Abstract
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.
Highlights
Laser metal deposition (LMD) is one of the metal additive manufacturing methods
During the LMD process, metallic powders carried by inert gas are injected from a delivery nozzle into the molten pool melted by coaxial laser beam
To investigate the characteristics of LMD of aluminum alloys without direction dependency, optical signals were collected by three coaxial sensors sensitive to visible light, infrared light, and reflected laser wavelength
Summary
Laser metal deposition (LMD) is one of the metal additive manufacturing methods. During the LMD process, metallic powders carried by inert gas are injected from a delivery nozzle into the molten pool melted by coaxial laser beam. Deposition layers are formed after the solidification of the molten pool. The LMD process is highly sensitive to many processing parameters, including but not limited to laser power, laser scan speed and powder flow rate [2,3,4]. Aluminum alloys are of great interest in additive manufacturing due to their high specific strength and low density [5]. The high reflectivity to laser beams (91%), high thermal conductivity (146 W·m−1K−1), and low melting point (600 ◦C) make the Al alloy LMD process challenging to keep stable [6,7]
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