Real-time measurement method of melt pool temperature in the directed energy deposition process

In metal additive manufacturing, the quality of the parts is closely related to the temperature distribution in the melt pool; hence, real-time monitoring of the temperature distribution has become a common method of evaluating printing quality. However, there are difficulties in the temperature measurement of a melt pool related to its small size, high temperature, and rapid melting and cooling. A high-speed measuring optical path for a temperature field using a single camera is designed based on dual-wavelength thermometry herein. A dual-waveband image-matching method with sub-pixel accuracy, and a multi-parameter cooperative optimization and calibration method of proportional coefficient K, lambda(1), and lambda(2) are developed. Moreover, it was found that the splitting ratio of a beam splitter is not a constant value, rather, it is a distribution; hence, an accurate calibration method for the splitting ratio distribution of the optical system is developed. An on-line temperature measurement system is developed, and its validation experiment indicates a measuring error of less than 1%. The temperature distribution of the melt pool in the directed energy deposition (DED) process was measured. It was found that the temperature distribution was uneven, and the position of the high-temperature peak region changed with time. The evolution law of profile size and temperature change rates during the formation, development, and cooling process of the melt pool are analyzed. The method developed herein significantly reduces the system development cost, and can realize real-time monitoring of the temperature distribution of the melt pool in DED processing.