基于图像的激光熔覆粉末粒子运动行为分析

Analysis of powder stream motive behavior in laser cladding based on images

为研究送粉参量(送粉量和送粉气流量)变化对激光熔覆过程同轴载气粉末粒子运动行为的影响,建立了数字粒子图像测速试验装置,开发了图像处理软件,得到了不同送粉参量精确的速度场云图以及z轴方向(垂直方向)浓度分布情况。结果表明,在送粉量一定的情况下,随送粉气流量的增加,粉末粒子的初始速度呈线性增大,并使z轴方向速度的增加值加大,而对粉末流浓度影响较小。在气流量一定的情况下,送粉量与粒子速度在一定范围内有一定比例关系,超出送粉量0.33g/s～0.83g/s范围,其影响将减弱。由于粉嘴结构的原因,沿出粉方向存在粉末发散汇聚再发散的变化。汇聚的实现与气体流量关系较大。

In order to study the effect of powder feed parameters on the motive behavior of coaxial carrier-gas powder in laser cladding process, a digital particle image velocimetry （DPIV） test device was constructed, a special image processing software was designed for this system. Lots of tests were performed on powder transport with carrying gas. The precision of velocity vector map of the powder particles in the coaxial was determined, and distribution of powder concentration at longitudinal axis from the nozzle exit was measured with the varied powder feed rate parameters by means of DPIV. Experiments show that the velocity metal-powder particle is linear with the powder mass flow rate. The powder concentration hardly changes with various gas fluxes and constant feeding powder amount. Outside the powder mass flow rate range （0. 33g/s -0. 83g/s）, the effect is lessened obviously. Because of the nozzle configuration of powder feed unit, powder flow has phenomena of expansion, focus and reexpansion along the nozzle exit. The focus distance and powder stream radius at the focus point also increase and focus depth decreases with increasing the gas flux.