Real time monitoring of cooling rate in laser metal-wire forming process under infrared thermography

Laser metal-wire additive manufacturing technology is an integrated manufacturing technology with high forming accuracy and small machining allowance. However, due to its non-equilibrium solidification, complex heat, mass transfer and other physical phenomena, the cooling rate is difficult to be monitored by conventional means. To solve this problem, a monitoring algorithm for monitoring molten pool temperature and real-time cooling rate using infrared thermography was proposed. The algorithm used FLIR x6520sc infrared thermal imager to capture the temperature field signal in the process of additive manufacturing in real time, obtained the real-time cooling rate of each point of the cladding channel by locating the position of the molten pool, and realized the real-time monitoring of the cooling rate of the cladding channel in the whole process. On this basis, the effects of different process parameters on molten pool temperature and cooling rate were studied. Finally, the effects of different cooling rates on solidification structure were discussed. The results show that when other process parameters remain unchanged, the scanning speed increases from 60 mm/min to 300 mm/min, and the molten pool temperature decreases by 339 ℃, but the cooling rate increases by 1741 ℃/s; Affected by the decrease in laser power (from 200 W to 100 W), the cooling rate and molten pool temperature are reduced by 264 ℃/s and 420 ℃ respectively; With the increase of wire feeding speed from 120 mm/min to 600 mm/min, the molten pool temperature and cooling rate decrease by 195 ℃ and 224 ℃/s respectively; In addition, with the increase of cooling rate, the solidification structure of cladding channel is significantly refined after rapid solidification. The scanning speed is the most important factor affecting the cooling rate, which provides a basis for the later study of the closed-loop control system.