同轴激光熔覆粉末的熔化行为表征与分析

Characterization and analysis of melting behavior of powder in coaxial laser cladding

同轴送粉激光熔覆过程中激光热量在粉末与熔池中的作用与分配对成形质量有着重要影响。针对作用形式最为复杂且难以红外实时检测的粉末与激光的热交互作用展开研究,首先建立了高速摄像系统并对标记的单颗粉末同轴送入激光后的熔化过程进行了采集与分析,研究了粉末熔化过程中不同特征阶段的热物理行为并建立了数学模型;同时由于难以根据有效的温度数据对模型进行验证和优化,故采用高速摄像统计分析了不同特征阶段的持续时间,与模型的计算结果进行了对比分析;最后在模型优化的基础上仿真预测了粉末即将进入熔池的温度与状态,为进一步分析粉末与熔池的热交互作用提供理论依据。研究结果表明:单颗粉末进入熔池后存在“固态→固液两相态→液态”的转变,不同转变过程的持续时间及热物理行为的变化并不相同;据此建立的数学模型可以动态描述粉末同轴送入激光后不同熔化阶段的持续时间与温度特征,通过与高速摄像统计数据对比验证了模型的有效性与准确性;仿真预测了粉末即将进入熔池时的温度特征,并分析了不同激光功率对粉末即将进入熔池时状态的影响与作用。

The action and distribution of laser heat in the powder and melt pool during coaxial powder feeding laser cladding has an important influence on the forming quality.This paper conducted research on the complex and chal⁃lenging thermal interaction between powder and laser,particularly difficult to detect in real-time infrared analysis.Firstly,a high-speed camera system is established and the melting process of a single powder coaxially fed into the la⁃ser was collected and analyzed,and the thermophysical behavior of different characteristic stages of the powder melt⁃ing process is studied and a mathematical model is established.Moreover,due to the difficulty in validating and opti⁃mizing the model based on valid temperature data,the duration of the different characteristic phases was statistically analyzed using high-speed cameras,and was compared with the calculated results of the model.Finally,based on the optimization of the model,the simulation predicted the temperature and state of the powder about to enter the melt pool,which provides a theoretical basis for further analysis of the thermal interaction between the powder and the melt pool.The results show that:there is a transition of“solid→solid-liquid two-phase state→liquid”after a single pow⁃der enters the melt pool,and the duration and thermophysical behavior of different transition processes are not the same;the mathematical model established by this can dynamically describe the duration and temperature characteris⁃tics of different melting stages after the powder is fed into the laser.The validity and accuracy of the model were veri⁃fied by comparing with high-speed camera statistics.The simulation predicted the temperature characteristics of the powder when it was about to enter the melt pool,and analyzed the influence and effect of different laser powers on the state of the powder when it is about to enter the molten pool.