作者：向锦, 殷鸣, 鲁俊, 李伟

作者单位：四川大学机械工程学院，四川 成都 610065

关键词：发射率标定;红外热像仪;液固相变;图像处理;熔池尺寸

摘要：

激光熔化沉积（LMD）工艺成形过程中温度测量可以为零件的实时质量控制提供关键信息，针对目前液相金属表面发射率测量不准确、误差较大的问题，搭建基于LumaSense MCS640红外热成像仪的熔池温度监测系统，实现熔池发射率标定及其尺寸测量。基于激光辐射区域中液固相变发生处温度梯度急剧变化这一特征，通过对沿扫描方向的温度二阶导数最大值点进行识别，确定液固相变发生的起始点，成功提取熔池边界辐射温度，标定熔池发射率，根据绘制的熔池中心点冷却曲线验证标定的合理性；通过设计标定实验，实现热成像仪的空间尺寸标定，获取熔池传热特征，并根据熔池红外图像上的特定等温线来提取熔池物理尺度的几何参数(熔池的长、宽和面积)。

Emissivity calibration and dimension measurement of LMD melt pool based on temperature gradient characteristics
XIANG Jin, YIN Ming, LU Jun, LI Wei
School of Mechanical Engineering, Sichuan University, Chengdu 610065, China
Abstract: Temperature measurement during laser melting deposition (LMD) process can provide critical information for real-time quality control of parts. Aiming at the problems of inaccurate and large error in the current measurement of liquid metal surface emissivity, a melt pool temperature monitoring system based on the LumaSense MCS640 infrared thermal imager was built, and the emissivity calibration and dimension measurement of the melt pool were realized. Based on the characteristic that the temperature gradient changes sharply at the point where the liquid-solid phase transition occurs in the laser irradiation area, the starting point of the liquid-solid phase transition is determined by identifying the maximum point of the second derivative of temperature along the scanning direction. The radiation temperature at the boundary of the melt pool was successfully extracted, and the emissivity of the melt pool was calibrated. The rationality of the calibration was verified according to the drawn cooling curve of the center point of the melt pool. By designing a calibration experiment, the spatial dimension calibration of the thermal imager was realized, and the heat transfer characteristics of the melt pool were obtained. The geometric parameters of the physical scale of the melt pool (length, width and area of the melt pool) are obtained by extracting specific isotherms on the infrared image of the melt pool.
Keywords: emissivity calibration;infrared camera;liquid-solid phase transition;image processing;melt pool dimension
2022, 48(12):133-139  收稿日期: 2022-05-25;收到修改稿日期: 2022-07-04
基金项目: 自然科学基金项目（51705347，52075352）；四川省重大科技计划专项项目（2020ZDZX0014）
作者简介: 向锦(1997-),男,湖北荆门市人,硕士研究生,专业方向为金属增材制造
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