Analysis of in situ optical signals during laser metal deposition of aluminum alloys

During laser metal deposition (LMD) of thin-walled aluminum alloy structures, the deposition height and width is hard to keep stable because of the special properties of aluminum alloys, such as high reflectivity to laser beams, low viscosity, and high thermal conductivity. Monitoring the LMD process allows for a better comprehension and control of this process. To investigate the characteristics of the aluminum alloy LMD process, three real-time coaxial optical sensors sensitive to visible light, infrared light, and back-reflected lasers ere used to monitor the aluminum alloy LMD process. Thin-walled parts were deposited with different laser power, and the characteristics of the three in situ signals are analyzed. The results show that there exists high linear correlation between reflected laser and accumulated deposition height. A laser reflection model was built to explain the correlation. Besides, the infrared light is linearly correlated with deposition width. Overall, the results of this study show that the optical signals are able to reflect the deposition height and width simultaneously. Infrared light signals and reflected laser signals have the potential to serve as the input of online feedback geometry control systems and real-time defect alarm systems of the LMD process.