中文摘要：

为了提高激光金属直接成形中光内同轴送粉喷嘴粉末流场的汇聚性，获得大的聚焦焦距、小的聚焦直径及小的发散角，对卸载及载气两种方式下不同保护气压力对粉末流聚焦参数的影响规律进行了实验研究。结果表明：在卸载方式下，随保护气体压力逐渐增大，粉末聚焦焦距逐渐增大，粉末聚焦直径变小，发散角减小，粉末汇聚效果变好；在载气方式下，随保护气体压力逐渐增大，粉末聚焦焦距先增大后减小，聚焦直径逐渐变小，发散角逐渐降低。因此，在载气方式下应选择保护气压力与载气压力大小接近为宜。研究结果对光内送粉激光金属直接成形工艺优化具有指导意义。

英文摘要：

In order to improve the powder convergent characteristics of flow field of the inside-laser powder feeding nozzle in laser metal direct forming （LMDF） and obtain longger converging focal length, smaller converging diameter and divergence angle, the powder converging parameters are studied by experiments with different shielding gas pressure under unloading and carrier gas conditions. The experimental results indicate that the powder converging focal length increases, converging diameter and divergence angle decrease with the growth of shielding gas pressure under unloading conditions. The powder firstly gets longger then gets shorter, convergent characteristics gets better. The powder converging focal length converging diameter and divergence angle decrease with the shielding gas pressure increasing under carrier gas state. The effect is preferred when the shielding gas pressure is equal to the carrier gas pressure. It has an important guiding significance for process optimization during LMDF with the inside- laser powder feeding way.