基于熔池动态特征的金属激光熔化沉积形状精度演化行为研究

Study on Evolution Behavior of Geometrical Accuracy Based on Dynamic Characteristics of Molten Pool in Laser-based Direct Energy Deposition

针对金属激光熔化沉积成形质量影响机制与过程特征不明确所导致的质量可靠性与效果重复性较低、自适应控制困难等问题,采用同轴实时监测的方法,对不同金属激光熔化沉积工艺条件下的熔池动态特征进行监测,揭示不同熔池动态特征对形状精度演化行为的影响机制。以典型沉积工艺为研究对象,单道单层沉积中熔池几何轮廓和边缘熔融过渡区域面积与沉积层表面质量和宽度稳定性直接相关;单道多层堆积中的熔池几何轮廓与尾部特征对薄壁件壁厚变化有重要影响;多道单层搭接中熔池宽度的累加与粉末利用率的变化导致了传统搭接模型最优搭接率下表面搭接质量的下降;单道多层偏移堆积中的熔池塌陷与沉积层两端熔池面积可直接反应极限偏移与两端倾斜的演化过程。结果表明,通过熔池动态特征可以揭示金属激光熔化沉积中关键形状精度的演化行为,并建立新的形状精度模型,为后续激光熔化沉积工艺路径设计及实时反馈优化提供重要支持。

Due to complex influence mechanisms and process features, low quality reliability, processing repeatability and adaptive control ability are important problems in laser-based direct energy deposition. Dynamic characteristics of molten pools are monitored by coaxial visual monitoring and present the influence mechanism of the dynamic characteristics on evolution behaviour of geometrical accuracy in laser-based direct energy deposition. Four typical processes are main objects investigated. In single-track single-layer cladding, contour profiles and special grayscale region area have a direct relationship with surface qualities and width stability of molten pools. In single-track multi-layers accumulation, geometry and characteristics of molten pool tails have important effect on the change of deposition widths. In multi-tracks single-layer overlap, gradual increasing widths of molten pools and different powders utilization ratios leads to a decrease of surface geometrical accuracy based on traditional overlap models. In single-track multi-layers overhang accumulation, molten pool areas in both sides and molten pool collapse indicate the evolutionary process of incline edges and the overhang maximum. The results show the dynamic characteristics of molten pools can be used to study the evolution behaviours of key geometrical accuracy, and helpful for building geometrical models. The dynamic characteristics of molten pools are also beneficial for the researches about process planning and real-time feedback control.