Comparison and analysis of hyperspectral temperature data in directed energy deposition

Directed energy deposition is an additive manufacturing process that allows the production of near net shape structures. Moreover, the process can also be applied for the repair of high value components. To obtain structures with consistent good characteristics, the directed energy deposition process requires the implementation of a control system. The currently applied approaches for control that are discussed in the literature have specifically focused on melt-pool temperature control. Pyrometers have been used for such purposes; however, they provide only a single scalar value without any spatial information. In this paper, the implementation of a high-speed hyperspectral camera-based system is discussed with a high spatial resolution unlike the pyrometers. Different calibration and temperature estimation procedures for this camera-based system are evaluated and analyzed. The number of effective wavelengths needed for temperature estimation will be discussed in detail and provide an outlook on the potential of this hyperspectral camera-based system. In addition to the number of wavelengths, another important aspect of the temperature estimation methods is the stability with respect to disturbances. Within this paper, the impact of the nominal laser power will be evaluated on the stability of the temperature signals for a control system.