obstruct the balling course of the former.Thus,if there is enough metal liquid in the lower pool,the balling of the upper pool during the SLM can be completely eliminated.The above-mentioned statements have been validated by the SLM experiments at a laser power of 150W or 80W and various scan speed and powder layer thickness,with Cu-based alloy powders in an ave-rage diameter of 75μm as material.