Online in-situ monitoring of melt pool characteristic based on a single high-speed camera in laser powder bed fusion process

Abstract

• A coaxial melt pool temperature measurement system with a single high-speed camera in the LPBF process is developed. • A dual-waveband image-matching method with sub-pixel accuracy, and an overall parameter calibration and optimization method are proposed. • The melt pool characteristics including the temperature distribution, profile, temperature gradient, and cooling rate are measured by the developed system, and the distribution of average temperature and peak temperature under different linear energy densities during single-line printing is compared and analyzed. In metal additive manufacturing (AM), the in-situ measurement of the melt pool characteristic plays a significant role in monitoring the quality of the printed components. In this work, based on dual-wavelength thermometry, a coaxial melt pool temperature measurement system with a single high-speed camera in the laser powder bed fusion (LPBF) process is developed, including the design of the relay and optical path amplification system, and the beam splitting and chromatic aberration correction system. Moreover, a dual-waveband image-matching method with sub-pixel accuracy, and an overall parameter calibration and optimization method are proposed to improve the accuracy of the coaxial temperature measurement system. Besides, the validation experiment measured by a high-temperature blackbody furnace and a standard photoelectric pyrometer indicates that the temperature measuring error of the developed system is less than 1%. The melt pool characteristics including the temperature distribution, profile, temperature gradient, and cooling rate were measured by the developed coaxial temperature measurement system, and the distribution of average temperature and peak temperature under different linear energy densities during single-line printing was also compared and analyzed. The single-line printing results of different parameters show that the higher the linear energy density, the higher the average temperature and peak temperature of the melt pool, and the optimized parameters minimize the fluctuation of melt pool temperature and are more favorable to the formation of high-quality parts. In multi-layer printing mode, the heat accumulation is strong, resulting in the slow cooling rate of the melt pool.