Temperature Feedback Control of Laser Cladding Using High Resolution Hyperspectral Imaging

Laser cladding is a technique that is frequently used for the coating and repair of metallic components. This technology can also be found in the additive manufacturing domain where it is more commonly known as direct metal deposition. The creation of freeform metallic parts using laser cladding is a promising area of research, with a lot of attention dedicated to the optimization of the process parameters and to automatic control strategies. A critical aspect of such feedback control systems is the accuracy of the sensor used for monitoring the process. This paper presents a feedback control scheme in which a hyperspectral camera is used to provide high resolution temperature information about the melt pool. A PI controller actuates the laser based on the measured temperature profile in order to maintain a constant melt pool size. Improved noise rejection properties are obtained by adding a model-based state observer to the control loop. The performance of the controller is evaluated by creating tracks with varying thicknesses on a base plate of AISI 316L stainless steel. Comparison of the on-line temperature measurements with off-line images of the tracks show that the measurements correspond very well to the true temperature profiles that were present during the process. As a result, the experiments demonstrate that the controller is able to successfully follow a given melt pool size reference with high precision.