红外热像下激光熔丝成形过程冷却速率实时监测

激光熔丝增材制造技术是一种具备成形精度高和加工余量小的一体化制造技术，但由于其非平衡态凝固和复杂的传热传质等物理现象，使得很难通过常规手段监测得到其冷却速率。针对这一问题，提出了一种利用红外热像技术的熔池温度和冷却速率实时监测算法。该算法利用FLIR X6520sc型红外热像仪实时捕获增材制造过程中的温度场信号，通过定位温度场中心位置得到熔覆道各点的实时冷却速率，实现了熔覆道冷却速率的全过程实时监测。在此基础上，研究了不同工艺参数对熔池温度和冷却速率的影响规律。最后，探讨不同冷却速率对凝固组织的影响。研究结果发现:在其他工艺参数不变的情况下，扫描速度从60 mm/min上升到300 mm/min，熔池温度减少了339 ℃，冷却速率却增加了1741 ℃/s；激光功率从200 W降低到100 W，冷却速率和熔池温度分别降低了264 ℃/s和420 ℃；随着送丝速度从120 mm/min升高到600 mm/min，熔池温度和冷却速率分别降低195 ℃和224 ℃/s；扫描速度是对冷却速率影响最大的因素，为后期研究闭环控制系统提供了基础。此外，随着冷却速率的增加，熔覆道经过快速凝固，其凝固组织得到显著细化。

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.