Wang Zhenhao, Hu Kaihua, Yang Lin, Zhang Jian, Ding Honghui, Pan Zelong
College of Mechanical & Electrical Engineering, Wenzhou University, Wenzhou 325035, China.
Pingyang Institute of Intelligent Manufacturing, Wenzhou University, Wenzhou 325409, China.
Materials (Basel). 2023 Apr 26;16(9):3403. doi: 10.3390/ma16093403.
Laser direct metal deposition (LDMD) enables not only the preparation of high-performance coatings on the surfaces of low-property materials but also the three-dimensional direct manufacturing and re-manufacturing of parts. In the LDMD process, the spatial coupling characteristics of the powder flow and the laser beam are the key factors affecting the forming quality of the cladding layer. Based on the gas-solid two-phase flow theory, a numerical model of coaxial powder feeding was established by CFD. The powder flow characteristics of the lower part of the nozzle, the powder particle motion trajectory, and the optical-powder spatial coupling morphology and law were studied, and the relationship between the powder flow morphology, laser beam, and powder utilization was explored. On this basis, the law between the optical-powder coupling characteristics and the geometric characteristics of the cladding layer is discussed in conjunction with LDMD experiments. The results show that the powder concentration scalar located in the focal plane of the laser beam can be used to visualize the optical-powder coupling morphology. When the powder feeding speed exceeds the loading capacity of the carrier gas flow, the powder concentration in the center of the spot and the powder utilization rate decrease. When the carrier gas flow rate is 4.0 L/min and the powder feeding rate is 4.0 g/min, the best utilization rate achieved is 81.4%. In addition, the (height) of the cladding layer is more sensitive to changes in the powder concentration than the (width). These findings provide new ideas for nozzle structure design and the optimization of LDMD parameters.
激光直接金属沉积（LDMD）不仅能够在低性能材料表面制备高性能涂层，还能实现零件的三维直接制造和再制造。在LDMD工艺中，粉末流与激光束的空间耦合特性是影响熔覆层成形质量的关键因素。基于气固两相流理论，利用计算流体力学（CFD）建立了同轴送粉的数值模型。研究了喷嘴下部的粉末流特性、粉末颗粒运动轨迹以及光粉空间耦合形态和规律，并探讨了粉末流形态、激光束与粉末利用率之间的关系。在此基础上，结合LDMD实验讨论了光粉耦合特性与熔覆层几何特性之间的规律。结果表明，位于激光束焦平面的粉末浓度标量可用于可视化光粉耦合形态。当送粉速度超过载气流量的承载能力时，光斑中心的粉末浓度和粉末利用率降低。当载气流量为4.0 L/min且送粉速率为4.0 g/min时，实现的最佳利用率为81.4%。此外，熔覆层的（高度）比（宽度）对粉末浓度变化更敏感。这些发现为喷嘴结构设计和LDMD参数优化提供了新思路。
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