利用激光光内送粉熔覆技术,在与水平方向成大于90°的仰面基体下表面进行了单道熔覆实验研究。分析了仰角、保护气压力与光粉耦合处粉束直径之间的关系; 研究了仰面姿态下熔覆层的宽度、高度以及熔池的流淌下垂趋势受激光功率、扫描速度的影响规律。研究发现, 光粉耦合处粉束直径随仰角的增大而变大, 随保护气压力的增大而减小。基体仰面与水平姿态下, 工艺参数对熔覆层的宽度、高度的影响规律保持了较好的一致性; 熔池在重力作用下, 激光功率、扫描速度以及仰角的变化对熔覆层高度的影响更加显著; 熔道顶点的偏移随激光功率的减小、扫描速度的增大和仰角的增大而逐渐增小。保持送粉量和离焦量不变, 利用优化后的激光功率、扫描速度, 以及保护气压力, 获得了最大仰角达150°、且具有较好尺寸精度和组织性能的激光熔覆立体成形件。

The cladding surface of the substrate was fixed at an upward angle which was greater than 90° in relative with the horizontal surface, where the single cladding tracks were formed by the laser inside powder feeding technology. The relationship among the tilted angle of the powder feeding nozzle, the pressure of the protection air and the powder spot diameter at the working plane were studied based on the experimental data. The effect of laser power and scanning velocity on the height and width of the tracks was analyzed, while the powder feeding rate and defocus amount kept unchanged. The liquid molten pool tended to drop by the drag force of its gravity, and the height peak offset was also studied. With the increase of the titled upward angle, the powder spot size at the working plane became larger, while the pressure of the protection air did the other way. For upward cladding, the effect of process parameters on the width and height shows a good accordance with the horizontal cladding. However, the height of the cladding layer was dramatically affected by the laser power, scanning speed and the tilted angle. The peak height offset of the molten pool got smaller with the decrease of the power and increase of the scanning speed and tilted angle. By using the optimized process parameters and the proper protection air pressure, a 3D part with the maximum titled angle of 150° was formed which also had the good feature accuracy and fine microstructure.