激光同轴送粉增材制造粉末束流关键特征表征与分析

粉末束流焦距和焦点位置处的粉末颗粒的空间分布是粉末束流的两个关键特征，对激光同轴送粉增材制造工艺特性影响较大. 利用高速摄像拍摄粉末束流的宏观形貌，以图像灰度处理技术为基础，建立了粉末束流焦距和焦点位置处粉末颗粒空间浓度分布表征方法，提出利用有效粉斑直径定量分析粉末束流的汇聚性，系统研究了载气流量、同轴保护气流量、送粉速率等主要工艺参数对粉末束流关键特征的影响规律. 结果表明，工艺参数的改变几乎不影响粉末束流焦点位置处粉末颗粒呈高斯分布这一规律；载气流量增加，粉末束流焦距变小，有效粉斑直径变大，粉末束流汇聚性变差；同轴保护气流量增加，粉末束流焦距变长，有效粉斑直径基本不变；送粉速率提高，粉末束流的焦距和有效粉斑直径变化均不大.

Characterization and analysis of key characteristics of powder stream in laser coaxial powder feeding additive manufacturing

The focal length of the powder stream and the spatial distribution of the powder particles at the focal position are two key characteristics of the powder beam, which have a greater impact on the characteristics of the laser coaxial powder feeding additive manufacturing process. Using high-speed photography to capture the macro morphology of the powder beam, based on the image gray-scale processing technology, a method for characterizing the spatial concentration distribution of powder particles at the focal positions of the powder stream was established, and the effective powder spot diameter was used to quantitatively analyze the powder beam. The main process parameters such as carrier gas flow rates, coaxial shielding gas flow rates, and powder feeding rates have been systematically studied on the key characteristics of the powder beam. The research results show that the change of process parameters hardly affects the law that the spatial distribution of powder particles at the focal position of the powder stream is Gaussian. As the carrier gas flow increases, the focal length of the powder beam will be shorten, the effective powder spot diameter will become larger, and the flow convergence becomes worse. With increasing the coaxial shielding gas flow, the focal length of the powder stream becomes longer, and the effective powder spot diameter is almost unchanged. With the increase of powder feeding rates, the focal length of the powder stream and the effective powder spot diameter change little.